This last weekend I dyno'ed my bone-stock 85 coupe 2.5/Isuzu with a hub-dyno setup. My first run (first image) peaked at 70.6 HP. I made a total of four pulls ranging from 70.6 to 74 HP.

After looking at the pull from run 1, I decided to extend my pulls to 5252RPM to make sure that I reached HP/TQ convergence to make sure the results were at least reasonably accurate. My advice to those of you who run over 5k RPM with a STOCK duke is- DON'T. There's no point in doing so, since you make like 40 HP up there anyway.

The subsequent runs were slightly higher, as I ran the second pull without an air cleaner element to see what kind of difference that would make. It pulled like 71.5 HP with no air cleaner and then 72.5 with no air cleaner. Last, I pulled the TBI off quick and removed the fuel atomizer restrictor plate thing under the throttle body and pulled an astonishing 1.5 more horsepower without it.

The moral of the story there is that if you want 1.5-2 more peak HP at the expense of cold starting and cold driveability nightmares and perhaps less even air-fuel ratio distribution between cylinders, take it out. The sane ones of us can leave it in.

Disappointingly, the lambda for whatever reason never got put in my exhaust, so I can't tell you where it runs on the factory calibration.

The other plot overlaid on my first run is some kind of 13B rotary (I put my car on in-between like 7 RX7s and they wanted to brag)
I told them that when their cars will break 30 mpg (They don't, and I get 37mpg at 75-80 with the headlights down) and I can get a rebuild kit for a rotary from Northern auto parts for $131, I might consider
switching over

First pull:

Pulls 2+3 or 3+4 (I forget):


edited to add: oh yeah, forgot to mention that the highlighted power/TQ values are for where the red dot (cursor) is.

[This message has been edited by KurtAKX (edited 10-29-2007).]

Plus to you for legit dyno charts and no BS. 70.6HP, thats about the same as a single overhead cam Civic. Not too bad.

And a stock duke no less. I've never seen the dyno for one.

If you get a chance, look at how restrictive the intake manifold is. I got used to that Holley paperweight and when I swapped it and saw the stock intake... man its just night and day. Unfortunately, the Holley doesnt give you a big boost up top like I expected. The cam is where its falling on its face at high RPM, not the intake.

I always knew the wankels were low on power down low, but it is interesting to see they are pretty much the same as the duke below 3K.

Tell the RX7 guys you will race, but you both have to shift at 3K!

Wow, cool. I wonder how a DIS duke compares?

------------------
1984 Fiero SE, White, first love, sold...
1986 Fiero SE 2M6, gold
1988 Fiero 2M4, the Fox
1987 Fiero GT, Blue, 3.4/4T40
Still looking for that perfect CJB 88 GT...

Thats always been my problem with the rotaries, if you really want to move you have to turn 7-8-9,000rpms.

This is the TB restrictor thing I was talking about btw:


AP2k: If you get a chance, look at how restrictive the intake manifold is. I got used to that Holley paperweight and when I swapped it and saw the stock intake... man its just night and day. Unfortunately, the Holley doesnt give you a big boost up top like I expected.
--Yeah I know how restrictive the stock intake is. Between the small runners, tight "y's" in the stock intake, and the puny 41mm TB (the 52mm on the V6s has 1.6 times the open area at WOT) she's gonna breath hard. This is not even counting the intake ports in the head, which are great for developing turbulence at low flow rates but are so restrictive you can't even hardly see the back of the intake valves with the manifold. Oh yeah, and the puny little 1.72 intake valves.

AP2k: The cam is where its falling on its face at high RPM, not the intake.
--Yeah I also figured that one out too, its hard not fall face-flat with a single pattern cam with 190 degrees of duration. I do believe that as soon as it had a cam worthy of 3000+ RPM the intake would be a huge problem.

fieroguru:
I always knew the wankels were low on power down low, but it is interesting to see they are pretty much the same as the duke below 3K.

Tell the RX7 guys you will race, but you both have to shift at 3K!
--This wankel was not 100% stock, it was a bastardized combination with some stuff done to it, so it was stronger than what they usually are. It makes sense that they do about the same down low given that the two most realistic estimates of the 13Bs rotary displacement are really 2.6 or 2.33 liters, and they have the same VE in the low end range as the duke.
--I am pretty sure there are even some guys with Powerstrokes that would be pissed if they had to short-shift at 3K!

fierodeletre: Wow, cool. I wonder how a DIS duke compares?
--I used to have an 87 Celebrity with the DIS duke and my educated guess would be that the power after 4k would be up relative to the early model and that both torque and power curves would be shifted up a few pound feet and hp across the range.

Kurt

Not sure how possible that would be, but I'm sure if you could do it you'd have the duke guys on here lining up for it. If it was cheap I'd do it while I wait to put an ecotec into my 88 coupe.

------------------
1984 Fiero SE, White, first love, sold...
1986 Fiero SE 2M6, gold
1988 Fiero 2M4, the Fox
1987 Fiero GT, Blue, 3.4/4T40
Still looking for that perfect CJB 88 GT...

You may want to get yourself a catalog from P.A.W. ( www.pawinc.com )
They have 3-4 different cams for the 2.5L as well as some different compression pistons.
Another thing is if I recall Toddster is selling a bunch of his Fiero items and had some SD4 parts. (shoot him a PM)
I do know the SD4 heads flow much better than stock. I've rode in a 2.5L with the SD4 head and it was a pretty decent gain.
Getting 120-130hp out of a "Duke" isn't that hard and should get you around 100 rwhp.

Here is some other "Duke" cam info:
http://go.mrgasket.com/pdf/pontiac.pdf (read the notes)

http://www.compcams.com/Products/188-211.PDF (scroll down to Pontiac)

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Happiness isn't around the corner...
Happiness IS the corner.
ZZ4 Powered !!

[This message has been edited by Oreif (edited 10-30-2007).]

Cool thanks for the info!

Oh yeah, I should say that a part of this goal was to do this with off-the-shelf and factory parts, without any super-limited production stuff, so that anyone could duplicate this if they wanted to.

quote Originally posted by Mr.PBody: Plus to you for legit dyno charts and no BS. 70.6HP, thats about the same as a single overhead cam Civic. Not too bad.

execpt hon-duhs have even less TQ, You CAN'T just compare HP.

It would be fun to build up a duke just to do it.

Thanks for doing this stuff. It should help me a bunch for my future Duke rebuild.

-Michael

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"A guy know's he's in love when he loses interest in his car for a few days." -Tim Allen

quote Originally posted by KurtAKX: This whole endeavor has got my mind sidetracked from my original goal. I have this little guy: which I was planning on dropping on soon, but since I've been thinking about it, there's more I'd like to do NA for the benefit of the people on here stuck with a 2.5 For example, I'd like to do: Holley TB dyno comparison and Holley intake + TB comparo. 84-86 head porting gains 87-88 head compared to the 89+ S10 head swap (the one with the D-port exhaust ports) I don't have a 87+ Fiero to test with tho. I'd like to compare various intakes to stock including Holley, Offenhauser, Clifford, GM Perf Parts, etc Isky said they'd regrind a stock roller cam for $110, I'd like to test a dual pattern grind with about 204/209 @ .050 Test cranking the timing. For some reason this whole experience has left me with this weird twisted goal that I want to make the car reliably put 100HP to the rear wheels naturally aspirated, and come up with a selection of parts such that anyone could duplicate it.

Not sure how I missed this thread. Anyway I have a Comp Cams 260 degree cam in my wifes Duke if you want the part number. BTW that supercharger would look nice on a Super Duty 4 barrel intake. We should have it back on the road soon.

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My sites
http://the-stickman.tripod.com

http://www.youtube.com/TheStickman

Stick, I thought the 260 was a flat-tappet cam... I am staying strictly hydraulic roller because I don't like cam wear (especially with the new low-zinc oils) and I don't like valvetrain adjustments.

I have been trying to sort out how to do this without using a single Superduty part (adapter plate) so that ANYONE could have a setup like this. (Also so I can have bragging rights on the fastest Iron Duke)
--------------------------------------
The problem comes in doing things in a balanced fashion. Before I even think about doing with this M62 other than spinning it at 1000RPM with a drill, I have resigned myself to coming up with a bolt-on kit that will boost a Fiero's output from ~70rwhp to ~100 rwhp reliably. This is actually taking quite a bit of time to approach from a holistic point of view.

More power without more revs (revs put rods and rod bolts in tension) means a higher average cylinder pressure, and correspondingly bigger torque impulses on the crankshaft. If you are not well-versed in "standard/non-superduty" 2.5 iron duke, then you may not know that Iron Dukes did not come with a harmonic damper installed on the nose of the crank.
Those who are very-well versed in Iron Duke, know this statement to be false!!!!

92 Lumina 2.5s (& perhaps 90-92 2.5l W and A cars) came with a harmonic balancer! Caveat: Engine must be switched over to serpentine accessories.

Changing to serpentine accessories in the simplest possible fashion (AFAIK) a different alternator, alternator/dogbone bracket, changing water pumps/housings (maybe just press on a different pulley?), changing the small 4-bolt end cover on the engine for the one with the integrated tensioner, and "AC stuff I don't care about since I purposely bought a non-AC car"
Of course, this would also eliminate the annoying "belt-eating" that 2.5s with V-belts are known for.
The serpentine stuff from the S10 does NOT swap, btw, since Fieros cannot accomodate S10s "deeper" accessory drives.

87+ Rods have a deeper I-beam section and are slightly beefier, so I'd like to see those in every rebuild. Additionally, 87+ cranks have a bit more mass and are a bit meatier in a one or two spots (namely where the oil pump drive gear is). These rods and cranks are a straight swap into earlier engines (already installed in my running 85 that I used to make the 5250 RPM dyno pulls)

I have burned the edges of the pistons down to the first ring land through careless use at STOCK power levels, so pistons are also a priority. I believe 92-95 TBI 350 pistons will work with no alterations providing only about a .3 increase in compression ratio whilst being tougher than stock Duke items, though ultimately I'd like to find a regular-stock-item 350 piston that's a little more robust/tougher for boost use.

All this just to get to the part where I can start to make more power! I am on the passive hunt for junked 1991 S10 2.5 5 speeds to rob the head/intake/wiring harness/ECM/distributor from. 1991-1993 are the best Iron Duke heads, and the 1991 S10s use the common GM '7165 ECM (A P4) which is FAR superior to the crap that came in ANY 2.5 Fiero. The bonus to this unit is that its set up to work with distributors as opposed to the DIS of other setups (I am in this to help the 84-86 guys)

1991 S10s make somewhere in the neighborhood of 105HP still on the stock cam which has a relatively modest 190/190 (@.050") grind. With the addition of a mild (no more than 210 deg) cam 120 crank horsepower without low end sacrifice should be easily accomplished.
Not only that, but the addition of a factory air temp sensor means better year-round driveability (yep, 84-86s don't even have 'em) and the newer ECM means smoother operation as well as a way to eliminate that awful 2000+ RPM cold high idle.

Ideally I could set these up as modular, "staged" kits:
1) Convert your annoying V-belt to serpentine with a complete package of carefully-chosen, OE quality parts. No guesswork, no one-offs.

2) Stage 1 + Convert your Model 300 TBI and heart-chamber head to newer Model 700, intake, and open-chamber head, ECM swap, stock S10 type power (+15-20 rWHP) for 85-90 rWHP, and improved driveability.

3) Stage 1 + 2 + addition of a performance camshaft (flat or roller depending on your block year), tougher pistons, custom ECM programming (100-110 rWHP) for 2.8-comparable performance with an all-stock look, and off-the-shelf replacement parts.
----------------------------------------------------

I could really do this much faster if I were to say, spend a summer down at Ed Parks, or Kick Hill, or somewhere where I could scrounge a dead 87 engine and a dead 85-86 engine to work with/mock up/test, and rob the 87 throttle cable/dogbone mount/fuel lines and life would be a LOT better with the aforementioned 2.5 S10 parts in-hand.

I've also had a slow start to building my flow bench, since I want numbers for each of the TBs/intakes/heads before I commit to anything. I've got some MDF and MAF sensor (I wanna do something a little bit-different than most home-brew benches) as well as some clear vinyl tubing to make a couple manometers up (ahh, the all-important 28" H2O). I am trying to figure out if a shop-vac based unit will really meet my needs.

Kurt

(A lot in my head, but much parts-gathering away from anything presentable, and currently approx $0 to spend on it right now.)

Sounds pretty awesome for those who have to keep their dukes.

Well if you don't want to use the SD-4 intake Offy makes 2 different versions. Single and Dual plane. I just mentioned the SD-4 one because to me it is more robust and i am not sure of the weight of that supercharger. That being said you could brace the intake to the block with some bracket's if needed. I will get the spec's on the cam. You can call up Comp Cams and tell them exactly what you want and they will cut it. That's what I did.

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My sites
http://the-stickman.tripod.com

http://www.youtube.com/TheStickman

I find your build very interesting!

It appears you used NA Pontiac 301 pistons. I recall looking at 301 pistons and found that they had a very unusual dish and dome shape to them. Do you have pictures of what you put in? Do you know what your head's chamber CCs are at this point and what CR they are generating? Maybe the funny shape was something peculiar to turbo 301s?

For your Comp Cam, thats a 212/212 single pattern cam @ .050" right? What kind of idle vacuum are you pulling and at what idle speed? What's your perception of the low-end "pull" when you attempt to accelerate from low engine speeds in the sub-2000 range?

Thanks
Kurt

quote Originally posted by KurtAKX: I find your build very interesting! It appears you used NA Pontiac 301 pistons. I recall looking at 301 pistons and found that they had a very unusual dish and dome shape to them. Do you have pictures of what you put in? Do you know what your head's chamber CCs are at this point and what CR they are generating? Maybe the funny shape was something peculiar to turbo 301s? For your Comp Cam, thats a 212/212 single pattern cam @ .050" right? What kind of idle vacuum are you pulling and at what idle speed? What's your perception of the low-end "pull" when you attempt to accelerate from low engine speeds in the sub-2000 range? Thanks Kurt

If I remember correctly the pistons were flat tops. I don't have any pics of anything but the rockers. I used a stock Fiero head if I remember correctly. The compression ratio is 10.1 to 1. I need to go down to the garage later to ge the exact specs on the cam but that sounds right. Not sure about the vacuum. The engine seems to pull well thru the entire rev range. But it has been along time since I drove it or since it's been on the road. We were also using the stock intake and TBI. We will be upgrading to the Edelbrock TBI intake. I also hope to find a Holley TBI. BUT I may consider using my SD-4 2 barrel intake that already has the bungs drilled out for port injection. I hope we can start soon on putting it back together and then get it dyno tested. I believe alot of people will be very surprised.

Update, BTW. Trying to get an engine together in time for the 25th. Ann. Fiero Show

I have so far accumulated:
1) Hedman Hedder
2) aluminum timing gears
3) late model iron duke harmonic balancer (serpentine)
4) set of pistons good for 10.2:1 compression
5) A new (stock) roller cam to be reground to a single pattern (going for 206 to 212 deg @.050" and .500"ish lift)

Still looking for:
Full roller rockers (roller fulcrum and tip)
87 2.5 Fiero engine to rape for serpentine conversion stuff
91-93 S10 ECM/wiring harness stuff

quote Originally posted by KurtAKX: Update, BTW. Trying to get an engine together in time for the 25th. Ann. Fiero Show I have so far accumulated: 1) Hedman Hedder 2) aluminum timing gears 3) late model iron duke harmonic balancer (serpentine) 4) set of pistons good for 10.2:1 compression 5) A new (stock) roller cam to be reground to a single pattern (going for 206 to 212 deg @.050" and .500"ish lift) Still looking for: Full roller rockers (roller fulcrum and tip) 87 2.5 Fiero engine to rape for serpentine conversion stuff 91-93 S10 ECM/wiring harness stuff

Kurt are you going to run that supercharger?

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My sites
http://the-stickman.tripod.com

http://www.youtube.com/TheStickman

I am not going to run it on 10:1 compression. I am trying to do a NA build for the 25th. Supercharger I am trying to decide what route I want to go. I am half considering buying a big 2 HP electric motor and just making it into a flowbench lately.

Do you still have those rockers?

quote Originally posted by KurtAKX: I am not going to run it on 10:1 compression. I am trying to do a NA build for the 25th. Supercharger I am trying to decide what route I want to go. I am half considering buying a big 2 HP electric motor and just making it into a flowbench lately. Do you still have those rockers?

You mean the ones for sale? Nope, sorry. But what you might want todo is find someone else on the board to go halvies wih you on a BBC V-8 set. It's cheaper that way. I was more wondering if you need an intake for your project.

Great insight and forward thinking. As an owner of a Duke, your approach gives me hope that I can at least be able to drive out of my own shadow. My question: I understand the crank is the Achilles heal. Many members swear that the current Duke crank cannot withstand more than 5K without disintergrating. With the added volumetric efficiency, should not one be looking at a different crank? With that being said, I also heard the block is as efficient as styroform! Any thoughts to these concerns?

Cordially,
Kevin

quote Originally posted by kevin: Great insight and forward thinking. As an owner of a Duke, your approach gives me hope that I can at least be able to drive out of my own shadow. My question: I understand the crank is the Achilles heel.

I would not disagree that the crank is one weakness.

quote Originally posted by kevin: Many members swear that the current Duke crank cannot withstand more than 5K without disintergrating.

I am not sure what the fatigue life at/over 5K RPM is. I can tell you that I have owned multiple GM A-body cars with the 2.5 engine/auto trans which have shifted at 5200-5300 at WOT per the factory calibration, DIS cars especially. Not sure if the added mass of 87+ cranks moves the resonant frequency of the crank away from the engine harmonics at 5000 RPM, or what. I am going to see if one of my old professors would be willing to do a test on some cranks with me, to measure frequency response.
This guy: http://www.kettering.edu/~drussell/bats.html

quote Originally posted by kevin: With the added volumetric efficiency, should not one be looking at a different crank?

Yes and no. The idea of a more cylinder filling is that you get more power without having to wind the engine up as much. If the failures are the result of crankshaft resonance at high RPM, then adding VE and not revving sky-high should preserve the existing crank. Conversely, if the crank failure is the result of torsional stresses due to the magnitude of cylinder pulses, I'll be killing it much faster. I guess we'll find out.

Either failure mode should be addressed by my addition of a harmonic balancer. I recently bought one for my build.
If there was another readily available crank to swap in, I'd be all over it. The old style and marine cranks don't fit without extensive modification.

quote Originally posted by kevin:With that being said, I also heard the block is as efficient as styroform! Any thoughts to these concerns? Cordially, Kevin

I could only wish that the block was as efficient as styrofoam. Styrofoam made by Dow Chemical insulates our house and it doesn't do too bad of a job when you compare the size of the house to the gas bill. Styrofoam is also very efficient at keeping my coffee warm and making molds for GM truck engines.

Seriously though, I am not worried about the block. I have broken a few rods, two pistons, and a crank. Never a block a failure.

Kurt

[This message has been edited by KurtAKX (edited 03-18-2008).]

Since Kurt posted a pic of that supercharger and since this is a Duke thread I thought I would post some eye candy.







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My sites
http://the-stickman.tripod.com

http://www.youtube.com/TheStickman

[This message has been edited by The_Stickman2 (edited 03-18-2008).]

The_Stickman2- you might want to edit your post. "Dike" LOL

quote Originally posted by craigsfiero2007: The_Stickman2- you might want to edit your post. "Dike" LOL

Thanx, that would make it an entirely different thread.

LOL, it sure would.

Use the Mercruiser 3.0L parts AND supercharge... heh, heh, heh...

Another + for some real Dyno info

One thing that I would point to is the amount of torque put down by just a 'stock Duke'. Almost flat at 115 lb/ft from 2k to 3k. That's already a whole lotta grunt to work with. Too bad it just falls on its face at anything over 4k. With a better cam/intake that torque band could realistically cross over the 4K mark and still be making power. Mods to a Duke bringing it up 100 rwhp, and the corresponding increase in torque, would mean this car probably runs as fast a stock V6. Not too shabby for the much maligned Duke.

We've been working along a similar line of thought for Duke Mods. Nothing that really trick, just off the shelf parts and a well planned build.

Before I located a Mercruiser crank, I had planned to use a 88 crank (they have a bit more durability as I understand). The biggest problem with the stock Duke cranks is that the middle rod throws are only partially balanced. Have a look. Two little matchbox size weights. It means the overall net balance of the crank is end to end. Once you increase compression and RPM those centre throws just start twisting the thing right out of its journals. A damper will only help for so much of that torsional vibration and then crack. You'll puke the bottom end. The Merc crank has counterweights on all throws which will make it much easier to balance. But....it is one awful heavy crank. I think it's going to have a date with the lathe (I don't like drilling holes for balance).

If you're going with a stock crank I'd say to weld some full counterweights on the centre throws and carve down the OD on the lathe to bring it into balance.

A couple other things I was looking at.

Pistons. SBC pistons with low tension, (1/16,1/16,5/16) gapless rings. I Found a nice set of .030 over KB flat tops for less than 30.00 each at summit. Should put the CR around 10:1 I still have to find out if the wristpin is on the piston centreline or not. (it makes a difference how the piston rocks over at TDC) KB lists a set of pistons for the 151ci but the compression ratio is something like 14.5:1 and I don't plan to run alcohol.

Timing gears. Rock Auto has a strait cut spur gears, a steel & ductile iron set.

Cam: Stick with a Roller. A regrind....or try A-motion cams. They have several profiles

Valvetrain. BBC roller rockers, recut the head for 1.94/1.6 valves, recut the spring seats for Beehive springs, custom pushrods.

Coatings.....For about 100.00 you can order a thermal barrier coating and couple antiriction coatinfg from Techline Coatings. They are a DIY. Might add a couple HP but more important for added durability.

Induction. DIY Ported head. One of those Holley big bore TBI/intakes would go nicely.....otherwise I'd just go strait to the wreckers and scavange a modern PFI setup, harness, and computer. I'd make my own manifold.

Exhaust. A hooker header.....or one that I weld out of J bends

A few other things
S-10 block. They are beefier.
Drill out main webs and block/head for 1/2-13 UNC ARP Studs (Superduty block prep)
Short fill with Hardbloc?
I'm wondering if the coolant flow can be reversed to cool the head first??

None of the parts are outrageously expensive or exotic, the only real bank breaker for this build is the machining work. I'm after around 140hp at the flywheel. When we're both finished there just might have to be a grudge race over who's got the fastest (non-SD-4) Duke

I'm working on keeping my buildup budget roughly the same cost as a 'brand new' engine would be. Not sure what the prices are down in the States but Carquest quoted 1650.00 new (I could get a rebuilt for around 1200.00). So far I've only spent about 20.00 for an engine and 65.00 for a Mercruiser rotating assy and cam....so I've got a lot of room to play. Just waiting for the weather in my garage to improve.

David

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His Fiero: 1984 2M4 Coupe

Her Fiero: 1984 2M4 Convertible

Besides the intake and came being very flow restrictive, the exhaust is also very restrictive for the duke. Back in 85 I installed a Hooker tri y headder and an 84 corvette cat on my 84 duke. It made a huge difference in performance. The tri y headder increases torque and flow also the corvette cat helped keep the flow.

Holy Crap!! This is pretty much the same build that I am doing right down to filling the bottom of the block with block filler!!

DPWood, I hope you're coming to the 25th, because we need to do some serious bench racing

quote Originally posted by DPWood: Another + for some real Dyno info One thing that I would point to is the amount of torque put down by just a 'stock Duke'. Almost flat at 115 lb/ft from 2k to 3k. That's already a whole lotta grunt to work with. Too bad it just falls on its face at anything over 4k. With a better cam/intake that torque band could realistically cross over the 4K mark and still be making power. Mods to a Duke bringing it up 100 rwhp, and the corresponding increase in torque, would mean this car probably runs as fast a stock V6. Not too shabby for the much maligned Duke.

I expect that 110-115 RWHP would make it comparable to or faster than a V6 Fiero, since they put down power in this range and have a tendency to weigh slightly more.

quote Originally posted by DPWood: We've been working along a similar line of thought for Duke Mods. Nothing that really trick, just off the shelf parts and a well planned build. Before I located a Mercruiser crank, I had planned to use a 88 crank (they have a bit more durability as I understand). The biggest problem with the stock Duke cranks is that the middle rod throws are only partially balanced. Have a look. Two little matchbox size weights. It means the overall net balance of the crank is end to end. Once you increase compression and RPM those centre throws just start twisting the thing right out of its journals. A damper will only help for so much of that torsional vibration and then crack. You'll puke the bottom end. The Merc crank has counterweights on all throws which will make it much easier to balance. But....it is one awful heavy crank. I think it's going to have a date with the lathe (I don't like drilling holes for balance). If you're going with a stock crank I'd say to weld some full counterweights on the centre throws and carve down the OD on the lathe to bring it into balance.

I wouldn't trust a stock Duke crank that's been welded on too much. I took an interesting materials course that spent a lot of time on iron and steel, and the consensus is that when your pour metal, depending on the composition and cooling, a certain grain structure forms, and when you weld on it, you create places where the grain structure is different. and/or doesn't line up in a favorable fashion for durability. On the journals, I wouldn't mind to much, but on one of the "arms" of the crank thats subject to more bending-type fatigue, I wouldn't do it to my motor.
I bought a late-model 2.5 harmonic balancer to damp some of the vibration of my shaft.

Have you figured out how to make the Mercruiser crank and rods fit yet? I have a heavy 45lb "old-style" 151 crank (like 1977 vintage, NOT a 153 crank) that is supposed to be good for 4 cylinder circle track racers, but it definitely won't work without serious mods. Also, the crank has a SBC style output on the tail, like yours.

quote Originally posted by DPWood: A couple other things I was looking at. Pistons. SBC pistons with low tension, (1/16,1/16,5/16) gapless rings. I Found a nice set of .030 over KB flat tops for less than 30.00 each at summit. Should put the CR around 10:1 I still have to find out if the wristpin is on the piston centreline or not. (it makes a difference how the piston rocks over at TDC) KB lists a set of pistons for the 151ci but the compression ratio is something like 14.5:1 and I don't plan to run alcohol.

I looked into 350 pistons, and I'll be using them (dished) with the supercharged iteration of this engine, but for the time being, I got a screamin' deal on some +.030 Pontiac 301 pistons. I probably could have gotten 350 pistons for the same price for my NA build, but the compression height is slightly taller, aiding "quench" or "squish", which should make the engine a little bit less sensitive to detonation (a concern when running 10:1 compression on an iron head engine.)

quote Originally posted by DPWood: Timing gears. Rock Auto has a strait cut spur gears, a steel & ductile iron set. Cam: Stick with a Roller. A regrind....or try A-motion cams. They have several profiles Valvetrain. BBC roller rockers, recut the head for 1.94/1.6 valves, recut the spring seats for Beehive springs, custom pushrods.

I have the Cloyes 8-1016 helical cut aluminum/steel gear set for the cam drive duties.

For cams, I bought a stock roller cam with the intention of sending it out for a regrind, but now I'm hearing comp can grind me a whole new cam for under $200. I believe A-motion is out of business, aren't they? They are Canadian, so I suppose you'd know better than me.

I have been trying to figure out if the BBC rockers would work. I am concerned because rocker arms are only ever listed by the ratio, and never by the actual distance of the tips from the fulcrum. For example, I could have a rocker arm that's 3 inches long, or 6 inches long, and both could be 2:1 ratio. Comp cams is always busy when I call (been on hold for 10min)

Beehive, conical, or ovate springs are definitely a part of the program, since I want to stick close to the 1.250 stock spring size, and these technologies are pretty much the only ones that offer good performance in that diameter spring pocket. Custom pushrods are going to end up being a necessity with custom rockers and a reground cam.

quote Originally posted by DPWood: Coatings.....For about 100.00 you can order a thermal barrier coating and couple antiriction coatinfg from Techline Coatings. They are a DIY. Might add a couple HP but more important for added durability.

What is the real value-add of those coatings? I read some articles that said showed those coatings are only worth it in maximum effort applications. We certainly won't be braking the 100hp/liter barrier.

quote Originally posted by DPWood: Induction. DIY Ported head. One of those Holley big bore TBI/intakes would go nicely.....otherwise I'd just go strait to the wreckers and scavange a modern PFI setup, harness, and computer. I'd make my own manifold.

Heads are super-important. I am planning on starting with a 91-93 style head, since they made more power than the other years.

I think I am going to see if I can find a cheap 1+ HP motor to drive my Eaton M62, to temporarily make it into a flowbench. I have an old drafting table that's open underneath would be just great for the purpose.

Ditto on the possibility of "my own intake manifold"... I think an OBD1 Quad 4 would make a good place to rob PFI stuff. They use the same pattern of cutouts on the crankshaft as the DIS 2.5 so the crank position sensor will be accurate and their DIS system wiring is compatible with "regular" DIS systems, even though they have that weird "in the cam tower" coil package. Just found out the welder my buddy bought (a Miller 250) will do aluminum too so I have more options than I thought. I want to make a long runner intake.

quote Originally posted by DPWood: Exhaust. A hooker header.....or one that I weld out of J bends

I already bought a Hedman Hedder. It only has like 18" primaries though, If everything else goes together without a hitch, I might consider working on a long-tube header, its last priority though.

quote Originally posted by DPWood: A few other things S-10 block. They are beefier. Drill out main webs and block/head for 1/2-13 UNC ARP Studs (Superduty block prep) Short fill with Hardbloc? I'm wondering if the coolant flow can be reversed to cool the head first?? None of the parts are outrageously expensive or exotic, the only real bank breaker for this build is the machining work. I'm after around 140hp at the flywheel.

You're looking for about the same power as me at the flywheel.

S10 blocks are not magical. They are full of the same cranks and rods as any other block. They don't accomodate Fiero water pumps, either.

I also thought about drilling the block out for 1/2" studs, but I don't think I'm going to because I don't want to remove that much strength from the top end of the block. I think the bore distortion when you crank the head down would be worse if you cut that material out for bigger studs.

I have even also considered reverse-flow cooling, like LT1, but there's a lot to be considered there. Water pump and thermostat orientation have to change, heater core feeds, among other things.

quote Originally posted by DPWood:When we're both finished there just might have to be a grudge race over who's got the fastest (non-SD-4) Duke

Aww, I wouldn't feel right taking your money like that! lol

quote Originally posted by DPWood: I'm working on keeping my buildup budget roughly the same cost as a 'brand new' engine would be. Not sure what the prices are down in the States but Carquest quoted 1650.00 new (I could get a rebuilt for around 1200.00). So far I've only spent about 20.00 for an engine and 65.00 for a Mercruiser rotating assy and cam....so I've got a lot of room to play. Just waiting for the weather in my garage to improve. David

Yeah, I'd like to keep the cost down on mine too. Ultimately I'd like to document what I do much the same way that Prostreet505 did with his small block build, so that anyone with $1000 and some free weekends can duplicate what I did.

I don't know if I'll make much more than a day trip to the 25th. It would be cool if we can hook up for some bench racing and compare build notes.

About welding a crank....Welding cast material can be done. It requires heating prior to the weld, and controlled cooling to limit how the structure of the steel will change. An error here can create a brittle weld that might crack and pitch off the counterweight at a high RPM. Definitly something to have an experienced crank shop do. I've done a bit of welding to cast (nothing on a crank) and it is tricky.

I'm going to have a look in the shed tomorow and see if I kept an old set of mains that I can use for a trial assy of the Merc crank this weekend. There was some info in an older post about using the Mercruiser crank. (I have it on a USB drive) They fail at around 6800 RPM. Not too shabby....but there was also mention of a 153 ci forged crank that could spin at 7400 all day. Stuff of dreams now. Easier and cheaper to locate a SD part

Pistons are still a question mark for me. I have the ones that came with the crank. They have a shallow D-shaped dish that should give a good quench area with the small head chamber. If the trial assembly looks good I'll go with them over anything else. The SBC pistons are something I've looked into but I'm not sure on how the wristpin location will affect an inline 4. As I understand it the pin location is offset for use in a V engine. Because it introduces an angularity other than the position of the piston rod it does affect how the piston comes to TDC. It is a question I need to ask someone with a whole lot better understanding of the subject. It might be of no consequnce or it could cause premature cylinder wear. ????

I hadn't heard anything about a-motion being out of business. Could be.....If that is the case for 200.00 I'd call Comp for a custom grind. I think I have the specs for the a-motion cams on my computer. Comp could work it out from that and a discussion of what mods you're doing.

The heads have to be machined for 7/16 studs to fit BBC rockers. Other than that they are a direct fit on a stock head from everything I have read. I'll have to wait a month or so to find out (not fitting in the budget right now). I'm not terribly worried about staying at the stock spring size because I plan to put SBC valves in. They are about 1/4" longer which will completely change the spring installed height. I'm sure there will be a factory application close enough to what I need, I can modify it from there. Still lots of stuff to consider with the top end.

Coatings. What can I say. My opinion is that the thermal barrier coatings will improve the engines resistance to detonation. It will also reduce carbon buildup because of a more efficient combustion event. Antifriction coatings on the piston skirts reduce parasitic losses and bore wear. The effect, by itself, will be small. But then what good is a hot cam without a ported head. It's the total of all the little things that make up the package. Oh and that 100.00 is enough to apply coatings to a V8 so it's pretty cost effective for a Duke

The engine isn't a strong performance foundation so making big compression or adding boost can quickly locate the weak parts of the block. Usually failure will come from detonation producing too much of a shock load for the bottom end to hold. Getting power out of a Duke is more of an exercise in improving efficiency. Anything that will reduce power loss. Lighten and balance the rotating assy, low friction rings, full roller cam/lifters, more efficient valvesprings, coatings, reduction of parasitic drive accessory losses. It's all power the engine was already producing but that you're just changing it to USABLE power. None of this will place the engine at risk of failure and it will last a heck of a lot longer than anything from the factory.

A few other things I forgot to post.

Electric water pump. Amp draw on the altenator is less than the parasitic loss of pumping at higer RPM
Main girdle. Nothing wrong with a little insurance. I have acess to a mill at work so I can just cut one out of 4130
Windage tray/crank scraper. Another home fab job
Shim the oil pump relief spring. Better oil pressure and not as much parasitic loss as a HV pump
Water injection. Well, on race days anyways. Better gas, more initial timing, and H2O to keep detonation at bay
Synthetic oil. Another minute improvement in efficiency.
Upgrade the ignition MSD, Mallory...take your pick....set your rev limiter

David

quote Originally posted by DPWood:I'm going to have a look in the shed tomorow and see if I kept an old set of mains that I can use for a trial assy of the Merc crank this weekend. There was some info in an older post about using the Mercruiser crank. (I have it on a USB drive) They fail at around 6800 RPM. Not too shabby....but there was also mention of a 153 ci forged crank that could spin at 7400 all day. Stuff of dreams now. Easier and cheaper to locate a SD part

I have heard the Marine cranks were good to much higher RPM's than that. Gerry at KRP told me that he knows of a drag racer in Ca. that spun one to 10K and had it live. If I remember he may have said that they are better than the SD-4 cranks, but I won't say positively on that one.

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quote Originally posted by DPWood: Main girdle. Nothing wrong with a little insurance. I have acess to a mill at work so I can just cut one out of 4130 Windage tray/crank scraper. Another home fab job David

When you make your main girdle, make a few. I wouldn't mind having one.

As far as a crank scraper, I talked with Kevin Johnson of Ishihara-Johnson crank scrapers about the one they've already made for the 2.5 (http://www.crank-scrapers.com/).

Its patterned off of an 88 Chevy S10 block, so it fits 2.5s with the "big gear" late crank, but without balance shafts. It sells for about $60 and can be optioned with a soft teflon insert which can be set up to run perfect (.000") running clearance from the crank.

The_Stickman2... I don't have personal experience on the upper RPM limit on the crank. I just recall it from another archived post. I'll have to look it up, I have a hard copy in a binder at work. If you get your balancing right on the money...I'm talking everything right down to a .01g balance, then it would take huge RPM's before the crank would be damaged in any way. That type of precision costs some pretty big $$. I have the ability to establish the bobweights that accurately but I don't know a local machine shop that has the equipment to do the crank to a similar degree. I wonder if the the crank shop would do the initial balance and then get a confimation spin done at someplace that balances electric motors and turbine shafts. Their equipment is set up for critical accuracy at high RPM but they wouldn't have automotive bobweights....Just random thoughts.... Probably not cost effective.

Balance becomes more critical as RPM increases. Any net imbalance weight increases exponentially as a factor of RPM.

KurtAKX.... No problem. Not much more work to make two girdles than it is to make one. With a manual mill it's the setups that take forever. hehe... Thanks for the tip on the crank scraper. Handy for a stock rebuild. I have one of those to do this summer as well.

You should have a look at http://www.metalwebnews.com/ Lots of stuff on home foundry as well as other metalworking topics. I've been going through several of the sites there for more info (primarily on machining because I want ot buy my own lathe and mill) but a bit on home built forges for aluminum and brass casting. If I can ever get a proper garage built I am going to have so many cool things. I buy tools...so I can make more tools.

David

quote Originally posted by KurtAKX: Which intake do you have? I have been wanting to fab up my own custom long runner intake, but I am seeing deadline approaching. The only potential hitch I can think of is that no matter which intake you have, it probably won't line up to the "new style" 87+ head I want to use. I bid on the last Edelbrock to come up on ebay but it went $155. I can't justify spending more for a Duke Edelbrock intake than a SBC one costs. Its getting to the point where I could be lost-foam casting my own intake to exactly what I want, if I knew of a foundry that was all about taking on small jobs. Lost-foam work is brain-dead simple. I had a friend who made his own foundry setup and cast his own 3800 NA S3 intake to S2 throttle body adapter, but he couldn't handle anywhere near as big a pour as I'd need to do an intake.

Well I have the Offy 4 barrel intake.

Here it is with an adapter plate for the 87-88 TBI
I have the adapter plate to mate it to a newer head.


and I may still have an adapter to mount a 2 injector TBI to that manifold.


You would need the TBI spacers in the above photo. I sold all but one when I needed some cash.
Any Super Duty Intake would work without the adapter plate but you MUST use a Super Duty intake gasket. In the end most Duke intakes be it the Offy or Super Duty ones will go for $150 on up.

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