So I got my 3.0 crank back from the machine shop tonight.

It started as a one-piece rear main seal crank. I asked for a 94-99 Mercruiser crank and this is what I got. It had the late SBC flywheel bolt pattern with a 3.0" bolt circle
(a real problem when you cut it down since the rear main seal diameter of a metric bellhousing Duke is 3.0"- machining it down involves "opening" the bolt holes from the sides)

I then took it into the crankshaft shop along with an old crank as reference, a new pilot bearing, and a rear main seal crank repair sleeve.
The machinist epoxied some Grade 8 bolts in the old SBC holes, ground the rear main down, and capped the whole surface with the rear main seal repair sleeve for a flawless smooth surface for the lip seal to ride on.

Here's the finished product, a 3.0 crank that fits a Fiero block!




I'll be test-fitting it in a block shortly.

This will be interesting since the "Big Bad Duke" mrossum built was actually running a 2.5 crank when it burned up. I might have the first Fiero actually running a Mercruiser stroker crank.

Is it too early to ask how much it costs?

wont the block explode if you start making biger orse (150+)?

No its not too early, the gf already found out what it cost me (oops). It is too early to ask for one though...

I've neither tested the setup yet (its usually important to make sure the piston pin doesn't come out of the bore at the lowest point in the travel) nor have I found a good source for cores yet. Also the machinist isn't thrilled about doing these in quantity so I might have to find another shop to source the work to.

Also if I ever finally get around to selling the stroker kit, its got to come with Mercruiser rods since the rod journal size is different, and you need a shorter rod to keep the piston in the deck with the longer stroke. That's one more hurdle.

well then i might not swap the motor out on my 2.5 let me know how it goes im watchign in anticipation

what would that cost as a kit?

IT WILL NEVER WORK, GIVE UP NOW!

quote Originally posted by darkhorizon: IT WILL NEVER WORK, GIVE UP NOW!

Sorry Kurt.. please keep us updated with this build.

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1999 GMC Jimmy 2dr 4x4
1996 Chevy Lumina LS

1986 Fiero Base Coupe...NO OPTIONS !!
1985 Fiero GT 3800 N/A-sometime this year 3800S/C..maybe
1984 Fiero Indy-Restoring back to former glory

[This message has been edited by KEV (edited 10-03-2008).]

quote Originally posted by darkhorizon: IT WILL NEVER WORK, GIVE UP NOW!

It'll work better than going to the bowling alley to pick up chicks- ha!

quote Originally posted by KEV: Man you never have anything good to say do you? Why don't you do us all a favor and go away. Sorry Kurt.. please keep us updated with this build.

He's just joking with me. I called him last night (at the bowling alley) as soon as I got the crank back. He wants me to go a little more radical than I'm planning. Right now I'm looking at cams in the neighborhood of 215-220 degrees at .050" so I don't totally knock the bottom end out of it.

I got another Holley TBI today, except this one came with the Holley intake manifold too! This is for a different engine I'm building tho.

[This message has been edited by KurtAKX (edited 10-03-2008).]

quote Originally posted by KurtAKX: He's just joking with me. I called him last night (at the bowling alley) as soon as I got the crank back. He wants me to go a little more radical than I'm planning. Right now I'm looking at cams in the neighborhood of 215-220 degrees at .050" so I don't totally knock the bottom end out of it. I got another Holley TBI today, except this one came with the Holley intake manifold too! This is for a different engine I'm building tho.

My bad..lol

There are those that thrive on the challenges of doing unusual and interesting rebuilds and this is certainly one of them. While success can never be guaranteed trying to move in a different direction provides for an interesting project. I believe the biggest challenge facing a Duke with high horsepower capabilities is the block itself. I cannot see any way to get around this but give it your best shot and see what results. It all depends on how much horespower you wish to make and the RPM range that the engine will see. The Mercruiser was a torque engine so perhaps the power curve should be designed to peak at 4800 RPM. IMO taking the Duke higher in the RPM range will be a risk but not being an expert oin that engine, this is only a best guess.
I've been here since 2000 and during this time I have seen several modified Duke engine builds fail and a Quad Four built by Bryson came apart a short time after it was built.. The only modified Duke that I know of that survived was the one built by Neil "The Stickman" Kline and his wife Dawn. Neil has spent years researching Dukes and S.D. Fours and is the man to speak with. There may be some of his posts here in the archives. Good luck with the project.

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87GT - 3800SC Series III engine, 3.4" Pulley, N* TB, LS1 MAF, Flotech Exhaust Autolite 104's Custom CAI 4T65eHD w. custom axles, HP Tuners VCM Suite.
87GT - 3.4L Turbocharged engine, modified TH125H
" I'M ON THE LOOSE WITHOUT THE JUICE "

quote Originally posted by Dennis LaGrua: I've been here since 2000 and during this time I have seen several modified Duke engine builds fail

Links to these failed Dukes?
The only failed one I can think of is mrossum. Two things about that build-up:
1) It "failed" when the car burned down because of a leak
2) He was actually running the 2.5 crank because he was using a DIS block.

quote Originally posted by Dennis LaGrua: The only modified Duke that I know of that survived was the one built by Neil "The Stickman" Kline and his wife Dawn.

I thought he bought the engine already running? At any rate his are all down for work and are made out of Superduty parts. I want to come up with a reasonably hot package that doesn't require any SD parts at all so anyone can build one.

Granted, it looks like I'll be putting this first 3.0 crank under the '801 uber-Superduty aluminum head to test the limits of the crank, but ultimately I plan to do something with a production block and head and forced induction and a 3.0 crank that can be built with common and cheap parts.

KurtAKX: Glad to see someone is making some progress on a 2.5/3.0 merc stroker. Your doing the same as I . Haven't done any work to the crank yet. Waiting to get a 87 block with DIS and external oil filter. Going to use an external crank trigger too. Still debating on a head 801 or 437. I don't think 801 has an intake made for it. This is the plan for my engine, CR should be around 9.5-1 and using FS cam 206dur/.483, 6" rods,custom pistons and a crank girdle. Hope to get the best of both worlds, mpg/torq. If your using a 801 head are you going with 1.94,2.02 or 2.08 intake valve, the exhaust can be 1.60,1.65. Will your holley intake and TB flow enough to feed the 3.0L ? Do you think the crank girdle will help strengthen the block ?

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85 GT 3.4
14.9 @ 90 1.9 60' Old TH125/3.06
Unknown New 4T60/3.42

quote Originally posted by KurtAKX: I thought he bought the engine already running? At any rate his are all down for work and are made out of Superduty parts. I want to come up with a reasonably hot package that doesn't require any SD parts at all so anyone can build one. Granted, it looks like I'll be putting this first 3.0 crank under the '801 uber-Superduty aluminum head to test the limits of the crank, but ultimately I plan to do something with a production block and head and forced induction and a 3.0 crank that can be built with common and cheap parts.

Neil built that 2.5L engine on his Fiero. Thats going back about 5 year. Last time I swa it was at Carlisle. There were no super duty parts on it but I remember him telling me that Chevy Small block pistons were used. I believe that Neil has been working on a SD4 but don't know if he installed it as yet. I don't want to discourage you from moving ahead on this project but just have realistic expectations on what to expect. For 135 HP I believe that you'll be OK but beyond that pomt IMO you will be moving into the unknown zone.
A while back there was a guy on this forum, I believe his name was Ira Crummy ( From NB Canada) that claims to have built a 190HP Duke but I don't know what became of the project or the engine.

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87GT - 3800SC Series III engine, 3.4" Pulley, N* TB, LS1 MAF, Flotech Exhaust Autolite 104's Custom CAI 4T65eHD w. custom axles, HP Tuners VCM Suite.
87GT - 3.4L Turbocharged engine, modified TH125H
" I'M ON THE LOOSE WITHOUT THE JUICE "

it sounds like a differnt project altho i think a cheaper way to get power would be a swap.
good luck if theres any thing i can do to help just PM what ever

quote Originally posted by Lilchief: KurtAKX: Glad to see someone is making some progress on a 2.5/3.0 merc stroker. Your doing the same as I . Haven't done any work to the crank yet.

Just wait 'till you get the bill!

quote Originally posted by Lilchief: Still debating on a head 801 or 437. I don't think 801 has an intake made for it.

Stickman has the only intake I've ever seen that's actually made for the 801 head.

quote Originally posted by Lilchief: This is the plan for my engine, CR should be around 9.5-1 and using FS cam 206dur/.483, 6" rods,custom pistons and a crank girdle. Hope to get the best of both worlds, mpg/torq.

You're going even milder than me. I'm looking for 10-10.5:1 and 220 degrees of cam.
What are you going to do for rods? SBC rods don't work with the marine crank, and you'll have a weird compression height if you use rods that long. When you add 5/8" to the stroke, you either have to run shorter rods or shorter pistons.

quote Originally posted by Lilchief: If your using a 801 head are you going with 1.94,2.02 or 2.08 intake valve, the exhaust can be 1.60,1.65.

The valves I ordered (still waiting) are 2.02 / 1.60 with stems that are .200" longer than stock SB Chevy (Ferrea brand)

quote Originally posted by Lilchief: Will your holley intake and TB flow enough to feed the 3.0L ?

Um, no. I'm going to use that stuff for something else. I think I'd break through the intake manifold walls before I could even port match to the 801 head. The ports are comparatively monstrous.

quote Originally posted by Lilchief: Do you think the crank girdle will help strengthen the block ?

Sure it would, but I honestly don't think you need it. With a cam as mild as what you selected, you're not going to make power over 6000 RPM and you're going to be under 200hp most likely. The boat makes 140hp and runs at high rpm and it seems to survive just fine on a 2 bolt main. I would like to have a main girdle though, just because I like to overdo things.

Kurt do you think this crank would be a better starting point than the one you used due to the much bigger rear seal area to start with to machine down?

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

http://www.youtube.com/TheStickman

quote Originally posted by KurtAKX: Here's the finished product, a 3.0 crank that fits a Fiero block!

Although I don't even have a Duke, I think that your idea of creating a 3.0L stroker crank for a 2.5L Duke is a very interesting one, and I hope it works out well!


You also seem to have thought this through, more than many might have, by not just recognizing, but pointing out, that the longer "throw" of a stroker crank needs to be compensated for in order to avoid the resultant overly high compression that otherwise would result from a stroker crank:

quote Originally posted by KurtAKX: When you add 5/8" to the stroke, you either have to run shorter rods or shorter pistons.

I agree with your assessment, but could you clarify if by "shorter pistons" you're referring to a wrist pin that's placed higher in the piston, pistons with less "dome" or more "dish" in them, both, or yet something else?

I'm not trying to give you a rough time here. I'm just curious about your plans because I find your experimental project very interesting.


This is the only part I didn't follow:

quote Originally posted by KurtAKX: I'm looking for 10-10.5:1 and 220 degrees of cam.

Might that be an overly mild cam to "bleed off" that much --- perhaps too much compression with pump gas --- or are you counting on, in part, the ability of an aluminum cylinder head (versus the standard iron Duke head) to help you out in that regard, versus always using high-octane race gas --- using both, or yet something else?

By the way, no matter how things turn out with it, yours, IMHO, is a very interesting experiment. Thank you for posting us regarding it.

quote Originally posted by project34: I agree with your assessment, but could you clarify if by "shorter pistons" you're referring to a wrist pin that's placed higher in the piston, pistons with less "dome" or more "dish" in them, both, or yet something else?

When speaking about "shorter pistons" in reference to a stroker crank, shorter means a smaller compression height (the wrist pin is closer to the top surface of the piston).

If you only adjust the compression height, and not dome/dish configuration, the additional stroke will result in higher compression. So, in order to keep the same compression ratio, the dish must be made larger or the dome reduced. On a 2.5L that is not usually the goal, 8.5-ish to 1 compression isn't the best for power, unless boost is involved.

Trying to follow this project, almost missed this thread. This looks like quite a facinating project, hope the progress goes well for you.

quote Originally posted by FieroJimmy: On a 2.5L that is not usually the goal, 8.5-ish to 1 compression isn't the best for power, unless boost is involved.

Uhh ohh kurt, I think someone tapped our cell phones!

quote Originally posted by The_Stickman2: Kurt do you think this crank would be a better starting point than the one you used due to the much bigger rear seal area to start with to machine down?

That IS the crank I started with. The bolt circle on the back of that (and my) crank is 3.0", which is the same diameter as the rear main seal needs to be. That's where all the fancy machining came in.

quote Originally posted by FieroJimmy: When speaking about "shorter pistons" in reference to a stroker crank, shorter means...the wrist pin is closer to the top surface of the piston.

Your explanation in regard to my inquiry regarding this subject of "shorter pistons" was for me excellent.

Thank you for your response.

I haven't put rods/cam in it yet, but I can already tell that the block is going to need minor clearancing in at least one spot for clearance of the forward counterweight for the #4 cylinder.

popcorn, man, popcorn. Looking forward to your progress.

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Kermit- "So you like your drums huh?"
Animal- "Oh yeah! Mwah Mwah Mwah" (kissing drum set)
Kermit- "Uh huh. More than food, huh?"
Animal- "They ARE food! Eat Drums! Eat Cymbals!" (eating noises)
Kermit- "Hm. How 'cymbal'-ic!"
Animal- (looking abused) "BAD PUN!"

In the block pics, as promised.

Does it fit in the block? Generally, yes:


A shot of the interference area with the counterweight (pointing to it)


Another shot with the counterweight coming from the other direction. Also note, plenty of cam clearance.


Here's the only reason I'll have to be careful grinding out the block a bit; its a where the distributor sits.


Pickup tube bracket is not used to having so much counterweight near it!


The crank was MADE to clear the stock Fiero style oil pump, thank god!

Things do look tight. And I know how heavy that crank is. Have you ever thought of doing something like this to it?

are you making a block girdle for this? if so what are you making it out of? and if you get me some sketches i will turn them into cad drawings and post them

quote Originally posted by The_Stickman2: Things do look tight. And I know how heavy that crank is. Have you ever thought of doing something like this to it?

Things are tight, but I don't think they're any tighter than they were in the original marine block.

I have thought of doing something like that for a crank, but the stock boat crank can't be cut like that, and a nice billet piece like you've got there would cost me 1800-2000 from the crank shop I'm dealing with. They told me they've done them before, but that they like my boat crank idea and want me to try it first before signing up to spend the big bucks. Which is fine, since I can't afford it anyway. There's Moldex too, but they're every bit as expensive.

ok just trying to get one of these and make this modification avalibile to other people

Ah, very nicely done. I've been preoccupied with a bunch of stuff lately and haven't worked on the Superdookie project at all... It'll have to come later. Glad to see somebody's taking care of business.

As the math seems to show, a 3.6" stroke crank with a 5.7" rod (stock Mercruiser combo) will work in place of the stock 3.0" stroke crank and stock 6.0" rods. It's possible, that with aftermarket SBC pistons designed for stroker or long rod applications, that you could get a 6" or longer rod in there with the Merc crank to get back some of the rod to stroke ratio - less sidewall loading, more dwell at TDC, more torque and HP, more detonation resistance.

On that note, I stumbled across something useful on E-Bay - a very late Mercruiser 3.0 crank that had rod journals set for SBC rods... I don't know any more details, but I think it was like 2006 or so. The Mercruiser engine uses the same rods uses in the Chevy I-6 and probably the 2.5 Chevy II 4 cylinder, which the mercruiser is really based off of. They probably figured it'd be more cost effective to switch over to the SBC rods. What does it mean for us? Unlimited possibilities when it comes to aftermarket rods - H-Beams, I beams, 4340 chrome moly, 6.0" length, 6.2" length, anything.

ill look into that tomarrow if the weather and school premits ( we have a lot of marine and boat shops around town) and i may have an answer for you

Was wondering if you have decided on an induction system yet ? If using the TBI style system, what TB and injector (injectors) size? Can't wait to get started on mine. Great write up, keep the info coming.

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85 GT 3.4
14.9 @ 90 1.9 60' Old TH125/3.06
Unknown New 4T60/3.42

Hey KurtAKX. I seem to recall part of the superduty block prep work was to drill out the main studs for 1/2-13. That would give you virtually any length main stud you desire from ARP to mount a windage tray as well as a crank scraper.

Lovin' the info you got on the 3.0 litre. I have 2 rotating assemblies myself but both cranks are the older 2pc seal so it looks like I'll be figuring out a block adapter for the oil seal. Looks like a an old 153 tooth flywheel will work....but I'll have to get a clutch assembly to see if it will fit within the confines of the fiero tranny. There is about 3/4" more length on the mercruiser crank that will probably create a headache

David

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His Fiero: 1984 2M4 Coupe

Her Fiero: 1984 2M4 Convertible

quote Originally posted by Lilchief: Was wondering if you have decided on an induction system yet ? If using the TBI style system, what TB and injector (injectors) size? Can't wait to get started on mine. Great write up, keep the info coming.

I am thinking that 4 3800 SC series two injectors or similar at 36lb/hour should handle this setup NA. Since I can't get an intake to fit the 801 head I have to make one, and if I'm going to fab it, it may as well be port injection. I'll probably do something like a TPI 305 throttle body for simplicity sake