Just ported my Duke cylinder head. Been reading up on what to look for via David Vizard's book, "How To Port and Flow Test Cylinder Heads" In that book Vizard shows the angles one wants to emulate, the tools and even how to make a cheap flow bench. I am not bothering with the flow bench and just basically doing the minimum required to try to get more HP and even gas mileage out of the stock 4 cylinder by porting the head. I am no pro and just using a 3,000 rpm drill, some grinding stones, a carbide flame bit of 5/16th". I did also get a porting sanding roll kit but it really can be done without, they seem more cosmetic than anything else. I used a black Sharpy marker, (no one has mechanic's prussian blue anymore!)
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84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White
[This message has been edited by White 84 SE (edited 08-02-2014).]
I opened up the end of the swirl quite a bit. The swirl as cast stops like a brick wall and I tried to let the air go where I thought it would want. Also the "throat" area was widened to 90% the intake valve size. Actually they measure 1.55 now. They were about less than 1.375" before obviously choking the air flow . I did not think that skinnying up the valve guides would help any, so I essentially left them as is.
Oh, and where the seat meets the chamber there is a little casting hill that seems to get in the way so that was blended but only as the swirl flow enters the chamber and not all around.
------------------ 84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White
[This message has been edited by White 84 SE (edited 08-02-2014).]
There are sharp angles to smooth out here and there and an attempt was made to work from 90* to 75* to 60* to 45* approaching the seat and 45* to 30* to blend coming out of the seat. But this was done by feel.
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One nice thing about working the throat first is that afterwards the standard 1.5" vacuum nozzle fit in snugly to extract the metal as I ground away! Here I have the head on its back which I think is best so as to concentrate on the ceiling area. There is a huge dime sized casting blip on each port roof.
------------------ 84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White
[This message has been edited by White 84 SE (edited 08-02-2014).]
I will not bother with the exhaust ports at all. The way I see it leaving them be may even deter back flow as a smaller area opens up to the ported exhaust manifold.
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This took a full day and I am in a hurry to get it done by end of day start to finish.
Anyway now off to wash it up and put it back together. Wish me luck!
------------------ 84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White
Let us know how it works, I hope it gives you a noticeable improvement. What year is your motor?
Csjag, yeah it's the original 84 although the head is a reconditioned one from Moore. It appears that it came from an 86 u code that has been re-drilled to fit Fiero. Everything lined up, the valve guides nice and tight but I am concerned about the rust evident in the water jackets... Perhaps it's a non-issue.
Improving the flow in the head should improve performance.
The head is what gives the SD4 all its power. The SD4 guide mentions that the SD4 head "out of the box" flows 88% more air than the stock Iron Duke head.
For what it's worth, after considering the stock Duke engine from a porting perspective... I'd say it's a natural for DIY porting. It's very simple, has only 2 valves per cylinder, there is plenty of room for larger valves, the design is not prone to overheating or any chronic reliability issues at all. The swirl port design is interesting too as it seems to attempt some pretty advanced shaping, not that the casting produces the intended result. First the passage funnels into 1/2 the normal size diverting ALL the air to one side of the valve eliminating any redundant flow areas thus increasing velocity. The angles of the intake passage is virtually horizontal with a rising floor (which was innovative for a production model) and then angles downward into the combustion chamber in a swirl. This I understand is a 1st draft attempt with the heads that went into the 1984 Fieros. Here's an old school iron 4 cylinder given an EFI and a try at a new swirl port idea put into a tiny innovative car aimed at efficiency that.....wink.....can use a little performance help. It seems like the designer went above and beyond within all the restrictions required by management. Bravo Hulki!
[This message has been edited by White 84 SE (edited 08-12-2014).]
In the archives, someone got the duke up to 180hp, I believe.
Good luck. I've always thought about buying a 4cyl Fiero for a challenge but I'm still not done with the V6...
Thanks man, I am just taking it slow. 1st porting> see what that might do. Next 30* valves same size> see what that might do. Next depending if 30* works or not conservatively larger valves>see what that might do etc. I like the idea of "super stock" if it means stock but tweeked as much as it can be tweeked. Actually the whole bolt-on/swap approach seems to me to take away from the unique originality of the car, and it is a unique original car. That is also why I like the 84 model with all its flaws. If Duke tweeking does not lead to a satisfying daily driver I will swap to the stock V6 and start tweeking that. Maybe retire the gloves and join up with the MG cats. I do like convertibles but rust is a very sad thing.
------------------ 84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White
[This message has been edited by White 84 SE (edited 08-12-2014).]
I will not bother with the exhaust ports at all. The way I see it leaving them be may even deter back flow as a smaller area opens up to the ported exhaust manifold.
Hey Kurt, you don't think that's ok? Honestly, I would have to enlarge the entire exhaust passage to open up any thing there. I could gasket match but why? I consider you to be a bit of an expert although Vizard suggested that really, the intake is where to concentrate your efforts.
------------------ 84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White
Assembling the cylinder head...AFTER porting I am finding that the reconditioned head assembled spring height is higher than specifications. If I were to install this I expect the engine would be quite damaged.
[This message has been edited by White 84 SE (edited 08-03-2014).]
Oops! The remanufactured head came with spring shims and I just removed them because that's not how my original was. With the spring shims it's in spec. Checked the valves and they are right.... just jittery I guess. Well it's good to have the specs so as to check. Phew!
[This message has been edited by White 84 SE (edited 08-03-2014).]
Improving the flow in the head should improve performance.
The head is what gives the SD4 all its power. The SD4 guide mentions that the SD4 head "out of the box" flows 88% more air than the stock Iron Duke head.
88%.... trying to get my head around that.... 88... that's like 2 heads. 88.....percent. I wonder what % flow improvement is possible with the production Duke head. I mean if an ideal head gets 88% better flow and gets 275 HP... What would 10% flow improvement get?.... let's see 88% = 175 HP extra... that's 2 HP per percent.... hmmm 10% x 2 whoah.....20HP That's alot! Who knows if opening up the throat, unlocking the swirl, 30* back cut on the intake valves, gasket matching the intake side can get 20 HP in the normal RPM range (it may only gain in higher RPMs) On the other hand say it's 15%...that's a crazy 30 HP boost! hahaha I am dreaming! We'll see. One thing that spooks me is that this reconditioned head seems not to fit right. The original rockers seem rather short not seating over the stem heads completely. The valve stems seem high which will (if so) cause the rockers to crush the push rods. I have to do a little research regarding rockers and rods of different year Dukes.
Well, you've got this far. You might as well throw a set of small block chevy full-roller rockers with a higher ratio on it. Open up those valves a little more and enjoy faster revs.
In the archives, someone got the duke up to 180hp, I believe.
Good luck. I've always thought about buying a 4cyl Fiero for a challenge but I'm still not done with the V6...
I believe that was about 15 years ago and it may have been a guy named Ira Crummy from the province of New Brunswick or Newfoundland in Canada. If its him, he hasn't posted here in a long time so its undetermined how the long term reliability worked out. Since joining this forum in 2001 we've seen 100's of Fiero owners come and go. Racincouple (Neil and Dwon Kline) also built a ground up high performance Duke but shortly after sold it due to Neils health issues. We seem to never get actual numbers on these engines but they are out there. The HP limitation seems to be the strength of the crankshaft.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Powerlog manifold, Northstar TB, LS1 MAF, 3" Flotech Afterburner Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
Nice website. Lots of 2.5L info compiled by Ira and he does have articles on the ports and other performance enhancements. For the Duke lover this is an excellent resource.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Powerlog manifold, Northstar TB, LS1 MAF, 3" Flotech Afterburner Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
Well, you've got this far. You might as well throw a set of small block chevy full-roller rockers with a higher ratio on it. Open up those valves a little more and enjoy faster revs.
Serious? If it makes the Duke smoother sounding I am all for it. On the other hand I am not going to pay hundreds of dollars for them... I will look into it, thanks!
------------------ 84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White
So after one ports the head and intake and exhaust, what else needs to be altered for it to work?
Nothing man, just put it back and light it up. I think one would start to get warning lights indicating lean fuel mixtures if VE improvements were so dramatic that the fuel pressure then could not keep up. Still I think such a condition would be at the higher than 5000 RPMs which is taboo anyway. Or the engine may kinda die when revved aggressively but operate normally at idle or when accelerating normally. Such a condition would warrant greater fuel pressure. I think the TBI can be inexpensively tweeked with a variable regulator to replace the existing one somehow or there's the rare Holley TBI.
By the way if a Fiero still has the original fuel pump there is a good chance that it is not operating optimally and a change out would give an instant little boost.
Any way, Even though I am a bit weary about this reconditioned head and its fit I will bite the bullet and get it installed this weekend and give it a go..... Or update you all in any case.
------------------ 84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White
[This message has been edited by White 84 SE (edited 08-05-2014).]
Nice website. Lots of 2.5L info compiled by Ira and he does have articles on the ports and other performance enhancements. For the Duke lover this is an excellent resource.
Most importantly I think will prove to be the "pocket porting" that Gary Ohst suggests on that site (he talks of hogging out just under the intake valves in an interview)... Well see, I mean these cars are cool and I think maybe the Duke swirl port is where the problem has always been. Not the design just the casting. The inherent design seems like it may increase flow by eliminating redundant areas and increasing velocity but the casting seems to have been pushing the limits of the time resulting in a bottle neck. I half think the designers designed this in so as to stimulate after market sales especially given the SD4 development and Indy models of the first year, Holley was on board, others..etc.
[This message has been edited by White 84 SE (edited 08-05-2014).]
Casting numbers are 552 or 702. There are cheaper places to buy them.
Compression ratio? Thanks this might be fun to mess with over the winter. I do have faith in the swirl port idea though but yeah in a classic sense this looks way more mod-able. Gonna go with new flat top piston then? That and porting...well then it might need help with the crank cause y'all might be flexing Yep, I think you have something there. I don't know...I like those swirl lines on the Indy air cleaner....they go better with swirl ports.
------------------ 84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White
[This message has been edited by White 84 SE (edited 08-07-2014).]
Ok Moore reconditioned head with 767 casting has the water spout on the wrong side. Have to plug the one side with a new cap and extract the cap on the drivers side. This is one of those U code heads that has been retro fitted to fit R code cars. What a pain. Every thing else SEEMS to line up.
Note: cap = "freeze plug"
[This message has been edited by White 84 SE (edited 08-07-2014).]
The Pontiac Sunbird that head was used in only had 85 hp
TBI + swirl port + dished piston in the Fiero aimed at same 90 h.p. previous market niche. I suppose a fairly cheap mod for the Fiero Duke might be to swap to flat top pistons and advance the timing? But porting the head is basically free. By the way, I have a copy of the original factory shop manual for the 1st year Fiero and it suggests intake valves can be fit up to 1.89" for a HO version. Might do that next summer. But one can see immediately that the casting of the swirl ports is not as design intention would lead to. It actually looks like a raw casting meant to be ported later.
[This message has been edited by White 84 SE (edited 08-12-2014).]
Ok Moore reconditioned head with 767 casting has the water spout on the wrong side. Have to plug the one side with a new cap and extract the cap on the drivers side. This is one of those U code heads that has been retro fitted to fit R code cars. What a pain. Every thing else SEEMS to line up.
Hey thanks! Good to know. Wait, it's vague but I thought a 767 casting head only came in R or U code. Is that the info you have as well? Forgot the website I got that from...
Can the dukes head be "decked" for more compression and power?
Having examined it closely I would say it is risky. This one seems like it has been shaved - perhaps just as part of the reconditioning process - but not very much. I'd guess that there is less than an 1/8" metal left between the bottom and the water jacket.
Just an update. Did get it running today after 3 years in the garage with the cylinder head off. (Previous porting found a crack so it's been laid up til now) It's pretty rough but it lives! Flat tires, tune up needed stickers etc before I can report back regarding performance improvements but I will get back.
