I rebuilt my engine 2 years ago but I really did little porting of the head. I did port match and put in the Fiero Store performance cam. Certainly there has been an improvement in performance although not huge or anything. Now it looks as though I wont be driving the car for a few months so it is the perfect time to do some deeper porting of the head. I have found a good bit of information on the Popular Hot Rodding site and now feel a little more comfortable doing some more porting. From what I've read the Duke swirl port head looks really restrictive around the intake valve port.

I plan to open/de-shroud the intake side of the chamber to about 1/8", blend all seats to chamber, skinny the guide bosses and blend to housing, and basically clean up any casting blips. Anything not so obvious to watch out for?

Here's a quote from Gary Ohst from one of the essays on Duke performance to do's on Ira's Duke site:
"Porting the head is most important. In the area under the intake valve in particular. Holly TBI & manifold will not add much. Stock intake manifold/TBI flows enough. You may need a higher pressure fuel pump and adjustable regulator. Use more fuel pressure to adjust for VE improvements in the engine. That saves messing with the ECM fuel maps."

Now I've been reading that for a few years and it's still unclear what he meant by the "area under the intake ports"... did he mean that whacked extreme kidney shaped compression chamber or the equally whacked swirl staircase delivery passage or the beefy valve guide bosses or all of the above?

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84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White

[This message has been edited by White 84 SE (edited 09-22-2010).]

I had a look at my rebuild thread and now find some advice given by Lou and Kurt more understandable. As for opening the compression chamber as was warned against via Lou... Yes I see now how that would be contraindicated to what I want out of this engine. Thanks a million, I will only smooth/blend and not alter the volume much and hopefully keep low end torque. Mostly I am excited about thinning down the guide bosses and blending. When I was in there last they intuitively seemed bulky and against good flow. And Kurt thanks again for pressing realistic expectations. If I gain 5 horses I know I will be lucky. It is just a weekend project (he says not knowing exactly what lay in store).....

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84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White

[This message has been edited by White 84 SE (edited 09-22-2010).]

..Just clean it up ,,smooth the flow ..I doubt if there is much gain in cutting down the guides .so go easy here.Theduke will not turn the RPM,s to benefit
,..A really good port match
..Equalize the ports size ,,make a plastic template..
..Remove the plate under the TBI..
make sure TBI screws are tight inside..it is a 2 piece unit
Headers for the duke have become scarce,,a used or new chevy V8 header exhaust manifold can be adapted if you can weld or have a friend who can weld to help..NOT EASY TO DO
..when doing modifictions go for performance AND improved Gas milage..
,,add a turbomuffler or free flowing muffler in place of the stock muffler (not a bolt on),,this muffler should be in the stock location
do a lite reseat of the valves ..hand reseat
..Use synthetic oil..
use stock air cleaner system
..Index spark plugs
..It takes a lot of small modifications working together to improve a modest engine like the duke .
make sure all wheels spin as free as possible

quote Originally posted by uhlanstan: ..Just clean it up ,,smooth the flow ..I doubt if there is much gain in cutting down the guides .so go easy here.Theduke will not turn the RPM,s to benefit ,..A really good port match ..Equalize the ports size ,,make a plastic template.. ..Remove the plate under the TBI.. make sure TBI screws are tight inside..it is a 2 piece unit Headers for the duke have become scarce,,a used or new chevy V8 header exhaust manifold can be adapted if you can weld or have a friend who can weld to help..NOT EASY TO DO ..when doing modifictions go for performance AND improved Gas milage.. ,,add a turbomuffler or free flowing muffler in place of the stock muffler (not a bolt on),,this muffler should be in the stock location do a lite reseat of the valves ..hand reseat ..Use synthetic oil.. use stock air cleaner system ..Index spark plugs ..It takes a lot of small modifications working together to improve a modest engine like the duke . make sure all wheels spin as free as possible

Thanks bro, I've got a header on the way but it fits like the stock so I don't expect it to be much better flowing, will re-seat for certain,...have 2 glass packs now which is pretty good but piping straight from the manifold to a cat back might be better. Indexing sparks...never tried that.... may help!, synthetic oil....seems impractical..what would be the benefits again?...Stock air cleaner?..I use a K&N and seem to notice improvement,,no?..

C'mon on the valve guide bosses...those are crazy bulky...there is no need for 1/2 of that metal and they get in the way of the flow path right at the point when it enters the bowl. It's an obstruction of justice I tell ya!

..The cutting away of the guides will add some air flow ,,but you lose some rigidity in the valve ,,just take it easy ,,smooth the flow ..
..I have a K&N but they add little power because the ECM controls the air flow .. I ment to use the stock factory Fiero plumbing
..Any one interested in more power or more efficient running,,should use synthetic oil..it is more slippery ,,it keeps the engine cleaner and because of increase lubricity it adds horse power,,your engine will be more reliable & have less drag/resistance on rings ,bearing,pistons..

NAPA has been having sales on thier Napa brand synthetic ,, this is Valvoline so watch for these sales on Synthetic,,
..Synthetic oil is win, win,win
..older engines with a lot of sludge in the crankcase should not be switched to synthetic because it cleans and loosens sludge and carbon..
..The best sounding muffler for a duke is the glass pack ,had one on my 88 duke,, beautiful sound going thru the gears ..a glasspack hurts performance , the slits cause turbulence that hurts performance..I used glasspacks for many years .but over the past 10 years ,,Dyno test have shown the new turbos are the way to go,,you are loosing power running glasspacks..
Running the muffler in the location where the cat was hurts performance ,,best to mount muffler in original location ,,because of spring mounting,,I realize what a pain it can be to mount muffler in stock location..
..Thefirst 2 are H.P./torque rating,,the 3rd racetruck is sound
Google>> Titantalk.com,performance-modificationflowchart for a few mufflers
Google>.Mustang50magazine.com,muffler comparison test
http://www.racetruck.tripod.com/muffler.html
..If you want a unique Duke engine compartment ,,adapt the Edelbrock Elite air cleaner or just the Top ,,eyeball one you will like it.. however its $50.00 & not a drop in..

[This message has been edited by uhlanstan (edited 09-23-2010).]

humor me and pick up a #552 crossflow head from a 1981-1983 car like a Phoenix, Citation, or Jeep that's non-swirl port.

Pop out an intake valve, snap a few pics and tell me what you think about the difference in the intake port.

373 and 767 castings really can't be used to make more than 130 horsepower, regardless of what you might find online.

Thnx Uls I will look into those ideas.

Kurt, now that would be tough. Do those earlier heads fit? Compression was 8 ish back then. Apparently the swirl port got more squish but that may be due to other VE improvements. How about later Duke engines? 87 is said to have an improved cylinder head. How were those improvements made? Perhaps these improvements can be made manually. Heck, maybe they have an 87 Duke at my local junk yard.

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84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White

hey since you've re built ure duke yourself would u mind taking a look at my thread? ive been having some problems with major water in the oil, ive tried thee different head gaskets and i don't see me getting three faulty gaskets,but i drove the car to the shop and drove it before and never had any problems like this, so we do a bunch of work to the motar and now im running into the problem as if my block cracked? any advice would be helpfult thanx.

those are head casting numbers; the last 3 to be exact

quote Originally posted by White 84 SE: Kurt, 373 767....is that a sort of steel alloy? Are you saying that 150 HP would blow a hole through the casting of a certain thickness? Honestly, that is a real concern that I can understand....

I think he's saying that you won't flow enough air with those heads to produce more than 130 hp, naturally aspirated.

..The Edelbrock elite air cleaner is aluminum with low fins,,I was going to adapt one to my duke,,I made a mistake and loaned the car to a friend ,he has not spoken to me since he returned destroyed car , ha, ha,,Another Fiero clutch adventure .
..This single feature would enhance the engine compartment the way the super duty valve cover does..NOT A BOLT ON...eyeball this cover !!!
,,the only real way to higher early Fiero duke performance is to install a 90/91/92 Duke engine ,,Any duke with dual coil ignition from crankshaft is far superior to 84,85,86 the next step up is improved duke head which can be installed on 87/88 duke..
..Google.""Edelbrock elite air cleaner"" this will bring up many options,,click on the summit option for a neat represetation..
..20 years ago,My first Fiero was a GT duke and had an edelbrock elite air cleaner & offenhauser valve cover (one off?)..NEAT O JET engine compartment..
..120 real horsepower is limit for 84 to 86 duke,,sorry ,,but I am a duke lover,,I like my engines simple & I like my women smart with brains as long as thier brain is cute,young and tight..

[This message has been edited by uhlanstan (edited 09-23-2010).]

quote Originally posted by White 84 SE: Here's a quote from Gary Ohst from one of the essays on Duke performance to do's on Ira's Duke site: "Porting the head is most important. In the area under the intake valve in particular. Now I've been reading that for a few years and it's still unclear what he meant by the "area under the intake ports"...

I think you misread it. He said under the intake valve not intake port. Look at your picture. See the intake valve? Look under it.... Under is relative to how you are viewing it. That is how I read it. My .02

quote Originally posted by Hudini: I think you misread it. He said under the intake valve not intake port. Look at your picture. See the intake valve? Look under it.... Under is relative to how you are viewing it. That is how I read it. My .02

Right......under the valve....directly would be....valve seat...then...what is refered to as deep pocket porting....I think he may have been speaking of that...not sure though. If he is speaking in terms of an installed head than right under the valve will be the seat to compression chamber with it's heart shaped bowl. Vizard suggests 1/2" on either side of the seat and of course the size of the valve itself as being the key areas. Thanx bro.

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84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White

quote Originally posted by baldlobo: those are head casting numbers; the last 3 to be exact

O.K. thanks Baldlobo!

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84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White

quote Originally posted by pmbrunelle: I think he's saying that you won't flow enough air with those heads to produce more than 130 hp, naturally aspirated.

correct.

I have a header/exhaust systum for a duke. I was made by paul vanderly when he was developing the SD parts. it has both bolt patterns and a turbo muffler. It is a try -Y ( 4 in to 2/ 2 in to 1 ). It is the first SD header ever for the SD-4. has a o2 sensor. Yes, THAT Paul Vanderly. I could part with it. I would like to see somebody use it. I know where the test mule fiero is that it came off is also.
frwihall@aol.com 228-868-5546 cell 228-380-7020 thats in mississippi on the gulfcoast.

quote Originally posted by FFIEROFRED: I have a header/exhaust systum for a duke. I was made by paul vanderly when he was developing the SD parts. it has both bolt patterns and a turbo muffler. It is a try -Y ( 4 in to 2/ 2 in to 1 ). It is the first SD header ever for the SD-4. has a o2 sensor. Yes, THAT Paul Vanderly. I could part with it. I would like to see somebody use it. I know where the test mule fiero is that it came off is also. frwihall@aol.com 228-868-5546 cell 228-380-7020 thats in mississippi on the gulfcoast.

Wow....what a coincidence...I just recieved my new manifold "header" in the mail today! Oh well, I am sure it nothing compared but check it out. It's nicely polished stainless steel from OBX in California.

One can easily see better flow happening in the arm bends. More subtle is the straighter and wider flow of the center and a cross section would show smoother angles and venturi like transition shapes. A steal for 99.00! It still needs some careful gasket match porting to the Felpro I matched my head to or it will actually obstruct flow. It's got nice 1/2" flanges so blending can be done far from the welds but it will need to be done.

I got my work cut out for me but anyone looking for a great Duke exhaust check out FFierored!!!


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84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White

[This message has been edited by White 84 SE (edited 09-24-2010).]

..The S 10 head or the latest model duke head will only fit the 87/88 Fiero Duke..


The offenhauser valve cover was custom made ,,a used offenhauser Valve cover was Obtained at Hot Rod flea market ,, the top cut out and fitted to a stock DUKE valve cover ,, the stock duke valve cover was cadium ?? Plated then the Offenhauser top screwed into the stock Duke valve cover a one off custom piece made by a perfectionist ..
..difficult to find used offenhauser valve covers now ,,some one bought the name,, they still make new ones
..To make any real power from a 84,85,86 duke you have to change the block,,go to the 88 S10 block or some thing like that,,
..The ultimate Duke is the OHC nitro version $10,000.oo,, a measly pitance for the average affluent duke owner

[This message has been edited by uhlanstan (edited 09-24-2010).]

quote Originally posted by uhlanstan: ..The S 10 head or the latest model duke head will only fit the 87/88 Fiero Duke.. The offenhauser valve cover was custom made ,,a used offenhauser Valve cover was Obtained at Hot Rod flea market ,, the top cut out and fitted to a stock DUKE valve cover ,, the stock duke valve cover was cadium ?? Plated then the Offenhauser top screwed into the stock Duke valve cover a one off custom piece made by a perfectionist .. ..difficult to find used offenhauser valve covers now ,,some one bought the name,, they still make new ones ..To make any real power from a 84,85,86 duke you have to change the block,,go to the 88 S10 block or some thing like that,, ..The ultimate Duke is the OHC nitro version $10,000.oo,, a measly pitance for the average affluent duke owner

Uhls you REALLY have to get another Duke Fiero.....Late model pronto!!

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84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White

quote Originally posted by White 84 SE: Just looked at specs on the various Fiero heads... Looks like ONLY the 84-86 heads got 9:1 compression. Is that right the 87-88 heads got 8:1 and yet got better HP?

the iron duke was only 8:1 befor 84, after is all 9:1; according to piston specs

the cylinder head shape changed from kidney or heart shaped to bathtub(after 88); both aren't great for airflow, one is less shrouded then the other; you could try singh groovying the head on the earlier cylinder heads(but most say the cylinder heads are thin)

[This message has been edited by baldlobo (edited 09-25-2010).]

quote Originally posted by baldlobo: the iron duke was only 8:1 befor 84, after is all 9:1; according to piston specs the cylinder head shape changed from kidney or heart shaped to bathtub(after 88); both aren't great for airflow, one is less shrouded then the other; you could try singh groovying the head on the earlier cylinder heads(but most say the cylinder heads are thin)

Now my Haynes manual states on page 2C-1 that the 84-86 2.5L engine made 9.0 to 1 compression and same page just below states the 87 and 88 2.5L engine made 8.3 to 1 compression. I would suspect an error since the later engines make more HP. Bore and stroke remained the same, no info on the valve sizes, Lift was lower on the later engines, springs were less strong, push rod length was very long on the 84 only, cams all have the same specs, they say the pistons were improved and a better head in the 87-88s but yet they had lower compression, lift,... It's a puzzle. Perhaps the intake ports are higher....they do have a different manifold...

Thanks for the idea....I dont know how to singh groove or much about the concept. Better atomization was it? It is something to do on the floor....I saw something about somewhere....don't recall.

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84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White

http://somender-singh.com/content/view/7/31/

Oh wow - How interesting! I will definitely put a central groove in the Duke head. Gets that hot spark ignited fuel to the far side of the piston quick enough to ignite the entire chamber maximizing use of fuel and wasting less. That would keep it cooler as well and quicker igniting.... What a terrific idea. It makes complete sense. Actually when I take the head off it will be interesting to study the chamber to see about dead pockets. That will indicate exactly where to groove to!! Thanx man so much!!

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84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White

[This message has been edited by White 84 SE (edited 09-25-2010).]

..A lot of duke performance info is lost forever ,due to lack of interest & low horsepower out put from these engines,,you want to get the most MPG from the Duke ,and hopefully the modifications will
increase power ..
..You and the orge(homage paid) are responsible for the shim rockers tip to quiet the duke,,unfortunately most will forget this important Duke tip,,
..My dream Fiero is an 88 GT T top with a 140hp duke,4 speed auto that gets 25 to 28 mpg around town,,unfortunately because of injuries,I will have to pay someone to do swap the Duke & auto into the GT,& i spend all my spare cash on women of unusual virtue,and trips to visit Ukraine girls..I have an 86 GT with 4 speed manual..
..You can not open up the stock head very much,,the head will crack
.. the porting HP gains are under the intake valve
.. the 87 ,88 exhaust manifold is great
..the 88 fiero crank is best BECAUSE of mass
,,you want mid range power with a Duke,asking for trouble at High RPM
..later S10 blocks have additional webing and better steel mixture.
.. the coil fired blocks have more power
..Marine engines & parts desirable but beyond average owners dedication and ability..
..The U vin number blocks are shorter ,use complete engine.
..use of PROM or complete ECM can increase power ,, this is determined by VSS car used
..superduty is still used in some forms of dirt track racing.
.. the exhaust system needs a header and free flow back to turbo muffler mounted in stock muffler location..
,, the 1991S10 duke uses 7165 ECM can be adapted to 87/88 for immediate power gain

[This message has been edited by uhlanstan (edited 09-25-2010).]

Some interesting reading:
https://www.fiero.nl/forum/F...2/HTML/023474-6.html
https://www.fiero.nl/forum/F...2/HTML/074087-2.html
https://www.fiero.nl/forum/F...2/HTML/093668-3.html

[This message has been edited by katore8105 (edited 09-25-2010).]

quote Originally posted by uhlanstan: ..A lot of duke performance info is lost forever ,due to lack of interest & low horsepower out put from these engines,,you want to get the most MPG from the Duke ,and hopefully the modifications will increase power .. ..You and the orge(homage paid) are responsible for the shim rockers tip to quiet the duke,,unfortunately most will forget this important Duke tip,, ..My dream Fiero is an 88 GT T top with a 140hp duke,4 speed auto that gets 25 to 28 mpg around town,,unfortunately because of injuries,I will have to pay someone to do swap the Duke & auto into the GT,& i spend all my spare cash on women of unusual virtue,and trips to visit Ukraine girls..I have an 86 GT with 4 speed manual.. ..You can not open up the stock head very much,,the head will crack .. the porting HP gains are under the intake valve .. the 87 ,88 exhaust manifold is great ..the 88 fiero crank is best BECAUSE of mass ,,you want mid range power with a Duke,asking for trouble at High RPM ..later S10 blocks have additional webing and better steel mixture. .. the coil fired blocks have more power ..Marine engines & parts desirable but beyond average owners dedication and ability.. ..The U vin number blocks are shorter ,use complete engine. ..use of PROM or complete ECM can increase power ,, this is determined by VSS car used ..superduty is still used in some forms of dirt track racing. .. the exhaust system needs a header and free flow back to turbo muffler mounted in stock muffler location.. ,, the 1991S10 duke uses 7165 ECM can be adapted to 87/88 for immediate power gain

Yea thanks for noting that shim trick. It really does quite the Duke valve train a noticeable amount. I came up with the hunch after trying to figure out how to quiet the Duke. Ogre was able to confirm after some research. I gave it a whirl on my Duke and it proved successful.

Regarding the ECM I think it would be possible to make general changes using variable resistors. I mean make it run at a different target air/fuel mix. Also go into open loop at a different temp. I dont see a way to change How the ECM responds just What info it gets.

About the double coil ignition system...How does that work. I think that may have a lot to do with late model Fiero Duke improved HP. Honestly this Singh groove idea may improve full combustion in the chamber to a similar degree. Getting exciting! Ha I have to keep reminding myself that were talking about a rather low performance engine but hey, this little stuff really cant hurt very much either.

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84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White

About those shims... Here's a pic of them installed..see how they push down the rocker a scant bit. But here we can see the gasket porting. Pretty good I think, didn't really know how well it all fit but here we see it pretty good. I was feeling around there and especially the ceilings of those ports/passage ways have a bunch of rough casting stuff to grind away.



I was feeling around especially on the roofs of the passageways and can find much casting flaws to smooth out. Last time I made sure not to go deeper than an inch but now I think I understand matters better and feel I could touch stuff deeper but in a careful way. By the way, the metal IS rather thin, I think less than a 1/4" in general. On the roof I wont be taking anything out but the bloops. I had hoped maybe the ceiling could be raised....no such luck for certain!

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84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White

..I have spent more time thinking and reading about duke performance ,,than actually working on the duke.. I was trying for better milage .

..Do not remove anything from the roof ,,when I sneak up on some gooner slopes I kept low to the ground.
for best performance ,,your Duke fuel/air mixture is the same way,,remove material from the top will hurt performance,port match extremely well,,then remove material from the bowl area ,,remember you will not be able to benefit from hi RPM WOT because the engine will come apart..
..with the duke you have to take small increases in power,where you can get them,,a lot of expense with little gain..
cutting into the combustion chamber is going to hurt performance..
..When you port ..make templates ,guides so each port and combustion chamber are the same ,,all ports equal pulling equal,,pulling together ,,Start by measuring the valve hole make them equally round ,,all the same size. cut out a template,mount it to a stick ,,eyeballing dont no,nyet, nada cut it ""measure""
..You have to go to another later model block and head..
..Swaping to another later model ECM ,will be easier than trying to improve your 84 ECM..I don.t know crap about Fiero,s,also been hit in the head to many times,ha,but I know a lot about engine basics.use to build performance scooter engines..
switch to synthetic oil,,the best modification you will do,buy it on sale,USE SYNTHETIC OIL.
make your next Fiero an already swapped 3.4 or 3.8 buick.good luck

..I likey, when some one works & modifies the duke with what is available,,YOU HAVE TO SWITCH BLOCKS TO GET THE POWER YOU NEED ..

[This message has been edited by uhlanstan (edited 09-26-2010).]

quote Originally posted by uhlanstan: ..I have spent more time thinking and reading about duke performance ,,than actually working on the duke.. I was trying for better milage . ..Do not remove anything from the roof ,,when I sneak up on some gooner slopes I kept low to the ground. for best performance ,,your Duke fuel/air mixture is the same way,,remove material from the top will hurt performance,port match extremely well,,then remove material from the bowl area ,,remember you will not be able to benefit from hi RPM WOT because the engine will come apart.. ..with the duke you have to take small increases in power,where you can get them,,a lot of expense with little gain.. cutting into the combustion chamber is going to hurt performance.. ..When you port ..make templates ,guides so each port and combustion chamber are the same ,,all ports equal pulling equal,,pulling together ,,Start by measuring the valve hole make them equally round ,,all the same size. cut out a template,mount it to a stick ,,eyeballing dont no,nyet, nada cut it ""measure"" ..Swaping to another later model ECM ,will be easier than trying to improve your 84 ECM..I don.t know crap about Fiero,s,also been hit in the head to many times,ha,but I know a lot about engine basics.use to build performance scooter engines.. switch to synthetic oil,,the best modification you will do,buy it on sale,USE SYNTHETIC OIL. make your next Fiero an already swapped 3.4 or 3.8 buick.good luck ..I likey, when some one works & modifies the duke with what is available,,YOU HAVE TO SWITCH BLOCKS TO GET THE POWER YOU NEED ..

Thanks buddy, as far as port floors- I will leave them be except where they meet the valve seats and only do a little blending there. Turns out that with sharp turn heads, like all Duke production versions, the flow inevitably looses contact with the floor and is concentrated in the upper 1/2 of the passage way. The technique pros use is to raise the floor and roof...this would be a disaster for a Duke head. Another thing to think about is widening the passage in the top 1/2 of the port only. I will look more into that but my standard will be that there must be 1/4" wall thickness by feel. But certainly I must smooth out the casting blips especially on the top and those hunky valve guide bosses are to be skinnied up. These can be used to direct flow a little and I will look into that. Great idea on the template! I will do that. Since I will be putting a Singh groove in each chamber I best keep them very close in size.

[This message has been edited by White 84 SE (edited 09-26-2010).]