This is actually for an S10. I've decided to forgo a swap and settle for a measly 120ish HP I can squeeze out of the duke. MPG, cost and all that. I figured I could hog out the intake mani/head, bore the TB, build a header and a mandrel 2.25" exhaust. I've got a flow bench and have ported dozens of cylinder heads so this is something I'm very comfortable with

Any good cam profiles? I think after 86? they were all roller cams

Last iteration of the duke '91-93 S10s had 105hp. I know that head is not a swirl like the Fiero duke, but I don't know what else. As far I've learned 89-90 didn't have swirl but the bowls weren't as deep, and they didn't have the exhaust ports with the raised floors,

Is the tune significantly different for the S10 in those years? New PCM? They weren't DIS so hopefully the wiring isn't too different. Aside from a cam and gaskets, it shouldn't cost me a dime so I'm gonna have some real fun with this

TopNotch, on this forum, did some interesting things with the Duke in his car.
He'll probably pop in at some point. If not, run a search on his name. He posted a fairly detailed thread.

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Raydar
88 Formula IMSA Fastback. 4.9, NVG T550

Praise the Lowered!

I read through his thread. It's too bad there aren't more people doing the simple stuff to dukes. I've read A LOT of "just swap it" and "it isn't worth it"

Head swap and a prom change and you're looking at 20hp right there. What? $100? Worth it.
I'll have before and after dyno sheets

I am in the middle of the same project, I have an older gm reman 2.5 with ~100,000km's.

I have a holley TBI, will bore the hole to 2" then port match the head and intake manifold and modify a set of shorty SBC headers.

That 89 head looks to have more bowl volume then the swirl port head, if so you will drop your compression ratio.

You're confusing bowl and combustion chamber. And this isn't a swapped head, this is the factory head on the S-10. The chamber volume is the same as the 87-88 Fiero head. There isn't much material for "port match" and you will see very little if any gains without a real porting job

Ok yeah that's what I meant, I have a swirl port head which was on the 82-86 I believe which are junk for flow. I read that the later year heads were better like yours. The problem with porting work is that the head is so thin you need to be careful.

Back to your post, if your looking for a mild cam for a roller lifter set-up, the fierostore sells one, If you want to switch to a flat lifter set up there are more choices, found a few on summitracing.

Custom cam grinds can be had from Delta for $85. I'm going to tune this best I can before changing the cam so I can choose the best profile

[This message has been edited by Slammed (edited 04-02-2015).]

I soniced the intake ports tonight and all the bowls. I won't be touching the exhaust aside from bullet nosing the guides and a polish. There is plenty of meat everywhere aside from the high side of the intake bowl and the pushrod pinch point (obviously)

Should have some flow numbers following this weekend

The most aftermarket I have seen for the dukes come from midget class racing suppliers. as they used 2.5s
Maybe something to look into.

Got most of the roughing in on the heads. Still have to smooth out the chambers and exhaust bowls/ports.

I hope you had your head checked for cracks before you put all that work into it. Duke heads are prone to crack, and there can be micro-cracks you can't see.
Anyhow, here are some links on my duke rebuild threads:
Head thread
Rebuild thread

It only has 68k on it and I magnafluxed it when I pulled it

I've been an automotive machinist for 12 years now. I've got everything at my disposal for this build
Excellent job btw.

[This message has been edited by Slammed (edited 04-07-2015).]

I was also thinking about taking material off the guides to better the flow but aside from the amount of work, would it compromise the strength?

Also, did the port match last weekend and your right, there was not much material removal...

quote I hope you had your head checked for cracks before you put all that work into it. Duke heads are prone to crack, and there can be micro-cracks you can't see. Anyhow, here are some links on my duke rebuild threads: Head thread Rebuild thread

Nice build, I like your roller rocker set up!

The guides and the short turn are the most crucial part to the port. You will not compromise the integrity doing the guides. We have taken crummy 882 smog heads, done nothing but bowl work, and made +20hp with no other mods

The bowls will only take a couple hours. Do it.

[This message has been edited by Slammed (edited 04-07-2015).]

quote The guides and the short turn are the most crucial part to the port. You will not compromise the integrity doing the guides. We have taken crummy 882 smog heads, done nothing but bowl work, and made +20hp with no other mods The bowls will only take a couple hours. Do it.

That's impressive looking to implement this on my even worst swirl port head, what did you use to remove the material from the guides?

How much did you enlarge the intake ports of the head and manifold?

Single cut carbide burrs for the intake(aluminum) and double cut for the head(cast iron)

When you do the swirl, don't try and eliminate it. The roof and back of the bowl is not that thick, so you want to just widen the ramp slightly into the sides of the bowl and bullet nose the guide. I took about 8.5mm vertically and 3mm horizontally all the way down. I also tubed the pushrod holes and straightened out the pinch until I broke through. Give the short side as smooth of a radius as you can

Do not touch the floor of the exhaust port aside from polishing. You want that as high as possible

Liking the thread

This is as far as I'm going to take it. Polishing the chambers past this point would just be for pictures and I really don't care. Customers get bling, not me. The places that look untouched in the chambers are just powder I didn't blow out before the pic

I'll be doing the valve job tomorrow. I'm going to try and fit 1.94s in the intake. If they do, I will enlarge the throat more

[This message has been edited by Slammed (edited 04-08-2015).]

Ok thanks.

Think I've found some bigger valves that will fit, gonna do some machining this weekend and see what I come out with