86Z24 hybrid engine build - Advice?

[Calvin]

I have another query to add to my list...

I just brought one of my heads in from the garage, and pulled one pair of valves out, and noticed a large fin(?) in the intake runner.
I was wondering if it served a purpose, or if I should hog them off when I do the porting?

Its usually pretty common opinion that the fin should be left in there, since the Chevy high performance 6-60 book says that it increases airflow and I have heard knocking it out can hurt you up to 10%

[Superdave]

I am building a 3400 shortblock with 3500 top end using 3.4 DOHC pistons. Its roughtly 12:1 range. I dunno where you got 18:1 with 3400 heads but that is just crazy. The DOHC pistons should not extend as far out of the deck as the 3400 pistons either.

Kinda what i was thinking...

I've often thought about swapping to those pistons. I'll have the chance tomorrow with the engine torn apart but i doubt i'd be able to find any that quick

[SappySE107]

I have a set of .030 that I need to finish deburring/sanding on if that would work. They are the ones I was doing for this block before it had to go .040 instead.

[Syn]

Its usually pretty common opinion that the fin should be left in there, since the Chevy high performance 6-60 book says that it increases airflow and I have heard knocking it out can hurt you up to 10%

its not commone from what i've seen mine are gone as well as many people i know of.

my .02

[SappySE107]

Well if someone in florida would stop procastinating I would be able to test some iron head porting/fin removal. The fin is supposed to be in there according to the GM Performance book but I have also seen people remove it anyway. I really couldn't tell you either way since I have no experience with it, but its probably best to leave it alone unless you know what you are doing.

Personally, i would trust GM over most of the work you will see from other people.

[sharkey]

there is a guy local that runs a shop out of his house, and he only does fiero stuff. he has built quite a few ironhead motors, and he says he has best luck with just reshaping the fin. taking it out creates a dead spot in the port, and the fin helps with properly mixing the fuel with the air. i would just reshape it a bit, thats what i did with my heads.

[Calvin]

I know from my own tinkering when the origional 2.8 was still running, what a drastic difference a little twist can make, and you just can't do that with DIS.

Yeah you can. It just sounds a little different, like the clicking of six keyboard keys followed by the click of your mouse and the snap of your ZIF releasing your new custom PROM with optimized timing fuel TCC lockup fan turn-ons, idles speed and more.

[Calvin]

its not commone from what i've seen mine are gone as well as many people i know of.

my .02

Um, aren't you running aluminum heads? This fin is a peculiarity to the Gen I iron heads.

[Syn]

Um, aren't you running aluminum heads? This fin is a peculiarity to the Gen I iron heads.

yeah i thought about that today i feel a bit stupid now

but the gen III heads have a bulge in the intake ports

[SappySE107]

That bulge is for the rocker arm stud and does nothing for flow when removed.

[Syn]

good to know,i knew what it was for. bahh owell

[86Z24hybrid]

My heads have been CC'ed at 52cc, vs. the aluminum heads at 25 to 26cc.

That's a major part of the reason I opted for the DOHC piston/Ironhead combination. Estimates from other sources put the C.R. at about 9.6:1, while the C.R. generator here puts it at about 10.35:1, which is JUST within the limits of pump gas (although expect it would run MUCH better on racing fuel, if and when I decide to take it to the track).

I just ran the numbers through the Updated CR Calc, and if I were to try to use the 3400 heads with my setup, it would put me at about 13.9:1, and there's no way that I'd get that to run properly on pump gas.

And my DOHC piston/ironhead setup now shows 9.66:1, which is just slightly over the 3400 CR stock (@9.54:1), which will run quite comfortably on 91 octane.

[86Z24hybrid]

Yeah you can. It just sounds a little different, like the clicking of six keyboard keys followed by the click of your mouse and the snap of your ZIF releasing your new custom PROM with optimized timing fuel TCC lockup fan turn-ons, idles speed and more.

Unfortunately, I don't have an extra thousand dollars to spend on the software and equipment to do that (according to the prices I found about 2 months ago).

Like I said, at this point, this has become a limited-budget project (due to employment reasons) to replace a blown motor and make my car a little faster, and I would like to actually drive my car THIS year.

At this point, I'm going to put the car together, and drive it to the shop that's going to dyno-tune it for me for $3-400, and let them set it up properly the first time, then if I want to tweak the timing up or down for driveability, then it doesn't cost me any extra.

I just don't want to run into crashing pistons the first time it turns over, hence the origional question I asked with this thread.

Thank you for the advice, though, I do know where you are coming from on that one.

[86Z24hybrid]

there is a guy local that runs a shop out of his house, and he only does fiero stuff. he has built quite a few ironhead motors, and he says he has best luck with just reshaping the fin. taking it out creates a dead spot in the port, and the fin helps with properly mixing the fuel with the air. i would just reshape it a bit, thats what i did with my heads.

any advice on shape? I was thinking of hogging it to act like a knife/wedge, to direct the airflow to the sides of the runner and avoid the short-side radius issue, or would I be better off to to flatten the top pf it to direct the airflow across the port towards the valve guide?Or should I just smooth it and round it off a bit?

open to suggestions...

[sharkey]

i basicly just smoothed it out a bit, made it a bit more of a point at the top side of it.

as for tuning the 86 cavy ecm (7302) there is pretty much nothing. you either need to convert it from a 24 pin rom to a 28 pin eprom before you can do anything, or swap to a different ecm, wich means rewiring the engine bay harness-ecm plugs and then you have to start with a clean sheet on tuning. it isnt that much, i priced it out to be under $300 for eveything i needed to start off tuning, but thats once i swapped the ecm over. for the time and hassle of it, im just gonna start with a megasquirt standalone. gonna cost me about the same amount of money in the end, and i never have to screw around with an emulator or burning chips.

if you need any help with anything, hit me up on msn or pm me, ive pretty much completly built 3 first gen cavies now.