piston questions

[Rootie524]

ok so i have to stick with gen3 heads from a 3100/3400. can i swap heads from any other car to gain more compression? and is 10.5:1 compression still a good choice for me if i decide to do pistons?

and just to get a vote..so everyone here thinks 28lb injectors are overkill for:
CAI, 56mm TB, Ported UIM, ported LIM, ported heads, 3500 valves, comp springs, comp cam...and soon to have full exhaust? its really not that much so i guess it would be overkill..but since i have a gen3..what pound are my stockers?

[95Grand-Am]

My 95 Grand-am came with 17lbs injectors. There should be a part # on the injector, witch hunter had some of GM injectors flow rated, you might be able to find out for sure there.

[Superdave]

ok so i have to stick with gen3 heads from a 3100/3400. can i swap heads from any other car to gain more compression? and is 10.5:1 compression still a good choice for me if i decide to do pistons?

and just to get a vote..so everyone here thinks 28lb injectors are overkill for:
CAI, 56mm TB, Ported UIM, ported LIM, ported heads, 3500 valves, comp springs, comp cam...and soon to have full exhaust? its really not that much so i guess it would be overkill..but since i have a gen3..what pound are my stockers?

Ok, break it all down even further..

#1. What year 3100 is it exactly?

#2. Who is doing all the porting?

#3. Which cam do you have?


There is more to consider here than just the static compression, depending on your cam specs you could run flat tops and still use pump gas.

[Rootie524]

its a 2002 large port

my buddie who specializes in head work is porting and lapping new valves for me

and here is a pic of my cam spec sheet:

[Rootie524]

bump

[Superdave]

the 5 HP you'll gain by going up to 10.5 from 9.5 hardly justifies the cost of all new custom pistons, rings, gaskets and the machine shop bill. I'd spend your money elsewhere.

[Rootie524]

the power increase is seriously only that much? what about 11.5:1? is that too much for NA? and what if i bore it over 40..would that help power?

[pocket-rocket]

what if i bore it over 40..would that help power?

That goes with the saying "There's no replacement for displacement", but they don't recognize boost with that saying either...

[Rootie524]

so since its been a long night im gonna need that dumbified for me. so i shouldnt bore it over? haha

[SappySE107]

its about 5 hp on a stock motor with your cam. Mod it and that goes up. The entire powerband sees more power so its more than just a peak difference when you increase compression. You want 28# injectors and you can tune that for idle no problem. You can use midgrade on 11.5:1 with tuning.

Hope that catches me up with the thread a bit now:P

[Rootie524]

so with the cam i have if i bore it over 40 and get the forged pistons 11.5:1 compression with 93 octane gas on 28lb injectors..that would be a hefty improvement or not worth the money?

[SappySE107]

The overbore isn't a big deal so go whatever is needed to make it straight and leave it at that. 11.5:1 is worth 11hp on a stock 3400 with your cam. Again, more with mods and that is an entire powerband improvement as well. It is up to you to decide if this kind of gain is worth the money.

[Rootie524]

well im probably going to get a 3400 block from someone here on the forums and start to build it up. new rod bearings and all that jazz. is there a "performance" crank shaft or is stock good..same with rods? are stockers ok? i cant see this engine getting over 250hp NA so i might be ok with stock crank and rods but im not sure.

[Superdave]

stock crank is good for 400+ HP, stock rods are forged and hold 400+ just fine, keep it below 7K rpm.