High Compression Pistons

[CoopDogg]

I'm running a GM Performance "HT 3.4" crate motor in my '85 S-10. It was fun for awhile but now I want to go fast. The Crower cam (Part # 03067) I've ordered needs at least 10.5:1, preferably 12.5:1. I can't seem to find anyone making off-the-shelf pistons for this motor. Am I going to have to pay through the nose for custom cut slugs, or do you guys know something I don't(Probably!). Thanks in advance for any help.



P.S. will my stock bottom end hold up to an 8000 redline?

[torq455]

there is a CR calculator at the bottom of the "Site Navigation" bar. You can experiment with different combos or with your own mods. try iron head pistons. that should shoot up your CR. your stock bottom end will only will hold to 7000 RPM.

[sharkey]

the aftermarket doesnt pay attention to the 3.4l much. as for pistons, well, there are none. about all you can use is 3.4l dohc pistons, and they will net you about 9.8:1 compression with .040" ironhead headgaskets. if you want higher compression, you are gonna need custom pistons.

the stock bottom end wont hold 8000rpm. stock rods are rated at 7000, and with beam polishing, shot peening and arp bolts, id think they would handle 8000rpm ok. however, there are some other options. you can use 327 smallblock "pink" rods with some work, or better yet, eagle rods makes a 2.2" journal H-beam rod to replace the pink rods. however to use either of these you need to machine the big end of the rod down, iirc, its .100" each side. you also need custom pistons with the wrist pin to fit the smallblock rods (they are .967", stock is .902"). this along with having everything balanced will make a solid bottom end.

what are your hp goals??? are you planning on fuel injection??? if so, i would think about looking into using gen 3 aluminum heads with this combo. if you want to, make sure you do it before you order pistons, cause the heads are totaly different

[Guest]

swapping to aluminum heads will get you close to 12:1. Its that or going with custom slugs.

Actually, GM might still offer their 12.5:1 pistons from many years ago. I don't think they have the proper bore though fora 3.4 as they were made for the 2.8 bore.

[CoopDogg]

Thanks for your help guys. I really do apreciate all I can get. Unfortunatley, sharkey, I was afraid I would need some/all of the bottom end mods you mentioned when I bought the cam. (Impulse buy!) I'm trying to do this motor on a restricted budget (i.e. wife & kids) but it looks like my budget just went out the window, along with my idle quality and manifold vaccum! The cam specs out at: 108 degree lobe center, 248/250 degree duration @ 0.50, with .470"/.479" lift.... Should go; "Rumpity-rump" huh? As for HP goals, ummm.........well I'd crap my pants if I got 300 out of this little guy. Fuel Injection; no. I'm keeping it old school with my holley 390. My goal with this truck is to make as much power as possible with a "stock type" powertrain, get it as light as possible, and see what I end up with. I'm not going racing (legally), just want to impress some people with "that tiny little motor" sitting between my framerails. About the gen 3 aluminum heads, I'm guessing they won't work with my carb and Edelbrock intake combo, right?

Again, Thank you all for your input, and forgive a newbie for rambling on!

[torq455]

you plan on running that cam to 8000 RPM on a little 390?!!!

[MMGT1]

I think someone needs to tell him just what these motors can do when done right! There will be a 3400 in Michigan at the end oof the month that will probably be in the 600 range for hp(Boosted). That enough for that little motor?? We have 3400's in the 12's now with boost or NOS. I'm trying to get the 13's N/A and then into the 12's with the addition of NOS! Right now I'm a 14.5 on factory manifolds all day long. 300 crank is not a "pipe dream" for these motors...not at all!!!!!!

[jackal2000]

I'm trying to get the 13's N/A

you and me both! i should be there once my build is done next week.

[CoopDogg]

you plan on running that cam to 8000 RPM on a little 390?!!!

Well, I'll start with it (cause i've already got one). Rev limiter's set to 6000, and it still wants more. Might need a 600, don't know yet. This will be an ongoing experiment.

Impressive #'s MMGT1! Thanks for the positive reinforcement.