flat top pistons

[joshcrowley]

Is anyone running flat top pistons? If I do this, what else should I do besides change the cam? I have a 360 that I am building with TBI and a either a torker or performer intake (I somehow aquired both).

[jeepsr4ever]

Flat top pistons will yeild around 12-12.5-1 with AMC iron heads. This means you either have to run E-85 or 92 octane and thats at a high sea level than most of america can run. Where are you located and what octane rating is the highest at your local gas station. Builds like this require special care and fuel can be determined by air density and changes above seal level. If you are running a TBI then your probly rock crawling and may not need that much compression. You can run any cam with that compression. Well most under a .600 lift and 260 duration (for oiling sake as well).

If you plan on utilizing that much compression you can use a Ross/Diamond/JE piston that has a flat top but make sure the mfg has the head chamber digitized so they know where to put the valve reliefs.

[1980_Cj7]

Fuzz is running Ross flat tops in his 401, and has to run racing fuel at something crazy like $12 per gallon. I'm sure he'll chime in though and give you more details.

I've been told by JB that you need to keep the DYNAMIC compression ration no higher than 8 to 1 to run pump gas with stock iron heads.

Got our fingers crossed with our 401 re-rebuild we just started with the KB 354 9.5:1 pistons. Depending on what I use for the intake closing, I'm getting anywhere from 7.3 to 8.6 dynamic CR. Of course 8.0 is smack in the middle of those two numbers.

If I use the .050 closing of 34 degrees + 15 degrees, like the KB calculator says, I get 49 degrees ABC and 8.6:1. If I calculate the closing from the advertised duration (294) and intake centerline (105), I get 72 degrees and 7.3:1.

I'm still not real comfortable with this cam stuff, so I sent all our specs to KB, and they calculated it and said we should be fine with 93 octane.

I'm hoping the fact that the KB pistons are designed to give better quench is going to help us too.

[fuzz401]

flat tops will give you 12:1 CR I can get away with 3/4 tank of 92 + some 110 gas

[dbesade]

Therotically you could probably run propane alright with the higher CR since propane is 110 octane. :mrgreen: .. hey its cheaper than 110 gas :t:

-Dave

[joshcrowley]

thanks alot for the info. By the way, does anyone know where I can get some new rods for cheap? I got to looking at mine and it looks like a few of them have tiny little cracks coming off the little indention for the bearing. thats bad huh?