i have been looking into swapping a 3400 top end onto my 3.1L (92).
But from a lot of searching i just get to much conflicting info on what the resulting compression ends up. Some say to get lower compression pistons, some don't.

i have a strong stock 3.1 getting a 3400 top end swap. I am not planning on a turbo.

What should i do as far as compression/ pistons??????

 

The best way, to use regular pump gas without any possible issues is to use the FWD 3100 pistons in your case, using the 3.1 block. 2.8L and 3.1L both share the same 3.503" (89mm) bore with the 3100. The 3.4 and 3400 use a 3.607" (3.60something anyway) (94mm) bore.

This would get you around the stock SCR of 9.6:1 SCR,

Using the RWD pistons will net you between 11:1 and 12.5:1 depending on the actual dish of your pistons, there were a couple different sizes I've seen over the years.

If you have the ability to tune, which would be an asset anyway, when building a hybrid, and you have decent gas in your area and not worried about your car being a daily driver, or possibly being down for a bit, while you get things sorted out, you can use the RWD pistons, you just have to be aware of what the higher SCR might do, or the headaches it might cause you.

 

thanks 6shooter. i think the 3100 pistons will be the way i go. The gas around here is diluted with something. you can't tell by this pic, but it is usually about 50% gas and i don't know what the other half is. I have to go out of town for gas for my hi performance dirt bike.

 

Sorry to revive this but I'm in the mist of doing the 3x00 swap as well. Using a 2.8 block and 3400 heads and intakes. But seeing how that 2.8 and 3.1 share the same piston bore as the 3100. Could I just use 3100 pistons with the 3400 heads? Or should I just get the 2.8 block bored out to make up for the 3400 piston diffrence?

Thank you

 

If you're also swapping the crank to a 3.1 crank, 3100 pistons will work well. If you're keeping the 2.8 crank, you will need to use 2.8 pistons. If you want to keep the SCR under 10:1, you will need to use gen2 2.8 pistons that will give you an SCR of approximately 8.9:1.

It's not recommended to bore a 2.8 or 3.1 block out to the 3.4/3400 bore.