im installing a new engine in a 97 eclipse gs. i came across a cheap 2000?? neon sohc 420a engine. im just curious when i stick the eclipse head on it, what compression ratio will i have?? i dont see why this setup wont work, and its sure as hell cheaper than finding a used eclipse engine. i just want to know if i need to run better gas, or if it will be less compression than the eclipse. from what i read, i think the sohc engine had 9.8 compression. but i dont know what the eclipse head will do. any way to calculate this?? thanks
doug

14b custom turbo kit, modified starion front mount, 9.6:1 JE pistons/Eagle rods....running 12psi
screw flanders

Easiest thing to compare would be the head cc between the SOHC and the DOHC, if the SOHC is less there is your difference in comression and your will have a stock 9.6:1. If the head cc's are both the same (52cc) then you will have 9.8:1.

The only couple of places I saw head volume listed for the SOHC can listed it the same as the DOHC, but I'm not sure. SOHC and DOHC could easily share the same pistons and the compression ratio difference is all in the cylinder head.

Exile Racing Technologies
http://www.exileracing.com
Go that way, really fast, if something gets in your way... turn. I was too lazy to do it myself.

It will be less than the stock 9.6:1.

Here's my reasoning:

The SOHC neon pistons are basically a flat-top, but are said to be 9.8:1. They do have an extremely slight dish that you can fill with your fingernail.

The 2gnt has 9.6:1 with a dome piston.

Since the SOHC neon has higher compression with a flat-top piston, the combustion chamber in the head is probably smaller than that of the 2gnt.

Your taking away the volume of the dome piston (or adding volume to total combustion volume), without taking combustion chamber volume away. This will lower compression.

If I'm wrong, slap me with a trout, but I believe this to be correct. You're basically going from a dome piston to a flat-top piston, similar to going from flat-top to dish.

How much does it change? I dunno, I don't feel like calculating it.

~Luke
Facebook
1969 Cougar - 11.91 - 380HP
2007 GSXR 750
1999 OZ - SOLD - 15.26 NA - 14.71 on 75 shot