djcondo

what would the highest compression ratio that i can run on a basically stock engine. im trying to plan a rebuild with a little more. i was thinking ported gt40p, .0040 over, stock cam or somthing smaller, and an eldebrock performer intake and carb setup. and i will be using pump gas. with the higher the compression ratio the higher grade gas, so i was wondering how high should i go to be safe and still use pump gas

mjr46

wow what a jumbled mess^^^^ first of all with flat top pistons and gt-40p head you'll be well with in the realm of pump gas at best 9.5 with that set up..running aluminum heads will allow a higher compression ratio to be run without detonation.. I ran .200 dome piston with 58 cc afr heads and came in at 11 to 1 on pump gas with no issues.. but around 11 to 1 is a safe level with aluminum heads of course and if your block is stock bore the typical over bore is to .030 not a .0040.. I think you may have meant .040

djcondo

yeah i hit the zero once to many. why do the alum head allow higher compression? Also wont i notice a resonable differeance with the raised ratio? sorry the first mesage was all over the place

mjr46

aluminum disipates heat quicker than cast iron and thus is less prone to hot spots in the cumbustion chamber.....spark detonation is a result of excessive cumbustion chamber temps..and it depends on how much you raise it vs how much seat of the pants feel you will notice.....I went from 9.7 to 11 to 1 and there was a huge difference but going from like 9 to 1 to 9.3.. not really noticable

djcondo

yeah i was looking to go from stock cr to like 10:1 or like at the most 10.5:1. looks like i would need alum heads. thanks

5spd GT

The camshaft is going to come into play when you start increasing the static compression.

You should have no issues.

irish1

You could take a pair of stock E7s, have thumper work his magic on them and get with a cam grinder like Jay Allen and have parts which played together nicely. I'd rather spend 1000 bucks once and have it run great then spend 750, have it run not so hotand then have to redo it for another1000. Cheaper/better to do it right once.

Matt

djcondo

cool thanks.