70cc head info

[Smileys84]

what are the pros and cons on running these size combustion chambers on say a 383 stroker or 406 with or without a turbo setup.

The reason I ask is because I just picked up a set of aluminum edelbrock rpm heads in that size for $400 complete(good deal I thought), but really wanted to run with a 64 cc head and Im not sure if I want to go the turbo route or not and if that size cc head would help me or not with my decision . Any info would be great thanks!

 

[Dyno Donny]

We need more info as to what type piston, how much in the hole the piston would be and the cc.s of the piston.
All of these and more go into planing the engine. With no more info than I have your compression ratio can be any where from 9 to 1 or as high as 10 to 1 or more with a 70cc head.
If you plan on running without a turbo then a F/T piston would work great with those heads and would allow you to run a decent cam.
If you plan on running a turbo then you would need to use a piston that would drop the ratio way down.

 

[gmtofd]

Before going any further, would make sure the combustion chamber size is what it's suppose to be, meaning to take them to a head shop and have one of the chambers CC'ed. Sometimes heads turn out to be larger than they are suppose to be, due to previous valve jobs.

 

[Dyno Donny]

Before going any further, would make sure the combustion chamber size is what it's suppose to be, meaning to take them to a head shop and have one of the chambers CC'ed. Sometimes heads turn out to be larger than they are suppose to be, due to previous valve jobs.

Good advice.
That sounds like a bargain for that set of heads. Just check the heads before you put them in service. One of the first things that I do when a set of assembled heads comes into our shop is to lay a straight edge across the tips of the valve stems. If there is a lot of variance from end to end then you know you could be headed for trouble. With most modern equipment used today to machine heads, the stem heigth can be controlled down to the thousands. You will often find a difference between the intake and exhaust steam heigth but all of the intake and all of the exhaust should be real close to the same between the sets and for both heads. If not then you'll have problems getting the R/A geometry right unless you use a bunch of different P/R lengths. Having to use two different P/R length for intake and exhaust isn't all that uncommon but it gets expensive when you have to use a bunch of different ones all through the engine.
Next do a quick check for valve leakage. Pour a small amount of liquid around the valve seat area and blow compressed air in the runner. If the valves are leaking the bubbles will show you how much and where.
Next check all of the bolt holes. You don't want to be repairing these after you get them bolted on.
Be sure you put a straight edge on the gasket surface. If the heads have been cleaned up using a Scotch-Brite pad then just bite the bullit and find a shop that uses a CBN mill and have them re-surfaced.

Hope this helps
Donny

 

[1720]

Before going any further, would make sure the combustion chamber size is what it's suppose to be, meaning to take them to a head shop and have one of the chambers CC'ed. Sometimes heads turn out to be larger than they are suppose to be, due to previous valve jobs.

Good advice.
That sounds like a bargain for that set of heads. Just check the heads before you put them in service. One of the first things that I do when a set of assembled heads comes into our shop is to lay a straight edge across the tips of the valve stems. If there is a lot of variance from end to end then you know you could be headed for trouble. With most modern equipment used today to machine heads, the stem heigth can be controlled down to the thousands. You will often find a difference between the intake and exhaust steam heigth but all of the intake and all of the exhaust should be real close to the same between the sets and for both heads. If not then you'll have problems getting the R/A geometry right unless you use a bunch of different P/R lengths. Having to use two different P/R length for intake and exhaust isn't all that uncommon but it gets expensive when you have to use a bunch of different ones all through the engine.
Next do a quick check for valve leakage. Pour a small amount of liquid around the valve seat area and blow compressed air in the runner. If the valves are leaking the bubbles will show you how much and where.
Next check all of the bolt holes. You don't want to be repairing these after you get them bolted on.
Be sure you put a straight edge on the gasket surface. If the heads have been cleaned up using a Scotch-Brite pad then just bite the bullit and find a shop that uses a CBN mill and have them re-surfaced.

Hope this helps
Donny

And, check the valve guide clearances. I've found most aftermarket stuff with tight clearances. Having a valve hang open is no fun. :shock: