Let's say you have a 30cc CC C5R head that is designed to be ported and polished and you just don't do it. You take no material out of the CC. How much would the dish (CCs) have to be in the piston to get the comp. ratio suitable for forced induction? 427, LS7, C5R, or whatever. Normal head gasket. More than 20ccs?

 

Alright, let's say we have the 30cc CC and the piston is dished 20cc. Standard GM 427. What would the static CR be??

 

what CR are you looking for. because there are guys out there running 13:1 CR with FI. it is all in the fuel you are planning on using.

 

Absolutely no race gas, so around 11.5:1. Even high octane 92 or 93 may be difficutl to get in a few years.

 

You may wanna go lower than that for boost, like under 10:1, it all depends.

You should be able to find the formula for calculating the Compression Ratio on your own pretty easily, just google. Need to know several other variable, like head gasket dimensions, etc.

 

11.5:1 on pump gas and no meth would be very difficult. i am building a boosted 347 and i am going with 8.5:1 CR, because i plan on running big boost on pump gas. i suggest you do not go over 9.5:1 if you are planning on using pump gas on an FI motor.

good luck

 

Why unported C5R head and FI

 

The heads are .090s and the CCs are untouched. The first builder left them as they came from the factory. We had detonation problems.

 

You will have problems with detonation on an un-ported C5R head. The combustion chamber is rough cast and meant to be finished. That will make for horrible flame propogation and hot spots.

Shane

 

The combustion chambers were never touched after they left GM. Actually SDPC. They were installed as/is.

 

What are u trying to build? Why were they left un ported/cleaned up? Why a c5r head on a FI motor?

 

The engine started out as NA. Builder thought FI would be a good idea. I don't know why he didn't port and polish the heads. Looks like it got over looked.

 

Most builders don't "overlook" porting castings such as the C5R heads . These heads are cast with the intention of a builder working the heads for the desired engine . That would be like not working a set of DRCE 3 heads .

 

Overlook, incompetent, ignorant....I don't know. All I know is it would run.

 

It will run. Just not well. As stated above, those heads are designed to be worked. The combustion chambers are NOT remotely ready for an FI build. It would be worthwhile to take the heads and have them finished if you are planning on spending money on a FI system.

Just my $.02...

Shane

 

Who can finish C5R heads? Does it take special programing or whatever?

 

Are there any recognized C5R head experts in the SE or do I have to send these head to God knows where?

 

PM me. I can either get the heads done for you or put you in contact with our porter to have them finished. It won't be cheap but in my experience, Craig Gallant can make the heads perform to whatever level you require.

Thanks,
Shane

 

Shane, I'll PM you.

 

Did I post these pictures? I'll have to figure out how to resize them.

Crap, it may be too small to see the details! This CC is as it came out of the box!