I was reading in GMHTP about the different designs of the C5R head. It seems the early C5 vettes were killing the competition so the sanctioning body made them reduce the flow of the heads...GMHPT referred to it as a sort of restrictor plate penalty. What was the dates and history of this? What about casting numbers? I've got .090s and have a feeling they are not the "good" heads. Anyone know which casting number is which???

My 427 never produced power and the addition of a ProCharger made it even worse. Detonation was uncontrollable without race gas. I think the heads may be the problem. 38cc combustion chambers BTW.

 

I'm sure Katech knows. I wonder if they would tell me??

 

Geez, what's your compression ratio? It's unlikely that the heads are causing the detonation unless something is just grossly mismatched.

 

With 38cc heads, unless you have large dish pistions you're compression ratio has to be very high. Most likely that's the KR problem, and you'd probably have the same problem with any head with a 38cc chamber, so I don't think it's a problem with the C5R head itself.

 

About what would the dish in CCs need to be?

 

090 is the later design and better head. Those heads out of the box have 30 cc chambers but a lot of work to be done. This is the BEST head for the LSx engine family LS7 deriaved from this head. Inroduced in 1997 was the first C-5r casting it had the 38 cc chamber and resembled the 98 model heads chamber in design. The early versions were somewhat weeded out for the 090 casting. Most head companies will not even talk about the early versions. We have built a 427 with these heads and a 43 cc chamber and we had to do a -31 cc dish piston just to get it back in the 11:1 range.

 

Thanks MAC. How much do you think the piston would have to be dished to use the 090s with a SC? 60 cc or more?

 

Keep it simple on figuring this for your motor. All you're doing is trading piston volume for combustion chamber volume. That piston we used was an off the shelf Wiseco with -31 cc dish. I think they could make it deeper but they already have to machine the under side of the piston so that the rod will have clearance to rotate on the small end, but 60 cc would get you around 9.0:1. You might be more benefical if you talked to some head shops and have them open the chambers up on your heads. This is different than a stock head and has a lot of material that can be removed.

 

Is there a good head shop in the ATL area? Can any shop do these heads or do they need a special program?

 

The actual reason for the smaller port is because they made them runn with smaller restrictors. This made the once efficient large port totally useless do to the decrease in intake flow. The new port is very optimized for the restrictors. This allows the engine to make as much torque before the restrictors go into effect. They still make a great street head because they have a very small cross sectional area and flow a lot of air. The whole downside to the C5-R head is still the cost of install.

 

The 090 is by far the head of choice in the lineup. Not sure what GMHTP was thinking... Possibly they weren't.

The exterior casting core on the 090's with a little welding can create a serious head.

 

Are there better after market heads such as Trick Flow, Edelbrock or whatever?
I've got some 090s but I'm not sure what we are going to do with them.

 

ETP Canted Vavles. . .

 

Several years after I bought my 090s I got some info from GM about them. It said they were endurance heads designed to run at high rpms and constant shifting. Also designed to function with some sort of restrictor plate. (Evidently to stop the Corvette's domination of the class) Definitely not for drag racing.

 

I have made over 1000 NA with the 090's.. I don't know of anything from edelbrock or trickflow that will do that. The 090 can be a very serious head.

 

For drag racing?

 

correct