Which Vortec heads?

[BillC]

I have the chance to buy some low-mile Vortec heads for a reasonably good price. They are casting #12557113. However, I found an old posting from jwaller that says he prefers the 12556140 castings because "they are better for porting" (no explanation on what he means by that, though). Is there a difference between the two casting numbers? If so, what's the difference?

Also, the guy selling the heads said the chamber size is about 54cc. Isn't the stock (and L35) chamber about 64cc? How badly will the smaller chamber screw up my compression ratio? Do any of the late model Vortec heads have larger chambers (around 60-65 cc)? If so, what are the casting numbers?

Thanks for the help.

 

[jwaller]

the vortec casting is ~ 63-64 cc and will screw up your CR if your dont build around it. stock and L35 is ~68cc. I only prefer the number you listed IF you are going to heavily port them. if you not going into heavy port work then ALL the vortecs are the same.

 

[0-60N4]

vortec

vortec

John, what do you mean by "build around it"? What's the size of the stock chambers? Do I need to be concerned?

Jim

 

[jwaller]

the vortec has a slightly smaller chamber than does the stock or L35. its not much (only 5 cc's) and if you are really concerned about hitting a particular CR. then you might need a little more dish in your piston. I've seen trucks running as high as 8.3 and 8.5 CR so as long as you know these factors you will know what CR your motor has. more CR means easier driving on the street, quicker spool. ETC ETC

 

[nightdiver]

I read an article from Cosworth and they say that they have done some tests and found that when you use smaller CR (eg.7)on a turbo you get much more HP when you turn up the boost
We have seen this in real life but why ? Is it because the whole volume is more or what ??????
Ill try two head gaskets with a spacer shim to go under 8 CR...........