I've been looking at many different heads for my 496 build up and have seriously been considering the GMPP heads. Though I would love AFR's or Brodix theyre a bit out of my price range (my wifes too graemlins/angry.gif )so Im looking at these as an option. Found some on ebay that a guy sells pretty cheap @ $1200 a pair complete , he gets them direct from GM.
They are 290cc oval port , 110 cc semi open chamber , 2.19 or 2.25 - 1.88 valves. I think these are the same heads used on the ZZ502.
My first question is what is the difference between closed , open and semi open chambers? What is the best for a street motor?
Being that these are semi open chambers would I still be able to find pistons to make streetable compression?
If anyone is running these heads or has any knowledge or comments please give me some info.
This is my first big block so sorry if the questions I ask are common knowledge too you all.

Thanks in advance. smile.gif Mitch

ttt.

I've not seen these on ebay, could you provide a link or point me to them??

Generally accepted principle that the smaller the chamber and the flatter the piston, the better the 'quench' ( which I would run a search on separately). So the better way to get compression is via smaller chambers, not bigger piston domes. Vizard has wrote that for years, btw.

Open chambers gave a bit better valve unshrouding, and I've read they were introduced to lower emmissions. Clearly compression ratios were on the way down when they introduced oc heads back in what 1969 or so.

The 110cc GMPP heads take a specific dome configuration, adn that is the key thing to look out for in the open v. closed v. semi open, is that not all pistons will work with each of those. THe piston must work with the chamber configuration. Of course, flat top pistons work with any.

I'm running those heads on my 439" and plan on swapping them onto the 498" over the winter. SRP makes pistons profiled specificaly for those heads. It's what I used for the stroker build. I had the heads cut .022" to get the chamber to 104cc. The finish cr is 11.53:1. I think the heads are a good value for the buck. Mine came CNC ported and bowl blended.

gspan1830,
You have to go to ebay motors and in the search box type in bbc aluminum racing heads he only has one auction going now for two diff. heads your choice , part #12363390 oval port w/ 2.25 valves or the #12363400 rec. port w/2.25's. Says he only has twenty sales to go to meet his quota from GM , I emailed him and ask what he ment by this and he said after these are gone the price will go up to $1500.Looks like he's already sold 11 pairs. BTW the auction set price for the #'s I listed is $1100 a pair. racesuppliers is his ebay username , out of Dallas Tx. Also ask if he had the 2.19 heads and he said he would start another auction for these if I wanted , $1200 a pair.


427L88,
Thanks for the info. I think I'll give Wolfplace a holler and see what he has to offer.


chevywidow,
What would your comp. be w/ the 110 chambers , Iwant to keep mine around 10.5 maybe lower.What thickness head gasket are you using?

Hamr, I believe the comp. ratio worked out to 10.5. SRP sells flat tops also. The head gasket is .039"

The emissions thing is b/c if you look at the surface area to volume on the heads, the more surface area you have, the worse the quenching action the colder head combustion wall surface creates!

Thus, an open chambered head will have less overall surface area then a closed chambered head by the time the burn goes all the way out into the quench regions and the piston flats.

Chevy made an almost completely quenchless smog chamber that looks really big b/c it is squared up by the exhaust valve like at the intake valve. But in reality it generally is small, cc-wise then the -781's or -049's so you really have to cc all BB heads to know just how big they are!! Looks can be deceiving!!

pdq67

I'm running the GMPP part #12363390 oval port w/ 2.25 valves on my 468. Compression worked out to 10.44 to 1.

Heads are stock 110cc. TRW-2465 pistons with valve relief cut into them. Piston is .005(had the block decked .020) in the hole and using .039 gasket.

Thanks Hamrdown, thats a really good price for a pair of heads.