3.3 vs. 3.2 Cylinder Heads

[Rich Buckner]

I am in the process of building a 3.3 EFI engine and came across a very interesting observation. After my tear down I was trying to decide on porting my 3.3 heads or just going with a set of 3.2 heads. I am using a Carrera intake and the 3.2 heads seemed like a quick and easy install.
I decided to stick with the 3.3 heads and go the porting route. In order to match the ports correctly I purchased a scrap 3.2 head for reference. Here is where it gets good.

The finish casting on my 3.3 heads is superior to the 3.2 heads. I noticed a significant difference in the cooling fins size, shape and surface finish. It appears that the 3.3 head would have a significant advantage in the cooling and dissipation of heat. The fins are finally finished and the spacing is consistent compared to the 3.2 head.

I have had numerous parties advise me to just go with the 3.2 heads. After seeing first hand the difference between the two heads I am glad I stuck the the "turbo" heads.

Here are two photos that show the difference.

Let me know your thoughts on this interesting observation.

[lite75]

The main difference is the 350R alloy used in casting 930 heads, withstands the higher temps a bit better. However, plenty of high H.P. 930 builds using 3.2 heads without any problems.

[911nut]

If you use the 3.2 heads, you don't have to spend the money to port and flow match that you will have to do on the 3.3 heads (big $$$ to do it right).

[spence88mph]

A dude on the Australian Regional Forum just put a set of freshly rebuilt 3.2 heads up for sale if any one's interested, no affiliation....

here it is:
http://forums.pelicanparts.com/new-zealand-australia/524126-3-2-heads.html

[JBL930]

You'll hear a lot of backwards and forwards with this issue.
The turbo heads are RR350 alloy, developed by Rolls Royce for aero engines. It's still the best alloy blend for dealing with high temps.
I know race engine builders that simply won't build your engine without RR350 heads as they WILL fail in a racing environment WAY before the RR350 heads will.
If you have a street car and want to cheat then opt for the lower heads as they already have the bigger ports. But if you are going to use your car properly, you will need the right alloy for the job, which is RR350.....

[Rich Buckner]

Thank you JBL930. I did not know the story behind the metallurgy. This clarifies the obvious material quality diffrences between the two castings.

Turbo heads all the way.

[fredmeister]

I just read in my service manual for the turbo 3.3 liter engine that the cylinder heads also included a change ot the included valve angles as well as additional material in the combustion chamber area via casting changes versus the 911SC heads. I assume this would apply to differences between the 3.2 heads as well.
You would want this additional material in the combustion chamber to better handle the higher turbo cylinder pressures and temps. More material has more thermal mass.
would like verification from others with more intimate knowledge of design details on the 3.3 liter engine. I am not an expert, just read alot on these engines and do my own mech work.

[jcge]

Fredmeister - does the manual give values for the valve angles vs SC ?

John

[DonE]

Originally Posted by fredmeister

I just read in my service manual for the turbo 3.3 liter engine that the cylinder heads also included a change ot the included valve angles as well as additional material in the combustion chamber area via casting changes versus the 911SC heads. I assume this would apply to differences between the 3.2 heads as well.
You would want this additional material in the combustion chamber to better handle the higher turbo cylinder pressures and temps. More material has more thermal mass.
would like verification from others with more intimate knowledge of design details on the 3.3 liter engine. I am not an expert, just read alot on these engines and do my own mech work.

Great info - thank you.

[911st]

subd.

I think the exhaust valves might be different to.

[fredmeister]

Originally Posted by jcge

Fredmeister - does the manual give values for the valve angles vs SC ?

John

here are the angles taken from a vertical line drawn thru the center of the bore:
exhaust A=30 degrees 15'
intake B=25 degrees 30'

I dont know what these dimensions are on stock 911SC or Carrera heads but maybe someone can publish this info.....all I know is that the manual says these values were reduced.
I see no mention of a material difference between the castings though.
Good luck.

[jcge]

Thanks Fredmeister

[aws]

Because of the intake pocket dimensions on the 930 3.3 heads they will never develop the the flow numbers that a 3.2 head will without major flow work being done. (and maybe not even then) As far as durability I feel that the 3.3 alloy is superior--but that if adequate oil cooling is provided for there should not be any problems--even in a racing situation---For a street engine I do not feel there would be any durability issues whatsoever---and with the flow numbers being over 30% greater on the stock 3.2 head well worth the any possible durability risk (if any) of using them.

aws

[Tippy]

My Carerra 3.2 has been turbocharged at 1-1.4 bar for at least 10 years. I wouldn't worry about the 3.2 heads being lesser alloy, they're just fine.

[930cabman]

I will be rebuilding a 3.0 soon and naturally on the search for more HP. Who is a good head man around? I have to assume the factory has done their homework, but I am sure someone out there has improved the flow of the factory heads.

[JFairman]

Go here for the best cylinder head work and porting.
Bill the owner is a really good guy.
Xtreme Cylinder Heads And Castings