# X6-4 v/s #17 heads



## par4n1 (Jan 28, 2010)

My '68 350 has #17 heads. Ive read they have good flow and have been under underated. I can get a nice set of x6-4 shipped to my house for 175.00. I am in the process or building a '73 455. Should I get the x6 heads for the build or use my #17?


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## oldskool (Apr 26, 2015)

Get the 6x-4's. The 17's will have too much compression. They also have press-in studs, and smaller valves. 

The 6x heads have screw-in studs, 2.11 intake valves, and factory hardened seats. With the correct set-up, you can get about 9.5:1 CR with the the 6x-4's(unless they have been shaved some). Or, if you wanna back off just a tad, you can go with slightly dished pistons. 

http://www.wallaceracing.com/cr_test2.php


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## par4n1 (Jan 28, 2010)

Thanks Oldskool. I had others a few moths ago recommend the X6-4 but at that time i didnt realize my car had #17 or if the 17s would work well on my 455. The x6 also seem to be a good value or at least worth a gamble buying site unseen


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## BearGFR (Aug 25, 2008)

Good decision. Make sure you cc the heads yourself to find out the actual chamber sizes. You never know if they've been cut before, and even if not - Pontiac heads are known to vary some from the factory nominal sizes. Probably would be a good idea to have them pressure tested, magnafluxed, and checked for flatness before you do that and build an engine with them.

Bear


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## par4n1 (Jan 28, 2010)

BearGFR said:


> Good decision. Make sure you cc the heads yourself to find out the actual chamber sizes. You never know if they've been cut before, and even if not - Pontiac heads are known to vary some from the factory nominal sizes. Probably would be a good idea to have them pressure tested, magnafluxed, and checked for flatness before you do that and build an engine with them.
> 
> Bear


Bear I was going to do that with the fellow that you sent you heads to. I live in VA. about 30/40 minutes from him. I figgured he could advise me on whats best for my application. I really dont understand the math, logic and all the porting and angle drilling. If too much is done maybe new aluminium is best. Hell I dont know if aluminium aftermarket is better then nice flowing OEM:banghead:
But im trying


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