[D.Cantrelle]

Does someone know if a # 6x head that has a square center exhaust ports would be good for a Pontiac 455 cu. in. compared to a #96. The heads were worked for a stock engine and the chambers were checked by the machine shop that worked them and has 92 CC's. Is there two different year heads, early and late and if so which is best all around ?

Thanks for any and all info, Don

[BOBCRMAN@aol.com]

6X heads come in 96 and 110 cc.

Try www.azalea.net/-steved/page5.htm

[jimfulco]

6x heads are D-port heads. Here's some info:

http://www.pontiacstreetperformance..../6XheadID.html

[adryan16]

I personally would use the #96, as they have the larger 1.77" exhaust valves, and with a nice "068" cam, they'd be good for about 9:1 compression on a 455.

[punchyponcho]

6x heads have an open chamber and a better swirl than #96
they also have the potential to flow over 260 cfm if you port them right..
6x's are the most advanced heads pontiac has used on those motors, so all previous signal, sealing, and combustion problems have been worked out-
You don't need a 1.77 exh. pontiac heads in general have no problem with cfm out the exhaust- it's the intake you have to focus on- no performance on N.A. motors will be made (unless you're using nitrous)

[RetroJoe]

Check out www.wallaceracing.com or join www.performanceyears.com or why not www.pontiaczone.com

[Grusome Goat]

If the heads you have are the 6X-4's then you have a good set of heads to use on a 455, if they are the 6X-8's then use the 96's. Both are excellent heads to use on a 455 and will get you right around 9.5:1 compression. The 6X's have a better designed exhaust port that compensates for the smaller exhaust valves. If you want to go fairlly radical with the engine both can be ported to flow around 285 cfm on the intake side and you can go with some fairly radical cam profiles and run pump gas. Either is a good choice on the 455 and when properly set up it's easy to get 450hp out of the lower compression 455's and they have killer bottom end torque. They are alot of combinations out there that have both the 96's and the 6X's that are making some tremendous power. And there are some really good hydraulic roller profiles that work great with this combination as well as some really good flat tappet hydraulics and solids. use some good pistons and have the rods prepped and replace the rod bolts and you can safely turn up to 5600-5800 with these engines. Jim Hand just released a book on Pontiac performance engines that can help you set up a really killer yet streetable 455 and he has done tons of testing on 455's and has a street legal 72 LeMans wagon that runs mid to high 11's without nitrous. He goes into how to set up ignitions and exhaust selection as well as prepping the block and rotating assembly for longivity and power. As far as intakes go the stock 68-72 are among the best you can get and the Q-jet is one of the best carbs to use when properly prepared.