[steve25]

Amen to how willingly they shared there many times hard fought knowledge and findings!

The 6X Intake port was redesigned with a higher short turn then the 96 casting and others.

The result of this is when bowl porting them you get the nice Mid lift to low high lift flow gains ( depending on the level of work ) without the loss of low lift flow gains like on the 96 casting.

In short, without the use of a flow bench it's easier to screw up a 96 and the like castings then a 5 series or 6 series when bowl porting.

[Jay S]

Pics of some cut aways for a 96 and 6x-4. Cuts are in different areas but you can still see the higher short turn on the 6x. My feeling is the short side on the 96 being better is more applicable for fully ported ra 4+ size ports blending the bowl into the bigger port. Mild porting most guys probably do have better results with the 6x.


6x-4 left, 96 right photo

[jonathonar89]

My opinion....just work what you have.

[mgarblik]

That cut away of the 96 shows how thin the casting is in various areas, especially on the long side. It's paper thin. Have to be careful.

[steve25]

Well all I can tell you is my results , that being in fully ported form or properly bowl ported form and then tested out on my Superflow bench that the 6X head is the better one, especially the Exh port when fitted with a 1.77" Exh valve.

Here the results of the A/B testing that Pete did back in 1992 on a street built 455 comparing both
heads.

The bottom line is that the 6X heads where at peak numbers 9 hp and almost 13 ft lbs better then the 96 casting and the even more important averages where better also!

I hope folks can read ok when the view it and expand it?

[Cliff R]

I've put this up here many times but the dyno sheets below show how much power can be made with a 455 build at 9.3 to 1 compression using well prepared #96 "D" port heads. The engine builder (I had nothing to do with this engine other that helping with the carb) owns a machine shop and a dyno. He specializes in big block Chevy and big Ford engines, it was his first Pontiac build.

There are two sheets with two different cams simply because he is a dealer for Comp and had them make the first recommendation (XR276HR) which turned out to be not nearly big enough for what they were doing and goals for the project.

The heads were ported and flowed 250cfm on the intake side. Pretty stout numbers from an iron headed 455 build at that compression ratio, plus they noted that it idled relatively smooth and made plenty of vacuum at idle speed.......Cliff

[android 211]

I'm going to start pulling the engine tomorrow. I always ran it on 93. The distributor advance curve was close to stock for a '70 GTO or GP. The quench clearance was around .040". According to to my laser temp gun, the hottest it ever ran was around 210 or 215. I don't think detonation made me lose a bearing. The charts and the cut aways are all very illuminating.

[455-4+1]

Wow, that " OF" certainly woke things up lol

[Cliff R]

For sure. The important thing to note about the cam swap was that the major reason it was done was to help with detonation. It's also cool that I really had nothing to do with any of it other than supplying the engine builder/shop owner with a custom rebuild kit with tuning parts for the Q-jet they were using.

Of course when they get it up on the dyno it isn't making chit for power everyone right down to the guy who takes out the trash was blaming the Q-jet. The owner calls me up and tells me it's not liking much total timing and power isn't anywhere near where he thought it should be for the combination of parts. So we have a discussion about how the big Pontiac 455 doesn't have much more intake port feeding it that an average small block Chevy head is capable of and it will respond very well to more camshaft than the 224/230/110 Comp HR. He's a bit confused as he's able to make great power numbers with his Big Block Chevy builds using warmed over passenger car (PASS) oval port heads and relatively "small" camshafts.

So he goes ahead and cranks up the timing and they also put their favorite dyno-tuned Holley carb on it and BAM, pound all the rod bearing right out of it on the dyno and power numbers didn't move. So off the dyno it comes and he cleans up the mess, new rod bearings and installs the OF clone cam I suggested on a 114LSA with the ICL at 110. No other changes made to the engine. So I get a call about a week later and the owner is quite pleased with the end result. He comments on how much smoother the engine was as far as idle quality and behaved better right off idle and low RPM's. Although he doesn't completely understand why they are still very happy with the end result. The jump in power was also dramatic, and clearly shows how the big 455's with good flowing heads absolutely LOVE a lot of camshaft to help feed them.

It also clearly shows how a relatively "small" cam with the intake closing pretty early and tight LSA can be a poor choice in some of these engines. Some folks just don't get all that, but what the readers need to realize here is that a 455 is a HUGE engine, it's under-square, and topped with head that don't have a lot of cross section or runner volume (factory heads). The are going to do very well at cylinder filling at low RPM's, which simply means VE will be very good early in the RPM range and the excellent cylinder filling will raise dynamic compression which will require higher octane fuel all else being equal. This is why there will NEVER be a 455 in any configuration leave this shop with a cam having less than 230 @ .050" duration and tighter than 112 LSA.

Look at the cam card and dyno sheet below. The big 455 Super Duty engine cobbled up that little cam like it was an RV grind for a 350 build. Smooth idle, plenty of vacuum, strong low end power, good average power but even using a hydraulic roller cam with 230/236 @ .050" specs and Harland Sharp high ratio rockers on it peak power was made at a relatively "low" 5200rpms.........Cliff

[Skip Fix]

Pete was always a great guy to talk to and would gladly answer phone calls and impart what he had learned.

Throw a bigger exhaust valve in the 6X-4s and you can easily get 80% E/I flow.

[android 211]

Halfway through pulling the engine. Coolant looked like it had a lot of oil in in. Oil was black. even though I changed it only a few days previous. The engine was also using a small amount of water. The coolant recovery tank was always empty down a couple cups worth. Maybe I should install a RA IV cam with Rhoads lifters when I find out whats wrong?

[77 TRASHCAN]

Originally Posted by android 211

Halfway through pulling the engine. Coolant looked like it had a lot of oil in in. Oil was black. even though I changed it only a few days previous. The engine was also using a small amount of water. The coolant recovery tank was always empty down a couple cups worth. Maybe I should install a RA IV cam with Rhoads lifters when I find out whats wrong?

Yes!!!

[steve25]

The oil got black because you burned up a Bearing for whatever reason that turns out to be.

The Crank will likely need to get cut now, or if the damage was too great then a new Crank maybe in your future!