[PontiacCrazy]

I recently latched onto A set of 6X heads for nuthin' and they have just been sitting out in my shop. I noticed reading the posts here that there are 6x-4 and 6x-8 heads, and on another section of this site, I found A link to A page showing where to look for that 4/8 mark. I looked on mine, and there is A "3H" where it indicated to look. What does this mean?

[PontiacCrazy]

I recently latched onto A set of 6X heads for nuthin' and they have just been sitting out in my shop. I noticed reading the posts here that there are 6x-4 and 6x-8 heads, and on another section of this site, I found A link to A page showing where to look for that 4/8 mark. I looked on mine, and there is A "3H" where it indicated to look. What does this mean?

[Rocky Rotella]

Listed is GTOKEN's 6X ID photo. http://www.ipa.net/~gtoken/6xident.html
In this location you will find either a "4" or an "8" If you see a "3H", make sure it isn't a 4X head. Check the center exhaust port to verify 6X or 4X. All 6X heads have the "4" or the "8" alone. 4X and 16 (73-74)heads will have "1H, 3H, 4H 6H or 7H" denoting which motor they are from.

[PontiacCrazy]

Ohhh..Brain fart. I have A set of each 6X and 4X and I was looking at the 4X by mistake. The 6X heads are cast 4, and the 4X are cast 3H..My bad.

So If I was looking to change the heads on my 455 (1970 YH currently 15 heads) Which head would be the logical choice and why?

Any help is appreciated.
Adam

[Big Injun]

What do you use your car for? The #4 6X heads will give you about 9.65:1 and the #8 will take you down to around 9:1.

Dave Bisschop of SD Performance (gtoracing@aol.com) has done a lot of work with the 6X head. Drop him a note.

Dave is doing a set of #4 6X heads for my street/strip (Pontiac Enthusiast) magazine car. It will be a .30 over 455 backed by a 200R4. We are looking at 12s on the motor and 11s on NOS.

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www.PontiacDragDays.com
Dave "Big Injun" Anderson

[Ken K]

The 3H 4X heads are from a 400 engine. These should work fine for a pump gas 455 engine.

[Rocky Rotella]

4X came in many variety. "3H" may be from a 400 but if it does has 2.11/1.66" valves and screw in rocker studs is the greatest concern. I have 400 4X(7H) on my 455 and I had them milled .035 to boost the compression. Check the valve sizes on the rocker studs on the 4X's. If they turn out to be large valve and screw in studs, I'd use them. If not, the 6X-4 will work just as well. Either way, they will perform about the same. If you can get away with the compression, I'd go 6X-4. I run 92 octane in my T/A and it has yet to ping. Rocky

[Ken K]

Rocky, I have a set of 3H 4X heads and they came from a 400. The heads have screw in studs and 2.11 intake valves and 1.66 exhaust valves.

[PontiacCrazy]

The 4X-3H heads I've got are screw-in stud type, with 2.11/1.66 valves. Far as I know, they are off A late 70's 400.

The 1970 LeMans (to answer A question) is used in the summer only (winters here are pretty harsh) and gets about 1200 miles A summer. It's mostly evening and weekend cruising and occasionaly to wipe out awnry fords..It does go to the strip once and A while, unfortunately, our local strip just closed up. 1/8th mile it goes 9.14@79mph. Not too shabby for A stock one-legger with only carb and ignition improvements. It has since been updated to 3.55:1 posi (67 gto-thank you) and A 2k stall converter, but hasn't been to the track with these additions. I am always being given 'extra' poncho parts, and always looking for A few extra ponies.

With the arrival of the 6X and 4X heads, I am just thinking of A head swap for some more go.

Opinions?

Thanks,
Adam


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* No mister, it just looks like A GTO, but thanks. *

[Rocky Rotella]

What's strange is that there are many versions of the 4X. Although some of the codes have been verified, some still remain a mystery. Another strange fact which I has been noted by other individuals is that Pontiac never produced a push in stud head after 73. All 74-79 heads including 301 have screw in studs. Now, I have personally seen small valve 4X. I have also seen push in stud 4X-3H. When purchasing my heads, this particular Grand Am collector had about 6 pair of 4X heads. I chose the 4X-7H because they were 98cc, large valve and screw in stud. He had a pair of 4X-3H with 98cc, large valve but push in studs. According to Pete McCarthy's book, the motor application chart provided by Pontiac for 1973 shows that only 4bbl motors received screw in studs. All 2bbl motors had push in studs. Keep in mind this is all theory based on what I have researched. With the many varieties of 4X available, it's better to know than to assume which head you have.

PontiacCrazy, in your quest for improved performance, I would suggest using the 6X-4's. They will bolt right on and the drop in compression will not be as drastic. Either the 6X or 4X will perform nearly identical. The 6X has lower port floors which will generate horsepower where as the 4X has a taller port floor which will yeild more torque. Keep in mind, this doesn't really apply to our street driven Pontiacs which see 5500 rpm max. Which ever head you use, consider doing some port work focusing on unshrouding the valves. Smoothen the short side and long side radius and remove any flashing from the bowl area. On the 6X, grind the EGR bumps out of the ports for increased flow.

For what it's worth, I started with a 1970 YH 455 with 15 heads in my 76 Trans Am. I replaced the 15 heads, log manifolds and 76 cast iron intake with worked 4X's, reproduction RA d-port manifolds and 73 cast iron intake. The car came to life and ran like bitch. I have since dialed in the combo and switching camshafts, adding roller rockers and an aluminum intake. These lowly smogged-out d-port heads will out pull my dad's 72 455 HO Trans Am with worked 7F6's. And that's not all bad [img]/infopop/emoticons/icon_smile.gif[/img]

[PontiacCrazy]

Well, one more thing I need to ask is this..I recently (real recently) had to tear down this motor (the yh 455) due to excessive strange noise on the top end..come to find out, I have cam lobes that are shorter than others, and I have A couple of lifters that you could just about drink A shot of whiskey out of (and I don't mean the pushrod end). I had this comp cams 268h cam and lifter set lying around, so I stuck it in (haven't even fired it yet) and i'm curious how well this will work with the 6X-4's?

Thanks again.


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* No mister, it just looks like A GTO, but thanks. *

[Rocky Rotella]

Damn, bad luck. If you're going 268H, I'd use the 4X's. When I purchased my car, the YH 455/15 heads had a 268H in it and it would ping on anything less than 91/100 octane mix. The Comp 268H is 268/268(218/218@.050) with .454/.454@1.5 lift. Its centerline is 110 and has 49 degrees overlap with extremely fast ramps. What it does is create a ton of cylinder pressure. Obviously, with higher compression motors more cylinder pressure will induce detonation. With as much cylinder pressure as the 268H creates, it generates tons of low end torque. Its definately not a bad camshaft, but I prefer others, personally. If it's a cam you plan on keeping, go with the 4X's and the 9.25:1(estimate) that'll go with them. Otherwise, if you plan on using a little racing fuel and want the compression, use the 6X-4's. I can not gaurantee that your motor will ping with that combination, but I know it will be close to the edge.

[Will]

One other thing you could do to make the 268H more liveable in a 9:1 (or higher) 455 is install it retarded 4 degrees. Because the cam has 4 degrees of advance ground into it (106 intake centerline) that would have the effect of installing it "straight up". This will reduce lower RPM cylinder pressures and shift the torque curve higher in the RPM range by a few hundred RPM. I would think that would work very well in a 455 that has no problem producing low-end torque, but needs some help higher up.

[Skip Fix]

Do you guys have a code break down for the 4Xs. Got a set with a motor that are as deep or deeper than my 6X-8s I forgot the exact code but does have an H after the #.

Skip Fix

[Rocky Rotella]

I hate making reference to other boards for fear of offending someone, but much has been addressed on the topic of 4X identification.
Check post numbers 6679, 15818 and 16253 on the Classical Pontiac Q&A board. These 3 posts should answer some questions for you.

[PontiacCrazy]

Sounds like it's not A bad cam then, the 268H, can you tell me exactly how it compares to my oem cam? I have reference that tells me the factory cam would be 198/208 @ 050 and .413/.413 lift at 1.5:1 Is this accurate information? The motor also is (supposed to be) 10.0:1 compression. Of course this is all taken directly from the big black Chilton that spans A 7 year period of 20 different auto manufacturers...

[Rocky Rotella]

What your motor has in it, and what it would come with stock is the 066 camshaft. It's officially rated at 273/283(197/207@.050) with .407/.407" lift @1.5 with 55 degrees overlap. While it is actually a decent performing camshaft, it is definately mild, especially for a 455. The 268H has 49 degrees overlap and fast lobe ramps which open and close the valves much quicker that the standard 066. What is strange is that there a variety of camshaft specs for Pontiac cams and Chiltos is always off. I still can not figure where .413" lift comes from in their books. If you are looking for advice between the 066 or the 268H, go the newer design. Camshaft technology has came a long way since the 066 was developed. Also consider the fact that the 066 had to pass many emissions standards.

[Will]

The Comp Cams 268H "High Energy" cam is 218/218 @ .050", .454" lift with 1.5 rockers, 106 ICL, 110 LSA. This is a much narrower lobe separation angle and more advanced intake centerline than almost all the factory cams. Curiously, the 066 has a 111 LSA and 106.5 ICL, which puts that part of it's specs very close to the Comp unit, but the Comp cam has much faster ramps with more lift and a bit more duration. Again, I would think this cam would perform very well in a 455 if you retard it 4 degrees. Should make a ton of midrange and decent top end like that.