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 Unmarked 6X-?? Heads
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eesinc
Tribal Scout

USA
2 Posts

Posted - 12 Jul 2016 :  12:59:18 AM  Show Profile  Reply with Quote
Help me speculate on which version of the 6X heads I have. Neither heads have the stamp marking (4 or 8). I've studied the photos of the stamp location on Wallace Racing, etc. The pads are blank.

Anyone heard of unmarked 6Xs? 1976 date code.

Compression tests 180-185psi on all cylinders. XE262 cam. 400 block.

Anyone with a XE262 have comparative compression data? Any idea of the compression ratio? Back calculating the CR using the Wallace calculator indicates 10.5CR, which doesn't seem correct with 6X heads.

The XE262 does everything folks complain about on here - loses power early, it knocks some on 93 octane, etc. I am thinking of going to a different cam, and concerned about determining CR without pulling heads.

I'm open to cam suggestions. 68Bird, street car with a 4sp/3.23. Has to have enough vacuum for power brakes.

Thanks in advance.

68bird/400/6X-?/XE262/Qjet/PerformerRPM/3.23/4speed

cortcomp
Coyote

USA
5335 Posts

Posted - 12 Jul 2016 :  10:26:55 AM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
probably 6x-4s. I ran the XE262 on a 428 with 670s...210-215 PSI. no knocking on 91, ran hard past 5k rpms. It's a street cam, not made to run hard to 6500. It's to wake up the millions of 250HP low compression 70's motors out there. I imagine it was a pretty good step or two above a stock cam in the anemic era, putting power down where you use it on the street, under 3k rpms.

I was still nervous about detonation even though i had no signs, and stepped down/up into a 455/6x-8/XE284 combo on that car. the xe262 didn't have the trademark clack, the xe284 had it though.

Only way to be sure is to pull heads and check them. You're losing coolant doing a cam swap anyways. Not much more to yank heads.

Maybe you have timing issues? Too much coming in, too much initial?

If i were to go the same route again, i'd likely just find a lunati cam close in specs, because i liked to low end rush on the street and i loved the sound of both cams, but i hated the clacking of the 284.
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Tub
Sitting Bull

172 Posts

Posted - 12 Jul 2016 :  11:29:52 AM  Show Profile  Reply with Quote
If you don't wanna try a Voodoo, you could always go with a Summit 2801. They are safe for a lot of street apps. Sorta like a higher lift version of the Pontiac 068 cam, which was used in both high and low compression engines 350-455.
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Steve C.
Crazy Horse

1675 Posts

Posted - 12 Jul 2016 :  11:36:42 AM  Show Profile  Reply with Quote
In the end if you end up with the issue if it knocks some on 93 octane then I'll suggest a Voodoo lobe with short seat timing and/or a narrow lobe separation would not be the hot ticket !
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cortcomp
Coyote

USA
5335 Posts

Posted - 12 Jul 2016 :  2:05:36 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
We forgot to ask, what are your goals for the car, where are you planning to use it most? Street? Any strip time?
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eesinc
Tribal Scout

USA
2 Posts

Posted - 12 Jul 2016 :  10:31:39 PM  Show Profile  Reply with Quote
"We forgot to ask, what are your goals for the car, where are you planning to use it most? Street? Any strip time?"

All street. It's a convertible. Maybe once to the strip.

Back in the day (mid to late 70s when 68s and 69s were just used cars), I had two 69 GPs, a 69 GTO and a friend had a 68 GTO. All had the basic 400/350. We could light up the tires on those cars at will. This car doesn't have that feel. It feels like my buddy's 78 low mileage all stock Z28 I drove the other day.

68bird/400/6X-?/XE262/Qjet/PerformerRPM/3.23/4speed
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cortcomp
Coyote

USA
5335 Posts

Posted - 13 Jul 2016 :  10:14:14 AM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
Something is up then. If anything, bringing all the power down low would give you tire roasting but maybe lose some ET at the track due to top end. Not to say the XE262 is the end all to all cams and you shouldn't consider others, but guys have no issues doing burn outs and roasting tires. Hell, i did at will in my car and it had 2.56s before i swapped them! Still had no issues with the 3.42s.

I'd guess you have 6x-8's with no compression but you shouldn't be pinging or knocking in either case. Again, not that you shouldn't switch cams, but i really wonder if there is something timing related here, or if the cam is one tooth off.
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