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Old 08-23-2019, 08:04 PM
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Default why are 5C head castings so ugly?

...ever notice how ugly the 5C castings are? I've got a decent set out in the garage sitting next to some 11's and 46's and they are the ugliest by far.
rough looking.
my friend has a pair that are just as ugly.
why?

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Old 08-23-2019, 08:12 PM
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Best looking head is I believe #77's nice ramp down from valve cover on ex side no A/C lugs or Air injection provisions

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Old 08-23-2019, 08:14 PM
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Just curious. What do you find so ugly about 5C heads ?

Look real close to the 6X heads to me. And not that much different from 4X.

The last pic is a #46 head. What looks so great about it ?
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Last edited by ponyakr; 08-23-2019 at 08:33 PM.
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Old 08-23-2019, 08:21 PM
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Quote:
Originally Posted by ponyakr View Post
Just curious. What do you find so ugly about 5C heads ?
those are much smoother looking than the ones I have seen. still I think my 46's are smoother...

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Old 08-23-2019, 08:24 PM
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I believe the 5c heads at pretty much the same as the 6X castings and have an early date code on the ones I have. January 75 actually and they look as good as the 6x heads I have.

Does anyone know if the early 5C heads are prone to cracking or was that sorted out on the 4X castings?

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Old 08-23-2019, 08:37 PM
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"...Does anyone know if the early 5C heads are prone to cracking or was that sorted out on the 4X castings?"

From what I've read, the 4X heads are the most crack prone. But, some of the engine builders say they have occasionally found cracks in most all numbers.

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Old 08-23-2019, 08:42 PM
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Quote:
Originally Posted by P@blo View Post
I believe the 5c heads at pretty much the same as the 6X castings and have an early date code on the ones I have. January 75 actually and they look as good as the 6x heads I have.

Does anyone know if the early 5C heads are prone to cracking or was that sorted out on the 4X castings?
Have yet to run across a crack problem with multiple pairs of 5C's. Have been fortunate with two pair of 4X 400 heads that I pulled for date codes & condition.

BTW, January dated 5C's was close to the end of the production line for 5C's. 6X's began to be cast in Feb of '75. Years ago, I stripped an original 350 engine with a 5C-4 on one cyl bank & one of the first 6X-4's on the other cyl bank.

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Old 08-23-2019, 08:59 PM
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I actually had a set of #62's that had porosity they obviously worked from day 1 or they would of been replaced under warranty early on but I trashed them

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Old 08-24-2019, 09:39 AM
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Ugly outside pretty inside.

Steve25 ported mine to 265cfm.

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Old 08-24-2019, 01:44 PM
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I've seen the same thing. I had sets of both 4X and 5C (both turned out to be cracked across the seats) that just looked rough and lumpy compared to the set of 6X's I wound up with.

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Old 08-27-2019, 07:07 PM
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Great information as always. The forums never cease to amaze me.

I guess one could say the 5C heads are no more prone to cracking then a 6X casting and all heads can crack. The 4X seem to carry this reputation for a good reason but one can still get lucky coming across usable heads.

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Old 08-28-2019, 06:05 AM
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I think at this point in time it's safe to say that cracks that have been seen in most bad 4x heads have been due to running hot due to poor tune, overheating or a combination of both.

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Old 08-28-2019, 08:49 AM
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Quote:
Originally Posted by steve25 View Post
I think at this point in time it's safe to say that cracks that have been seen in most bad 4x heads have been due to running hot due to poor tune, overheating or a combination of both.
So, are you saying that most engines which had 6X heads were run cooler & had a better tune than engines which had 4X heads ?

I've read that the 4X heads were more crack prone because of the seat hardening process used. Pontiac supposedly modified this process, by the time the 6X heads came along. So, is this info not correct ?

Paul Carter posted "...As P-Dude said, the 4X is very prone to cracking so I would try top avoid it...".

Here's a whole thread about it.

http://forums.maxperformanceinc.com/...66#post5928466


Last edited by ponyakr; 08-28-2019 at 09:03 AM.
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Old 08-28-2019, 12:16 PM
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All I mean to say is that the basic 4X casting was used across the board on every V8 motor Pontiac made in 74 so where looking at some 80,000 or more castings out of which not even 1/2 of 1 percent have turned up cracked from what we have seen over the years.

When you look at the fact that it's rarely both heads on the same motor that crack you would then have to point to reasons like inconsistent induction hardening depth and stuck Exh Manifold heat riser flaps, and likely in combination with each other!

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Two pairs of brown leather flip flops, never seen more then 2 mph.

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Old 08-28-2019, 02:02 PM
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I could use a single 5C-4, I somehow ended up with one.

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Old 08-28-2019, 03:11 PM
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Quote:
Originally Posted by Bill Eveland View Post
I could use a single 5C-4, I somehow ended up with one.
That sucks Bill, what was the date code of the cracked 5C head if you don't mind me asking?

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Old 08-29-2019, 05:48 AM
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A 6X-4 would function the same Bill if not a motor for a show car or to make a sale of such.

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And he was not talking about 1/8 or 1/4 mile ETs!

1) 1940s 100% silver 4 cup tea server set.

Two dry rotted 14 x 10 Micky Thompson slicks.

1) un-mailed in gift coupon from a 1972 box of corn flakes.
Two pairs of brown leather flip flops, never seen more then 2 mph.

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Old 08-30-2019, 06:44 AM
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While we are on this subject here's a handy chart of percent of HP changes made by changes in compression ratio.

Just keep in mind that once a NA motors compression gets below 9.2 any Cam used will feel a lot bigger then what you think it might!
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And he was not talking about 1/8 or 1/4 mile ETs!

1) 1940s 100% silver 4 cup tea server set.

Two dry rotted 14 x 10 Micky Thompson slicks.

1) un-mailed in gift coupon from a 1972 box of corn flakes.
Two pairs of brown leather flip flops, never seen more then 2 mph.

Education is what your left with once you forget things!
  #19  
Old 08-30-2019, 05:23 PM
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I've had a couple pair of nice crisp 5Cs, and a craap looking 5C set.

Same goes for 1968 16s.

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