what are the negative side of using a fat head gasket? - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 11 Old 04-28-2010, 04:26 PM Thread Starter
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what are the negative side of using a fat head gasket?

I'm looking at these cometics...
Cometic C5511-075 - Cometic Head Gaskets
They're a bit thicker then what I was running before, which is what I am looking for, lower static comp....


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post #2 of 11 Old 04-28-2010, 06:24 PM
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I'm in the same boat as you. I had to go to a bigger gasket size with Cometic to lower compression.
However, the gasket thickness is .096 on my build. One thing to come up for sure is the intake relative to the heads. I'm going to run two intake gaskets to make up for the increase in space.

The other thing would be valve geometry. Recheck that the roller tip still rides correctly on the valve stems.

Also, the guy at Cometic said he's sold them thicker than that {.096## so I don't think there will be a problem. If I could have a piston that made the compression number that I was looking for then it wouldn't have been a problem, but Wiesco said that in my case
540FE Ford that due to the long stroke the piston could only be dished so much, which is why I'm going to the thicker gasket.

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post #3 of 11 Old 04-28-2010, 07:26 PM
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Thick HG= poor quench. Whats your CR now?

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post #4 of 11 Old 04-29-2010, 08:46 AM Thread Starter
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Quote:
Originally Posted by stangjumper View Post
Thick HG= poor quench. Whats your CR now?
didn't take long to hear....This is what I recall discussing with someone a while ago. I am at 9.3 or something now. I found pistons, but to change pistons means rebalance, etc so probably $800 or so total to do that and lower me to 8.6...Doesn't seem worth it, but I'm trying to find little bits here and there that will help out.

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post #5 of 11 Old 04-29-2010, 10:09 AM
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Unshroud valves and lower comp with slightly larger chambers..??

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post #6 of 11 Old 04-29-2010, 02:23 PM
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Quote:
Originally Posted by my8950 View Post
didn't take long to hear....This is what I recall discussing with someone a while ago. I am at 9.3 or something now. I found pistons, but to change pistons means rebalance, etc so probably $800 or so total to do that and lower me to 8.6...Doesn't seem worth it, but I'm trying to find little bits here and there that will help out.
How much boost do you want to run ?

9.3 is fine under 17psi or so.

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post #7 of 11 Old 04-29-2010, 03:40 PM
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He might have the same issue as me with the chambers. I unshrouded the valves, but according to my machinist that is all I can cut on my heads.
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post #8 of 11 Old 04-29-2010, 03:41 PM
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Also what is your dynamic compression ratio? The cam that I have, plus head gaskets put mine at about 7.7:1
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post #9 of 11 Old 04-30-2010, 08:27 AM
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we've always run .062-.075 head gaskets on our race car with no issues.. been doing this for 10yrs... i NEVER have head gasket problems and can be seen in between rounds watching my friends race after i just made my 7sec pass

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post #10 of 11 Old 04-30-2010, 08:54 AM Thread Starter
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I've got 58cc Canfields, and also was running the 9cc federal mogul MLS gasket. While this gasket is a little thicker its not a whole lot. I won't be boosting it to high hell, just want to keep things together this time around.


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post #11 of 11 Old 05-01-2010, 12:40 PM
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quench distance is everything. low compression cars can detonate wildly with poor quench. high compression cars can survive high boost with the correct quench. (all fuel and timing factors being correct mind you.) I had FT pistons .005 out of the hole, and found that .050 quench height worked well. (9.0:1 CR, 110 L/C cam, Procharger F1R @ 16 LBS. on PUMP GAS!) The thick gaskets may be fine, do a search about quench. (Or just bolt 'em on and go!)

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