FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: Twinibeam66 on March 20, 2019, 04:47:32 PM
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Hey Everybody first post here but have been reading a lot on here great forum. This is my build.
390-416 CI
Barry's Heads
RPM intake
Mahle flat tops with 2 valve reliefs
Comp roller cam @50 243-251 Lift 638-643 LSA-108
My pistons are 0.021 in the hole so with a Fel-Pro 1020 head gasket that's 0.062 Quench, from what I read that's way to much ?
Was thinking of going with a cometic 0.027 head gasket to get the quench better but have heard a lot people have had trouble with them sealing ? What's the best thing to do here ?? Also can somebody figure my compression ratio ?
How bad would it hurt me to leave it at 0.062 ? Thanks Everybody
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I think your measurements may be off. .21 in the hole would be some way low compression on a 390 and not typical on flat top pistons if they are 390 pistons. Unless maybe you ended up with some 360 over bore pistons but even then they are not normally that low in hole.
The 1020 Head Gasket is .041(spec) compressed. If you can confirm your measurements it will help on getting some answers. I am sure someone will chime in but the numbers are what it will all be based off of.
I hope that does not come off as rude, it is not intended to be, but to do the math the result will only be as good as the info that gets plugged in.
Do you have your deck height or any of the other build info?
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I think he meant 0.021 + the 0.040 gasket for 0.061
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You probably mean 0.021" in the hole, right? And the 0.027" head gaskets? That sounds like the right combination to me. As long as your decks are flat you should have no problem sealing with the Cometics. If you want to hedge your bets, spray them with some Copper Coat before you install them, but if the head and deck surfaces are good, and the Cometics are new, you shouldn't need to do that.
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Sorry everybody yes I meant 0.021 in the hole and 0.027 (hard day at work) haha
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Try this place for a compression calculation.
http://www.wallaceracing.com/Calculators.htm
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Edited for bad math
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Just gotta watch about the finish. I've seen Cometics leak with a broach-mill surface. Most shops do not employ that kind of milling machine anymore. If your shop uses an insert mill, I'm sure it will be fine. I use Cometics and Felpro MLS head gaskets on a lot of engines and don't have issues. I'd rather have the .048" quench distance than the .060" and I would aim for that if possible.
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Thanks everybody for the help
My427stang the bore is 4.080 and stroke is 3.98 thanks, my bad should have put more information.
Brent the finish seems to be pretty good, i bought this engine after it had all the machine work done so i don't know what they used, i will try and post a picture but not sure if you can tell much about a picture. Also really like your rocker arms they are FINE pieces Thank You
What do y'all think of the Mr Gasket head gasket they are 0.020 but they say not to use them with aluminium heads ?
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Just put it together with the .062 and run it.
The normal target for quench is .040-.060
You are getting within measurement error of your tools
If it were a smack down race engine I might chase that little bit, but for what you are doing I would run the proven, known commodity head gaskets and get that thing running.
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Finish appears to be ok on your block. I'd run the Cometics.
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Just put it together with the .062 and run it.
The normal target for quench is .040-.060
You are getting within measurement error of your tools
If it were a smack down race engine I might chase that little bit, but for what you are doing I would run the proven, known commodity head gaskets and get that thing running.
+1 Quench is not as important with "modern" aluminum heads. Even some iron heads aren't fussy , while others are critical to a VERY tight quench to avoid detonation. The important thing is to NOT generalize what you read into "all" engines thinking. Similar to "use the longest rod possible" which was quoted out of context from Smokey Yunick relating to a specific Chevrolet engine only.
Randy
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Thanks everybody.
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Edited again for bad math....have to get back to you guys after the flooding is over....AF has me running ragged
Bottom line though, the quench discussion should really be a movement discussion not a number discussion. It is true that a good chamber does not need as tight of a quench because you generally have a better and more purposeful churn, especially if the chamber has some sort of pad on both sides of the bore to move the mixture around. However, even though you can find a smidge of torque from tight quench, especially with a piston that matches your chamber, the more your fuel changes (pump gas versus a more stable mix of race gas) the more you want to have movement toward the location you want your burn. A street engine is not a race engine, and you never know what is coming out of the pump nowadays, so having the right quench pad design for the head and a logical distance does matter. It's not just tight versus loose, it's a decent distance and close in the right places
In your case, There is no choice that will be bad. The quench distance at .062 at max of "good" and there the compression is a bit lower, if you get it to min distance, you do have a little more compression and power, single digits of power and it will still be good. The chamber has a good shape, and a flat top piston has quench pad pretty much wherever it's needed for the head
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My427stang Thanks for all your help and reply's really appreciate that.
TwinIbeam66
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Just gotta watch about the finish. I've seen Cometics leak with a broach-mill surface. Most shops do not employ that kind of milling machine anymore. If your shop uses an insert mill, I'm sure it will be fine. I use Cometics and Felpro MLS head gaskets on a lot of engines and don't have issues. I'd rather have the .048" quench distance than the .060" and I would aim for that if possible.
I used Cometic on my first go with AL heads on an iron block. Had the shop finish specifically for the Cometic items. Leaked like hell. Switched to Felpro Performance - no issues.
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Falcon67 that's what im afraid of, that would be just my luck Thanks for the reply
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I use Cometic and Felpro MLS gaskets on a regular basis for street engines. I've never had one leak.
On big bore aftermarket Windsors, an MLS gasket is about all you can find.
I use a little bit of silicone around the coolant holes and it's very important to watch where the rivets are as they can get in the way of mating surfaces. It's not a problem on FE's, but on Windsors/Clevelands, the rivets can sometimes be located in between two surfaces and they have to be removed before installation.
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ok Thanks Brent