How important is Quench? - Team Camaro Tech
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post #1 of 8 (permalink) Old Nov 20th, 12, 01:42 PM Thread Starter
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How important is Quench?

For a basic 327 in a daily driver car, just how much impact does the Quench have?

Being it's the original block and not wanting to mess with the stamp, I didn't have it decked when I rebuilt it. but then I put in "rebuilder" pistons...standard .040 over flat tops. Now I'm learning that the optimal quench is .035 to .040...but GM started with a .025 deck height, and the "rebuilder" pistons are normally .020 shorter than the stock originals to accomodate expected decking! So now, without looking, I'm probably sitting .045 in the hole, and the thinnest gasket I see is going to add ~.020 to that.

so instead of the "ideal" .040...I'm running ~.065. Just wondering what that's doing to my car? It runs fine, but maybe I'm missing something...

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post #2 of 8 (permalink) Old Nov 20th, 12, 02:31 PM
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Re: How important is Quench???

Octane rating of the fuel you run this car on will have an effect, but once you get above that "optimum" quench, detonation becomes much more likely, which could result in engine component damage.

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post #3 of 8 (permalink) Old Nov 20th, 12, 04:11 PM
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Re: How important is Quench???

This has a dirrect impact on compression. By what you're telling us, I would suggest that your compression is lower than original set up. This may be a good thing or a bad thing depending on what you want to accomplish.
With the lower compression, you are less likely to get detonation, but I suspect you have lost some overall HP capability in the motor.

I have seen head gaskets with compressed thickness of .015. In fact, that is what I plan to use on my build...but it won't buy you much since the new pitons are .020 lower than originals.

If you are happy with the way the engine is running and perfroming, than you probably don't need to change anything. Other than a marginal loss of potential HP/Torque, I can't see any ill long term effects.


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post #4 of 8 (permalink) Old Nov 20th, 12, 07:48 PM
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Re: How important is Quench???

I wouldn't get too hung up on quench with what you're doing.
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post #5 of 8 (permalink) Old Nov 20th, 12, 08:02 PM
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Re: How important is Quench???

Originally Posted by Straight-line-69 View Post
I wouldn't get too hung up on quench with what you're doing.

The quench on a factory 327 was probably more than that. Until you are pushing it on compression or really optimizing the package you won't notice a difference.


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post #6 of 8 (permalink) Old Nov 20th, 12, 08:03 PM
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Smile Re: How important is Quench???

IMHO quench is one of those things that if you want every bit of power out of your engine...then it is important. I like to use FelPro "Blue" head gaskets and for my 327 they were .041" thick. On my not decked engine that equates to .066" definately not optimum, but it works. If you are building your engine, Measure how far down your pistons are. If it's not broke... don't fix it. Again IMHO.

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post #7 of 8 (permalink) Old Nov 21st, 12, 12:25 AM
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Re: How important is Quench???

put the thinnest gaskets in it that you can find- but honestly i don't think quench is nearly as important on older wedge style heads as it is on something like the new vortec heads..

here's my experience with quench: when i built the 355 that was in my Nova, i used a set of TRW forged lightweight pistons with 2 valve reliefs and a set of vortec heads. when i first put it together, i got anxious and bought a cheap gasket set that had some insanely thick head gaskets. i think they were .045 thick and the engine builder said they'd give me a little over 9:1 compression.. the engine ran good, but had audible detonation on 93 octane gas with only 34 degrees of timing.
one winter, i swapped in a set of .015 Mr Gasket head gaskets and made no other changes, which i was told gave me about 10:1 compression.. i couldn't get it to ping on 89 octane with 36 degrees of timing, and it only pinged a little on 87. throttle response was crisper, it ran stronger, and i gained 2mpg just by tightening up the quench and adding compression.

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post #8 of 8 (permalink) Old Nov 21st, 12, 07:05 AM
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Re: How important is Quench???

Originally Posted by 68rs406 View Post

The quench on a factory 327 was probably more than that. Until you are pushing it on compression or really optimizing the package you won't notice a difference.
I have seen this a few times lately.

While the quench is not a serious issue on your build the lower compression ratio could be costing you big power.

A friend of mine recently had an engine rebuilt for his dad. He had it broken in and dynoed prior to installation. The engine that was rated for 290 hp new now dynoed at 210 hp. btw (the engine sounded great) Pulled the heads and found that the builder had used pistons designed to accommodate decking.

He had the shop replace them with the standard height pistons and the motor then dynoed at over 300 HP!

So while quench in itself may not be a big factor in a moderate build the combo of lower compression and excessive quench can make a big difference.

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