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optimum quench/compression

 
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maxxman04
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Joined: 20 Feb 2013
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PostPosted: Wed Feb 20, 2013 12:28 pm    Post subject: optimum quench/compression Reply with quote

looking for opinions, real world use, etc .030 over 350, flat top with 4 valve relief @ 5cc, .012" deck height, 65cc heads, 1.94 valves, 218/224 @ .050,462/469 lift cam, 110 lsa,

motor is built for daily driving/ weekend cruising. will see some track time, but not being built for it. i have no illusions of blistering speed or fast times. this isn't about how to get the most power. this is trying to get optimal parts together, and get optimal tuning for best economy, and reliability.

head gaskets. tons to choose from. some give me mid 9:1 CR, but high quench, .051 or higher. some raise compression to 10.25:1 but drop quench way down to .040. i've read posts that say one is better than other and vice versa. originally i was gonna use just a basic small block fel pro gasket, 4.125 bore/.039 thick. this is the one that puts me just under 10:1 but has quench at .051. i did find another gasket, 4.130 bore/.028 quench, which gets compression up to 10.25:1, give or take .15 or so, depending on calculator. both gaskets have my DCR just under 8:1, which from all i've heard is great.

so can i get away with the higher compression and tighter quench on pump gas, or should i go with the higher quench and lower compression?
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Paul P
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Location: Townsend, Mass.
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1971 Chevrolet Chevelle

PostPosted: Wed Feb 20, 2013 3:57 pm    Post subject: Reply with quote

The tighter you can run the quench the better it will run. I have read posts on this site in the past where the engines ran really well and upon inspection during overhaul there were slight kiss marks on the head from the piston. This was running the motor if I remember correctly at near 8000rpm. If you are not going to buzz it that high a tight quench is the way to go.
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2001 Focus 2.0 Zetec
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1971 - Chevelle 408 SBC N/A
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af2
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Location: grassvalley, ca
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1933 Willys Coupe

PostPosted: Wed Feb 20, 2013 7:34 pm    Post subject: Reply with quote

Actually it is called squish. .028" and .012" gives you .040" squish.
That would be better than .051" any day.

Squish is the mechanical part. Quench is what the end product does to keep detonation at a minimum. I have always used .010" per 1" of bore.
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squeeezer
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1991 Chevrolet Camaro

PostPosted: Wed Feb 20, 2013 8:33 pm    Post subject: Reply with quote

Idk............they call it a "quench pad"..its just symantics

Either way hemi's suck cause they sont squish Laughing
i run. .039 in my 4.155" bore

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af2
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1933 Willys Coupe

PostPosted: Wed Feb 20, 2013 9:56 pm    Post subject: Reply with quote

Here is why it is so confusing. If you read this artical they go from squish band to quench band.... WTF???

http://www.crankshaftcoalition.com/wiki/Quench

And another long one to ponder....

http://speedtalk.com/forum/viewtopic.php?f=15&t=7682&hilit=squish

Sorry Smoke for the other forum but it is important. Since I started the thread.. Laughing
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Big Dave
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PostPosted: Thu Feb 21, 2013 7:34 am    Post subject: Reply with quote

Compression will be your deciding factor. Squish or Quench (a rose by any other name ...) is a means of mixing the fuel and air in the chamber for better combustion. But if you are getting into detonation to achieve it it isn't worth the effort.

With cast iron heads and compression above 9.5:1 with your cam you will be burning premium fuel not regular. If that is not a trade off you are willing to make open the Quench up to lower the compression.

Big Dave
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af2
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Location: grassvalley, ca
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1933 Willys Coupe

PostPosted: Fri Feb 22, 2013 9:41 pm    Post subject: Reply with quote

Big Dave wrote:
But if you are getting into detonation to achieve it it isn't worth the effort.

With cast iron heads and compression above 9.5:1 with your cam you will be burning premium fuel not regular. If that is not a trade off you are willing to make open the Quench up to lower the compression.

Big Dave


Dave, I disagree!!! The OP is looking at 10:1 vs 10:25 static. The better squish,quench or push whatever you guys say is the fact he has less unburned fuel to deal with...
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squeeezer
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PostPosted: Fri Feb 22, 2013 10:17 pm    Post subject: Reply with quote

And potentially more timing to burn it too
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Big Dave
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PostPosted: Sat Feb 23, 2013 3:44 pm    Post subject: Reply with quote

I am offering my thoughts based upon his expressed desire for an economical street driven car out weighing the desire for optimised performance.

To some people when they say pump gas, they are not thinking of living on the ragged edge with 93 octane fuel, but instead they are looking for the lowest priced, water logged,stale 87 octane fuel that they can find at the local corner station.

I agree keeping everything tight increases horsepower cube and involves less ignition lead to get a complete burn of the fuel (especially in an EFI car).

I think for a street driven car being on the safe side is better than being efficient. You have no control over the quality of the fuel, air temp or any of the many factors that contribute to detonation with a carburetored car running up against the upper limit of static compression with cast iron heads.

We know how each and every factor that leads to detonation can be mitigated and controlled, but I do not assume that knowledge is common to everyone who writes in asking a question. Admittedly he is asking it on a board dedicated to engine building and high performance, but we do not test our members as to their skill sets when they join (if we did we would have fewer SPAMers from CHina to worry about).

Big Dave
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