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Old 08-01-2004, 01:01 PM
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Quick Quench Question

Building... well... Planning an engine out, and regarding to qunech, Ideal quench would be somewhere between .025-.035" right? And quench is the piston down bore + comp. head gasket thickness, correct?
Stock head gaskets get compressed to .040, which would mean the piston would be above the deck to achieve proper quench? The only pistons I can find for this engine bring it .008 above deck or .017 below deck. But with the .017 below deck, I would have to get a head gasket thats less than .020" which would be kind of thin. And with the .008 above deck pistons, if the head gasket is .040", quench would be .032", but with the piston being above deck, and rod stretch, would it end up kissing the head?

Let me know if any of that doesnt make sense.



Engine is a SBC

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Old 08-01-2004, 01:30 PM
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There are a few coated steel gaskets that are .015 to .017 thick. I've ran them with no problem. Keep in mind that .040 quench gap isn't too bad unless you're needing max compression. When you push the limit on a tight quench gap ,.025 is really tight, you need to consider rod bearing clearence and piston to bore clearence. Some pistons will require a lot of clearence such as .0055". That much clearence will allow the piston to rock in the bore quite a bit thus part of the piston will get closer to the head.
The most common way to get the correct deck height is to assemble the engine without rings and measureheight and record the deck then go get the block decked as required.
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Old 08-01-2004, 01:51 PM
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The .0055 you're talking about is piston to bore? or quench?
I thought the .015 etc gaskets were really shims instead of gaskets? And the .020 was the smallest gasket?

As for decking the block, its a new block, and I'd rather not start machining a new block unless it was absolutely necessary.
Although I know you're not supposed to adjust gasket thickness to adjust quench/comp ratio.
As for assembling the engine, I wanted to make sure I was buying the right parts before I started. I hate buying something I know is right, then finding out I have to send it back and get the correct part. (Shipping prices these days........)
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Old 08-01-2004, 09:19 PM
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The confusion lies in the name given to this style gasket. For decades there have been steel or stainless steel shim head gaskets. These are truely gaskets. To farther complicate things there are solid copper .020 thick head gasket shims. These shims are used in stock spec rebuilds when the block or heads have been shaved excessively and an increas in compression is not desired.

Long ago steel shim head gaskets were just stamped steel and you had to put a sealer on them. About 10 years felpro and others came out with a steel shim style gasket that is coated so no sealer is required nor should sealer be applied. The Felpro gasket is .020" thick and the Mr. Gasket one runs .018-.020" thick.

I was refering to piston to bore being .0055". No you shouldn't shim a head gasket to adjust quench but there is nothing wrong with using a thinner gasket in order to get the desired quench. I can understand not wanting to deck a new block but often even new blocks are not square. You might find one corner of the block having a deck height .010" different than the opposite corner. Also take in consideration that many off the shelf pistons have .020-.025 taken off the head compared to stock because they assume that you will be decking the block and shaving the heads. So even with the best planning everything must be dry assembled and checked. When it comes from Detroit it fits on the outside. When it comes from a hot rod shop it fits in the shipping box.
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Old 08-01-2004, 10:05 PM
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Read this article from the Knowledge base about quench.
http://www.speedomotive.com/Building%20Tips.htm

Some piston makes will not end up at the correct deck height. They will be .020" or more below deck. There are other members on this board that can be more specific about this. I have never actually delt with it.

On my 400, I had the machine shop mill .014" of my deck. They referenced of the crank centerline. I used a normal .039" head gasket. My quench came out to .044".
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Old 08-02-2004, 01:49 AM
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...read that article 100x over before...
Hows your engine run with that quench?
And is it a street motor? or strip or both?

About the gaskets... never knew that...
As for the pistons, its not a stock bore, and I've only found two available pistons, because I've been looking at the compression height closely.

Last edited by arch; 08-02-2004 at 01:59 AM.
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Old 08-02-2004, 04:23 AM
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Why is it that that web site is saying the quench should be .035 when every body i've talked to about this tell me that you should'nt go below .040 on quench, and some whare between .040 to .060 on the quench. I had some .020 taken off the top of my 350sbc, and when i installed the piston and rod at home on the engine stand, The piston was .010 down in the hole, and the rod is a stock rod and the piston is a Speed Pro piston with a stock compression height. Now i've read about quench and i've talked to the tech guy's at Summit and Jeg's and they all say that the quench should be .040 with the distance between the piston and the top of the block plus the head gasket thickness. Now the guy that does my work has been at it for around 30 yr's and he's old school, and in his oppinion if it's for the street he's never had a customer complain about a .050 quench.
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Old 08-02-2004, 06:21 AM
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Quote:
Originally posted by bowtieorbust
Why is it that that web site is saying the quench should be .035 when every body i've talked to about this tell me that you should'nt go below .040 on quench, and some whare between .040 to .060 on the quench. I had some .020 taken off the top of my 350sbc, and when i installed the piston and rod at home on the engine stand, The piston was .010 down in the hole, and the rod is a stock rod and the piston is a Speed Pro piston with a stock compression height. Now i've read about quench and i've talked to the tech guy's at Summit and Jeg's and they all say that the quench should be .040 with the distance between the piston and the top of the block plus the head gasket thickness. Now the guy that does my work has been at it for around 30 yr's and he's old school, and in his oppinion if it's for the street he's never had a customer complain about a .050 quench.
You certainly don't want to go more than .060. The adverage motor usually runs from .040 to .060 but to get the max compression and still be able to run on pump gas or say running 14:1 but you have to run whatever race gas they sell at that track you got to keep tha quench as tight as possible. In the days that we set everything at .040-.060 we never even thought about piston rock and such. The biggest concern was with aluminum rods. Not many people running aluminum rods anymore. Nowdays I tend to shoot for .030 to .035. I'll run .025 if the motor is set up tight and it happens to fall on .025.
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Old 08-02-2004, 06:54 AM
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quench

There is always alot of things going on to consider what the actual quench numbers should be. I have talked to fellow engine builders and get all kinds of different ranges from them ( .030 to .055). The one thing to remember is not to make more of it then what it is......

Quench does one thing, it helps to stop a engine from detonation. So if you have a 8.5 to 1 engine running on 97 octane gas the quench being .040 instead of .035 is not really going to make any difference. But if your running a 11.5 engine on the same 97 octane then it becomes a tuning aid to stave off the detonation.......

I might have missed it but i don't think you told us what the end use fof this engine is????? static compression???? Octane of gas your planning to run?????? Dynamic compression?????

I know you don't want to cut the block but that is they way it's done. You could get a custom set of pistons made with the pin height you want......If this is going to be any kind of performance engine i would have it zero decked. You can get the deck height very easy buy using your rod length stroke, compression height. Tell the shop what size you want it cut to.......

I would not run it with the pistons out of the hole. I built one engine like that and i have had no problems but i just does not seam right to me......

Then after all this you see something like this,,,,,, I tore a motor down once that the pistons were down .180 in the hole. It was a blower motor.... Not one sign of any problems with it........

So like i said before don't loose any sleep over a .005 difference!!!!!!

Keith
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Old 08-02-2004, 09:14 AM
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Quote:
You could get a custom set of pistons made with the pin height you want
This will also increase the weight of the pistons, reducing reliability of sustained high RPM, and if the balance is dead on, it won't be any longer.
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Old 08-02-2004, 02:31 PM
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i know it's been mentioned already, but seriously man, have the deck blocked. it's just way easier. My SBC build was decked approx .020" from stock, so the deck height was set at 9.005". With the assembled pistons ending up down in the bore between 4 and 5 thou. I'm using a composition style gasket .039" compressed height.

Final quench .043- .044" varying slightly from cylinder to cylinder.

.025-.035 is just too tight in my opinion... unless you are trying to squeeze every last drop of power out of the motor, and you have vast amounts of parts and labor available to you, and the desire to truly push the limits (and probably bust up some motors in the process) just stick with a .040 or so quench. Aim for 040, then you can go probably + / - .005" somewhere in the assembly, and still be okay once the motor's running.

the key here is to spend more time adjusting your ignition timing and intake charge than you do trying to get the quench "dead on" at a certain spec. the only goal in the entire process is avoiding detonation.

also... if you want more options for compressed gasket thickness, go to scoggin dickey's website and consider their factory GM offerings.

cheers

tbw
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Old 08-02-2004, 06:46 PM
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Re: quench

Quote:
[i]

Then after all this you see something like this,,,,,, I tore a motor down once that the pistons were down .180 in the hole. It was a blower motor.... Not one sign of any problems with it........

So like i said before don't loose any sleep over a .005 difference!!!!!!

Keith [/B]
Blower motors can get away with things like that. The blower makes the turbulence. I'll agree normally .005 extra isn't worth hualing the block back to the machinest.
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Old 08-02-2004, 08:29 PM
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blower

Tresi, i have also herd that about blower motors.

I was wondering how much difference there really is tho after the intake valve is closed and the piston is pushing up on the mixture???? I can see the charge entering the cylinder with the turbulence and even having some right after the intake valve closes but sometime during the rest of the compression cycle ( after the intake closes) i would think it would take the same form as a N/A motor????? Whats your take on this????

I don't know of a way you would ever see it tho to prove one way or the other.....

Keith
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Old 08-02-2004, 10:18 PM
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Re: blower

Quote:
Originally posted by k-star
Tresi, i have also herd that about blower motors.

I was wondering how much difference there really is tho after the intake valve is closed and the piston is pushing up on the mixture???? I can see the charge entering the cylinder with the turbulence and even having some right after the intake valve closes but sometime during the rest of the compression cycle ( after the intake closes) i would think it would take the same form as a N/A motor????? Whats your take on this????

I don't know of a way you would ever see it tho to prove one way or the other.....

Keith
The only reason I could give is that with a blower motor the fuel air charge inters the cylinder with more inertia than a N/A motor. Thus the fuel air stays tumbling and swirling longer.
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Old 08-02-2004, 10:44 PM
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I LOVE these types of threads.... the more technical the better!!!!
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