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DriveWFO said:
What's the range of ideal quench distances??? Just for kicks, let's assume the pistons is ".025 in hole and I'm using a ".028 compressed thickness head gasket. Is the quench decent???

isnt that possibly too much quench....I think you want around .035-040" quench you will have .053" quench if I am not mistaking.


Not sure if this will be helpful to you or not.
http://kb-silvolite.com/spistons.php?action=details&S_id=275
 

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DriveWFO said:
What's the range of ideal quench distances??? Just for kicks, let's assume the pistons is ".025 in hole and I'm using a ".028 compressed thickness head gasket. Is the quench decent???
I found this interesting article from Chevy Hi Perf on quench. It was a good lesson in this particular engine building principle (at least it was for me, knowing nothing about this term before reading that)

http://www.chevyhiperformance.com/techarticles/94138/
 

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Discussion Starter #4
69NovaSS said:
isnt that possibly too much quench....I think you want around .035-040" quench you will have .053" quench if I am not mistaking.


Not sure if this will be helpful to you or not.
http://kb-silvolite.com/spistons.php?action=details&S_id=275
From CHP:

According to Ken Duttweiler, the tightest quench he recommends is around 0.050-inch.
So, .053" would be pretty good?



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That is interesting, I had heard you wanted to be like .045-.048 or better.
 

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NovatoriusRex said:
I found this interesting article from Chevy Hi Perf on quench. It was a good lesson in this particular engine building principle (at least it was for me, knowing nothing about this term before reading that)

http://www.chevyhiperformance.com/techarticles/94138/

That is a real cool article. Very informative. Have you done a search on this site for the word quench. You might be surprised with the wide range of results. There is even an engine builder that is quoted as saying the proper quench is from .035"-.045". :confused: (this topic seems to be more confusing than you would think it should be)
 

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There is no one right answer to what is the correct squish dimension.
Squish is a real engineering term that dates back to the 50's if not WWII.
It relies on near collision between a quench surface and the piston to work. Not all engines have a quench type cylinder head (like some Chryslers) so the squish effect is not possible on every engine design. Because the tighter you go to minimum squish, the more you risk hitting the piston on the head and collapsing a ring groove or worse.

Since piston clearance plays such a big part in piston-to-head clearance, it is possible to run a piston-to-head clearance tighter than 0.040-inch if you feel brave. Noted horsepower hero John Lingenfelter says that clearances of 0.037 to 0.040 inch are possible, but you must know what you’re doing. The late Smokey Yunick also recommended a quench clearance of 0.040 inch as a safe but critical clearance.
Kenny Duttweiler just prefers to be safer than sorrier and probably runs looser piston to bore clearances on his turbo V-6's to prevent seizing. I've been to his shop and talked to him. Piston stability, rod stretch and weird mechanical problems dog him at the stratospheric power levels he gets. I get the impression he'd rather turn up the boost than risk a physical collision of the piston to head or seizing a piston in the bore.

It's all risk vs reward. IMO running minimum quench is for EXPERT builders, especially if the rpm is going to be high. A static dimension can get a lot tighter at high rpm.

I ran .038" squish on DD's Wright Stuff 331 and it worked....but I sweated bullets pulling it off. I limited the rpm to 6,400 rather than go for higher output but lower reliability.

When you stand close to the precipice and walk the tightrope, you better have your sense of balance or you'll fall. It's not very forgiving if you make a mistake.
 

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So what would you recommend for an engine builder of less then expert ability? (ie your average builder) ;)

EDIT: OPPS I just noticed Dave beat me to the question...lol...Ok what he said then. :D
 

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There is no one answer to that question. Bore size, clearance, CH, skirt design, rod material, crank material, rod clearance, and rpm all play a role on how tight you can go.

The squish effect is more pronounced the closer the piston gets to smacking the head. The problem is the risk of destruction goes up as well.

I've heard from other builders of engines that made the best power with the pistons just ticking the heads but they decided it wasn't worth the risk.

Since the squish dimension must be determined by repeated sessions of mocking up and using measuring tools to determine actual deck clearance of every piston and rod, the amount of piston rock, the estimated stretch tolerance, the actual compressed gasket dimension..... and then machining the deck square and true to the desired dimension is not something you can do in your garage anyway. You'll need an excellent machinist who knows what he's doing.

Over .065" is safe but it won't give you much benefit.
Less than .035" gives great squish but is too risky even for most pro's.

Your answer is somewhere in between.
 

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Discussion Starter #11
Paul Wright said:
There is no one answer to that question. Bore size, clearance, CH, skirt design, rod material, crank material, rod clearance, and rpm all play a role on how tight you can go.

The problem is the squish effect is more pronounced the closer it gets to smacking the head. The problem is the risk or destruction goes up as well.

I've heard from other builders of engines that made the best power with the pistons just ticking the heads but they decided it wasn't worth the risk.

Since the squish dimension must be determined by repeated sessions of mocking up and using measuring tools to determine actual deck clearance of every piston and rod, the amount of piston rock, the estimated stretch tolerance, the actual compressed gasket dimension..... and then machining the deck square and true to the desired dimension is not something you can do in your garage anyway. You'll need an excellent machinist who knows what he's doing.

Over .065" is safe but it won't give you much benefit.
Less than .035" gives great squish but is too risky even for most pro's.

Your answer is somewhere in between.

So .050" would be decent.



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DriveWFO said:
So .050" would be decent.
Sounds good to me :D

Man I love this site. Between all the BS and joking around that goes on there is tons to learn. :)
 

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Did some reading on Quench/Squish last night. In one of the books I have they say "optimal quench movement is in the neighborhood of .0037 to .0039. Seems pretty tight.

In reading Rex's article I noticed on one of the sidebar photos they say "The piston type that uses a full dish (concave design) eliminates most of the quench effect regardless of the piston to head clearance" If your stock 400 pistons look like the ones that came out of my 400 I pulled apart recently, (I can take a photo if you want) you won't be getting much quench effect anyway. Correct?
 

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Perfect Paul,
One of the things guys miss when they build to absolute tight squish is piston rock in the bore. All of a sudden you have the piston kissing the head, and or valves, yet, your perfect math, says no way that can happen.
Had my rotating assembly together 4 times before I was happy with quench, and other clearences, and the only way you can make sure, is to screw things together, the math can lie, the micrometer does not.
 

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Discussion Starter #15
68SSGrandpa said:
Perfect Paul,
One of the things guys miss when they build to absolute tight squish is piston rock in the bore. All of a sudden you have the piston kissing the head, and or valves, yet, your perfect math, says no way that can happen.
Had my rotating assembly together 4 times before I was happy with quench, and other clearences, and the only way you can make sure, is to screw things together, the math can lie, the micrometer does not.
Piston rock? Is that the movement of the piston about the wrist pin?



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DriveWFO said:
Piston rock? Is that the movement of the piston about the wrist pin?

I don't think so. The piston rocks a little in the cylinder near the outer edges of the piston as it travels up and down the cylinder. Picture the piston like a teeter totter. The center pivot point of the teeter totter in this instance is the piston pin and connecting rod. The center of the piston does not rock as it is going up and down the cylinder just like the center of the teeter totter stays pretty much the same height while being used. BUT the edges of the piston can rock somewhat as the pistons are going up and down the cylinder. Just like the ends of the teeter totter can. Of course the piston doesnt rock nearly as much as the teeter totter does. It was just the best way for me to describe it wil my limited knowledge of it.

Hopefully that is clear like mud...(not sure I explained that clearly) :awkward:
 

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HI,

I have ran some of flat top steel rod 283- 350 style motors as close as .017" in certain drag race engines. You can see that the piston is "very" close to the head. You can some times read the part number of the piston off the deck. The motors seem to like this clearance so we still use it. These are not real high rpm motors, usuall 7800 to 8000 max.. On the LT1 style or 302 (mech cam type engines) I shoot for about .025" in these type engines.


On the 400 the closest I have ever ran one with steel rods is about .030", and I never saw any signs of contact. RPMs were about 7200 max..

I agree with Paul and everyne else, I have no Idea what the perfect one woul be.

The .039 figure is handy because most head gaskets are about that size, so a "0" deck and the gasket thickness and you are very close. I guess.


The only technical thing I would add to this discussion on quench is, the effect of the shape of the outer edge of the piston. I have seen a lot of engineerig about the best design of this part of the piston. I have seen several different types and Im not sure sure what the best one is for the best swirl generation.


Good luck guys
Jeff
 

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Discussion Starter #18
stock z/28 said:
The only technical thing I would add to this discussion on quench is, the effect of the shape of the outer edge of the piston. I have seen a lot of engineerig about the best design of this part of the piston. I have seen several different types and Im not sure sure what the best one is for the best swirl generation.


Good luck guys
Jeff
Could you please post some part #s of pistons with good shapes for creating swirl?



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Quench

After reading several opinions on the proper head clearance to get the best quench effect,I would like to have more discussion on this subject.
I have always use a range of .37 to .39 of head clearance on a motor that doesn't go past 6500 rpm with steel rods.
I've have read that this is too tight,I've read that this is just right.I'm aware of the many varibles ,such as piston rock etc.I would like to hear more opinions.
Lets do some "BENCH RACING".
Mike
 
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