Quench Height???
03-12-2002, 05:34 PM
#1
Drifting
Thread Starter
Quench Height???
How do I calculate quench height? I just can't figure out what a .041" head gasket thickness will do to my engine.
With .022" steel shim (GM stock): 11:1 compression
With .041" aftermarket gasket: 10.5:1 compression
Thanks!
With .022" steel shim (GM stock): 11:1 compression
With .041" aftermarket gasket: 10.5:1 compression
Thanks!
03-12-2002, 05:42 PM
#2
Drifting
Thread Starter
Re: Quench Height??? (rainman69)
Thank you Mr. Murphy and your stupid law. As soon as I posted this question, I found the answer on the Keith Black website.
Excessive cylinder pressure will encourage engine-destroying detonation and no piston is immune to its' effects. An important first step is to set the assembled quench (a.k.a. "squish") distance to .040". The quench distance is the compressed thickness of the head gasket plus the deck clearance (the distance your piston is down in the bore). If your piston height (not dome height) is above the block deck, subtract the overage from the gasket thickness to get a true assembled quench distance. The quench area is the flat part of the piston that would contact a similar flat area on the cylinder head if you had .000" assembled quench height. In a running engine, the .040" quench decreases to a close collision between the piston and cylinder head. The shock wave from the close collision drives air at high velocity through the combustion chamber. This movement tends to cool hot spots, averages the chamber temperature, reduces detonation and increases power. Take note, on the exhaust cycle, some cooling of the piston occurs due to the closeness of the water- cooled head.
If you are building an engine with steel rods, tight bearings and pistons, modest RPM and automatic transmission, a .035" quench is the minimum practical to run without engine damage. The closer the piston comes to the cylinder head at operating speed, the more turbulence is generated. Unfortunately, the operating quench height varies in an engine as RPM and temperatures change. If aluminum rods, loose pistons (they rock and hit the head), and over 6000 RPM operation is anticipated, a static clearance of .055" could be required. A running quench height in excess of .060" will forfeit the benefits of the quench head design and can cause severe detonation. The suggested .040" static quench height is recommended as a good usable dimension for stock rod engines up to 6500 RPM. Above 6500 RPM, rod selection becomes important. Since it is the close collision between the piston and the cylinder head that reduces the prospect of detonation, never add a shim or head gasket to lower compression on a quench head engine. If you have 10:1 with a proper quench and then add an extra .040" gasket to give 9.5:1 and .080" quench, you will create more ping at 9.5:1 than you had at 10:1. The suitable way to lower the compression is to use a KB dish piston. KB dish (reverse combustion chamber) pistons are designed for maximum quench area. Having part of the combustion chamber in the piston improves the shape of the chamber and flame travel.
If you are building an engine with steel rods, tight bearings and pistons, modest RPM and automatic transmission, a .035" quench is the minimum practical to run without engine damage. The closer the piston comes to the cylinder head at operating speed, the more turbulence is generated. Unfortunately, the operating quench height varies in an engine as RPM and temperatures change. If aluminum rods, loose pistons (they rock and hit the head), and over 6000 RPM operation is anticipated, a static clearance of .055" could be required. A running quench height in excess of .060" will forfeit the benefits of the quench head design and can cause severe detonation. The suggested .040" static quench height is recommended as a good usable dimension for stock rod engines up to 6500 RPM. Above 6500 RPM, rod selection becomes important. Since it is the close collision between the piston and the cylinder head that reduces the prospect of detonation, never add a shim or head gasket to lower compression on a quench head engine. If you have 10:1 with a proper quench and then add an extra .040" gasket to give 9.5:1 and .080" quench, you will create more ping at 9.5:1 than you had at 10:1. The suitable way to lower the compression is to use a KB dish piston. KB dish (reverse combustion chamber) pistons are designed for maximum quench area. Having part of the combustion chamber in the piston improves the shape of the chamber and flame travel.
03-12-2002, 06:19 PM
#3
Team Owner
Re: Quench Height??? (rainman69)
With my dial indicator I came up with -.006 piston to block deck. then .038 compressed height of the copper ring head gasket for aluminum heads for a quench of .044 total. Which might be marginal for 7500 rpm and very short JE SRP pistons for 3.750 stroke and 6 inch bushed rods.
03-15-2002, 01:37 PM
#4
Re: Quench Height??? (gkull)
So it would be better to have a 11.17 CR with .041" quench than it would be to have a 10.52 CR with .066" quench?
gkull, what compression ratio do you have? I am curious as to what people are using out there. I know there are at least a couple of you out there using higher than 11.0 CR on pump gas. What did you do to make this work? What octane fuel are you using?
gkull, what compression ratio do you have? I am curious as to what people are using out there. I know there are at least a couple of you out there using higher than 11.0 CR on pump gas. What did you do to make this work? What octane fuel are you using?
03-15-2002, 02:43 PM
#5
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Re: Quench Height??? (aobrien)
Mine's at .036.
Head gasket is .045 and the pistons are +.009 OUT of the block.
I only have 10.44 compression, but the huge bore can be more detonation prone so I set it to make sure I would be OK.
I run 93 octane with 39-40* with no problems at all at essentially sea level.
My old 427 was at .038. Head gasket .021 and pistons .017 IN the hole. I had 11.2 compression with iron heads and it also did fine on pump gas with 40* timing.
Tight quench is one of the keys to running pump gas. Tighter the better.
Jim
Head gasket is .045 and the pistons are +.009 OUT of the block.
I only have 10.44 compression, but the huge bore can be more detonation prone so I set it to make sure I would be OK.
I run 93 octane with 39-40* with no problems at all at essentially sea level.
My old 427 was at .038. Head gasket .021 and pistons .017 IN the hole. I had 11.2 compression with iron heads and it also did fine on pump gas with 40* timing.
Tight quench is one of the keys to running pump gas. Tighter the better.
Jim
03-15-2002, 03:29 PM
#6
Team Owner
Re: Quench Height??? (aobrien)
AObrien - Static compression is just a number. Dynamic compression is what your concerned with. What I'm saying is a low overlap 9.5-1 c/r might have detonation problems on 92 octane and my nearly 11 runs fine with a hot cam to bleed off cylinder pressure at lower rpm. With aluminum heads, thermal coatings, and correct advance curve. Mid 11's would be fine with 92 octane.
This is how I figured out my compression. I wish I would have went 1/2 point higher.
http://www.smokemup.com/utilities/ca...sion_ratio.cfm
Calculate Compression Ratio
You entered the following information:
Bore - 4.030 inches
Stroke - 3.750 inches
Cyl head volume - 64 cc
Deck height - 0.006 inches
Head gasket bore - 4.060 inches
Head gasket thickness - 0.038 inches
Piston dish volume - 6 cc
Compression Ratio is:
10.886 : 1
This is how I figured out my compression. I wish I would have went 1/2 point higher.
http://www.smokemup.com/utilities/ca...sion_ratio.cfm
Calculate Compression Ratio
You entered the following information:
Bore - 4.030 inches
Stroke - 3.750 inches
Cyl head volume - 64 cc
Deck height - 0.006 inches
Head gasket bore - 4.060 inches
Head gasket thickness - 0.038 inches
Piston dish volume - 6 cc
Compression Ratio is:
10.886 : 1
03-15-2002, 05:57 PM
#7
Re: Quench Height??? (gkull)
I have a Hydrolic Roller Cam, 224@0.50, 0.525 lift, 110 lobe separation, with forged SRP Pistons, aluminum heads, fuel injection, and 91 octane fuel. What would be a good static CR and quench to go with this combo. I have the parts (except the injection)... but it will be about a year before I start building the engine.
427Hotrod: :cool: thanks for the info.
427Hotrod: :cool: thanks for the info.
03-15-2002, 11:53 PM
#8
Re: Quench Height??? (rainman69)
Just to clarify a couple things.
Positive and negative deck height of the piston should not be confused with actual quench area.
Combustion chamber design helps depict the actual quench area.Piston design comes into play as well.
It is not always practical to 0 deck a block as all pistons are not equal.One 427 piston might set .025 in the hole.Another 454 piston might set .008. It might not be either practical or desirable to deck a block .030 to obtain 0 deck.
A 76cc 882 Small block head casting for example offer little to none in the way of quench area squeeze .Neither does the Mopar Wedge motors heads.But the after market piston companies have caught on and are developing pistons for the Mopars to help in that area.
In general,run the smallest practical combustion chamber available that will not excessively shroud the valves and get the piston height in relation to the block deck as close as possible to 0 as possible when running a steel rod if a .038-.042 head gasket is used.
Positive and negative deck height of the piston should not be confused with actual quench area.
Combustion chamber design helps depict the actual quench area.Piston design comes into play as well.
It is not always practical to 0 deck a block as all pistons are not equal.One 427 piston might set .025 in the hole.Another 454 piston might set .008. It might not be either practical or desirable to deck a block .030 to obtain 0 deck.
A 76cc 882 Small block head casting for example offer little to none in the way of quench area squeeze .Neither does the Mopar Wedge motors heads.But the after market piston companies have caught on and are developing pistons for the Mopars to help in that area.
In general,run the smallest practical combustion chamber available that will not excessively shroud the valves and get the piston height in relation to the block deck as close as possible to 0 as possible when running a steel rod if a .038-.042 head gasket is used.
03-16-2002, 01:56 AM
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Re: Quench Height??? (mountainmotor)
Maybe I wasn't real clear.
I used positive deck height to establish the quench distance that I wanted. I needed to do that because of the head gaskets that I planned to use.
On the other hand, the 427 had a virgin uncut block and the negative deck height figure required me to use a thin steel shim head gasket to get the distance I wanted to achieve.
But, yes you are correct. Quench AREA is a whole 'nuther matter. Many engines have chambers designs without any. A Chrysler Hemi comes to mind. Unless you have some serious piston to head fitting it's just not there by design. I know Landy makes a reverse dome piston to try to achieve it.
If the head and piston design you have has quench area designed into it, then put it as tight as you dare. I actually know of steel rod race motors in the .020-.025 range, but they are on the ragged edge. They don't worry much if they touch a little!
I used positive deck height to establish the quench distance that I wanted. I needed to do that because of the head gaskets that I planned to use.
On the other hand, the 427 had a virgin uncut block and the negative deck height figure required me to use a thin steel shim head gasket to get the distance I wanted to achieve.
But, yes you are correct. Quench AREA is a whole 'nuther matter. Many engines have chambers designs without any. A Chrysler Hemi comes to mind. Unless you have some serious piston to head fitting it's just not there by design. I know Landy makes a reverse dome piston to try to achieve it.
If the head and piston design you have has quench area designed into it, then put it as tight as you dare. I actually know of steel rod race motors in the .020-.025 range, but they are on the ragged edge. They don't worry much if they touch a little!
03-16-2002, 08:25 AM
#10
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Re: Quench Height??? (mountainmotor)
This is an excellent thread! Very educational!
I'm glad I stumbled on to it because I was about to deck a SB to "0" after mocking up the assembly to determine the cut. However I didn't realize that the pistons varied that much. .008"~.025" is a big swing. How does a person compensate for that? Literally measure pistons in some parts warehouse? I'm assuming you'd mic the top of the wrist pin hole to the top edge of the piston, right?
Up until now I was planing on building a 383 stroker, decking the block to zero, use 72cc heads, .040" head gasket and flat top pistons with 2 valve reliefs, thinking I'd come close to a 10.4:1 comp ratio. Your thoughts?
Secondly, if a person was rebuilding a mid-year BB and didn't want to deck the block to achieve the proper squish, could you have a custom set of pistons made to maintain the blocks originality?
Thanks Gentlemen. :seeya
I'm glad I stumbled on to it because I was about to deck a SB to "0" after mocking up the assembly to determine the cut. However I didn't realize that the pistons varied that much. .008"~.025" is a big swing. How does a person compensate for that? Literally measure pistons in some parts warehouse? I'm assuming you'd mic the top of the wrist pin hole to the top edge of the piston, right?
Up until now I was planing on building a 383 stroker, decking the block to zero, use 72cc heads, .040" head gasket and flat top pistons with 2 valve reliefs, thinking I'd come close to a 10.4:1 comp ratio. Your thoughts?
Secondly, if a person was rebuilding a mid-year BB and didn't want to deck the block to achieve the proper squish, could you have a custom set of pistons made to maintain the blocks originality?
Thanks Gentlemen. :seeya
03-16-2002, 12:13 PM
#11
Team Owner
Re: Quench Height??? (kahuner)
The piston manufacturer will give you the correct skinny. I would never deck a block. You have too many other options on how to get compression. I have them blue printed and surfaced for studs. I totally agree with the least CC chambers statement. That was an additional factor in my sellection of 64 cc Dart Pro1 Heads
i might just go to .030 head gasket if I ever have to pull my heads for a .036 quench.
kahuner - The 66 looks like show quality!
:D
[Modified by gkull, 10:19 AM 3/16/2002]
i might just go to .030 head gasket if I ever have to pull my heads for a .036 quench.
kahuner - The 66 looks like show quality!
:D
[Modified by gkull, 10:19 AM 3/16/2002]
03-16-2002, 01:15 PM
#12
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Re: Quench Height??? (gkull)
gkull;
Thanks for the compliment on my "ol' bucket of bolts". It's not show quality but it looks pretty good.
About the squish, I'm left with the impression that zero deck clearance is something that engine builders now realize to be an advantage. Why did GM design and build engines that had a -.020" deck clearance that would've created a gas trap creating hot spots? Was the octane so high that gas traps weren't a concern?
Again, if a person doesn't deck the block to achieve zero deck clearance, how do you do it? My goal was not to just achieve 10.4:1 compression by decking the block, it was to eliminate the gas trap.
Thanks for the compliment on my "ol' bucket of bolts". It's not show quality but it looks pretty good.
About the squish, I'm left with the impression that zero deck clearance is something that engine builders now realize to be an advantage. Why did GM design and build engines that had a -.020" deck clearance that would've created a gas trap creating hot spots? Was the octane so high that gas traps weren't a concern?
Again, if a person doesn't deck the block to achieve zero deck clearance, how do you do it? My goal was not to just achieve 10.4:1 compression by decking the block, it was to eliminate the gas trap.
03-16-2002, 01:49 PM
#13
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Re: Quench Height??? (rainman69)
The problem I'm having is my 400 block is already decked 90 degrees parallel to crank centerline. My pistons are forged SRP flat tops, so my only choice is 72cc heads if I want to stay with 10.6 CR or find a way of running 11.6 on a semi-daily driver/racer and 92 octane. I don't want to gamble on detonation because I'm going to use .39 Fel-Pro 1014 gaskets. I'm still thinking the larger chambers will be better for the 2.08 valves as far as shrouding goes,,,I just don't want to go over 11CR even though I'm getting the pistons and heads coated by Swain Technology,,any ideas?? I guess I'm going to have 0 quench or very close to is!! HELP!!
03-16-2002, 11:45 PM
#14
Team Owner
Re: Quench Height??? (autoxer)
autoxer - The best choice is some dished pistons. I'm not sure at what point shrouding is an issue. Because all the 360 ci motors in sprint cars are limited to 23 degee heads and they run any where from 2.10 to 2.20 intakes. Before my darts i bought Brodix -11 heads with 2.15 down ports. So my major problem was spread port headers
What i'm saying is you have more than 4.034 bore with a 3.75 stroke and they have max flow without a worry of shrouding. I had 2.10's cut down to 2.08 because I had the choice of 2.10/1.6 or 2.08/1.625 and my plan was for max exhaust with NO2.
Once you get into big exhaust ports. The real problem is header size with 23 deg . heads . You need adapters to use the headers. I have 1 3/4 hooker S/C and i had to spend allot of time to hog them out to even be close to the Dart heads exhaust port size.
What i'm saying is you have more than 4.034 bore with a 3.75 stroke and they have max flow without a worry of shrouding. I had 2.10's cut down to 2.08 because I had the choice of 2.10/1.6 or 2.08/1.625 and my plan was for max exhaust with NO2.
Once you get into big exhaust ports. The real problem is header size with 23 deg . heads . You need adapters to use the headers. I have 1 3/4 hooker S/C and i had to spend allot of time to hog them out to even be close to the Dart heads exhaust port size.
03-17-2002, 01:29 PM
#15
Moderator
Re: Quench Height??? (gkull)
Wow, this is great info, although still somewhat confusing. I'm building an engine up right now ('73 sbc). It's at the maching shop now. I've got the TRW L2256F30 forged pistons on order. I have 64cc WP Sportsman II heads. TRW says 9.72 cr. I would like to be at 10+ to 1. What do I need to do? This block has not been decked or surfaced yet. What would be the deck height for these pistons? Should I go with a thinner head gasket than the stock Fel-Pro stuff? I bought the kit from Summit. Thanks fellas :)
03-17-2002, 05:34 PM
#16
Re: Quench Height??? (MasterDave)
Dave,
One of the reasons it is confusing is the many variables in combustion chamber and piston design.Your motor though with the 64cc heads absolulutley needs mocked up imo to see how much the piston sits in the bore so as to get it as close to zero deck as possible.My resources says 9.6-1 with a Felpro head gasket.That head and piston design will allow for a little squeeze as opposed to if you were using a smog 76cc casting
Trust me,mock it up.The benefits far outweigh the hassle.One piston w/o rings installed will suffice.You will not need to fully torque the rods and mains either.
[Modified by mountainmotor, 3:36 PM 3/17/2002]
One of the reasons it is confusing is the many variables in combustion chamber and piston design.Your motor though with the 64cc heads absolulutley needs mocked up imo to see how much the piston sits in the bore so as to get it as close to zero deck as possible.My resources says 9.6-1 with a Felpro head gasket.That head and piston design will allow for a little squeeze as opposed to if you were using a smog 76cc casting
Trust me,mock it up.The benefits far outweigh the hassle.One piston w/o rings installed will suffice.You will not need to fully torque the rods and mains either.
[Modified by mountainmotor, 3:36 PM 3/17/2002]
03-17-2002, 07:11 PM
#17
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Re: Quench Height??? (autoxer)
I guess I'm going to have 0 quench or very close to is!! HELP!!
03-17-2002, 07:23 PM
#18
Instructor
Re: Quench Height??? (CFI-EFI)
Pistons nowadays don't really vary that much but you still need to check if your running tight clearance. You can flycut the higher pistons a little if you really need to.
03-18-2002, 01:18 AM
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Re: Quench Height??? (RACER7088)
GM set them .020 give or take a few thousandths to allow for production tolerances and to allow for future block decking if needed without needing new piston designs. Remember, in many cases the factory engines used the steel shim gaskets and total quench distance was in the .040-.045 range. Not too bad.
Now take that same motor and throw on some Fel-Pro blue gaskets and now you're out to .060 or so.
And if you rebuilt the engine with stock replacement pistons, you will find that the great majority of the less expensive "rebuilder" qulality ones are made about .020 shorter so they can easily end up .040 or more IN the hole, plus you use the .038-.040 gasket and you just lost all your compression. Even with those nice flatops you find your self in the 8-9.0 compression range if you're lucky. Then if the heads were done and the old valves were ground, your 76cc heads could easily have 80 cc plus! It all adds up. They make the pistons that way so the rebuilders don't have to worry about these issues on assembly lines.
So the best advice here is still to mock it up. You'll never know until you measure it.
Jim
Now take that same motor and throw on some Fel-Pro blue gaskets and now you're out to .060 or so.
And if you rebuilt the engine with stock replacement pistons, you will find that the great majority of the less expensive "rebuilder" qulality ones are made about .020 shorter so they can easily end up .040 or more IN the hole, plus you use the .038-.040 gasket and you just lost all your compression. Even with those nice flatops you find your self in the 8-9.0 compression range if you're lucky. Then if the heads were done and the old valves were ground, your 76cc heads could easily have 80 cc plus! It all adds up. They make the pistons that way so the rebuilders don't have to worry about these issues on assembly lines.
So the best advice here is still to mock it up. You'll never know until you measure it.
Jim
03-18-2002, 01:52 AM
#20
Drifting
Thread Starter
Re: Quench Height??? (rainman69)
So, on my original post...Here are my thoughts.
The pistons sit .028" down the hole at TDC. They are TRW L2304 .030 over .100 domed pistons. I have 64cc heads (large valve) that have been milled 10 thousandths. I figure on using a .018 thick steel shim which should provide .046" quench height on a fairly tight quench area.
What do you all think? :smash:
The pistons sit .028" down the hole at TDC. They are TRW L2304 .030 over .100 domed pistons. I have 64cc heads (large valve) that have been milled 10 thousandths. I figure on using a .018 thick steel shim which should provide .046" quench height on a fairly tight quench area.
What do you all think? :smash: