How to measure quench
01-20-2018, 07:48 PM
#1
Instructor
Thread Starter
How to measure quench
Doing a head swap on my LS7. I think rule of thumb is don't go tighter than 0.035" quench.
Question: Is that a nominal measurement on the pin centerline axis, or does the 0.035" have be added on top of any possible piston rock?
Question: Is that a nominal measurement on the pin centerline axis, or does the 0.035" have be added on top of any possible piston rock?
01-21-2018, 12:48 AM
#5
Instructor
Thread Starter
I took measurements of piston #8. I'm guessing in this example I should use a value of 0.008 inch out of deck. This equates to a gasket thickness of 0.045 inch to get just a hair over 0.035 quench. And repeat 7 more times to see which piston is worst case scenario....
On piston centerline:
0.008 inch (left and right side)
Piston rocked down at top side:
top .002
bottom .011
Average = .0065
Piston rocked down at bottom side:
top .009
bottom .005
Average = .007
On piston centerline:
0.008 inch (left and right side)
Piston rocked down at top side:
top .002
bottom .011
Average = .0065
Piston rocked down at bottom side:
top .009
bottom .005
Average = .007
01-21-2018, 12:14 PM
#6
Measure over the pin, as that part of the piston will not give. Remember that as the piston sees heat, it will expand and rock will be reduced. 35 is tight. I shoot for 40. LS heads are more forgiving than gen 1, but I still like to use old school rules until they are proven to be false.
01-21-2018, 01:45 PM
#7
Burning Brakes
I use the total amount of indicator travel divided by two. Either way is fine unless you have a non flat top piston obviously. Piston shouldn’t be doing a whole lot of rocking at the top unless you are one of those guys that like to free-rev your **** to redline in the parking lot
01-21-2018, 09:50 PM
#8
Instructor
Thread Starter
I notice the piston can rock in any direction and the only place I get stable readings is the center of the piston. Just take one measurement there for each cylinder?
I did just that and got 0.006 - 0.007 across all the even cylinders, and the odd cylinders were 0.003 - 0.004, except #5 which was even lower at 0.002.
Is that kind of spread normal/reasonable?
I did just that and got 0.006 - 0.007 across all the even cylinders, and the odd cylinders were 0.003 - 0.004, except #5 which was even lower at 0.002.
Is that kind of spread normal/reasonable?
01-21-2018, 10:37 PM
#9
Melting Slicks
I notice the piston can rock in any direction and the only place I get stable readings is the center of the piston. Just take one measurement there for each cylinder?
I did just that and got 0.006 - 0.007 across all the even cylinders, and the odd cylinders were 0.003 - 0.004, except #5 which was even lower at 0.002.
Is that kind of spread normal/reasonable?
I did just that and got 0.006 - 0.007 across all the even cylinders, and the odd cylinders were 0.003 - 0.004, except #5 which was even lower at 0.002.
Is that kind of spread normal/reasonable?
01-21-2018, 11:29 PM
#10
Instructor
Thread Starter
Did it again with two dial indicators at 12 and 6 o'clock positions and leveling out the piston before taking a measurement. This produced less variation.
Even side, all at 0.006 except #4 at 0.007
Odd side, all at 0.003 except #3 at 0.004
#3 and #4 share the same crank journal, right? That would explain why those two are both taller by a tad.
The way things are patterning out I could run a different gasket thickness left and right hand side. Anybody ever do that?
Even side, all at 0.006 except #4 at 0.007
Odd side, all at 0.003 except #3 at 0.004
#3 and #4 share the same crank journal, right? That would explain why those two are both taller by a tad.
The way things are patterning out I could run a different gasket thickness left and right hand side. Anybody ever do that?
Last edited by QwkTrip; 01-22-2018 at 12:17 AM.
01-22-2018, 11:07 AM
#11
Are you using a bridge? The variances you have noted suggest that your method of measuring is suspect.
I would expect +/- .002 from lowest to highest in an OEM block.
Don't mix gaskets.
I would expect +/- .002 from lowest to highest in an OEM block.
Don't mix gaskets.
01-22-2018, 07:41 PM
#12
Instructor
Thread Starter
Yes, using a bridge (Proform). I have 2 dial indicators.
Ignore Post #5. It is junk data due to bad method. I was literally rocking the piston all the way from one extreme to the other. Abandoned this after growing my understanding.
Post #10 is much improved method and good data, I think. The variance per side is tight, just have different height on left bank vs. right bank. Another strong piece of evidence my method is good is the extra +0.001 stroke shows up on both pistons #3 and #4, which I think share the same journal, correct?
I have also measured at center of pistons and it delivered same conclusion as post #10.
Ignore Post #5. It is junk data due to bad method. I was literally rocking the piston all the way from one extreme to the other. Abandoned this after growing my understanding.
Post #10 is much improved method and good data, I think. The variance per side is tight, just have different height on left bank vs. right bank. Another strong piece of evidence my method is good is the extra +0.001 stroke shows up on both pistons #3 and #4, which I think share the same journal, correct?
I have also measured at center of pistons and it delivered same conclusion as post #10.
01-22-2018, 08:03 PM
#13
Instructor
Thread Starter
Why is that?
I can't see why the engine cares what gasket is there, it should just care what chamber geometry it produces. If I use same gasket then I will have almost 0.1 compression difference side to side and the left bank will always be more prone to detonation. So which is the bigger sin... different gasket thickness per bank, or different quench and compression ratio per bank?
Cometic has some catalog options of 0.036, 0.040, and 0.045 compressed thickness. They tell me they can make a 0.042 but can't do anything between 0.036 and 0.040 (Apparently that's not a stack height they can come up with). Running a 0.045 and 0.042 would even things up with 0.038 quench on both sides.
I can't see why the engine cares what gasket is there, it should just care what chamber geometry it produces. If I use same gasket then I will have almost 0.1 compression difference side to side and the left bank will always be more prone to detonation. So which is the bigger sin... different gasket thickness per bank, or different quench and compression ratio per bank?
Cometic has some catalog options of 0.036, 0.040, and 0.045 compressed thickness. They tell me they can make a 0.042 but can't do anything between 0.036 and 0.040 (Apparently that's not a stack height they can come up with). Running a 0.045 and 0.042 would even things up with 0.038 quench on both sides.
Last edited by QwkTrip; 01-22-2018 at 08:18 PM.
01-22-2018, 10:05 PM
#14
Burning Brakes
Yes 3 and 4 are on the same journal.
I would only run different gaskets if it was the last variable in the compression ratio equation, meaning you have measured everything else and it is exactly the same. That is unlikely in my opinion.
I wouldn’t do it but it’s not gonna be the end of the world if you do.
I would only run different gaskets if it was the last variable in the compression ratio equation, meaning you have measured everything else and it is exactly the same. That is unlikely in my opinion.
I wouldn’t do it but it’s not gonna be the end of the world if you do.
01-22-2018, 10:13 PM
#15
Why is that?
I can't see why the engine cares what gasket is there, it should just care what chamber geometry it produces. If I use same gasket then I will have almost 0.1 compression difference side to side and the left bank will always be more prone to detonation. So which is the bigger sin... different gasket thickness per bank, or different quench and compression ratio per bank?
Cometic has some catalog options of 0.036, 0.040, and 0.045 compressed thickness. They tell me they can make a 0.042 but can't do anything between 0.036 and 0.040 (Apparently that's not a stack height they can come up with). Running a 0.045 and 0.042 would even things up with 0.038 quench on both sides.
I can't see why the engine cares what gasket is there, it should just care what chamber geometry it produces. If I use same gasket then I will have almost 0.1 compression difference side to side and the left bank will always be more prone to detonation. So which is the bigger sin... different gasket thickness per bank, or different quench and compression ratio per bank?
Cometic has some catalog options of 0.036, 0.040, and 0.045 compressed thickness. They tell me they can make a 0.042 but can't do anything between 0.036 and 0.040 (Apparently that's not a stack height they can come up with). Running a 0.045 and 0.042 would even things up with 0.038 quench on both sides.
01-22-2018, 10:50 PM
#16
Instructor
Thread Starter
It was a legitimate question and I can't understand the reason for that kind of response. I think I've made it pretty clear I'm not experienced with this. I ask a lot of questions for clarity and to seek understanding. Still interested in your answer.
01-22-2018, 11:28 PM
#17
Instructor
Thread Starter
I have cc the heads and they are all the same for all practical purposes (Mamo heads). Anything else that is really important to measure? I've been using nominal spec values for bore and stroke in my compression calcs. All I have is rulers, a basic cheap caliper, and 1" dial indicator.
01-23-2018, 12:44 AM
#18
Burning Brakes
I have cc the heads and they are all the same for all practical purposes (Mamo heads). Anything else that is really important to measure? I've been using nominal spec values for bore and stroke in my compression calcs. All I have is rulers, a basic cheap caliper, and 1" dial indicator.
The volume of the valve reliefs in the pistons, length of rods, how far the top ring is from the piston crown, stroke length. I’m looking at this from a compression ratio point of view. I want each hole to have the exact same compression ratio and that would trump quench distance in my opinion. You are mainly concerned with quench and running different thicknesses will get you what you are trying to achieve assuming your measurements are spot on. The only thing it’s gonna hurt is your wallet for buying custom gaskets lol. I don’t think you will gain anything either. I mean we are talking .003” here, carbon buildup on the piston will be more than that! As an extreme example if you had a pair of rods on the same journal(like 3 and 4) where the stroke was a half inch short and the rods were a half inch longer you would have pistons that came out of the hole the exact same amount as all the others. However your compression ratio would be way off due to that half inch of swept cylinder volume you lost.
01-23-2018, 12:52 AM
#19
Le Mans Master
The volume of the valve reliefs in the pistons, length of rods, how far the top ring is from the piston crown, stroke length. I’m looking at this from a compression ratio point of view. I want each hole to have the exact same compression ratio and that would trump quench distance in my opinion. You are mainly concerned with quench and running different thicknesses will get you what you are trying to achieve assuming your measurements are spot on. The only thing it’s gonna hurt is your wallet for buying custom gaskets lol. I don’t think you will gain anything either. I mean we are talking .003” here, carbon buildup on the piston will be more than that! As an extreme example if you had a pair of rods on the same journal(like 3 and 4) where the stroke was a half inch short and the rods were a half inch longer you would have pistons that came out of the hole the exact same amount as all the others. However your compression ratio would be way off due to that half inch of swept cylinder volume you lost.
I like the point about the carbon buildup. I wouldn't over think it; the next post from the OP might be describing 16 different pushrod lengths (just a friendly poke). OP, it is good you are asking questions, keep it up, but listen to those with experience. 
Last edited by Dan_the_C5_Man; 01-23-2018 at 12:56 AM.
01-23-2018, 01:02 AM
#20
Instructor
Thread Starter
