Proper way to measure quench
Proper way 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?
I'm guessing the spec for 0.035" quench already takes into account piston rock plus other factors such as parts growth, and I should measure at the piston pin centerline axis. But I don't want to work on assumptions and have a piston kiss the cylinder head!
Thanks for the help.
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?
I'm guessing the spec for 0.035" quench already takes into account piston rock plus other factors such as parts growth, and I should measure at the piston pin centerline axis. But I don't want to work on assumptions and have a piston kiss the cylinder head!
Thanks for the help.
I measure the rock and use the number in between. So if one side rocks .020" above deck and .010" below deck, that's .030" of travel. Divide that by 2, and when either added to the below deck number or subtracted from the above deck number, you end up with .005" above the deck.
So basically you use an average value and not worst-case. Similar concept to checking on the pin centerline axis, but you don't have to know where is the centerline axis.
I wouldn't think of the higher piston rock measurement as worst case because if it were rocked one way or another and it got too close, it would be able to give a little bit by rocking the other way. Where it is relative to the deck when the piston is square in the bore is worst case IMO, since it won't be able to rock if that measurement is too close at TDC.
I took a stab at this with 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.... sound reasonable?
Measurement 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
Measurement 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
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Verdad Gallardo 1.Bring the piston up to top dead center using your deck bridge.
2.Rock the piston each way, until the gauges read the same, both 12 o’clock, and 6 o’clock.
3.Re-check top dead center, with the gauges.
4.Record the number with a sharpie, on the deck surface.
5.Repeat 7 more times.
The distance out of the hole here is what you add to your gasket to achieve quinch. So whatever quinch your looking for, let’s say .040” for easy math, you’ll add the out-of-hole number to this. If your decks are perfectly square, which I doubt, but if they are, you take the .040” and add the out-of-hole number to this.
For instance, .040” (quinch)plus, say .005” (OOH) for your numbers (if decks are perfect...) would give you a .045” gasket.
If your decks are like most of ours, with 8 different numbers, you’ll take your piston the farthest out, and use that number. If your decks are terrible, it might require two different gaskets. Prolly not, but it’s possible.
I used to use the average number method, with means, as KCS is describing. It works just as well, until Tony Mamo talked me into a deck bridge. Easy peasy.
I got 0.006 - 0.007 for all even cylinders, and 0.003 - 0.004 for all odd cylinders except #5 which was lower at 0.002.
I will redo it again using your method and see what numbers it comes up with.
Did it again with 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.
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.
Last edited by QwkTrip; Jan 21, 2018 at 11:16 PM.
Squish Measurement Method Hi Frank, I agree with your observation, the Pin Offset effect.
The Side/Side is opposite with an off set pin.
The piston is MORE balanced with the OEM Pin Offset, GOOD for Turbo use.
My Squish measurement is completed AFTER the engine is raced.
I "scribe" the cylinder # on both of the Head Squish Pads, each side.
After the race I can read the head cylinder number on the piston crown !
This is when the head is removed, though a Bore Scope could do the same read.
Lance
The Side/Side is opposite with an off set pin.
The piston is MORE balanced with the OEM Pin Offset, GOOD for Turbo use.
My Squish measurement is completed AFTER the engine is raced.
I "scribe" the cylinder # on both of the Head Squish Pads, each side.
After the race I can read the head cylinder number on the piston crown !
This is when the head is removed, though a Bore Scope could do the same read.
Lance
I called Cometic tech line today. They have 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). Cost of a 0.042 is same as other catalog options.
So I could do a 0.045 and 0.042 gasket combination and even out the sides perfectly with 0.038 quench. Or I could do a 0.042 and 0.040 combo and nearly perfectly even things out at 0.036 quench.
Do you think the LS7 can handle quench as tight as 0.036?
So I could do a 0.045 and 0.042 gasket combination and even out the sides perfectly with 0.038 quench. Or I could do a 0.042 and 0.040 combo and nearly perfectly even things out at 0.036 quench.
Do you think the LS7 can handle quench as tight as 0.036?
In my opinion .005"-.010" additional quench is not going to make a significant difference in power or tuning.
If it's an aluminum block it will grow with heat, so your .035" cold is more like .040"-.045" at running temperature.
If it's a drag race only engine that operates at a much cooler temperatures for much shorter durations the engine can handle a tighter quench.
For a "street car" that has the potential to see elevated temps (200°F+) on an occasion, I'd stay closer to .040" as the minimum.
If it's too tight, you find out the hard way with a pinched ring, broken ring land, broken piston, hole in the block, etc. Not worth it in my opinion unless you are trying to set a world record and need every last .5 HP.
Again, just my opinion.
If it's an aluminum block it will grow with heat, so your .035" cold is more like .040"-.045" at running temperature.
If it's a drag race only engine that operates at a much cooler temperatures for much shorter durations the engine can handle a tighter quench.
For a "street car" that has the potential to see elevated temps (200°F+) on an occasion, I'd stay closer to .040" as the minimum.
If it's too tight, you find out the hard way with a pinched ring, broken ring land, broken piston, hole in the block, etc. Not worth it in my opinion unless you are trying to set a world record and need every last .5 HP.
Again, just my opinion.
Good points. This engine has cost waaaaay more than I told my wife it would and I sure as hell can't take a chance ruining anything. This is probably the last time daddy gets to spend money like this for a long time. 
Got a note from Tony Mamo and he advised that a stock LS7 short block can go as tight as 0.040 gasket if the tallest piston is 0.006" or even 0.007" out of hole. That's some pretty tight quench!
Got a note from Tony Mamo and he advised that a stock LS7 short block can go as tight as 0.040 gasket if the tallest piston is 0.006" or even 0.007" out of hole. That's some pretty tight quench!
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Occasionally I do get blocks that one side is a few thou lower across the board and I will order say a .034 thick and a .036 thick etc., just a hypothetical example
Hope this helps!
-Tony
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Anything worth doing is worth doing well. Build it right the first time....its alot cheaper than building it twice!!
www.mamomotorsports.com
Tony@MamoMotorsports.com
Anything worth doing is worth doing well. Build it right the first time....its alot cheaper than building it twice!!
Last edited by Tony @ Mamo Motorsports; Jan 23, 2018 at 06:26 AM.
It more than helps, Tony. Thank you!
I've got the time to sweat the details with this engine. I'm not very experienced so I'm going through learning curve of what that means but I'm definitely putting in the effort this time.
I've got the time to sweat the details with this engine. I'm not very experienced so I'm going through learning curve of what that means but I'm definitely putting in the effort this time.