Although I am aware that popular opinion states "quench" should be from .035"-.045" i'm sure there is much debate.
I recently pulled the heads on my 406 to do some additional port work and to minimize my quench. After calling Cometic today I have decided to shoot for .040" quench and get their .030" MLS gasket. This is with a .010" deck height. This would yield a 10.47:1 SCR and a 8.0277:1 DCR.

My question is would it be worth it, or just too risky to run a .027" gasket for a total quench of .037". This would yield a 10.55:1 SCR and a 8.0817:1 DCR.
This difference is negligible, but I would like to optimize my quench just short of being **** about it. :lol:

I am going to get a deck bridge to confirm each piston's exact position at TDC.

Think .037" would be flirting with disaster?

Heads are AFR 195 with 74cc chambers
Pistons are SRP flat tops, 5cc relief
Steel H-beam rods
.0034" main bearing clearance
.0022" rod bearing clearance

Hopefully I will get these ordered within a few days.
At $160 a set you don't want to order the wrong thing! :smash

Thanks! :cheers:

 

i'd stay with the .040 clearence, the extra 1-2 HP ain't going to out weight my
not waiting for it to SMACK, my 2

 

Set optimum quelch is not as much about compression as it is about eliminating detination and heating. The closer you get quelch to .035 on a steel block motor the less chances you will see of detonation and the engine will run cololer. It is so important that on aluminum block motors I set quelch at .030 because the block will grow .005 when it get to operatig temp.

That being said you also have to look at the quality of parts you run. .035 is for very good quality parts. This means quality rods under 625 grams, pistons under 425 grams and pins under 130 grams. If you are running heavier parts than you have to increase quelch accordingly because they can increase distortion of the crank. Aslo if you are runng a chinesse crank or rods will will need to increase quelch because they distort more than a quality part.

If it is a tried and true tested combinations of parts than keep quelch as low as possible. But if you are unsure, than it is better to error on the high side, better safe than sorry.

 

I just saw your question after answering another person. Read the last two articles that I'm listing. I run .041 because of short piston skirts and 7500 rpm.

QUENCH, the distance between the cylinder head and the pistons flat area in the combustion chamber read the links below, its worth the effort.
I run mine as near to .040 as possible. Right now I have 11.2 compression and use 91 octane. I also drive and race 1000's of miles a year without a problem.

Run less than about .035 thousands and at high rpm levels the pistons might hit the cylinder heads, run more than about .044 thousands the QUENCH effect of forceing the fuel air mix to the center of the cylinder from the cylinders edge area looses both speed and effectiveness, remember the quench area must be so tight that virtually all the fuel/air mix is forced into the center area and none is allowed to burn untill its squirted into the burn area increaseing turbulance and burn efficiency
in theory the much better quench, combined with the shorter more compact area the flame front needs to cover and the far higher turbulance combine to allow more of the pressure to build AFTER the crank passes TDC on the end of compression and begining of the power stroke

its mostly an advantage in that you get a more even burn in the cylinder and less chance of detonation.
look, it takes approximately 40 thousands of a second for the flame from the ignition to cross a 4.25" bore,at low rpms and still takes about 15 milliseconds at high RPM due to the much faster movement of the compressed fuel air mix in the cylinders, lets look at what that means
if the chevy plug is located 4/5ths of the way to one side thats a time of about 32 thousands for the pressure to build as the flame travels 3.4" in the chevy but in a compact combustion chamber it could only take the cylinder flame front less than 10-20 thousands of a second to travel acrossed the combustion chamber for a complete burn at low rpms, this of course speeds up as the swirl and turbulance increase with increased engine RPMs but the ratios stay similar. this results in more useable energy WORKING on the piston AFTER IT PASSES TOP DEAD CENTER ON THE POWER STROKE. BUT MODERN WEDGE combustion chambers use increased QUENCH to speed the flame front and lower the burn time combined with a smaller combustion chambers look at this chart http://www.iskycams.com/ART/techinfo/ncrank1.pdf

keep in mind that the cylinder pressure starts, builds to a peak and drops off all before the piston moves more than about 1/2 inch away from TDC and that if your wasteing 10-20 degrees of rotation compressing the burning mix in a slow to ignite combustion chamber your wasteing engine power http://naca.larc.nasa.gov/reports/1939/naca-tm-914/ [URL=http://www.me.gatech.edu/energy/ICEngines/8_CylinderCombustionProcesses.pdf]http://www.me.gatech.edu/energy/ICEngines/8_CylinderCombustionProcesses.pdf</A> http://www.combustion-net.com/library/articles/PDFs/0210-spark-ignition-engine-cycle.pdf</A> http://www.nedians.8m.com/Comp_IC.html <A HREF="http://mb-soft.com/public2/engine.html" TARGET="_blank">http://mb-soft.com/public2/engine.html
http://hpp.primediaautomotive.com/ar...hpp_fire.shtml


Things to read

http://racehelp.com/article_racing-10.html

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




[Modified by gkull, 4:44 PM 2/10/2004]

 

gkull Thanks for the links :thumbs:

 

gkull great reading :thumbs:

 

those are good reads, but i did not see anything about rod length playing into the equation. if memory serves me correctly, Travis is running 6.0" rods. longer rods keep the piston near TDC longer in the crank rotation, this will have dramatic effect relating to post combustion cylinder pressures resulting in a different idea of what the propper quench height should be. Travis, i run .039" quench and spun her higher than i should have, no damage luckily. i would say .037" won't get you unless your going over 6500rpm. i do agree that .040" sounds a lot safer though, Brian

 

AK - None of these articles really deal with piston rock in it's travel up the bore. Or .020 - .080 offset pin pistons like i use. Or even longer rods. Short piston skirts add the whack factor. I have been Okay. Some of the big guys in the 540 - 632 cubic inch range whacked in the first few minutes of start up.

Quench has never been my problem. It's always been valve impact in past motors running 2.055 intakes and a little over rev. That's untill I learned that bigger springs were always better.





[Modified by gkull, 8:50 PM 2/10/2004]

 

comp I am thinking along the same lines, but .037 really doesn't sound unreasonalbe. I am going to order the gaskets tommarow, maybe i'll chicken out. ;)

Pete79L82 Thanks for the input. I confirmed the deck height of .010" this evening with the piston rock somewhere in the .005-.006" ATDC.
I don't plan to run over 6500rpm with this motor.

The Rods are Scat-H beam 6.0" weight - 645g
The pistons are SRP flat tops weight - 424g
The Crank is Scat 9000
Main Bearing Clearance is .0034"
Rod Bearing Clearance is .0022"

Gkull Thanks for all the great info, I'm currently reading the "racerhelp" article. Good stuff. They say to go for .035. I'm beginning to think .037 "may" be too close. I don't mind being on the edge, but i'd hate to screw it up.

AKRAY4PLAY Yes, that is correct i'm running 6.0" rods. The piston clearance with the 4032 alloy Pistons is pretty tight at ~.0025", but there is a fair amount of rock ATDC (short skirt?). It sounds as if the .040 would be what I should shoot for, but those extra .003" are just so easy. :)

I am going to Mill .008" off the heads to clean up the IMPRINT from the felpro fire rings, so compression with a .037" quench would be 10.66:1 or 8.16:1 DCR. At 4000ft elevation on 91 octane I think i would be fine.

The heads are currently getting "worked." I'm curious to see how it runs as I'm trying to locate an Engine dyno for initial tuning.

Thanks for all the help!

:cheers:


EDIT: I should also note that I plan to run 100-150 shot of N20 this summer. I'm sure this will effect my choice somewhat, I'm sure the gaskets are up for it, but it sounds like i should go .040.



[Modified by VETDRMS, 10:46 PM 2/10/2004]

 

With a Scat 9000 cast crank I would really be hesitant to go under .040. Personally I would lean closer to .045 to be on the safe side.

On the entry level motors that I have tried to use any Scat cranks on I had to open quelch up to .042 to keep the piston from smaking the heads.

Pete

 

Thanks for all the great input and help. I just ordered the .030" gaskets and they should be here in a couple weeks.

This will yield a .040" quench, with .010" milled off the heads static compression ratio will be 10.61:1. And DCR will be 8.13:1.

Thanks again, much appreciated!
I also ordered some Titanium Retainers...:cool:
:cheers:

 

Hey gkull. I gott'a say thanks for posting those sources. I really liked the one from the old NACA. :thumbs:

 

Your how to install a line lock question - I did a better write up and pictures but it must predate the archives. Or it's somewhere else like tech docs.
http://forums.corvetteforum.com/zero...413646#1413646