How Low Can You Go ???

Indycars

Administrator
Staff member

Just how low can you go with the deck clearance? Now you always see the .040-.045", sometimes I've seen .035", but it depends on many factors.

Such as:
Max RPM, Piston to Cylinder Wall Clearance, Rod Bear Cl, Main Bearing Cl, Piston Pin Cl, Materials (Cast or Forged) and how you measure the deck clearance. If you were to split hairs, I suppose you would have to include oil film thickness.

Most people rotate the crank until the piston is at it highest point in the cylinder. But when the engine is running on the exhaust stroke, all the clearance shift to let the piston travel a few thousands higher in the cylinder. So when someone says they have .040", they really only have maybe .038-.037" when the engine is just idling.

So what's the lowest deck clearance you have successfully run and what parameter did you use, to best of your memory or notes ???
 
the lowest quench/squish clearance I can remember personally is .038 and that was on a 383 with steel rods and a cam that would never support over about 5500rpm.
remember the piston deck can be below or above the block deck its the head gasket thickness plus the piston distance below the block deck or minus that distance the piston distance is above the block deck that determines quench
IM much happier with .040-.042 as a minimum with steel connecting rods, and anything under .050 certainly helps the reduction of the engines tendency to detonate . now in theory getting the quench really tight has significant advantages, in reducing detonation but its a compromise between that and preventing mechanical interference of the rotating assembly
if youve ever pulled down an engine with a .036-.038 quench,distance you have very likely seen faint aluminum transfer on the heads quench areas
BTW When a head gasket thickness is listed its supposed to be the compressed gasket thickness ,this can be important in determining quench distance.
http://www.chevyhiperformance.com/tech/ ... index.html
deck.jpg

valclear2a.jpg

p173610.jpg

read thru these links
viewtopic.php?f=52&t=4081&p=11104#p11104

viewtopic.php?f=53&t=5440&p=16228&hilit=aluminum+rods#p16228
 
grumpyvette said:
the lowest quench/squish clearance I can remember personally is .038 and that was on a 383 with steel rods and a cam that would never support over about 5500rpm.
How did you measure the .038, with the piston pushed down in the cylinder???

remember the piston deck can be below or above the block deck its the head gasket thickness plus the piston distance below the block deck or minus that distance the piston distance is above the block deck that determines quench
IM much happier with .040-.042 as a minimum with steel connecting rods, and anything under .050 certainly helps the reduction of the engines tendency to detonate . now in theory getting the quench really tight has significant advantages, in reducing detonation but its a compromise between that and preventing mechanical interference of the rotating assembly
if youve ever pulled down an engine with a .036-.038 quench,distance you have very likely seen faint aluminum transfer on the heads quench areas
"Really Tight.......Significant Advantages"
Are we talking something much smaller than .038???

Has anyone ever measured the actual clearances at max RPM or does it come from EXPENSIVE EXPERIENCE ???

One factor I've never heard mentioned is the surface area in the quench area. The higher the surface area, the MORE turbulence or more volume that's pushed at high velocity into the combustion chamber when the piston goes thru TDC. Also the more cooling of the gases that would occur.
 
How did you measure the .038, with the piston pushed down in the cylinder???

I used both MATH IE measuring piston deck and head gasket thickness and cross checked it with thin 1/4" diam. modeling clay strips on the piston top that were sprayed with WD40
(so the clay wont stick to piston or combustion chamber surfaces)
and compressed as the engine was rotated 720 degrees


remember the piston deck can be below or above the block deck its the head gasket thickness plus the piston distance below the block deck or minus that distance the piston distance is above the block deck that determines quench
IM much happier with .040-.042 as a minimum with (forged steel connecting rods), and anything under .050 certainly helps the reduction of the engines tendency to detonate . now in theory getting the quench really tight has significant advantages, in reducing detonation but its a compromise between that and preventing mechanical interference of the rotating assembly
if youve ever pulled down an engine with a .036-.038 quench,distance you have very likely seen faint aluminum transfer on the heads quench areas
"Really Tight.......Significant Advantages"
Are we talking something much smaller than .038???

Quench01.jpg


Has anyone ever measured the actual clearances at max RPM or does it come from EXPENSIVE EXPERIENCE ???



Ive seen and done on occasion, the math, where the rod and piston stretch, based on inertial weights of both and thermal expansion etc. was calculated and it shows WHY the piston almost, or actually might contacts the heads at high rpms,and the faint piston to head contact marks,on engine disassemble, naturally rod length, rod design, pin location, bearing clearances, connecting rod cross sectional area, actual rpms and total bob weight of the rotating mass effects this, thats why on BIG BLOCKs you generally try for no less than .040-.044 vs .038-.042 on small blocks (forged steel connecting rods)
ID SUGGEST IF YOUR GOING TO SELECT THE QUENCH CLEARANCE ITS BETTER TO BE A BIT ON THE LARGER END OF THE CLEARANCE RANGE, IT MAY NOT PROVE AS EFFECTIVE BUT ITS LESS LIKELY TO CAUSE A MAJOR PARTS FAILURE
Detonation, lack of lubrication,loss of complete valve train control, or actual rotating assembly parts, touching the heads or valve train, spell near instant destruction, You may not hear it, but it will quickly destroy a motor in many ways. It will find the weakest part.



One factor I've never heard mentioned is the surface area in the quench area. The higher the surface area, the MORE turbulence or more volume that's pushed at high velocity into the combustion chamber when the piston goes thru TDC. Also the more cooling of the gases that would occur.

[/quote][/quote]


READ THESE THREADS



viewtopic.php?f=53&t=5199&p=15129&hilit=burn+patterns#p15129

viewtopic.php?f=53&t=726&p=2302&hilit=groove+quench#p2302

viewtopic.php?f=50&t=2883&p=7484#p7484

viewtopic.php?f=52&t=4081&p=12339&hilit=quench+groove#p12339

viewtopic.php?f=50&t=501&p=11829&hilit=clay+clearance#p11829

http://www.badasscars.com/index.cfm/pag ... prd109.htm

http://www.enginebuildermag.com/Article ... oices.aspx


P12CHARTS.jpg


lets do a bit of math with a high rpm 383 combo, it might help here

lets take this connecting rod (645 grams)
http://www.summitracing.com/parts/ESP-6000B3D/
this piston (527 grams)
http://www.summitracing.com/parts/UEM-9909HC-060/
and just temporarily ignore the rings,and bearing weight

thats about 18210 grains at 4500 fpm in piston speed thats 75 ft per second
6588 inertial pounds the piston weights at just over 7000rpm, and your looking to reverse its direction of travel , at over 116 times PER SECOND at 7000 rpm, effectively doubling even that load of the stress on the exhaust stroke ,if you don,t think thats absolutely amazing that its potentially possible to do without instantly self destructing you have zero grasp on the potential levels of stress, then we add the fact that theres potentially 600 psi of pressure on the power stroke over a piston or about 7700 pounds resisting the piston on the power stroke but not on the next exhaust stroke and it mind boggling it holds together for even a second or two if we throw in the rings and bearing weights
http://www.summitracing.com/parts/ESP-6000B3D/


btw if your weak in math

grains of weight times velocity squared times .450240= inertial energy

1 gram = 15.4323584 grains
 
quenchcheck.jpg


On most engines, Id suggest connecting rods with 7/16" ARP connecting rod bolts and a .038-.044 quench distance
 
Last edited:
.030" quench clearance is the Tightest I have used Rick.
Positive deck height of +.010".
Piston above the deck at TDC.
I like .039" quench.
Zero deck height on Pontiac 455.
Fel Pro 1016 Race HeadGasket is .039 compressed. Verified with a 0-1" micrometer.
A few Pontiac Racers have used .010" quench clearances.
Claimed 20-30 HP gain Vs .039"-.040". Must use Billet Crower Rods or Crower Titanium Rods only.
Titanium has a lower coefficient of expansion than steel. 2:1 strength ratio. Same Dimensions Ti Rod has double HP Compression load capacity. 4,000 HP Rated Ti Crower Rod.
 
Back
Top