squish or quench area 1

[slowkaw]

This is my first post on this forum and I am hoping that someone can enlighten me on something.

On another web page forum the discussion was on quench area. The vehicle being dicussed has a piston-to-head clearance in the neighborhood of .073". I stated that this seemed too large of a measurement for good performance and thought about .040" would be much better. A well known performance engine builder of this marque pretty well dressed me down, stating that it was an unimportant measurement and over-analyised. My understanding has always been that the tighter you can make this area, without piston-to-head contact, the better performance, economy, and emissions would result. If anyone (MaxRace?) can shed some light on this for me, it would be appreciated. Thanks.

David

 

[dynodan]

The squish or quench height should be as tight as possible like you said without the piston touching the head. The distance will depend on whether it is a aluminum rod or steel rod motor. Who ever this engine builder is bring him on and then I will school him on the details.

 

[NickB]

I think that a lot of these so called engine builders like to tell you things won't work, or try to confuse you so you can't keep up with them at the racetrack. At least that's been my impression on a few message boards/mailing lists, but here..... well, here things are much better!!

 

[MaxRaceSoftware]

i have to definetly agree with DynoDan and NickB

the SuperStock racers i've worked with
especially Jimmy Faul's SS/IA 350 that set the NHRA record a few years back , had most all the pistons lightly hitting
the heads ..it was that tight ...thats the way it ran the fastest down the track in the real world !!!

a very well known Greg Stansfield ...Pro Stock Truck driver/engine builder.....definetly had some very good things to say about Jimmy's engine ..definetly had respect on how much HP/Torque the SBC Chevy was making back then
...it was a whole bunch of things ...some of it was extremely close squish/quench area clearances ...
not hitting hard enough to do any damage or move the head around ..but just tight enough to add Torque/HP .

i'll look up engine specs and post head gasket thickness and deck clearances to give you an idea how much you can get away with a 3.480 stroke , rpm, etc.
Sunday night
Larry Meaux (meauxracing@mindspring.com)
Meaux Racing Heads
MaxRace Software
ET_Analyst for DragRacers

http://www.mindspring.com/~meauxracing/

 

[slowkaw]

Thanks guys for the quick response! MaxRace, I look forward to the info you mentioned. I know well-known people like the late Smokey Yunick specified tight squish areas.

One of the other people on this forum (Cycle) and I are good friends and work together part-time. Several years ago, I assembled one of my dragbike engines with a fiber head gasket and miscalcutlated the crushed thickness slightly. The engine was a 999cc Kawasaki, with street cams, 10.5 c.r., slight porting, and turned a best of 9.99 e.t. It ran great for a while, till the top ring lands broke from hitting the head too hard. What I am trying to say is that I have some real world experience and am not some airhead that bolts on a Holley carb and thinks he's an engine builder. I do alot of research on these subjects. I guess this guy really ticked me off. Once again, thanks.

David

 

[MaxRaceSoftware]

with GM rods/good ARP bolts
3.493" stroke (NHRA legal .013" stroker in SS was OK)
.0105" piston-to-wall clearance BME
.015" thick head gasket
.017" average decks
8300 to 8500 max rpms

a total of .033 clearance piston-to-head

i think we ran tighter than this
but can't find those notes yet !

Larry Meaux (meauxracing@mindspring.com)
Meaux Racing Heads
MaxRace Software
ET_Analyst for DragRacers

http://www.mindspring.com/~meauxracing/

 

[MaxRaceSoftware]

! MaxRace, I look forward to the info you mentioned. I know well-known people like the late Smokey Yunick specified tight squish areas.

------------------------------------

David , this info ONLY APPLIES to Jimmy's combo !!

Type of rods , piston-to-wall clearances,
Max-RPM , piston/pin weight , etc....
all influence what each particular combo can tolerate as to minimum total deck clearance !
Each engine builder should science out their own combo.
Larry Meaux (meauxracing@mindspring.com)
Meaux Racing Heads
MaxRace Software
ET_Analyst for DragRacers

http://www.mindspring.com/~meauxracing/

 

[Craighell]

I agree with all those above. Your local forum expert was either not too knowledgeable or just trying to keep you from building a better (faster) engine.

I don't have a ton of experience (like some of the folks around here), but I can offer that on several race teams I've worked with, we seemed to use a routine. Start at 0.075 with an unproven combo. As the engine developed we would push toward 0.030 'ish.

Like the KZ900 example, the latest dragbike I work on is now running with light contact when using the "small motor" which is well developed. The new bigger engine is back to 0.035 just to be safe. It too will progress towards light contact.

Even with the same compression ratio, we ceratainly see power gains by getting the quench right. No doubt about it.

I think you are now in better company than your other forum.

Enjoy,
Craig

 

[Snork]

The point of squish bands is to increase the mixing of the charge through increased lateral velocity. A smaller squish band gives more velocity and generally improves combustion. But keep in mind two things.

One, as you decrease the squish clearance the compression ratio goes up pretty quickly. Improvements in performance may have more to do with this than they do to tighter squish clearance by itself.

Also, I have seen situations where the piston crown and the head were parallel through the squish band creating what was in effect a ring land crevice volume. In other words the flame front couldn't travel into the squish band so the charge trapped in this area didn't burn. This not only hurt power, but also increased HC emissions. The problem was fixed by tapering this zone at about 3 degrees toward the center of the bore. This lowered the compression ratio very slightly but resulted in better power, due to improved combustion, and lower HC emissions. A greater taper - 5 deg - did not had no additional positive effect, and greater than that dropped the compression ratio enough that a power loss was noted.

 

[sbc]

The proximity of the piston to the cyl. head also
helps to cool the piston. On a 350 chev. if you
increase from .035 to .060 quench you loose .482
compression points. The ignition timing must be
LESS advanced with the lower comp. because the
piston runs that much HOTTER.

 

[MaxRaceSoftware]

One, as you decrease the squish clearance the compression ratio goes up pretty quickly. Improvements in performance may have more to do with this than they do to tighter squish clearance by itself. -ScottMc
-----------------------------------------

Basically , trying to get the most Compression Ratio
possible was all we were after , in tightening up the squish/quench area . About all the CR you can get with the SS/IA Chevy 350 was 11.46:1 CR
We tried a bunch of cams , rocker ratios, centerlines,
valve lash...until we found the best camshaft and where it wanted to be installed in at for degrees ...then ordered another set of pistons with shallow notches and then flycut the bare minimum to keep CR as high as possible !

Likewise did the same efforts for the 360 cid Chrysler
, but that engine has a bunch more squish/quench clearance,
and about all you can get in that combo was 9.46:1 CR
From observations of those two engines , it was mainly the increases in Compression Ratio that were mostly responsible for Torque/HP increases ...and the actual squish/quench clearances seemed to be secondary gains.

NHRA Specs;
Chrysler 360 = -.052" deck clearance and .030" head gasket thickness = .082"
Chevy 350 = -.002" deck clearance and .018" head gasket thickness = .020"

on the SS/IA 350 we ran the total as close as .025" to .027" in experiments...
at which point the pistons definetly were hitting the heads lightly
at 7500 on the SF-901 dyno tests........but at the track, the engine crosses thru
at around 8300 RPM and the RPMs in the water burnouts and the effects after
shifting gears down the track, and coasting down after finish line,
pistons hit harder...decided to increase clearance to .030" to .032"
and make up power elsewhere.

from what i saw the total squish clearance of the Chrysler 360 in NHRA Super Stock form was a close enough distance to provide enough squish/turbulence effect
and the Torque/HP increases beyond tightening this clearance up more seemed to be
primarily-caused by increasing the compression ratio and secondary from the reduced clearance.

it seems as long as you are around .030 to .060" in total squish clearance
the major gains are from Compression Ratio increases, and the secondary gains are from squish turbulence/direction .....but if you are trying to build a maximum
HP SS-engine with limited legal specs...you have to max every avenue out or your competitor will . Larry Meaux (meauxracing@mindspring.com)
Meaux Racing Heads
MaxRace Software
ET_Analyst for DragRacers

http://www.mindspring.com/~meauxracing/

 

[cycle]

It is my understanding that a engine with large? squish areas are also less prone to detonation.In that case The slight increase in compression(and the risk of detonation)is more tolerated. This is assuming a properly designed combustion chamber. Current streetbikes are 12:1 compression ratio and tolerate 93 octane pump gas with no detonation problems..2ND.. I and slowkaw setup up engines at no less than .040 piston to head. I have tried .035 on a 1325cc Kaw., Piston was hitting the head(to hard) and fear of a crack starting between gas ports had me set it back up to .043. Absolutely the minimum for a large dragbike engine.Whats interesting is how a car drag engine can run so close a piston to head when there slinging around components twice as big and three times heavier!!As an example a JE flatop for a 1000cc motor weighs 190 grams.Very light,however max r.p.m. on this engine is a skyhigh 13000... Craig

 

[NickB]

The strength of the connecting rod makes a difference in how close the piston gets as well. A stronger rod wil stretch less.

Higher rpm means higher acceleration and more load on the rod to stop the piston from hitting the head, and thu more stretch.

 

[slowkaw]

At this point, I have to add something. Cycle is right about the dragbike engines running about .043". Several years ago, I had an engine in my bike that displaced 999cc. I miscalculated the crushed fiber gasket thickness and it ended up about .037"-.038". This engine ran very well until the top ring lands on a couple of the pistons broke from hitting the head too hard. In my current engine, with copper head and base gaskets, I run .043"-.044", with no carbon buildup at the squish areas, which I believe means ever so light contact. This is where I compare apples to oranges. NickB states rod strength has a great effect on stretch, which is probably true. The rods in my Kawasaki were designed for a 80 hp engine, but we know from experience, that those rods can withstand 250 hp with no modifications. Still, Cycles' question about the tighter piston-to-head clearance in the car engines with much heavier reciprocating weight is puzzling. Maybe the automotive gurus could shed some light on this for us. It would be appreciated and educational. Thanks.

David

 

[jagman]

David,
One point which no-one seems to have mentioned is that the squish area needs to be above a critical percentage of piston area to make any difference. I can't remember the exact figures but I think its around 20%. Below this figure(whatever it is) squish does not create enough turbulence to make any difference to preventing detonation. As some have observed, the improvement from having a small clearance is probably due to increased compression ratio and smaller crevice volume. So the criticism that people are too obsessed with squish is probably valid where small squish areas apply.
Regards Angus.