Has anyone or any publication built and compared two similar engines; one built with the same CR and quench. I am just curious as to HOW much difference there is exactly.

My understanding is that proper quench also allows for more accurate cylinder to cylinder timing which is where more HP is found.

the by far #1 adv of quench is that it lets you run a much higher static CR on the same octane that would ping on the same CR wo quench. CR is squeeze and squeeze is power. CR is one of the most important parameters of an engines power potential. It is what an engine is all about. I'd suggest getting an actual mocked up/measured twice .035-.040" (no more/no less) piston to head clearance in EACH hole. Takes alot of work to get it spot on. .035" is more efficient but requires minimal piston rock (tight P/W clearances) and dead on measuring so .040" is safer and very efficient. Is it a PITA? yes Is it worth it? absolutely

David Vizard has written up a comparison experiment he did where he kept
the compression ratio constant
but altered the quench clearance.

I can't remember whether
it was in one of his books,

http://www.amazon.com/s/ref=nb_sb_noss?u...amp;x=0&y=0

or in a magazine article,
but in a hazy way I seem to remember that Vizard claimed most of the horsepower gain benefit occurred by 0.060 inches total quench clearance.
However, the theory is that less quench would have allowed the compression ratio to go up safely on the same octane fuel, which would have increased hp a bit more.

The Internal Combustion Engine in Theory and Practice,
Volumes I and II,
by the father and son team both named
Charles Fayette Taylor

http://www.amazon.com/s/ref=nb_sb_noss?u...amp;x=0&y=0

has several pages and
a big graph devoted to
General Motors research on
quench clearance versus gasoline octane where detonation begins.
If memory serves me right
in contrast to David Vizard's finding,
GM found more benefit kept being shown down to a quench clearance equivalent to 0.026 inches at a bore of 4.00 inches.

The 0.026 number later stuck in my mind because in the magazine article
'Feeling Lightheaded'
in 1999 High Performance Mopar
about the Edelbrock aluminum SB Mopar V8 cylinder heads,
McCandless wrote that he used 0.026 inches as the piston to deck height clearance of his test engine, which would make the total quench clearance that plus the compressed gasket thickness, and probably near the 0.060 that Vizard found.

sample quote

When it comes to choosing a suitable block, I prefer a '75 or earlier piece due to the extra material and strength of the castings. Our block was bored .060 over (371 cubes) and milled .010, just enough to clean up the deck surface and set the piston-to-deck-height at .026, the aluminum head's 65 cc's chambers, and using a Fel-Pro O-ring head gasket (sold through Mopar Performance) which adds 9 cc's of volume to each cylinder, the resulting compression ratio was 9.9:1. This was with a cast .060-over, flat-top piston with valve pockets I had custom made years ago

Are there any benefits in a tighter or looser quench depending on the RPMs of the motor?

I've read that .040 in the average hot-rod engine is usually considered optimal. I've read that going any less than that is risky unless the rest of the engine (crank, main bearing journals, ect.) are machined.

The theory being that, like stated, rods and/or pistons could be slighly loose and impact the head at higher RPMs.

The .060 is interested because I've not read that anywhere else, but I will definatly look more into it. Thanks for all the information already. I think I may go talk to my mechanical engineering professor and see if he has any insight as well!

Really because I had always read that quench started to become ineffective at .055" and greater.

This may be interesting:
http://www.enginebuildermag.com/Article/2266/surfacing_equipment_can_increase_horsepower.aspx

Quench just lets you run higher compression without detonation compared to the same non-quench engine. I'd guess it probably starts to become an issue around 10:1 compression (maybe lower with iron heads). My understanding the the quench or squish creates a much more turbulent air/fuel mixture inside the chamber and that delays/prevents detonation. Think like the difference between a category 1 hurricane compared to a category 5 hurricane, there's a lot more chaos going on with the 5 storm (maybe not the best analogy).

http://en.wikipedia.org/wiki/Harry_Ricardo

The early work on quench and squish was done by Sir Harry Ricardo. Interesting reading if you can find a copy of his book, The High-Speed Internal Combustion Engine.

http://www.ricardo.com/About-Ricardo/Our-History/

FWIW, I called Ross pistons a few weeks ago about having a set of flat tops I have cut for a dish. Reason being is so I could get 10 to 1 comp with a .040 quench. The guy at Ross (cant remember his name) asked me why I was wasting my time with trying to get a tight quench. He replied that trying to obtain a tight quench is more or less a waste of time, maybe 5hp or so. I told him I was more worried about detonation and again he told me a waste of time.

He talked me into using .086 head gaskets with my flat tops to get down to 10 to 1 comp.

So I dunno.

....a waste of time ? .... Just using common-sense - it makes SENSE to me.

From the standpoint of POWER, A/F swirl, prevention of detonation.... etc ...

In my years of farding around with this kind-of-stuff ...I wonder sometimes WHERE they get the guys who answer-the-phone at some of these places.

The year I went to quench in my current combo, I gained 6 tenths.

Same, cam, carb, gears, converter, etc..

The switch was 452, to 915.s Both home ported by me, with stock size valves.

Most builders agree a full point of compression in a given combo is only worth 3%.

Even if we say I gained a full point (after cc ing it, it was a little less than that) and tha I had 500 hp to begin with (which is debatable) I should have only gained 15 hp on the head swap.

I also switched to 1.6/1.5 combo rockers at the same time. Again, builders say this swap isn't woth much. like 6 hp or less.

There must have been something in the quench, cause 21 hp isn't giving up 6 tenths with a heavy pig, like my car .

There is a section in one of the books )
about the Honda V-Tech engine, which originally was also lean burn.
I remember that it listed the quench clearance as 0.75 mm,
and I had to get out a calculator to figure:
(1/25.4) times 0.75 = 0.0295 inches

If my memory is not faulty I think the Honda engineers wrote that the 0.0295 quench was necessary to both successfully get ignition on the 22 to 1 air to fuel ratio at part throttle,
and to run at full throttle without detonation on 87 octane gasoline.

It certainly seems true that many engine manufacturers don't make the quench very tight even if the cylinder head has quench pads and the piston is either flat top or has an outer quench area.
Quench is unquestionably designed in,
because the pads are there,
but not made very tight for some reason.

The 1995 Magnum 5.9 V8 seems to be about:

9.585-6.123-1.622-(3.578/2) = 0.051 inches in the hole
plus the 0.0475 compressed gasket
adding up to a whopping big 0.0989

Did Chrysler really need that much clearance to make up for sloppy factory tolerances?

Anyone know the tightest factory Chrysler engine quench clearance, at least the 'blueprint' value ?

Is it possible that in time carbon deposits naturally 'close up' the quench clearance to the minimum that does not hit?

I have also wondered
how much thickness of carbon deposits is really built up on both metal surfaces of opposing quench pads in the real world,
and if the surface roughness of the deposits
either adds to,
or takes away from
the strength of the jets of gases shot out into the main combustion chamber.

On a racing engine
using leaded gasoline
I wonder if the lead deposits close up the quench clearance.
Lead deposits certainly formed a hard coating at the valve seats in the old days.

Pollution-wise,
I have read that too much total metal area for quench can lead to higher unburned hydrocarbons.
Some fuel droplets get absorbed down into the tiny metal surface pits and does not burn when the quench is close together, then, as the fuel
'comes out of the sponge holes in the metal surface' in the second half of the power stroke
this partially burned fuel goes out into the exhaust and has to be handled by the catalytic converter.

I wasnt saying I agreed with the guy at Ross. Ive read too much suggesting that quench is valuable.

With that said, my current mota has about .150 quench (452s with a .045 gasket). Static compression is 10.5 to 1 and has no ping on pump premium with the timing at 34-35 degrees. At 38 I do get some pinging. The combo runs pretty good for what it is, ET/MPH in my sig.

Yes 12.5's to 11.9's that year

Neither head were flowed on a bench. Both sets were ported in the same fashion by me, and the valve jobs done at the same machinist.


I'm not saying the .6 is from the quench

I'm saying that some of it had to be from the quench, as there isn't enough in the other changes to justify the gain.


I'm simply saying that quench is worth something, and the piston guy is flat out wrong about quench being unimportant.

ok, maybe I'm still a lot confused about how to get a "quenched" engine, but after read some replies here:

how you can get a propper quench without affect ( reducing, keeping or increasing ) the CR ? I simply don't get it

ok, nice thread, but I think not answered yet LOL

for example, I got KB240s for my 400 ( flat tops/valve reliefs ). They supposelly sits around 015-020 down the hole. My block was decked due sleeves long time ago so maybe I can get closer to 015-010.

then I got metallick gaskets what suposelly are rated on 020... then I got my engine almost quenched BUT I HAVE OPEN CHAMBERS. I can get ( and is what I have proyected to get 84-86 cc chambers and close to 9.5 CR ) maybe 045 milled down, but they will be still open with that job. lets say I'll get 070-080 total "quench"

Ok, let say I use closed heads... I theorically will get the perfect quench on 040-050 rate. I'm UNVARIABILY CHANGING THE CR, I think is imposible not affect that, even slightly, making the heads change.

or even milling down the open heads, not converting into closed chambers, what really affects engine geometry and valve to pistons clearence, but making a more radical heads mill down job definitelly CR will be affected!!!

beside this, then it looks there is no way to get a perfect quenched engine on an open chambers head unless you raise over the block deck the piston... well another CR variable being affected at this moment

then this reply:

Quote:

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Picture of a typical dished piston designed to obtain quench with a closed chamber yet retain a sane compression ratio...



BTW image was stolen from 440 Source Thanks Brandon, hope you don't mind...

---

hell WOW! a dished piston will afect total volume too so do the CR against a flat top or domed.

I think anything you build inside a cilinder affects the CR... more or less.

I get the quench deal, and I can understand some setups can be build to MAKE the quench, but I don't get how do you change anything on engine without change CR.

are open chambers heads owners far away from a good quenched engine built ?

Unfortunately the effect of quench, which is an affect from the movement of the intake charge, not the gap between parts, is very individualistic. It's the combination of parts and timing that makes more power. The piston to head clearance, combined with the piston shape and chamber design of a given haed all have to work together to get a good qeunching effect and all the bonuses that come along with it. Something to realize is the time a burn takes is directly related to the power that burn produces, and the faster the pressure spike that results from a faster burn, the better able a builder is to time that spike where it puts the most force on the crank. Building for quench does give nothing but positive results and one of these is more power from the same given displacement, stroke, cam, and carb. With no other changes, on lower octane fuel, you will make more power if it's done right. Now, as far as the distances... The closer the piston and chamber top get, the harder the gases are pushed and the more effective teh quenching is. So further is not better. Closer is better, right up until they hit.

Here's a quench dome with D dish I had made by Diamond recently , sorry for the crappy cellphone pic.

Here is the explaination of how "quench" or "squish" works I got when I asked about it in an engines design class. The instructor had his PHD in engines engineering and also worked with formula 1 teams.

The reason that squish works to prevent detonation is actually fairly simple. Detonation occurs when the air fuel mixture combusts outside the flame kernal(sp?). In an engine with a wedge shaped combustion chamber the spark plug is located to one side of the chamber. The flame front can only travel so fast across the piston, thus it takes longer to reach one side of the piston than it does the other. This allows the opertunity for detonation to occur at the farther side of the piston due to compression (auto ignition). As most of you know auto ignition happens when the mixture is compressed to the point of igniting without a spark.

In the case of "squish" the volume of the cylinder at the furthest point from the ignitor is very small and thus can't easily support auto ignition, basically most of the mixture "squishes" out of that area into the larger part of the chamber. Once combustion starts and the piston is travelling down the pressure then drops and auto ignition cannot be support.

Remember the pressure inside the cylinder has to be the same throughout the volume. The CR for the area of squish is higher but the actual pressure throught the volume of the cylinder is determined by the total CR.

I would suspect that there is a threshold where the volume in the squish area becomes too small to support auto ignition. Because volume is based on the area of squish I would imagine that the point where the clearence from the head to the piston required to reap the benefits is going to depend on the percentage of squish area to the area of the piston. So I don't think you can put a hard and fast rule on how much clearence you need, at best it's a rule of thumb.

I hope this makes sense.

Let me add to that detonation is not caused by colliding flame fronts. The only effect that multiple flame fronts have is that they will reach the outer edges of the cylinder quicker. Thus the reason the modern HEMI has 2 spark plugs.