Does quench affect power?

[Bill Chase]

You guys are #reading about and repeating about the benefits of quench. but are not testing to see if. when and where this benefit is realized..

I had a 350 sbc.. 10.30:1 cr with (shaved down) old open chamber 882 heads. Right on the edge WOT and roll on knock.
Swapped to vortecs. different thicker gasket, cr was now 10.02:1 cr. .Bigger quench , but lower cr by .30 cr.
Engine could not be made to knock no matter what.
Quench was .033". VS .055". But CR was .30 lower.
Same carb cam etc same car. same gas
Engine wanted Same WOT timing.
No difference in timing. yet loss of effective quench.

The combo with less quench and slightly lower cr made A lOT more power and tiorue. (vortec heads). Again best WOT spark advance and carb jetting did not change.
More than 1 carb was tested on each.
On removal the 882's were inspected for a fault etc. No faults found. In good very re-usable condition.

You're making the assumption it was just a reduction in squish volume, and a slight reduction in static compression. You also moved the spark plug toward the center of the bore, maybe closer to the piston crown. and changed the intake flow with a head capable of introducing a much more homogeneous air fuel mixture. It also had superior low lift flow, all these things allowed it to use same roll in timing without knock. less compression and looser squish volume were not the only factors at play here.

[skinny z]

Assuming 2 equal-ish builds, the only difference being a .040" quench and an .080" quench (different piston types to give the same compression ratio, and timing curves to give the best performance in each scenario), and assuming detonation isn't an issue in either case...would you expect to see any difference in power?

On a related note...does chamber shape really have an effect on detonation resistance once the quench distance gets bigger than the "no man's land" of .060-.080"?

So, is it safe to say (and let's be sure to include the similar builds aspect) that quench DOES affect power?
If the Pro Stock guys (so as to keep it NA) are getting so close so as to have the slightest of contact, I'm going to say the benefit is real and worth pursuing even on a modest street/strip engine.
And not just power it seems but efficiency as well. As in fuel economy.
For the record, what the position to head clearance on something like a stock LS7? That's a flat top piston and heart shaped chamber is it not?

[RDY4WAR]

It's also why Pro Stock uses steel rods. I can't show the piston top, but here's a picture of the underside and the rods. This engine had >40 passes on it. You can still see the dimple in the bearing coating from the dial gauge.

Pro Stock Teardown - Jeg Coughlin Jr.jpg

[F-BIRD'88]

You guys are #reading about and repeating about the benefits of quench. but are not testing to see if. when and where this benefit is realized..

I had a 350 sbc.. 10.30:1 cr with (shaved down) old open chamber 882 heads. Right on the edge WOT and roll on knock.
Swapped to vortecs. different thicker gasket, cr was now 10.02:1 cr. .Bigger quench , but lower cr by .30 cr.
Engine could not be made to knock no matter what.
Quench was .033". VS .055". But CR was .30 lower.
Same carb cam etc same car. same gas
Engine wanted Same WOT timing.
No difference in timing. yet loss of effective quench.

The combo with less quench and slightly lower cr made A lOT more power and tiorue. (vortec heads). Again best WOT spark advance and carb jetting did not change.
More than 1 carb was tested on each.
On removal the 882's were inspected for a fault etc. No faults found. In good very re-usable condition.

You're making the assumption it was just a reduction in squish volume, and a slight reduction in static compression. You also moved the spark plug toward the center of the bore, maybe closer to the piston crown. and changed the intake flow with a head capable of introducing a much more homogeneous air fuel mixture. It also had superior low lift flow, all these things allowed it to use same roll in timing without knock. less compression and looser squish volume were not the only factors at play here.

The spark timing and fuel jetting stayed the same.
Thus the combustion stayed the same.
If squish quench effect was such a big deal in the grand scheme these things would have been effected.
They were not.
If combustion burn time was shorter the best WOT spark advance amount would decrease. It did not.

The change that MATTERED most was the compression ratio.
The vortec head did have a better intake manifold.
Perf RPM VS the lowly performer.

Yes , the vortec heads are a much better more powerfull cylinder head. The combustion burn speed did not change.

[hoffman900]

You guys are #reading about and repeating about the benefits of quench. but are not testing to see if. when and where this benefit is realized..

I had a 350 sbc.. 10.30:1 cr with (shaved down) old open chamber 882 heads. Right on the edge WOT and roll on knock.
Swapped to vortecs. different thicker gasket, cr was now 10.02:1 cr. .Bigger quench , but lower cr by .30 cr.
Engine could not be made to knock no matter what.
Quench was .033". VS .055". But CR was .30 lower.
Same carb cam etc same car. same gas
Engine wanted Same WOT timing.
No difference in timing. yet loss of effective quench.

The combo with less quench and slightly lower cr made A lOT more power and tiorue. (vortec heads). Again best WOT spark advance and carb jetting did not change.
More than 1 carb was tested on each.
On removal the 882's were inspected for a fault etc. No faults found. In good very re-usable condition.

You're making the assumption it was just a reduction in squish volume, and a slight reduction in static compression. You also moved the spark plug toward the center of the bore, maybe closer to the piston crown. and changed the intake flow with a head capable of introducing a much more homogeneous air fuel mixture. It also had superior low lift flow, all these things allowed it to use same roll in timing without knock. less compression and looser squish volume were not the only factors at play here.

The spark timing and fuel jetting stayed the same.
Thus the combustion stayed the same.
If squish quench effect was such a big deal in the grand scheme these things would have been effected.
They were not.
If combustion burn time was shorter the best WOT spark advance amount would decrease. It did not.

The change that MATTERED most was the compression ratio.
The vortec head did have a better intake manifold.
Perf RPM VS the lowly performer.

Yes , the vortec heads are a much better more powerfull cylinder head. The combustion burn speed did not change.

I disagree with that assessment and think Bill is on the money.

[RDY4WAR]

Remember the other side of the squish velocity equation which is the quench area size of the head. More gap but more quench area could cancel out to give a similar squish velocity.

[F-BIRD'88]

The squish area of these 2 heads is not significantly different. The only sbc head that does seem to want less WOT spark advance is the TBI swirl port heads.
These oem TBI engines with dished pistons do not have
active squish/quench in oem build form.
If it was the be all, you'd think GM would have employed active squish/quench as a design priority in the quest for low emissions and fuel mileage thru more net efficient combustion.

[brentry]

It looks like the vortec has alot bigger squish area.
Or squish pad as some call it
Probably 10 to 15ish %. Guessing.
That's a big difference. I don't see how you can say there the same.
To say the compression was the biggest change is totally false.
It may have more msv now with the vortec head.

[skinny z]

If it was the be all, you'd think GM would have employed active squish/quench as a design priority in the quest for low emissions and fuel mileage thru more net efficient combustion.

For the record, what the piston to head clearance on something like a stock LS7? That's a flat top piston and heart shaped chamber is it not?

[F-BIRD'88]

If active squish and quench can extract more power energy from the fuel then BSFC numbers should improve in controlled A-vs-B tests. If the combustion burn speed is changed the best spark timing should change.
If combustion detonation sensitivity is improved then this should show up as tolerance in some amount of over timing above what is best for best power.

[rgalajda]

"If it was the be all, you'd think GM would have employed active squish/quench as a design priority in the quest for low emissions and fuel mileage thru more net efficient combustion."

They did , but not neccessarily for the reasons you stated.

[F-BIRD'88]

Not on these and many other oem engines where effientcy should be a priority in design.
I conclude by my limited testing that quench squish net benefit is over promoted in the grand scheme of things. There seem to be other design factors that are MUCH MORE important than squish/quench.
I am not saying it has NO effect.

[skinny z]

For the record, what the piston to head clearance on something like a stock LS7? That's a flat top piston and heart shaped chamber is it not?

I'll answer my own question and that the P to H clearance looks to be anywhere from .041" - .046".
Piston .005" - .010" out of the hole with an OEM .051" gasket.

[F-BIRD'88]

For the record, what the piston to head clearance on something like a stock LS7? That's a flat top piston and heart shaped chamber is it not?

I'll answer my own question and that the P to H clearance looks to be anywhere from .041" - .046".
Piston .005" - .010" out of the hole with an OEM .051" gasket.

So, now throw on an additional head gasket.
Does the spark timing change? Is this engine more or less knock prone..? Do BSFC numbers change?
Are exhaust emissions changed?
Does the power output change?
Does the power out change beyond what would be expected by the simple change in mechanical compression ratio?
Is the combustion profile different?

"Does squish and quench effect power"?

[David Redszus]

Squish velocity, both before TDC and ATC, are critical to the combustion process.

But squish is not merely a matter of piston to head clearance. Squish area and shape must be considered along with
inlet temperture and rpm.

Tumble does not survive for very long, usually not even up to TDC, due to the chamber shape.
Swirl can and does survive longer, even longer to assist flame propagaation. It comes at the expense
of chamber filling.

Squish has twin turbulent peaks; one BTC and one ATC to assist flame propagation.

When an engine demonstrates large cycle to cycle variances, it is difficult to measure incremental improvements.

David,

In regards to tumble decay, you may want to read SAE Paper 2018-01-0366 ‘The Development of a New V6 3.5L Turbocharged Gasoline Engine”. It sticks around more than you think and also has two peaks, with one as it approaches TDC.

It’s about the development of the Toyota engine that had 442lb ft of torque, 420hp, and had a thermal efficiency of 37%, while meeting emissions and warranty standards.

I have read the SAE paper and recommend it be read by anyone who would like to learn more about the combustion process.
Contained in the paper are several items of note.

Tumble was developed by a change in the approach angle of the inlet port. It uses only a portion of the valve curtain
area which reduces flow. Low lift flow coefficients become important. Being a turbo, it can increase air density with boost.

Tumble is created and peaks at low inlet valve lift and decays thereafter. But as the piston moves upward, it scrapes air
from the cylinder walls to support the tumble motion, reaching a second turbulence peak as the piston approaches the head.
As the chamber changes aspect ratio (becomes a flat disc shape) tumble decays substantially near TDC. There is no tumble ATC.

But that is where squish turbulence takes over, peaking near 10 deg BTC, and again at 10 deg ATC.
The two sources of chamber turbulence are seen to overlap and are often indistinguishable from each other.
Much depends on the shape of the piston dome and chamber bowl.

The main purpose of tumble is to improve mixture preparation and reduce ignition delay. It does not persist during combustion.

Swirl is also produced by the angulation of the inlet port to the cylinder centerline. But it produces a rotational
motion, its axis parallel to the piston surface, which can persist even as the chamber changes its aspect ratio.

Chamber turbulence, used to reduce combustion burn angle and improve thermal efficiency, has become the focus
of engine development. As such, remember that port attack angle, port curvature, piston dome shape, chamber
bowl shape, are all used to increase combustion turbulence and reduce burn angle.

Moving forward, direct injection will improve volumetric efficiency (mass flow) and will produce chamber
turbelent motion as well. Looking back, we will see that issues such as carbs vs inj, compression ratios vs air
flow, etc, et all, will resemble a comparison between a stopwatch and a sundial.