F-BIRD'88 wrote: ↑Fri Sep 09, 2022 12:29 pm
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.
Chamber turbulence will improve performance along many fronts. And has done so for over a hundred years.
Unfortunately, most readily available measuremnt methods are much to crude to properly observe the improvements.
And advanced prototype testing is much too expensive and time consuming.
The solution is to make use of advanced simulation programs. Which is exactly what is being done at the higher tech levels.
skinny z wrote: ↑Fri Sep 09, 2022 10:04 am
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.
In a block that gets .006 or so taller at temperature.
skinny z wrote: ↑Fri Sep 09, 2022 10:04 am
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.
In a block that gets .006 or so taller at temperature.
There's that too.
Still, my potential .034" (cold at that) is looking pretty tight.
Don’t you think direct injection as it’s benefits partial because of the turbulence that the tremendous fuel pressure brings to the chamber, similar to what we are discussing pertaining to squish and it’s turbulence?
All else being equal , the answer appears to be "most definitely".
Based on what? Somebody said so on the internet?
I purposed a simple test to get a simple usable real answer. Does not require millions in test equipment.
KISS.
F-BIRD'88 wrote: ↑Fri Sep 09, 2022 12:29 pm
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.
Chamber turbulence will improve performance along many fronts. And has done so for over a hundred years.
Unfortunately, most readily available measuremnt methods are much to crude to properly observe the improvements.
And advanced prototype testing is much too expensive and time consuming.
The solution is to make use of advanced simulation programs. Which is exactly what is being done at the higher tech levels.
This is lawyer spin.. I did not say chamber turbulence.
The question is does squish and or quench effect power.
Simulation programs are only as good as the programing and truth of...
The benefit ya or na of squish quench +/- is not hard to test nor measure for results..
KISS. .
The general concept of squish and quench as pertains to an internal combustion engine design has been accepted as basic practice for decades, unless we are playing word games as to whether it “makes” power, I don’t understand the issue.
Is it the most important consideration, probably not, should it be considered, probably yes.
One man’s thoughts keeping it as simple as I can.
F-BIRD'88 wrote: ↑Thu Sep 01, 2022 12:38 pm
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.
How can you say the combustion burn speed did not change, my guess is that's exactly what happened, there was no unburnt air fuel mixture left to auto ignite. So the extra timing didn't matter. It may have even made the same power with less timing. Just because it tolerated the ignition lead doesn't mean it was optimal. I am definitely not an expert on this stuff, but if I have learned anything it's this.. there are many variables at play and to get hung up or convinced it was one or two that made the difference without extensive data to prove it is a good way to get lead down the wrong path, or miss the bigger picture. Awesome conversation guys. Love it when this place has topics like this. It's a good reminder of how much I don't know.
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.
In a block that gets .006 or so taller at temperature.
There's that too.
Still, my potential .034" (cold at that) is looking pretty tight.
My Dart block has 0.030" piston to head,I know someone has run 0.028" without issues.
If I remember correctly on one of Darin Morgan's videos he said softening the chamber helps the pumping loss created by two smooth surfaces coming together and sticking so to speak.
On the latest video from MBE he has a NA cylinder head with a softened chamber,MB says the customer run 16:1 compression so my mind says at that compression there could possibly be a auto ignition problem and or the flame front is to fast causing excessive detonation.
It has been said before if you are really getting after power potential you will end up running into some form of detonation but controlling that is another thing.
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.
How can you say the combustion burn speed did not change, my guess is that's exactly what happened, there was no unburnt air fuel mixture left to auto ignite. So the extra timing didn't matter. It may have even made the same power with less timing. Just because it tolerated the ignition lead doesn't mean it was optimal. I am definitely not an expert on this stuff, but if I have learned anything it's this.. there are many variables at play and to get hung up or convinced it was one or two that made the difference without extensive data to prove it is a good way to get lead down the wrong path, or miss the bigger picture. Awesome conversation guys. Love it when this place has topics like this. It's a good reminder of how much I don't know.
I tested the vortec heads for what created best WOT power . It was the same 36° btdc.. Not different.
This has been my experience with all sbc heads over 40 years. (All that I have used) I've had multiple sets of the vortec heads in various firms... All run best @WOT with 36° btdc timing, including the current ported big valve 062's on my 406 which has exactly .040" quench clearance.
Don't know about power but I built an L26 that had the pistons above the deck, don't recall measurements but suspect it had less than 25 thou clearance. Lot of rattling when the idle dropped and got rough setting up the Hitachi carbs, once setup ran for years no more noises.
Ignorance leads to confidence more often than knowledge does.
Nah, I'm not leaving myself out of the ignorant brigade....at times.
steve cowan wrote: ↑Fri Sep 09, 2022 5:52 pm
My Dart block has 0.030" piston to head,I know someone has run 0.028" without issues.
.030" ? .028" ?
To me, that's unheard of. But I guess if Pro Stock is making contact then that's the tightest of all.
There's plenty to support the effectiveness of a tight quench (from wherever that information comes from) so now the decision, with parts in hand, is whether to go for .034", which by most accounts, (but not all obviously) is tight or use the .039" and settle for .047".
Whatever one's opinion might be on quench, I think one thing that could be said is that the difference between those two options aren't likely to measurable by any metric.
