Quench, or lack there of

[95GTSpeedDemon]

Using engine analyzer to look over the effect of compression, boost, ignition lead, and fuel ratio i feel better about the 9.8:1. (allows an OTS piston).
It seems 1200psi cylinder pressure is the safe cut-off for 93 gasoline in the program. with a rich mixture 1400psi is the safe max.
It seems i could use 15* ignition lead, 93 with a rich mixture, 30psi (uses a in port temp of 161*, which is probably accurate @ that pressure even with some water) and it be just under 1400psi. Estimating a 726rwhp @ 6000 @ 12% drivetrain loss. Thats 813hp @ the crank.
It got my 302 combo damn near dead on. Conventional wisdom says 30psi on pump gas, esp at 9.8:1 isnt happening.
So i thought about the quench factor and changed the head spec to a compact wedge for very tight quench. The calculation changed that it would detonate @ 15*, so i backed it down 1* at a time and found that 12* brought it down below the threshold again. It showed it to make 23hp more power than the looser quench motor.
I think a more efficient burn and less timing will go faster & make more power.

Anyone made 800hp on pump gas with 357 cubes and 20+ psi? (with typical OTS cylinder heads)

Thoughts?

[jsachs1]

My findings ( several #1 plates) are boosted engines, whether nitrous or blown, don't seem to care about quench.
John

[cjperformance]

What makes a chamber crap?

Yes a loose term! Basically a lot of the typical older tub shaped chambers typical if older iron head 6 cyl engines or chambers that are a semi open like the large BBF chambers where they have a small quench area , or later 351/302 w chambers,, as opposed to a more modern 'fast burn' chamber.
When stuck using these types of chambers having a flat top thats down .080"/.100" or more is no problem. Will that 'crap' chamber make more power at the same CR than the 'good' chamber with the same boost, NO, but you can often use a little more boost, 1 or 2 psi, to regain 'some' hp and still have no detonation problems.
So really, if you have an older, poor design chamber that you cant or dont want to fix, run the piston down the hole. Or if you have a good chamber you can either run the piston down the hole OR run tight quench with no problems. Either way I would avoid the quench zone of .050" - .080" for safety off boost or light throttle low boost driving.
Running the piston right down the hole unboosted is a totally different scenario.

[95GTSpeedDemon]

https://www.google.com/search?q=e7+cyli ... 2672102800

Vs my heads. I guess a little difference goes a long way.
My car made peak n/a power at 32* at 6500. I would call that a decent burn speed. I hope that doesnt hurt when boosted with decent compression for the octane/boost i will be using.

Im pretty sure im going to go the 9.8cr route.

[cjperformance]

IMG_20170814_55590.jpg

This chamber fine with boost and tight quench.

IMG_20170814_35739.jpg

This chamber very detonation prone at 10# & 8.2:1scr with circular dished piston .5" squish band and .045" pistin to head but with flat top, 8.4:1, iirc .187" piston to head and 12# no problems. And I have done this chamber before by grinding it into an open chamber, using a shallow (.0180" deep) circular dish, .5" squish band , 8.5:1, 11# no problem.

[95GTSpeedDemon]

So its either very tight or very loose on the chamber and then do the piston the same. Weird.

[cjperformance]

So its either very tight or very loose on the chamber and then do the piston the same. Weird.

Yes thats what I have found with boosted stuff. The main reason for the piston changes from dish to flat in my case with a poor chamber is to be able to achieve the same or more CR as well as open up the quench area, basically just dropping the squish band and raising the floor of the dish in essence.

IMG_20170814_22491.jpg

This chamber/head , stock but for larger valves (not a great shot of it) was fitted to replace a very modified head with a nice chamber that had cracked. The short block (186 ci 9 port holden 6 cyl) stayed as is with flat tops down the hole .125" with both chambers (I cant find the pic of the original chamber sorry) , final CR with nice chamber 8.65:1 , final CR with the replacement tub chamber 8.68:1, so not much in it CR wise. Power dropped by iirc ~7 or 9rwhp , then going from 15# to 17# boost gained 13rwhp over the original head. (321rwhp@17#)This is sort of off track as both combo's were not having any detonation problems. More of a boosted "modified head to stock head" comparison but I thought it may be of interest simply because it still had no detonation problem with 2# more boost than prior.

[Orr89rocz]

Anyone made 800hp on pump gas with 357 cubes and 20+ psi? (with typical OTS cylinder heads)

My 401" motor made closer to 1200 on pump gas 9:1 with 24 psi. .041 piston to deck. As seen in na builds


My faster burn style afr 195 heads and smaller cam made closer to 800 hp on same bottom end 9:1 comp, .041" piston to head deck.... 15 psi pump gas but required nearly 10 deg less timing. Just different heads and cam, designed for lower rpm range. More pressure, less timing is needed

Your 357 with half decent heads should not need 30 psi to get 800 hp lol. No way. Plus a single 69mm likely wont get there anyway

[95GTSpeedDemon]

Anyone made 800hp on pump gas with 357 cubes and 20+ psi? (with typical OTS cylinder heads)

My 401" motor made closer to 1200 on pump gas 9:1 with 24 psi. .041 piston to deck. As seen in na builds


My faster burn style afr 195 heads and smaller cam made closer to 800 hp on same bottom end 9:1 comp, .041" piston to head deck.... 15 psi pump gas but required nearly 10 deg less timing. Just different heads and cam, designed for lower rpm range. More pressure, less timing is needed

So if you were to push for 1200hp with the fast burn head, could you retard timing to the point of firing after TDC? Does that create problems?

[Orr89rocz]

I could retard timing more but it would have been low. I suppose it could work but hard to say. The combo just wasnt intended for that power on the fuel i had

Too small a cam and head to make rpm to make power. Too much cyl pressure. Bgger cam and head allowed the rpm to go up and dropped cyl pressure all the while.

[Schurkey]

I built several 454 BBC boat engines with 8-71 superchargers with .040 deck, intercoolers and 8.5 CR. the engines made over 900 HP and never gave any problems and boat owners are hard on engines.

Boat engines get run hard, but "most" of them also run cold--lakewater cooling and no thermostat. Sometimes they struggle to get to 140 degrees. Makes some difference in terms of detonation.

What temperature did your supercharged engines run?

[dwilliams]

You can only get so much dish before the underside hits the rod. You can move the pin down and shorten the rod, or you can just get rid of the lip around the dish. That's how I wound up doing a 4.1 Buick with the pistons way down in the hole to get a 6:1 CR for a customer with a boost fetish.

[pamotorman]

I built several 454 BBC boat engines with 8-71 superchargers with .040 deck, intercoolers and 8.5 CR. the engines made over 900 HP and never gave any problems and boat owners are hard on engines.

Boat engines get run hard, but "most" of them also run cold--lakewater cooling and no thermostat. Sometimes they struggle to get to 140 degrees. Makes some difference in terms of detonation.

What temperature did your supercharged engines run?

we tried to run them at 180/190 degrees by the use of a adjustable size restrictor in the thermostat housing.

[fastblackracing]

so it seems tight is fine.
its custom piston time i guess.
28cc dish @ 1.550 c/h gives me .047 quench.
30cc dish @ 1.560 c/h gives me .037 quench.
Both are 9:1

The closest off the shelf piston was 1.560 and 21.1cc D shaped dish. Thats 9.8:1
It would take a .085 head gasket to bring it back down to 9:1, then it would have .075 quench. Maybe that could still work?

ALL of our turbo buick factory 86/87 engines were basically a quenchless design with only the outer most
1/4 inch of the piston top presenting anything resembling quench since the basic piston design is a dish....
and they seemed to do ok for themselves including driveabilty even when you deleted EGR.(8.3-1 cr)

On medium power and up nitrous engines...say 4 pounds per hour and above per cubic inch the engines seem to benefit opening the quench up to .080" minimum....and chamber softening which turns the chamber into a shape similar to a drum set cymbal....a bunch of radial step cuts all to help eliminate little pockets that can can trigger detonation....

And there really does seem to be a range say .040 to .080 where some chambers can be detonation sensitive

I would build your turbo engine around your desired rpm range and the camshaft duration that is needed..
you can go Higher boost/lower rpm/lower compression but higher cylinder pressure with less cam,
or go A bit lower boost/higher rpm/ higher compression lower cylinder pressure with more cam....

Charge air temps, Exhaust back pressure and fuel choice are major players that will limit you here when you start to lean on it...
and with a good 69mm compressor wheel you can make 800FWHP Many ways to get there with a turbo engine.

[In-Tech]

And there really does seem to be a range say .040 to .080 where some chambers can be detonation sensitive True and after ~.100" it doesn't care.

I would build your turbo engine around your desired rpm range and the camshaft duration that is needed..
you can go Higher boost/lower rpm/lower compression but higher cylinder pressure with less cam,
or go A bit lower boost/higher rpm/ higher compression lower cylinder pressure with more cam.... Within reason, the cylinder pressure will be approximately the same on a short cam/high boost (800hp for a number) as it will be on a larger cam lower boost combination. Boost is just a restriction of air flow.

Charge air temps, Exhaust back pressure and fuel choice are major players that will limit you here when you start to lean on it...
and with a good 69mm compressor wheel you can make 800FWHP Many ways to get there with a turbo engine.

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