Quench, or lack there of

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95GTSpeedDemon
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Quench, or lack there of

Post by 95GTSpeedDemon » Fri Aug 11, 2017 6:41 pm

i want to know what happens when you put a flat top .172 down in the hole with boost.
SBF 351w 9.5 deck
3.5 stroke crank that dictates a 6.200+ rod
canfield 195 head 54cc chamber
4.100 x .047 gasket
93 octane and water injection for a safety net
intercooled EFI
69mm turbo
all the boost it will handle to make 800hp. turbo will be out of steam if it can make 800 at the crank.

I found a cheap wiseco 4032 flat top for a 383 SBC with a 1.425 C/H, @ .172 down i would have 8.7:1 CR... any ideas if it would be detonation prone like most people figure?

Another option is a 1.560 c/h D shaped speed pro, it will need another 10cc's removed to bring down the compression. With .037 quench (.010 out the hole) its 9.8:1 (21.1cc dish) @ 30cc dish im 9:1.
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cjperformance
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Re: Quench, or lack there of

Post by cjperformance » Fri Aug 11, 2017 9:19 pm

Boosted I would happily use the flat top that far down the hole. The 'worse' the heads combustion chamber is as far as detonation resistance is concerned the more the lack of quench helps when boosted.
I have done turbo builds on some engines with crap chambers and always have found that in this case having a flat piston with no tight/quench areas gives better detonation resistance than the same CR and chamber with tight quench and a dished or step dish piston.
Craig.

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Re: Quench, or lack there of

Post by 95GTSpeedDemon » Fri Aug 11, 2017 9:23 pm

What makes a chamber crap?

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Re: Quench, or lack there of

Post by bigjoe1 » Fri Aug 11, 2017 10:30 pm

Very little experience with boost, but on several street blower engines I have done, I ran the piston down to where the compression was what I wanted, and they ran VERY WELL that way




JOE SHERMAN RACING

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Re: Quench, or lack there of

Post by 95GTSpeedDemon » Fri Aug 11, 2017 11:06 pm

bigjoe1 wrote:Very little experience with boost, but on several street blower engines I have done, I ran the piston down to where the compression was what I wanted, and they ran VERY WELL that way




JOE SHERMAN RACING
Are we talking .060 or .120+?
Also, what kind of power were those engines making?
Did the ignition timing increase or decrease vs the typical build with tighter quench?
Did you spec a different cam for the lack of quench?
Were they closed chamber heads?

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Re: Quench, or lack there of

Post by pdq67 » Sat Aug 12, 2017 12:41 am

Back more years than I care to remember, onna the mag's did a compression change test using, if not mistaken, the old '71 or maybe '72, 400" MOPAR smog engine that is 100 percent quenchless. No quench at all!!

To start the test, they went with something like --

12, maybe 13 to 1 CR and race gas;

Then they started dropping the CR by juggling head gaskets to like down to 8 to one CR or so in either 1 point or maybe a 1/2 point runs.

It turned out that the only thing that happened way down low was that the engine ran fine, but got lazy! No knock or any other problems, BUT they admitted that they wished they would have switched to pump gas as they dropped the CR's.

I want to say that they ended up with a head gasket stack of maybe 3/16" or a 1/4"...

This may NOT be of much value to you but it was very interesting to me back then.

pdq67

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Re: Quench, or lack there of

Post by travis » Sat Aug 12, 2017 6:10 am

I remember reading somewhere that once you get past around .080" quench, you have no quench and are much less detonation prone. Somewhere around .060 to .080 is the "danger zone" where most engines tend to be most detonation prone.
I also remember that "back in the day" most everybody built their low compression blower motors with the pistons a mile in the hole...back before aluminum heads with heart shaped chambers...and there never seemed to be any issues.

Late model 440's in dodge motor homes had their pistons ridiculously far in the hole, and even with no compression they pinged like crazy

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Re: Quench, or lack there of

Post by mag2555 » Sat Aug 12, 2017 6:11 am

Make sure the valves have a break ( rounded edges) from the chamber face to the start of the seat, especially the Exh valve as these can make for detonation.
Don't ask me how I know this!
Also on the Exh side floor of your chamber I see a sharp machine edge left just before the seat incert.

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Re: Quench, or lack there of

Post by 95GTSpeedDemon » Sat Aug 12, 2017 10:36 am

travis wrote:I remember reading somewhere that once you get past around .080" quench, you have no quench and are much less detonation prone. Somewhere around .060 to .080 is the "danger zone" where most engines tend to be most detonation prone.
I also remember that "back in the day" most everybody built their low compression blower motors with the pistons a mile in the hole...back before aluminum heads with heart shaped chambers...and there never seemed to be any issues.

Late model 440's in dodge motor homes had their pistons ridiculously far in the hole, and even with no compression they pinged like crazy
i forget what site i read it on, but they discussed the old mopar RV engines when mopar dropped the pistons way down. they said they overheated to the point the valve cover gaskets melted, oil leaked onto glowing manifolds and caught them on fire. they said they were gutless and pinged/detonated. they said if they tightened the quench all of that went away.

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Re: Quench, or lack there of

Post by 95GTSpeedDemon » Sat Aug 12, 2017 10:45 am

mag2555 wrote:Make sure the valves have a break ( rounded edges) from the chamber face to the start of the seat, especially the Exh valve as these can make for detonation.
Don't ask me how I know this!
Also on the Exh side floor of your chamber I see a sharp machine edge left just before the seat incert.
I will be sure to do this. When i put the 302 turbo motor im running now together, i didnt know to look for some many small details.

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Re: Quench, or lack there of

Post by PackardV8 » Sat Aug 12, 2017 11:31 am

IIRC, David Vizard once wrote that boosted chambers behave differently than NA and quench/squish was not as critical on those applications. Seems the the boost is putting more volume to be compressed, so the lower static compression ratio from the piston being lower in the cylinder/further from the head, but compressing the greater volume, works the area differently.
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Obsolete Engineering

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Re: Quench, or lack there of

Post by 95GTSpeedDemon » Sat Aug 12, 2017 12:11 pm

What concerns me is the off boost street driving. will it be more prone to knock in that condition, and if i pull timing to fix that, will it cause excess heat and issues due to that?

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Re: Quench, or lack there of

Post by CGT » Sat Aug 12, 2017 12:38 pm

I run a LS3 at close to 14lbs with .030 piston to head and a flattop. Im not saying its optimized, but haven't had any issues at all. It was an NA engine that I was trying to get the most out of first, then I supercharged it. Makes more power than the forced induction purpose built stuff that Ive seen, comparing on the same chassis dyno, whether it lives as long is yet to be determined. Not exactly scientific research or an answer to your question , but there you have it.

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Re: Quench, or lack there of

Post by pamotorman » Sat Aug 12, 2017 2:35 pm

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. :D

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Re: Quench, or lack there of

Post by 95GTSpeedDemon » Sat Aug 12, 2017 3:12 pm

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?

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