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Why wouldn't you want quench in a supercharged motor? #2715682
11/14/19 11:38 AM
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I posted a question about using a high-quench, reverse dome piston in a pump gas centrifugal blower motor in a street car over on A-Bodies only. The majority, if not all of the responses were that it was unnecessary to have high=quench in a blown application.

I started thinking, once the valves are shut and the compression stroke is nearly complete, the induction part of the cycle is out of the picture. Right? so why would the benefits of quench be muted? I don't understand how that could be the case. Quench is directly related to creating turbulence in the cylinder's remaining higher volume area by squishing about half the cylinder's volume into the remaining combustion chamber volume.Why would the effect of supercharging the intake charge render that effective design strategy ineffective?


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Re: Why wouldn't you want quench in a supercharged motor? [Re: jbc426] #2715695
11/14/19 12:00 PM
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I can’t answer for anyone else, but it’s not the idea/ theory that is the problem. In most cases, the issue is getting compression low enough to run gasoline. If you mimic the piston shape to the chamber shape, you would need to start out with a piston forging with enough material in the dish area as to not be too thin when it is carved out to finished shape. Every engine is different, and on some, this is probably feasible. Look at a sbc chamber compared to the mopar chamber. Probably a lot easier to do on the sbc because of the deep chamber.
On alcohol or some derivative of alcohol, compression would be higher, and detonation is not an issue that needs a fix.


"use it 'till it breaks, replace as needed"
Re: Why wouldn't you want quench in a supercharged motor? [Re: TRENDZ] #2715733
11/14/19 01:02 PM
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I don't know how to properly answer that. I don't think Hocus Pocus stuff like "quench" enters the mind of anyone making big power. Hemi's and Mountain Motors don't have quench and they run alright. If you are supercharged you should be making big power and you don't have to worry about quench.


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Re: Why wouldn't you want quench in a supercharged motor? [Re: rickseeman] #2715746
11/14/19 01:40 PM
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I'm not 100% sure why, but quench isn't necessarily a good thing on a nitrous engine either. When they "soften" a chamber, they are relieving the quench area on the head. Sort of making an "open" chamber area on a closed chamber head.


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Re: Why wouldn't you want quench in a supercharged motor? [Re: an8sec70cuda] #2715750
11/14/19 02:09 PM
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My opinion; Too many statements are generalized. The octane of the fuel being used is critical. The engines that seem most impressive are the ones that can reach or get very close to MBT with a bunch of boost thrown at them. If its pump gas these engines are the ones that don't need 34+ degrees of timing for MBT NA. If you're running C16 it MAY not matter much. I think less is known than we think we know.

Last edited by GTX MATT; 11/14/19 02:10 PM.

Now I need to pin those needles, got to feel that heat Hear my motor screamin while I'm tearin up the street
Re: Why wouldn't you want quench in a supercharged motor? [Re: rickseeman] #2715765
11/14/19 02:44 PM
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If you mean "quench small enough to be an effective anti-knock method, .060" or less", many don't.
However: to not have any quench (in which the area of the charge is reduced as the piston approaches TDC, forcing the charge toward the plug and/or exhaust valve and imparting turbulence, swirl, tumble, whatever): everything does.
Only a soup can cylinder, chamber and piston have constant area throughout the rotation.

HRM ran an article on a Duttweiler LS engine (Poteet's Speed Demon LSR) with loose quench distance (definitely not an open chamber), 2,600 hp.
But: 40 psi boost + methanol, so not a valid comparator.


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Re: Why wouldn't you want quench in a supercharged motor? [Re: polyspheric] #2715856
11/14/19 06:19 PM
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Isn't there a school of thought that says because the fuel air charge is boosted/compressed on a blower motor, it is denser so a wider quench distance can cause the same effect because the air is "thicker"?

Kevin

Re: Why wouldn't you want quench in a supercharged motor? [Re: Twostick] #2715910
11/14/19 07:53 PM
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it is denser so a wider quench distance can cause the same effect because the air is "thicker"
Hadn't heard that, I'm sure it's a factor.

AFAIK no reliable math so far as to "what is happening in a small port @ 50 psi?", other than "use what worked, and change when it doesn't".
On paper, my 3000cc L6 produces 220 hp with DOHC, 4 valves, 8.5:1 CR, designed in 1990 for automatic transmission, A/C, overdrive, and excellent mileage in a 4,000 lb. sedan. Not a "performance option", but the base engine, in every full size RWD Toyota sedan built at the time.
That same engine can produce 700 hp with the same unported head, with a single 64mm turbo. Other projects with similar engine designs (on paper) are 200 hp short using the same parts. How and why?
Toyota doesn't know...


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Re: Why wouldn't you want quench in a supercharged motor? [Re: TRENDZ] #2715919
11/14/19 08:03 PM
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Originally Posted by TRENDZ
I can’t answer for anyone else, but it’s not the idea/ theory that is the problem. In most cases, the issue is getting compression low enough to run gasoline. If you mimic the piston shape to the chamber shape, you would need to start out with a piston forging with enough material in the dish area as to not be too thin when it is carved out to finished shape. Every engine is different, and on some, this is probably feasible. Look at a sbc chamber compared to the mopar chamber. Probably a lot easier to do on the sbc because of the deep chamber.
On alcohol or some derivative of alcohol, compression would be higher, and detonation is not an issue that needs a fix.



Has absolutely NOTHING to do with compression ratio.

Quench is a fix. Quench isn't the do all, be all, end all. Many N/A engines make power without quench. A blower/turbo/nitrous engine doesn't need it. In fact, it's detrimental to power.


Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
Re: Why wouldn't you want quench in a supercharged motor? [Re: madscientist] #2715949
11/14/19 09:21 PM
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Originally Posted by madscientist
[quote=TRENDZ]. In fact, it's detrimental to power.


That really depends on the build...650HP CF blown engine will actually like the flat part of the piston .040 away. Especially if it's on pump gas.


Brian Hafliger
Re: Why wouldn't you want quench in a supercharged motor? [Re: ou812] #2716004
11/15/19 06:45 AM
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The reason I don't look for quench in supercharged engines is because every stupidly high powered one I've seen has none. Enough evidence for me. lol

Re: Why wouldn't you want quench in a supercharged motor? [Re: madscientist] #2716005
11/15/19 06:56 AM
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Originally Posted by madscientist
Originally Posted by TRENDZ
I can’t answer for anyone else, but it’s not the idea/ theory that is the problem. In most cases, the issue is getting compression low enough to run gasoline. If you mimic the piston shape to the chamber shape, you would need to start out with a piston forging with enough material in the dish area as to not be too thin when it is carved out to finished shape. Every engine is different, and on some, this is probably feasible. Look at a sbc chamber compared to the mopar chamber. Probably a lot easier to do on the sbc because of the deep chamber.
On alcohol or some derivative of alcohol, compression would be higher, and detonation is not an issue that needs a fix.



Has absolutely NOTHING to do with compression ratio.

Quench is a fix. Quench isn't the do all, be all, end all. Many N/A engines make power without quench. A blower/turbo/nitrous engine doesn't need it. In fact, it's detrimental to power.


So, compression has nothing to do with it. Cool. I’ll just start ordering zero deck flat tops for blown pump gas engines. Much simpler!


"use it 'till it breaks, replace as needed"
Re: Why wouldn't you want quench in a supercharged motor? [Re: TRENDZ] #2716026
11/15/19 08:42 AM
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I'd say how you achieve quench is more important. I have a turbo application and run a small efficient chamber, 58cc, and then use a reverse of the chamber as the dish in the piston. So technically, the quench area around the chamber on the head mirrors the piston, forcing the mixture into the chamber "ball". Whether it matters, makes a huge difference or none at all, don't know. It works well for N/A engines, so I can't see why it wouldn't help with higher cylinder pressures in forced applications.


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Re: Why wouldn't you want quench in a supercharged motor? [Re: madscientist] #2716064
11/15/19 10:19 AM
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Has absolutely NOTHING to do with compression ratio.

Ricardo developed quench (and patented it) 100 years ago to allow engines to operate at higher power and fuel efficiency levels with 4:1 CR instead of 3:1.
Harley-Davidson used quench in every low compression (flathead) engine since 1926, and every OHV engine since 1983.


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Re: Why wouldn't you want quench in a supercharged motor? [Re: dthemi] #2716101
11/15/19 12:33 PM
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Originally Posted by dthemi
The reason I don't look for quench in supercharged engines is because every stupidly high powered one I've seen has none. Enough evidence for me. lol


I bet if they could they would, no reason the laws of physics would be suspended just because it is a higher pressure than 14.7 PSI. I would be willing to be the reason has more to do with other things that make more power than good quench would that prevent quench from being an easily acomplished goal. Things like big valves and compression ratio are just bigger factors than quench, for example... if good quench adds 20 HP but but a bigger valve might be worth 50HP and make it impossible or very hard to get quench witch one are you going to choose?


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Re: Why wouldn't you want quench in a supercharged motor? [Re: HotRodDave] #2716102
11/15/19 12:43 PM
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am i missing something here?

Tight Quench speeds up combustion

Nitrous, Boost speeds up combustion so tight quench is not needed and actually detrimental with power adders as combustion gets too fast and you get detonation

SO just like you retard timing with power adders, you open up the quench also to slow your combustion




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Re: Why wouldn't you want quench in a supercharged motor? [Re: n20mstr] #2716133
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It is (in theory anyhow) making a more uniform mixture for a more consistent burn speed not really a higher burn speed. It makes a NA engine less likely to detonate and allows it to light the fire later so as to prevent spark knock, both of those should help a forced induction also. Just because the air starts compressing at 30PSI (or whatever) instead of 14 PSI does not mean it needs to be mixed less evenly. I still think it comes down to other more important compromises, like air flow, hot spots, compression ratio...


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Re: Why wouldn't you want quench in a supercharged motor? [Re: HotRodDave] #2716197
11/15/19 06:19 PM
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I suspect the reason a max effort boosted combo doesn't care about quench is because they are using the appropriate race fuel to support the combo. A pump gas combo doesn't have that luxury.

Kevin

Re: Why wouldn't you want quench in a supercharged motor? [Re: Twostick] #2716260
11/15/19 11:21 PM
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I've been told that the blown alcohol Hemi motors need around 11.5 to 1 or higher mechanical compression to make good power with 30+ Lbs. of boost shruggy work
I'm thinking of finding out on a wedge all aluminum street motor with a Pro Charger with EFI devil luck


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Re: Why wouldn't you want quench in a supercharged motor? [Re: Cab_Burge] #2716335
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Lets back up a second... and answer what the purpose of quench actually is...

Think of the fuel mixture as a series of fireworks, all connected by lines fuses. You light the fuse at one end and it slowly moves towards the first firework. Once it reaches the firework, it rapidly goes off. The fuse continues slowly to the next firework, and it goes off... on and on. When the burn is moving through the fuse, it moves slowly, but once it gets to the firework you have an enormous release in energy. Then it goes back to moving slow on the fuse again. This is an analogy of what's going on with fuel mixture. As you have lean spots from the mixture not being evenly distributed, the burn slows down as it moves across the chamber through the lean areas with no fuel (like the fuse). Once it gets to the pocket of fuel molecules again, it rapidly releases energy (like a firework).

Now this isn't exactly how it works, because we are talking about VERY high speed, and chemical reactions to create the heat release in chamber. But gives you an idea.

So you can see how pushing all of the fuel molecules together (essentially shortening the fuse length between each firework), would have a benefit to burn it all as quickly as possible. This is essentially what quench is doing.

As the piston gets to TDC, in the area of quench you get a localized "squeeze". The air/fuel mixture is then essentially "squirted" (for lack of a better term), towards the spark plug side of the chamber where the burn has started. This helps not only create turbulence and mix the fuel up for better even distribution, but also gets the molecules closer together to speed up the burn as described above. Faster burn means lower timing numbers. Remember any pressure created in chamber at TDC doesn't actaully rotate the crank, When the crank is at zero degree's, and the rod is straight in the cylinder... all it does is try to push the crank out the bottom of the block!!!

So why is quench less meaningful in a boosted engine then? If you think about it... the turbo/blower has already "packed" the molecules closer together to start with. This means there is less space for these "lean" pockets to hide like there would be on an N/A motor. The "fuse" length is essentially shorter between fuel molecules on the boosted motor, because the molecules of fuel are pushed closer together.

This is the primary reason why boosted motors run less timing. The burn speed in chamber is much faster, because everything is packed closer together. As boost goes up, timing comes out... its just a function of packing the fuel tighter together in chamber from shoving more air and fuel into the chamber.


So it's not that boosted motors don't "need" quench, it's just that effectively the boost pressure is already doing the same thing as the quench would.

Now I'm sure on some very high HP stuff with mega boost, we could debate if quench is detrimental to those motors... but for most of us living in normal HP land... it really doesn't matter.

Put the flat top in it that gets the compression right, and let it rip.

For reference... my boosted motor has the piston .050" in the hole with a .040" gasket... so doesn't have really any quench. It's been ran at 23psi non-intercooled on E85 with ~22 deg of timing. I am very confident it's not detonating, because if it were... the cast 360 crank would have been in many pieces years ago.

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