OK, I did some generic searching both on SpeedTalk and elsewhere across the interweb for "tapered quench" & "tapered squish", and found a few(?) things.
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Re Toyota taper squish: "...the other thing the taper squish design enhances is the "reverse squish".....when the piston goes down and opens up the squish area, the taper speeds up the sucking of the burning mix to the outer wall.....thereby speeding up the burn which shortens the burn time..."
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"Toyota research (SAE 1999-01-1494) showed knock limit improvement from better reverse squish flow in the early expansion stroke. Burn reaches bore wall more quickly reducing the tendency of end gas to autoignite."
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"... a tapered squish, 2 degrees, will allow lower octane and more advancement of the timing before detonation. This equals more power. This is done by increasing the squish clearance by the combustion chamber and reducing it at the piston edge. Flat squish bands are a thing of the past."
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Re SAE 981087 - Development of Toyota 1ZZ-FE Engine: "... one other major flaw in the model being used now: a larger squish volume in an otherwise identical engine will take longer to empty (more squish volume, AND less discharge area), and as the squish ratio increases, there is likely a point where it's too late to be useful, due to excessive, delay, heating, and an approaching flame front."
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[David Redszus]: "The squish passage ways can be parallel or tapered. If the length of the squish band is short, a parallel passage can be used. If the flow length of the squish is long, a tapered passage must be used to prevent choking the squish flow through the squish window area. If a tapered squish is used, you must then use the average clearance in your calculations.
The shape of the corners of the squish area window has an effect on flow. A sharp edge window produces higher velocity BTC but inhibits squish flow into the quench area ATC.
While compressibility factors should be considered, there are other even more important factors to consider regarding squish. The D'arcy friction factor must be considered since the very narrow squish passage area exposes the flow to surface wall texture.
In addition, the rising piston will scrape heated gases from the cylinder walls and force them into the squish volume that is being compressed. The heated gases produce significant changes in temperature and consequently in fluid viscosity. Local fluid viscosity produces the shear forces in the air fluid and produces non-uniformity of flow.
Lastly, the Reynolds number should be considered which employs area, velocity, density and viscosity. It determines the transition point to turbulent flow and which point a whole new set of equations are necessary."
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"... it sounds like those [Singh] groooves[sp] are just a "poor mans" tapered squish zone"
[David Vizard]: "Funny you should say that. I have only recently come to a tentative conclusion that every two valve engine quench area I have ever seen including mine are not what they should be - not even close.
As of now I am into some CFD stuff on what happens in the quench but I fear the stuff I have access to is not up to what I might need.
what I can say for almost sure is that the way most people think Singh grooves function (whether they work or not) is not really what happens."
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[?]: "That's the way I see it. The pistons in the motors without the grooves would be clean at the outer edge of the squish region. Putting the grooves in they would have a uniform color across the entire piston. I don't think the grooves act as 'jets'.
[David Vizard]: "You and I agree Larry, the grooves appear to have more of an impact on "reverse squish" to help complete the burn."
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[John Marcella]: OK, what about the tapered quench? A lot of max effort NA motors use up to a 3* taper on the quench pad.
If you had 1 inch of quench from the bore this would add .051 to the .040 you may have started with.
I think this would prob be good for both N2o and NA. The taper should direct fuel towards the center of the bore and away from the rings.
And it should help get the flame front across the hole[sp] cyl earlier.
I believe that you would want the flame front to get all the way across the bore ass fast as you can.
(not a expert , just thoughts)
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[David Vizard]: "The reality is that the [Singh] grooves may provide more of a benefit by providing ‘quench relief’ and drawing in some of the flame front into the quench gap and burning it more effectively earlier on in the combustion event. That however, is only supposition on my part as I have not investigated that part of the cycle – only the compression side.
Is that going to guarantee results? Hell no – there are still a host of other criteria to consider and that is why I said a real investigation of Singh grooves will take a giant budget – way more than anything I can come up with...
At this moment in time I think that there is much more to be had from what is commonly known as ‘Tapered Quench’. Am I putting any effort into that? Same answer - hell no! I will tell you what the latest thing is and that is RQC or ‘Radical Quench Control’ I can’t go into details here because it is subject to patent applications..."
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OK, so it sounds like it's being used in some applications, and may show benefits under the right scenario.
What caught my attention -- and now has me looking for my asbestos BVDs -- were the comments equating Singh grooves to a "poor mans" tapered squish zone. That triggered a memory (doesn't happen often these days) of something I saw w/ the BES BB Chevy entry in the 2005 EMC challenge... Tony B. put "fire grooves" in the piston tops.
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BES EMC BBC 3.jpg
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He said he'd never tested them before and didn't know if they made any difference (and may have never tried them again), but the picture I've attached looks as if they did help extend the range of coloration on the piston tops. That's one of the benefits people above have also said was a benefit of "reverse squish" from a tapered squish/quench channel.
Hey, this isn't the direction I'd intended to go w/ this post, but just a slightly(?) off-tangent FYI.
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