Do you have a formula(s) to use ?
I did a quick search and it seems there are website calculators out there, but it also looks like a possible candidate for an Excel spreadsheet.
Well that's a new one on me, I've never read that quench could produce too high of a velocity or mixing.
Intriguing subject, how did you come up this !!!
I've been using this calculator some
http://www.torqsoft.net/squish-velocity.html but I also have an XLS based calculator that was given to me by a Dr. with an automotive research company that is very similar and uses bowl diameter directly instead of using %Squish Area, it gets SUPER interesting because the 2nd tab of that particular XLS takes the squish velocity calculations as input, and then lets you measure the "Flame Path Radius" (basically measure from the spark plug electrode to the furthest reach of the chamber), the initial laminar flame speed (which it says depends upon what fuel you're using your air fuel mixture and especially IATs), then your engine's ignition delay (.2 - .8 ms range) and at what crank angle you're targeting to have peak cylinder pressure occur at and it tells you your engine's expected turbulent flame speed, burntime, burn angle, and ignition firing angle required in your timing table. (You could theoretically recalculate the squish velocity at multiple RPM points and use the resulting ignition firing angle for an initial engine base tune...)
I am pretty certain the author doesn't want me widely distributing that XLS, though..
I've been collecting recommendations for max squish velocities over the past week and Professor Gordon Blair says max squish velocity shoudl be 15 - 20m/s at your desired peak HP RPM, the Dr. who gave me the XLS says 25-35 m/s at hp peak is ok on many NA engines, and TSR which I guess is a big professional automotive engineer software suite recommends a max squish velocity between 15-30 m/s.
Many of the recommendations I believe come from 2 cycle engines where it's more important and where squish is more plentiful.
I've also heard some nitrous-focused engine builders who try to get squish near ZERO so that they don't accelerate the burn speed any more than it already is with tons of nitrous and knock engines to death.
All the Nitrous and forced induction tapered quench pad / "chamber softening" enhancements SEEM TO BE focused on reducing squish velocity (when you change the squish area taper angle using the calculator above you'll see that even VERY SMALL tapers like the "chamber softening" folks recommend DRAMATICALLY lowers the max squish velocity). -Taper angle changes the max squish velocity the most, then the squish distance, then all the other factors. Changes in the % area I haven't played with much because I don't want to waste my time with junk numbers; I'm hoping to get some decent numbers to model some actual engines.
-I THINK the reason that we don't hear about Squish Velocity being too high on 23 deg SBC engines is because squish area is so much harder to come by. -That's actually why I wanted a calculator, I wanted to be able to model typical SBC engine combos and se what the max quench velocity looks like, but I can't get good enough quality data on actual chamber diameters or quench area percentages to get good results out of the calculator.
(I could see a really big bore SBC like a 4.165" bore with a small chamber and a D-dish or a mirrored piston dish with a close piston to head clearance actually exceeding 35 m/s max squish velocity, but I just don't know as I don't have real data on the critical quench area %...)
Thread I started on ST to help me figure out how to get quality information to enter into these calculators to start modeling different engines' max squish velocities:
https://www.speed-talk.com/forum/viewtopic.php?f=15&t=65157
-The most interesting thing that I've learned in all of this is that there's actually 2 squish events: the one we normally talk about where the air-fuel mixture in the quench area gets forced rapidly into center of the cylinder, mixing it well, and evening out any hot spots, but then after ignition occurs and after TDC as the piston is traveling down, the quench area then actually pushes the burning air-fuel mass back out towards the cylinder's extremities and increases the burn rate and cylinder pressure (it dramatically increases the turbulent flame speed that's responsible for the actual rate of burn largely).
This idea that because the max quench velocity drives the rate that the flame front spreads and is a / the major factor driving timing requirements was something that I was missing before...
On the discussions I've come across so far, many folks coorelate the max quench velocity with the rate of pressure rise in the cylinder due to combustion and it becomes one more variable that they try to control -I believe that's why these calculators look at the timing of the exhaust valve opening event -if they have an early exhaust valve open I believe they try to push the rate of pressure rise to be faster to get more work done on pushing the piston down the bore before the valve opens -but the engine and bearings take more of a beating, if you have the luxury of the exhaust valve not opening for a while then you can run less on the ragged edge with a super fast rate of pressure rise and have a slightly slower pressure rise that isn't as hard on parts and bearings -that's my current best guess understanding like a week into this and reading way too much about it in a short period of time...
Interesting idea: Maybe pushing the quench velocity as high as you can get it is a good thing for someone running a CompCams Thumper cam with it's stupid early exhaust valve opening so you can lose slightly less torque with one! ;-)
Adam
from "both sides", no real conclusion.
