Singh Groove testing redux and CFD for groove positioning.

[LJW]

Prof. Blair has a set of software programs that correspond with the 2-stroke and 4-stroke texts. They are very basic DOS programs, but they allow experimentation without the fear and loathing of calculus.

For a "central" head type (spherical bowl with concentric squish band), the target maximum squish velocity ranges from 15 to 30 meters per second. This is divided into two groups, High and Low. Lower MSV (15-19 m/s) makes good power from peak torque to max RPM. Higher MSV (20-30 m/s) makes good power up to peak torque, then tends to go flat. High MSV kills over-rev and can incite detonation.

Factors that RAISE MSV:

• Smaller Bore
  Longer Stroke
  Shorter Rod
  Lower Compression Ratio
  Less Squish Clearance
  Larger Squish Area Ratio
  Higher RPM

Factors that LOWER MSV:

• Larger Bore
  Shorter Stroke
  Longer Rod
  Higher Compression Ratio
  Greater Squish Clearance
  Smaller Squish Area Ratio
  Lower RPM

[KennyM]

lJW,
We may have experienced this with a FORD 351w engine used for dirt sprint racing.
The heads are fast burn N351 with flat top pistons and very small squish clearences.
The engine exhibited very high low end torque to the point of being hard to hook for up handling.
The engine would still deliver great power up the rpm band but may have been better with more squish clearence.
Also the ignition timing needed to be kept under 30° even on alky fuel.
Thanks for offering another piece of the possible puzzle.
The head grooving may, in this case, have modified the conditions to some degree but we may not know since we are not running a car this season.

[putztastics]

It seems like that software isn't available anymore.

I've been wondering if higher quench velocities can trip the unstable reacted end-gas hydrocarbons into detonating. I've wondered if a quench groove could do the same thing. The first grooves test seems to support that something happened in the upper RPM range that caused a slight loss of power. That engine had .040 quench clearance, the quench groove gained power in the lower RPM testing but lost in the upper RPM range testing.

One would think the groove could concentrate quench flow, more of the total quench flow might come out of the groove meaning less will come out everywhere else. Who knows what the effects of quench manipulation is.

I think the key in further testing will be in recording knock, I haven't got a clue if the first test engine was knocking at high or low RPM, it didn't seem like it knocked at all - but that was determined by listening and looking at the plugs.

One approach would be something like:
o Put together a stout test engine with ~14:1 CR and a cam giving at least 240 psi cranking pressure.
o Rigorously controlling oil and coolant temp, etc., tweak spark and fuel for best possible steady-state power on 87 octane with no more than trace knock, at 500 RPM intervals from 1,500 RPM (or lowest revs that will accept WOT) to red line.
o Groove heads and repeat.
o Compare power, idle RPM, quality and vac., EGT, BSFC, jetting, SA, etc.

Good idea on the steady state only testing. I'm afraid I could go nuts tweaking things like timing on the dyno. Every test will have to be done at least twice. And I'd want to get all the testing done in one day - well - at least not be testing through a major change in weather.

If I'm going to deliberately run an engine into hard knock it will be my own test mule engine, not the one in this proposed second grooves test.

[mpgmike]

It is my opinion that the Grooves are tuning tools. To apply characteristics to the Grooves is like stating OHC engines act one way versus a push rod engine. The cam lift and profile has much more influence on an engine than the location.

If an engine has an overly large squish pad, a groove (or 2) could be used to vent the back side of the pad. If an engine has too slow combustion chamber activity requiring too much timing advance, the action can be excited by strategically placed grooves. By carefully studying the chamber and pistons, grooves can be designed to help inherent deficiencies in the engine.

Testing has been done on various engines with randomly placed grooves. I think AB has done more to try to put characteristics on the Grooves than probably Somender himself. AB has tried different angles, different numbers, different depths, and so forth, then track tested. Sooner or later he will probably land on the epiphany of how they can be changed from engine to engine to get the engine to do what he wants it to do.

If an engine is tested stock, then grooved and retested, then grooved differently, then grooved differently again, there will probably be a plethorah of different results...all from Grooves. Once you know what you want more of, design the groove to do it for you. That's what I've been using them for as best as I understand them.

Mike

[automotive breath]

…If an engine has an overly large squish pad, a groove (or 2) could
be used to vent the back side of the pad...

... If an engine has too slow combustion chamber activity requiring
too much timing advance, the action can be excited by strategically
placed grooves. By carefully studying the chamber and pistons,
grooves can be designed to help inherent deficiencies in the engine…

Mike

Mike,
Your thoughts about venting pressure with a large squish pad are
identical to mine. A very large percentage of the cylinder heads I
work have over 25% squish to bore ratio with most of the squish
area being on the opposite side of the chamber from the plug. During
combustion this area builds excessive heat and pressure that commonly
leads to auto-ignition.

Some people like yourself and I have realized that by relieving and
directing this pressure, increased burn speed and resistance to auto-ignition
can be easily achieved. As you know, this is something that can be proven with
out a dyno, it can easily be done by the average person with minimal skills.

Unfortunately the people that were involved with this type of thing years
ago in NASCAR have not come forward and shared much of what they
learned back then. It’s clear that they were able to prove no benefit with
what they were doing with that specific engine design and application.
I’m sure much of it was documented, it would be great if someone would open up.

Mike, you and Jessie as well as many others have a different desire, that
is to improve performance with out the need for expensive high octane
fuel. You and I have proven that it can be done. Despite the critics, many
others are quickly realizing the same!

[mpgmike]

Thanks AB. I wish I could do just that...run an engine, create problems by taking things too far, then play with different groove configurations to see what happens. I do know that different groove layouts yield different results. I've proven that to myself with the Chrysler 2.2 turbo. I have ruled out some designs, but don't exactly know if what's going on in the cylinder is what I'm imagining.

Mike