In cylinder turbulence/ burn rate

[rookie]

Having just recently spent hours reading Larry’s info on his web site, and years reading David’s work, along with various other’s. I now find my self more confused than ever, but I’ve learned one important thing, and that’s that I have a lot more to learn.
I’m not a big fan of grooves and lands in combustion chambers because of carbon build up and chance of detonation.
I lean more to the polished and coated approach, but the power made from improved combustion chamber design shows that there are still improvements to be had.
So now, the ball is in David’s court. David you responded to In cylinder turbulence/ burn rate Page One.
You stated the need to cover this in greater detail in some up and coming articles, and in response to For just $30 a day you can feed this starving car
You spoke about a big, I mean BIG story on high compression low octane fuel engine making good power.
This sounds like it would answer the million dollar question (or at least the 100 mile per gallon without sacrificing performance question). I'm not asking to much I hope, all I'm looking for is, a car that will run 7 second quarters, handle like a Porsche, with the top speed of a Mclaren Supercar, win a car show or two, pull down 30 miles to the gallon with A/C running. Oh and if you can make it self cleaning that would be great, and all that for around say, $2500.00 and I would be happy to make weekly installments of say $3.00 per week, and it must include undercoating and free tire rotation. (Car dealers hate me) and you can to, for less than that cup of coffee @#$$*^. OH Sorry i got lost.
Let me know what you can do. Thanks

[automotivebreath]

Originally Posted by rookie

Having just recently spent hours reading Larry’s info on his web site, and
years reading David’s work, along with various other’s. I now find my self
more confused than ever....

To add to the confusion here's another view from Jim McFarland. I enjoyed
the information he provides on fuel atomization and flame speed.

Two things I know for sure;

If the fuel is still burning when the exhaust valve opens, the burn was way
too slow.

If the fuel is still burning when the intake valve opens, you've got big
problems. Back in the day of points ignition this was common.

combustion patterns

combustion

airflow

exhaust

induction

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[rookie]

Yes, Circle Track has Jim McFarland and Dennis Wells work on a regular bases, back in 2002 Circle Track did a long Air flow Article that led me to dye testing.
I also have used dimpling just in case of fuel crash on the chamber wall as Dennis calls it. I don’t know if it helped or hurt because I cannot afford to do back-to-back Dyno test.
The dye testing is questionable as well, unless you can do it with intake and carb, and some how duplicate engine conditions IE; heat, speed and pulse from ram effect.
Plus trying to duplicate the flow disturbance from the overlap of the opposite runner is near impossible. However, I guess if it’s done enough in conjunction with Dyno time and you see improvements, it’s worth the extra effort to learn as much as possible.

[automotivebreath]

Originally Posted by rookie

...I have used dimpling just in case of fuel crash on the chamber wall as
Dennis calls it. I don’t know if it helped or hurt because I cannot afford
to do back-to-back Dyno test...

I have never used the dimples, I suppose the would work as claimed. When
working with a race engine that has plenty of camshaft overlap, it's relative
easy to determine if a modification helps combustion at idle. Measuring it at
high RPM is not so easy.

With a long overlap period, idle quality suffers from the effects of reversion
and poor exhaust scavenging. With poor signal to the carburetor and large
amounts of residual exhaust gas in the cylinder, idle can be so poor we resort to
raising idle speed substantially. Increasing ignition advance will also help to
burn the weak mixture.

Any modification that improves low speed combustion will show drastic
improvements in idle quality, to an extent that a SBC with huge amounts of
duration will idle at 500 RPM or lower (cold with no choke).

This is just me thinking aloud; the reason this is possible is with improved
combustion, flame reactions are no longer happening during overlap. This
results in improved signal to the carburetor as well as reduced exhaust
residual gas in the fresh charge. It works this way with EFI as well.

[automotivebreath]

The work of Michael May has always attracted my interest. When we study
burn patterns left on combustion surfaces, it becomes obvious that heat has
a huge impact on combustion. May devised a clever way to combine this with
mixture motion, it was promising enough to make it into production. Personally
I believe the concept has huge potential if further developed. If anyone has
more information on his work let me know.

It's difficult to find much information on the design, I thought you might be
interested in the views of one Jaguar power train engineer:

"I'm quite familiar with the May Fireball head. Over here on 5 star 100 octane
fuel that engine was supplied with a 12.5 : 1 CR in production!
In retrospect however we've moved on: although that chamber had good
initial burn characteristics, (0-10 %), later in the cycle it didn't burn all that
fast. Also, that engines CR made it supremely suitable for part load
operation, but it was quite knock limited all the way up the rev range even
with quite modest VEs at WOT. For after market performance applications of
this engine I recommend using the flat head as the ports flow better then
thge swirl inducing May ones.It should be noted that one CAN have too much
of a fast initial burn that leads to knock also!"

"I think squish/quenching the intake side of the chamber the way the Jag may
head did is actually good for combustion stability. This means the engine can
run lean and still remain stable without running into the lean misfire limit. In
modern day terms it can also mean that the engine can have a high EGR
tolerance at part load and still have stable combustion-again good for fuel
economy if you design your package to take advantage of this."

"In terms of tumble, swirl and squish-for me squish is used in tandem with
tumble. Swirl decays less then tumble ( as the piston comes up)and isn't
so confined and contrained to peak gas velocities during the intake stroke.
squish can be used to make the tumble motion into smaller eddies -which is
ideal to speed up combustion in some situations."

"Squish on its own, as here doesn't necessarily do much (It takes place too
late in the cycle and the speed at which the crown approaches the head at
lower engine speeds is fairly slow). In practice this may seem rather vague,
as it often is with combustion, it's alot less clear cut even in terms of trends
then something like maximizing your VE for full load performance."

"To be fair to the old May head -in the V12 it was barely lower then the more
conventional flat head design in terms of outright WOT performance -but this
was WITH the high CR versus the lower CR!"

[Pinhead]

Wow, there's a LOT of info in this thread already. Can't wait to see the article!!

[tommurphy73]

How do short Vs Long conrods effect the swirl and squish. With short conrods the piston speed is much slower when it is half way between TDC and BCD but as it approaces TDC it is moving faster and also the piston stays at TDC for a much shorter time.

Rgds
Tom

[automotivebreath]

Tom,

This is merely opinion and could be way off.

Your point is a good one, when we look at squish as it relates to
stroke/rod ratio we must consider piston movement. A long rod engine
has good piston movement as it approaches TDC, a short rod example
would not (it has long been used up). So what we have is the ability to
control when “squish action” happens by altering stroke/rod ratio.

So the question becomes, when do we want turbulence? First thoughts
are the long rod example has the advantage. Squish action just before TDC
and reverse squish just after TDC. Maximum turbulence generated at the most
critical time during the burning phase. But higher RPM changes everything;
with less time available to burn the mixture the process must speed up, the
tide turns in favor of the short rod combination.

Thoughts?

[rookie]

This may be part of why timing needs are different now days.

In the old days there was a good bit to be had by retarding timing in the upper rpm range, but I’ve read where guys are reporting better et’s by adding 1 or 2 degrees at upper rpm.

Joe Sherman did a 350 Chavy build and made coments that on 10.5-1 pump gas engines they had good results with 41 degrees in the upper rpm.

Where is a good Tech writer when you need one?

[automotivebreath]

There are so many variables and opinions it gets confusing. Throwing rod length
in the mix adds to the countless variables that must be considered. I’m
searching for some sort of standard. If you do this, you can expect this; is
seems quite simple. As David said early on “…the overall picture is not quite as
simple as it at first may seem…”

If you look at aftermarket combustion chambers for the SBC, every
manufacturer uses a completely different design. How can they all be right, or
perhaps they design for different goals in mind? Compare the open chamber
design of Brodix to the closed chamber of the RHS, 23 degree SBC. Surely one
must be better than the other. Can the average consumer look at the layout
and chose the best design for his application, I think not.