In cylinder turbulence/ burn rate

[automotivebreath]

Originally Posted by shrinker

First off I would get rid of the HP carby and go with an old 60's 850 or I'd
retune the HP's emulsion, but it wont work as well as an Oldy. At least don’t
run it rich. The carby is the start of the process and there is no point
analyzing anything if its not right and an out of the box is not going to be right.

What would be the best way to upgrade the HP for improved emulsion? Can
I replace the metering blocks with aftermarket units? I do understand how
improvements in fuel atomization affect the combustion process, when the
carburetor is in the main circuits. Running rich is not my doing; the
owner/tuner is convinced that his over rich setting is ideal.

Originally Posted by shrinker

I would use a wider LSA on the cam if the revs are 7000 max and probably at
smaller duration. The cam is in the zone for 7500 max however If you fixed
the push rod pinch choke on the as cast heads it will be a very big benefit.
Those AFR heads won’t support 7500 properly with there as cast push rod
pinching ports. It’s probable that the LSA on the cam in use is to overcome
this problem.

The engine pulls great to 7500 RPM, a smaller cam would likely require a gear
change. As for the wider LSA you lost me there, what would this benefit?
The push rod pinch is now as delivered from AFR, I haven’t measured the
CSA. I could open it up with-in the limitations of the casting with out offset
rockers, Is that what you are referring to? Here we are talking about
improved VE and resulting increased cylinder pressure, I’m with you on the
impact this has on combustion at WOT in the engines RPM range.

Originally Posted by shrinker

The compression is fine, I wouldn't use a fuel that’s
too high octane for the job because I'll bet it is at the moment. I would
suspect the VE to be lower than it could be at max revs so that alters the
dynamic comp and hence the octane. It’s just that it’s common for people
to use fuel that’s too high octane.

Yes the owner runs more octane than needed with C12 heavy leaded racing
fuel, again not my choice. What impact does this have on combustion?

Originally Posted by shrinker

When the carby is set better and the vaporization is improved the octane
requirement goes down. If these things were done the engine would have lots
more power and it wouldn't be comparable anyway to what it is now with the
grooves. It would burn cleaner at all points with a correct carburetor to start
with. That’s just some quick ideas. Really need lots of info and time to make
a better posting.

Thanks for taking the time to explain.

I’m certain that the cylinder head wet flow characteristics are poor with the
current carburetor (as is with a large percentage of engines world wide). This
I will explore, if you will get me started in the right direction.

As for improving the cylinder heads, I’m willing to do the modifications, many
people refuse to spend additional money porting CNC ported heads, this
owner is the same. I agree improvements can be made to effect cylinder
filling, trapped charge and dynamic compression resulting in improved
combustion.

I’m all ears on changes in camshaft design; first I need to understand the
benefit of widening the LSA with this combination. As for shorter duration,
the cam matches the current engine RPM.

I understand the benefits of most of the above and can visualize
improvements implementing most of this with the current combination. This
could result in improved combustion at WOT in the engines RPM range and
throttle response.

The question now is would the grooves help the combination with the
recommended changes? I say yes, but I do get your point, some people
that work at higher levels in the sport feel they have accomplished more
of the same benefit using other methods as described.

[shrinker]

Hi AB, Do you still have my email address? pop me a line if you have. If you go to a wider LSA and a corresponding smaller duration to keep the IVC etc the same you will get much more vacuum and a better mid range pull. But you need the porting to go with it. Port flow and cams have to match. It depends on the transmission etc as to what find works the best for what you need. A lot of the top end problems of carburation come from the tune of the low end. If the combo requires inappropriate corrections it can influence what happens up in the top end of the power. The carbys can only do so much to correct things. See the low speed circuits of a carby work all the time they effect top end .

Fuel with high octane generally has higher distillation temps. Not all fuels follow that rule but 99%do. As the distillation temps are raised it takes more energy to get the fuel components into a gas. That energy is limited by the engine combination. Things like dynamic comp, exhaust gas retention, wall temps, oil temp on the piston, are energy sources, things like vacuum in manifold, carby size droplet size are things that lower the temp necessary to gas the fuel and the time taken to do it. Tuning these areas reduces all this wet flow that everyone keeps talking about now days. Control the wet and it goes harder.

These HP carbys are sold with calibration that doesn't work on the fuel here in Australia thats all I can say. They always run too lean at the top and changing the main jet is not the beat way to fix it. Changing the high speed bleed smaller is the first thing to do then chase the e-bleeds and the low speed circuit to suit the motor. I wouldn't use aftermarket metering blocks, the Holley ones are fine when they are fitted with the correct e-bleed calibration for whatever motor fuel combo. If you havent got the ultra version then you need to thread them. Its just you can spend time on them and then swap in an old 850 and it will beat it. Also power is not everything drivability is a big factor to most people. An Old 850 with a stub stack is hard to beat. Even if you copy the calibration of the oldy they still dont perform the same way. Holleys with a stub stack tuned to the stack work ery well and the HPs are a differnt air horn so its not like a stub stack tune. Some engines love the Hp's some don't, but every engine will go good on an old 850. There a good reference.

Dont bother tuning carbys with a WB you have to use a gas bench to figure this stuff out. A gas bench shows the difference in burns from a modern carby to the oldy.
The problem you face is the other guys are not in sync with your thoughts. While their tuner does it the way he is you wont get what you need. The grooves do something to the combustion there is no doubt but you have to qualify it. Its possible the over rich/over octaned environment is being corrected by the grooves somehow that might not happen the same way if the environment was different. See good racing engines actually burn extremely clean. They even have low emissions at power settings compared to lesser engines. You dont make power from poor combustion and thats what is the source of emissions.

[automotivebreath]

Thanks for the information Shrinker, now I understand your point about the
wider LSA with shorter duration. The port modifications would improve VE,
combine this with shorter duration and the same IVC and you get higher
cylinder pressure for improved fuel vaporization and combustion.

You said something that gives me an indication of why the owner insists on a
rich mixture. If the HP is leaning out on the top end, he may be compensating
with a larger jet as opposed to a smaller high speed air bleed. Remember he
runs a throttle stop most of the time, so most of his decisions are based on
high end charge (trap speed).

You mention a gas bench for determining air fuel mixture. What equipment do
you recommend for this?

[shrinker]

Hi AB; Gas benches are expensive.
I think Bridge Analyzers Is a smart man and would be good to talk to. Bob Schraeder is his name. Seems to know his stuff.

[mpgmike]

FWIW the IM-280 program is mostly a thing of the past. This means you can find 5-gas analyzers for around $4k and 50HP dynos for about $1k. Check in areas that used to have the IM-280 program that no longer do.

Mike

[crazyman]

In Illinois, it used to be the IM-240 program. I think it varies by state, but Mike hit the nail, not his thumb.

[comp]

Originally Posted by seattle smitty

AB, I wasn't commenting about Singh's ideas, but what I have seen in a lot of his enthusiasts: a seeming unawareness of ordinary engine-building practices combined with improbable claims about their before-and-after experiences. All seat-of-the-pants, nothing measured, little allowance made for the effects of other changes made during the engine-build or the tuning process. I don't criticize their reporting their experience and impressions, and don't expect backyarders to shell out $300 or more a day for dyno time. I won't dyno a street motor either, and have to do my dialing-in by accelerating up a long local hill over and over. In the next couple of weeks, when the milling machine is free of paying work, I intend to make and photograph my own intuitive but utterly non-scientific notions about grooves. If the engine works as I hope (tolerates low octane gas with a high-octane compression ratio) I'll report that with pleasure. But if it turns out to be a cranky brute that demands water injection to keep its pistons intact, I'll report that too. And in either case, I will make what I feel are proper disclaimers about not generalizing from my particular experience.

I'm surprised at your reaction to what I said, AB, since you have surely seen the kind of posts that bothered me. I imagine you have also been around long enough to see wild claims for miracle oils, miracle sparkplugs, miracle carburetors, complete with testimonials by real customers who really think their mileage has gone up by 38%. YOU don't do anything like that. You know what you are talking about, have loads of experience, and you don't make claims you can't back up. So maybe the problem is that I quit looking at the sites where the novices seemed to congregate, including Singh's, some time ago. Maybe Singh's site has attracted more veteran engine-builders recently. Or maybe it was never as bad as I remember, and I am mixing it up with another site. If so, AB, mea culpa. But I still like Tom Murphy's style.

any update's on your project ??