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 Post subject: Re: Engine upgrade
 Post Posted: Mon May 07, 2012 3:37 am 
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As for dyno correction factors etc either obtain or work out the actual power produced. Thats what your engine really makes and its what it races with. Ive used depac dynos, there no different to any other. Anyone who claims their dyno is 6% different to other dynos is playing games. In any case correction factors are only accurate to a maximum of 4% correction. Recently the SAE altered the maximum deviation for atmosphere accuracy limit to a larger amount, something like 6% to 8% I think, and they introduced other standards to appease manufacturers basically. I grown suspicious of correction factors over the years, they correct for crankshaft inertia, friction losses, etc its all rubbish. How the hell can you correct for crankshaft inertia when it has to be there/ Its part of the natural order of things. Its annoying. So I look at measured power now days and dont care about correction. The combustion that happens in certain types of combos varies according to different weather factors whereas the correction system just assumes every engine reacts the same, well they dont. Sorry for ranting.


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 Post subject: Re: Engine upgrade
 Post Posted: Mon May 07, 2012 6:52 am 
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The ability of an engine to increase RPM with sufficient pressure rise rate to provide useful power is directly related to the burn speed. To obtain a fast burn speed a few things have to be correctly in place to start with. The fuel has to be vaporized because any time the gaseous state is leaner than 12.5 to 13 AFR the burn will be slower than the fastest possible. It's not enough to measure the overall AFR of a chamber, you have to achieve the optimum AFR at ignition time and have that mixture around the sparkplug. Its no good having a lean area around the sparkplug, the flame kernel takes too long to grow and the start of the process is then inefficient and the cylinder wont make power at High RPM. Also the compression has to be sufficient to provide a small enough space for the mass fraction to burn quickly. The mass fraction that is burnt at around 15 degrees ATDC is important. its usually around 85 to 90% by then. All engines are different.
The vaporization and homogenization directly effect the mass fraction burn angle. The turbulence (squish) has to be directed into the mass fraction that's burnt at around 10 degree BTDC so that the speed of the flame propagation can be increased by the turbulence to the fastest possible rate while the chamber is at the tightest volume. By doing that you get the greatest mass fraction burnt at the optimum conrod angle of around 15 to 18 degrees ATDC. This position of the rod and crank is an average for most stroke rod ratios with mostly correctly burnt fuel etc. Its not an exact defined factor but its one that makes all the difference and you can see how well this factor is performing on a gas bench.

The most important factor is the squish directional control. I have performed tests on our own race car engine by altering compression and cams and squish direction etc over the years and the results confirm that the maximum HP RPM point is moved by thousands of RPM by mainly squish direction. With a dished piston the worst possible situation is created. The surface of the piston is further from the valves and the squish action doesn't serve to scavenge the exhaust from the base of the dish. The engines I've seen with dished pistons have a lot of CO and unburnt O. They basically suffer from exhaust contamination.
The squish action into a dish at TDC on the combustion stroke is of little advantage too because the blow is directed to the unburnt fraction. its not until there is a reaction is turbulence of much use. Blowing fresh mixture into a flame is far better than blowing into an unburnt zone and stirring it up to wait for the flame to get there.

These basic reasons (and a lot more) are why engines loose combustion efficiency as the RPM's increase. Years ago I did a substantial development program on 2 strokes and once I'd done some other things with fuel control it enabled me to keep increasing the compression ratio. As we did so the HP RPM moved higher in step with the compression ratio changes. One ratio of compression moved it 1000RPM higher. It kept that relationship all the way to 21:1@21,000 RPM where we stopped, because the engine made too much power for the metallurgy and parts wore out in 2 minutes. Ive done similar less dramatic results on 4 stroke engines. I've even done it to stock cam engines where Ive run 17.5 compression and they rev much higher each time you increase compression. Compression isnt just about detonation avoidance, its about matching the fuel suitability and the control methods of the fuel to the engines RPM range, BUT doing it in step with the head flow etc. High or low compression WITHOUT sufficient turbulence in the right places results in detonation.
Detonation in small amounts causes vibrating flywheels.


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 Post subject: Re: Engine upgrade
 Post Posted: Mon May 07, 2012 9:30 am 
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shrinker wrote:
The vibrations shaking the flywheel are from poor combustion. Ive seen it a few times, engines with poor combustion spark the starters etc on engine dynos...

...Thats just how I see it so please dont take offense. I think your engine could be made to be quite good but I fear its going to be a long road of tuning.


You do realize I was talking about the flywheel on the end of the dyno brake. The gouged place in the flywheel ring gear was closer to the inside of the inner diameter of the flywheel than the starter gear could reach so we determined it couldn't be from the starter engaging, it had to somehow be the flywheel moving away from center. It's a little hard for me to describe. I talked to Lynn this morning and he said the engine felt awful good to him for something like that to be going on. He said it felt very smooth and he said he's had engines that were just a little out of balance and he could feel and hear the difference. I realize you're talking about a different kind of vibration but wouldn't it have a similar affect? Is there some way of verifying this is what is happening?

shrinker wrote:
As for dyno correction factors etc either obtain or work out the actual power produced. Thats what your engine really makes and its what it races with. Ive used depac dynos, there no different to any other. Anyone who claims their dyno is 6% different to other dynos is playing games. In any case correction factors are only accurate to a maximum of 4% correction. Recently the SAE altered the maximum deviation for atmosphere accuracy limit to a larger amount, something like 6% to 8% I think, and they introduced other standards to appease manufacturers basically. I grown suspicious of correction factors over the years, they correct for crankshaft inertia, friction losses, etc its all rubbish. How the hell can you correct for crankshaft inertia when it has to be there/ Its part of the natural order of things. Its annoying. So I look at measured power now days and dont care about correction. The combustion that happens in certain types of combos varies according to different weather factors whereas the correction system just assumes every engine reacts the same, well they dont. Sorry for ranting.


I may not be stating this properly. He said the numbers are corrected to certain atmospheric conditions and the old SAE (I think) standard was something like 29.9 and the more realistic standard is 29.32 or something like that. I understand this is to give a standard because different elevations and other weather conditions will change performance.

I try explaining to the best of my limited ability to Lynn some of the stuff you are telling me here and he said he had never heard of this and it sure makes him feel dumb. I told him to join the club. Thanks for the input.

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Last edited by gearhead1011 on Mon May 07, 2012 10:43 am, edited 1 time in total.

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 Post subject: Re: Engine upgrade
 Post Posted: Mon May 07, 2012 10:02 am 
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It sucks you couldn't see the difference between fuels or get some good pulls. But I guess you like the 800 number O:) \:D/ \:D/ \:D/

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 Post subject: Re: Engine upgrade
 Post Posted: Mon May 07, 2012 5:11 pm 
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All flywheels react the same when subjected to vibrations. It doesn't matter where the flywheel is unless its separated by long enough shafting to dampen or rubber etc. Flywheels bend, flex, distort etc. Flywheels store energy and when the energy is input erratically many harmonic vibrations are setup inside the wheel and it distorts the wheel.

When I said detonation I'm using it as a general term, its a word instantly understood by most people. It's too hard to describe erratic combustion, its a very random event. Detonation occurs on many levels, you can detonate just around the sparkplug and not elsewhere in an engine. Mild detonation sends out a shock wave that permeates all the way through a drive line it causes speed sensitive vibrations that people often chase for years by getting drive-shaft's balanced etc. It snaps high tensile steels at torque loads that should be handled. A Mild detonation shock-wave in the cylinder is not always a bad thing for the combustion, you've heard of the term detonation limited engine, well that's just a combo where the detonation has gone too far so that its destructive but think of it backwards like this---before detonation is destructive it was increasing the power of the engine. The detonation wave actually adds energy fast enough to molecules that are ahead of the reaction zone to better prepare them for reaction. The detonation wave travels at the sonic speed of the mixture not at the very slow flame growth rate. The trick in engine tuning is to be able to recognize when an engine is burning this way, the first sign is flywheel troubles or harmonic balancer issues or even just watching the belts on the front of the engine. Then once you've recognized it figure out how to fix it. Doing this little emoticon helps ](*,)
Of course in cylinder pressure equipment can detect mild detonation but so can an Innovate Wideband setup. Its not going to do it with a single sensor in a collector you have to have one sensor in each primary pipe, then the speed of the Innovate gear comes to the fore. Its shown me this form of detonation in cylinder and helped me a lot.
Race engine are actually very strong engines with components capable of handling mild detonation pressure pulses. They cant handle full on detonation of course but beneficial detonation is no trouble. However detonation is never a correct thing to do on purpose, an engine will make more power by redesigning whatever it is causing the mild detonation.


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 Post subject: Re: Engine upgrade
 Post Posted: Mon May 07, 2012 5:15 pm 
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Chuck,

How many inches did this engine end up being?

Dog

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 Post subject: Re: Engine upgrade
 Post Posted: Tue May 08, 2012 6:58 am 
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shrinker wrote:
All flywheels react the same when subjected to vibrations. It doesn't matter where the flywheel is unless its separated by long enough shafting to dampen or rubber etc.


This dyno has a coupler that attaches to the crankshaft with a driveshaft that is about 2 ft. long that connects it to the brake. The engine flywheel isn't used.


want-a-be wrote:
Chuck,

How many inches did this engine end up being?


436

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 Post subject: Re: Engine upgrade
 Post Posted: Tue May 08, 2012 7:23 am 
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Well these something broke on the dyno then.


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 Post subject: Re: Engine upgrade
 Post Posted: Tue May 08, 2012 7:31 am 
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A good inquiry to make would be to find out what the dyno does with the next engine on it at 7500 RPM.


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 Post subject: Re: Engine upgrade
 Post Posted: Tue May 08, 2012 9:08 am 
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shrinker wrote:
Well these something broke on the dyno then.

He said he would let me know what he found out when he got it looked at.

shrinker wrote:
A good inquiry to make would be to find out what the dyno does with the next engine on it at 7500 RPM.

I was left with the impression that there wouldn't be another engine on the dyno until he found the problem.

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 Post subject: Re: Engine upgrade
 Post Posted: Tue May 08, 2012 9:40 am 
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Overall Nice Job Chuck...It will put a smile on your face when you get that 1st
time slip ;-) ...Keep us informed!!!



Shrinker, I think you had said that you run Fords so what is that perfect combination or piston dome,chamber size,cam size duration,lift,stroke and rod length that you have found that has the best combustion burn???

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 Post subject: Re: Engine upgrade
 Post Posted: Tue May 08, 2012 3:56 pm 
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Beretta wrote:
Shrinker, I think you had said that you run Fords so what is that perfect combination or piston dome,chamber size,cam size duration,lift,stroke and rod length that you have found that has the best combustion burn???
I tune anything and the answer to the life the universe and everything is-------------


BMW.


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 Post subject: Re: Engine upgrade
 Post Posted: Tue May 08, 2012 3:57 pm 
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What????????

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 Post subject: Re: Engine upgrade
 Post Posted: Tue May 08, 2012 4:00 pm 
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If you want to know how or why something, anything, on any form of car is done best a certain way then go look at a BMW and figure out why they did the compromises they did on a certain model or figure out why they designed the physics that way.


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 Post subject: Re: Engine upgrade
 Post Posted: Tue May 08, 2012 4:03 pm 
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Your not answering my question..It seem that you always find a issue with our home built bracket motors. But never seem to tell how to fix them or how you have built your engines to preform so well??
I am not being a smart a$$ just need to here it from you "why"

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