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Read the postscript I added to my post for more about the why for aspects while you were posting. Ed |
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You are missing some things that are important here Anthony and confusing others.
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The products of combustion take up more space than the fuel and air components prior to oxidization (ignition). The increased volume attributable to the combustion process at high pressure, push on the piston which is part of a crank slider mechanism that translates linear motion into rotary motion. Quote:
Intuitively the natural instinct is if a little is good more is better. That is true to a point. The point is once you have burnt all of the fuel and air as fast as possible without detonation. Further increasing compression at this point does not increase power output. What it does do is introduce detonation which saps power and destroys parts. Once you have burnt all the fuel /air in the chamber by 7 to 10 degrees ATDC you have done all that is possible to do. Quote:
This is why when you run any of the ethanol fuels while you can produce good power you can not produce the economy of the gasoline fueled equivalent engine. The ethanol fuel's energy content is just lower. All the other stuff is just interesting window dressing. Quote:
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Lower octane fuel can have a higher energy content. The problem is burning the entire volume of combustible fuel in time to maximize the pressure on the piston crown between 7 to 10 degrees ATDC. The fuel can not burn fast enough without detonating to produce the maximum down force on the piston between 7 and 10 degrees ATDC. The burn rate of the high octane fuel is actually slower and more manageable than that of the lower octane fuel. By choosing the proper ignition point it is possible to optimize the down force on the piston between 7 and 10 degrees ATDC at a much higher level than with the lower octane fuel. All the energy conversion, energy conversion efficiency, heat content etc. terminology sounds good but is being misused and is not informative nor helpful in describing or understanding the processes occurring in the combustion chamber. Quote:
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If UHF TV's were around when you were growing up you will remember they had two tuning dials. Essentially a coarse and a fine adjustment. You would get the channel with the coarse adjustment and fine tune its video quality with the fine adjustment. What you are talking about are the equivalent fine tuning controls on the engine and they should not be confused with the big dial that brings the horsepower. Ed |
A few more factoids for the inquiring minds.
It appears that they have a engine building company (Willis Performance Enterprises) that is offering these engines in completed form for sale to enthusiasts. This is their website => WillisEngines.com Joyridin's sharp eyes caught the C16 fuel annotation on the Dyno chart. For those that missed it here it is again; https://www.willisengines.com/upload...-data_orig.png Although they have a provision for a description of the blown version of the engine on their website, it is not yet populated with any data. When you review the piston offerings on their site for the engine, the do have a 10:1 c/r offering. This would argue for joyridin's suspicions about a 10:1 c/r offering for the blown version the engine. Ed |
I contacted Brian Wolfe to get an answer to the compression ratio question because it was an itch that needed scratching. His answers were interesting.
The blown version of the engine does in fact run 12.5:1 compression with C16 fuel. To avoid detonation they back the timing down to a "safe" number but, you really do have a 12.5:1 c/r in a Whipple blown Godzilla. This approach is similar to what John Mihovitz started doing a number of years ago in Modmotors. John ran high compression (only about 10:1 at that time not 12.5:1) and pulled timing (or added timing depending on your point of view) until he found the engine's knock threshold. John got some fairly impressive power numbers out of the engine, 962 hp at 7000 rpm — from 281 inches. The engine definitely wasn't a wimp. John used 18 psi of boost (2.2 BAR) intercooled and 10:1 c/r for an effective c/r of 22:1. Because of a late closing intake valve (for upper rpm performance) the dynamic compression was closer to 8.5 to 9 to 1. Making the effective c/r 18.5 to 19:1. John ran C16 fuel like Brian does. The lower compression build model will be easier on engine parts, especially if the engine is street driven. High ambient air temps and high engine temps can encourage detonation. It appears Brian Wolfe pursued a similar build model with his Godzilla. I need to give him a fairly significant attaboy for the success he has had with the build. However, it is important to recognize that while he used C16, which didn't hurt his performance, if you use any of the many varieties of pump gas available today, you will need to exercise a bit more caution because of the lower octane fuel's predisposition to detonate My personal preference is still the 9:1 c/r solution particularly with a 93 octane grade of gas. Fuel becomes dramatically less expensive, readily available, and capable of quite stunning power levels. While the following statement is true of almost any supercharged engine, if you experience a whoops on a high c/r blower motor it is much more devastating than a whoops on a lower compression equivalent engine. The trick (if that is the right word) to getting the high c/r engine to live and work is using just enough timing that the fuel air mixture has fully or nearly fully burned by that 7 to 10 degree window ATDC. Too much spark and the cylinder pressure rises too soon occurring "in front of" the target 7 to 10 degree window ATDC. Too little timing will have the max pressure point occurring after the target 7 to 10 degree window ATDC. Either way it will cost you power. One way to will cost you parts also. Experimentation will be necessary to find that optimum ignition timing for that 7 to 10 degree ATDC window. Ed p.s. The high compression and reduced timing window size changes and moves around as rpm and load change so a programable EFI system is necessary to "follow" that optimal timing window as it moves around throughout the rpm range. |
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