QUIZ: What is the lowest possible compression ratio?
12-01-2001, 04:49 PM
#1
Race Director
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QUIZ: What is the lowest possible compression ratio?
Pretend you are back in school, and, for the final exam, you have to build an engine (a Briggs and Stratton will do) with an absurdly low compression ratio. The lowest ratio gets the highest grade. It has to run for at least 5 minutes without stalling or tinkering with it.
How low can you go, and why?
How low can you go, and why?
12-01-2001, 05:17 PM
#2
Race Director
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Re: QUIZ: What is the lowest possible compression ratio? (drives61)
i wouldnt go under 6 or 7 but might keep it at 8... dont ask why those are just cool numbers...
I think that there is probably a compression where the gas burns slower and the flame pattern is to slow for the cam... i guess that would be a pretty cool project, i think that the head gasket would blow if you shimmed it that high though.
good question i'd like to know the answer also.
ZD
I think that there is probably a compression where the gas burns slower and the flame pattern is to slow for the cam... i guess that would be a pretty cool project, i think that the head gasket would blow if you shimmed it that high though.
good question i'd like to know the answer also.
ZD
12-01-2001, 06:27 PM
#4
Le Mans Master
Re: QUIZ: What is the lowest possible compression ratio? (73Ken73)
This sounds like a question for Thud....better post it in Off Topic. :D
AC
AC
12-01-2001, 06:45 PM
#6
Burning Brakes
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Re: QUIZ: What is the lowest possible compression ratio? (A C)
Well i think early ford V-8's had a compression of around 6.7:1, of course, they made only 80 horsepower, but that was cruisin for back then. I'm sure that depending on RPM range, you can get a smaller CR, say 4:1, but this will make the combustion last longer b/c it has a greater volume. Now w/ a hot spark, and modern tuning of injectors for duty-cycle and such. Now if you have Gasoline in a fine mist form, it is combustible in mid air through a lighter; self ignition i guess. 1:1 is not viable, b/c there would be no piston travel. Then again, you could boost it to 4.0 Bar. and probably run 3:1 compression because your dynamic compression would be significantly more. But anyhow. So to summarize, Definitely less than 6.7:1, Possibly 4:1, maybe less depending on circumstance.
12-01-2001, 09:21 PM
#8
Race Director
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Re: QUIZ: What is the lowest possible compression ratio?
thanks for all your responses!
while i have not attempted to actually find the answer, it would be a good project for students.
But, i will submit this evidence that compression is not needed; just an explosion to push the piston down:
How many times has a member put the distributor in 180 out, and complains that it runs but won't rev up? It is firing as the exhaust valve starts to close as it completes the exhaust stroke, yet there is a big enough bang to run the engine!...it is not on the compression stroke at all!!!! So i submit that compression is not needed..... Just don't try to drive it like that!
:lol:
while i have not attempted to actually find the answer, it would be a good project for students.
But, i will submit this evidence that compression is not needed; just an explosion to push the piston down:
How many times has a member put the distributor in 180 out, and complains that it runs but won't rev up? It is firing as the exhaust valve starts to close as it completes the exhaust stroke, yet there is a big enough bang to run the engine!...it is not on the compression stroke at all!!!! So i submit that compression is not needed..... Just don't try to drive it like that!
:lol:
