cylinder pressure February 04, 2010 01:49PM
wondering if you are better off to build cylinder pressure with compression ratio or camshaft thanks for imput
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Re: cylinder pressure February 04, 2010 11:33PM
Interesting discussion - not quite the same topic, but it relates:
http://www.forumromanum.com/member/forum/entry_ubb.user_436568.1195344536.1106171452.1106171452.1.how_much_compression-tractor_pulling_tech.html


Floating Finish - the German Tractor Pulling Web Show and EU Live Streams: [www.youtube.com]
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Re: cylinder pressure February 04, 2010 11:47PM
Did you ever find out who that guy was? Probably the most concise and the best explained technical article I have read on these boards ever.
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Re: cylinder pressure February 05, 2010 03:01AM
Hi Patrice!
Yes, I did. Performance engines and heads are his daily buisiness...Not only for pulling but "asphalt race tracks", too. He for sure knows what he is talking about.


Floating Finish - the German Tractor Pulling Web Show and EU Live Streams: [www.youtube.com]
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Re: cylinder pressure February 05, 2010 01:54AM
That is very interesting! I'd like to know how it realtes to diesels since detonation isn't as much of an issue with diesels.
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Re: cylinder pressure February 05, 2010 04:44AM
For a more simpler version it can be stated as this:

Whether boost pressure or static CR increases are used to gain, they both come close to same effect of increasing peak cylinder pressures.

Boost pressure increases the mass air flow rate and provides a denser charge which gradually builds cylinder pressure through the compression stroke.

A static CR increase stresses the rods/pistons by spiking the peak cylinder pressure at the top of the stroke.
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Re: cylinder pressure February 05, 2010 09:09AM
what about connecting rod length is shorter or longer better thanks
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Re: cylinder pressure February 05, 2010 11:04AM
A long rod will hold the piston at TDC or increase the dwell time. In the previous message Sascha posted the link to, the benificial effect was piston dwell. A long rod will help produce this result also. During combustion, the ideal situation is to have a complete entrainment (right word) of the entire mixture and convert all fuel and gasses to heat/pressure. If the piston moves down to quickly, the flame is quenched by the head and cylinder walls. With a slower moving piston at TDC, less advance is needed (at least with spark ignition engines).

In any situation, it is best to use the longest rod you can, provided you don't have to move away from your ideal bore and stroke. Most engines will make more power with a deck plate adding 1 inch between the block and head and one inch longer rod than standard deck heights and 1 inch shorter rod, stroke remaining the same and the extra rod length/weight has little effect on peak rpm limits due to tension loading of the rods.
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Re: cylinder pressure February 07, 2010 03:08PM
It's been 15 years since I did this analysis so my memory is a little fuzzy about the exact crank angles, but I used a spreadsheet to compare rod/crank angles & the torque produced by a long rod vs short rod. As Debaard mentions not much work is done near TDC becasue the angles are terrible. By 45 deg the long rod is moving the piston faster (makes sense since they have to end up at the same point @ 90°). Anyway I assumed a constant burn rate (mass of exhaust created) to keep things simple & used the same rate for both. The long rod did not make significanlty more torque. Maybe using the same burn rate isn't realistic - will the higher pressures near TDC increase the burn rate? As CoersDzl mentioned the side loading was decreased which would result in reduced friction losses.
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Re: cylinder pressure February 05, 2010 11:09AM
Longer, however the gains are minimal in comparison. A longer rod will create less cylinder wall friction since there is less sideways force through the piston.
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Re: cylinder pressure February 05, 2010 02:39PM
do you think there is less tourqe with a longer rod producing less rod angle to help swing the crankshaft
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