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Old 08-21-2007, 07:58 PM   #19
Mark C.
Scooby Newbie
Member#: 157244
Join Date: Aug 2007
Location: Florida

Originally Posted by Homemade WRX View Post
relatively low timing numbers is actually beneficial so long as you have the heat (i.e. pressure) to make a complete burn (100% never happens though)...constant volume combustion is a wonderful thing and actually makes for higher bmep as less imep is lost with advanced timing (lots with rod ratio and bore sizing here too).
Yes, both intake and exhaust manifolds as well as port design and cam design all need to be addressed in a high revving build. Bore size also should be addressed too. Instaneous piston speeds and accelerations should be known to design your cam so those are already considered in this case.

with those rpms don't forget you get into the nitty gritty of individual cam lob timing if you really want to make peak power...that crankshaft does twist and an events "real" timing

then of course you have the quench height/rod stretch issue to work out too.
I absolutely agree that low timing is beneficial if you were getting that '100 percent' burn we are always looking comment was more directed towards the fact that from what I have seen, these engines use comparatively low timing numbers compared to what you would normally see on a nearly 4" bore. As you obviously know, it takes a certain amount of time for the flame front to make it to the edge of the bore. This amount of time increases with cylinder pressure, higher octane, etc.

Maybe I haven't seen enough examples of high powered EJ engines, this is very possible.

I must admit though, I'm not sure that I completely understand what you saying with BMEP and IMEP. I think you are referencing the optimal 100 percent combustion which (obviously) has a higher BMEP. In reference to you saying less IMEP is lost with advanced timing, of course that's true since IMEP is simply an average of the cylinder pressure through a cycle of the piston. The sooner you light off the plug, the quicker the pressure is ramping up. If I misunderstood you, I apologize.

BMEP is really what anyone is after since it's simply a rating of how efficiently an engine is producing torque. The question is how long does the engine live if you give it that high BMEP.
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