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Old 08-21-2007, 07:01 PM   #17
Mark C.
Scooby Newbie
Member#: 157244
Join Date: Aug 2007
Location: Florida

Originally Posted by japslapr View Post
This is exactly why I was asking. I figured that displacement was going to be my limiting factor. All I've ever heard about as far as getting the motor to rev higher is shims and oil... never anything else so I was wondering why I just can't spin it a bit higher. I obviously didn't think about nor consider most of these other factors. I'm actually running a stock exhaust header right now... stock intake manifold (rotated)... So how do I play this out? Get the car on the dyno and see if it's continuing to make power as it approaches 8k? I had a 7cm Green and new that it would be well choked up before 8k. The SZ55 should have more room... but how much more? Will it be restrictive as well? I am NOT trying to destroy this motor so there is certainly a "for safety's sake" here.
Well I tell you what, EJ engines have a big bore and a decent head. They make alright power although from what I've seen they run relatively low timing numbers which hurts them. (I'm assuming it's for safety sake though so it's necessary).

The comments about shims and oil are absolutely worthy of mentioning, and honestly they are more important than everything I listed above because they have to do with the engine actually living...most of what I was discussing is just suiting the powerband.

There are many things to consider in terms of reliability and even oiling just past using a 12mm pump and keeping pressure high. There are things like bearing velocity at high rpm (the larger the journal, the more you're at risk in that regard), the oiling of the crank itself - dependant on the angles and radii of the crank's oiling holes, at a point it would actually be possible for the oil flow to slow, and potentially even start moving backwards due to centrifugal force.

As for the stock exhaust header, I haven't done any true testing on it in terms of backpressure at given power levels with given turbos, but it's most likely not going to be very efficient flow wise. If I were you I'd try to improve efficiency of the system before putting unnecessary stresses on the engine. You have to look at it this way, if you have a restrictive exhaust/turbine system, the burnt mixture has a harder time clearing the cylinder. What this does is effectively lower your dynamic compression ratio - which means there is less fresh air getting into the cylinder - aka less power.

I don't know if you're doing this yourself, if you are - Godspeed...otherwise if your shop REALLY understands how an engine works, they will be able to explain this to you. Sadly those shops are few and far between.

One word of advice though...don't make things too complicated if this is a street car, sometimes simple is faster, and it's more reliable almost always. I'm basically having an engineering discussion with you and these aspects usually would only need to be looked at if you were getting into a very competitive race class.
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