Newbie L30ET Build

[EvilC]

Gollum - thanks for the feedback. My understanding for the design I am going with starts from the pistons were given to me by Rags. Ok to make sense out of that statement, after reading threads going back almost 7 years - I am going with the P90 head for several reasons. The chamber design is key even though I am not maximizing its use but to me that use is during boost. The other L series heads I have looked at don't give me the CR I want on and off boost and for my HP goals. Granted this is my first engine build but I am going with my "feel by the pants" knowledge, theory and what I know works for this build. Like you said, it isn't a "bad" combo but my goal isn't to get everything out of the engine.

 

 

To pick up on the theory end of what you were saying as the air starts to act as a "fluid" and using the quench area to "push" the air out, if you had to guess what do you think the percentage would be for inefficiency or maybe to a guess to what hp is being lost or more likely not gained? Guess I can look at what the volumetric flow diffence would be with the piston 1mm down in the whole vs another 1mm up and a .3mm quench area. Again this would be just theory as different HG would play a differnce there also.

 

 

 

Chuckles, thanks.

[Gollum]

I think that given that you'll still be well under 9:1 compression you'll most likely be fine, even with the boost. You might have to back the timing out as much as 4-8 degrees under boost compared to an "ideal" setup, which at WOT under boost could be as much as a 5% power difference, or roughly 15hp at 300whp. That might not sound like much, but if that's roughly how much you were loosing, you have to remember that you'll be loosing much more down at the lower RPM. As RPM increases detonation becomes easier to avoid. Of course it's usually high RPM detonation that will blow an engine, but 9 times out of 10 that's from a bad tune that didn't account 100% for things like multiple pull temp increases.

 

Down low, where even a stock NA engine will ping with bad gas and too much timing you could be loosing potentially 15% of your power potential as compared to if you'd set it up tight. This would dramatically effect things like off throttle response, turbo spool, and general cruise characteristics.

 

The upside is that you're a full 1mm down, and you'll have a good 1mm+ of gasket with an OEM gasket, or at least .4mm of gasket with a felpro. Either way you're going to be at least 1.5mm down from the head, which means you'll probably be far enough to be out of the dangerous detonation zone. So your "flat top" piston should have detonation characteristics more like a dish piston in a sense. If you were exactly flat with the deck I'd be worried, as you'd be right in the middle of where you don't want to be. Close enough to cause detonation proneness at low RPM but without the quench to suppress it.

[Lazeum]

Since I'm the "quench story" as well. I believe it is important to tell that head gasket thickness should be checked. My personal experience shows me stock (Ishino) or Felpro are having a quite similar thickness.

Edited January 12, 2012 by Lazeum