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      03-31-2013, 07:47 PM   #133

Drives: N54
Join Date: Aug 2012
Location: USA

iTrader: (0)

Originally Posted by V8bait View Post
Yes, with increased VE, no matter how you accomplish it, you get more air/fuel into the cylinder. But this is a twofold event you are talking about with a larger turbo here in relation to power and heat. Part of the reason you are getting more air/fuel into the engine, is because you are removing more spent gas (and heat) from the engine (you know this very well from your singles great performance on pump even with the same boost/IAT's, due to increased exhaust flow/scavenging). Less volume taken up by old, used gas, more taken up by fresh, cool gas. In fact, from this standpoint alone you can also argue that thermal management (such as octane requirements and water injection) is easier on high VE engines, because spent gas really only serves the purpose of heating up the incoming air, which forces you to reduce timing to prevent knock, and thus increases EGT due to deviating from MBT.

I see what you are saying here though. More air/fuel in a cylinder gives you more potential energy during the combustion event, and this energy must be dealt with somehow. You've made this point throughout the thread and it's critical no doubt. Just remember, that the total (in essence) EGT is a sum of heat leftover from the previous combustion event (decreases with higher VE) + wasted heat from current combustion event (which increases with VE), and that the ladder form is the least destructive to the engine when due to retarded timing. Now if you want to look at it from a turbo life expectancy well there's really no argument there (heat and pressure as you say), but this is looking at safe power for the engine IIRC.

EGT is a number. How it's generated, and thus the analysis, is key for engine life. Some things, like turbo's, O2's, etc really only care about the number, but not everything is about the turbo. On your ST, I would presume EGT plays a much larger role due to the O2 placement and closed loop nature of things. But for this build, EGT is more just a stress for the turbines in this regard.

My $0.02c