Going Bigger Turbo....Any Suggestions?
I understand what you are talking about though. I see that higher compression results in more complete burn and higher egt. Thus creating the need to decrease ignition timing or add fuel to keep the burn cooler to maintain target egt. I'm not arguing the point of mechanical knock threashhold.
Higher compression equals more power per lb of boost (you said it yourself)
At high compression or low compression engine (at sea level) is already over 14 psi...without a turbo. This being said, a higher compression engine outputs more power per cc.
We just have to know the mechanical limit of out internals and keep that fu(king knock away.
Higher compression equals more power per lb of boost (you said it yourself)
At high compression or low compression engine (at sea level) is already over 14 psi...without a turbo. This being said, a higher compression engine outputs more power per cc.
We just have to know the mechanical limit of out internals and keep that fu(king knock away.
But there's also a limit to the other side of your curve that you "don't' have labelled, and that's the the peak value. If designed incorrectly, you may actually lower that peak value by hitting detonation first. You can get compression all kinds of ways, by decking the block and heads etc... or even a piston with a high compression height. And while it's mostly true that area under curve wins street races--mostly because people don't row through all the gears--the peak part of the curve can cause you a loss if too low. There are simulators for this if you're super into it. It can even tell you what kind of gearing will pair up with your curve and rpm limits.
If you're a street racer, you would look at your curve before deciding whether you want to start from a roll or from a dig. It's all math in the end. (I don't street race in my slow STI).
It's a gamble whether the increase in compression will allow you to make gains all over the curve. You could actually bring that ceiling lower by not being able to hit MBT before knock. Data on Nasioc seems to support this for a lot of high compression setups on pump gas.
This is when you have to look at the whole setup. Everyone says here "build it", which to me is meaningless. Actually it pisses me off, as do the terms conservative and aggressive. Imagine if Bran808 replaced your paint conservatively or installed your fender aggresively. What the hell does that mean? I have a dent in my car. Oh well "build it." I got punched in the face the other day, but the dude did it conservatively, so it's "safe." But my other friend heard that his friend got punched aggresively by another guy, so that's bad and dangerous. And well I heard from a reputable puncher that my aggressive bruise will be offset by conservative doctor's bill. Okay?
This is a claim and not a fact, but I'd bet that most of the intelligent high compression setups are running cams with a lot of overlap, and so their dynamic compression is moderate, while their static compression may be high. So what they did was make up the loss in dynamic compression from the cams by bumping up static compression. But on a stock cammed motor, you''ll probably end up lowering your curve if you go to high on compression (also a claim and not a fact), as the stroke on the 257 already necessitates high timing figures from the high piston speeds. And then when you lower the timing to compensate for the increase in compression ratio, you may not make up that difference (and may if it's designed correctly).
Last edited by reido; Jul 18, 2010 at 07:14 PM.
Thread
Thread Starter
Forum
Replies
Last Post
steen80
Sacramento & Reno
1
Dec 27, 2013 06:45 PM
Subaru AWD
Hawaii Classifieds
10
Oct 18, 2013 04:38 PM
modwrx
Engine/Power - EJ20T (pre-2006 WRX and JDM)
6
May 10, 2003 05:44 PM



sure

