a technical discussion, engine efficiency |
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a technical discussion, engine efficiency |
r_towle |
Aug 15 2005, 08:27 PM
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#1
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Custom Member Group: Members Posts: 24,624 Joined: 9-January 03 From: Taxachusetts Member No.: 124 Region Association: North East States |
so, I have been thinking (not always a good thing)
If an engine is basically an air pump, and the objective is to make it as close to 100 percent efficient, why is the exhaust valve so much smaller than the intake valve? Forget emmisions, forget fuel delivery, just want to understand why this is so...it is so on most engines... Rich |
lapuwali |
Aug 18 2005, 08:21 PM
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#2
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Not another one! Group: Benefactors Posts: 4,526 Joined: 1-March 04 From: San Mateo, CA Member No.: 1,743 |
Bondo, you're correct up to a point. A given L-Jet system WILL max out if you increase the power of the engine enough. Higher fuel pressure and/or bigger injectors will mean more fuel ALL of the time, even when you don't need it, which usually means running rich a low loads. There's a calibration curve of airflow to injector flow, which is basically tied to the size of the injectors and the fuel pressure, and this curve is built into the ECU. So, at some point, you'd need to recalibrate the ECU AND fit bigger injectors. You'd also have to fit a bigger airflow meter, so the easiest route is to just get a complete setup from a bigger engine and use that instead.
However, you have to pump the engine up quite a ways to hit this point. I've seen 150hp engines be served by their stock L-Jet systems up to 200hp after cam, exhaust, and compression changes, so at least for those systems, a 30% increase in power can be handled. How far the 1.8 L-Jet system can go, I have no idea, though I'd expect it to be pretty high. FIAT used L-Jet on the very last 124 Spyders, and US dealers offered turbo setups that only consisted of the turbo and plumbing. 80-ish hp to 120-ish hp, or a 50% increase, without touching the L-Jet. |
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