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Quote:

Originally Posted by Jackknife

So, are you saying that a boosted car benefits from a little "back-pressure"?

Jackknife

There is always going to be a pressure differential between intake and exhaust, even when not using any output from the turbo or s/c as they are always spinning. (a turbo less connected than a beltdriven s/c) The unit's boost is generally a measurement of the increase of this pressure differential. Without changing pulleys you cannot cause a s/c to overspin while operating, it has a designed in max rpm, regardless of what you do up or downstream. A turbo on the other hand will spin as fast as the exhaust gas can cause it to go, if you remove restriction you can potentially see the turbo run too fast for its own good. A littl ebackpressure helps moderate teh output for street driving.

Just like when we talk of adding 14.7 psi boost, we always ignore the fact that at sea level we already have 14.7 psi in the air around us. And thus a reason that unless tuned for the Denver or higher altitudes, a boosted vehicle, while exceeding the performance of a non-boosted vehicle in the mountains, will fall short of its sea level output. A turbo's max output is regulated by not only size of the unit, location in the stream, wastegate operation, but also downstream restrictions in the exhaust. Eliminate restrictions downstream from the turbo outflow (which is basically exhaust) and you will raise hp. Keep the wastegate shut longer and you also will raise hp. "Real" racecars don't run mufflers or CATS, nor do they use airboxes, just velocity stacks. Less retrictions at both ends, but if they didn't build more strength into the engines themselves they would blow up more often. There is a margin of safety in the design of the ecotec that allows for a certain level of higher output prior to "building" the engine. There is a GM book on it and somewhere on this forum a link to it. An ecotec can easily (with enough $$$) be built to spit out in the neighborhood of 900 hp, IIRC. Will a 2.4 boosted to ahigher output than a LNF be as durable and reliable over time? Possibly not, but that's the risk you take when you mod.

__________________
When more than one friend wants to ride shotgun

No, I do not work for GM,
but if I did, the G8 ST would not be DOA!

	achieftain Moderator Join Date: Jul 2004 Location: turning right to go left	Quote: Originally Posted by Jackknife So, are you saying that a boosted car benefits from a little "back-pressure"? Jackknife There is always going to be a pressure differential between intake and exhaust, even when not using any output from the turbo or s/c as they are always spinning. (a turbo less connected than a beltdriven s/c) The unit's boost is generally a measurement of the increase of this pressure differential. Without changing pulleys you cannot cause a s/c to overspin while operating, it has a designed in max rpm, regardless of what you do up or downstream. A turbo on the other hand will spin as fast as the exhaust gas can cause it to go, if you remove restriction you can potentially see the turbo run too fast for its own good. A littl ebackpressure helps moderate teh output for street driving. Just like when we talk of adding 14.7 psi boost, we always ignore the fact that at sea level we already have 14.7 psi in the air around us. And thus a reason that unless tuned for the Denver or higher altitudes, a boosted vehicle, while exceeding the performance of a non-boosted vehicle in the mountains, will fall short of its sea level output. A turbo's max output is regulated by not only size of the unit, location in the stream, wastegate operation, but also downstream restrictions in the exhaust. Eliminate restrictions downstream from the turbo outflow (which is basically exhaust) and you will raise hp. Keep the wastegate shut longer and you also will raise hp. "Real" racecars don't run mufflers or CATS, nor do they use airboxes, just velocity stacks. Less retrictions at both ends, but if they didn't build more strength into the engines themselves they would blow up more often. There is a margin of safety in the design of the ecotec that allows for a certain level of higher output prior to "building" the engine. There is a GM book on it and somewhere on this forum a link to it. An ecotec can easily (with enough $$$) be built to spit out in the neighborhood of 900 hp, IIRC. Will a 2.4 boosted to ahigher output than a LNF be as durable and reliable over time? Possibly not, but that's the risk you take when you mod. __________________ When more than one friend wants to ride shotgun No, I do not work for GM, but if I did, the G8 ST would not be DOA!