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, Tue, 30 Jan 2007 14:34:02
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It's a combination of both.
Primarily it is simple pressure physics -
On a turbocharger, the less pressure after the exhaust turbine, the more the pressure drop from the exhaust port past the turbine to the outlet - the exhaust spins faster, thus the intake spins faster (and the feedback effect creates runaway until the wastegate opens) Thus a larger exahust on a turbo (up to the point of a fully open exit) will always allow the turbo to pump better.
In the case of a full open (no exhaust) there can be some unique pressure problems to solve dumping straight to atmosphere, but in physics the simple answer is always the best, and in this case it involves the engine management system on the car - it literally can't handle an open exhaust! I ran it once that way myself and noticed the same thing. dropping the post cat it ran great, but dropping it all it seemed to be suffering - it wasn't as loud as no exhaust on a V8 (because the turbo partly quiets the exhaust) but the spool was still limited - the computer couldn't keep up and was dialing back the timing and boost and it was off the maps.
Why would I think that? I've dealt with turbos for a long time on early CPU and non-ECU cars - one good example is a rotary turbo (RX7) - the hard pulses from an open port are much more violent than a slow opening valve, and the turbos on that car spin up fast - when I ran one of those with no exhaust (AND with an old carburator) it would spin the tires in three gears as the boost gauge slapped the needle hard. I also ran a 63 corvair (sidedraft carb) and no exhaust - being an OLD turbo it still had lag even with no muffler (the pipe out has a dent in it to clear the spare tire!) but it still ran quickest (and ate the most gas...)
So the twofold answer is that you're just tweaking for more power, but still have to stay in the ballpark. Just like steroids cause problems because the system wasn't designed around them the same applies to your car - that's why racing cars that are designed around only high rpm operation would be dogs on the street if they carried the weight a normal car did.
So keep your good sounding exhaust on (and the cops off your back! - ever noticed how slow a harley is with no weight but all that noise! No backpressure means less torque on those motors than an equivalent japanese or german motorcycle... all show and no go)
posted by 70.244.20...
, Tue, 30 Jan 2007 14:34:02
, Thu, 1 Feb 2007 20:02:39, Fri, 2 Feb 2007 16:00:05, Fri, 2 Feb 2007 12:00:27
, Sun, 4 Feb 2007 13:50:18, Fri, 2 Feb 2007 12:18:40, Fri, 2 Feb 2007 07:44:17, Wed, 31 Jan 2007 11:46:12, Wed, 31 Jan 2007 12:36:21, Wed, 31 Jan 2007 12:23:24, Wed, 31 Jan 2007 17:23:55, Wed, 31 Jan 2007 19:47:44, Thu, 1 Feb 2007 13:01:29, Thu, 1 Feb 2007 10:08:02, Thu, 1 Feb 2007 08:53:29
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