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Everyone says high flow exhaust systems are good for horsepower but what happens when u have too little backpressure? How does that effect torque and low end performance? Also, how does someone know if this problem happens to their car? Any info would be great. THANKS! grin.gif" border="0

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I try to explain it this way. In general, reducing restriction (some people like the word 'backpressure') will improve engine performance, as long as the air/fuel ratio is enriched correspondingly. For instance, getting rid of the stock single exhaust and bolting on a dual 2.5" system with low restriction mufflers will be a nice improvement on a typical 350 or 455 car. Reducing exhaust restriction and ignoring the carb jetting and/or ignition timing can actually decrease performance, especially if a drastic change is made.<P>Even when the carb has been adjusted to work with a free-flowing exhaust, another problem some folks see is choosing headers with primary tubes too large for their application. Rather than talk of restriction, it's a little easier to understand that with larger diameter tubes, the exhast pulses move slower on their way out. Since exhaust scavenging is responsible for helping the intake of air/fuel during valve overlap, lower rpm performance can suffer from oversize tube diameters. That's why lots of folks have good results with 1-7/8" primary tubes for most applications.<P>Throw in a monster camshaft, 1150 cfm carb, high compression, single plane intake and better-flowing heads, and the 2" or 2 1/8" primary tubes start to work better. The idea is to choose headers that work well with other engine mods so that exhaust flow stays fast enough to do the job (better low speed performance) while still being unrestrictive enough to work well at high rpm too.<P>If you think your performance is suffering due to a free flowing exhaust system, try looking at carb jetting (increase enrichment) and experiment with ignition timing.<P>Tell us more about your engine/car!<P>Sorry for the lengthy reply.<P>Devon<p>[ 12-03-2001: Message edited by: 462 Wildcat ]

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Dear Devon,<BR> thanks for the info. Don't worry, I enjoyed the long reply. Now, you want to know about my car right. Here goes. It is a 1985 Buick LeSabre in almost perfect condition.(hence 85 2 NV on the license plate) The engine is the 307 olds 5.0. For the exhaust, huh, I have a hollow cat and a 40 series 2 chamber flowmaster muffler, all connected by 2-1/4" pipe. Exhaust mannifolds are stock. Other mods include an open air cleaner that houses a 14"x2" K&N filter charger. Next is a new 3 core radiator and a 160 degree thermostat. Finally, a 1" phenolic spacer under the carb. There are many more mods but I won't bore you with them. Not much more will be done to soup up this car because as soon as I save up the money, I will be looking for a 403 olds engine to replace my 307. However, I would like to get the old 307 to run to its fullest for the time being so any other tuning tips for my car would be helpful. Thanks again 426 wildcat! rolleyes.gif" border="0

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