FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: Qikbbstang on June 09, 2012, 09:31:36 PM
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On my first engine powered anything I intalled a cast-iron wrap-the-rope around the pulley on the flywheel of a Briggs and Stratton off a reel mower on to my bicycle Never forget one day riding around the potato fields I cam across a junk pile. There was a steel tapered table leg and I laughingly slipped it over the muffler where it fit tight. Firing it up, it made a hilarious ping ping ping exhaust noise, there was about a 1/8" drain hole for all the exhaust to exit. Of course, laughing I tried riding it and surprisingly found it had gained low end power, it would now idle up steep hills with ease and could not be stalled at low rpm, something that it never could do before. The pipe destroyed any kind of higher revs and was discarded.
There was a discussion on another forum on this subject and someone mentioned his installing Flowmasters on his late model F150 had killed low end and mid-range especially when trailer pulling. Given that almost any cam has overlap and the racier the cam, generally the more overlap hence more rumpty rump the idle. So I'm wondering IF the back pressure were increased significantly could it effectively knock off or tame down the effects of the overlap and allow the motor with overlap to make more low end power, perhaps smooth out the idle etc? ................I know your dyno is not happy at low rpm and this would really be low rpm but any chance you might try to see what a really restricted exhaust does way down low to a mild or aggressive motor at part thgrottle? ...................... That said possibly a butterfly valve could be installed to back pressure up a motor and make it perform better really low, putting around town etc.
I reiterate if this would ever work the exhaust needs to be literally strangled, scavenging is not even on the menue.... Obviously it is not for anything over 1,000-1,500 because IF it breaths beyond that then the exhaust (closed down) is not restrictive enough. If it works on idle then perhaps it can be expanded to lets say restrict flow add backpressure at 2,500rpm on a 7,000-8,000rpm motor.
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Just a hunch ;) but I would say a more restrictive exhaust would dilute the mixture more due to lack of scavenging and make overlap cause an even more lean mixture
Exhaust can't burn twice
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It's not about restriction, it's about tuning the length and diameter of the exhaust.
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Some excellent reading:
http://reocities.com/MotorCity/track/6992/vizard.html
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It's not about restriction, it's about tuning the length and diameter of the exhaust.
Exactly, and I am not sure I buy these stories about guys losing power with cat-backs.
The most influential part of the exhaust is the primary pipe, then comes the collector. A muffler being too free flowing really doesn't add up to killing low end power.
More than likely, during install they did something to confuse the computer.
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Interesting reading Rcodecj
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Backpressure can generally be good for low-end torque. Because the exhaust doesn't escape as rapidly, more expansion occurs inside the cylinder and the average cylinder pressure is a bit higher.
As revs go up, that benefit is lost. Leftover exhaust starts piling up in the cylinder and dilutes the intake charge. At high engine speeds it's a game of how many buckets of air you can get through the engine in a given time.
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The thing to be concerned with is exhaust velocity. If you have the primary and secondary pipe diameter and length correct, you will have optimum exhaust velocity.
If you do that with zero restriction, that would be best. I think the confusion comes when let's say you use too large of a pipe and lose velocity and back pressure at the same time. The loss of power is blamed on not enough back pressure when really the velocity was compromised. Two different things and just my opinion.
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There is some engine of some kind that
have variable exhaust ports that i have
been involved in somehow but i dont
remember wich.I have had two strokes
so much of my memory is gone
But something say me it was a German
engine and it was big and old.......
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I believe BB is referring to my post on the FE Forum. Both my '99 F150 with 4.6 and Dodge Ram with 5.9 had single catback exhaust installed using 3" pipe and Flowmaster 40's I believe. Both lost bottom end after the conversion. It was very noticeable.
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Some excellent reading:
http://reocities.com/MotorCity/track/6992/vizard.html
Excellent indeed.... except page 5 is missing..
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Some excellent reading:
http://reocities.com/MotorCity/track/6992/vizard.html
Excellent indeed.... except page 5 is missing..
bitch, bitch bitch, :) just kidding, I think this is the same as the magazine article I have, but I can't find it at this time. It's a little easier to read.
http://www.superchevy.com/technical/engines_drivetrain/exhaust/0505phr_exh/viewall.html
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Some excellent reading:
http://reocities.com/MotorCity/track/6992/vizard.html
Excellent indeed.... except page 5 is missing..
bitch, bitch bitch, :) just kidding, I think this is the same as the magazine article I have, but I can't find it at this time. It's a little easier to read.
http://www.superchevy.com/technical/engines_drivetrain/exhaust/0505phr_exh/viewall.html
Hey man, I just learned to read last week, cut me some slack! ;) I vaguely remember this article but it's certainly worth a re-read. Thanks!