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I was riding yesterday and met up with a Harley Guy.....Super nice, BTW.

I'm currently running Fuggin Mayhems with no baffles. This guy said he thought if there were baffles installed (creating some back pressure) the engine would make more power. Thoughts?
 

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I was riding yesterday and met up with a Harley Guy.....Super nice, BTW.

I'm currently running Fuggin Mayhems with no baffles. This guy said he thought if there were baffles installed (creating some back pressure) the engine would make more power. Thoughts?
Some say that "an engine needs back pressure to work correctly." Is this true?

No. It would be more correct to say, "a perfectly stock engine that cannot adjust its fuel delivery needs back pressure to work correctly." This idea is a myth. As with all myths, however, there is a hint of fact with this one. Particularly, some people equate back pressure with torque, and others fear that too little back pressure will lead to valve burning.

The first reason why people say "back pressure is good" is because they believe that increased back pressure by itself will increase torque, particularly with a stock exhaust manifold. Granted, some stock manifolds act somewhat like performance headers at low RPM, but these manifolds will exhibit poor performance at higher RPM. This, however does not automatically lead to the conclusion that back pressure produces more torque. The increase in torque is not due to back pressure, but to the effects of changes in fuel/air mixture, which will be described in more detail below.

The other reason why people say "back pressure is good" is because they hear that cars (or motorcycles) that have had performance exhaust work done to them would then go on to burn exhaust valves. Now, it is true that such valve burning has occurred as a result of the exhaust mods, but it isn't due merely to a lack of back pressure.

The internal combustion engine is a complex, dynamic collection of different systems working together to convert the stored power in gasoline into mechanical energy to push a car down the road. Anytime one of these systems are modified, that mod will also indirectly affect the other systems, as well.

Now, valve burning occurs as a result of a very lean-burning engine. In order to achieve a theoretical optimal combustion, an engine needs 14.7 parts of oxygen by mass to 1 part of gasoline (again, by mass). This is referred to as a stochiometric (chemically correct) mixture, and is commonly referred to as a 14.7:1 mix. If an engine burns with less oxygen present (13:1, 12:1, etc...), it is said to run rich. Conversely, if the engine runs with more oxygen present (16:1, 17:1, etc...), it is said to run lean. Today's engines are designed to run at 14.7:1 for normally cruising, with rich mixtures on acceleration or warm-up, and lean mixtures while decelerating.

Getting back to the discussion, the reason that exhaust valves burn is because the engine is burning lean. Normal engines will tolerate lean burning for a little bit, but not for sustained periods of time. The reason why the engine is burning lean to begin with is that the reduction in back pressure is causing more air to be drawn into the combustion chamber than before. Earlier cars (and motorcycles) with carburetion often could not adjust because of the way that back pressure caused air to flow backwards through the carburetor after the air already got loaded down with fuel, and caused the air to receive a second load of fuel. While a bad design, it was nonetheless used in a lot of vehicles. Once these vehicles received performance mods that reduced back pressure, they no longer had that double-loading effect, and then tended to burn valves because of the resulting over-lean condition. This, incidentally, also provides a basis for the "torque increase" seen if back pressure is maintained. As the fuel/air mixture becomes leaner, the resultant combustion will produce progressively less and less of the force needed to produce torque.
 

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Tony, maybe my brain has had too much alcohol.... So, in conclusion, was the Harley guy right or wrong? Does Jimmy need baffles or not?:confused::D
 

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Tony;

You've done an excellent presentation! Commendable! Very well written.

Cheers
 

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Tony;

You've done an excellent presentation! Commendable! Very well written.

Cheers
I don't take credit for the write up. I researched this before, and had the link saved. (Back in the days of my fuel controller investigation)
Thanks for the props, but it was not me that written it..
 

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Discussion Starter #6
Tony.....you MUST be a scollar, oops, scholar.....LOL

Very well written.....I recently sold a 2005 Cadillac CTS-V.....That had Katech aftermarket long tube headers....(no baffles, Ha Ha)....no Cats, and Corsa exhaust....The car made "insane" power.....It (like the Fury) was tuned..... Ran the quarter mile at Milan, Michigan.....12.8 @ 112......

So, I'm guessing the Harley guy "meant well".....but baffles are NOT necessary for a properly "tuned" ECM.
 

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Baffles

I was riding yesterday and met up with a Harley Guy.....Super nice, BTW.

I'm currently running Fuggin Mayhems with no baffles. This guy said he thought if there were baffles installed (creating some back pressure) the engine would make more power. Thoughts?
Jimmy,
The Mayhem pipes you have do have baffles, un-less you removed them. We weld in the baffles so the pipes are tuned for the bike. Our baffle are designed for each style exhaust sytem we make. We want you to have the best performance the bike can produce with and exhaust change. If you pulled out the baffles you have lost the performance and back-pressure we designed in to them.

Doug
Fuggin Fabrication
 

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Hey Doug,

Thanks for the update....I DID NOT know the baffles are in there.....Never checked....The exhaust is sooooo loud, I kinda' figured they weren't installed......

Appreciate the input.
 
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