Backpressure is a myth???

[JEEPRUSTY]

No they don't, over heated valves from the resultant lean mixture is what burns them.

Alll them there V12 Merlin engines done burned out their valves on acccounta they was open exhaust ports! Well purt neer open.

Whatever was Pops Yosimura and his team thinking with the freaky exhaust systems? or is this a theroetical statement with an engine balls to the wall so to speak?

And this is the 2 stroke animation that graphically illustrates backpressure.

[JEEPRUSTY]

You wouldn't think so just from the term backpressure ... but it does.

By creating a restriction in the tailpipe you force the gases to speed up. Though it's not always obvious the gas flow in the pipe is not at a steady speed. the increased flow speed through that slightly restricted tailpipe, actually causes a vacuum in the header inbetween exhaust pulses at lower than max rpms and can actually boost midrange performance over a nonrestricted tailpipe. I've seen it work on the dyno, it's a fact.

There was this drunk guy at the bar the other night name of Bernoulli fighting with a guy named Venturi over this very subject.

[GSexpress]

There was this drunk guy at the bar the other night name of Bernoulli fighting with a guy named Venturi over this very subject.

Bernouli and Venturi have their opinions.....but Dyno don't lie.

[GSexpress]

This is a neet graphic...but it doesn't show back pressure. It shows sonic reversion. That's what the arrow lines are depicting. That is what an expantion chaimber is all about. Not so much the back pressure.

Alll them there V12 Merlin engines done burned out their valves on acccounta they was open exhaust ports! Well purt neer open.

Whatever was Pops Yosimura and his team thinking with the freaky exhaust systems? or is this a theroetical statement with an engine balls to the wall so to speak?

And this is the 2 stroke animation that graphically illustrates backpressure.

[Katarat]

Race bikes are race bikes, not street bikes. You dont ride dynos. It is very possable to move torque ranges around with back pressure to make a better riding street bike by means such as a Supertrapp pipe by removing or adding discs or an open or closed end cap. For all out horsepower you are correct but that doesnt make the best street bike. Check out the dyno queens that are built just for dyno shootouts. They give up the bottom and mid range in a trade for topend power

[JEEPRUSTY]

I lifted the graphic from wikipedia.
I do not know if sound can force unburned air\fuel mixture back into a combustion chamber. The graphic seem to illustrate this.

But seriously we are talking about a WFO engine such as a dragster that sees its low end and midrange as a path to full throttle and little more?

I still recall a lot of voodoo going into race bikes. The Yoshi pipes with the little connector tubes between the headers fer instance.

[Tom R]

how come drag bikes get away with it then?

Was tongue in cheek - exhaust valves burn from getting too hot.

[Fizzyhair]

Narrowing pipes creates pressure but it's not slowing the flow it's speeding it up. But exhaust pulses coliding with baffles causes reverberation that physically slows the air flow. A muffler is designed to get rid of the uncorking pop from the exhaust end the same way a guns one does. It's got to create eddies within the flow also restricting flow. Don't confuse backpressure with just regular pressure.

[sharpy]

They say no back pressure is good but you do have to have a slight reverse cone on the exhaust. This was mine back in the late 70"s/early 80"s and could slip steam a Kawa Mk2 1000 down the straight. Braking was a no contest lol. Little bit loud, them was the days.