Backpressure ALWAYS decreases power

[Howard]

Who's going to take the bait?

EDIT: Thanks to spidey for clarifying

 

[spidey07]

Not me.

It's not a true statement. Especially with 2 stroke motors. The sound pulse back to the cylinder increases power.

 

[RbSX]

Originally posted by: Howard
Who's going to take the bait?

... doesn't increased backpressure lead to more power?

 

[Cattlegod]

True.
by backpressure, you mean increased right? i.e. not zero?

 

[Syringer]

5" Mufflers on Civics double horsepower.

 

[Krazy4Real]

ummmmmm.... sure?

 

[nakedfrog]

Mmmm, buffalo jerky. Has anyone else had this stuff?

 

[mwmorph]

Increased backpressure to a point increases torque. decreased backpower like a 4" or 5" exhaust off a civic or almost any car for that matter will decrease power.

 

[radioouman]

Too salty.

 

[Kelvrick]

Originally posted by: nakedfrog
Mmmm, buffalo jerky. Has anyone else had this stuff?

No, I haven't yet. I want to though. Deer jerky, turkey jerky, beef jerky, all good stuff.

 

[Vic]

It's not a true statement. Power is a function of torque and rpm (work over time). In other words, all things being equal, power is the ability to produce a similar amount of work (torque) but at faster speeds (shorter durations of time). An increase in backpressure (to a reasonable extent of course) will actually increase torque and thus power at lower rpms but will hamper the ability of the engine to rev efficiently at higher rpm, thus reducing torque and consequently power at higher speeds. Reducing backpressure reduces torque (and thus power) at lower rpm, but allows the engine to rev more efficiently at higher rpms and thus retain more torque at those higher speeds, hence more power.

 

[broon]

Originally posted by: Kelvrick

Originally posted by: nakedfrog
Mmmm, buffalo jerky. Has anyone else had this stuff?

No, I haven't yet. I want to though. Deer jerky, turkey jerky, beef jerky, all good stuff.

Not as good as a Boston Cream Pie...which is really cake.

 

[OS]

backpressure is a myth

 

[Syringer]

Originally posted by: nakedfrog
Mmmm, buffalo jerky. Has anyone else had this stuff?

What do they call buffalo jerky in buffalo?

 

[SagaLore]

Originally posted by: nakedfrog
Mmmm, buffalo jerky. Has anyone else had this stuff?

No, but deer jerky is good.

 

[JulesMaximus]

Originally posted by: nakedfrog
Mmmm, buffalo jerky. Has anyone else had this stuff?

I like pie.

 

[Scarpozzi]

When she's on her back, there's less need for power....and pressure.

 

[JulesMaximus]

Originally posted by: Syringer

Originally posted by: nakedfrog
Mmmm, buffalo jerky. Has anyone else had this stuff?

What do they call buffalo jerky in buffalo?

Canadian bacon.

 

[broon]

Originally posted by: Scarpozzi
When she's on her back, there's less need for power....and pressure.

Actually you've got it backwards. When you're on your back, there's less need for power and pressure.

 

[batmang]

Originally posted by: Howard
Who's going to take the bait?

a full free flowing exhaust right from the manafold does not always result in more power all around. you may gain hp but you might lose torque. on turbo cars having a full free flowing exhaust may increase both hp and torque but it also depends on the exhaust size. btw, get this thread back on topic.

 

[Howard]

The very definition of backpressure means is that it's a pumping loss.

By properly sizing the exhaust, you REDUCE backpressure and free up lost power. Who disagrees this time?

 

[imported_goku]

Well from what I know, if you have too large of an exhaust, it will hurt power.

 

[randay]

Loss of horsepower from backpressure can easily be made back with a few vinyl stickers.

 

[GalvanizedYankee]

Vague question designed as bait

A high performance 4 stroke gasoline engine w/o variable valve timming can suffer from
a huge flat spot in it's mid-range when run w/o any backpressure. This hole in the torque
curve is caused by over-scavaging the cylinder, not only causing an increase in pollutants,
but a real reduction of cylinder filling. It can approch 15% or more.

EXUP Valve from a Yamaha FZR1 http://www.motorflash.it/provemoto/r12002/exup.JPG
A smooth strong mid-range is much more important than top end in real world riding/driving.

Google for more info Howard. I *think* BMW is using a similare system in some of thier cars.


...Galvanized

 

[Howard]

Originally posted by: Vic
It's not a true statement. Power is a function of torque and rpm (work over time). In other words, all things being equal, power is the ability to produce a similar amount of work (torque) but at faster speeds (shorter durations of time). An increase in backpressure (to a reasonable extent of course) will actually increase torque

I disagree. If this were true, choking an oversized exhaust at any point (with a physical bottleneck of sorts) would increase power.

In fact, what we are really after is increased exhaust gas velocity, which increases volumetric efficiency (so to speak) because more of the cylinder can be filled with fresh air and fuel. The scavenging effect, as it were. By decreasing the exhaust pipe diameter, velocity must increase because mass flow remains constant.