Physics/mechanical: Can a different muffler affect RPMs at speed?

[FightingChance]

I was pretty sure it couldn't because engine RPM's and speed are linked by gear ratios, a question of numbers. But I want to make sure.

So, could a less restrictive muffler alter the engine RPM's shown on a tach? (versus the original muffler at the same speed)

 

[InlineFour]

no, it would not alter the RPM.

EDIT: changing mufflers won't really make any difference performance wise, if any. you'd need to change the header, cat. converter, b-pipe, then the muffler.

 

[MikeMike]

cant alter RPM's, but it can alter Torque, which in turn alters HP.

 

[Rubycon]

Perhaps in relation to throttle position?

Tachometer readings will be the same because the sensor measures crank rev/min.

 

[Goosemaster]

Originally posted by: MS Dawn
Perhaps in relation to throttle position?

Tachometer readings will be the same because the sensor measures crank rev/min.

Cool. Never thought of that.

 

[FightingChance]

The reason I pose this question is that on a car forum I visit someone is insisting that by replacing their muffler, they cruise on the highway at the same speed but at lower RPM (and get better gas mileage, and other things that are either untrue, physchosomatic, or don't make sense.) So I want something logical sounding to fire back with.

 

[InlineFour]

Originally posted by: FightingChance
The reason I pose this question is that on a car forum I visit someone is insisting that by replacing their muffler, they cruise on the highway at the same speed but at lower RPM (and get better gas mileage, and other things that are either untrue, physchosomatic, or don't make sense.) So I want something logical sounding to fire back with.

changing out the muffler won't do jack ******.

 

[Kenazo]

Yup, tach doesn't measure anything but the number of times your engine spins in one minute. Hence "revolutions per minute". Perhaps you should think these things through.

You could be pulling a boat without a trailer behind your car, but if you're going 60mph in 5th gear the tach will show the exact same thing as it would if you were driving the same car, sans boat at 60mph in the same gear.

Your gas guage is the one that will show a difference.

Originally posted by: InlineFour

Originally posted by: FightingChance
The reason I pose this question is that on a car forum I visit someone is insisting that by replacing their muffler, they cruise on the highway at the same speed but at lower RPM (and get better gas mileage, and other things that are either untrue, physchosomatic, or don't make sense.) So I want something logical sounding to fire back with.

changing out the muffler won't do jack ******.

Not true. If the muffler was actualy restrictive enough it could be decreasing mileage.

 

[Pepsi90919]

NOH

 

[Evadman]

Unless the muffler is ground into the shape of a smaller gear (less teeth) and put in the transmission, the RPM at speed with be exactly the same.

This is probably one of the guys that thinks adding a wing on a FWD car is a good idea.

 

[jagec]

Originally posted by: FightingChance
The reason I pose this question is that on a car forum I visit someone is insisting that by replacing their muffler, they cruise on the highway at the same speed but at lower RPM (and get better gas mileage, and other things that are either untrue, physchosomatic, or don't make sense.) So I want something logical sounding to fire back with.

He MUST mean throttle position.

Unless his car was so powerful before, that he would be spinning his tires the whole way down the freeway, but now that he put on a more restrictive muffler he can't break them loose, thus decreasing RPM at the same speed.

 

[Kelvrick]

Originally posted by: Kenazo
Yup, tach doesn't measure anything but the number of times your engine spins in one minute. Hence "revolutions per minute". Perhaps you should think these things through.

You could be pulling a boat without a trailer behind your car, but if you're going 60mph in 5th gear the tach will show the exact same thing as it would if you were driving the same car, sans boat at 60mph in the same gear.

Your gas guage is the one that will show a difference.

Originally posted by: InlineFour

Originally posted by: FightingChance
The reason I pose this question is that on a car forum I visit someone is insisting that by replacing their muffler, they cruise on the highway at the same speed but at lower RPM (and get better gas mileage, and other things that are either untrue, physchosomatic, or don't make sense.) So I want something logical sounding to fire back with.

changing out the muffler won't do jack ******.

Not true. If the muffler was actualy restrictive enough it could be decreasing mileage.

Well, depending on the engine, having it too open might decrease mileage.

 

[Kenazo]

Originally posted by: Kelvrick

Originally posted by: Kenazo
Yup, tach doesn't measure anything but the number of times your engine spins in one minute. Hence "revolutions per minute". Perhaps you should think these things through.

You could be pulling a boat without a trailer behind your car, but if you're going 60mph in 5th gear the tach will show the exact same thing as it would if you were driving the same car, sans boat at 60mph in the same gear.

Your gas guage is the one that will show a difference.

Originally posted by: InlineFour

Originally posted by: FightingChance
The reason I pose this question is that on a car forum I visit someone is insisting that by replacing their muffler, they cruise on the highway at the same speed but at lower RPM (and get better gas mileage, and other things that are either untrue, physchosomatic, or don't make sense.) So I want something logical sounding to fire back with.

changing out the muffler won't do jack ******.

Not true. If the muffler was actualy restrictive enough it could be decreasing mileage.

Well, depending on the engine, having it too open might decrease mileage.

Of course. There's a bit of an optimal range beyond that on either side and you lose power which translates into decreased mileage.

 

[FightingChance]

Originally posted by: Evadman
Unless the muffler is ground into the shape of a smaller gear (less teeth) and put in the transmission, the RPM at speed with be exactly the same.

This is probably one of the guys that thinks adding a wing on a FWD car is a good idea.

Not to nitpick, but increased traction in the rear from wing downforce could also benefit a FWD car, just not by pressing down on the drive wheels (it would help prevent oversteer though)

But I always thought wings were pretty useless for the street, you need to be going pretty well to reap the benefits.

 

[Kenazo]

Originally posted by: FightingChance

Originally posted by: Evadman
Unless the muffler is ground into the shape of a smaller gear (less teeth) and put in the transmission, the RPM at speed with be exactly the same.

This is probably one of the guys that thinks adding a wing on a FWD car is a good idea.

Not to nitpick, but increased traction in the rear from wing downforce could also benefit a FWD car, just not by pressing down on the drive wheels (it would help prevent oversteer though)

But I always thought wings were pretty useless for the street, you need to be going pretty well to reap the benefits.

A wing will pretty much always do nothing besides decrease your mileage.

 

[InlineFour]

Originally posted by: FightingChance

Originally posted by: Evadman
Unless the muffler is ground into the shape of a smaller gear (less teeth) and put in the transmission, the RPM at speed with be exactly the same.

This is probably one of the guys that thinks adding a wing on a FWD car is a good idea.

Not to nitpick, but increased traction in the rear from wing downforce could also benefit a FWD car, just not by pressing down on the drive wheels (it would help prevent oversteer though)

But I always thought wings were pretty useless for the street, you need to be going pretty well to reap the benefits.

FWD are known to have understeer.

wings for the most part are just for looks.

 

[InlineFour]

Originally posted by: Kenazo

Originally posted by: FightingChance

Originally posted by: Evadman
Unless the muffler is ground into the shape of a smaller gear (less teeth) and put in the transmission, the RPM at speed with be exactly the same.

This is probably one of the guys that thinks adding a wing on a FWD car is a good idea.

Not to nitpick, but increased traction in the rear from wing downforce could also benefit a FWD car, just not by pressing down on the drive wheels (it would help prevent oversteer though)

But I always thought wings were pretty useless for the street, you need to be going pretty well to reap the benefits.

A wing will pretty much always do nothing besides decrease your mileage.

drag FTL!

 

[FightingChance]

^ Agreed.

Can anyone rig up a fancy sounding way of saying 'a muffler can't change RPM's at speed' ?

 

[Iron Woode]

Originally posted by: FightingChance
The reason I pose this question is that on a car forum I visit someone is insisting that by replacing their muffler, they cruise on the highway at the same speed but at lower RPM (and get better gas mileage, and other things that are either untrue, physchosomatic, or don't make sense.) So I want something logical sounding to fire back with.

that is not possible unless there is a final drive ratio change or tire height change.

 

[Iron Woode]

Originally posted by: FightingChance

Originally posted by: Evadman
Unless the muffler is ground into the shape of a smaller gear (less teeth) and put in the transmission, the RPM at speed with be exactly the same.

This is probably one of the guys that thinks adding a wing on a FWD car is a good idea.

Not to nitpick, but increased traction in the rear from wing downforce could also benefit a FWD car, just not by pressing down on the drive wheels (it would help prevent oversteer though)

But I always thought wings were pretty useless for the street, you need to be going pretty well to reap the benefits.

what downforce? At 40 mph?

no spoiler is doing anything usefull at under 130 mph.

 

[Rubycon]

Originally posted by: FightingChance
^ Agreed.

Can anyone rig up a fancy sounding way of saying 'a muffler can't change RPM's at speed' ?

Sure wire the galvanometer that displays piston engine rev/min to the output on your Bruel & Kjaer Type 2305 Graphic Level Recorder. When you take the muffler off (redneck mode) or put a coffee can Type - R on (riceboy mode) the tach will go MUCH higher but your neighbors will go potato shopping.

Originally posted by: Iron Woode

But I always thought wings were pretty useless for the street, you need to be going pretty well to reap the benefits.

what downforce? At 40 mph?

no spoiler is doing anything usefull at under 130 mph.[/quote]

70 mi/hr wind directly perp (90 deg) is ~20 pounds/sq foot. No wonder those park benches are on the back of those civics.

 

[Goosemaster]

Originally posted by: Evadman
Unless the muffler is ground into the shape of a smaller gear (less teeth) and put in the transmission, the RPM at speed with be exactly the same.

This is probably one of the guys that thinks adding a wing on a FWD car is a good idea.

AHAHAHAHAHAHA

 

[Kenazo]

Originally posted by: Iron Woode
no spoiler is doing anything usefull at under 130 mph.

This thing looks useful sitting still!

 

[Evadman]

Originally posted by: FightingChance
Not to nitpick, but increased traction in the rear from wing downforce could also benefit a FWD car, just not by pressing down on the drive wheels (it would help prevent oversteer though)

Limited benefit until ground speed is > 80 MPH IIRC. I would have to break out my calculator and know the wing characteristics like angle of attack and such (which actually make a big difference). There is some good info at Chassis Works, as they design functional downforce inducing wings for race cars. I looked into it for a project I am working on.

Pretty much every car in the US is designed to go into understeer before oversteer to keep lawers happy. Of course, RWD cars can induce oversteer with some application of the go pedal. E brake doesn't help the FWD.

Putting a wing on a Civic will only slow it down. By pushing on the rear, the nose will pivot roughly on the centerline of the front axle, thus raising the nose into the air. This allows more air under the front of the car (thus lifting it) and providing less grip on the axle that in a FWD does not only the steering work, but also provides for forward motion.

Even the largest wing that Chasis Works manufactures will only produce about 200 lbs of down force at 150, with something like 8 lbs of drag (might have been 11. It has been a while). the force goes up exponentialy with speed, so at 300, the wing would be in the 800 lbs range. I was looking to add 200 lbs of downforce at 120 with 2 canards for my project, but the canards would have been a total of 8' wide, making my vehicle about 10' wide. Obviously, this was not a solution

 

[Iron Woode]

Originally posted by: Kenazo

Originally posted by: Iron Woode
no spoiler is doing anything usefull at under 130 mph.

This thing looks useful sitting still!

WTF does Laura Croft have to do with this?

Ohh, but this looks interesting:

http://www.mopo.ca/2006/04/most-expensive-wagyu-beef-sandwich-148.html