first off, I work at a tractor dealorship, so these guys know a lot about diesels and think that I know nothing about gas engines cause I'm 19. one of the guys there has a '98 ford heavy duty with a 5.4, he wants to cut the muffler of like he has on previous trucks and two guys at work said that he is loose a lot of back pressure, I said that he wouln't loose but a pound or two of torque and not to worry about it cause you'll pick up a couple horses, but they said I was dead wrong and that you could definetly feel the difference. I told them that removing a cat would loose more torque, but the said the muffler yet again.

 

You'll lose Velocity and backpressure. Backpressure is bad, not matter how you look at it. You do however, want to have a certain amount of velocity I suppose. You'll lose some low end torque but it'll be made up in high end HP. So it kind of cancels out, that's why people like running open headers. But just to state again you don't want any backpressure. This came up about a month ago and discussed very thoroughly, just search.
Removing the muffler would help a little, but nothing that drastic, and if the sound police are strict they'll get him.

 

Gee Mark have enough posts latelty? All good stuff so no flames


Marks right.

Just dont let the guy cut that cat off!!!!! On the newer cars and trucks mostly fNords they put an O2 sensor behind the cat and if you remove that converter it really screws up the o2 reading and he will really loose some power. For some odd reason you cant go aftermarket either so if you cut it off expect to hand fnord a nice chunk of your paycheck $300.

 

When you go to college in the middle of nowhere, there ain't much else to do,.

 

I hear ya there. When I went to CU I was so bored I got 4 years of school done in 3, of course it would haven taken 4 If I knew about 3rdgen.org.

SSC

 

Is backpessure bad just because it's the result of restriction(is it?)Do you think maybe alot of people confuse backpressure with velocity, and that's where alot of arguements start?

 

Exactly.

 

It would be SOOO much easier if other peole could figure that out the way you did.

AJ

 

An arguement I always have with friends is about open hedders. They say there wouldn't be enough backpressure and low end torque would suffer, IF I didn't burn a valve in the process.I don't quite understand that, but if they are confusing too little backpressure with too much velocity then burning valves would make a bit more sense.Am I on the right track or am I grasping at straws?

 

You won't burn a valve with open headers. Think about how many people have ran open headers. You'll only burn a valve if cold air enters the valves, which your headers would have to be extremely short, which they're not.

 

Have you guys ever heard of a pressure wave terminator box?

It's a special tear drop shaped piece that goes on right after the collector. Then slowly tapers down to the exhaust pipe to get rid of the exhaust.

The main purpose is to create a near zero 'backpressure' area for the exhaust to come out of the header/collector. And if you put a muffler that flows at least 2.2 times more cfm than the HP (HP x 2.2 = required cfm), then you can have a quiter setup than open headers, but achieve the same flow + or - 1%.

BTW, that applys to a single exhaust. So a 400 HP SBC would need one 880cfm muffler for a single exhaust, or two 440cfm mufflers for dual. And the loss would be no more than 4HP.

And an open chamber Flowmaster right behind each header will serve as both the terminator box, and muffler.

All learned from David Vizard's writing/experience in the book titled "How to build Max Performance Chevy Small Blocks on a budget".

I would imagine the Flowmasters that he's talking about would be the 40 series? They're the loudest and best flowing, right?

AJ

 

Flowmaster 30 series are the 'best' flowing. They are not the loudest either, and are pretty big 5"x10"x17". The larger volume allows a better wave action. which helps scavenging by creating a tuned low pressure. You cannot measure a muffler by pure CFM flow because they do not operate like that in the real world.

 

good discussion, but none the less, would the pick up loose any lbs of torque by removing the muffler?

 

Low end Torque is lost, but made up for in high end HP as I recall, anyone know otherwise.

 

Thanks. I couldn't remember which was which. I haven't used Flowmasters very much.

Well then you need to tell David Vizard that his flow tests and dyno pulls are wrong.

He says in this book that Walker has been pushing the issue for mufflers to be rated by cfm, so the consumer can have a direct comparison when shopping for mufflers. Kinda like carbs are rated. But many manuactures have been avoiding the issue for obvious reasons.

He also says that someday, it will become enforced by SAE regulations. But that day may be something even our children will miss.

He's done many tests to prove his theories. In case you haven't heard of him, he's a very well know engineer. Primarily dealing in race engines.

AJ

 

Mmmmmmmmmmm, open headers (Homer Voice):hail:

 

I'm the opposite. I'm going to have 4 years of school done in 5 1/2...6.... well eventually.

 

Im a little lost. When you say high end HP, do you mean at higher RPMS you will gain HP?

 

HP=(tq*rpm)/5252

so as you can hp is based on torque
so if you have two motors that are making the same amount of torque but one is at 2000 rpms and the other is at 5000 rpms the second motor will make more hp.


and if he is just removing the muffler and cat off he should gain through most the rpms range I would think, even in the low end. though this is exluding the O2 thing that was brought up and tuning issues which shouldn't be that bad.
now if he was to just cut the muffler off and not put a tail pipe back on he might have a loss of some low end but that is not really due to backpressure or velocity but pressure waves and with a shorter exhaust pipe it is setup better for higher rpm runs while a longer pipe will be better suited for low rpms

 

Cool Thanks Rx