Cal Club Autocross Forums

Mako Koiwai wrote:I Vote for Honest Abe Kalman to do the comparison runs

Oh, if I must...

Bob Beamesderfer wrote: So everything says, however, the differentiation is that what's being measured isn't the same thing. Dinkel's been SAE chairman in addition to R&T editor, so no offense Marshall, I'll stick with his approach.

Turning or twisting force such as the force imparted on the drive line by the engine. Usually measured in lb-ft. It differs from work or power in that torque does not necessarily produce motion. Basically, the magnitude of a torque acting on a body is the product of the magnitude of a force and its force arm (perpendicular distance from the axis of rotation of the body to the line of action of the force). This product is called the moment of the torque about the axis or the torque.

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As I say many times, there's no such thing as "back pressure." There's only pressure. You're directing the flow of a gas through a tube so you're guaranteed to see an overall pressure increase above atmospheric inside the tube. That pressure increase varies throughout the length of that tube (wave flow), must be lower then the pressure at the exhaust port when the exhaust vale opens (a given), and in some spots, with a properly designed exhaust system, you might see a momentary pressure decrease below ambient. Exhaust system tuning is placing the low pressure in the correct spot at specific points in the engine operating range.

Generally you want to see the lowest overall pressure in the exhaust system (throughout the engine operating band) within 6" of the final merge collector/Y-pipe junction - where all the pipes finally meet. There are specific reasons' to move this point to different places in the exhaust and the headers will have their own low pressure point that gets tuned based on primary OD and length. A very, very general rule of thumb is 2 to 3 psi over ambient for a race tuned engine measured halfway between the final merge collector/Y-pipe junction and the tailpipe.

Thanks John ... so what is your take on my SuperTrapp set-up?

Bob Beamesderfer wrote: So everything says, however, the differentiation is that what's being measured isn't the same thing. Dinkel's been SAE chairman in addition to R&T editor, so no offense Marshall, I'll stick with his approach.

Turning or twisting force such as the force imparted on the drive line by the engine. Usually measured in lb-ft. It differs from work or power in that torque does not necessarily produce motion. Basically, the magnitude of a torque acting on a body is the product of the magnitude of a force and its force arm (perpendicular distance from the axis of rotation of the body to the line of action of the force). This product is called the moment of the torque about the axis or the torque.

Bob,

They really are the same thing.

Dinkel's response that you quoted is not proving your point either. He was merely stating the differences between torque and power. Not stating that it should be noted as lbs-ft.

Whether you have 100lbs @ 1ft, or 1lbs @ 100ft, it doesn't matter. The torque produced is the same.

Thanks John ... so what is your take on my SuperTrapp set-up?

No opinion. There's much more to quick course times then horsepower or torque. If the car is easier to drive fast or the numbers from the dyno make you drive better then it doesn't matter what anyone posts here. Your ultimate gauge is: Am I quicker?

IMHO, take a practice day and do 3 run sets changing the exhaust configuration at least twice.

Mako Koiwai wrote:All I know is that John Edwards looked it up (the 3 to 6 lbs of back pressure) in one of his books ... and said to stop by anytime to check it out. As a reference book, it has to be used at the facility.

... of course most pure racing engines have straight through pipes ... but perhaps that's because it's typically all about HP and not Torque ? What about motorcycle (and go-kart) engines with those chambered exhausts. Aren't those all about resonance ?

Saying "you need X pounds of backpressure" for some application is not correct. "Backpressure" is never a constant: what you really have are positive and negative pressure waves resonating in the exhaust system. Also, pressure waves and sonic waves are two different things, and travel at different speeds: both have to be considered in any sond-controlled (muffled) system. Go back and read Will's post again, as I believe he most accurately describes what's going on here. What you found is a result of interaction between pipe length, converter restriction, and the nature of the Supertrapp design.

Forget quicker on course (since I'm not that great a driver, ever practice lap is usually faster! ... it's so apparent driving it on the street. With the exhaust open, it's a dog off the line, and I'm not talking drag racing, just leaving a stop light going to the gas station! The engine is so much more tractable with the Discs in place. I'm sure the dyno test was inconclusive in showing what a difference it makes. It hinted in what direction things were going but didn't show the relatively dramatic difference. "Back pressure" ... I guess an unsophisticated "description" of pressure waves and resonance ...

I'm always curious if these holier than thou debates on semantics ever result in a change in result? Does it ever "matter"?

Foot Pounds sounds a lot better then Pound Foots ... end of discussion! ;)

Webster Jessup wrote:

Bob Beamesderfer wrote: So everything says, however, the differentiation is that what's being measured isn't the same thing. Dinkel's been SAE chairman in addition to R&T editor, so no offense Marshall, I'll stick with his approach.

Turning or twisting force such as the force imparted on the drive line by the engine. Usually measured in lb-ft. It differs from work or power in that torque does not necessarily produce motion. Basically, the magnitude of a torque acting on a body is the product of the magnitude of a force and its force arm (perpendicular distance from the axis of rotation of the body to the line of action of the force). This product is called the moment of the torque about the axis or the torque.

Bob,

They really are the same thing.

Dinkel's response that you quoted is not proving your point either. He was merely stating the differences between torque and power. Not stating that it should be noted as lbs-ft.

Whether you have 100lbs @ 1ft, or 1lbs @ 100ft, it doesn't matter. The torque produced is the same.

That wasn't John's definition. Can't find my copy of his book, or much of anything in my office. Like, I said, it's a nomenclature thing.

Careful, Marshall, Isley wouldn't want you take his SmartAss Crown™ away. }:)

Steve Ekstrand wrote:I'm always curious if these holier than thou debates on semantics ever result in a change in result? Does it ever "matter"?

You're right. Clarity of language is unimportant. R&T and Edmunds and several others should just shove accuracy up their collective butt.

From now on, I will first consult the Great and Magnificent Isley on all matters relating to speakin' good English.

Bob Beamesderfer wrote:
From now on, I will first consult the Great and Magnificent Isley on all matters relating to speakin' good English.

We speak American around here. English is for those moldy folks across the pond.

Jason Isley BS RX8 wrote:

Bob Beamesderfer wrote:
From now on, I will first consult the Great and Magnificent Isley on all matters relating to speakin' good English.

We speak American around here. English is for those moldy folks across the pond.

Hey, Max don't speak no 'merican!

Yeah yeah yeah.....

Its in situations like this.... Every engine builder or exhaust guy knows what you mean when you discuss back pressure. Every brake guy knows what you're talking about when you come in talking about warped rotors. Doesn't matter if up in some ivory tower people want to argue about the accuracy of the description, its not going to get me what I want in most places.

I'm always curious if these holier than thou debates on semantics ever result in a change in result? Does it ever "matter"?

This coming from a lawyer...

Just thought I'd weigh in on the whole lb.-ft./ft.-lb. thing, as my former boss Mr. Dinkel was mentioned earlier. Either way, it's correct, but we tend to stick with convention and say force first, distance second. In Europe, torque is expressed as Newton-meters, and it'd sound odd to say meters-Newton.
So we go with lb.-ft., spoken as "pound-feet." Maybe part of our tradition comes from our Euro-centricity, covering the GPs in the 1960s and such.

See you guys at the practice on Dec. 12; I'm dusting off the MR2!

Doug Kott, Road & Track

R&T, cool ... hope to meet you out at our Dec. event! I believe I was the only one that placed in both of your R&T Photo Contest back in the early '70's.

Nice! Maybe we'll bring back the contest, and you can go for a 3-peat!

I'll look for you at the event. I've got a yellow MR2 Spyder, and my friends are bringing a black 944 and possibly a red 968.

--Doug

Was checking out the data because I need a new muffler for my Lola engine swap. From what I see on your first overlay graph, the blue line is best or tied for best all the way from 3000 to 6500 rpm. Don't get tied up in that torque vs power thing...they're both the same but dressed up differently. We had this discussion before...the water wheel analogy was great. And you published peak torque and peak power numbers. Again...of no importance. What you want to pay attention to is the area under the rpm curve of the actual rpm range you regularly use on course. Doesn't matter if you're reading the torque plot or power plot. The winner certainly appears to be the blue trace which I think you said was 8-discs. Thanx for posting the results. And just so you know, you're lucky. Some people have reported that installing a Supertrapp created a big dip at a specific rpm...presumably a tuning issue. Yours came out good. I'll be dynoing mine down at Shlossnagels to be confident that I'm not one of the unlucky.

Please keep us posted on your results.