twice pipes diameter

[IdahoKidd]

I can't find the diameter of the twice pipes. Even on the MSA site that isn't listed. I am going to get exhaust work done shortly for "Manny" (L28, 6 into 2 header) and am running dual pipes. Any reason to not use 2 1/2 pipe all the way back? My old set of twice pipes were quite small, less than 2 inch I think even. Backpressure issues?

Thanks!

Leonard

[ezzzzzzz]

2.5" twice pipes on a stock or mild engine would not flow very well. Velocity is an important part of scavaging/filling the cylinder. I'd likely stay in the 2" range maybe even 1.75" concidering that only three cylinders are feeding each pipe. Others will likely have their own opinions though.

[Arne]

My info was that the old Clifford system as sold through Datsun Comp was apparently 1 3/4" tubing. Certainly no more than 2". My recollection is that MSA's system is 2" as well, but I can't remember where I saw that.

[madkaw]

I ran duals all the way back from a MSA 6-2 header and the collectors were two inches. I wouldn't run anything bigger than that. Two 2" pipes would be about equal to 3" single, which has been run by many with success. The twin 2" pipes run well on my slightly modified motor and sound dreamy.

[LeonV]

MSA twice pipes are 1.75" per pipe, and I think the old Clifford system is 2" pipes. BTW, can everyone lose the "back-pressure" idea already, it has nothing to do with improving pumping efficiency. You want your exhaust pipe big enough in order to not incur losses in the system. That's it.

Before trying to justify the myth, please at least read this thread explaining exhaust dynamics.

As for the OP's second question, a single 2.5" to 3" pipe is better than duals because of weight concerns, price and possibly loss of secondary scavenging effects if you plan on true dual pipes. I have a Clifford header and plan to use it to replicate the old dual system because I like the look and sound not because it is the best performer.

[ChrisZ]

My twice pipe is 1.75 inch, should equal to 2.25 inch

Chris

[IdahoKidd]

I am guessing the old original (to me) pipes are 1 3/4 then. I know they seemed pretty small.

As for the back pressure, I had always been under the belief that it kept from burning up the valves. Never any first hand experience that I can think of I guess. Having had some 40+ cars, I've never lost a motor and have abused a few.

[ajmcforester]

I am guessing the old original (to me) pipes are 1 3/4 then. I know they seemed pretty small.

As for the back pressure, I had always been under the belief that it kept from burning up the valves. Never any first hand experience that I can think of I guess. Having had some 40+ cars, I've never lost a motor and have abused a few.

To give you an idea the vintage Supersprint exhaust I got is 1 3/4 inlet and splits to 1 1/4" duel outlet. A friend of mine was arguing with me that twice the pipe is the same as twice the diameter. Of course I proved him wrong, but to do I had to make this chart and do a math proof. The nice thing is you can look to see what size pipe you want.

If it would post:

Single to Duel

Take the single diameter and place in the equation

D= single diameter

d= duel pipe diameter

r=D/2

area= (Pi)r^2

area= (pi)(D/2)^2

area= 2*(pi)(d/2)^2

(pi)(D/2)^2=2*(pi)(d/2)^2

((pi)(D/2)^2)/(pi)=2*(d/2)^2

(D/2)^2=2*(d/2)^2

(D/2)^2=2*(d/2)(d/2)

(D^2)/4=2*(d^2)/4

(D^2)/4=(d^2)/2

2*(D^2)/4=(d^2)

(D^2)/2=d^2

X^(1/2) equals the square root of X

((D^2)/2)^(1/2)=d

So first D*D

then divide by 2

and lastly take the square-root

Edited March 19, 2011 by ajmcforester
Numbers mashed together when posted

[Mike B]

deleted.

My original post is meaningless now after ajmcforester deleted his chart of numbers and replaced it with formulas.

-Mike

Edited March 19, 2011 by Mike B
related prior post was changed

[ajmcforester]

Not sure I can read your chart there Ajmcforester, but it should make for some darn accurate pipes carried out to 9 decimals places though .

-Mike

Mike a habit of mine not to round anything till I'm done with the number. My physics professor was a subatomic theorist and I helped my Biometrics professor run advance algorithms rounding early meant big errors. In Biometrics the errors would have cost around a $1M each

[madkaw]

Oh, and the biggest reason for duals is they are WAY-COOL

[Arne]

Oh, and the biggest reason for duals is they are WAY-COOL

Yeah, especially split duals like yours, on cars where you don't expect to see dual exhaust. Too bad it requires so much modification to do it on a Z - props to you for going the extra mile there.

I've seen this in the past on some of my own cars. In both of the examples below, if someone comments about the car (or commented, in the case of the long-sold BMW), 3 times out of 4 it was about the exhaust.

The BMW was factory - the 323i was the euro top-end model of the 3-series (2.3 L inline six, 4 wheel disc) and came with factory dual exhaust.

On the Golf TDI (diesel) I converted to the GTI dual exhaust. Changed the whole look of the rear of the car.