Don Terrill’s Speed-Talk

I currently run a 3" collector on my headers that is pretty short at around 8-9". I would have room to extend the collector at the same diameter another 8-9". Would that do any good ?

If nothing else, it would be a great test. I suspect you'll find positive results.


Shawn

swatson454 wrote:If nothing else, it would be a great test. I suspect you'll find positive results.


Shawn

Shawn,

It's a little more involved than just doing a test. It requires welding, so it's a permanent thing. I would like to know in advance if it would actually help or would do nothing.

FWIW the pipemax program seems to suggest a 17-18" collector of 3.250 for my engine. Exhaust further upstream is 2.25"

I would go with what Larry says. He also stated that collector length is the most important dimension on the exhaust system.

Belgian1979 wrote:
Shawn,

It's a little more involved than just doing a test. It requires welding, so it's a permanent thing. I would like to know in advance if it would actually help or would do nothing.

FWIW the pipemax program seems to suggest a 17-18" collector of 3.250 for my engine. Exhaust further upstream is 2.25"

I see. Does Pipemax have your current length close to the predicted worst length? If so, I'd do as suggested above and make the change.

swatson454 wrote:

Belgian1979 wrote:
Shawn,

It's a little more involved than just doing a test. It requires welding, so it's a permanent thing. I would like to know in advance if it would actually help or would do nothing.

FWIW the pipemax program seems to suggest a 17-18" collector of 3.250 for my engine. Exhaust further upstream is 2.25"

I see. Does Pipemax have your current length close to the predicted worst length? If so, I'd do as suggested above and make the change.

Yes, worst length is actually what I have now. More even, I seem to have an obnoxious banging in the collector at lower rpm, which made me think that I might use a longer collector with more volume.

If you don't want to do the weld route get a set of stainless band clamps from your local truck shop or order them off the net.

Made easy work on the dyno, even found out what made best power didn't perform the best on track.

Your application try the 18inch length collector.

Remember that changing the exhaust can/will affect the tune so when you add collector length (usually a good idea) you will have to re-optimize your tune-up to see the benefit

Belgian1979 wrote:

swatson454 wrote:

Belgian1979 wrote:
Shawn,

It's a little more involved than just doing a test. It requires welding, so it's a permanent thing. I would like to know in advance if it would actually help or would do nothing.

FWIW the pipemax program seems to suggest a 17-18" collector of 3.250 for my engine. Exhaust further upstream is 2.25"

I see. Does Pipemax have your current length close to the predicted worst length? If so, I'd do as suggested above and make the change.

Yes, worst length is actually what I have now. More even, I seem to have an obnoxious banging in the collector at lower rpm, which made me think that I might use a longer collector with more volume.

My experience with Pipemax is that when a collector is recommended, there are also alternate lengths suggested that are half and twice the recommended with the worst lengths being about half way between so your 8-9" is right at the half of recommended 17-18" and should be OK. What you have should not be the worst length. That is not to say that there may not be some advantage to extending to the recommended length but you are not far off.

You mean alter the collector lenght on a full exaust system? Or open pipes?

On a full system the gains would be minimal, unless your car have a reduction just after the collector you have now.

If we're talking open pipes , the power gain can be significant.

Consider Jim McFarlands formula of: Peak Torque RPM = Pipe ID Area x 88,200
-------------------------
Single Cylinder Volume(cubic inches)
If your engine makes peak torque below the rpm figure, lengthening the collector will 'rock' the torque curve closer to your torque rpm. The peak torque number will remain the same. Basically, 'rock' = length change. The above formula can also be used on the induction side as well. Yes, the ID area of the induction/ports can be made to offer a peak torque rpm differently than the exhaust side. Which would obviously broaden the entire torque curve of the engine. Good if the engine operating rpm band is wide. Bad if the operating rpm band is quite narrow. -Dave-

This is what pipemax said :

--- Single Primary Pipe Specs --- for 347,466 CID from 4800 to 7300 RPM
Diameter= 1,789 Length= 32,6 to 35,0 also 22,8 to 25,2 inches long
Note> Maximum Primary's Tuned Length= 54,4 to 56,8 inches long

--- Header Collector Specs (Conventional Straight Tube) ---
Diameter= 3,278 Tuned Lengths= 17,9 best and 9,0 or 35,8

H-Pipe= 17,9 X-Pipe= 71,6 distance behind end of Primary Tube ends

-- Total Exhaust System Tuned Lengths (Primary ends to TailPipe end) --
Best HP/TQ Tuned Collector Lengths= 17,9 , 35,8 , 71,6 , 143,2 inches long

Worst HP/TQ Loss Collector Lengths= 26,9 , 53,7 , 107,4 , 214,9 inches long

Note=> measured from where the Primary Pipes end inside the Collector to
the point the tailpipe exits into the atmosphere.
H-Pipe is located at end of Collector, and X-Pipe is located
usually half-way between end of Primary Pipes -to- tailpipe end

Note-> all Pipe Diameters are OD and based-off .0625 inch Pipe thickness

---- Primary Pipe's Harmonics ----
1st Harmonic = 143,0 inches long ... typically never used
2nd Harmonic = 54,4 inches long ... longest recommended
3rd Harmonic = 32,6 inches long ... highly recommended , best Torque Curve
4th Harmonic = 22,8 inches long ... shortest recommended
5th Harmonic = 17,2 inches long ... typically never used
6th Harmonic = 13,6 inches long ... typically never used
7th Harmonic = 11,1 inches long ... typically never used
8th Harmonic = 9,2 inches long ... typically never used

---- Collector's Harmonics (includes Intermediate, Muffler , TailPipe) ----
1st Harmonic = 143,2 inches long ... longest with Mufflers and TailPipes
2nd Harmonic = 71,6 inches long ... longest recommended with Mufflers
3rd Harmonic = 35,8 inches long ... more bottom-end Torque
4th Harmonic = 17,9 inches long ... highly recommended , best Torque Curve
5th Harmonic = 9,0 inches long ... reduced Torque , more top-end HP sometimes
6th Harmonic = 4,5 inches long ... reduced Torque , not recommended

Actually from where and to where do you start measuring your collector ? I started from the end of the primaries to the flange.

BrazilianZ28Camaro wrote:You mean alter the collector lenght on a full exaust system? Or open pipes?

On a full system the gains would be minimal, unless your car have a reduction just after the collector you have now.

If we're talking open pipes , the power gain can be significant.

Full exhaust. This is still a road legal car.