exhaust pipe extension beyond the collector

[Dragsinger]

In order to help put the Methanol fumes and the noise behind the driver, I will need about 30" of tubing after the collector. The engine is SBC of about 725 horses. The headers are 1 7/8 x 2 x 3.5

What is the size and length guideline? Would it be reasonable to add a 4" x 30 extension? Also, I am considering aluminum pipe for the extension.

[BLSTIC]

Assuming your engine doesn't actually want more collector length... A sharp step up to a much larger pipe (say 5" or larger pp) should keep your tuning the same and allow you to point the exhaust somewhere else. You can gradually neck it back down to 3.5 if you actually need to fit it through something, the important point is the sharp increase in area looks like the end of the pipe for wave tuning. DV details this in a couple of his articles as a termination box I think.


I wouldn't use aluminum except on a drag car. If you've ever seen your collectors glow, just remember that aluminum melts before it gets to that temperature

[MadBill]

https://musclecars.howstuffworks.com/cl ... r-duty.htm

"To shave another 40 pounds, the factory would fit aluminum exhaust manifolds. They were intended only for quarter-mile competition; Pontiac warned that subjected to more heat, the headers would melt." (max of 15 sec. WOT.)

[Dragsinger]

Reading my text about the car using Methanol will point to this being a trailered drag race car. In addition, my talking about helping put the noise behind the driver will suggest no mufflers

Just poking fun.

Anywho, I should have asked in a different way. What I want to know is how can I add 30 or so inches to the collector without hurting performance.

[MadBill]

In the PipeMax header design program, optimum suggested collector lengths are specified as 'best = x", 2nd best = 2x", 3rd best = 4x"'. It also specs. worst as 1.5x, 3x, etc. Often x is in the 15"-17" range, so if yours is in that range, 30" added to a current 15" would be a 'worst' 45" and you'd be better off extending them to 60".

[ProPower engines]

Reading my text about the car using Methanol will point to this being a trailered drag race car. In addition, my talking about helping put the noise behind the driver will suggest no mufflers

Just poking fun.

Anywho, I should have asked in a different way. What I want to know is how can I add 30 or so inches to the collector without hurting performance.

Testing is the best way. Make several extensions and test. Time slip should tell you if you dropped of
enough to worry about.
This is assuming that ground clearance is an issue by using a larger diameter pipe for the extra length.

The other option is to re-design the system to exit out the side of the car through the lower fender area
which seems to be becoming much more common these days to free up clearance under the car. 30 inch's
is a long extention when using the same size collector diameter but the other thing is you can make the extensions
and stripe them to see where the stripe burns off at and call that total length.

I know this is not apples to apples but methanol burning circle track cars have the same issue and they do not seem
to mind the extra collector length and 30" would be very close to what some with a cross over the top style header
would be using before any noise dampening device but the longer length may give some extra scavenging affect
the engine may like.