On shovelheads I've heard that 39" or 40" is the ideal length for exhaust pipes.. My question is do the two pipes need to be the same length? can one be like 39" and the other 43"..

 

On a stocker, with 1 7/8" pipes, go with 39 1/2" on BOTH pipes. You can jet them in from there. On WELL built stock stroked and big strokers, start at 40", and chop a 1/8" at a time after 3 dyno runs. When you see a slight drop in torque, stop cutting and jet in from there. Nine times out of ten, it'll be around 391/2 +/- 1/8th. On the well built motors, I found that an exhaust system like a SuperTrapp is the best way to go. This is assuming you are running the normal street cams offered in the aftermarket. When you get into the bigger cams, higher compression, and motors over 96", all bets are off, and you are riding a dragster, and stepped exhaust (commonly known as the megaphone) come into play. I hope I didn't cloud up you original question. I've run some badass, horsepower snortin' shovels and ironheads, and this is what I've encountered over the years, under the direction of a great tuner.

 

Thanks for the info.. it was helpful.. I guess my main objective was to know if both pipes should be the same length and you did answer that... What happens if one pipe is longer than the other.. and I mean by a couple of inches or more?

 

I love the supertrapp 2 into 1 I run 22 diffuser discs on my 96 ci S&S

 

As you know, but in the event someone else is reading this down the road, diameter of the pipes is important. Too short of pipe, as well as too large of diamter, will kill the torque and/or HP. The above lengths mention work with only the diameter mentioned..., and IMO the 1 7/8 work best on a shovel...

Later

Hogback

 

You are right HogBack. I've never run anything less than 1 7/8". Shovels seem to run good, and sound good with them.
As far as running two different lengths, You'll never be able to dial it in exactly right. I would have to assume the cylinder with the shortest pipe would lean out more than the other. Probably wouldn't hurt it, but I don't have data for different lengths.