Custom Exhaust Help

[cartierusm]

OK So I'm getting close to being finished with my custom build. I built the exhaust the other day. It's exactly the way I want, but the rear pipe is really short.

SO my question is what do I need to do to make this exhaust work for my 1992 sportster evo motor. I'm not looking for extreme engineering and tuning my exhuast for maximum perfection. I'm just looking for a little guidance on how to make this exhuast work.

Since I need back pressure to make the engine run well should I add some round discs with holes in it to the inside of the pipes, multiple discs, to create the back pressure? So what should I add? Thanks.

[Jimmy_Hoffa]

IMO, back pressure is over rated. I put torque cones in my exhaust and I went from pulling hard (unloading the front suspension) at 100+mph to now I can't get past 93MPH, so I'll probably remove them at some point.
The only thing I'd be worried about is the cops, that will be LOUD!

[cartierusm]

Should I put some discs in there to quiet it down a little?

[maru]

I think you will have to finish the bike up and run it down the road to see if you can live with both the noise and the performance. With stock narrow overlap cams you may be able to live with the reversion issues an exhaust that short is likely to cause. Noise is between you and the boys in blue. In some areas a loud bike is not much of an issue, in others that is not the case.

[cartierusm]

Stupid question running short exhaust won't hurt the motor in any way?

[Bob F]

Welcome to the XLForum.

[jharback]

Originally Posted by cartierusm

Stupid question running short exhaust won't hurt the motor in any way?

I believe, tho' could be wrong, that the only danger is that they make it extremely hard to get the motor properly tuned. Large diameter, short exhausts are a real bitch when it comes to getting the bike properly tuned. Normally the exhausts should also be the same length.

As for trying to prevent some reversion (back pressure) I'd just install some lollipops. It'll cost about 12 bucks and they're adjustable. Just do a search here on the forum at the bottom of the page. You'll find different ways to do it along with instructions. They work quite well tho' with those pipes you'll get popping on deceleration no matter what you do.

[Jimmy_Hoffa]

Originally Posted by cartierusm

Stupid question running short exhaust won't hurt the motor in any way?

2 things. I've heard you can get burnt exhaust valves (whatever "burnt valve" even meens?) and I've also heard that with an open (and very short) exhaust like that, it will quickly let cold air get up to the valves when you shut off the engine and that rappid cooling can warp exhaust valves. I don't know if either is true, or just slightly more likely to happen, or what.

Oh well, valves are cheap, right?

[cartierusm]

@Jimmy Hoffa, I've heard that before about 20 years ago, but not sure if it's a wives tale or what. I'll have to consult my local header manufacturer.

Thanks to everyone for the advice.