Help with my custom exhaust

NickDK · #1 09-19-2009, 01:19 AM

I have read that putting on exhaust without proper back pressure can cause damage to the engine. I designed a custom exhaust that is essentially a loud straight pipe -- for safety, of course

! It is about 4.5 to 5 feet of 3/4 inch diameter pipe ending with a cap with a 5/16 inch hole in it (slightly larger than a pencil). This is my fourth build but my first stretch cruiser which is the reason for the long pipe. Its a 80/67 cc 2-stroke. Will this set up with the 5/16 inch hole keep my engine safe? BTW, 5/16" is very close to the size of the outlet hole on the stock mufflers.

I have driven about a mile with the new exhaust and I noticed that I have dramatically increased my low end acceleration -- without any doubt. I haven't taken it over 20 MPH yet so don't know about top end. During idle it cackles and pops like a Harley (a Harley with ovaries that is). The cackling is not rhythmic and seems to come in spurts of 10 or so before pausing a split second.

I will really appreciate any input you guys have!

xlite · #2 09-19-2009, 09:03 AM

I have considered doing that. Sounds like it's behaving like a tuned pipe. I'm sure it's not going to damage the engine because there IS back pressure.

Any more details? What kind of pipe? Pics?

NickDK · #3 09-19-2009, 12:45 PM

Here are pics of the exhaust. First pic is just the end cap with hole drilled. Third pic is just of the home depot rigged coupling I made. Second and Fourth pics are of the whole exhaust. Luckily, most of the hideousness is hidden by my saddle bags. I will post pics of the whole bike when I get it done and cleaned up.

Kevlarr · #4 09-19-2009, 12:50 PM

Can't tell from the pics but do you have the black iron pipe supported behind your saddlebag?

BTW you can do away with the black pipe coupler by getting a female compression fitting.

NickDK · #5 09-19-2009, 01:03 PM

Quote:

Originally Posted by Kevlarr

Can't tell from the pics but do you have the black iron pipe supported behind your saddlebag?

BTW you can do away with the black pipe coupler by getting a female compression fitting.

Yes, the iron pipe is firmly mounted to the frame with hose clamps behind the saddlebag. I plan on doing away with the iron coupler as you said and replacing it with a nice brass fitting. I wanted to make sure this would work first as the brass fitting was 4 times as expensive. I am also gunna use a slightly shorter iron pipe so the exhaust dumps under the saddle bag so you can't see the hideous tailpipe at all!

Thanks for the replies! Any input on the effect a set up like this can have on my engine? Is it safe?

Kevlarr · #6 09-19-2009, 01:08 PM

Was just wracking my brain a bit (I spend a lot of time at HD lol) and I think they have chrome pipe for towel rods and such that is about the same size as the exhaust. If you used a double compression fitting to the chrome pipe then a brass compression ell to act as your turn down and to attach your cap that wouldn't look bad at all. Or just use a small length of electrical conduit.

NickDK · #7 09-19-2009, 11:35 PM

If I could find a chrome pipe with 3/4 inch threads that would be awesome. Thanks for the info. I never would have thought to check out towel rods!

Still calling on someone with some exhaust experience to give me any info on back pressure and safety to the engine...?

Humsuckler · #8 09-20-2009, 07:12 AM

well,

the popping and crackling is a sign you have BP, when its not popping is when you worry. in other words stay out of the "sweet spot" as much as you can and yo should be alright