Help with my custom exhaust

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!

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 said:

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.

Click to expand...

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?

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...?