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!