Bonneville America Forums Forums Technical Forums Exhaust straight pipes question

hey all, I know countless bikes are running open pipes but it seems like I have always heard that engines need some sort of backpressure....As long as you rejet to accomdate the engines deeper breath is it still harmful to an engine? I have a set of BuBs now and I love em, however I want to go into a little bit more of a custom direction. Maybe the iron city cycle fishtails/wrapped header or possibly even a straight cut of brass tubing clamped to the end of the pipes with a nice wrap. Was also thinking of flexible stainless steel instead of wrap. Any suggestions?

All you need is a little back pressure or you lose bottom end torque. Won't hurt the engine.Just for an example the 5th baffle down is plenty.It's the 4" baffle.
http://www.jpcycles.com/search.aspx?search=baffles&store=All

thanks for the info, will that hamper the sound any? and also, does anyone know the characteristics of brass? As in- would it do well in a high heat environment? And how do most baffles fit into exhaust? welded? bolt? rivet?

I have 10" samsons in mine, and they just takes the high edge off, but not much more. Look at the ones from khromwerks, too. More money, but very low restriction.

Most of the baffles I have seen use a single bolt. I put the hole at the bottom slightly to the inside where it won't be seen.

The 4" baffles I posted I used to use in 1 3/4 drag pipes for some back pressure and it doesn't effect sound at all. Make sure when ordering any baffles you measure the dia. where you want them to go and be sure to get the right size.

The straight pipes (or Drag Pipes) are just that, they produce power at high RPM, a 1/4 mile drag with full on the gas. For around town and lower RPM's you need some back pressure for more power at lower RMP riding....The drag pipe will not hurt the motor, you just lose power at lower RPM....

If you like to wind the engine out, go to the straight pipes. I have the 16" JCWhitney shorties, they sound great, are a helll of a lot lighter than stock. The 16T front sprocket helps it spin up fast. Remember, the alternative is to have more back pressure and run out of breath at the top end. The 790 has more top end cams anyway. Maybe with the 865 it would make more sense.

Naw, spin it and grin it!

I'm going to hijack this thread a minute- I think I put my baffles in the wrong way. Does the cupped opening face the engine or the exit?



I put them in to "scoop" the exhaust, but the bubs site looks more like they just act as "bumps" with the air moving over the domed backs as opposed into the cupped fronts. Is my question clear?

They should not be like scoops.

FWIW, once I pulled the baffles from my Specialy Spares and ran for a few days. It was incredibly, neighbor-losing loud. To me, it seemed like I lost all the bottom end torque. It wasn't a good feeling and the baffles went back in, much to the delight of everyone in my neighborhood.

So looking at the pic above, the engine side would be to the left and exit side would be the right?

yes