WHY DO WE HAVE SLIP-ONS?

[OB_Dirty Pete]

Why do all high performance bikes, not just stock ones but all 4-stroke racing bikes too have great whackin' huge slip-ons?

I'd a thought tuned straight-through pipes or dumps/dry stacks would produce more hp. Certainly it always works that way on cages and (4-stroke) boats of every kind.

Low efficiency mills like H-Ds and old English bikes seem to thrive on tuned straight throughs.

I understand about expansion chambers for 2 strokes, but what purpose does a slip-on serve for tuning a 4-stroke...expecially those cans that do not use their internal volume for resonance or back-pressure but rather just blow the exhaust charge right through an unobstructed tube that runs down the middle of a packed slip-on?

I don't believe it's for noise reasons on the track...race cars blow much more noise and run on the same tracks. And besides, if you've ever run your bike with straight-through slip-ons removed, even on a 4-2-1 system, you know there's no decibel difference at any revs or engine loading.

There's got to be a solid tuning reason for slip-ons.

If there isn't, I'm throwing mine out and tuning straight pipes that dump with a twist right after they exit the fairings.

 

[OB_ducmanic]

Today, Turbo Rick set a new SCTA Producion Speed Record of 203MPH with stock pipes on one of his bussas at El-Mirage California. His unfaired turbo bike went 197PH with no fairing. Bert Branson was there and phoned in the results. Stock pipes on the bussa' seem to be a nice trade off between social acceptability and performance. Untill a bussa with aftermarket pipes tops this, there is a lot to be said for stock pipes/cans.

ducmanic
LA

[This message has been edited by ducmanic (edited 13 November 1999).]

 

[OB_jeffw]

For 30 lb, the stock exhaust should also do the dishes. I'll keep my "low performing" yosh ti exhaust, all 7 lb of it. Hell I might even take it to bed with me tonight

 

[OB_KawAbuser]

Jeff that maybe illegal in some states, you better call a senator first.



[This message has been edited by KawAbuser (edited 13 November 1999).]

 

[OB_maui]

Maybe sonic packing like on 2-strokes? I don't know, here's what little I got on headers........

Primary tube, and collector length, affects torque and horsepower. It's usually a trade off, one for the other. Just as you need to have your gearing right for every track, tuning your exhaust is no different. Longer primary tubes increase torque, at the cost of horsepower. Collector length changes cylinder scavenging. To compare a 4 into 1, or 4 into 2 into1 against a set of zoomies is hard. Usually we run the zoomies on blown cars as the scavenging effect is not needed, as you push the air/fuel charge in. At that point, you just need to get it out.

Drag "cages" also pick up quite a bit of down force, and even some forward thrust. 1000 to 1200 lbs. of down force is not unusual. Last year a fuel dragster in Texas lost his clutch on the line, and caught a partial stuck throttle at the same time. With no driveline, at 4000 rpm, I think he did 130 mph in the 1/4.


[This message has been edited by maui (edited 14 November 1999).]

[This message has been edited by maui (edited 14 November 1999).]

 

[OB_Dirty Pete]

Thanks for taking a run a the question Maui. Are there any other pipe experts out there like someone who works with Muzzy or Hindle or...? Frank A., you probably have some experience on this.

BTW Maui, did you mean to say that the thrust from the fuelly's zoomies sent it to 130 in the 1/4?

That aside, I'm asking why we all hang these freaking great barrels off the sides of our bikes. They look like lifeboats on a 32' Skater ocean racer.

I have some extra pipe-to-can circle gaskets on the shelf. The next ride I take I'm just going to drop the cans off and see how it affects acceleration. Will report back soon as the freezing rain stops.

I have heard that straight pipes will heat up the exhaust valves and the whole head, so I'll pull plugs right after a fast run.

 

[OB_ducmanic]

Pete,
Its not that straight pipes heat up the head, quite the opposite. Its that scavenging
may draw cold air over your hot exhaust valves and warp them. With the long headers
on the bussa' this may not be a problem. This is academic, until its your bike -

LA

 

[OB_Dirty Pete]

There's a workable theory. The cans hold heat after shut down so that cold air doesn't get to the exhaust valves and warp them.

Probably true for the street, but racers wouldn't hang cans unless there was a hot-running advantage to them.

I'll phone Lang Hindle, who lives down the street, and ask him tomorrow.

He oughta know.

 

[OB_maui]

Dirty Pete, yes, a thrust only run netted 130+, but to be fair, I think the clutch went out in the first tenth of a second, which would give you about a 30 mph bump to start off with. Fuel car telemetry I've seen usually starts at 9+ mph .01 in to the run. They don't start at 0 and go to 0.1, the first registered speed seems more like an impact.

We cover the zoomies right away after a run. This keeps the cool air off. Zoomies will cool faster than any other type of exhaust! I also do a valve job after 50 passes, our installed seat pressure is 375-380. We're +900 open. This just means we beat the hell out of the valve, so the faster cooling doesn't help matters.

If you do run without your slip-ons, just cover the end with a rag when you turn the motor off. You can roll it up and plug it. Let it cool down to the touch and you should have no problem. I would guess you'll loose a little bottom end power if you run this way, which might not be to bad traction wise. You will pick up on the top end if this is the case. This could result in a lean condition, so watch the color on your pipe. If it starts to burn the paint off, abort your test. Probably won't be that bad though.

Thanks for the commentary on the "wannabe" thread, I couldn't believe the sh it that flowed from that comment. Just when I thought I'd done a pretty good clarification, kevtec throws a cyber sucker punch. Caught me off guard with that. Sure, I "wannabe" a busa owner, and will soon I hope. Maybe he thinks I'm not smart enough to be on the same page as him. I'll just "hang around" till then.

 

[OB_Dirty Pete]

You better.

 

[OB_maui]

So what did Hindle say about the titanic size slip-on?

 

[OB_Dirty Pete]

He said that managed back pressure is necessary to give track and street bikes mid range usefulness. Even packing around a straight through can changes back pressure and tuned resonance. If you want to only produce power at one narrow peak rev band, go dumps or pipes with megaphones, which would accord with a lot of what you said.

He also said that noise is a consideration on tracks in many parts of the world. He wanted to know if I had dynoed my old V-Max 4-1 with and without the can. I hadn't. I'll encourage him to do a can/no can dyno test at his shop when I go for the high pipe fitting.