Tuning the exhaust is complex but the long and the short of it is that a straight pipe would favour the high end with improved HP.

The same pipe with a restrictor favours the low end with improved Torque.

When you open up the stock pipes you'll notice that the torque is 'missing'; there needs to be some restriction for the exiting gases.

Doc

It's weird Doc...I did not really notice the reduced torque after the stage one...I have a new set of unmodded pipes I may throw on just to test the theory

Regards, Ted

I think your right Doc. I've been riding around with stage 1 modified stock pipes since last August and didn't notice the drop in low end torque until I rode my fathers totaly stock silverado this past February in Florida. It's not like this small drop in torque at low rpms means that much on a torque monster like the Road* though.

I doubt you'll notice a drop in torque for Stage 1 as they're is only a little difference in the back pressure between Stage 1 and Stock.

However, once you go to Stage 3, where the internals are gutted and the exhaust becomes free-flowing, I believe you will notice the difference.

When I first put on my Nasties (which are similar to a drag pipe), I noticed a significant decrease in the 'snap my head back' feeling. I did not like this loss of torque so made up some restrictive baffles with which I was able to regain a notice increase in torque.

Over the years I've noticed that the free-flowing exhausts (like drag pipes) may be good at high revs (and for that loud sound) but they generally decrease 'performance' for normal stop-light to stop-light around-town driving.

Doc

yes, it's a common mis-conception that open drag pipes makes your bike faster... due to the complexities of the modern 4 stroke engine you need back pressure to get the maximum performance from your bike.. the exhaust valve opens a moment before the completion of the power stroke and the back pressure keeps the piston moving -- and other factors such as resonance and sound wave disturbance (don't ask me - I don't know - it's much to complicated - and I think most of the people who study this crap are just making up untested theories - but I also admit, they know more than me)
as Doc said you gain a little top end, but loose a little low end when you open up the pipes... now I'm not sure where the exact pressure should be, and I don't know of anyone who is sure where it should be (I can't even imagine how you could determine that - given all the posible influencing factors such as temp, pressure, fuel, and little gremlins who always introduce a slight bit of varibility - just ask anyone who's dyno'd their bike), but generally we say that the stock exhaust is a little to restrictive, and open pipes don't have enough restriction.. now as to pipe makers, most pipes are made for sound and appearance, not performance (thats what sells - get the look right and the performance close)... if you're looking for performance you will pay for it, though generally it's belived amonst racers you get the best performance from a 2 into 1 pipe (shared back pressure)... and I agree (strangely - I don't agree much)... I do get a good laugh out of harley riders who think that loud = fast... but of course if your talking speed, you'd be better served by adjusting the gearing (front sprocket), you loose a bit on gas milage, but man you would be hell to beat of the line... but thats another story all together... ~Guido

Guido--

You had me lost at "common misconception" LOLOLOLOL...

but I do dig the slots

regards, Ted

You must be talking about rpm below 2000 ..studying the charts for the varying stage configurations in the Speedstar from my accessories catalogue shows increased torque due to drag pipes at 2000 rpm and dropping off as rpms increase and with HP the opposite is true... HP increases as rpms go up. Do you have these charts at your disposal??? Of course these pipes have fixed baffles and probably have the neccessary back pressure for proper tuning.Without baffles you would have all the problems you mention even negative back pressure
Post edited by: Pop Rivet, at: 2006/04/29 04:47<br><br>Post edited by: Pop Rivet, at: 2006/04/29 08:22

I should clarify.. by saying drag pipes I was meaning open / straight pipes.. speed star pipes which do have baffles in them will provide better tuning of course.. being from yamaha, I assume that they've done a little more research as to how it effects their product and I know I'd be really pi$$ed spending that kind of cash and have a loss of power, when they advertise a gain... as I said, if you're looking for performance, you're gonna pay for it.. but really for the look 500 isn't that pricy.. now personally I liked the look of stock (I've got the midnight star siveraldo) so for me, the cost of modifying the stock pipes was perfect... ~Guido