pipe tunning

[RMgrind]

Iv seen mentioned on other post the idea of putting a shim at the exaust flang to lenthen the pipe and thus change the power band. i have a 83 rm 250 that i would like to get more bottom out of . this is a non power valve motor. But i have a few ?s

1. is this safe for the motor

2.will it broaden the powerband

3.will it soften the harsh hit

4.how long should it be to start with? I think i can get about 1 inch with out much problem

I ride mostly woods so if i loss some on top i wont notice .

what do you all think :clue:
thanks bill

 

[marcusgunby]

1 yes
2 maybe
3 might do but may just as well make it hit harder
4 try 6mm

its really one of those mods that works on some but not all models-it depends alot on what pipe is fitted.If the pipe is well designed for bottom end power you may find no gains.

 

[RMgrind]

the motor is a screamer, all mid and up so i have a feeling that the pipe is not well desinged for low rpms. also pipe selection for this bike is vary limited, Iv only found the DG pipe and im betting that it is desinged for MX and wont offer much in the way of low end. But what the heck if wont hurt the motor its worth a try and a lot cheaper than haveing a pipe made up for it.ill try the shim as time allows and post back the results. Also if any one knows of other pipes for this bike please post

 

[marcusgunby]

I think the spacer has potential to help-let us know how it works.

 

[Rhodester]

FRP Racing makes a "torque ring" for KDXs (only) that fits between the cyl. and pipe that adds 5.5mm to the pipe length. I used it on my KDX200H with the -30 FMF (rev) pipe to see if it would add to the bottom power range. What it did was to drop the power band (curve) about 200 to 300 RPMs. The power band charateristics (the hit, etc.) were exactly as they were before only at 200 to 300 RPMs lower. What I'm trying to say is that it really didn't add anything to the low end power or positively change the power characteristics to that of a "torque" pipe. I later went to a torque pipe (-35 FMF) and am now much happier. My torque pipe will actually out rev my rev pipe when I have the rev pipe on with the torque ring.

 

[cujet]

I find that adding length to the headpipe (2 stroke pipes) is a very effective tool in tuning the torque peak. I generally use 25mm (1 inch added or subtracted) as a place to start. While this seems excessive to most, it will give you enough of a difference to feel. Smaller numbers may not be so easy to feel by seat of the pants. In particular, if the engine/pipe combo is so biased towards top end, adding 1 inch will move the power down to a more normal feeling combo. This is not to say that you will gain HP! Just that the torque peak is easily moved by changing the head pipe length.

Chris