Reducing Bpipe stinger diameter?

A Bpipe outlet diameter is 2" od, 1.825" id. Powerfactor pipe is 1.625" id. A reduction of about 26% in area. Of the few books and papers on expansion pipe design, they all recommend a stinger diameter of 60-70% of the headpipe diameter. This is a bit difficult to measure considering this is a 2-into-1 exhuaust. My guess is the powerfactor's smaller stinger size is still on the safe side, considering it's used for just about any engine from 701-1200cc. Probably not good for long periods of wide open throttle, but should suit my riding style. It seems to be a smaller stinger diameter will increase the pipes back pressure and raise power everywhere at the expense of higher engine/piston temperatures. I'll be turning some 1-1/2" schedule 40 aluminum to slip inside the existing stinger and use a second hose clamp to keep it secured in place for testing.
 
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I believe that xscream basically did the same thing. I'm not sure what the Id of the reduced stinger is though. Im.also curious to know how it will change for you. I have a reducer for my tnt so chamber that I have yet to try. From whave I've read about 2 stroke pipes, reducing stinger diameter will give more power in the upper rpms but may hurt bottom. But it's all according to the diameter of the headpipe too.
 
The xscream mod seems to be a sleeve over the original stinger , not making it smaller. I cannot confirm, only based on pictures I've seen. I currently have the manifold/headpipe bored to 50mm and a 4mm restrictor in the stinger nozzle.
 
After finding some better pictures one showed the outer sleeve as 60mm, which makes sense so you can use a straight elbow to the waterbox. I did some caliper "screen measuring" and the inner sleeve is around 1.600". If someone has one to actually measure that would be great. Aluminum came in today and the id is already 1.61". I plan on cleaning that up to around 1.650"-1.675"

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As you make the stinger smaller the back pressure increases. Note: Most small twin cyl Jetski race pipes are 41mm-44mm

If you do decide to make your stinger smaller for increased performance. Please note you may need to revisit your dome profile (cc, squish,shape) , timing, prop load! and carb tune. That’s assuming you have it optimized for your weight/setup

So many people on here run 701’s, b pipe, ada 35cc and pump gas. Try that with a “good pipe like a dry race pipe” and/or a performance dome profile at 35cc and you will have issues.

Adding more: More CC’ s changes the game some and some race / serious freestyle pipes were sleeved way down because the waterbox was gutted or a resonator was used.
 
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I currently have a 5mm stroke 85mm ported stock topend with 37cc domes giving me 195psi. Zeel timing is 28 degrees from 1500rpm to 4500rpm and tapers down to 18 degrees at 6000rpm. Burning 93 octane without issue. Plugs look good, piston wash is typical for reverse jetting. I'd love to look at the bottom of the pistons, but that won't happen till I pull the topend off this winter for a refresh. I'm hoping to put a few tanks through with the stinger reducer in and look for overheating/detonation around the piston crown with my bore scope.
 
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dfw
The more civilized riders know they can just use a VERY quiet muffler and have NO power loss! Remember this applies only to tuned pipes. Any backpressure will act as a throttle with untuned exhausts.
 
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Flash-FX

No Square..No Round..FX-1
The xscream mod seems to be a sleeve over the original stinger , not making it smaller. I cannot confirm, only based on pictures I've seen. I currently have the manifold/headpipe bored to 50mm and a 4mm restrictor in the stinger nozzle.
Xscream changes the inner tube to be smaller, then adds the outer sleeve. (I've done that same thing on a couple "B" pipes) . The water stream is introduced between the two tubes. On the original style of stinger, it has water injected into the exhaust gas stream, somewhat reducing the area, achieving almost similar performance. The problem is you can inject too much water and create a power loss, where as with the stinger mod you can run it drier.

Remember the "B" pipe was originally designed as a bolt on for a STOCK Yamaha 701 motor. It worked great by adding 19-20hp (advertised). It has limitations on large CC motors and can give you tuning fits and frustration. The Power Factor pipe was designed for larger displacement motors and will give you more than the "B" pipe ever could. Even though the PF pipes aren't perfect and have their own problems too...
 
Flash, thanks for the insight. If this works out I'll plan on doing a similar inner/outer sleeve this winter. I also edited my first post. The bpipe inner diameter is 1.825", not 1.875". I have the sleeve turned and hole drilled for the stinger water passage to pass through. Its a press fit so I don't expect it to go anywhere, but I also ran a second hose clamp to keep it from moving. Hoping to test tomorrow. I noticed now that I'm running a kart tank, is the ability to roll a new convergent cone without the gas tank cutout. Another thing to test at a later point.

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Jcary85

Site Supporter
Location
Glenmoore pa
I haven’t done too much testing but I did experiment with an insert on a power factor. It ran worse all over on my TPE 12. I then cut the stinger off and welded on just the larger tube. Made a nice power increase across the whole power band. Obviously every motor is different but that was my experience.
 
I haven’t done too much testing but I did experiment with an insert on a power factor. It ran worse all over on my TPE 12. I then cut the stinger off and welded on just the larger tube. Made a nice power increase across the whole power band. Obviously every motor is different but that was my experience.
When we were racing superstock SXR’s once the CC was allowed to go to 850 we would cut off the 41mm and go larger. The waterbox became the air throttle on BP. Until we got over 850 the stock water box was fine. Sure some people drilled some holes but overall it was just fine for top Pro level boats at 850cc.
 

IceRocket1286

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Location
Metro Detroit
Flash, thanks for the insight. If this works out I'll plan on doing a similar inner/outer sleeve this winter. I also edited my first post. The bpipe inner diameter is 1.825", not 1.875". I have the sleeve turned and hole drilled for the stinger water passage to pass through. Its a press fit so I don't expect it to go anywhere, but I also ran a second hose clamp to keep it from moving. Hoping to test tomorrow. I noticed now that I'm running a kart tank, is the ability to roll a new convergent cone without the gas tank cutout. Another thing to test at a later point.

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This is the same concept for the stinger insert that R&D made for the SXR. An extra hose clamp has kept my stinger insert in place for many years without issue. Interested to hear your results, especially if you try different diameters...we messed with our diameters 1mm at a time. Fun stuff.
 
Was able to test it on sunday. Overall I'd say no change to overall power with a slightly longer time to get to peak rpm. I took it out again yesterday with it removed and it felt normal again. I've been running a 4mm restrictor in the stinger outlet and moved down to 3mm and that made more of a positive difference in throttle response. I was getting too much water in the waterbox.
 
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