I'm still not positive that a multi-stage diffuser is better for our engines. The M&D pipe and the Quickdraw Hot Pipe are very hard to beat. They have two cones and a straight header. Simple length adjustments adapt them to any rpm range I want to consider. We've tested them on Quickdraws, and several Zenoahs. I have just begun a Zenoah pipe program. The high horn coefficient diffusers help with stock intake timing by creating a strong suction pulse, but timing and other changes negate this advantage. It's possible to get higher peak power over a narrower range, but getting a high, broad power band is hard. It's also possible to get higher rpm, as we did with the CMB program, but high power and high rpm is also hard.

Lohring Miller

Here is a quote from a two stroke forum:

"The shape of the diffuser and the baffle cone need to compliment the engine design and engine application. The diffuser shape must match the scavenging flow pattern as well as the bulk flow of the scavenging process. Every engine design will usually need a diffuser shaped to match it’s own unique scavenging characteristics. Diffuser shapes have changed over the years as the port layouts and scavenging characteristics have changed. The exponential shaped diffusers do work well but I believe others and myself, got too carried away years ago in trying make the diffuser visibly resemble a trumpet in the early years of exponential shaped diffusers. It was not uncommon for the diffuser angles to progress as much as 7 to 10 degrees or more between stages. Today, many of my diffusers may not change more than 2 or 3 degrees between stages."

Lohring Miller

Finished pipe Lohring have not tested it in the water yet i will let you know how i go , tried to send picture but i cant get it to post

Mark you should be able to post the pics on here...click on "additional options" below the text box when composing your message to add attachments. Keep the pics under 3meg and your good to go!

Run pipe for first time today and are very happy it turned out to be a broad power range with top end to be tuned in a bit more for a few extra revs , going to shorten mid section 5 mm as i designed pipe for 17,000 revs may be a bit on the conservitive side. It turned out to be more of a curcuit racing pipe rather than a straight line pipe but i are still happy the way it turned out . Cupped the prop a bit more and was good through bottom end mid range but felt a bit flat at topend. Thanks for the advice Lohring it steered me in the right direction

I think I would shorten the header section Mark.

Looking at the pipe it would be better at header Marc . Welding with MIG with .6 wire it`s a touchy . I managed to keep the dags outside the pipe thats why weld look a bit ordinary. I know TIG is the way to go but MIG was nearby

Shortening the diffuser section requires shortening each section proportionally. To see that, change the tuned rpm in your pipe design program. I did extensive experiments on a Zenoah pipe with a multi cone diffuser where we could change both the header length in a parallel section at the exhaust port end of the diffuser and the parallel band section length. The diffuser had a sweet spot that was the design length. The power peak rpm was best adjusted by changing the band position. At the same time we did similar experiments with an M&D two cone pipe with a parallel header. There, changing the header length was the only way to change the tuned length. This is also true with the Quickdraw Hot Pipe. When you shorten the header length on these pipes the peak is at higher rpm, but you loose peak power. The total pipe length from the piston to the start of the stinger usually a good predictor of peak power rpm. How high this peak will be is the hard part.

Lohring Miller