Tuned Exhaust for Rotax 912 (Lost!)

It seems the conversation I started on the cost benefits (or not) of fitting a tuned exhaust system to a Rotax 912 has somehow evaporated.

I would like to restart the discussion -

Last post I was attempting compared the 912 with an small car/ motorbike engine and I suggested if these power plants experience benefits in power production why would the 912 not do the same.

Dan3111 on this forum is doing one now. JimG on here who is a engine guru machinist and builder for race car engines has done the design. They are getting the bits together now for it to start getting it done so maybe watch this space. The biggest issue is getting some of the parts at a reasonable price. Donuts and the hearder connections and clamps are the issue without getting raped by Floods

Do you know if JimG designed a 4-1 or a 4-2-1 system?

Given the very crude factory design, I don't think it would be difficult to get a few more HP out a 912 and a bit more efficiency.

Its a 4 into 1 at this stage. Yes Jim said the only way to get the extra grunt from engines in the days before electronics and turbos was the exhaust...they used to spend lots of effort on exhaust systems and he is a guru with them. If the engine cant breathe properly it cant perform. The later Sav's are choked badly. This system will be designed the the Sav at this stage

The bloke in Melbourne making the turbo Rotax's has a great exhaust. Beautifully made.

Looks to be mandrel bent.

Chopping up "donuts" at wierd angles and welding them to straight tubes looks "ruff as guts" in my opinion....

The donuts are so we can get the design right..there is a cnc tube bender guy not too far from us for anything done later but while making stuff to get the length and bends right first donuts are the easiest way

Hi Kyle - it would be great to get some befor tuned exhaust and after fitting performance figures & general comments

Yes...before it get changed Danny will take some figures on his then do the changeover. Without changing anything you will see a change in RPM. He will be using a accurate tacho and also 4 EGT and a wideband oxygen sensor to also check the jetting required

Dannys intention I think is to supply a kit for for it after they get it done. I think though yesterday he was saying maybe 2 exhausts at first. so it will be 2 into 1 on both sides with little hotdogs on each one. Once they sort out the bend paths to get the correct lengths then they will go from there

I like my two into one on the 80hp 912. It’s definitely not a performance setup but it makes a nice square install with the exhaust cans under the pots

Hi Mark,

Has as this project exhaust system evolved any further?

Many thanks

Robbie

He has all the bits now..donuts and exhaust fittings for the head outlets etc. I think they have done the design but one issue is I had to make a mandril for the tube bender to suit the tubing size on my cnc machine. That is done except the bending/locking bar. I should hopefully get that done after I get back from holidays. Finding tube benders that do more than one inch size tube are rare or very expensive. Dont confuse a pipe bender with a tube bender they are 2 different beasts. The hope is once its done then we can get a CNC tube bender place to do all the bends but during development you need to do it yourself. 

So the short answer is we are still working on it.