My KTM 500 EXC turbo project

We will run the same type of fueling as previous turbo build.
We're using MCX piggyback fuel injection. It has worked fantastically well!
The system is completely independent from the bikes OEM fuel injection.
We think you avoid a lot of hassle not having to mess with the bike's fuel system.

MCX EFI box is an entirely indipendent system with an additional fuel injector at the intake of the throttle body, supplying extra fuel at boost.
As we´re running fairly low boost, we made the assessment that it is not necessary to change to a larger fuel pump or install a fuel pressure regulator. OEM pump has been found to provide sufficient fuel pressure at 0.7 bar boost.

Here are some pictures of how the piggyback fuel system looks like on the previous turbo build.

Fitted EFI box under the seat. We will most likely choose another location because the space is less under the seat on the 2017 bike.



The injector that delivers additional fuel. Running Bosch blue injector, not black as pictured.



Picture inside the plenum. Here you see the injector pointing at the throttle body.



The only thing that has affected the bike's OEM fuel injection is that the FI warning light sometimes starts to indicate a faulty map sensor. This is because the sensor reads overpressure which is considered abnormal. It can be solved by soldering a voltage limiting diode on the sensor but have not yet taken the time to do it. In any case it is not affecting the performance, only a minor imperfection as you don´t like to see the FI-warning light flashing all the time...

There are other systems such as Power Commander, Rapid bike etc. We haven't seen any benefits of these except that on some systems, you can retard the ignition.
Thanks to good high octane fuel, intercooler and low boost, it has not proved necessary to retard the ignition. Such may possibly be necessary in the case you're running higher boost or that you want to run on pump gas.

Not many project updates in the thread recently. All my free weekend time goes in to building a cabin in the Swedish mountains. I will hopefully put some time on it in the beginning of January.
My buddy an cobuilder Jonas has however made some good progress on his turbo build.
Our builds are both the same ideas and design. Instead of my build, I post some pictures of his progress.

The location of the turbocharger will be similar to the previous build. However, with some different attachment points.




Since the new track kit has a suspension movement, the intercooler has to be mounted on the bike.
For a more leaner piping we test to use the intercooler in both flow directions, three cooling element ducts in each direction. A simple endcap reverses the flow forwardly. The front end of the pipe connections has a partition that channels the air in the correct direction. Some automotive intercoolers like the old Saab 900 turbo had the same solution to their intercoolers.



Optional fuel injector in the plenum.




The air intake gets a simpler solution with a rubber hose bend and a short piece of aluminum pipe before the mesh filter.


Jonas has been working on really good, just a few oil lines and electronics left, so we are planning putting it on the dyno shortly. It will be exciting to see how well it will perform!

Many have asked what turbochargers we use. Have not known to the model designation, but here you see it. It is a Mitsubishi Charger that obviously sitting in some kind of Iveco truck. It has proven also to be a really good choice on a KTM500 snowbike!

Finally some dyno testing at MCX.
We had a little trouble with rpm signal from the injector to the piggyback EFI box but eventually we got it to work.
We mounted additionally a pressure equalization can on the hose to the EFI box so it could stable readings.
Really good power. 93 rwhp at 0.55 bar (8 psi) of boost.
On this build, the engine is left totally untouched. Previous turbo build boosted 0.7 bar and 96 bhp with a modified engine. In this comparison, we feel very pleased with the result!

https://youtu.be/X2EGdPH2o-I

Working on relocating the intercooler. Previously, it has been mounted directly on the tubular frame on our home built snowbike kit.
The reason for the move is that we have ordered a Yeti. On this snowbike kit, with an enclosed tunnel design and a sprung strut, it had to be mounted on the bike under the rear fender.




Here a previous photo as the intercooler sits mounted on the tubular frame.

Completed the relocation of the intercooler. Have concluded that my current placement of the turbocharger is not optimal. The intercooler ends up unnecessarily far back and its also tight between the pressure pipe to the plenum and the wastegate acutator. Had to make a special bracket for the rear rubber pad. There was a lot of work for this simple build but will hopefully work out good.
Next turbo build will have a more refined placement of the turbocharger that will make an easier fit.



Aluminum welds could have been nicer but I'm an amateur. Practice makes training and I get better with time ... Profesional welders maybe cry by looking at this crap ;-)


A picture of how it all looks from below after rebuild.

Made the intercooler relocation build before I got the delivery of the Yeti kit. There were rough guesses how everything would fit. The angled fuel hose nipple for the fuel rail to the extra piggyback injector is maybe the only thing that gets tight. Currently waiting for the shipment of the sprung strut. With just a moderate suspension movement of the snowbike kit might end up in some redesign of this fuel connection...

After our first test rides, we have noticed that the location of the intercooler is not providing sufisiant cooling. Previous location had a lot of snow spray, but now as it sits placed under the rear fender, it offers limited airflow . When boosting hard and by feeling temperature by naked hands on the intercooler, the temperature was felt like between 35-40 degrees C! This turbo build may work just fine without intercooling, but we look for good reliability and try to reduce any risk of detonation. We believe that a good intercooling can offer that.
The planned solution is electric fans that will pull air flow through the intercooler.
Have found some high quality moisture-proof electric fans that we believe can solve the problem.
Plannning to install some temperature probes to monitor the efficiancy of the intercooler.
Stay tuned... ;-)

Corban_White said:

I always love your work. What are your thoughts on the Yeti vs your home built kits?

Click to expand...

Thanks Corban White.
I think we are one of the first to get Yeti kits in Scandinavia.
The delivery arrived on December 23rd. What an awsome Christmas "gift"! ?
Have only ridden the Yeti for two days. Need to test more to get a better feel of the handling.
I´m really impressed with the build quality of the Yeti!
I dont think there is any competitor that comes even close in terms of build quality.
Well thought out and many beautifully designed details.
It feels very light. Weight-wise, the 129" Yeti about 7-8 kg (15-18 lbs) lighter than our GEN 2.6 136" home-built kit.
We are awaiting delivery of RRS strut. Have currently only ridden with a fixed strut.
It will be really interesting to see if RRS can provide further improved handling.
This thread is mainly about our turbo build and not a review of the Yeti, but I throw in some pictures of it here.



Smart solution of chain tension. An eccentric bracket moves the kit backward that tensions the chain.

Interestingly, the Yeti has a different theory about the ski bolt placement. We always run with ski bolt upright in the wheel axle which has worked just fine. Instead, Yeti has chosen a lead of between 5-7 cm (2-3”) behind the wheel axis.
The back moved the ski spindle provides a very stable ride but also a bit more heavy-controlled. This topic is always a compromise between less control input or more stable and predictable ride. Maybe Yeti is right on this. Comparative tests on various ski spindles will show what we like the best.

Carbon fiber is always nice!


So far, I´m very pleased with the Yeti.
If you try to compare it with our homemade GEN 2.6, the Yeti feels very light when you lift the rear. However, you might not notice the weight difference that much when riding.
Yeti rolls very easily. Especially when you for example pull it off the trailer. However, I´m not sure that there are any noticeable difference in transmision losses at full speed and full load when comparing between belt drive or chain?

In summary, the Yeti feels like a wonderfully solid and well-built kit.
High quality in all components, beautiful details and high tech materials.
At the same time, I would say that our home-built GEN 2.6 handling is not far behind. Feels great that we built something that performs close to professional manufacturers ;-)
Here a photo of the completed GEN 2.6

This is our latest prototype,the GEN3 that is currently under testing.

I'm way far behind my cobuilder Jonas turbo build. He has already run his bike as I posted in this thread here earlier. My brand new bike is all in bits waiting for completion of the turbo kit. Another close friend of mine chose to build a turbo on his bike, identical to mine and Jonas bike, a 2017 KTM 500 EXC. To build fast, easily and accurately, I took the time to make a welding jig of the exhaust, mounting brackets and turbocharger flange. As Jonas had all the fixings completed, I used his design as a template.
The jig is not beautifuly engineered, far from technical perfection. Built the jig out of scrap steel. Very helpful and makes it more easy to weld and assemle quickly and accurately. All known mounting points are used as reference. Will perhaps be useful for future turbo builds? ;-)

We use no restrictor in the oil feed line. The turbocharger is a plain bearing Mitsubishi. We feed full oil pressure from the engine. The flow rate is quite low and is only from the internal leakage through the bearings. The oil return is gravity fed to the oil plug at the bottom of the engine connected to the oil plug beneath the engine sprocket.
I suspect when you mean restrictor is when you use a ballbearing turbocharger. Some of those don't need oil pressure and a restrictor is a solution not to drain all oil pressure in the engine.

Work proceeds on my turbo build. Most of it is in place. Left is to make the intake to the intercooler, machine the oil feed connection cover on the oil filter, wire electrics and connect fuel lines to the additional injector. With some luck I will be completed and have my first test ride of this build next weekend

We connect directly to the filtered part of the oil system. Therefore no additional oil filter is required. We machine a special oil filter cap where the oil line to the turbo is connected.



This solution requires that the oil filter has holes on both sides. We first tested just to drill the hole but there is a chance to get metal shavings inside the filter which would be really bad. Instead, we made a hole punch where you quickly and easily punsh the hole in the filter. The rubber gromit that goes inside the hole is reused from the old filter. We buy many filters to have available and punch a bunch of filters. Takes a only a few seconds in a vice or a tool press.



Here's a photo where the oil return line is connected to the engine.


Current build uses a double banjo bolt, and a spacer that uses olnly the outer banjo. A better and simpler solution than these photos show.

Our first turbo build had the intercooler mounted on the tubular frame of the snow bike kit. A really good location because of the snow spray offering very good cooling.


Our goal of the new location of the intercooler is to have the simplest and shortest possible route of airflow. Furthermore, we're now running with a third shock, causing movement of the kit relatively to the bike. We want to avoid flexible joints, hoses etc. This requires the intercooler to be mounted on the bike, not the kit.
Additionaly, the tunnel is now enclosed which unfortunately minimizes snow spray.


After just a few test rides, we've noticed that the new intercooler placement doesn't offer suffisiant cooling as its tucked up under the rear fender. The intercooler temperature reached up to 40-45 degrees C when boosting for just a coulpe of minutes. High air intake temperatures reduces power and increases risk of detonation. Better cooling is the next improvement.

Testing a fan that will provide better air flow. Using a moisture protected ball bearing fan of hopefully high quality. This perticular fan could probably have had more power and better air flow but worth testing. Maybe this can be the solution. The fan case ended up quite close to the muffler. Keeping our fingers crossed that the fan can handle the heat radiation from the muffler. More test runs will tell if this will work....




Turbo power!

After five years of turbocharging our snowbikes, we’ve encountered the first mayor engine breakdown. My cobuilder Jonas blew his 2016 bike. This bike runnin 0,7 bar boost and 10:1 i compression ratio. We have no idea what was the failure. Probably a broken rod. I’ll post more pics as soon as the engine is disassembled.
On our second bikes we’re boosting 0,5 bar and stock 11,8:1 comp ratio. Keeping thumbs crossed that this looks to be a more reliable setup....

Quick question: Does Carillo make rods for KTM500?

Here is an update on the engine failure. It actually seems to look better then we expected. We had expected significantly more damage. Both bearings on the conrod were flawless, indicating that no seizure was the cause. Looks promising as we have been confident that the pressure lubricated journal berarings would hold up better than rollar bearings.
The conclusion is simply that the original OEM conrod is too weak for this kind of power.
Cylinder, head and valves were completely undamaged. As it seems, new block halves, new conrod and piston are the only parts needed to get it running again.








We have been looking for stronger aftermarket conrods for the KTM500 but unfortunately it seems impossible. The demand of stronger rods are non-existent as there are not many in the world who turbo a KTM500:face-icon-small-win
The solution is to order a custom made rod, but it is unfortunately more than 2 months delivery time. By that time, the riding season is almost over which doesn't makes this as an option.
For this reason we continue to run with standard conrods and boost less, aiming for 0.4-0.5 bar.
In the upcoming summer we take the engines apart and order custom rods. At that time of year delivery time isn't an issue.

Since the KTM500 2016 and 2017 are completely different engine generations with different conrods, it is likely that the 2016 bikes will be replaced by a new bikes. This in order to use the same custom rods on both bikes. We hope that we will get a better price if we order several identical custom rods at the same time. At least, thats the plan as it looks for now.