96 KTM 360 EXC INDUCTION CRANK BUILD IN A 2021 GAS GAS CHASSIS

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96 KTM 360 EXC INDUCTION CRANK BUILD IN A 2021 GAS GAS CHASSIS

Post by Sandblaster » Mon Nov 13, 2023 1:42 am

This is going to be an interesting build..
No, it's not green but it is a two stroke and I can work with that 8-)
I've done induction cranks for a few KX500's, a KX250, a KTM 300, and now a KTM 360.
But why?
I could go on and on about all the info I have on them but lets keep it simple...
Over rev..
Through many many dyno runs we know that over rev is the one thing that the Induction crank does.
Why do you want more over rev?
Have you ever been on the trail or track and you wished that you didn't have to shift to that next gear, but the engine is winding it's guts out... and if you shift, then you will have to almost instantly down shift while going into the corner?
Yes, we have all been there..
Sure, the induction crank will not make any more HP or Torque until after peak HP has been exceeded... It simply hangs onto usable power longer.
The goal for this build is to have more hp, more torque, and more over rev so we will see...

Here is the donors..
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Hold the phone.... Ian Burke over at the Facebook group: KTM SX/EXC 360/380 CLUB just shared this info...

Here some info regarding topics of discussion in this group lately. I held of on posting until I had time to get solid numbers worth sharing.

On the crank case volume issues....there is the typical reed block spacer we all know about. For those doing a full build like Mike Weir , here's a few more ways I increased volume, and it will make sense to you.

The 360 engine case halves are not perfectly semantical. A quick example is obvious when looking down the intake tract towards the crank/cylinder. You'll see that one case half (usually the right) is not flush with the other half at the mating surface. With a milling machine and porting tools, you can remove the excess material from the half that was cast larger and extends beyond the gasket mating surface. Ultimately, it's just blueprinting, or matching the case halves, which is a typical practice of any good builder. In this particular instance, there is volume to be gained by matching the haves. In addition, I chamfer, clean up, and de-burr, the main bearing oiling holes. There a little volume to gain there as well.

As for the crank and nylon stuffers.....in every 360 I've done, the stuffers had a radius greater than the crank webs/wheels. Indexing the crank halves in a lathe, then use a turning operation to remove stuffer material that has a radius lager than the crank wheels. There's some volume added with this process. Since I balance with a 65% factor, and true to .001" or less, there is no concern about about removing stuffer material. I know the stuffers are not weights, I just mention this for those who believe they are critical to crank balancing.

With the cylinder porting, there is so much performance to gain, especially on the exhaust side and power valve components. An exhaust tract should be polished to the finest finished possible, as Mike has shown in other posts. A highly polished surface is ideal for the exhaust tract only. The intake side is different, and requires a different, and very specific finish that promotes laminar flow. What that surface looks like is a topic of debate, so I won't suggest one. The intake side surface finish that I prefer is based on extensive flow bench testing. There's many different viewpoints, so research hydrodynamics and Thermodynamics then apply the intake finish you believe is best.

The 360 engine is very sensitive to cylinder deck height changes. This is refered to as the "X" dimension, that's top edge of piston to cylinder deck. Raising or lowering the cylinder with different gasket thicknesses will result in very different power delivery characteristics. Again, finding the best "X" and "Z" number will depend on the type of power delivery one prefers. The "Z" number is the height of the PV control flap, this also changes with gasket thickness. I run between 47.5 and 48.5mm depending on what I want from the engine. Changing the cylinder deck height also changes port timing, and what the ideal ignition timing will be. The cylinder head and combustion chamber profile is also a major consideration when working in the X and Z axis.

When it comes to the cylinder head, the '96 was not great and KTM did offer an updated '97 design for owners of the '96 model. The cylinder head stamped with a "3001" is the early design and prone to detention. For inexperienced builders, I recommend the "3601" head. It's OK as is and will help amateurs with every aspect of tuning. I prefer the "3001" cylinder head because combustion chamber volume is lower than the "3601" head. The extra material that give the early head a lower volume is perfect for those who understand combustion chamber design and have the machine tools required to cut a good chamber. Starting with the early head, I machine a squish band that will increase squish velocity. A hemispherical dome that's highly polished, with radiused transitions from deck mating surface, to squish band, to dome works great for me. To prevent detonation, compression ratio should be reasonable and adjusted by the material removes while developing a combustion chamber profile. I can't recommend a specific combustion chamber displacement because what's ideal is determined by every other aspect of your build. I will say, there's 8 cylinder heads worth of testing in the KTM360 area of my pallet rack.

Ignition timing is huge with 360 engines. If you have the SEM ignition which I think is absolutely awesome, but everyone else hates, setting timing is tough. To do the job best, special tools are needed. The adjustable piston stop I made is helpful. You'll also need to consider your piston location and deck height when setting timing. I run 1.9mm (approx. 17 degrees) before top dead center for daily use. I'll increase for short, tight conditions and decrease (retard) when top speed is desired. If you have the Kokusan ignition, timing is set the same way you'd set a typical motocross bikes ignition.

Here's the information on exhaust stingers that I've come to like though testing and adjusting. I'll also share some other number's that might help. For these additional numbers, refer to the includes pictures. The combination I found best is an FMF Gnarly pipe with modified flange, descending cone, and stinger. I've cut 3 brand new Gnarly pipes up into several pieces to get these numbers, so it wasn't easy and people cringe seeing a pipe cut up right out of the package., but it's necessary. These final results include testing hand made pipes, modified stock pipes, and many other combinations. The modified Gnarly just works best for me. First, the head pipe length between the flange and ascending cone is too long. I cut the flange off and remove 8mm of head pipe length. This is a good time to fix the flange too. From FMF the socket side of the ball and socket exhaust flange is off by a mile. It need to be aligned with the cylinder outlet as straight as possible. You've gotta shorten the head pipe anyway, so make the pipe actually fit right at the same time. Stinger is 31mm I.D. 77mm long. That is measured from the original stinger end inwards. Don't shorten the stinger, shorten the descending cone so the stinger starts closer to the pipes belly. Because the inner diameter is 31mm, you cut the descending cone at the exact point that it's inner diameter is also 31mm. This make a perfect transition from descending cone to stinger. From the welded seam, the stinger should measure 77mm to its end.

The best silencer I've tested was hand made by me. The the inner diameter of the lead in pipe is 31mm, like the stinger. The best results from the silincer came with a +2mm perforated tube I.D. In the end, silencer length was exactly 10", perforated tube I.D. 33mm with a 33mm I.D. turn down outlet that was 36mm long at its greatest radius.

Remember, the 96 engine is very different than the 97 engine. Bore and stroke are both different. However, I've had 3 1997 KTM360EXC's and spent hundreds of hours developing and testing. Much of this information is applicable to both years. There is so much more to getting the most out of a build, but my hand is smoked from typing and ultimately, your own testing and experimenting is the path to what you'd consider a good engine.

Reference the pictures for pipe numbers, and other visual examples of what I've stated above.

UPDATE FROM POSSUM VALLEY RACING!!

possum_valley_racing
Now that the @motocrossactionmag test is over and we’ve had time to process all we’ve learned, we all really want to try it again using what we’ve learned. If we’re going to do that, we need to build something special. Of all the bikes we have going, the 2021 Gas Gas with the KTM 360 has the most potential. @weirkxgururacing and @usmc_500 of @kxgururacing and I sat down after the MXA test was over and hashed out a new plan. Yep, Possum Valley Racing and KX Guru Racing are planning a joint project! The Gurus are handling the engine, while @chopperman69 and I will handle the engine mounts, pipe mods, and assembly. Mike is going to port the cases and cylinder, modify the exhaust valve and cylinder head, raise the port timing, and most importantly, add an induction crank. We have a @smartcarb carburetor to add and will be modifying an actual 360 @fmf73 pipe to fit the Gas Gas frame. We’ll get more in depth on the motor in later posts. Brian at @n2_dirt will be handling the suspension as usual. Brian and I will dream up something fun, I’m sure. This one is getting out of hand in a hurry. Stay tuned!
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96 KTM 360 EXC INDUCTION CRANK BUILD IN A 2021 GAS GAS CHASSIS

Post by Sandblaster » Mon Nov 13, 2023 1:44 am

The engine is out and ready for disassembly..


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Re: 96 KTM 360 EXC INDUCTION CRANK BUILD IN A 2021 GAS GAS CHASSIS

Post by Sandblaster » Wed Nov 15, 2023 4:47 pm

I will be posting a pictorial to show how it comes apart.
These pics are for reference so that I remember how it all goes back together :lol:


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Re: 96 KTM 360 EXC INDUCTION CRANK BUILD IN A 2021 GAS GAS CHASSIS

Post by Sandblaster » Tue Nov 21, 2023 7:32 pm

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Re: 96 KTM 360 EXC INDUCTION CRANK BUILD IN A 2021 GAS GAS CHASSIS

Post by Sandblaster » Tue Nov 21, 2023 7:39 pm

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Re: 96 KTM 360 EXC INDUCTION CRANK BUILD

Post by Sandblaster » Wed Nov 29, 2023 5:21 pm

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Re: 96 KTM 360 EXC INDUCTION CRANK BUILD

Post by Sandblaster » Wed Nov 29, 2023 5:27 pm

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Re: 96 KTM 360 EXC INDUCTION CRANK BUILD

Post by Sandblaster » Wed Nov 29, 2023 5:31 pm

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Re: 96 KTM 360 EXC INDUCTION CRANK BUILD

Post by Sandblaster » Wed Nov 29, 2023 5:35 pm

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Re: 96 KTM 360 EXC INDUCTION CRANK BUILD

Post by Sandblaster » Wed Nov 29, 2023 5:40 pm

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