Lots of Questions, uS'ing motocross 4 stroke

Aaron Silidker · Post by **Aaron Silidker** » Tue Oct 09, 2007 8:05 pm

Hello-

I have been doing a ton of reading here, but have a few questions still about the uS'ing of a fast revving large bore single cylinder 4 stroke motocross engine.

I assume MAP use in general for SD is impossible given the nature of the short intake and high amplitude of pulses in the intake. Are there any algorithms that can average signals below a certain RPM? What about only taking the low pressure, ie what the engine is actually sucking?

If MAP is not available, can you do an Alpha N system with Wideband and Barometric correction factors and feedback?

How well does the hardware work at high rpm's and engines that change engine speed very quickly as motocross engines do?

As far as ignition control is concerned, is the stock flywheel on my bike with one "tooth" and sensor good enough to trigger MS? It triggers the stock CDI box fine, but I am not sure if it is hall effect, VR, etc.

Thanks!
Aaron

gboezio · Post by **gboezio** » Sat Oct 27, 2007 8:35 am

I know that some throttle bodies have a vac port, but I don't know about damping it so it reads right on the mark, I may go this way, so I made some research, I find that most bike run them all linked together, I don't know about singles, maybe a small damping chanber, but it will delay the signal to the ECU messing up the throttle response, one fix would be a plenum between the velocity stack and a throttle before the plenum, but singles plenum need to be huge, messing up throttle response again...

Edit : I think that the pulses may be bad at lower RPM, past the low end I think it may run ok with MAP only, the way I see it from the engine, throttle body/airbox/MAF/filter. Taking the MAP from the TB

Edit 2 : why not try the MAP first and see how it behaves ?? Then add the MAF if the low end in bad ?!

wes kiser · Post by **wes kiser** » Sun Oct 28, 2007 6:17 am

The KTM I have experience with sounds just like the bike you are dealing with.

Although I planned for alpha n from the get go, the map signal at idle was suprisingly stable (although we built a custom intake with a plenume). This year I am trying to use speed density only (this is for a universities FSAE program). Last year I was using a standard MS2 as well.

From an ignition standpoint (if using the factory trigger), treat it as a 2 cylinder of double the displacemnt. Then the crank trigger looks just like a 2 cylinder distributor from a signal standpoint. It is also a "trigger return" type signal (the tooth is relativley wide, correct?). They are normally setup so that the leading edge of the trigger passes under the VR sensor very close to the maximum advance the stock CDI box would run. This way, very little error is incurred in the calculation dispite having only 1 tooth. As an example, on the KTM, maximum commanded advance is 37 degrees, and the trigger passes at about 40. Also the tooth is about 30 crank degrees wide.

Obviously this is really fired as a wasted spark arrangement on a single.

Aaron Silidker · Post by **Aaron Silidker** » Mon Oct 29, 2007 12:59 pm

Wes, did the KTM run ok using the stock VR sensor and trigger? It is a very wide tooth (there are actually two of them right next to each other, one short, one long). I will try to post a link to a picture. The bike has an extremely short intake, TB is less than a foot from the intake valve. I really don't think the map signal will be stable. Hybrid doesnt turn MAP off until a certain RPM value does it? I thought hybrid SD/AN used both MAP and TPS as factors in the VE table.

Thanks guys!

wes kiser · Post by **wes kiser** » Mon Oct 29, 2007 1:44 pm

If you are running the factory bike throttle body (or one in a simalar location), you likely want to run aplha-n, or if running boost blended SD alpha n.

Also, if the bike you are dealing with has two teeth close together, I think you would be looking at a custom wheel decoder code. Would it be possible to remove the narrow tooth? To know the answer to that question, you need to know exactly how many degrees BTDC the leading and trailing edge of the tooth is.

I actually don't have the KTM running yet on the factory trigger setup, but am sure it will work OK. This is because due to the placement of the tooth, there is very little time to incur and error (think an offset of 40 degrees, with a commanded timing of 20-36 degrees, so only 4-20 degrees). It may be necessary to run higher than normal lag factors, but if the factory ignition worked OK, I can think of no rational reason it wouldn't work.

BrentP · Post by **BrentP** » Tue Oct 30, 2007 8:44 am

I have a 2001 KTM 520 (540) in my racebike running on MSII, which is pretty close to MicroS for this purpose.

This bike only has one reluctor on the rotor, pretty wide, about 30deg.

After watching the vacuum traces on the oscilliscope, I did not bother with trying speed-density and went straight to Alpha-N control. Mine is running with oversize intake valves, aftermarket cams, and a 54mm throttle body.

Setting up fuel only was fairly easy. Going to ignition control yeilded some surprises.

The difference between the intake/compression revolution and the power/exhaust revolution was a change in 30% at lower RPM. Kinda plays games with the controller, the RPM varies so much between revolutions.

What I did was to use a 7-pin HEI controller for VR sensor conditioning and spark output. By using one of the programmable outputs, the HEI can fire at 0deg until 1300RPM and then the programmable output can assert the crank override pin so MS can control the timing. By 1300RPM the difference between cycles is less pronounced.

Aaron Silidker · Post by **Aaron Silidker** » Tue Oct 30, 2007 5:18 pm

If you are idling below 1300 you are idling too low in an MX bike!

Do you have a V3 or V2.2 board? If V3, I though the HEI module was not necessary. Where did you get this programmable module?

Thanks...pictures would be fantastic!

BrentP · Post by **BrentP** » Wed Oct 31, 2007 10:00 am

The bike idles around 2kRPM. With the lightened flywheel and 13.5:1 compression, it is pretty rough below that. The 1300 number is to get it started. The starter is not strong enough to keep the RPM stable, and the startup is also pretty variable.

I am running the V3 board, and it is theoretically possible to make it work without the module. This works quite a bit better tho. In order to make it work properly without the module would take some code tweaks, and the free compiler no longer works.

The module is a simple 7pin HEI as on
http://www.megamanual.com/ms2/GM_7pinHEI.htm
and I think I got it from sherco-auto.com for under US$20.

I have enclosed a photo of the finished bike. It is getting some cosmetic work done during the off-season.

Aaron Silidker · Post by **Aaron Silidker** » Wed Oct 31, 2007 1:43 pm

can you email me your phone number so I can ask you some detailed questions about your ignition setup. Not sure what you mean by programmable output. aslids at gmail dot com .

Thanks!

BrentP · Post by **BrentP** » Thu Nov 01, 2007 9:13 am

Actually, it is probably better to discuss here, for future reference that someone else may use.

By "programmable output" I was using MCU speak. Using MS speak, it would be called "spare port settings".

Look for "spare port settings" in the MegaManual URL I provided above. It shows how to use some of the outputs of the MS to control external things. In MegaTune
Fuel Set-up->Port Settings
Allows you to set the conditions that (de)activate MCU outputs that can be used to control things like the 7pin HEI override pin, shift light, ejection seat and whatever else you can think of.