DPM on XP turbos

Brian @ C3 Power Sports · Nov 11, 2009

What is everyone doing with the DPM on turbo XP setups?

Can they be setup to work on the turbos for off boost response and elevation changes?...Or is it even worth trying.

Will the DPM components withstand boost if it is applied on both sides of the manifold?

Or is it better to scrap it all together and stick with manual jetting?

Lets hear some opinions.

Brian @ C3 Power Sports · Nov 11, 2009

My understanding of the system is that it uses a solenoid to quickly alternate between atmospheric pressure and the lower pressure in the venturi of the carbs (duty cycle) and applies it to the float bowls... allowing the computer to lean the amount of fuel.

If you put boost on the vent side of the DPM, wouldn't the pressure differential between float bowl pressure and intake (or boost pressure) be the same, resulting in the same amount of fuel removed by the computer? Couldn't this allow automatic adjustments for altitude and temperature? -ie) no rejetting

All this is of course assuming the system can withstand boost presssure.

Any extra fuel required for boost would still be added via power jets.

CBX · Nov 12, 2009

I've sat and pondered this very question for a good amount of time.

I'm sure its do able. It'll take some engineering to acomplish it though.

The dpm is a great little system. Uses "negative pressure" like you stated. Now, i've never experimented or tried anything, yet. Once my turbo build comes to life I will, but I dont know if it will happen this year or not.

Anyway, Dpm simply modulates subtraction of fuel by lowering pressure (suction) in the fuel bowl. It cant add to the jet thats there. Only subtract. (perfect fail safe too)

The issue i see is taking it from a vacuum system to a pressurized system is that the low pressure area in the venturi isnt any longer driven by air flow through the carb. The main driving force becomes added pressure. True there will still be the siphon effect, but the carb has to be pressureized much higher now in relationship to the air flow.

I think..............

Heck just try it. Hook up the Air box vent of the dpm directly to manifold pressure. See what happens.

One thought I had was to utilize the voltage refrence of the DPM somehow.

I just thumbed through the manual,

"using pre defined maps, the ecm is constantly activating (duty cycle) the dpm solenoid to optimize the air/fuel mixture"

"Ecm recives different signals........yada yada..... which indicate operating conditions at Millisecond intervals."

(most important part) "the engine RPM (though trigger coils) and TPS are the primary sensors. Other sensors (air pressure (located on the ecm itself) air and coolant temp) are used as secondary sensors."

"3D map is used to maintain Air/fuel at optimum."

"The Ecm begins to lean fuel mixture when engine RPM is above aprox. 3500."

All the above bits are from the 09' shop book. There has to be a way to make it do what we want.

Thoughts? I plan on testing this theory one of these days.

triple7 · Nov 12, 2009

Well, I will never say it cant be done, because there is always a way if you can think of it. But heres my take on it.

When you straight jet the carb, you eliminate variables. When the DPM is eliminated you eliminate complexity. There are two things that any full tilt hotrod can do with out in my book and those are variables and complexity. It is one less thing to fail, to cause a tuning problem, to cause a hole in the fuel curve when all the variables fall into place, ect.

As stated above DPM is an enleanment device. This is great on the NA sled! However, with a boosted application, the entire engine dynamic changes. The turbo is effectively creating atomosheric pressure for you and when done correctly a turbo setup will actually create a more flexible fuel curve. We have not found any issues in bottom end response through big temp changes and big elevation swings with the DPM eliminated. It is certainly something to play with, but Im of the opinion if you eliminate the potential for any issues that DPM can cause by removing it, and there doesnt seem to be a need to run it, there is no reason to deal with any potential problems that it may cause.

With that being said, I remember someone posting that they had a turbo setup working with DPM and it worked well.

Jake

maxwellzx · Nov 12, 2009

what about creating a billet version of the dpm manifold and using braided vent lines or something that will hold the boost.

Brian @ C3 Power Sports · Nov 12, 2009

CBX said:
Anyway, Dpm simply modulates subtraction of fuel by lowering pressure (suction) in the fuel bowl. It cant add to the jet thats there. Only subtract. (perfect fail safe too)

The thing that worries me about using it under boost is that it might not be a failsafe anymore... if the system is capable of leaning, and if the solenoid/valve components fail, could it fail in the 'leaning' position?

These are all very interesting replies. In my opinion, in an ideal boosted application, the stock fuel system (carbs in this case) would continue to feed the same amount of fuel as they would in NA form regardless of boost pressure, and the extra fuel required due to boost pressure is added strictly by the power jets. As CBX stated, the DPM is a 3-d system, and it makes changes primary changes based on throttle position, RPM, etc, and secondary changes due to elevation and temperature. Its effectively changing the jet size for any changes to these inputs... So with the DPM removed, you have a constant jet size... but hey, that's the way things have been done for years... and under boost, these fine changes are small compared to the amount of fuel being added by the power jets for boost.

CBX · Nov 12, 2009

maxwellzx said:
what about creating a billet version of the dpm manifold and using braided vent lines or something that will hold the boost.

I had that thought as well. A metal rpm manifold would solve the plastic issue. It also has metal air jets inside stock.

My idea of voltage reference was off. Did some checking, would have to use frequency instead. Dpm solenoid is 12 v constant.

Brian @ C3 Power Sports · Nov 12, 2009

CBX said:
I had that thought as well. A metal rpm manifold would solve the plastic issue. It also has metal air jets inside stock.

My idea of voltage reference was off. Did some checking, would have to use frequency instead. Dpm solenoid is 12 v constant.

That is a very interesting idea... i am curious of the frequencies... maybe you could even use a different high speed solenoid if you needed to... just as long as you reuse the jets in the DPM to control flow you should be good right?

triple7 · Nov 12, 2009

Ok, now this may be just a bit off topic but it needs clarified right away. You cannot make the carb act just as it does NA and add ALL of the required extra fuel through a powerjet.
A carb works off of pressure differential. When you add boost to the carb, pressure differential becomes larger. That means that the air stream siphons harder and draws more fuel out. That is how the tuning is so easy with a well done carb turbo. The carb naturally wants to supply the correct amount of fuel. If you run a baseline carb setup capable of supporting the horsepower output you want, a powerjet really isnt even needed and the motor will be crisp and clean and still not have lean burndown issues on top. A powerjet is really just a tuning tool but isnt an absolute necessity in a boosted application.
Now, I am still curious about this whole dpm issue. If you could reference it to boost and make it basically only effect the bottom end where the motor isnt on boost (not running in manufactured atmosphere effectively) it might be possible to keep the motor even more crisp through big elevation changes. I would just try to make sure it cant fail and go lean. I know that dpm has the ability to effect main jet size by 10 sizes effectively. If it effectively backs 10 jet sizes out, your motor is toast.

Jake

Brian @ C3 Power Sports · Nov 12, 2009

Thanks for explaining that Jake, I didn't know the carbs would act like that... I've worked a lot more with fuel injection, so carbs are all new territory for me :beer;

CBX · Nov 12, 2009

Not sure of the freq of the DPM Brian, I'm going to test it once i'm on the snow with a pretty schnazzy DVOM that i have. Just to see what gets thrown at it by the ECM.

I'm thinking along the lines of modulating the fuel pressure regulator boost reference. Some math and a few S.W.A.G's (scientific wild *** guess)

should get in the ballpark for how much fuel will need to be pulled up high.

Seems the most ideal. I have no experience with this, but i just have a hard time beliveing that the factory DPM manfold will work under boost.... however, if it somehow did, just how cool would that be.

I cant help but think someone hasnt already tried this?

Shouldn't be too hard assuming i can find the right parts. Might have to get hi tech and simulate a 2k ASL atmosphere on the ECM and a 10k ASL atmosphere to see what type of range there is to work with. Once the range is known then we could make something happen.

Too bad I just cant call someone at BRP or Rotax and save me all of the reverse engineering

How bad is it going to be be when some dumb cow milker from idaho gets a turbo to work with factory on board fuel management....

If i only had more time to do research and development.

I have been looking into a standalone EFI system. Its very doable. With the right $$ and time. I just have this feeling that about the time i get that thing setup rockstar that doo will release EFI the next week and i'll want to go lay down on the road and wait for traffic

stalefish_132 · Nov 12, 2009

DPM cant react quick enough between being on boost and off boost, lean pop occurs and the reed cages blow apart. talk to mitch at powderlites.

10001110101 · Nov 12, 2009

I spent the better part of last season trying to get the dpm working on my turbo 800r. It can be made to work, the problem is in the response time it takes to fill the manifold and pressurize the bowls, it is not fast enough to react with changing manifold pressure. I wish I had a picture of all the reed cages I bent from lean backfires! I must have changed out at least 20...

The Dpm works on a principle of pressure differential. There are two calibrated restrictor orfices in the dpm manifold, one in the vent line and the other in the line that goes to the carb throats. These allow the venturi vaccum to be applied in a controllable fashion with the solenoid operation in relation to duty cycle, more duty cycle more vaccum, less fuel.
The vaccum signal is drawn from the venutri of the carb from around the needle jet shield (the brass piece that sticks up into the carb throat where the jet needle slides into). If you simply hook up the vent line to boost reference the pressure goes to the bowls as well as to the venturi vaccum source and leans out the mixture because it gets rid of the pressure differential behind the shield which would normally draw fuel up from the float bowl. You would think that this wouldnt matter because you are pressurizing the bowls but the vaccum signal is greater than the amount of reference signal that can get past the first orfice in the vent fitting of the dpm manifold so you actually get no pressure reference to the bolws and the motor wont even start to go into boost without leaning out. If you get rid of the orfices you can get it to go into boost but now the dpm function wont work becaust you have no pressure differential off boost and the sled runs rich off boost because of that but runs. Another problem with the dpm manifold is because of the size of the fittings and volume of the manifold it causes a delay in keeping the float bowls and airbox equal and you get a lean condition as the turbo spools, and especially when you are at full boost and let off and get back on it again....pop there goes another reed cage.....

I had it working the best with a hobbs switch set at one psi and a bypass solenoid to bypass the dpm manifold when it switched but I also had to turn off the dpm power supply to stop the boost from going to the carb throats, It still didnt work fast enough to keep up with a fast spooling turbo. I ditched it, jetted the sled for boost and called it a day, and the sled ran flawless for the rest of the year! Ditch it and forget about it, not worth it in my opinion.

triple7 · Nov 13, 2009

10001110101 said:
I spent the better part of last season trying to get the dpm working on my turbo 800r. It can be made to work, the problem is in the response time it takes to fill the manifold and pressurize the bowls, it is not fast enough to react with changing manifold pressure. I wish I had a picture of all the reed cages I bent from lean backfires! I must have changed out at least 20...

The Dpm works on a principle of pressure differential. There are two calibrated restrictor orfices in the dpm manifold, one in the vent line and the other in the line that goes to the carb throats. These allow the venturi vaccum to be applied in a controllable fashion with the solenoid operation in relation to duty cycle, more duty cycle more vaccum, less fuel.
The vaccum signal is drawn from the venutri of the carb from around the needle jet shield (the brass piece that sticks up into the carb throat where the jet needle slides into). If you simply hook up the vent line to boost reference the pressure goes to the bowls as well as to the venturi vaccum source and leans out the mixture because it gets rid of the pressure differential behind the shield which would normally draw fuel up from the float bowl. You would think that this wouldnt matter because you are pressurizing the bowls but the vaccum signal is greater than the amount of reference signal that can get past the first orfice in the vent fitting of the dpm manifold so you actually get no pressure reference to the bolws and the motor wont even start to go into boost without leaning out. If you get rid of the orfices you can get it to go into boost but now the dpm function wont work becaust you have no pressure differential off boost and the sled runs rich off boost because of that but runs. Another problem with the dpm manifold is because of the size of the fittings and volume of the manifold it causes a delay in keeping the float bowls and airbox equal and you get a lean condition as the turbo spools, and especially when you are at full boost and let off and get back on it again....pop there goes another reed cage.....

I had it working the best with a hobbs switch set at one psi and a bypass solenoid to bypass the dpm manifold when it switched but I also had to turn off the dpm power supply to stop the boost from going to the carb throats, It still didnt work fast enough to keep up with a fast spooling turbo. I ditched it, jetted the sled for boost and called it a day, and the sled ran flawless for the rest of the year! Ditch it and forget about it, not worth it in my opinion.

That sounds just about right. Im with you, jet it and forget it.

This example is exactly what I was talking about with the added complexity and added issues. Look at the work this guy went too and got nothing for his efforts but piles of broken reeds. Carb turbos are great BECAUSE they are simple. IMO dont add complexity!!

JMO

Jake

vadnaiskid · Nov 13, 2009

So what do you have to do to delete the DPM

DWHalverson · Nov 13, 2009

I think Brian needs his turbo quick

.!! The differential in the carbs is so much greater with boost, that we actually lean the main jet curcit out

. It pulls more fuel though a smaller jet because the "signal" is so much stronger now. The power jets are there, if needed. Sometimes, depending on the conditions you wont even have them open. The DPM is a cool idea and I'm all for it in NA form, but on a boosted sled the consistancey is so good with your new "atmosphere" it really isn't needed like the NA sled. If someone has the time to make it work, great. I'm sure it can be done. I just haven't been able to justify the time required to make it work when I feel it isn't an issue.

Dave

CBX · Nov 13, 2009

I'm gonna give it whirl. I'm not going to even attempt using the dpm. I only want the signal. Assuming I can find a modulator that fits in range and I don't have to buy it from NASA ...... LOL

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DPM on XP turbos

Brian @ C3 Power Sports

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