Using EBP in fuel calculations

[Wroom]

What are the pros and cons on using exhaust back pressure in the fuel calculations?

Based on the following information in the thread at: http://www.mrm-racing.se/forum/showthread.php?p=164#post164
...Don't be tempted to use the EBP input for streaming because the value is used in the fuel calculation as soon as you enable the Analogue input.

I am a bit curious on this, since i am trying to make a good implementation of twin turbos on a four cylinder engine with sequential spoolup. The intention is to get the behaviour of a small turbo up to about 4000 rpm and the behaviour of a much larger turbo from about 4000 rpm and upward.

The overlap that occurs in the intermediate state where the second turbo gets blocked/unblocked is a problem, since there will be variations in backpressure not only from switching between one and two turbons, but also due to the fact that the second turbo will have a delay period due to spoolup where it's wastegate will be fully closed and the turbo revving up. And sometimes it will have decent revs and the spoolup will be neglectable. And there will also be some "wastegate chatter" for the first turbo when the second turbo engages.

Maybe i am looking at this the wrong way, and that i should aim at having a common wastegate? But the idea was to split the exhaust flow early by the exhaust ports with something like an x-pipe, and have a decent lengt of runners to each turbo. And that dual wastegates could be a good means to balance the two turbos.

If enough compensation can be achieved just by adding the backpressure to the fuel equation then the idea of sequential spoolup twin turbos would work very well. And i could possibly vary the engagement point for the second turbo by LOAD, or use of antilag, time hysteresis and maybe other reasons?

[roberto arano]

on an SM2 application i used the VDO oil pressure sensor input and used manifold/EBP mapping, but when i wanted to use it on an sm4 project i noticed that manifold/ebp mapping was not available, Ray was going to ask Richard about this, but we never resolved it.... i think it was listed in the software menu but not usable...i can't remember

I am going to also do sequential turbos on a 4 cyl , but that car has a an SM2 1.94 so i will definitley use the EBP mapping. On our rally car we chose to use EBP input to maintain accurate fueling in the event the EBP changed drastically from crimped or ripped off exhaust!

it sounds like you are using two turbos of the same size, but during spool/low rpm you are going to duct all exhaust thru one turbine, i think the supra or 300z did it this way i can't remember. SO i see the problem with "pre-spooling the 2nd stage turbo", i have found on a supercharged & turbocharger EVO i built that bypass valves can be made to open very progressively with wastegate actuators...and the piloting was not complicated

In my project I am planning to use two different size trubos , one small and one large, all exhaust gas will flow thru the large turbine and then all thru the small turbine. then once spool is achieved for the large turbo ,exhaust flow will be stopped thru the small turbine by a valve (downstream of turbine. this method has less complication with pre-spooling issues, but maybe other complications compared to the method you are envisioning...or not...i have not spent enough time considering the other method.

[Kelly2264]

Hi Guys,

Back in the '80s Porsche did a bypass setup in the 959. I've worked on a few and I believe I may still have a intake/exhaust system layout chart around here.

If I remember correctly, the 959 used two of the same sized turbos with a smaller turbine housing for the 1st stage and a wastegate that stayed closed until a certain point, when it opened. It then bled exhaust over to the second turbo so it could begin spooling up. The inlet to the second turbo's turbine housing was fed by this "bypass" pipe. There were a few "bleed" valves in the intake tract as well to handle the onset of boost from the second turbo to blend it with the spooled up 1st stage. The second wastegate simply bled off the excess exhaust back pressure, as with a normal turbo system.

If you are interested, I will see if I can the layout chart. Just let me know.

[Ian]

but when i wanted to use it on an sm4 project i noticed that manifold/ebp mapping was not available,
On an SM4 EBP correction is ON all the time. However it uses the Baro value as the EBP value if there is no EBP sensor selected. So the correction is a factor of 1, therefore is is not noticed in the fuel calibration.

As soon as you select an input for the EBP variable the SM4 applies the input value instead of the Baro.

That was the reason for the reference in the other thread about not using the EBP input to data stream another variable as the ECU applies the value on the EBP input as soon as it is turned on.

[Wroom]

it sounds like you are using two turbos of the same size, but during spool/low rpm you are going to duct all exhaust thru one turbine, i think the supra or 300z did it this way i can't remember. SO i see the problem with "pre-spooling the 2nd stage turbo", i have found on a supercharged & turbocharger EVO i built that bypass valves can be made to open very progressively with wastegate actuators...and the piloting was not complicated
Yes, that's the idea. One turbo is constantly in there, and the other turbo is blocked in the exhaust outlet until a certain point. The runners to that turbo will act like "dumb resonator tubes" after the x-pipes when it is blocked. The inlet path will be controlled either by reed valves combined with an electronically controlled, (force open), dump valve to freeflow turbo2 when it is exhaust blocked or in prespool. Or i will use an electronically controlled butterfly valve.

Hi Guys,

Back in the '80s Porsche did a bypass setup in the 959. I've worked on a few and I believe I may still have a intake/exhaust system layout chart around here.

If I remember correctly, the 959 used two of the same sized turbos with a smaller turbine housing for the 1st stage and a wastegate that stayed closed until a certain point, when it opened. It then bled exhaust over to the second turbo so it could begin spooling up. The inlet to the second turbo's turbine housing was fed by this "bypass" pipe. There were a few "bleed" valves in the intake tract as well to handle the onset of boost from the second turbo to blend it with the spooled up 1st stage. The second wastegate simply bled off the excess exhaust back pressure, as with a normal turbo system.

If you are interested, I will see if I can the layout chart. Just let me know.
Yes, i've seen that diagram. And the 959 solution is what made me think of this in the first place.
If you have that chart it would be very nice if you could post it up.

The Porsche solution for the boxer is quite neat by treating the engine as two banks of three cylinders.
But using that same concept on a four cylinder inline engine will not be as good. And i want to have optimal design of the runners, and also that the exhaust header can take a lot of heat. Then one must avoid putting blocking valves in there. So i thought of blocking after the exhaust turbine instead. Less heat to handle, and less problems with mechanical parts and leaks, and a more optimal design of the manifold. And carefully designed it would be beneficial with "blind resonator pipes" when one turbo is blocked of. Caveat to that part is that i am not entirely certain that the blocked turbo will give the right wave reflection.

Another interesting solution is the one that Lancia used in rally, (or was planning to use), before the group B ban. Four valves per cylinder ordered so that inlet is at top, and half of the exhaust valves distributed to the left side, and the other half distributed to the right side of the engine. Then one turbo on each side of the engine. One slightly larger than the other. Then they shut one of the turbos off on low rpm's by means of shutting of exhaust valves. Interesting solution. But i think that concept is above my current level of engineering. :D

Anyhow, everything stands or falls with the ability to fuel the engine properly, so EBP compensation is very useful here.

On an SM4 EBP correction is ON all the time. However it uses the Baro value as the EBP value if there is no EBP sensor selected. So the correction is a factor of 1, therefore it is not noticed in the fuel calibration.

As soon as you select an input for the EBP variable the SM4 applies the input value instead of the Baro.

That was the reason for the reference in the other thread about not using the EBP input to data stream another variable as the ECU applies the value on the EBP input as soon as it is turned on.
That's great news!

And the nice guys at Mitsubishi has already provided me with a nice route of exhaust gas from cyl4 exhaust port and going near the thermostat housing to cool, and then straight to the intake manifold flange, so only thing i have to do is to make a hole for a VDO pressure sensor in the intake manifold flange to get an EBP signal. I guess they intended it for EGR. ;)

[roberto arano]

i don't know if the reason you want to use two turbos of ther same size is because you happen to have two turbos already that you want to use.

but if you are looking for ultimate performance, maybe there is advantage in using two turbos of a different size in a sequential,but not compound arrangement. If you are after high pressure ratios for the final stage in might be best to use one large turbo with very good efficiency at high PR's (a high exducer to inducer diameter ratio). i don't know what your goals or practical parameters design are so...it's just a thought

[roberto arano]

On an SM4 EBP correction is ON all the time. However it uses the Baro value as the EBP value if there is no EBP sensor selected. So the correction is a factor of 1, therefore is is not noticed in the fuel calibration.

As soon as you select an input for the EBP variable the SM4 applies the input value instead of the Baro.

That was the reason for the reference in the other thread about not using the EBP input to data stream another variable as the ECU applies the value on the EBP input as soon as it is turned on.


P.S

Ian, I'm already impressed with the technical info and timeliness of your responses keep up the good work!!! Long live AUTRONIC!!!

[Wroom]

i don't know if the reason you want to use two turbos of ther same size is because you happen to have two turbos already that you want to use.

but if you are looking for ultimate performance, maybe there is advantage in using two turbos of a different size in a sequential,but not compound arrangement. If you are after high pressure ratios for the final stage in might be best to use one large turbo with very good efficiency at high PR's (a high exducer to inducer diameter ratio). i don't know what your goals or practical parameters design are so...it's just a thought

I changed this posting a bit to be more specific.

I am not looking for higher pressure ratios for my purposes. Only need to achieve quick and early spool, and provide enough flow at top end for power.
The base engine has a usable range from about 2000 rpm and up to some 9000 rpm or when the rods will fly out. For what i know, there is no turbo that can serve this big range.

For the strip, or pure race track one would optimize for top range and forget about the rest. But i want the car to be nimble enough for something that in sweden is called SuperStage, or RS Challenge.

Heres a picture to show:

http://www.mrm-racing.se/forum/image.php?u=2&dateline=1203084964&type=profile


In this type of competition one needs both top end power and also power that is accessible in tight cornering. Very often it is useful to stay in gear round the bend. If you got the top power on a turbo engine, then the boost is all gone when you exit a tight turn. Both "double braking" and antilag to stay on pressure disturbs control of the car when cornering, so best would be to have a small turbo round the bend, and a huge turbo in the straights. Parallell turbos with sequential spoolup will do this trick.

To optimize a parallel configuration one should go for one of the turbos to be slightly bigger than the other. But that will affect the length and volume of the runners so that one needs to do lots of testing before it will run well. (For a boxer or v-engine with short runners to twin turbos they will of course need to be of exactly the same size).

To keep cost down i want the turbos to be as balanced to each other as possible. Therefore i want to start with two turbos that are exactly alike, and an exhaust manifold that is as symmetrical as possible.


PS: Yes, Ian has godsend knowledge about the Autronic. And it has been a while since we had contact just before PMs where shut off in the previous forum.

[roberto arano]

do you find it hard to modulate the throttle with ALS even with TPS trimmed boost?

[Wroom]

do you find it hard to modulate the throttle with ALS even with TPS trimmed boost?
Had to change the post, since i misread what you said.
TPS trimmed boost pressure introduce a very small lag penalty, so therefore i do not use it.

And throttle modulated antilag is very good for control, generally speaking.
But in a tight turn when you are on slip limit then the slightest bog will send you over the slip limit.

[roberto arano]

yes, it's been too long since i have has a chance to use my rally car, i do seem to remember some lag increase from the tps trimmed boost.

back to the antilag retard setting, have you tried an ALS table that more gradually returns the timing vs TPS position, so that it is easier to "feather" the thottle ....your making me want to go start my rally car up and refresh my memory!! LOL

i'm in no way trying to discourage the sequential twin turbo idea as i am doing the same thing, just wanted to discuss ALS while we were on that topic.

[Wroom]

yes, it's been too long since i have has a chance to use my rally car, i do seem to remember some lag increase from the tps trimmed boost.

back to the antilag retard setting, have you tried an ALS table that more gradually returns the timing vs TPS position, so that it is easier to "feather" the thottle ....your making me want to go start my rally car up and refresh my memory!! LOL
Yes. I have put a lot of work into the ALS table. Maybe it could be perfected if one could add an extra axis for turbospeed. :D

i'm in no way trying to discourage the sequential twin turbo idea as i am doing the same thing, just wanted to discuss ALS while we were on that topic.
You mean "while we are off topic"? Topic is using EBP in fuel calculations. :rolleyes: