MicroSquirt.com read only forum (Jan.15,2018)

yes indeed you could use throttle based boost control IIRC, light throttle gives low boost, heavy throttle gives full boost.

Throttle position is reflected in the manifold pressure

Hi Lance.

The above is kind of the point im getting at. yes, tps is reflected in the manifold pressure, but, you can often have different throttle positions, and yet get the same manifold pressure. Best example i can think of is:

If you are on a long steady incline, at around 70mph in a high gear, i would be using around 10psi of boost, at a throttle opening of perhaps 30%. I could floor the throttle, and the car would accelerate, with the engine consuming more air and fuel, BUT, the manifold pressure would remain the same. This could be becasue i have limited the boost to 10psi, but it does happen in lots of situations naturally.

My question is, how can MS tell the difference between these two situations? It clearly needs to add more fuel when the throttle is opened. Is MAPdot and TPSdot sufficient to do this? it would seem to me, that the part throttle scenario would lead to rich mixtures.

I think where you are confused here is that AE mostly is a function of CHANGING map. There other things that get into the formula but the changing manifold absolute air pressure is the biggest issue. For this reason MAPDot is almost always the best triggering mechanism. Now in the case of a turbo car the manifold can vary drastically adding one more veriable into the mix. Bottom line is for turbo applications, X-Tau may be to only true workable approximation. Having TPSDot and the original B&G algorithm may never be more than a groose/generaly untunable WAG. Extra and the rpm based triggered by may be a little closer but still not what you realy need.

X-Tau is coming soon in MS2

AW

RickRST,

At a given MAP and RPM (and IAT) then engine will consume the same amount of air, and thus will operate the same (ignoring ignition factors).

If the engine is at a steady speed, it won't accelerate unless one of the above changes. The change in your example probably comes about because the rpm climbs (or there might be a slight effect from the operating point on the compressor changing, but this will be minimal).

Do a datalog, you'll see what I mean. To accelerate from a steady state, you have to change one of the MAP, RPM, or IAT. TPS doesn't come into it (except to drive the MAP).

Lance.

I was trying to think of a way to say that ^^ but I ain't too durn good with woords.

RickRST wrote:

Throttle position is reflected in the manifold pressure

Hi Lance.

The above is kind of the point im getting at. yes, tps is reflected in the manifold pressure, but, you can often have different throttle positions, and yet get the same manifold pressure. Best example i can think of is:

If you are on a long steady incline, at around 70mph in a high gear, i would be using around 10psi of boost, at a throttle opening of perhaps 30%. I could floor the throttle, and the car would accelerate, with the engine consuming more air and fuel, BUT, the manifold pressure would remain the same. This could be becasue i have limited the boost to 10psi, but it does happen in lots of situations naturally.

I think I can see what's tripping you up.

In your example, the turbo is producing 10PSI of boost before and after you floor the throttle.

But it's only making 10PSI of boost on the upstream side of the throttle plates. On the downstream side, between the throttles and the engine itself, the pressure will be less than 10PSI. The throttles are restricting the airflow, and the engine is gulping down the air that does get through.

And it's in this area, between the throttles and the engine, where you want to connect the MAP sensor.

In your example, the turbo is making 10PSI of boost in both cases, but only once you floor the gas does the engine actually see 10PSI of boost.

So the MAP is not the same in each situation.

is this intake setup

1) filter
2) turbo
3) blowoff valve
3) intercooler
4) throttle body
5) injectors
6) intake valve

If so the MAP and IAT needs to be taken between 4 and 6

The more efficient way to plumb the setup if given the choice is

1) filter
1a) optional MAF
2) throttle body
3) turbo/waistgate
3a) optional BOV (emergency only set higher than waistgate)
4) alcohol injection
5) intercooler
6) fuel injectors
7) intake valves

If so the MAP and IAT needs to be taken between 5 and 7

fscott, I can confirm that even with throttle plates semi-closed that case holds true - under gentle load on the motorway at I can see 1bar and floor it and still see 1 bar (limited) - hence throttle position is irrelevent to the MAP after something around 25%.

CB wrote:fscott, I can confirm that even with throttle plates semi-closed that case holds true - under gentle load on the motorway at I can see 1bar and floor it and still see 1 bar (limited) - hence throttle position is irrelevent to the MAP after something around 25%.

I find that really hard to believe.

The whole point of the throttle is to restrict airflow to the engine. If, as you say, there's no difference in restriction between 25% and WOT, then there should be no difference in the engine's power output between 25% and WOT.

Not buying it.

Fred

CB,

Yes, this is true on any engine, even a NA engine, if the throttle is reasonably sized. For example, on my 406cid engine, I see 100 kPa at 25% throttle at 2000 rpm. Opening the throttle more at that point doesn't make any more power, since the MAP is already at it's maximum (This doesn't mean the engine can't accelerate, it means it cannot accelerrate any faster). However, at 6000, the throttle has to be opened fully to reach 100 kPa.

This makes sense if you think of the VE and the resultant airflow at varying engine speeds. Even if the VE was 100% at 2000 rpm, then engine is only drawing ~1/3 as much air as it would at 6000 rpm (and 100% VE), so the max. MAP is reached with much less throttle opening.

If the engine required 100% throttle opening to reach 100 kPa at 2000 rpm, it would be very seriously choked at higher rpms, and the kPa at WOT would actually drop significantly (in fact, that's how you tell if a throttle is large enough - if it is large enough, then the WOT manifold pressure doesn't drop at higher rpms).

Lance.