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Do 's Works' Cars Need An Adjustable Fpr?


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#16 Bat

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Posted 23 July 2018 - 10:50 AM

Hi,

It's a combination of things, as you mentioned the injector size is one, the other is the Siamese port.

The shared port means you have a limited injection window.

The window refers to the time you have to get the fuel into the open valve, which gets smaller as revs go up, because if you just inject at anytime you can easily end up with all the fuel going into one cylinder and not a lot in the other!

Cheers  :proud:



#17 Bat

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Posted 23 July 2018 - 10:54 AM

Further more the ECU cannot compensate for performance mods as it can't be mapped and it only adjusts the mixture when cruising and idling, the rest of the time it runs from the map and cannot detect increased airflow with the MAP sensor.

Cheers  :proud:



#18 Wiggy

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Posted 23 July 2018 - 07:41 PM

What do you mean that it can't compensate?

How do people make extra power then?

#19 Bat

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Posted 23 July 2018 - 09:14 PM

Hi,

If you think about it the ECU has no way of knowing how much air is going into the engine.

The MAP sensor as it's name suggests is a pressure sensor, one gram or one tonne of air it's still only measuring the pressure, or vacuum to be precise.

The air temperature sensor allows the ECU to correct for air density nothing else.

I've been told the ECU isn't mappable so you can't change that.

The lambda sensor is a narrow band so that only works around an afr of 14.7:1, cruising throttle openings, so that's no use at full throttle and  therfore is ignored by the ECU.

The only option available is a rising rate pressure regulator. This increases fuel pressure indexed to manifold vacuum, so as the vacuum drops, due to more throttle opening, the pressure goes up and more fuel goes through the injectors.

That to my knowledge is the long and short of it, bet you're glad you asked now! >_<

Cheers  :proud:


Edited by Bat, 23 July 2018 - 09:18 PM.


#20 bluedragon

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Posted 24 July 2018 - 12:54 AM

The statements about using the FPR to increase fuel delivery are quite accurate. The MPi injection system is maxed out at the 76-85 hp level. Tolerances and production variances probably explain why some kit installations yield 75hp and other installations of the same parts give 80+.

 

I'm pretty sure the original Cooper "90hp" ("S") kits for the MPi back in the 90's used a fuel pressure regulator that was crushed (yes, squeezed with pliers or other crimping device) to crudely raise the fuel pressure, thus supplying extra fuel to support higher airflow. Even if this gives a predictable increase in pressure, the drawback is that it may well overfuel at lower speeds.

 

As recounted above, the MPi is not a mass-air injection system that measures the amount of air coming in to the engine. It's a speed-density meterless system that estimates the amount of air based on the physical characteristics of the intake system, the barometric pressure, and the air intake temperature. In theory, the lambda sensor should detect that the air/fuel mixture is over-rich at lower speeds and reduce injector flow, but I've been told this doesn't really work that well in practice and the result is abysmal fuel economy.

 

So a rising-rate FPR should in theory deliver extra fuel pressure when needed. The trick is to get one that increases fuel pressure as vacuum increases, which is what a normally aspirated (non-boosted) engine needs. Most FPRs increase fuel rate with boost pressure, which doesn't do much for non-boosted application.

 

https://www.calverst...ic-information/

 

 

(I wish the prototype ECU he mentions in that old article had actually reached production, but I haven't heard anything about it in at least 7 years.)

 

 

Dave


Edited by bluedragon, 24 July 2018 - 12:54 AM.


#21 hazpalmer14

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Posted 24 July 2018 - 08:22 AM

 


 

https://www.calverst...ic-information/

 

 

(I wish the prototype ECU he mentions in that old article had actually reached production, but I haven't heard anything about it in at least 7 years.)

 

 

Dave

 

 

They did make them, i can remember seeing the last one they had advertised recently. It might have been through instagram or facebook. It was a german site IIRC, and was only for the SPI not MPI



#22 Bat

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Posted 24 July 2018 - 10:44 AM

Hi,
The MPI part is the problem! You bin the inlet and go to a throttle body with the injector in it and you'll see an improvement if the engine is being held back.
I think Rover only made the MPI for emissions reasons and you can get through the MOT without it as that's never as stringent as what the manufacturer has to meet to get it approved for road use.
All you need for the MOT is the right mixture in both tests and a sensible idle speed and you've passed.
Cheers :)

#23 bluedragon

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Posted 24 July 2018 - 04:27 PM

 

 


 

https://www.calverst...ic-information/

 

 

(I wish the prototype ECU he mentions in that old article had actually reached production, but I haven't heard anything about it in at least 7 years.)

 

 

Dave

 

 

They did make them, i can remember seeing the last one they had advertised recently. It might have been through instagram or facebook. It was a german site IIRC, and was only for the SPI not MPI

 

 

 

I should have mentioned it was the MPi I was thinking of. Yes, the SPi version of the ECU (made by some fellows in Germany if I recall correctly was released. But no MPi version to my knowledge.

 

 

Dave



#24 bluedragon

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Posted 24 July 2018 - 04:34 PM

Hi,
The MPI part is the problem! You bin the inlet and go to a throttle body with the injector in it and you'll see an improvement if the engine is being held back.
I think Rover only made the MPI for emissions reasons and you can get through the MOT without it as that's never as stringent as what the manufacturer has to meet to get it approved for road use.
All you need for the MOT is the right mixture in both tests and a sensible idle speed and you've passed.
Cheers :)

 

If sheer power is the primary goal, sure, single point injection is fine. SPi is basically a more sophisticated carburetor. It doesn't address uneven fuel flow to each cylinder due to the siamesed intake ports. MPi technically is far superior, but the siamese port problem is the barrier to max perf. The injectors can only squirt so much fuel into one cylinder within the limited time window before the other cylinder starts to suck in the fuel charge.

 

The MPI's torque curve is more robust and broad than any other stock Mini. That's what allowed Rover to fit the 2.76 final drive to meet noise regulations - the MPi had the torque curve to pull the tall 2.76. If you read what Mike Theaker, the developer of the MPi system, said, when fitted with 3.1 final drives the MPi's were like little rockets.

 

 

Dave



#25 Bat

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Posted 24 July 2018 - 06:04 PM

Hi,

Looks like everyone's tuning the MPI wrong then, just swap the final drive out and away you go!

Cheers  :proud:



#26 bluedragon

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Posted 24 July 2018 - 11:43 PM

Hi,

Looks like everyone's tuning the MPI wrong then, just swap the final drive out and away you go!

Cheers  :proud:

 

That's just what a lot of guys like Keith Calver recommend - switch to 3.1 or 3.2 diffs.

 

 

 

Dave






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