Load sensing - Throttle position or MAP? (or both)

[Pupp]

Another one for the aftermarket ECU guys

Interested in experiences/views (especially Emerald)

Cheers

[trackcar]

I hate mapping MAP sensed cars, you end up doing loads of constant-load work which is really bad for inlet temps and engine bay temps generally and puts the cooling system under a lot of strain .. I have no idea really why people use MAP sensors they're the work of the devil as far as I am concerned. If you're keeping the stock-style plenum arangement then TVR have already given you a nice reliable stable throttle pot. My advice is use it!

[Johno]

I've had exactly the same advice form a number of people . . . Steer clear if possible and go with Throttle Pot . . .

[Pupp]

Phew!!! Was hoping that would be the answer

[dnb]

I disagree with Joo somewhat here, but if we were all the same it would be a boring place

I think throttle pots can be troublesome. They get old and the tracks wear. Also, I found they generally have poor resolution.

MAP sensors can work well too, provided the cam isn't too lairy (it's usually only idle that is affected by this so I blend the TPS and MAP strategies in my car around idle), and they don't need much more tuning if you carefully analyse your data logs - a clever analysis tool can pick out steady state constant load areas (and even offer table corrections) from a datalog far better than human eyes can... (Joo - I'll demonstrate this when I finally manage to get up north with my car... )

I was far happier with my car running with a MAP sensor than with the TPS as the primary load sensor - part throttle driving was MUCH smoother with the MAP sensor driving things. I do use the TPS for transient fuelling, as TPS does respond fractionally faster than MAP to step changes. Aside from the MAP at idle being 60 to 65kPa, I have no resolution problems and no noise problems with the sensor readings.

Try both, and settle on the one you (and the ECU) are most comfortable with. Aftermarket ECUs are all different - some have more advanced alphaN algorithms and some have more advanced speed density algorithms.

[Graham]

I've run 2 cars and 3 engine configs and run throttle pot on them all with no probs... 1 road car and 1 race car

G

[350Matt]

I ran my wedge on both flavours and found that I couldn't get the throttle response quite as sharp with the MAP sensor as I could with the throttle pot. Also as Joo says it was a b#gger to map as you can't just hold a constant throttle and wind the load off as the vol eff of the engine changes with revs, so you end up all over the place trying to get the sites in-between.

To drive they were about the same with possibly slightly smoother transition between sites for the MAP but I think I could have tidied things up a bit with the TPS ( moved load sites around etc) and got the same result.

Use a pot is my recommendation with the MAP correcting for atmospheric pressure on an offset.


Matt

[GreenV8S]

350Matt said:

I ran my wedge on both flavours and found that I couldn't get the throttle response quite as sharp with the MAP sensor as I could with the throttle pot.

Presumably the transient fuelling is best done from the throttle pot in either case, surely this is what determines the throttle response?

[rev-erend]

350Matt said:

Use a pot is my recommendation with the MAP correcting for atmospheric pressure on an offset.

Matt

This I would see as the big benefit of a MAP sensor - to compensate for altitute (lower o2)..

If you lived in the Moutains and worked in the valleys - then it would seem possible that the fueling would be out at one or the other without MAP.

[350Matt]

GreenV8S said:

350Matt said:

I ran my wedge on both flavours and found that I couldn't get the throttle response quite as sharp with the MAP sensor as I could with the throttle pot.

Presumably the transient fuelling is best done from the throttle pot in either case, surely this is what determines the throttle response?

It probably depends on the ECU Pete but on most aftermarket ECU's I've seen they work off a multiplier off the main map so depending on where the engine is currently sat, it adds fuel at a certain percentage over the map value. So if a TPS based map is given a bootful then it will always be ahead of the engine response as you'll chuck fuel in regardless whereas the MAP based system has to wait for the engine to respond to add fuel as the engine accelerates.

It wasn't night and day between the two but defintely a bit sharper with the TPS based set-up

For OEM ecu's I think you're correct they use the TPS for the transient fuelling but then OEM's also tend to take a year to map a car......

Matt

[dnb]

350Matt said:

It wasn't night and day between the two but defintely a bit sharper with the TPS based set-up

I tend to agree there - I tried TPS based on my Griff, and the throttle response was extremely good. But everything else was no good for a road car. (specially one that Nic likes to drive)

When I got the transient stuff set up properly using TPS (this did take a long time because I wasn't sure how best to do it) then the MAP based load setup worked just as well for throttle response, and had better road manners.

Yes, OEMs take ages to calibrate new engines, however they are trying to satisfy a lot more requirements than we are!