NineMeister

The standard 964 injection system uses a barn door type volumetric air flow meter and two throttle switches (idle & WOT or Wide Open Throttle). The ecu runs on three basic maps: idle, WOT & part throttle where it uses the signal from the AFM. The problem with this set up is that the AFM is slow to resond and is not calibrated for the full scale of air flow demand (it opens fully at approximately 4000rpm & above 70% throttle) and therefore without accurate re-mapping of all 3 maps the fuel supplied does not perfectly match the engine demand.

Hot film is another name for MAF or Mass Air Flow, in the case of these conversions the MAF unit is a hot film device (rather than the 928/968 hot wire) which cools down as the air flows over it, so giving a calibrated voltage to the ecu depending on the mass flow of air into the engine (obviously). The range of the MAF allows the ecu to run on one main map which covers the full scale of operation from idle to redline and from zero to full throttle. In theory once the MAF is calibrated (chipped) the mass air flow and fuel supply will be a constant relationship and therefore the ecu should supply optimum fuelling at all times. This is the system fitted to the 993 and later Porsches as standard.

Alpha-N is the mapping strategy adopted by most race engine tuners using aftermarket ecu's. Alpha refers to throttle angle and N refers to RPM, thus ecu's running this strategy ignore air flow and instead fuel flow is calculated solely by a 3D map of the throttle position and RPM of the engine. There are usually additional sensors to apply corrections & aid the accuracy of the fuelling, like Manifold Absolute Pressure MAP, Barometric pressure (BAP) and air temperature. Generally Alpha-N mode gives an engine the fastest possible throttle response and track driveability simply because the ecu is looking at the same input that the driver controls, i.e. throttle position.

Motec are just one manufacturer of aftermarket ecu's, but in the case of the 964 the term applies to a full conversion package that covers the ecu, correction sensors and larger fuel injectors (I believe that we pioneered the conversion on RS models in the UK, no doubt that many others now offer similar conversions). We found that the standard fuel injectors at the standard fuel pressure maxed out their flow at 300bhp, therefore the larger injectors were fitted in order to accurately time a more dense shot of fuel into the cylinder.

In my experience I have found little to choose between a 964 properly mapped with the standard AFM and one fitted with a MAF, whereas with a Motec based Alpha-N conversions we see appreciable gains undoubtedly because of the improvement in fuelling accuracy.

Chris M.

Thanks for the explanation Colin. Does this explain why a friend that drove my car for the first time thought that the "turbo" (NA car) was kicking in at 4000 rpm?
So you're saying the Alpha N conversion is the way to go? What kind of gains are we talking here?

c

Heirsh

Intakes are tuned to operate most efficiently at different velocities and volumes. Same sort of idea as tuning the exhaust. In the 964 it actually has 2 modes instead of the 1 most cars have. The varioram stuff in the 993 has even more. Basically that big butterfly opens allowing an area for air to cross between the 2 sides of the intake. I think its actually a shock wave or pressure front that sort of vibrates. Theres all sorts of theory on this stuff and I dont know enough to get more in depth than that. My point is that is probably what your friend felt at ~4000rpm. We all feel it.

Lets say you have a conveyor belt wide enough to fit a cup on. You have 2 feeder slots, one on each side that the cups come from. If you try to feed cups at the same time they dont fit and just fight each other. If you feed one, allow time, then put the other, and keep repeating that you get the densest loading of the conveyor possible. Now the intake and exhaust stuff is similar, but MUCH more complicated as you are dealing with compressible flow, harmonics, friction, etc.

I wonder do the Motec conversions incorporate any of this? I had read somewhere Motec "could" control the varioram stuff if it was so desired.

Red rooster

The jump to Alpha N / Motec usually involves a set of 6 seperate inlet trumpets as an inlet system . This will always give more maximum power, if mapped properly , than a combined inlet . A bit like fitting Webers in the old days.

The down side is that the ECU is running on information not directly related to motor load , usually rpm and throttle position with air/oil temp compensations .
This open loop operation is OK for racers but is doubtful for road cars with a potential need for repeated mapping to cater for any change in motor fuel needs.
In mainline production ,motor air mass consumption or manifold pressure are the comonly used load indicators, together with Lamda signal and compensations.This closed loop operation automatically corrects for shifts in motor mechanical performance.

The other benifit , for some tuners , of aftermarket systems, is that mapping software is available and understood , unlike Motronic.
Thats my 2c.
Geoff

Geoffrey

The MoTeC systems can control any type of intake system originally equipped on a Porsche engine. In fact, it can even control the infinately variable camshafts in the newer engines. It can select three different methods for load and can be different between the ignition timing tables and the fuel tables. They are a) Throttle position (alpha - N), b) Manifold Pressure (MAP) and c) Mass Air Flow (MAF). While it is most common to use TPS as the fuel load method for individual throttle bodies, I almost always use TPS for fuel load for all naturally aspirated engines. This is because it better reflects the airflow through the engine than manifold pressure. An example is when an engine is running very low VE% such as 2000rpm, you will very often see 100kPa manifold pressure (full load) at 1/2 throttle. Therefore, you cannot program between 1/2 and full throttle in a MAP based system at low VE% and the airflow does in fact change whereas a TPS based system will allow for tuning under those conditions. I would use this strategy for either a street driven engine or a race driven engine, and use the same method to write the program.

If the compensation tables are written properly, then the engine will have 100% consistency on any of the above mentioned methods of Load, even when running in open loop lambda (no O2 sensor input). In fact, you will want to tune the car in open loop to get the tables set properly. While you can run a car in closed loop, there are a lot of reasons to not do it, and many people use closed loop lambda control as a band-aid to a poorly written program. As a practice, I never use closed loop lambda with the exception of on a dyno when during the process for tuning variable camshafts advance rates and only then to allow concentration on one aspect (camshaft timing) without as much worry of engine destruction from a lean condition.

Lastly, in general the individual throttle bodies will probably not produce as much low end torque as a variable manifold all other things equal.

Pesty

They used to make Air flow meters for Range Rovers at my factory(make the odd batch every now and again still). they use a very,very thin wire and wrap it around a piece of ceramic. the end result looks like a conventional through hole resistor(without the bands)

Pity I can't use em as there is still a few kicking around

Red rooster

Geoffrey,
I agree with most of your points except that TPS is a completely acceptable load indicator for road motors.Surely an intake mass measurement , with TPS as an input for acceleration enrichment and load range indication is a better system ( as per 993 ).During a motors working life its VE will alter and maybe require ECU recalibration using TPS?

Colin was claiming more peak bhp from Motec , which I still believe is more to do with the intake system used than any motor management improvement.

With the 993 ,I have converted the standard DME to Alpha-N + throttle bodies and got bigger bhp. I would consider this setup only good for track use.

Sorry to sound argumentitive but I think it is good to kick these things around so that correct conclusions can be drawn.On the other hand different people have different views, so I guess in an area like this complete agreement is maybe impossible !!
All the best
Geoff

Geoffrey

I understand and agree with your point about engines changing VE% as they wear. I believe this is why most OEMs use MAF since they are required to meet emissions for 100k here in the the US. However, the kinds of engines (and people) that would invest in a fully programmable engine management system such as MoTeC whether street or track probably care little about the small changes in air fuel ratio as the engine wears. Further, I'm not sure at what point you'd see a large difference 50k? 100k? 150k? I would still recommend TPS based load measurement for a street car and I believe it would run just as long and just as well as a MAF system.

The big power gains come from being able to accurately create an ignition timing map which has been optimized for your given combination, not from the fuel tables all other things being equal. The other big power gain is the elimination of the air flow meter which is a restriction. Beyond that, I don't think the ECU makes all that much difference, whether MoTeC or Motronics (as long as you can program it properly).

Colin is a super guy and really knows his stuff.

Lorenfb

" I believe this is why most OEMs use MAF since they are required to meet emissions for 100k here in the the US." - Geoffrey -

That's the bottom line!

To claim that a MAF in itself produces more HP is misleading. It just basically produces
a more precise measurement and allows a complete input measurement beyond the 70%
throttle limit of an AFM.

Most late model engines (post OBDII) use both a MAF and a TPS input. A TPS only input,
alpha-N, would never achieve the emissions requirements even though it's used
on motorcycles, e.g. BMW, with an O2 sensor. The TPS is only a proxy for the true
air flow/mass input.

"Beyond that, I don't think the ECU makes all that much difference, whether MoTeC or Motronics (as long as you can program it properly)." - Geoffrey -

Right on! Could have been used to replace the entire thread discussion.

NineMeister

Just to put the record straight, Colin was not talking about different intake systems, Colin was talking about running a Motec ecu with larger injectors in Alpha-N mode on a standard 964 plastic intake system with a standard throttle body on a standard 964 engine.

Classic example of the benefit of this strategy came off the chassis dyno this morning. It is a 964RS Lightweight that had been fitted with a set of sport cams and a German mass flow conversion kit (hot film). Arrived at the shop with 314bhp flywheel (corrected) & 286lbft, not a bad curve either but it had horrendous driveability with flat spots throughout the range. A minor revision to the intake helped but the customer wanted a proper solution, so on went our MoTeC/injector package.
Today's result was 341bhp @ 6050 (corrected) with 314bhp at the tyre (uncorrected) and 310lbft at 5200, has over 286lbft from 4200 to 6200. Same intake, same throttle body, same exhaust, same engine, same cams.
We then took the car out for a road session. It pulls 5th gear on the idle map from 900rpm, will take full throttle at any revs and pulls cleanly in any gear at any rpm. Almost goes without saying that it is as fast as heck and has a lust for getting to the redline.

I am not trying to be provcative or opinionated, but I have drawn my conclusions from a good few years of hard earned experience. For the record my opinion is that any hot film conversion on the 964 is a waste of time, money and effort if the end goal is performance.

Yes, the Motronic system can be made to perform in a similar way to the MoTeC, but when you have no access to the emulator packages required, nor the experience to radically alter their functions, an aftermarket ecu is the foolproof way to go.

As for the MoTeC system being unsuitable for road use, this is a complete myth. In my experience the reason that most "tuners" quote this line is that they cannot map the system well enough with accurate corrections to cope with all running conditions. It takes time, experience & understanding to remap any ecu properly, which is why I stick to what I know best and chose to fit the market leader only.

Red rooster

Colin ,
Pretty good result ! I guess the German kit was miles out for fuel and timing?
I agree that if Motronic or any other system isnt calibrated properly then the end result is poor.
I can very well understand that if you dont understand Motronic ,then starting again with a system you have control over makes sense ,in spite of the extra hardware cost.
I am personally still not happy to use a TPS only system on a road car .The most uncertain area will be around idle , a comonly used area on the road.
The reason I say that is that the ECU will have a throttle position signal but no feedback on what the motor is making of the fuel / timing provided. A mass meter will be sending the ECU that information and acting on it.
At big rpm/load this is probably of less concern.
As far as I know, no series production car has used a TPS only system , probably for this reason.
Sorry if this sounds a bit negative but I do know a bit about Motronic and so feel honour bound to defend a world class system.

Geoff

NineMeister

I respect your comments Geoff, but I do not agree with all of them.

No real idea why the German MAF system ran so poorly, to be honest I was never going to waste my time working out why because we were going to fit MoTeC nomatter what. I do understand Motronic, have access to an emulator and at a push can reprogram them, however for the 964 I prefer to use MoTeC in combination with larger injectors because the finished results are always better (in terms of power, response & driveability).

99% of our MoTeC 964 conversions have been on the RS model fitted with a lightweight flywheel. Every customer comments that the idle is improved over stock, every engine has such a strong idle that it will pull 5th gear at 0 throttle. The reason that our installation runs better than stock is that I incorporate a MAP sensor, thus when the idle valve is regulating the air flow into the manifold, the MAP sees the vacuum change and regulates the fuel mixture accordingly. This is a better system than the MAF because MAP variations at idle are more easily measured, giving finer adjustment of the fuelling. I suspect that this is the one factor that makes or breaks a MoTeC installation, hence why I have invested more time and effort sorting this out than I have finding the hidden power. In comparison I defy anyone with a Motronic/LWF combination to say that they are 100% happy with idle 100% of the time!

For a production car you are probably right about TPS & Alpha-N, but in this instance w.r.t. the thread question about fitting MAF onto a 964 for performance gains, I believe that an aftermarket MAF conversion has nothing to offer.

Red rooster

Colin,
It was interesting to see MAP becoming involved. I would have thought that with big cams that would be a dubious input BUT you are doing it and thats what counts !Your result of 341 bhp from a stock motor with cams is very good so you are obviously getting something right !!
For interest , do you use the same approach with throttle bodies ?

My position is that in the end a motor just needs the correct fuel and timing to make best power. How those are arrived at is down to the tuner .In principle Motronic can do the same job as Motec. It is just a management system !

All the best

Geoff

NineMeister

In theory you are right, in practise some ecu's process the information quicker and are therefore more accurate.
In my experience we always make more power with an engine on MoTeC in comparison with a perfectly mapped Motronic.

Red rooster

Colin ,
Sorry to carry this on but the " perfectly mapped Motronic " is using what load sense system - Flap or Hot film ?I believe that the Flap is a problem at 300 bhp.

Have you ever tried putting a Flap in the inlet as a restrictor on a Motec equipped motor to see what kind of power loss results ? Be good to know how the 341bhp RS was affected !!

Geoff