Engine question about M49

m5bb

m5bb

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So how did BMW control the AFR on the M49 race engines?
No air box or plenum to meter the air.
Mechanical injector.
Mechanical distributor.

Is there a book or write up about this?


BMW_Engine_M49_from_E9_CSL_zpsd8f950cf.jpg
 
It's mechanical fuel injection so there is an injection pump with an internal cam that can be adjusted to raise or lower fueling. It was and still is very difficult to tune for prolonged periods and would normally be set for each race start. Ambient temperature increases in the same day could even cause an engine to run lean and destroy pistons. Fantastic when it is set but not a step forward these days. One of those with a modern ecu would make even more power and more reliably.
 
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Polariscsl said:
It's mechanical fuel injection so there is an injection pump with an internal cam that can be adjusted to raise or lower fueling. It was and still is very difficult to tune for prolonged periods and would normally be set for each race start. Ambient temperature increases in the same day could even cause an engine to run lean and destroy pistons. Fantastic when it is set but not a step forward these days. One of those with a modern ecu would make even more power and more reliably.
Click to expand...

Yes, I thought that might be the case. So do you think the pump was timed for each cylinder firing as well as the amount of fuel?

Would it be possible to do this today with lets says some S38 independent throttle bodies on an M30 motor?
 
The whole sheebang was run off the cam drive, and the housing for the fuel pump also contains the distributor as you can see in the pic. The cylinder firing is based on vacuum and cam speed. It looks like there is a feedback system from the intake manifold (post-runners) to the fuel pump, but I don't think it is vacuum, since if that was the case they could just T-off the dizzy vac line.

You can see the production version of this system on the M88, as used in the M1.
http://upload.wikimedia.org/wikipedia/commons/2/2a/BMW_Engine_M88_from_a_M1.JPG

The big housing on the front of the fuel pump is apparently for cold start conditions, hence it is tied into the cooling system loop. The pump itself is also tied into the oil loop. You can also see the throttle lever is tied to the fuel pump as well.

Nowadays, rather than setting up the mechanical fuel injection system, they run an Alpha-N setup, which does allow for altitude/temperature correction. Still lets you get away without an intake metering system, but much less likely to detonate to destruction than the system used in the picture.
 
Yes it was, it was driven by the fan belt so ran at a set variance to engine rpm.

It is theoretically possible to run this system but I doubt it would be financially realistic. Kugelfischer systems are designed to work as a unit with slide throttles and cost a fortune to buy and maintain (£10k for the last complete kit I saw). There would be no idle control or ability to get low rpm mixtures right.

You would be better off ignoring mechanical injection and using a highly developed ecu like omex, motec and emerald with s38, or any other throttle bodies.

These systems are only used by people that need to for FIA historic racing - even they would choose not to if they had the choice to preserve their M49's for the long term. (Which can cost upwards of £50k!)
 
Polariscsl said:
Yes it was, it was driven by the fan belt so ran at a set variance to engine rpm.

It is theoretically possible to run this system but I doubt it would be financially realistic. Kugelfischer systems are designed to work as a unit with slide throttles and cost a fortune to buy and maintain (£10k for the last complete kit I saw). There would be no idle control or ability to get low rpm mixtures right.

You would be better off ignoring mechanical injection and using a highly developed ecu like omex, motec and emerald with s38, or any other throttle bodies.

These systems are only used by people that need to for FIA historic racing - even they would choose not to if they had the choice to preserve their M49's for the long term. (Which can cost upwards of £50k!)
Click to expand...

Thanks guys.
I'm not trying to buy or run a mechanical fuel injection system.
I am interested in running ITB on a M30 motor open stack. No air box.
 
m5bb said:
Thanks guys.
I'm not trying to buy or run a mechanical fuel injection system.
I am interested in running ITB on a M30 motor open stack. No air box.
Click to expand...

In that case, your best bet is, like I mentioned, an Alpha-N setup. Rather than relying on a mass intake signal, you calibrate the intake flow manually for each throttle position and RPM. Then you can apply corrections for things like altitude and ambient temperature using well-known equations, usually built into the ECU already. You are really finding the Volumetric Efficiency of your setup, so you are creating a VE table, then linking the throttle position to a particular VE value.

MegaSquirt (V2.0 and up) does allow Alpha-N tuning. You can read about it here:
http://www.megamanual.com/v22manual/mtune.htm
 
m5bb said:
Thanks guys.
I'm not trying to buy or run a mechanical fuel injection system.
I am interested in running ITB on a M30 motor open stack. No air box.
Click to expand...

I would recommend an airbox if you can - most of the racers put them on due to heat in the intake air
 
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