Transaxle

We just want to share some impressions from the first rollout of the latest engine-project from "good old Germany". The engine is based on a M44.41 with a modified KKK turbo. It is installed in a 924 Carrera GT.



One goal of the project was to create an affordable motor for track events. So mainly stock parts are used. The engine management is still based on the original Bosch DME/KLR units with modified software. In addition a Bosch HFM5 MAF Sensor was adapted. The MAF unit develops compatible signals like the originbal flapper-box. So both units can be used without changes.



The engine is expected to produce "at least" 400hp.

Additional pictures of the engine and the car are published at the website of the engine developer.

http://www.ttt-motorsport.de/Garage/

A (german) discussion started at:

New Engine Development

WolleMS

Hi... Great car... nice to see that also in germany good engines could be build... *thumbsup

Regards,
Wolfgang

David Floyd

Very nice

Peckster

Are you guys really running Slick 50 on it, or is that just an old decal?

Tom M'Guinn

It is nice to see new things on this board. Looks good. I like the use of hose couplers rather than fabbing up tubes and runners. Do you know if the intake flows ok like that? Did you relocate the coolant resivoir? WHere is the battery? Did the MAF come out of a Porsche? If so, what model? Great work so far! Keep us posted!

The Slick 50 sticker is a joke, right? Please.

PorscheG96

I really like how the intake manifold is done...looks like you can just remove the plenum if you need to pull out the turbo. I hope it can hold under the boost pressure.

Do you have more details & part # for the Bosch MAF you used? Like how much power can it handle before the voltage peaks and did it come with a section of intake tube?

Transaxle

> Did you relocate the coolant resivoir?

Yes - it's now where the battery was.

> Where is the battery?

It's placed in the back (spare-tire bay) - as in the original 924 Carrera GTS.

> I hope it can hold under the boost pressure.

Until now we tested up to 1.4 bar w/o problems.

> Did the MAF come out of a Porsche?

No - it's from Bosch.

> The Slick 50 sticker is a joke, right?

No comment

> Do you have more details & part # for the Bosch MAF you used?

We use the Bosch HFM5 series devices. It looks like they use the same sensor and just scale the measurement range by the diameter. The range is up to 1000 kg/h with 92 mm diameter. It includes a temperatur-sensor.



We played around with these devices for a while now. You can adjust the input values directly in the DME tables or simply add a converter between the MAF and the DME to make it a direct replacement for the old flapper box.

PorscheG96

Man that's really cool...I looked on the Bosch USA and German websites but couldn't find any info on HFM5. Where can I get more info? Thanks!

Transaxle

Here....

Red 944

Incredible man. I love seeing what ingenuity rather than money can do.

Tomas L

Very interesting to see this as I have an 1000 kg/h AFM5 in a box waiting to be installed!

From the pictures it looks like you are taking the 5v needed for the HFM5 from the AFM connector. Is that correct? From the circuit layout of the DME it seems that this output is not capable of giving enough current.

One concern of mine is that the HFM is much faster in reaction than the AFM, this could result in poor idling. Have you had any problems with this?

Tomas

Transaxle

The configuration in this project looks like this:



+5V are taken from the original connector. It is the reference current and compatible. You'll need additional +12V for the MAF. That is taken from the battery and cleaned by the CPU board. We use a simple one-chip CPU with a little stuff around it.




The differences in reaction time are corrected by the software. The biggest problem in a configuration with a closed BOV is pulsation. When the BOV opens the air tries to flow back. The flapper box just closes the flap - with the MAF we have to measure the back-flow. Most HFM5 sensor are able doing this.

Tomas L

I didn't read the datasheet carefull enough, the 5v needed is just reference voltage, as you said, and the current should be low. The 5v output to the AFM can source up to 30.mA and that should be enough. It's the 12v supply that have to supply up to 100 mA.

Exactly what does the CPU board do? Do you filter the signal in any way or is it just adjustment of the signal level to match the AFM signal level?
I've been considering a similar correction box for signal filtering but since I have not done any tests yet I'm not sure if one is needed.
According to the datasheet the current HFM5 series can detect reverse flow.

Tomas

Transaxle

Since we want to keep the costs low, we're still using the original DME and KLR. The DME expects a volume value - the MAF delivers a mass value. So the CPU measures the MAF output via a A/D converter. The value is corrected to the corresponding volume. That is why we need the NTC signal. The volume value is than send via a D/A converter to the DME.

It is simple. The tricky part is in the simulation of the slower flap and the measurement of the reverse flow. We are still working on that to get it perfect...

Tomas L

You could connect a constant resistor to the DME NTC input, then the DME would not do any volume to mass conversion and you could use the mass flow signal. The downside of this is that the DME probably also uses the air temp for cold start enrichment.

The problem with reverse flow could perhaps be reduced by carfull design of the BOV outlet into the MAF pipe?

To compensate for the faster response of the HFM5 I have thought of a rpm adjusted low pass filter.

Tomas