I'm remote tuning a 997.2 Turbo in Turkey and thought I'd share an example of just how badly the 997.2s need fuel to make power. This car is on stock VTGs and the only modification is an exhaust and our custom tune. Even at these relatively low-ish boost levels (33.4psi absolute logged is around ~19psi gauge at sea level) the car is having quite a serious fuel pressure drop in the top end.

This is a 3rd gear pull and as you can see the customer is at WOT all the way through (TPS is at 85%). With higher load in higher gears the situation would look even worse. We're targeting ~2000psi to redline as you can see in the graph but the pressure drops close to 600psi down from target into 1400s.

We're waiting to receive a secondary fuel injection kit here from SRM to test on a fully bolt-on 997.2 that has Champion's 68mm turbos and these issues should be history and some incredible performance to be squeezed out of 997.2s to come. Alternative is adding meth for a little more headroom or an inline fuel pump.

Let me know if any questions.

Dzenno@PTF

 

Awesome. Thanks for this. I'm running into weird fueling issues as well on my 997.2. We REALLY need a fuel system. This car is would be so capable with the right fuel system. Does this mean the 997.2 basically maxes out on pump fuel since even on race gas you can't really add more boost because it of fueling issues.

What are you seeing in STFT's as well as actual AFR? Is it all over the place at high rpms because of this?

 

Yes, even on pump gas they're out of fuel and I bet they'd drop out with the stock exhaust and our custom tuning but everyone we've had a chance to work with had an exhaust on the car at the least.

Lambda is on target in this case and short term fuel trims are in the acceptable range (6-7%) most likely because even with the drop its still able to hit the desired lambda but on direct injection setups you don't want your fuel pressure in the rail dropping further than 4-500psi as its usually misfire territory at the least.

People should at the least try as simple as adding an inline pump in the tank to help keep the pressure on target. Its a simple change and given volume is still there for starters it'd be most likely help to keep at least the pressure in check to a point.

Dzenno@PTF

 

Sorry what does "I bet they'd drop out with the stock exhaust and our custom tuning.." mean? You mean you think you'll see the same problem even on stock exhaust?

Also when you say add meth for more headroom, you mean as protection against detonation if fuel pressure drops and you run lean? If that's the case you can just add 2gal of E98 or E85 as well.

As far as the inline pump, which specific inline pump would you use, where would you install it and how would you wire it? Can you make a kit?

 

Also I can't tell from your graphs but at what rpm does the fuel pressure begin to drop?

 

Yes.

Meth as a secondary fuel source in this case. It'd take some load off the HPFP as the DME is running closed loop fueling and it'd automatically pull back on the HPFP via injectors/fuel trims.

I'd convert a Walbro 455 into an inline or even as simple as an inline 255 to see if it keeps the pressure up. When you're fighting volume delivery (not this car) adding a pump in parallel helps. When you're after fuel pressure drops you'd add an inline....or, you could just swap in two 455s running in parallel if you can fit them in the stock bucket.

Mid 6k.

Dzenno@PTF

 

We used to run with inline Walbros on the BMWs for quite a while until secondary port fueling became mainstream.

Can't wait for that hardware to get here!

Dzenno@PTF

 

That is fantastic. What will control the brushless? You have a controller?

What dynojet WHP will each stage support on E100?

Thanks!

 

Also the one you're shipping to PTF - is it for the 997.2?

Thanks!

 

Watching all of the .2 development carefully. Pretty cool stuff. What's the deal with all the weird variable names (Gxx)?

 

Its going on a 997.2.

Da Vinci Code Its probably some internal canbus stuff Cobb uses to differentiate from one data channel to another.

Dzenno@PTF

 

BTW just wondering (I'm still getting my head around on DFI fuel systems)... I thought AFR's on DFI engines are supposed to run really lean. Or are AFR targets (the magic .82 lambda or whatever) the same on DFI vs non DFI engines under full load?

 

DFI motors are typically run leaner than PFI as direct injection allows for it. Same goes for compression ratios where you'll typically see the DFI motors run about .8-1 point higher than a similarly powered PFI motor. Atomization of fuel and in-cylinder cooling is far superior to port injection. For instance MIT did a study on effective octane with ethanol fuels on direct injected motors and its over 160 points! E85 works great on port injection as we all know but it has even larger benefits on direct injection setups provided you have the necessary fuel delivered the factory way. The more port fuel you inject the further the benefits of direct injection get reduced and the more you have to tune the car like a port injection setup at full load.

Dzenno

 

You add the inline pre-FPR and the pressure is kept stable/on target by the FPR. Nice thing about BMW DFIs is they come with the low pressure side sensor that sits right before the HPFP from the factory and you can log both the LPFP and the HPFP side at the same time via the AP. Its really easy to see the full picture that way. I think this channel was the first thing I asked Mitch about when we started tuning 997.2s when the AP just came out. I wish it was in there.

Current draw was in check. OEM runs within the 20A fuse range. Once you go dual Walbro 455s you run into the current draw issue and the easy solution there is to run the 2nd pump off a Hobbs switch+battery+relay setup and only use the OEM pump wiring for one of the two pumps.

Dzenno

 

Does the 997.2 have a low pressure fuel pressure sensor or has that variable just not been defined yet?