Query on Turbo AFR Dyno chart

[cole.bin]

Hi,
I'm wondering what an AFR chart should look like for a road car doing a few trackdays per year?
Here is the AFR & Boost result of a dyno run today. I wanted some performance baseline data before a track day and before thinking about any modifications.

http://picasaweb.google.co.uk/folliard/Pictures?authkey=Gv1sRgCOi19qv2tPXlGQ#5508681317768680818
Is there such a thing as a target AFR chart for 944T? The helpful dyno bloke said my AFR looked lean, particularly at the top end. He reckons I should be aiming for 12:1 at 3500rpm to 5500 and then richer at the top end. So from 5000 onwards my AFR is headed in the wrong direction.

The dyno league charts on the excellent Cannell site certainly look richer than mine but I do not yet understand how significant the differences are. Any guidance or experience the forum can share would be appreciated. Also any recommendations on where to find a beginners guide to turbos?

Cheers.

 

[Alexw]

IIRC thats about right. When I was at the dyno day with mine I recall someone mentioning it should stay at 14:1 (stoichiometric?) then go a bit rich when on boost as thats the safer way to go.

I'm sure some people with lots of BOOOOOOOOOOOOOSSSSSSST will know exactly whats happening

 

[bertelli_1]

Thats not too shabby for a 944. Generally for full throttle you are looking for 13 - 13.5 afr, turbo cars will normally run a bit richer. You are at the lean end of what is acceptable at high revs. A 944 will usually dip into the 10's (very rich) during full throttle so yours is a bit leaner than normal. However, maximum power (on any car) is acheived at 13 - 13.5 afr.
If your car is mappable I'd be tempted to take some fuel out between 3900 and 5500rpm and maybe add a little higher up just to increase the safety margin.

 

[barks944]

Extra fuel is put in on the turbo engines to help cool the charge air and prevent knock. My turbo was down in the 10's on boost at high rpm.

The 944's injection system is blind at WOT, its just guessing how much air the engine is sucking. For the system to run lean there is either more air getting sucked into the engine than the system thinks (Boost pressure increased slightly?) or there is less fuel getting injected than the system expects (Low fuel pressure?).

 

[cole.bin]

Thanks. Keep the comments coming.
I will check the fuel pump pressure and regulator checked.
If I am running lean on the dyno using a fan does that mean real on the road AFR would typically be more lean?
Can the standard setup be mapped? Are there any switchable maps available?

 

[DivineE]

Certainly would worry about where its at now. 13.5/1 is about spot on where my car sits on throttle 14.5/1 when cruising on light throttle. This is with a stand alone ECU but the figures are perfectly safe and according to the little notations on the guage ideal for power /economy. I heard someone once tell me that 12.5-13/1 is the ideal mixture to get maximum power for most uk fuels. This was at a high level of geekiness at a dyno, I reckon if you're in that ballpark its good.

Might still be worth investigating longer term why its leaner than others are normally seing though? Could be something failing, restricted in the fuel system or just a chip on the car that has been mapped to those figures?

 

[cole.bin]

DivineE, ok I thought your post was good news, but you said "certainly would worry".Am I being thick/hopeful or did you mean "certainly would not worry". The dyno AFR is under 13.5 all the time.

I'm squinting at your avatar.....do the guages on your A pillar give you AFR data logging on the road? Have you noticed how much on the road AFR data differs from dyno AFR data?

cheers

 

[robwright]

Many of us with modified turbos have AFR meters to check for excessive leaness. They are called wideband lamda sensors that you have to install into the exhaust yourself. The other half of the kit is a dash meter that gives you real time AFR. Typically at cruising mine will sit around 14.2 mark but when you bury your foot it will dip into the low 12s showing that the chips are running the car rich to cope with the excess boost (currently mine runs a comfortable 15 psi). They are a good everday tool as well to let you know how your car is running. At the minute mine is running a tiny tad lean, which I think I have narrowed down to my Air Flow Meter playing up. Check out Lyndsey Racing for Innovate Wideband AFR. It seems to be the kit of choice

http://www.lindseyracing.com/LR/Porsche//IM-3781.html

 

[944Turbo]

Does look a little lean - take it from the boost level the car is relatively standard? You may risk head gasket damage if its running too lean. Is the vacuum pipe connected to the fuel pressure regulator? AFR gauge is very useful if you are planning mods/chips in the future. If its a late cat equipped car (or formerly cat equipped) then you can run a narrowband gauge of the standard sensor which isn't much good for tuning but handy as a monitoring device.
Tony

 

[DivineE]

ORIGINAL: cole.bin

DivineE, ok I thought your post was good news, but you said "certainly would worry".Am I being thick/hopeful or did you mean "certainly would not worry". The dyno AFR is under 13.5 all the time.

I'm squinting at your avatar.....do the guages on your A pillar give you AFR data logging on the road? Have you noticed how much on the road AFR data differs from dyno AFR data?

cheers

I meant wouldn't worry. Sorry. Yes I have a couple of AFR readouts in the car[] previous owner did rather like his gauges[]

 

[PSH]

Does look a little lean - take it from the boost level the car is relatively standard? You may risk head gasket damage if its running too lean. Is the vacuum pipe connected to the fuel pressure regulator? AFR gauge is very useful if you are planning mods/chips in the future. If its a late cat equipped car (or formerly cat equipped) then you can run a narrowband gauge of the standard sensor which isn't much good for tuning but handy as a monitoring device.
Tony

I agree with Tony, looks a little lean. Not to bad for a standard car but if you raise the boost it could become a problem.

Pete

 

[DivineE]

Hmmm Tony 944turbo and PSH Pete are two people who's opinions I respect very highly. I would listen to them WUF to all intensive purposes isn't really a 944 in that department and I'm only going off the in car gauge.

Surely the curve of that graph shows the perfect shape though? Is it really that bad?

 

[333pg333]

Is the car bone stock? How are you going to change your afrs then? Looks a little lean for the track to me. I notice that the dyno was in 'Standard Shootout Mode'. They have different levels of loading in certain modes. I know Shootout mode was designed to increase the h/p figures but I'm not sure what Standard means in this case. Might be worth asking the workshop just the same. I assume that's bhp not whp? Might be worth getting a chip that you trust?

 

[Diver944]

ORIGINAL: cole.bin


Is there such a thing as a target AFR chart for 944T? The helpful dyno bloke said my AFR looked lean, particularly at the top end.

Your Dyno guy is right, you are pretty lean everywhere and especially after 5000rpm

Here is a standard Dyno chart from a very healthy 944T that was running standard chips at one of our 944 Dyno Days:

As you can see it stays richer than 12:1 all the way from 3500rpm to the redline and only gets richer than 11:1 for a brief period around 4200rpm. This will keep the cylinder temperatures a lot cooler than your chart and ultimately the engine should last a lot longer just as Porsche designed it. It's okay to be as lean as 13:1 at the lower RPM and indeed this will create more heat and help reduce lag from the turbocharger, but in the higher RPM's you want to be between 11:1 and 12:1

I would get your fuel pressure tested as it could be a little low, also checkout your AFM because something is causing your engine to receive less fuel than it should when on boost

 

[cole.bin]

thanks everyone. I will work out a way to get the AFR richer by fixes or changes.could be a good excuse for some mods.

Patrick, sorry I was not clearer. 240 was whp running 97 ron. I do not yet know the full mod history but wish I'd bought a 944 years ago.superb cars.

cheers, simon.

 

[DivineE]

ORIGINAL: cole.bin

I do not yet know the full mod history but wish I'd bought a 944 years ago.superb cars.

cheers, simon.

Does anyone have a dyno chart for a car running the chips with a 2.5bar fuel pressure regulator? I've heard it mentioned before, could this be the case here?

I would love to hear your love story with the 944, what makes you feel its different. I never tire of hearing other peoples reasons for loving them