Dea_944t

Shorting the little DME plug connector gets you race fuel settings but I just can't find what difference it makes in the maps or ignition in the documentation.

From some posts I got the impression that with pump fuel settings it backs off ignition above 15 psi but with the race settings it doesn't.
Does anyone know?

/Dea

schip43

Not an expert by any means but yes that sounds correct, the whole point of more octane is more power and more timing does that.
If you have E85 and can add 30% more fuel, your set, if it's Vitesse it might already be capable of doing that!

JohnKoaWood

Sort of partially right... more below..

The total chip image is 7 maps, 3 deep (so really 21 total maps, sort of..).

The "little 2 pin DME connector" is the global region connector (Euro, US, ROW) and this affects the 7 primary maps (FQS positions 0 - 6)... the chips can be set up many many ways, dependant on the FQS positions, AND the region selections..

IIRC the region selection is open for US, shorted for Euro, and 2K resistor for ROW, but I could be wrong about the resitor and the arangement, although I am sure it is open for US cars...

ANYWAY

The coding plug selects the depth of the image at each FQS position, and these are set up by the chip immage writer, whoever sets them up controls the affect.

NOW

For race gas, E85, or really any high octane fuel, you can get away with running more ignition timing, as the octane makes the fuel LESS prone to ignition, and makes for a slower flame... so more ignition timing will permit proper ignition of the fuel, while the fuel itself will resist pre-ignition caused by the higher cylinder temperatures resulting as a side affect of the advanced timing... higher octane fuels also allow for higher boost levels, as the fuel will resist pre-ignition at higher cylinder pressures...

More boost + more fuel + more ignition timing makes for massive gains in power and torque..

HOWEVER

these things are pushing the motor closer to the edge of destruction.

I can go on and on all day, but will leave it at this.. for a street driven car, running pump gas (E10, or straight gasoline) the street settings alow for a larger margin of error in the fuel, as this is needed because the same fuel, from the same source will vary day to day. these small variations can kill the motor if the margin for error isnt there, hence the street tune for street cars.

The more radical the tune, the smaller the margin, small margins are OK if you have tightly controlled fuel sources, or a motor built to tollerate the smaller margins, or a better engine management system, or optimally all 3 (as is found on developed race cars...)

For a daily driven street car, stick with the street settings, tighten the controls where you can, or prepare for big repair bills... but this is just my oppinion.

apitts73

this just happened to me with my new 3.0l motor....ace mechanic left it in race fuel mode....and it detonated @ 15lbs boost and around 5000rpm....might have been other issues but it definitely didnt help!

Dea_944t

Thanks for the info! Seems that I should stay with the pump fuel settings as long as I am not running real race fuel (>102 octane).

The thinking behind the question is that when everything is set-up and working at 15psi I want to increase boost to around 17psi. If the program backs of too much on the timing the only thing I'll get out of it is higher exhaust temps and not more power. Probably better to stay at 15psi and change the cam instead to get more power.

I remember my old car (non-Porsche) where I had an Autronic EMS and accidently increased timing by 7 degrees all over the rpm/boost range. It was insane in lower gears but of course there was knock in higher gears where the load was more static.

/Dea

JohnKoaWood

There are ways around that...

FWIW retarding timing will reduce your EGTs... not elevate them... your WB will reflect a sudden rich condition though... as will the smoke / flames, and yes I have seen a 951 on the street throw a flame ball... before we tuned it to get AFRs and timing under control!

Last report was it was running like a raped ape, even though I still think there is something being left on the table power wise!

Dea_944t

Are you sure on the EGT, most mapping instructions I've seen says that EGT increases as timing is retarded as the combustion is closer in time to the exhasut valve opening. I saw this on my old car as well and when mapping I tried to put the ignition between knock (to advanced) and increasing EGT (too retarded).

You can PM me the way around it

I thought the PB could n't change the timing?

/Dea

fast951

Dea, The differences between Pump gas and Race gas (or pump and E85) are timing and fuel. On pump gas we recommend you stick to 1bar boost so you keep a good safety margin.

When you purchased your kit, the previous owner should have sent you a list of images on the chip/board. Make sure you select the appropriate image.

With V-FLEX images, on pump gas, we do not want you at 18+psi. We kill the power so no need to go there.

Make sure to set your overboost and rev-limit.. It will save your engine one day!

Enough timing retard causes the mixture to burn in the exhaust and will raise EGTs.. Ignition, boost and EGTs require a balancing act...

Tom M'Guinn

Did you mean "advancing"....?

TurboTommy

Andreas, to answer your question;
once you are in full throttle mode you will have the same timing at 17 psi as you would at 15 psi boost (the race maps will just have more timing at full throttle)
This is of course if you have the basic kit (which doesn't allow the user to custom tune his own timing).
I think this is what you want to know.

fast951

Hi Thomas. Your statement above is true for the generic non V-FLEX software. However, with the introduction of the V-FLEX software a bit over 2.5 years ago, we enabled the DME to read actual boost (from a MAP sensor). With the V-FLEX, ignition is based on actual boost. So the PT and WOT tables have a new dimension added to them: Boost.
Ignition at 15psi is different than ignition at 17psi (of course, ignition for pump gas at 15psi differs from ignition for race gas at the same boost pressure).

TurboTommy

Yes;
I understood he bought an older used kit without the V-Flex.

Dea_944t

thanks for the answers.! Sorry for the confusion on what kit it is. It is a very early v-flex. I am expecting just above 300 rwhp at 15 psi with current mods. Target is 330 rwhp but I should probably go for a new cam instead then if I want to use a v-flex image. ./Dea