DER951

I bought a much modified '86 951 track car with way less than complete
documentation. Saturday, I took it to the dyno, and got about 275 WHP at
10 lbs. boost (didn't get a print out of that run). The boost was
increased to 15 lbs (Apexi EBC) and the power went to 344 at 5500 rpm
and 364 ft. lbs at 4000 rpm.

The dyno run was halted at 5500 rpm as the A/F ratio went to 13.5, from
a low of 11.25 at 4800 rpm.

Is the leaning out of the mixture due to:

1. injectors are too small. They have green tops with nos. 0280 150 803
and 645 on them. No add-on resistors are evident. Several charts
indicate these are stock injectors, and cannot make anywhere near 340
whp.

2. Fuel pressure low. I do not have a gauge for the fuel rail, so could
not test this.

3. DME needs an add-on fuel controller

If the injectors are really stock, how could I get to 344
whp? The dyno is reportedly a load type - "DYNOmite".

toddk911

What are you using to control the a/f ratio???

toddk911

If you went from 10psi to 15psi, and did not adjust the fuel acordingly, then it will obvioulsy go lean.

Stock injectors, supposedly run out at about 300whp, but if there is internal motor work done, then more hp might be made and the stock injectors might be able to hang in there.

dand86951

Unless you happen to have some chips and MAF from Vitesse.

special tool

Very nice!! Sounds like you are just learning about what has been done to the car. What turbo is it?
If you have very large fuel pump and high pressure, it could be stock injectors. Have any pictures?

DER951

Nothing that I know of (other than the DME) is controlling the fuel now. The dyno shop wants to install an Apexi controller. I'm trying to figure out if that is whats needed.

The only internal engine work I know of is an o-ringed head and baffle in the oil pan. The only marking I've found on the turbo is "F27" stamped on the edge of the cold side.

special tool

The Apexi is good (for DSM), but it is not what you want on your 80's 951. Do some searches about management here.

fast951

DER951, As per my discussion with Dr. R. The reasons that could cause your car to run lean (one or more condition is a possibility):

- Injectors size - Based on the Bosch part# the injectors you have are WAY too small for anything over 300rwhp. You can get few more ponies, but will have to run over 4bar fuel pressure
- Chips not mapped to instruct injectors to flow enough at certain RPM
- Fuel pressure dropping over certain RPM or not enough pressure for injectors
- AFM or MAF maxing out and chips not handling condition properly

Unless you have a way to handle any change to the above items your AFR will be all over the board.
I'm guessing you have the APE chips??

DER951

The DME chip only has a yellowed sticker with "MASS AIR DME" hand printed on it, so I don't know who made it.

If I go with larger injectors and an add-on fuel management system, would I be bettor off with a stock chip?

fast951

If you have a MAF it's better to use a MAF chip. If you go to larger injectors, you have to handle the extra flow (rich before 5000rpm). What type of fuel management system do you want to add?
There are lots of solutions, however there are very few proper solutions.

hosrom_951

DER951: Those fuel injectors are stock:

944 Turbo 1986-91


Porsche Part Number

951 606 110 00



Bosch Part Number

0 280 150 803


I am suprised that you got over 310whp, you should be using a 3bar Fuel Pressure regulator, i doubt the stpock 2.5bar could go that far (i could be wrong).

DER951

The dyno shop sells, and therefore recommends, the Apexi S-AFC unit. What are the proper solutions?

daniel951

i have the apexi safcII and i love it. so much better compared to my old fuel controller