Damian in NJ

Just got back from having the car dynoed, on a Dynojet 248. 84 degrees ambient temp, high humidity.

Max power is 205.2 at 6560 hp, and torque is 202 at 4250. I've got a feeling I can get more out of the car, as the air/fuel ratio is pretty lean-the dyno guy felt I could pick up at least 5-8 more hp if I richened it up. I'm going to have the car dyno tuned and have a custom chip burned after I get the Cargraphic 100 cell cat and exhaust-I'm hoping for a total gain of 15-18 hp after this is all done. That would be, say, 232rwhp, which would be in the mid 250s at the crank.

Trevor, what would be the optimum a/f ration for a na 968??

flash968

with 232, would you not have mid 260s? still a nice number by the way, and very achieveable, but i thought the drivetrain loss was 15% 232 to 250 is only about 9%

RajDatta

Damian, 270 crank hp equals to 229.5rwhp. I think these numbers might be possible. I will look at your duyno sheet when I stop over. Your car is quite strong in stock shape so there can only be more to be gained. Good thing you tuned it up before or else who knows how much you would have lost.
Raj

BruceWard

How do you plan to richen it up? Will an adjustable fuel regulator allow sufficient adjustment or will something else be required?

Do you think 968s in general run lean or is the lean condition due to modifications?

Damian in NJ

Bruce, my car is bone stock. I don't know what a/f ratio's other people have shown, so I don't know if mine is abnormally low or std 968. I would imagine Porsche would like it lean for fuel mileage reasons, but the dyno guy thought that 13 is where it should be, and I was up over 16 at low revs, and only down to 14 in higher rev ranges. I should be able to have a chip burned while the car is being dyno tuned to correct the ratio-shouldn't need to go to higher fuel pressure, or injectors.

BruceWard

Would it be possible to adjust the fuel air mixture with an adjustable fuel pressure regulator? I wonder how much can be gained just by increasing the fuel part of the ratio.

I would love to see exhaust only and exhust + more fuel numbers from your next session!

I wish there was a Dynojet available locally. The only dyno I know of in the area is a Mustang which reads 20% lower than a dynojet and more importantly does not integrate with the engine in any way. You just back on and make a run, no wires at all. Perhaps Jay has found one to use in testing his project.

Damian in NJ

Bruce, that would raise fuel pressure across the board. I need it increased a lot at low revs, and somewhat at higher revs. Chip tuning is the only way to optimize this, so that's how I'll go. Usually the turbo guys need to crank up the fuel a lot, change injectors, etc-with an NA the stock set up should be enough to deliver sufficient fuel.

I will have that data, as I'll dyno the car again after the cat and exhaust go on. I'll do a baseline, then they'll start fooling with a/f ratios, timing, etc. So I'll have 1)stock, 2)stock plus cat/exhaust, and 3)exhaust and custom chip. The only variable is that 2&3 will be done at a different shop that 1, but the dyno will be the same Dynojet.

BruceWard

Great, I look forward to seeing some reliable dyno numbers.

Thanks!

RajDatta

Damian, ideally at part throttle and idle 15:1 is what you should be aiming for. AT WOT is where you need to richen things up a bit. 13:1 would be a nice number at WOT. So in your case, a FPR will increase fuel across the range, which is what you need. You need to be 1 point down all across it seems. In most cases, the adjustment needed is only in a certain rev range, that is why a FPR can only fix things in one section and screw them up in another section. I say you have 6-8rwhp with just tinkering with a FPR. In your case a FPR might be the answer.
Raj

flash968

with what increase from the stock 50 setting do you think you would see that 6-8hp increase? is that all by itself on an otherwise stock car?

Damian in NJ

Since the dyno chip tuning will do this for me, why would I need to have the adjustable fuel pressure regulator? I'm happy you offered me your spare, but if I don't need to swap it then it'll save some wrench work (on your part, he he).

BruceWard

At the bottom of this page http://www.connact.com/~kgross/FAQ/944faq12.html

I found

"There is a provision on the Motronic cars (944 and 911) to make small adjustments to the fuel mixture (injection pulsewidth) and the ignition timing in order to compensate for the quality of fuel available in your particular country or region.


There is an board-mounted eight-position rotary switch accessed through the little hole in the back side of the DME box. These adjustments can be made without opening the cover of the DME box"

Is this true for the 968?

If the range of -3% to +6% seems like it would be enough to to bump the ration to where Damian wants to be.

RajDatta

Bruce, Its not available for 968s. It is available for 951 and other models. Damian, what I meant by letting you use the FPR is that when you go there the next time to test the exhaust, you can turn the fuel pressure a bit if its still off. Its a 5 min job, 2 bolts and thats it.
Ra

RajDatta

Bruce, Its not available for 968s. It is available for 951 and other models. Damian, what I meant by letting you use the FPR is that when you go there the next time to test the exhaust, you can turn the fuel pressure a bit if its still off. Its a 5 min job, 2 bolts and thats it.
Raj

gman

Damian, great numbers. When do you plan to have the exhaust in? Could you dyno the car with just the cat back and then with the entire exhaust?

I have a few more dyno days up my sleave too. I will keep everyone posted.

Graham Rippel