PorKen

S4s with X-pipe must be hurtin' with 19# injectors, even with the LH 1/2ish inj. rate feature. I reckon you need 24# or more.

If you are going to SharkTune, you might as well start with bigger injectors (S4), or a higher pressure regulator (S3), and use the ST injector selector. (There are online guesstimators for how pressure change equals a larger injector.)

After doing some logging (Logworks) on my '86.5 w/X-pipe, I found I was at 100% injector dwell >6200rpm. AFRs were not consistent past 90%. I put in a '87 S4 FPR, and now I max out at 84% at 6500rpm with a 13.2 AFR (89% at 12.4). For me, 24lb inj. with a 3.8bar S4 regulator pretty much matched my original AFRs with a 28.7lb injector selection.

Ignition misfires will show as lean, too. Might explain the smoke, too.

mark kibort

I ran 19lb injectors at near 12.5 to 13:1 at 72psi and got a consistant 335 to 320rwhp for years!

I think the only issue with the 19 lb injectors is that you have to run them on the high side of pressure capability. But the duration was not over 95%

mk

mark kibort

there is not enough information to claim that the flappy is causing any fuel problem. Looks like the fuel is normal for a stock S4. the variance is slight. since flappy is closed up top on all the runs whether working or not, it did look like you gained some HP. . cant wait to try them out!

anyway, I would just get a fuel regulator and bolt it on with some additional pressure. (near 70psi) After all I do have 7 years of all our racing on my motor, lots of dyno runs, and an engine disassembly that proved it was all in good shape. (not to mention a high of 335rwhp with stock 19lb injectors)

mk

mark kibort

so im confused. It looks like your old run is 394, then you ran 290 on the same day that you ran 302hp? why was there two different runs with two different AFR levels?

what kind of O2 sensor were you using and where was it located? (i.e. tail pipe, bung in the header, etc?)

My AFRs were all over the map until I started using the version that was mounted to the header pipe. even then, it was only one side.

The point of all this, who knows if the side plates are due to a change of fuel ratio or the plates themselves?

EDIT: oh, we are looking at your automatic "sharky". I cant keep all your code names straight!!

mk

mark kibort

I would bet that the o2 sensor was tail pipe mounted, if not, its a real strange 02 output. did you have more than 1 or 2 runs? mine usually takes about 3 runs to stablize out on any given dyno session. Thats the entire thing about dyno runs, you have to have a good baseline, both on the day and on prior runs. sometimes it just means lots of dyno time.

anyway, when I was doing my tail pipe runs for all these years, my curves would look like yours. lean and then 12.5 at the end. just thought that was the way the ecu was on S4s. THEN, I did the wide band mounted in the header. what a difference. it was 12.5 all the way flat across the rpm test.
Same thing with my new stroker engine. big difference. (but richer due to all the changes, getting a flat 11.5:1 run). In the end, the plug appearance was verifying the output of the dyno sensors.

It seems that the initial tail pipe runs are very sensitive to the rpm you start at. maybe its a function of the time that the 02 sensor is exposed to the exhaust heat.

If there is such a difference with the dyno output HP numbers, could it be mixture if that is being read correctly?

PorKen

335 to 320 is not consistent.

As I said... if you are going to SharkTune, then larger injectors are a good starting point. You can up the fuel pressure to mimic a somwhat larger injector, but there are fewer variables with a stock regulator. Plus, no additional stress on the fuel pump, hoses, and injectors, and you end up with a fuel map for all loads and rpms, not just WOT.

PorKen

The injectors are basically stuck open, and you are tuning with fuel pressure, as if it were a CIS engine.

11.5 is just silly rich, BTW.

mark kibort

Thats over 7 years. dyno to dyno were less than 5hp at the MOST.

for the first 3 years it was 325 to 330. then it was 315 to 320, then it was 308 to 315. the engine was getting a little tired, and that is not surprising on how I was using it.

Remember, this is a race car. The only load he should have is WOT!

mk

IcemanG17

MK
All wideband readings on the race shark (widow) were from a 2nd bung welded right at the X pipe....the standard narrowband O2 sensor is placed on the downpipe just after the header on one side (passenger?) So the wideband location gets both banks...vs only 1 for the stock sensor.....

The original super rich measurements were tailpipe....then verified by the new location at the X..... Maybe I'll install a wideband with narrow emulation in the stock location to see what it reads? That also will make sharktuning easier

mark kibort

Just trying to figure out why the fuel curves look so different than what i had.

the steep decending lines were from the tail pipe, which didnt nessarily made anything richer, just didnt read the full richness until the later RPMs. when using the wide band in the header, the fuel curve was flat. its flat now as well with the bigger motor.

mk

IcemanG17

I will check the plugs after my next track session....assuming it runs fine (always has) the plugs will be VERY telling..... My thinking is they will be fine......

IndyMatt

Mark and Porken,

I have an S4 that will have an X Pipe on it, it will be a street car. Would increasing the fuel pressure a good idea with the stock injectors? Also if I use the larger injectors, I am assuming that I will need to Sharktune. Basically what I am getting at is what is the best option for a streetcar without having to sharktune?

mark kibort

as i said, by raising fuel pressure, i was able to get 335rwhp out of a stock S4 with GT cams.

i think its probably a fine way to take advantage of your mods, without having the need to shark tune, unless you want to optimize. even then, the stock injectors are fine (to a point)

mk

IcemanG17

"sharktuning" is the best way to "tune" a 928's engine......since it allows you precisely tune the fuel-spark maps vs just dumping fuel across the board like a pressure bump.......