Tampa 928s

86-S/C:
I have a Fmu and just received an adjustable FPR as a gift. So should I install it and if so what would the base line pressure be; I have the Ford Blue Top 24 Lbs injector. If I do install it what hooks up to what? I will be going to 36 Lbs injectors once I get this Shark Tuned so this is a temporary install.

zoltan944

I wouldn't. The FMU increases fuel pressure with increased manifold pressure(boost), the AFPR adjusts the 'set' or idle fuel pressure and increases on a decrease of vacuum.

If you can sharktune to increase FP on boost levels you can switch then, but you would need a MAP and piggyback to do that.

Also, are you able to sharktune your S3 computer?

John Speake

It will just add an unecessary complication. You only need to raise fuel pressure if your injector duty cycle get above (say) 90%. If you can fit 42# injectors then you can most likely throw away the FMU.

Tampa 928s

With the 24's it does go above 90% and there is that quick lean out when boost kicks in due to the Fmu. Since it will be a while untill an intercooler is in the mix I thought this might be a good thing to do. John, if your telling me you can put 42's with out an Fmu and shark tuning only I will look at that.

John Speake

I'm not sure if 42# are available in the barbed fitting that is used in your 85/86 car. But if you do go to 42# then without an FMU, and standard fuel pressure you can go to more than 600HP crank without the injectors maxing out.

That is the combination used by Tim Murphy with his Stage 3 kits, and also John Kuhn's twin turbo...

Cosmo Kramer

85-85 uses Ford injectors, so no problem there.

So John, you are saying that you can go larger injectors and tune them with the Sharktuner and no FMU? Interesting, I imagine the duty cycle would be pretty low when not on the boost.

123quattro

The duty cycle should be fine. I can get my Audi to idle reliably at 800 rpm with 60# injectors on a 2.3L engine.

John Speake

Yes, that is correct. Although the duty cycle is low, there is another problem that can happen at idle/low cruise when using oversized injectors. The injector on time is so small it is almost the same as the time to actually get the injector open. So with typical tolerances, this can result in erratic fuelling in these areas. The Sharktuners have a special technique to keep injector opertation in these areas consistant and repeatable under all conditions.

Rick Carter

So you can use 42 pound injectors in model year 85/86 with ST2 but not ST1?

John Speake

Hi Rick, sorry that was a typo, you can use injectors up to 64# with ST1 and ST2.

John Kuhn is Sharktuning a twin turbo with 64# at present.

Rick Carter

OK, thanks John.

John Speake

Tampa, there are several ways to "skin the cat". You could use 36# plus a RRFPR and without the FMU to achieve a correct result, as I believe you have already been advised by another party.... but whatever your final choice I strongly recomend ditching the FMU.

Tampa 928s

86 Super Charged with 24 Lb ford 4-hole injectors.

John,

I will refer to you in this debate, considering maybe in the distant future I will add an intercooler. What would you suggest as far as a good size and set-up that would work with what I have now and if I add an intercooler. I have one shot at this Shark Tuner and am still worried about the lean out during transition into boost and the car runs hot here in Florida during the summer. So I will need to acquire the injectors ahead of time and install them when the tuning can be done. I assume that I can add the adjustable AFPR now and set it up for factory pressures now.
Any feedback on which lines connect to the AFPR.

John Speake

Hi Tampa, what's you ultimate HP target, and the expected boost pressure ? This is not my area of expertise.

John Kuhn modifed an EZ-F with a 2 Bar map sensor and then was able to map with SharkTuner from off boost to full bost on a turbo'd 928. That gave full control of igntion under alll conditions.

I think removing the FMU should help the lean out, but others can contribute better then me to this discussion.

Z

If you're going to put in larger injectors anyway, and will be installing an intercooler and/or upgrading to stage-3 at some time in the future, I'd suggest contacting Tim and going straight to the 42lb injectors. The 42lb injectors are what the stage-3 kits use, Tim would be able to supply you with what it would take to make them work in your car, including an LH chip to go along with the 42lb injectors. That should eliminate or greatly reduce any need for SharkTuning. The 42lb injectors and chip were installed into Hacker's '81 that we put the '85 LH/EZF system into. His car started right up and ran nice and smooth, without any SharkTuning, and even without there being any O2 sensor and closed loop operation adjusting the mixture.