I'm using Mobil 1 synthetic 10/30.

 

thank you, I’m probably going to use the same as I have always had good experiences with Mobil.

 

Reviving this thread and I’m going to be taking the advice given and ditching the FMU.

after about a month of driving with a lot of cruising and some hard driving I feel like there is a lot of power being left on the table and I need some new injectors as two of mine went bad and according to blowerworks website I believe This is due to the FMU locking up the injectors so I’m just going to put some bigger injectors in the car, I’m thinking 36lbs but my question is what is necessary for this? I do know I’ll need a different pressure regulator but my big question is do I absolutely need an aftermarket computer with Moates being gone or is there a way I can burn a new prom for the bigger injectors?

also will the factory pump be sufficient for the injectors or does that need to be upgraded to?

 

Before I switched to the Megasquirt, I used the stock ECM and larger injectors.

I had an 86 ECM and I had to "lie" a little about the size of the injectors for the chip, it was determined that the engine would have smaller injectors than it actually was, at least that's how I got 33lbs Bosch IV EV14 injectors to work with my standard ECM.

The fuel pump needs to be updated
I still drive with the original fuel pressure regulator, I've just modded it so that now the fuel pressure is around 44PSI with idle and increases progressively as the load increases.

 

After a very informative conversation with Driveit (Thank you once again!) I have decided to keep the FMU but with larger injectors.

I have already ordered TunerCAT and I will be running either 30LB or 36LB Injectors with this setup, any input would be great.

The reason I am choosing to keep the FMU with larger injectors is so I do not have to program the PROM to increase fuel with boost as this a portion of the build i would rather not do and the FMU will increase fuel pressure with Boost enough for me to be happy.

On that same note I do know the constant needs to be changed for the larger injectors, would anything else need to be changed?

 

just wanted to give a shout out to driveIT as he spent a lot of time answering my questions also.
he is a great source of info and very willing to spend his time to share it.

thank you.

 

An FMU with larger injectors does not solve anything.

The problem with an FMU is the high fuel pressure that is required to deliver the appropriate amount of fuel for even modest boost levels. For 7 psi boost, you need about 96 psi of fuel pressure in order to flow 48% more fuel for a given injector dc (assuming the same injector dc is adequate at zero boost and 43 psi fuel pressure). This is independent of the injector size.

For 7 psi boost, an FMU gain of 7.5 (or 8:1) is about right if the fuel system can handle operating at this pressure (fuel pump and injectors). This is about the practical limit.

Now if you tune it to be crazy rich at zero boost, you can reduce the fuel pressure demands somewhat for the boosted condition, but this is far from an ideal compromise.

This example is based on the pressure required for a 24 lb/hr injector to flow at 36 lb/hr, or for a 36 lb/hr injector to flow at 54 lb/hr. The pressure requirement doesn't change.

 

Thank you for the insight, this makes sense as the need for high fuel pressure is still there.

The big issue with my current injectors which are some generic replacement as I just discovered is that I have my FMU set at approximately 10:1 and when I start to build boost it is about the leanest I am comfortable with at about 11:1ish and I noticed it leaning out momentarily under boost which I suspect to be from the injectors locking up and I had two different ones go bad as the OHM readings are much lower on the two.

Please correct me if I am wrong but If I throw in some larger injectors wouldn't I be able to lower the FMU rate as at about 43 PSI they are flowing more than the my current injectors and when under boost they wouldn't need much more of a fuel pressure increase as my current ones do?

 

My 8:1 FMU ratio estimate above is admittedly on the low side, since it doesn't account for the increased manifold pressure which will reduce the pressure differential (between the fuel rail and the manifold) a bit and it doesn't account for the richer AFR that you really want to have under boost, so 10:1 is likely more realistic.

Here's an example log with 42 lb/hr injectors and proper fueling, sensorics and tuning to help illustrate my point about injector size:
https://datazap.me/u/tequilaboy/feli...3&mark=478-492

Note the two yellow markers. The first marker represents roughly zero psi and the second marker roughly 7 psi. Note the load and injector
pulse width values for each sample.

If you were to try to blindly fuel these two very different load conditions with an FMU (and the same injector pulse width), there is no way
around the ~96 psi fuel pressure requirement without seriously compromising one or the other independent of the injector size.

While both the rpm and load values are different in each sample here, the lower load (zero psi) condition could be easily duplicated at a higher
rpm simply as function of the throttle, so rpm based PE tuning is not the answer. The higher load condition is more rpm dependent with a
centrifugal supercharger than it would be with other supercharging methods, so the need to fuel a high load at lower rpm is reduced. That said,
you don't really want to be pig rich at mid-high rpm and part-mid throttle in a manual trans car, where you might operate often.

Second problem: The ecm is blind to load > 255 (and MAF > 255 gm/sec).

The example posted is nearly ideal behavior but this is not what you will get without specialized tuning, programming knowledge and appropriate hardware.

 

Thank you, It is basically looking like I either need to get a full tune and ditch the FMU or to make the FMU work.

I read up on Blowerworks website and I do see that the Ford Blue top 24LB saturated injectors have been successful in similar setup's with an FMU and as I just started my semester for school I don't have too much time to put in the car so I am thinking I will give the new Injectors a shot, if this course does not work I will start doing my homework on tuning so I can ditch the FMU and go with larger injectors alone.

 

Also on that same note regarding Blowerworks, is anyone aware if they still do custom Prom's for these applications? If they do that is another route I will keep in mind.

 

Blowerworks has been trying to sell all his inventory and was closing down. https://www.dynamicefi.com/EBL_Flash.php Yep it's the simpler method make the FMU work or the EBL is a good way to go. With the EBL it is a steep learning curve to learn from scratch, but is rewarding. You need to leave the MAF in place to pass visual. Those wires then go down into the harness and deadend out of sight. The other end of them to the MAP and you need to repin a few wires at the ECM. The ECM is up under the dash-so you're still good on visual.The check engine light still functions correctly with the EBL so still good on visual.

 

From what you explained it sounds like the EBL is the best way to all around.

As you mentioned the programming and learning curve will be steep and that is out of the cards at this current moment so I will just make the FMU work with better injectors.

Using Tunercat would there be any other adjustments you may recommend to help the FMU work? such as lowering the throttle position to engage power enrichment earlier or anything else?

 

Main thing is to have a live data scan program and get a wideband in it.

 

I will be ordering the TunerCat cable and software within the next couple days to have a live data scan.

I also realized that the car currently has on some disc style Multec injectors that can not handle high Fuel pressure which would explain my issue.

I went ahead and ordered some 22lb Bosch D3 Injectors and I spoke with the customer service at SouthBay. These are the 4 nozzle design that can handle up to 100PSI so I am hopeful that I will have better performance with these injectors while using the FMU until a complete tune is feasible for me with the EBL

 

Sounds like you'll have plenty of books to read in school, but I'll add one for your "free time". This will give you the basics for tuning, or even just understanding the live data

that you're looking at.

 

Thank you for the recommendation. I will make sure to pick this up as I am interested in being able to understand the live data on these cars.

Especially as I am a Mechanical Engineer major, I am only in Math classes this semester so I'm not burnt out of reading.

 

How often do your drive your supercharged C4s?, I work Monday-Friday and I have to deal with rush hour traffic both ways so It is not driven on a daily basis so I am just curious as to how often you guys drive these.

 

Further question regarding you guys who have deleted the AC with a supercharger.

TPIS has been taking forever to ship out the AC delete pulley and I have heard of others waiting for close to a year to get their orders from them so I need to explore other AC delete options right away as the compressor is starting to lock up and causing very fast belt wear.

Have any of you guys just removed the compressor and bracket and used a shorter belt? If so what size belt was used or is there another company that makes an AC delete Pulley?

Any other options or ideas would be greatly appreciated.