What is the maximum injector size that could be installed with the stock ECU and an SAFC without having to add a fuel pressure regulator?

I believe in 2nd gen DSM's it was 660's 680's after that u needed a FPR to bring it back to the tuneable area of the SAFC.

Im guessing it should be a little higher on Evos ? 720's 750's anyone?


Thanks in advanced

 

good question, FYI i just put on the Logic performancd FPR and the craftsmanship is great..considering the walbro 255 increases baseline fuel pressure from 43.5 to 52psi, it might not be a bad investment for your fuel system.

 

Definitely planning on it, but the stock fpr should be good enough to strecth it a lil more, thats why i dont want to go too big on the injectors and then be forced to buy one, on the other hand, i dont want to spend money on 650's and then regret it when i could buy 720's for a bit more, as long as the safc can handle the task, eitherway a FPR will come handy in the future.

Was that fpr bolt on?

Thanks

 

yes.. the only problem with the fpr is that its a very tight fit and requires you to move the crank angle sensor for the gauge to fit in place.. If you do this the gauge is pretty stealth as its really not noticable with the hood up as its behind the valve cover. We decided to make some custom plumbing for $4 of brass fittings and positioned the gauge above the valve cover. This didnt require moving the gauge.. plus you could easily hook up an additional in cabin fuel pressure gauge this way. Im getting on the dyno on saturday with my safc and im excited to see what kind of power im going to put down. Im hoping that the fpr is going to prevent overly rich conditions at lower rpms

 

An AFC can make adustments +/- 50%, so theoreticly you could use an injector that slows 50% more. In reality, 780cc injectors (36% larger than stock) are about the largest for an AFC and stock ECU. It could be done comfortably with play/tuneabilty either way.
I don't think I understand you fully about the FPR. Do you mean if you run bigger injectors, you'll need to raise the fuel pressure? Are you refering to an adjustable fuel pressure regulator (AFPR)?
The only times a DSM would require a AFPR is when they run a 255lph pump. It over runs the stock fuel pressure regulator making tuning difficult. Once the AFPR is on, it's still set to the base fuel pressure of 43 psi.

 

780's sounds good i think i will go for 720's just in case, On my 97-GST i had 660cc, walbro 255lph no "AFPR" and an safc with stock computer, i had a 20g with a 57trim compressor wheel on it boosting 21-22psi on pump , My Hi settings were all in the -39 -42 range, almost out of range for the SAFC, but it got the job done. on a friends car with the same setup using 720's we had to install a FPR to lower the fuel pressure and bringit back to the tuneable area of the safc. The stock computer on 2nd gens was programmed for 450's since the evo ecu is set for 560cc im guessuing with an safc 720's are possible without having to lower fuel pressure, but iwas curious if someone had dont it before. And thanks for the suggestion

Joel

 

the report on the 255 pump is that it will increase the baseline fuel pressure to 52 psi.. this mean the fuel pressure is not completely linear so the fuel pressure will stay at 52psi even while at idle when it should be 43.5, regardless of the fact that you may be able to squeeze more hp out the car and tune more efficiently i would think this is a waste of gas at the least, plus with the new fpr you can also raise the baseline to say 48psi then at X amount of boost you would be flowing more fuel then with the stock unit, while idling with lower fpr as well. My understanding is limited.. but im getting this part correct.

 

Anyone using 750's with SAFC and stock fpr?

 

I wouldn't worry about uping the injector size unless you are running too lean in the higher rpms. If you are running lean in the upper rpms and you can't bring it in with the + 50% on the Safc, then you need to up the injector size otherwise the stock ones should be good enough.

 

I'm trying to buy injectors that will be managable with my setup and also work with an upgraded turbo ... dont want to spend money on the same part twice.. But i get your point, ive heard of people getting close to 90% Duty cycle on the stockers, im thinking between 680's and 720's ..

 

On my Eclipse before I went with a modified ECU using DSMLink I had a Super AFC, 660cc injectors and a few other tricks. The tricks were backing out MAS adjustment screw which was about 10% leaner and a dime store fuel cut defencer which was basically fooling the baraometer. This let me lean things out another 10-15% as well as advance the timing at the same time, then I used the Super AFC to do the fine tuning adjustments. At that time I only used an OBD2 logger to verify air fuel voltage and verify that timing advance was climbing in all gears without any retard.

I haven't looked at the MAS closely yet to see if there is a similar adjustment screw or if you can lean out the mixture by adjusting the Baro sensor so this is just theory on the Evo. Anyone know if it's the same as my Eclipse GSX was? Keep in mind that any adjustments done to these should only be attempted with close monitoring of the engine since you could really blow things up quickly if you aren't carefull.

 

My AFPR helped out idle and fuel economy quite a bit to bring my 660's back in line. But I also think that you want one to avoid using aggressive cuts with the AFC to make your timing curves look better, its better to "use up" your injectors so to speak and have the duty cycle around 75-80%.

 

Stocks are already up to mid 90%

 

you don't want to go larger than 660cc or 680cc. The AFC has to be dialed back too far. You don't want to take it past -20%. Any more than that the ECU will start advancing timing and cause detonation.
The AFC tricks the MAS to think there is less air going into the engine than there really is. The ECU sees thinks that there isn't enough air going in and advances the ignition timing to unsafe level. I went through 5 motors in my GSX before figuring this out. That's why a reflash is alot safer than a AFC. but you can still use a AFC to fine tune even with a flash.

 

5 motors, holy crap man. An EGT and a wideband work wonders.