Injector Upgrade

This article was originally written by Wayne, aka WAC.

I finally got myself motivated to swap out the OBS fuel rails for a set of Legacy Turbo fuel rails, including injectors. The side-feed EJ22T rails are compatible with pre-MY98 EJ22 intake headers, so the swap was relatively painless.

At 5 psi, these were the settings required at 5000 and 6000 rpm to keep EGT’s under control and retain good engine response characteristics:


Type Color Flow Fuel Press EGT S-AFC correction

—- —– ———- ———- —— —————-

EJ22 Grey 220 cc/min 80 psi 1550°F +25% (Note A)

EJ25 Red 280 cc/min 75 psi 1425°F +15%

EJ22T Pink 360 cc/min 50 psi 1250°F -15% (Note B)


A. MAF output voltage maxed out at 5.0V, so any further correction was useless.

B. RRFPR disabled.

With the big injectors, the engine runs extremely rich on cold start. But once warmed up, it idles as well as the stock injectors. I’ve even had to crank the S-AFC’s LO settings to -10% to smooth out the transition from closed-loop mode to open-loop mode. Otherwise, it would bog briefly during that transition.

I’ve only done 15 minutes of tuning on the EJ22T injectors, enough to realize that the RRFPR was a hindrance, and what ballpark corrections were required. Needless to say, there’s no pinging at all. An S-AFC or equivalent is required to obtain good driveablility at part-throttle, since the RRFPR (if used) is only useful to correct for the high end. And even then, it’s sometimes insufficient by itself.

I hope that those considering running EJ22T or SR20DET injectors (similar flows) on an RS-T may find this informative. Of course, you will have to use your imagination to interpolate the data for an EJ25. Or get feedback from RS-T’s with fuel injector upgrades.


P.S. Bill, thanks for the use of the EJ22T injectors. The SR20DET injectors are waiting for new o-rings.

cool so it works. is there any way to solve the rich cold start issues? have you tried lowerign the fuel pressure?

I can think of three options:
1. Aftermarket ECU.
2. Lower the fuel pressure. This would require either a replacement FPR or a vacuum pump contraption to lower the reference pressure during cold start.
3. Some sort of custom anti-Torque Chip II. Instead of fooling the ECU into thinking that the engine is cold, we need to tell the ECU that it’s hot. I’ll look into this…

I don’t think the cold start issue is a big deal – just a small price to pay for more boost. It’s either that or having to deal with the learning curve for an aftermarket ECU.
Bill: increasing injector size works against the stock ECU. It has no idea that the injectors have changed, and apparently uses open-loop settings for cold start. For example, it may open the EJ22 injectors for x pulse duration. But the ~2x larger EJ22T injectors are pushing almost twice as much fuel! I saw similar effects when I was running the EJ25 injectors on the stock ECU. But most of that was fixed with the EJ25 ECU.

Matt: no, the EJ22T rails and injectors won’t fit any EJ25’s as far as I can tell. The injectors are too different, and the rails have different mounting flanges. However, if you are handy with a welder and sheet metal, I’m sure you can adapt an EJ22T fuel rail to fit your intake manifold, in the same spirit as what Mcgyver did in addition to his SR20DET injector swap. I’m at about 1000′ elevation.

Steve: cold start idling is not bad at all, since the ECU starts out at about 1300 rpm. It’s the engine cranking that has “issues”. I’ve trained myself to simply keep cranking until it fires up for good, ignoring whatever the engine may be doing during cranking.

Update: cold start is still quite rough (occasional sputter and coughing), but warm start is as smooth as they come. I have taken the RRFPR out, and the engine runs good, albeit still quite rich at partial throttle. I can’t seem to tune out the slight bogging at rare transitions from closed-loop to open-loop mode. But under boost, it works like a charm, without the time delay I used to see with the RRFPR – in effect, throttle response is better than with the RRFPR. I have a feeling that the 360-380 cc/min injectors will work better on an EJ25 than on my EJ22.

I did a fam run up the route for the Okemo Hillclimb this weekend. EGT’s were 1200-1250°F under max loads. The only times I saw anything between 1300-1450°F was during highway cruise at 75 mph, and deliberately modulating for partial throttle at off-boost conditions.
More updates:

1. Increased boost from 5 psi to 7 psi (w/MBC). That was good enough to knock 6 seconds off my times.
2. EGT’s under full boost never went above 1450°F, all the way up to 6500 rpm.
3. More fine-tuning of S-AFC settings brought the corrections down to -20% virtually across the board. At -15%, EGT’s were slightly below 1400°F, and I could feel that the engine was still running a bit rich.
4. Throttle response and turbo lag has improved by several hundred milliseconds without the RRFPR. Throttle response is also more linear than before.
5. Cold start is still rough at times, but will always start after cranking for maximum of 5 seconds.