97 6SPEED Z

Okay, first off I'm a real newbie to all this computer tuning stuff, but, I may(???) have a real easy question for you guys who DO know tuning.

I have the '97 Z with the mods shown in my signiture, and it's running fine on my current mail order tune. Over the Winter I picked up a set of Ford SVO 42 lb (green top) fuel injectors, to replace the Ford SVO 30 lb (red top) fuel injectors I'm currently running on my car.

I do have access to both Tunercat and all the ALDL cables, etc. I know I need to re-program my PCM, but, my question is ........ what all needs to be done if I just want to "upgrade/tweak" my current tune to reflect the addition of the 42 lb/hr injectors, in replacing my current 30 lb/hr injectors?

Is it an easy thing to do to re-program/re-tune for just an injector size change if you already do have a good tune for your car running the smaller injectors? Any "step by step" tutorials that a real tuning newbie could use to make this change?

TIA for any replys!

97 6SPEED Z

Okay, its been over a week and ....... not a single reply.

I guess "tweaking" an otherwise "good" tune for just an injector size change is NOT so easy, eh?

ChrisLS1Bird

This board is dead...at least this section of it is. Try posting in the main LT1 section, and note that you posted in this section but didn't get any traffic.

Try other message boards, too. LS1tech surprisingly has a good LT1 contingent.

ChrisLS1Bird

LT1 PCM Tuning - Tips & Tricks for DIY Tuning!

bobdec

Have no answer so I hesitated replying.. as your setup (mods) is complex, aftermarket TB, Cam, 1.6 RR's, head work. Lots of variables that may require unique settings. New injectors require setting 'injector flow rate' correctly for fuel pressure you are running, 'injector minimum pulse width' for low RPM operation and 'injector offsets' for the specific injectors. After all that you need data logs to verify AFR and engine performance is correct. Some mail order tuners may have all this info without you having to dig through forums, you can ask and maybe get a mail order file from them. A dyno tune is the best but will cost $$. Or you can DIY after reading and researching on your setup. PS there is a sticky up above on injector offsets , not 42's but the topic is generic....

97 6SPEED Z

ChrisLS1Bird and bobdec, Thank You for your replys!

ChrisLS1Bird, I will spend some time looking at the link you provided, and bobdec ........... you sort of addressed my concerns/questions about this re-tuning procedure on a somewhat modded car.

I was just (maybe wishfully?) hoping that if one already has a pretty good "mail order" tune for their current modded set up, and then just wanted to go to bigger fuel injectors, (i.e. change only one (1) variable in the car's set up), that the re-tune would simply involve changing just injector related values and constants.

That much I think(?) I could handle.

bobdec

Email or contact some of the mail order turners with your mods and concerns. If you have data logging capabilities most will offer re-tunes to tweak the settings. You mentioned TunerCat in your OP, have you converted to ODB1, or do you have one of the old grand-fathered TC ODB2 packages.

97 6SPEED Z

Bobdec, first off, Thanks! for your reply, and yes, I have converted to an OBD-1 PCM on this car.

When I contacted the original mail order tuner, (the one I used for the OBD-1 PCM conversion), he now wants $50 a pop to change anything on my tune.

And, since I do have TunerCat and all the cables needed to re-tune, I was just hoping that this injector size swap would just involve changing a few simple constants in my current tune.

FireHawk409

Real question is why are you wanting bigger injectors? With mods listed the 30s are just fine. The bigger injectors are not going to help.

97 6SPEED Z

FireHawk409, but ........ they are not going to hurt, right. Please see my posts No.s 7 and 9 in this link:

PCM Re-Tune For Just An Injector Size Change? - LS1TECH

Thanks

Injuneer

What are you using to data log? DataMaster duty cycle numbers always seem to be higher than they should be. A 30# injector will support 430 flywheel HP at 85% DC, and 500 flywheel HP at 100% DC. You can't possibly be making that kind of HP with your mods, unless the ehads are flowing closer to 300cfm.

97 6SPEED Z

Injuneer, first off the data logging was done on a Genisys I unit from OTC. Secondly, the only time this car was on a chassis dyno it made 406 (SAE corrected) RWHP.

Now if that RWHP number is good, and we ASSume a 15% drivetrain loss for a manual trans car with a tube (i.e. non IRS) rear axle we have:

FWHP = RWHP /.85 = 406/.85 = 477.6 FWHP, right?

If we ASSume an 19% drivetrain loss ..... then we are right at your 500FWHP, and 100% DC numbers.

Finally, what effect might "dirty" fuel injectors have on duty cycle? If the PCM is commanding more fuel due to O2 sensor feedback, and the injectors may NOT be passing a TRUE 30 lb/hr, (maybe because they are "sticky"?)............ does the injector duty cycle go up?

97 6SPEED Z

Guys, I got the information I requested in my original post from a thread in another forum, but ........... I did want to stop back here and sincerely thank all of you who replied here.

Thanks (again) to all who responded!

Injuneer

I've measured the drivetrain losses through a T56, comparing engine dyno figures to chassis dyno figures. At 500 flywheel HP, the loss through a McLeod steel flywheel Street Twin, stock T56, 3" chrome moly DS, 12-bolt with 3.73's and 17x9.5" wheels with 275/40-17 street tires was 12.6%. The loss dropped to 12.1% at 760 flywheel HP.