I recently bought an '89 IROC-Z convertible, TPI, 5 speed.

The previous owner had 24 lbs injectors installed in combination with a "dyno tuned" chip from a Miami area speed shop which no longer exists.

It runs pretty good, but I can tell that at really low idle, (like when engaging the clutch in reverse), the 24 pounders are cranked pretty low.

So, because I really don't know what this "dyno tune" consists of and am sort of a worrywart, I am considering switching those brand new 24 lbs injectors out for factory sized 19 pounders.

I have the factory PROM from my '89 LB9, T5, IROC, hardtop (switched it for a Hypertech back in the day so I could use a 160 t-stat and lower fan temps), and would like to use it after swapping injectors.

Seems straight forward to me, since they are both 5 speed, LB9s, or am I missing something? Any reason I wouldn't want to swap the hardtop's PROM into the 'vert?

 

Unless there's something in the car you're unaware of that the prom is tuned for then you should be all set.

 

I can't imagine that they'd be different. Unless the G92 hardtop with ZR rated tires and the non-G92 convertible with VR rated tires had a different speed limit.

 

They probably do. That's the difference in AXXD and axxc

 

In what?

 

AXXD and axxc are the SD Tpi manual bins.
The difference is tire speed rating only.

 

SD?

 

Speed density. Or "Map, not maf."

 

The '89s are mass airflow.

 

I know.
That was in direct response to post #3.

 

So other than top speed programming, (if that), they ought to be identical?

Wonder what differences the 1LE Players cars had - if any?

 

I would think but I do not know as I've never looked at them.

 

Realistically for what you want and how you drive, I would go stock chip set up for 24#'s and leave it alone.

One constant to adjust maybe a little tweaking at idle for them, assuming they are a quality injector.

Set it and forget it.(its a 99% near stock car)

Try finding someone to tune it on a dyno now

You would need Jeremy(me) or Jeremy(South Bend) or someone else with similar knowledge and a dyno.

Although there are a few things you can do to smooth it out some, but instant easy you can feel kind of stuff is harder in a stick than an auto, like changing lockup points and mph.

 

Jeremy, do you think there is any advantage to sticking to the 24 pounders with reprogramming, rather than reverting back to 19# and stockish tune?

 

The advantage is not getting dirty.

 

Well, I've already ordered a set of rebuilt Bosch 2, 19# injectors, several days ago.......

 

I'm really bummed I couldn't datalog the car at the Expo, that's the first car I've not been able to communicate with ever. Among many things I wanted to see what the pulsewidth was at idle. 24lb injectors are pretty good sized for a 305, and my primary concern with a stocker like yours is that they are barely pulsing at idle, making smooth idle and tip-in troublesome. I wanted to see what the fuel trims were doing as well to see how close the tune really is. Does the car ever stall or idle weird with the AC on? Does it start OK at various ambient and coolant temperatures?

I like going back to 19lb injectors and a stock chip. I know the 1LE tune is the same as the G92 cars had, players cars I'm not sure. I thought about a year ago a guy put a Player's car tune up on here but I can't find it now. It would be interesting to see the changes, but I'd guess they leaned it out a bit at wide open and bumped timing up.

So put your 19s in and run the PROM from your black car, or I can send you something custom that will work too. If I de-soldered the chip from your PROM I could read and copy the tune the car has now and just change the injector constant.

 

1989 prom was ANYN or ANYX. I think it was ANYN was in my car from the factory.

 

Sounds like a plan!