Hello all,

I am trying to get into prom burning, and to be honest, starting out is kind of intimidating. I bought this car, and it needed an engine rebuild. I couldnt stand to put it back stock, so I ended up modifying it. Its an 89 L98. I've changed to vortec heads, SD Base, zz4 cam, slp runners, and all related intake mods. I'm also switching to a t-5 and 3.27 gears as well.

I've looked and found an APYS (305 vin F t5 3.08gr) bin as a starting point. Im just trying to get it close enough that I can run the car to start datalogging and making changes. Here are some questions I have that I havent really found good answers for while searching.

I'm using 24lb LT1 Injectors, and tunerpro RT asks for the size of injectors at 40psi. I will need to make it a little different than just simply putting "24" in as the value wont I? Is there a formula to figure that out?

When I change the injector size, will I need to change any tables in proportion to the size change in the injectors or should I just wait until the car is up and running?

Can I make changes to accomodate the different gear ratio I'll be running?
(its a mechanical speedo car, but i've learned that the ecm requires the reading from the speedo)

Any answers to those questions or any other thoughts would be greatly appreciated. I was considering letting someone else tune it, but the more I read, the more interesting this gets, so I'm diving in and doing it myself

 

From my experiences with MAF, all you need to do fuel wise is to change the injector size. If the MAF sensor can keep up and is accuratly reporting the airflow, your covered. you will, however, need to change the startup fueling. This can get really involved with some of the later stuff, but with the $6E, its somewhat simplistic. for starters, you should scale the crank fuel pulsewidth vs. engine temp down to compensate for the large injectors so you dont flood out on startup.

as far as teh speedo goes, you may just be able to leave it as-is, as youll be compensating for the different gears by changing out the speedo gears in the tail housing. IIRC, the MPH term shouldnt need to be changed for the older mechanical driven VSS', but I could be wrong.

 

I am far from an expert, but I am currently using $6E to tune my car and have had decent results so far.

Regarding the injector constant - it depends on what psi the LT1 injectors were rated 24 lbs at. It probably isn't too far from 40 psi, so you could safely start by entering "24" as the injector constant. Once it goes closed loop, monitor the BLM numbers and make the adjustment accordingly. You really wouldn't make any MAF table adjustments until you've datalogged. Then you'll be able to see if it is lean in some areas and rich in others.

On my car, there is a VSS (vehicle speed sensor) connected to the ZF transmission that supplies vehicle speed to the ECM. I think there is some type of gear in there that needs to be changed for a rear gear change (which I haven't done yet), but there really aren't any mandatory changes that need to be made in the bin.

Data logging is really the key. Find a nice, long, uphill road and go through the gears using various throttle positions, rpms, etc. 30 minutes of data is generally enough to start analyzing and making some adjustments.

 

I changed my rear gears to 3:73 and used the correct speedometer gear in the tailshaft of the transmission. Before I corrected this the lockup would not occur and mileage suffered greatly. I think lean cruise was affected as well and charcoal canister purge. However once the speedometer error was corrected everything went back in line and my mileage came back. No other changes were necessary. Mines an automatic, small cam, 2600 stall, with iron heads. I started with an ARAP bin and MAF tables. I'm still tinkering but it appears to be working well.

 

dimented,

In terms of "scaling down" the crank fuel pulsewidth vs. engine temp table, would I just multiply all of the values by .7916 (19(original 305 injectors) divided by 24(LT1 Injectors))? Or is my line of thinking way off?

 

Start with the "APYP" bin, it's the aluminum headed L98 manual trans corvette bin.

Running $6E on my setup, Vortec heads, SD base, fairly mild cam, manual trans, and it works pretty good. Too much timing for the Vortec heads though.

 

dyeager,

I looked at the spark tables, and they looked WAY high on the apyp bin. I've read that the corvette bins have too much timing for efficient heads such as vortecs.

Would I have any kind of advantage to start with too much timing, or not enough? I'm just afraid of knock occuring with the apyp bin.

Thanks for all the great replies guys.

 

Yes there is too much timing, but the bin works. It's for a 350, the 305 specific stuff (open loop especially) is going to be even more off than the 350.

You of course need to tune it, but it's the same displacement engine, so it's going to be closer.

 

Yes, that would be correct. This delivers roughly the same fueling out of the injectors during cranking.

 

Might want to try f bod, ve and timing from a 350.

Use the IAC settings from a vette bin.

Might be a better starting point for you.

later
Jeremy

 

3.8TransAM

When you say "350 bin" do you mean a F-body 350 bin? Like from my original prom?

 

Its funny, you described almost exactly the engine I rebuilt in my car. I switched to the equivalent $6E code (the car was '87, $32B). I used a 350 calibration. I don't have the info with me, otherwise, I could give you the BCC. Just get the latest 350 BCC for $6E.

I changed the injector constant to roughtly 24 (24.7? something like that) to bring the blms to 128-ish (MAF is never dead on over the whole load table), and turned the fan temps down. I can't even remember if I adjusted the road speed and it's good to go. It needs more tuning, but it runs and fires well.

now I need more stall since the stocker is pathetically low, and with the zz4 cam, the off-idle is a little soggy. That is what is keeping me from tuning any further.

with the $6E, dont forget to disconnect the cold start system, either yank the wire off the injector, or pull the fuse.
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my bad...I thought i read your car was an '87. Its an 89, so I would start with the latest 305 manual cal. That would give you all the manual trans logic, and then update the injector constant, etc and compare all the other tables to a 350 auto calibration and make some changes and check the results.

 

I'm sorry 3.8TransAm, but that all is gibberish to me. What exactly are you referring to?

People are saying "change tables to 350 values" exactly what tables need changed? I'm just starting, this, so I know very little. Sorry to be such a pain.

Anyone who would have some free time and would be willing to chat on AIM or something, I'd very much appreciate it.

Thanks for all the input guys.

 

3.8 is referring to the VE tables. These are volumetric efficiency tables used to estimate the airflow on a speed density setup. You dont have these as you have MAF. The only thing you may want to change initially for the fueling other then the crank fuel and injector constants could be how the LV8 is calculated. The LV8 (load value) provides a term thats similar to the manifold pressure. It gives an estimate of load. High airflow, low RPMs = high load. Low airflow, high RPMs = low load. The engines desplacement along with the airflow are used to estimate the LV8. Just snagging the constant from a 350 bin should have you covered.

Other then that, the other thing would be to adjust the timing to match your combo. Since you have MAF, theres not alot to be adjusted initially. Once you do a few basic items, you should be good to go. After that, itll be tweaking the small stuff and timing table.

 

I am looking at the constants in tunerpro, which one(s) do I need to change to change how the LV8 is calculated? I see several that involve LV8 in the description.


Thanks for all the help

 

Do a compare between a 350 MT vette bin and a 305. That will show you what GM changed. You can also do a 350 Fbody & vette comparison too.

 

Even with a world class T5, you'll probably regret that move down the road when you are picking up pieces of case and gears from the road. The T5 is rated for something like 300 ft lbs of torque, for the world class box