Hey yall,

I need some help. I've tuned some LT-1 forth gen cars, and now I have an early model (91) caprice that a friend of mine wants me to help him get straightened out.

The caprice came with a 305 ci engine, stock ECM is 16136965 BCDU. He put a 400ci engine with a midrange cam back into the car.

I need to know, where do you increase the engine displacement value on tunercat? On the lt-1's, there was a figure that we entered that was the cylinder volume in ml/cyl.

I don't see that on the tunercat definition file for the caprice, the ECM_62. This will be the first one like this for me, so I'm all ears.

I know that I have to play with the VE tables for tuning throughout, but I thought there would be someone where on the definition file constants that I could put the 400ci in for the baseline calibration, then go from there.

Please Help!!!

Thanks

D Moss

You are going to need alot more injector than the stock 55# 305 pieces. I would suggest some 80 lb/hr 454 injectors. The setting is called BPWC (Base Pulse Width Constant).

DynamicEFI

I've already told the guy that he was going to need bigger injectors for this engine, and he said that he was going to get one later, he just wanted to get it going now until the funds get right for the bigger injectors.

I see the BPW constant under the ECM constants on tunercat, and mine has 132 const.

Thing is, I have 2 different stock bin files, one is for a 5.0 caprice, and the other is the 5.7 caprice (I was told), and the BPW's for each engine is the same, but they have different displacements.

I did compare the two bin file constants, and the only thing that I saw that was really different was:

1. Min Async Injector Pulse Width -219.53
2. Max async Injector Pulse Width -317.34
3. Async to Sync Inj. Pulse Width Threshold .93 msec
4. Sync to Async Inj. Pulse Width Threshold -5.51 msec

Now the main Fuel table #1, %Volumetric Effeciency was pretty much the same all the to 90kpa, then small differences, around 5% between the two. But the main Fuel Table #2, %volumetric Effenciency between the two bin files was a big difference, from -12% to -33%. This was with the compare feature on with tunercat, comparing from the 5.7 to the 5.0.

I thought the injector pulse width's would have changed with the different sized injectors, not with the different engine displacement, but I don't know. I'm all ears, if there is something else that I can look at or check out, please let me know.

D Moss

GM used the same BPC of around 135 on alot of higher reving engines. On a truck with a 350 the BPC is 135 and on a 305 it is 148. With the stock 55 lb/hr injectors you should be running a BPC of 173 (I would round to 175). Keep in mind that your DC will be over 85% possibly as low as 3,500 RPM and you will be out of fuel.

Flow = 6.93 gm/s (55 lbs/hr)
Cyl Vol = .819353.819353 L
BPWC = 173

TBI Flow Data (BPW constants)

Thanks 355,

I didn't know the mathmatical equation for trying to figure this out.

I have a wideband O2 sensor, and we'll be tunning using the LM-1, so as soon as we run out of injector, I should be able to see it. I don't have any datalogging software to use with the caprice, so I'll use this calculation and figure out just how far 55lb injectors will go, watch the o2, and make sure we don't run lean.

I'll keep yall posted.

D Moss

My friend found some 454 injectors before the ECM got back from socketing. It should be here monday or tuesday.

From the website above, the injector flow rate is 80.51# an hr, so what I came up with on the BPWC was 118.

BPWC=Scaler* (cyl vol/ flow rate)
Scaler=1461.5
Flow= 10.144 gms/sec
Cyl Vol=819353 L

If all want to double check and make sure that's right, please do so. Now any tips on the first thing I should be looking at when we begin the tuning on this car that I might overlook. I'm hooking up the wideband and going straight to the v/e tables.

Thanks

D Moss