Baseline for 7.4l Vortec long block w/TBI induction?

**Casey** · 12-22-2023

Hey guys, I've been driving around my '91 Suburban with the 7427 swap for a couple of years now and it's been great with the stock '95 5.7/4l80e tune. I've been slowly gathering the parts and making the supporting modifications to drop in a big block and I'm at the point where it makes sense to start getting the baseline tune figured out. I've been told my setup is a common one so I was hoping one of you guys might have a good place to start.

It's a stock 7.4l Vortec long block bored .030 over with the Edelbrock TBI Intake and Doug Thorley Tri-Y's. Its running a '95 TB with the early big block injectors. Cam specs are pretty mild with a crazy (to me) 118 LSA
Screenshot_20221031-214309_Chrome.jpg

I left a WB02 lead when I did the 7427 swap so I plan on getting that hooked up and have an Autoprom, though in all honesty I wouldn't mind driving it to someone and paying to have it fine tuned provided I had a good enough baseline to get there safely.

TIA!

**ralmo94** · 12-22-2023

Are you planning on running a MAF or keeping speed density?

You could probably pull a stock timing table from a vortec truck file,
If you need I could get one from ho tuners.

I would say main thing is to have your injectors properly calibrated
And tune from there.

**Casey** · 12-22-2023

I was planning on keeping SD for simplicity and convenience, but I'm certainly open to persuasion haha. One issue I've run into with the 4l80e and 7427 is that sections used by other people for conversions and mods are occupied by the stuff needed to make the transmission operate (such as electric fan control). Would MAF make a huge difference? I've read about some kind of improvement feeding the WB02 data in conjunction with the MAF conversion but I didn't 100% understand it.

The TB is currently at SPR getting worked over so the injectors will be cleaned and calibrated along with new sensors, rebushed shafts, etc.

**ralmo94** · 12-22-2023

So, I understand you are using tbi, somehow I missed that in the first post.
I think I would start with a 95 454 tune. Again make sure you get the fuel settings right for the pressure you are running.
Get the VE dialed in and the try a vortec timing table if you want and recheck ve.

Also, you can take the pin that goes to the cruise control and apply ground from a toggle switch and use the cruise shift schedules like a tow haul or performance shift schedules.

**Casey** · 12-22-2023

Ah, SD it is haha! That's cool about the cruise signal, I left a lead for it as well even though I deleted all of my cruise stuff, I'll have to dream up a good use for it.

I'd love a timing table for the stock Vortec, and I'll try to track down a stock '95 7.4l/4l80e tune. If anyone has a CAJR .bin handy let me know!

**dave w** · 12-22-2023

Originally Posted by Casey

I'd love a timing table for the stock Vortec

Attached .pdf's with 1999 7.4 Vortec Timing Tables.

Gearhead-efi link for some 1994 7.4 .bin files, likely with injectors @ 28 PSI: http://www.gearhead-efi.com/Fuel-Inj...Information-OE

**Casey** · 12-23-2023

Hopefully Dave never gets tired of swooping in and saving the day! Just to make sure my understanding is correct, C=2wd, K=4wd, G=van, P=medium duty? In which case BJKX or BHDF would be the best starting point?

**ralmo94** · 12-23-2023

The last two digits of the BCC code is how late the revision is. For example AA would precede BB

I would go with the latest one for a CK truck.
I have been told that the van tunes are detuned somewhat I have never actually looked at them myself to see but I've always used the truck tunes

**Casey** · 12-23-2023

It looks like BJKX would be the latest, and is for a truck so I'll start there. In '95 it went BMHM->BPRK->CAJR, and I imagine that might prove difficult to find but I understand there were issues that the revisions corrected. I guess we'll see how it goes!

**ralmo94** · 12-23-2023

Another thing to keep in mind, Incase you weren't already aware, the 95 454 tbi runs a lot higher fuel pressure than the small block, 20 or 30 psi, if I remember correctly. So make sure you get the correct Base Pulse Width setting for your injectors and fuel pressure.

So are you running a big block tbi, or your stock one with the large injectors?

**Casey** · 12-23-2023

Right, it's a '95 TB with '87 injectors.

**1project2many** · 12-23-2023

The last two digits of the BCC code is how late the revision is. For example AA would precede BB

I would not use this logic when looking at calibrations. Calibrations can be released that solve specific issues in certain vehicles but are not appropriate for most vehicles.

I have been told that the van tunes are detuned somewhat I have never actually looked at them myself to see but I've always used the truck tunes

Sometimes van calibrations have some reduced timing values and sometimes the transmission calibrations are milder. I agree with using truck calibrations in trucks.

In '95 it went BMHM->BPRK->CAJR,

BMHM is the initial calibration.
BPRK was released to eliminate code 32 setting under heavy load. See TSB 57-65-09.
CAJR was released to resolve No Upshift/2Nd Gear Only After Cold Start-Intermittent DTC 87-High Ratio Error. See TSB 67-71-53A

It looks like BJKX would be the latest, and is for a truck so I'll start there.

That's a leaded fuel compatible calibration. At a minimum closed loop needs to be enabled. Other related functions may not be correctly calibrated.

16198042, 8055, BJKX N/A -
ECU: 16196395 MODULE, PCM (REMANUFACTURED) *** S/S BY 16197427
Transmission : MT1 AUTO 4 SPD THM R2 (4L80);
Emission System : NM8 EMISSION SYSTEM, LEADED FUEL;