you have to have the computer tuned for a 58mm throttlebody don't you? cause the volume of air is larger and i heard it does something to the tranny shift points???

 

I installed a Holley 58mm TB a few weeks ago, so I’ve been there and done that. According Bryan at PCMforLess, reprogramming is not required and my LT1 performed well without any additional programming. However, there are some items that will need attention with the 58mm install and they must be done in the correct sequence. First is the mechanical linkage adjustment (end-stop at idle and butterflies 90 degrees at WOT). My LT1 has the ASR servo, so the WOT adjustment wasn’t easy, but I figured it out and the TB is working great (PM me if you have the ASR "Traction Control"). The next step is the TPS adjustment. You’ll need to slot-out the two screw holes and adjust the TPS voltage for 0.60 volts (600mv) at idle and about 4.8 volts at WOT (measured on the blue TPS wire with a digital multimeter, with ignition on, but not running). You can us a straight pin to push into the connector next to the blue wire, then connect the meter ground lead to the battery (-) terminal for a good connection. If the TPS voltage is not adjusted correctly, or the butterflies exceed 90 degrees you my get trouble code (P0123 High TSP Voltage) at WOT. My Z28 (with the mods is have) ran about two-to-three tenths faster with the 58mm. I hope this info helps and your LT1 runs great with the 58mm!

 

when you bought yours did it come with those instructions you just told me?

 

Yes, the Holley had some decent instructions, however, they didn't cover everything in detail, like checking both ends of the TPS voltage range (idle & WOT), where to measure the voltage and ensuring the butterflies were 90 degrees. The PCM uses the TPS voltage for several functions, so it is important to get it correct and not have problems, or get a trouble code. Do you have the Holley 58mm, or another brand?

1997 Silver Z/28 LT1-Auto
w/ 30 th Anniversary navy blue stripes and Chrome ZR1 wheels
Kooks Long-Tubes w/ Off-Road Y-Pipe and Cut-Out (no Cats), LT4 Hot Cam, Valve Springs and Crane 1.6 Roller Rockers, GM Performance Roller Timing Chain, Holley 58mm TB, Aeromotive Fuel Regulator, 3.73 Gears, TCI 2600 Flash Stall, TCI Super 2nd Gear Servo, B&M Trans Cooler, MSD Coil and Plug Wires, K&N Air Intake, PCMforLess Performance Program, LT4 KM, Jegs Under-Drive Pulleys, Aluminum Driveshaft, Aluminum LCAs w/ Relocation Brackets, Mickey Thompson ET slicks and a few undisclosed performance upgrades. (Best ¼ time; 12.68 @ 108.3 MPH, last Friday night). "engine only, no NO2"

 

Engineer I am guessing you have a M6 car not an A4 because ALL the tuners agree that A4 cars need tuning unless you have modified it for vacuum modulation. With a 52mm a Transgo can be enough too but at any rate the A4 does require attention be it the shift kit, the vacuum modulator, or pcm work or the pcm work and shift kit combined.

 

Engineer you replied while I was typing, did you already have shift firmness programming BEFORE you did the TB? That could explain why Bryan said no update needed because you already had what was needed.

 

BBK is what i got or ordered.

 

Yes, the PCM had already been programmed by Bryan w/ firm shift and new shift points (no shift kit installed, just TCI 2nd grear super servo) when I installed the 58mm. I checked with Bryan and he said, "no reprogramming whould be required for the 58mm." The 58mm seems to be good both on the street (shifts good w/ regular driving) and at the strip. I've probably got about twenty five 1/4 mile runs at the strip with the 58mm and I'm running faster. Before the 58mm my best ET was 12.93, now I've run a 12.68. Also, the air was cooler.

 

It is just part throttle you hyave to worry about. The 58mm allows more air at the same part throttle TPS position more air is more power, the pcm scales shift firmness off of TPS and some other factors this is why the program tweaks. I am sure he meant no update needed for you because you already had shift improvement and tranny hardware modification that could take care of it. I have a 58mm TB in the garage just need to open up an intake for it I have a vacuum modulator on my 4L60E though so I am all set. I went 13.2 at 101 with a 4300lbs car the other night. The TB is on my short list of things to get put on to try for that oh so close 12 second slip, there is a lot of weight I can easily remove too.

 

When I installed a 52mm the part throttle shifts were softer than with the 48mm. I have a TransGo using 3 washers. Told Bryan about it, and I assume he boosted the hydraulic pressure. Shifts are back to the way they were now.

 

The partial throttle shifts seem to be OK with my car and if they are somewhat soft that really isn’t an issue with me. As long as it’s shifting correctly at WOT and running 100 percent in the ¼, WOT is the important part. Additionally, partial throttle TB air-flow is also a byproduct of intake vacuum, which the cam (large or small) will play a major role.

My Z28 weighed 3410 (I’m 175) total 3585 when it ran the 12.68.

 

Yeah vacuum is another part of the tranny tables the TPS is just one part of it not the whole thing. At WOT it should be going max pressure reguardless of the TB so programming is actually less important there.

 

He will have a different answer per application and what has been done already. You should always check with your tuner before making a decision on if it needs a retune or not.

 

How does vacuum play a part?

 

Vacuum as in MAP sensor reading is how the pcm knows what kind of load is on the engine, less vacuum as in closer to atmospheric pressure, it knows there is more load and therefore needs more tranny line pressure.