Bruceb66

Finally considering a gear upgrade from my factory 2:73's. When the install shop gets to the reprogramming aspect, how will they likely determine the shift points? Is there a factory default for a 2003 C5 with an A4 that they simply would go with? Any feedback on what to consider (or ask for) during reprogramming is appreciated. Thanks.

tblu92

1st when making a gear change on a C5 you do NOT have to make a speedo correction
However with an auto trans you do have to make a shift point correction for both P/T and WOT
Going from a 2.73 to a 3.15 is an approximately MINUS 15% change that needs to be tuned in--Generally we do leave the P/T 1-2 shift table alone and adjust only the 2-3 and 3-4 P/T tables - 15% -----At WOT you need to adjust ALL of the WOT "upshift and downshift tables " -15% The WOT shift RPM' s should remain the same if you have a stock internals

Bruceb66

Thanks for the input! The work will be done at a very reputable shop in my area, so I'm confident they'll cover all bases. Just trying to educate myself a bit. Now I find myself looking at a TC upgrade....they'll already have it on the lift, right!! 2500 or 3200 is my next dilemma....Picking names for our kids back in the day was easier than this!

tblu92

ALSO remember this at P/T all the shifts are commanded strictly by 1. throttle position and 2. speed
However when you go to WOT the WOT shifts are commanded by the "shift at WOT RPM table" and NOT speed or throttle position
On a stock engine with bolt ons only there is NO benefit to raising the shift at WOT RPM table beyond STOCK as the stock camshaft makes less HP and TQ past 6000 RPM Ideally you would want the car to shift at peak HP so if you add a cam and the peak HP is at 6500 then you should shift at 6500
Shifting past the peak HP level gains you nothing on a stock cammed engine--

Bruceb66

Thanks for the follow-up! Slight change of plans the past few weeks....I ended up going with a 3.42 diff, just arrived last Thursday. If the inside looks as nice as the outside, it's a winner! With the car being bone stock otherwise, my intent is to simply do a mail order PCM flash for $149 through East Coast Supercharging. They seem to be highly reputable and touted by many on Corvette Forum. Hopefully they'll get me exactly what I need for the programming.

tblu92

One of the best mods you can do on any auto trans car is to install a higher stall TQ converter---
This will really wake up the bottom end and launch
The stock converter stalls at approx 1400 RPM
If you don't know how a stall works here is a brief summary
The stock stall at 1400 RPM's means that when you floor the throttle the converter will slip until 1400 and then go to a 1:1 ratio
So when at launch at 1400 RPM your engine is only making about maybe 100 HP----
NOW switch to a 3000 stall ----at launch the converter will slip and go to 1:1 at 3000 RPM ---Now at 3000 RPM's your engine is now making 300 HP at take off without even touching the engine !! rather than the stock 100 HP that is huge !!! Lower gears yes do help get into the higher RPM's much quicker BUT a stall converter multiplies the TQ so you get close to max TQ right from idle
On my 98 C5 I installed 3.42 gears from a 2002 Z06 and installed a 3000 Yank Stall converter-----This car ran 12.00 in the 1/4 mile with a mild tune ( hds and cam eng)

Bruceb66

Appreciate the additional feedback. I thought about adding a higher stall T/C, but based on my overall goal and bouncing the idea around with other CF members, I think factory T/C will be fine. A higher stall would be a 3 part negative for me: 1) I'm not one to do hole-shots, burn-outs or drag and for what I'll be spending on new tires, would prefer to keep the rubber ON them. 2) The added expense of the new T/C and install. 3) The likelihood of additional heat and potential need for a tranny cooler (even more $$). Also, my wife takes it occasionally and I want her comfortable with it. I'll be ok with this set-up. The 3.42's alone should be night and day over the 2.73's and make for some spirited driving now and then. Thanks again.

Rkreigh

while the cost and install of a torq convertor are not cheap, the benefits are there!! remember with a lockup convertor you don't get all the high heat from a high stall and honestly the only difference you will notice is very slightly reduced gas mileage and dramatically increased wear on the rear tires.

He's giving you great advice!! I went to a multi disk convertor on my turbo car and it was one of the "best mods"

even with a stock engine, the car will get with the program quicker and not have any real drawbacks.

modern "lose" convertors don't slip much at all at low torq and have much better driveability than a race convertor.