Injuneer

I go an e-mail from someone asking me about programming the shift points in the 4L60E, after a gear change - its a 1999 Firebird V6. I don't know anything about the A4 programming. Can someone advise?

Any assistance will be appreciated.

WS6T3RROR

Speedo will need recalibrated for sure, and shift point mph will also need to be adjusted. Most of the time if you use a generic tuner to adjust everything the mph values are just scaled by the change in gear ratio including converter lockup and unlock. This does not always result in a satisfactory shift table imo.

It can be driven as it sits but it is going to drive funky, and wot shifting may be a problem (didn't do any math here just speaking from experience). Results here may differ depending on what the original gear was and what the new gear is. In general I do not recommend it at all.

I hope thats what you were looking for.

Injuneer

Yep.... he went from 3.08 to 3.73, a 21% change. That would appear to be substantial enough to require that it be done right.

Thank you.

Injuneer

Appears you prediction was right on target. He already had someone tweek the speedo, but not the shift points.

WS6T3RROR

Have to scale all the mph settings in the shift tables, tcc tables, kickdown tables, etc by the change in the rear differential gearing.

Usually on tuning software that is worth using there is a wizard that will fix the speedo and scale all appropriate tables at the same time. Otherwise you can manually go in and scale all the tables but its a pain and any that are missed will cause drivability issues.

Part throttle shifts are usually commanded by mph and tps (never worked on a v6 of that year so speaking generically here). Now the factory tables are set up to shift and keep the engine where it is 'happy' and so it feels positive to the driver. With the change you have made by not scaling the tables what you get is an engine that has to rev 20% higher to meet the mph setting to command a shift, also to do this the throttle input and resulting tps position will be altered as well. Do not confuse shift feel with a proper shift point. Changing part throttle shift points by only a 3-5mph can drastically alter the feel of a shift.

Wot shifting is usually done by a mph flag (called kickdown on an lt1 not sure on yours) and an rpm flag both must be set to command a wot shift. What I usually do here in the interest of performance is to put the mph flag very low and shift based on rpm. What you see in rpm is not what you get either though it will take a few hundred rpm for the shift to happen so trial and error is the way it is there.

The tl;dr version of this is scale your stock tables by the amount you changed the rear gears for a good start (hint; the new shift mph's will be lower). Adjust the points to taste and to suit your driving style. You may have to mess with the converter lockup tables a bit to make you happy, too many variables to say what to do here although it may be 100% good just scaling it.

Injuneer

Thanks. He followed up with e-mail that indicated they did utilize the automatic scaling. Just didn't get the expected results. So they did some more adjusting.

I'll give him a link to this thread, so he can read you detailed post, in case he wants to tweek it some more.

I learned a lot too. Thanks, again!!