This make sense to anybody?
there is a reason i asked about the shift points in my first post. If you do almost anything to an automatic car, you have to tune for it. there is very few things you can modify in an automatic car without compensating for it in the tune. one way or another the tune controls everything.
This is why you need a correct tune, if you change your stock gears to a 3.73:1, or numerically higher.
First, the EEC knows the stock gear ratio and tire size and assumes they are correct. When you change the gears, you increase the acceleration rate of the engine. Yes that happens.
The stock '94-'97 4.6L Thunderbirds and Cougars (same with mustangs) have a rev limiter set at 5,500 rpm (tach may read 5,250 rpm).
Your engine accelerates approx 800 rpm/sec. The EEC-V commands the WOT 1-2 upshift at 4,250 rpm on your year. The 4R70W in stock form takes 1 second to fill the clutches before the engine speed starts coming down. So with 3.27:1 gears or even 3.08:1 gears, all is fine. The engine is accelerating at 800 rpm/sec. You have a 1 second clutch fill time and the EEC commands the WOT upshift at 4,250 rpm. So the shift happens at 5,000 rpm.
When you start adding power or higher numerical rear gears, the engine starts accelerating faster and faster. The engine is now accelerating at 1,200 rpm/sec. and you still have a 1 second clutch fill time while the EEC-V commands the shift to occur at 4,250 rpm. Guess what? You just hit the 5,500 rpm rev limiter.
How do you fix it? A tune or the J-Mod to the tranny. I don't want to get into extreme detail on how it works, and there is a plethora of good info already out there on it. The tune would move the rev limiter and add line pressure during the shifts. The line pressure will also help reduce the clutch fill time. The shift kit (aka J-Mod) will also reduce the clutch fill time. A tune would also change the shift points and tell the EEC to command the shift at a different rpm.
