I currently have a 98 camaro T-top 3800 V6 ,5speed live in Texas where people do 80-90mph normal. Also make 13-16 hour drives on a regular basis. Problem is @85/90mph in 5th gear it's going at 3000rpm ,not so kind on the gas. My idea was put in the 6speed from the corvette, my mechanic says it won't bolt up to the 3800 v6. So I need ideas for this vehicle, change bell housing and trans? Switch to the 4.3vortec and 6speed? Or would it be possible to just rebuild the transmission using the current housing adding a 6th gear? Vote for the best answer and opinions welcomed. P.s I would rather spend a few thousand in this car than buy a cheap rice burner
There are a few things you can do:
1st, change the rear end gears. Your car may have 3.08:1 rear end gears (RPO Code: GU4) in it. If so, you can easily find some 2.73:1 gears (or complete rear end) for cheap. This will effectively lower the engine speed while in transit down the highway by around 12%. This will have a side effect of giving you a little less effective power/torque while driving at lower speeds, but that's the trade off.
2nd, you can do something like add a Gear Vendors overdrive unit. This option installs at the back of a transmission and mechanically acts as another overdrive (on top of the one you have). You wouldn't use this until you get to highway speeds, then it will dramatically drop your engine speed. I don't know exactly by how much (though it would be by more than doing the rear end gear swap). You'd have to get the drive shaft shortened in this instance.
In either of these cases, you'd also need to recalibrate the speedometer.
If you have a huge emotional attachment with this vehicle, then you won't want to read my next suggestion. Sell it and buy a Camaro Z28 with the 6 speed in it. While this may seem counterintuitive (V6 v V8), I can tell you you can run at 75mph in 6th gear @ ~1600rpm. In my Camaro, I was pulling down around 25-26 MPG average on a 2800 mile road trip (mixed driving, but ~90% highway). I know of guys babying their LS1 4th Gen 6-speed Camaros to over 30mpg. To do so, the car needs to be well maintained while keeping light on the go pedal. Insurance will be a bit more as well.
You cannot just take the transmission out and fill it with 6-speed guts. You could replace it with a 6-speed (Tremec T-56), but you'd have to find an aftermarket bell housing to mate it up, as well as figure out how you would do the clutch. I don't know, but would assume the input shaft on the tranny is a different spline than what is on your transmission. Let's just say mating the two would be of a large cost. Again, driveshaft work would again need to be done.
You could also replace your engine/tranny with one out of a Z28. To do this, you'd need to change out the K-member (engine cradle which also supports the front suspension), powertrain control module (PCM), driveshaft, front brakes, and probably the rear-end to a 3:42:1 ratio (RPO Code: GU6). You'd want to change out the rear or you'd be running about 1000 rpm @ 70mph ... definitely not optimal. All the money you'd have tied up in your little go buggy would exceed what it would cost just to purchase (after selling yours, of course) a Z28 of the same year. It just does not make fiscal sense.