TKO swap into G-body?

[DIYShifter]

Hey guys!

I have an '85 Cutlass into which I swapped an M21 Muncie and 355 SBC. The gearing on the Muncie is a little lame with its 2.20 1st gear ratio, and there is no OD, so I was considering a TKO 500/600.

Anyone bolted one of these up to a G-body? Anything I should look out for? I'm told the transmission tunnel will need to be modified...can anyone confirm this?

 

[85 Cutlass Brougham]

The trans tunnel will need to be modified from the original 4 speed setup because of the shifter location. The TKO is a modern internal rail design and the shifter is centered on the tailshaft, not offset to the driver's side like a Muncie, T-10, Saginaw, etc. You would probably need to remove the 4 speed hump and cover it with metal then cut a new hole for the new shifter location. I can't imagine it being so large around that it would need too much modification to the trans tunnel, but am unsure as I have no experience with this setup. You may also need some crossmember mods too, but nothing too difficult. If I were to order one, I would try to get a close ratio gearset and then just compensate by calculating the proper rear gear to use with the tire height and overdrive ratio in the trans. You don't want too short a 1st gear ratio because the drop to 2nd could drop you out of the torque band, like happens in some TH700 R4 applications.

One more thing: The Tremec transmissions were initially built with the 5.0 Mustang in mind and have been adapted to fit GM applications. I don't know if this is still true, but when they first came out they were only available with a Ford 10 spline input shaft. So, you had to use a Ford clutch disc with a GM pressure plate and flywheel.

 

[DIYShifter]

Well, the TKO series of transmissions can be obtained with a shifter in various locations for a few extra bucks, including a stock Muncie location so it can fit in Camaros, Corvettes, etc, and keep stock consoles...

Yeah, there are different ratios available, including one with a 3.27 1st gear a 1.97 2nd, which is a pretty severe difference...I'm thinking on getting the 2.87 1st gear ratio with either the 3.73s in my 8.5 now or bumping down to 3.42s; I'll have to run some numbers.

I DO know the crossmember will have to be modified; I'm told crossmembers.com has ones for this application, but I'll see what has to be done.

I have a GM 10-spline input shaft already; new TKOs have either teh Ford 10 spline or GM 26 spline; in either case I'm going to have to get a new clutch disc. Oh well.

...at least I already have a screwed up transmission tunnel: the Saginaw I had originally and the Muncie I have now both have different shifter mounting locations, so about 1/3rd on my tunnel is cut apart already! 😀

 

[KrisW]

Don't change your rear end gears until you run your transmission first. I have found that with overdrive I can enjoy much deeper gears and still maintain mileage I can live with.

The gears you mention are similar to the 2004R automatic gears. When I run those (2.76 first, I believe) I like to run a 3.90-ish rear gear. I run 3.73s when I have a deep first gear, like the 700R4 (3.08?) has. My T5 is more 2.7-ish so 3.90s are on the way behind it.

Don't drop to 3.42s with overdrive. It's too much of a sacrifice in performance for me!

All of the above is usually run with either a 235/60-15 or 245/50-16 tire.

 

[85 Cutlass Brougham]

Meh, I have 3.23 gears and would not want anything more. It fits my engine perfectly with it's low revs and low to mid range torque. That being said, pick your gears to work with the engine you have and the intended driving. The 406 Camaro I put together for a friend a few years back had a 3.73/T-5 and 1st gear was practically unusable because it wound out too fast. The car was actually faster when we put in a 3.27 gear in it because it matched the car better. Plus, he didn't have to start in 2nd all the time. You have to consider the total effect of the compound gear ratio on the car and not just an initial feeling of acceleration. If the engine is high strung, it needs more gear to get off the line because it lacks the torque down low to get the car moving. With gearing, there can be too much of a good thing. If you make 400ft lbs at 1800 RPM, you really don't want more gear as it will just translate into tire smoke. If you only make 190 ft lbs like a stock 3.8 2bbl V6 or a high strung SBC (which can be even lower), you need more gear to get it moving because you need the extra multiplication. It also gets you to the power band faster and a high HP engine typically can handle the extra revs.

One of my current theoretical problems I am playing with on paper for fun is how to keep the fuel economy of an old Benz turbo diesel but improve it's dismal acceleration off the line. I came up with swapping from a stock 2.88 rear gear with 1:1 4th 4 speed auto and going with a 3.69 rear gear with a 0.8:1 5th in a 5 speed. It raises the final compound ratio to a 2.95 instead of a 2.88, but would let the car get off the line better to compensate for it's lackluster performance when it is out of boost (comes in at around 2500-3000). Compound first is now 14.74 vs 11.52 stock. In this case, shorter gears make more sense. I am also playing with a 2 stage turbo setup, propane injection and a water to air intercooler as other ways to improve initial acceleration--but I am getting off topic. Anyhow, just consider the engine and car it is in before choosing a gear.

 

[85_SS]

The following site details a TKO install into a G-body:

http://www.spnkzss.com/tremec.htm

 

[itsnotanova]

I'm bringing this thread back from the dead!! I've been thinking of getting a TKO and wonder what TKO people think has the better ratio. The 500 comes with a 3.27 first, which I don't like but it has a .68 fifth and it's $100 cheaper than the 600. Now the 600 has a 2.87 first and a choice of .64 or .82 fifth gear. Seems to me the .64 would rev to low and the .84 would be to high for my application. I have a ZZ4, 700R4 and 3.42 rear. I think the 700R4 has a .72 fourth and it kind of felt like my motor would rev out above 100mph. First was good for burnouts but my car isn't set up for the 1/4, so the 2.87 might actually let me get off the line faster. I'm torn on what to get??

 

[Malihoochie]

I have a TKO600 in my Malibu. I modified the factory trans crossmember. I also cut off a section of the trans that is there to make it usable for 3rd gen F bodies (I think anyways).
The mods to the trans that I did make it so that you do not need the huge forward facing plate on the crossmember. I'll post pics in a few.

 

[Malihoochie]

Itsnotanova - definitely go with the TKO600 over the 500. It is way stronger and I'd lean toward the .64 OD. I do not think you'll be too low in RPM's at all.

 

[pontiacgp]

I have 2 T5 WC's...one has a .68 5th and the other a .73....I'm running a 3:08 posi with 245-60-16 tires and at 75mph with the .68 I'm reving 2000 and with the .73 the revs are 2400..I have a VDO tach so those numbers are accurate