Tremec Magnum in Big Block SPF Cobra

Doggone · #1 (**permalink**) 12-28-2017, 01:30 PM

Looking to install the Tremec Magnum 6-speed and a QuickTime SFI rated bell housing in a Superformance Cobra with a big block 460. Installed a 3550/TKO back in 2001 when they were apparently rated at 425 ft. lb.

Searched extensively online for anyone who did this particular install, but no luck. Not sure I want to be the first to do an installation in an SPF. Any help would be appreciated. Thanks.

RodKnock · #2 (**permalink**) 12-28-2017, 01:47 PM

Not the first to install a T56 into an SPF, but I’d bet you might be the first to install it behind a 460 in a SPF.

Panavia or Steve Wood did a T56 into an SPF many years ago.
T56 in a SPF -- We did it.

joyridin' · #3 (**permalink**) 12-28-2017, 02:22 PM

This is probably more info than you requested, but if you do not have EFI or a pretty high rear gear ratio, you might want to think twice on the T56. I love it, but I can cruise down the road at 1700 RPM with a reasonably hefty cam and EFI with 3.7 rear gears and the car still runs good.

I couldn't imagine doing that in a carb car with a hefty cam. Usually you find out with a T56 either 1st or 6th is pretty worthless.

Pman1961 · #4 (**permalink**) 12-28-2017, 07:19 PM

I did the T56 magnum swap in ACE23 Superformance recently. The work required would be the same big block or small block. Requires moving the cross member back and lower, a modified shifter to center shifter in tunnel hole and a short ass driveshaft! Will do mine soon. I love the T56 so much better than the TKO’s!! As far as 1st and 6th worthless talk to someone who has done it. We put 4:30 rear gears and 325 tires. First gear is equivalent to my first gear with 3:46 rear and he can cruise at 75 mph in sixth gear 2500 rpm.

Pman1961 · #5 (**permalink**) 12-28-2017, 07:32 PM

Panavia did it but moved the engine forward so not to cut the drive shaft or modify the crossmember. He also went under car exhaust because with the motor moved forward would not allow the headers and side pipes to work. My assumptions viewing the video.

Doggone · #6 (**permalink**) 12-29-2017, 01:23 AM

RodKnock... Yes, Panavia's thread was one of the first references I found but thanks for bringing it up.

Panavia... Thanks for creating that thread... great information. Maybe it's time to try it again, only using a big block this time. Let me know when it's finished

joyridin'... I don't have EFI but do have a 3.73:1 rear gear ratio. Funny you should mention 1st and 6th since that's the problem I have now... only with 1st and 5th. 1st (3.27) is too low, great for casual driving but worthless otherwise. 5th (0.68) is too high for 70 mph on the interstate. Since I need to replace the trans anyway, I figure it would make more sense to choose a more appropriate 1st and 5th gear to accommodate the 3.73's in the rear.

Pman1961... Thanks for the info.... especially in your second post since I wasn't aware of those particular changes. Obviously I can't do the same thing with my big block, so cutting and moving the trans mount would be my only option. Not what I wanted to hear, but definitely better to find out now instead of during the installation.

In my younger days, I would have likely tackled it head on, but between my age and other projects, I'll be passing on this one... so it will be a new TKO instead. However, and this is one reason I began looking into the Magnum, I plan to have the TKO upgraded... i.e. carbon blocking rings... for smoother shifts up to 8,000 rpm since the new motor will handle 7,000+ rpm shift points.

Thank you all for chiming in. Really appreciated it.

joyridin' · #7 (**permalink**) 12-29-2017, 06:14 AM

I have 3.73 in mine also. I have a M12 T56, so 1st through 3rd is pretty close whereas 4th is a fairly large drop. My 6th is .54, so for me, it works pretty decent. I can drive around in 4th or 5th at a nice clip, then drop it in 6th for the highway.

Good luck!

olddog · #8 (**permalink**) 12-29-2017, 07:57 AM

Quote:

Originally Posted by Doggone

1st (3.27) is too low, great for casual driving but worthless otherwise. 5th (0.68) is too high for 70 mph on the interstate.

I'm confused by that statement.

Are you saying that you have to run in 4th at 70 MPH because if you shift into 5th the engine rpm drops too low and the engine is unhappy?

With a 3.7 rear ratio, I would find that hard to understand unless you had wheels off of a mud runner (tall).

Doggone · #9 (**permalink**) 12-29-2017, 10:29 AM

joyridin'... I figured that would have been my best bet but I'm sure a new modified TKO will fit the bill just fine.

olddog... Just have the standard 15" tires that were meant for the car but otherwise, yes... that's what I was saying. Don't forget, there are a lot of factors involved, including the power band of the motor. My motor was built more for top end. I figured it made sense at the time considering the car is light. I don't regret that choice but it just so happens the rpm's I'm in when in 4th or 5th at 70 mph don't work so well. Yeah, I could increase my speed but the state troopers won't be so forgiving.

Once you take into consideration the rear end ratio, every transmission ratio and the power band of the motor itself, it's not surprising something like this would happen. Most people could probably tweak at least one area of the car and improve how well the car performs within a specific area. But use caution when changing the rear end ratio because it affects everything. I'm sure I could find a ratio that would fix my problem, but it would probably create problems in other rpm's/gears.