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Tremec TKO II with 3.54 diff ratio
My Toploader WR with a 3.54 ratio rear end ( 305/50-15 tires) makes my 427 C/O turn too high rpms at cruising speeds (4000 rpm at 80mph)
I am thinking of installing a Tremec TCO II with .82 5th gear. With the gearing calculator I see that the 1st gear is shorter than in the TL, which I don't really need , but the gears I use most when trashing around the mountain roads is 2nd and 3rd. 2nd gear is already too short and 3rd too long for me in the toploader . In the TKO II 2nd and 3rd are even more wider spaced . So I am at a dilema at what to do. Anyone running 3.54 rear end and TKO II can give me some experience input? Or should I leave the toploader as is and change to a 3.31 or even a 3.07 ratio rear end ? Your comments wellcome Stefan |
Hey fellas !!!!!
really no one with a Tremec TKO II and a 3.54 ratio RE out there ????? I wouldn't want to dish out $2000 for a trans and then not like it. How is the TKO doing in your cobra ??? |
There is no way the TKO II, 15 inch wheels, and a 427 going to turn 4000 RPM.
If I remember correctly, 2600 at 60 MH, 2700 at 70m, and 2900 at 80. I could be wrong, I no longer have the car. Dan Semko does. Dan take it out and drive it and let us know what the numbers are. You have something other than a 3:54 rear end or not shifting it to 5th. or something!! TURK |
My mistake. Looking at the subject matter I thought you HAD a TKOII.
You have a Toploader. You knew that already. 3:31 with the toploader will put you down to 3300 RPM or so, again if my memory serves me right |
3300 rpm is still kinda high. I like the idea of going with a five speed. You know back in the 60's various methods of getting an overdrive gear some way, any way, was pretty popular, and they were HARD to come by!
Five speeds basically did not exist. 5th gear was the best thing to ever happen to a transmission. Ernie |
Maybe it was 3100 RPM
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Basically I have no doubt that the 5th speed/overdrive is wonderfull.
The only issue really is 1st gear. Kind of short at 3.27 ratio compared to 2.78 in the toploader. with a toploader if you accellerate in 1st to 6000rpm(40mph), shifting to 2nd will drop you to 4000rpm. With the TKO II if you shift at 6000rpm (46mph) to 2nd you drop to 3500rpm. Is this not too much? You can check this out with the Second Strike Gearing Calculator at www.secondstrike.com/Technical/GearCalc.asp Stefan |
Tremec, Top-loader ratios
In my 67 Corvette, I have a 3:36 rear.
At 70mph it is at 3000 RPM...I little buzzy, but liveable with rear exhausts...puts the mild 327" right about at it's torque peak. On my ERA 289 FIA car I have a Tremec TKO and a 3:54 rear end coupled to a 347 stroker small block. In 5th gear, ( I think it is the 0.85 5th ) I get 2100 or so at 70mph. I could not drive that car more than an hour without 5th gear...and I wear foam earplugs on any drive anyway. First with the Tremec is just too low for my tastes...it hits the rev limiter faster than I can shift...I am not a drag racer, even if I was, this 3:54 rear end may be too low combined with the 3.27 first gear. Wish the gears were closer, but still had the 5th overdrive. With side pipes, 4th gear at 70 is LOUD!!!!...5th, is like...relaxed. I have a mild 347 small block, so it will not pull in 5th, but a big block would I suppose have enough torque. When you want to run, drop down to 4th, cruise, 5th. Pete |
Pete,
if you are doing 70mph with only 2100rpm your TKO has the 0.68 ratio 5th gear. That is really a looooong overdrive. If I would use that ratio I could probably do over 200mph if wind resistance does not get into the way too much. Or cobra could get very light in front and try to take off!!!! Hmmm!! |
Eljaro-
I am running a TKO II with a 3.31 rear and it is great. first is short, but still very usable and 5th is a dream. At 75 the engine is turning about 2600 rpm. I wouldn't worry too much about the drop from 1st to 2nd or 2nd to 3rd, these motors have so much torque that it doesn't matter. Also, you need to consider the power curve for your cam when deciding whether to swap trannies or rear gears. With my current cam, the rpm range is 2500-6500 and I think a 3.54 rear would be perfect for it, even with the TKO II. I may wind up going to a smaller cam, in which case, the 3.31 and TKO II will be perfect, IMO. |
Kep your wide ratio, and change the rear to 3.07's. 1st gear will be just right, and your cruising rpm's will drop by 400 rpm's.
I run a wide ratio with a 3.07. perfect. |
Eljaro,
My spreadsheet tells me that you're actually running 4723 rpm at 80 mph in your current configuration. My spreadsheet also tells me the "effective" ratios of each gear, by multiplying the gearbox ratio by the differential ratio. Wasn't there a guideline for the preferred "effective" ratio in first gear? Wasn't it 10:1? It probably has much to do with the weight of the car, track/street conditions, etc. I'm just looking for a guideline as a start. If anyone would like the Excel sheet, shoot me an email at timshops@hotmail.com. TT |
Roxie,
very good your spreadsheet gear calculator. Maybe I should keep the WR TL and get myself a 3.07 ratio PL Salisbury diff ?. eljaro |
I would do what you suggest first. It may be a less expensive alternative.
I don't own a Cobra, but my '66 Mustang has a WR Toploader and a 3.50 rear diff. It's quick around the city, but very "busy" on the highway. For my normal street use, it's fine. I'd rather have quick than fast. My plan for the Cobra kit is the big block, TKO or TKO II, and something near 3.08 in the rear diff. That way, I can have the best of both worlds, while keeping the rpms down on the highway. Best of Luck. |
Who sells jag diffs in the States?
Or in Europe (if any clubcobra member this side of the pond reads this post)? Thanks eljaro |
I have the Tremec 3550 with a 3.27 rear. I like it. 1-2-3 around town and 4th-5th on the highway.
Great cruising on the highway. You can actually listen to the radio or have a conversation with your passenger. |
I can't decide between a 3.31 and a 3.07 rear. I will be using a WR TL and a stroked Shelby BB engine. I am leaning toward a 3.31. If I want to switch down the road, is it easy to change the r & p for a different ratio or do I have to swap out the entire differential?
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Jag Diffs and 5 Speeds
Terry's Jaguar Parts sells rebuilt diffs. They are out of Benton Il. You can also get new Dana 44 Gears ( that is what a Jag IRS rear is ) from various SPicer distributers. You can switch out the ring and pinions of the Dana with those from the (84-88)Vettes. You will have to change the pinion bearing, flange and make bolt spacers for the ring gear bolts since the new bolts are smaller on the OD than the originals. Tom's diff's in Paramont CA. makes the spacers.
I have a new .80 OD set for the Gforce 2.95 ratio 5 speed kits coming out in a few months. I don't like the low 3.27 1st in the TKO or the way they shift. Some of my T5 / Gforce links are here: Gforce T5 Stuff Take care, Paul |
Hi Paul,
it really a dilema to decide what to do. I do like the toploader and the shift ratio and so having a 3.07 ratio diff would be quite better. I have contacted Barratt in England and there are only used 3.07 diffs if any. The replacing of gears in the diff is another possibility . I do not mind doing that if I have the proper instruction Is replacing the gears with a Dana set straightforward or does it require machining? I have seen that G-Force sells a complete T5 transmission, which has a gear ratio similar to the WR TL. Is that a strong box, will it hold well with a really strong 427? Will it fit as a Toploader does in the drive tunnel and on the support or does it require mods there ? Thanks for you suggestions, more options now for the regearing dilema. Appreciate your aswer to these questioins TK Steven |
Jag Diff - Gforce gears
The Jag rear is a Dana 44 and no machining is required. I was at the track last week and saw people in stangs hitting the G-orce transmissions with at least 600HP. However just because it survives a blast or two, shouldn't mean it is a stable rating. That is the problem with ratings in general. The lower you go (numerically ) with the axle gear, the higher the torque is shifted towards the transmission.
Personally when we set up a gearbox, it is all new. The potential problem is people retrofitting gears in stretched out cases, or not knowing enough about blue printing the T5. This can lead to variables in terms of some transmissions surviving while others don't --Paul-- |
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