Engine / Transmission. Which way to go.

[deano59]

i mean you could go with ford after all it was shellbys second choice as he wanted the chevy in the first place but gm wouldn't play the game due to them been in competition with the corvette.............or you could build it how shellby really wanted it and stick a chev of some description in it :-)......... at the end of the day its only a look alike not a true replica stick what ever in it that makes you happy once the bonnet is shut the bloke sitting at the lights next to has no idea whats under that hood and prob does not care there still drooling over the looks ..
flame suit on now and 123...........

[Gaz64]

Originally Posted by Modena

A stock T-56 might have these issues, but with careful setup and shimming, they go straight from 2-3 in one push, I know because mine does. The stock ones I've had in other cars are pretty **** in comparison.

6th is certainly not "wank factor" in my cobra, I have a 3.7:1 diff, and at 110kmh I wouldn't want to be sitting in 5th for a long time. In 6th it's about 1850rpm which is just nice for long highway work. Agreed TKO600 is a "better" box, in any case.

Yes, a 6 speed does help for cars with low rear gears. 3.7s and up,

[Treeve]

Having two overdrive gears is a wank... especially when 5th in a 5 speed is not the same as 5th in a 6 speed. The 5th in a T5 is 0.68:1, where’s a T56 normally has a 0.8 5th and a 0.63 6th. So you’re giving up 0.05:1 in ratio in 6th and you’ve got a 5th gear for... wank factor. The difference at your quoted 1850rpm at 110km/hr with a T5 is that you’d be doing a bit less than 2,000 rpm with all the rest of your drivetrain the same. And you’d do the same revs for all other scenarios in 1-4 gears with 5th in the T56 being the standout as not having an equivalent.
Plus the T56 weighs more. A lot more.
Interested to know what you shim to improve the gearchange though - got more than a couple of LS conversions with T56’s attached that I’d love to improve. Link to an article on how to do it?
Cheers,
Treeve

[Modena]

Originally Posted by Treeve

Having two overdrive gears is a wank... especially when 5th in a 5 speed is not the same as 5th in a 6 speed. The 5th in a T5 is 0.68:1, where’s a T56 normally has a 0.8 5th and a 0.63 6th. So you’re giving up 0.05:1 in ratio in 6th and you’ve got a 5th gear for... wank factor. The difference at your quoted 1850rpm at 110km/hr with a T5 is that you’d be doing a bit less than 2,000 rpm with all the rest of your drivetrain the same. And you’d do the same revs for all other scenarios in 1-4 gears with 5th in the T56 being the standout as not having an equivalent.
Plus the T56 weighs more. A lot more.
Interested to know what you shim to improve the gearchange though - got more than a couple of LS conversions with T56’s attached that I’d love to improve. Link to an article on how to do it?
Cheers,
Treeve

pretty sure, from my calculations, that my 6th is 0.5:1. Aussie Mike built the box, he's the one to ask on technicalities.

[MKS427]

The Coyotes have been doing very well in road racing and autocross. If you are going naturally aspirated a, used Mustang, budget version of the Boss or Cobra Jet push 500 hp and rev high. Basically everything except CNC heads. If money is no object and you want big power, a new Cobra Jet or supercharged Coyote would be sweet.
If you plan on racing it, a dry sump is necessary.

[Treeve]

Thanks for the heads up Modena, I’ve asked Aussie Mike by PM.
Treeve

[gjkrv8]

Originally Posted by Modena

pretty sure, from my calculations, that my 6th is 0.5:1. Aussie Mike built the box, he's the one to ask on technicalities.

FWIW I have the T56 but with the 3:45 diff ratio. 1st-4th are good (around town and at the track). 5th is good for cruising at above 90. 6th is useless - even at 110kph (Engine at 1500rpm sounds like it labours)

Even tried changing into 5th at Phillip Island this week at 210Kph (was doing about 5900 rpm) - no difference, probably a horsepower v Cobra "brick" aero deficiency problem :-)

Wish Mike did my box conversion as I keep changing from 4th into 5th when going for 3rd. (Then I normally spin off as am in wrong gear)

cheers Gregg

[Donunder]

Originally Posted by Modena

pretty sure, from my calculations, that my 6th is 0.5:1. Aussie Mike built the box, he's the one to ask on technicalities.

Or....if you're up near Godzone, Mal Wood at Warwick is a TKO/T56 guru. Our own Mrs Flatchat (Chris) is your contact there.

They built mine with the .82 fifth and it's spot-on for the road. It's also fitted with the centre-mounted gear shift which positions the Hurst gear lever perfectly in my car.

My son's (700hp,Craig) 452 Contemporary has a similar box but with the .68 fifth which is simply too tall for anything under 120 kmh.

[Tenrocca]

Originally Posted by gjkrv8

FWIW I have the T56 but with the 3:45 diff ratio. 1st-4th are good (around town and at the track). 5th is good for cruising at above 90. 6th is useless - even at 110kph (Engine at 1500rpm sounds like it labours)

Need more torque greggy - I use mine quite a bit on the freeway.

[Dimis]

Dear Coldcomfort,
It all about combination. We potentially are quickly going to go down worm hole that's about to cause you great confusion (at least it did me when I was at your stage). If you want a summary, take home message its this:

Originally Posted by Gaz64

Yes, a 6 speed does help for cars with low rear gears. 3.7s and up,

There is no right and wrong here in terms of gearbox. Gaz64 pretty much nailed it here. Both Tko600 and T56 can be made to work, It all about the combination, ie: Engine power band range (where's the torque), Rear end ratio.

One of the main benefits of the 6-spd is the ability to gear cars to manage fuel consumption ratings. That's often why you see more and more gears in newer cars. Potentially NOT and issue in a cobra.


For the record: I have TKO600 box with 0.82 5th gear, 3.42 rear ratio, and a very flat torque curve, that comes on fairly early. Its bang on for me. No regrets.

[Aussie Mike]

It's no secret I'm a fan of the T56. I've spent some time playing with them.

With any gearbox choice it's not just about the box it's also about the rear end ratio you use with it. The box will have a selection of ratios and these combined with your rear end ratio will give you your speed vs gear and RPM.

Years ago when I was first looking at them I did a lot of math about what the right ratios and looked at lots of different boxes. At the time the TKO 600 wasn't available. The Tremec 5 speed was the TR3550 and it had a pretty ordinary set of ratios. The TKO600 is much better.

I wrote spread sheets and did a bunch of math working things out. I just knocked up a new spread sheet to compare the ratios of the T56 (Holden variety) and the TKO600. I'll do another one to compare the TR3550 as well.

My original calculations lead me to believe the T56 with 3.91 rear gears was ideal.

In the graph below I'll compare a T56 with 3.91 Rear gears to a TKO600 with 3.46 rear gears (a popular ratio in donor cars) and also probably a reasonable choice for the TKO. Rear tyre in my calcs is a 315/35/17 which is about 25.7 Inches in diameter. Traditional 15" tyres will be taller and gear these numbers up a bit.



The graph shows the speed versus RPM of each of the ratios. 1 through 5 for the TKO and 1 through 6 on the T56. TKO traces are in Orange and T56 in Black.

1st Gear and 5th gear are pretty close between the two boxes with 3.91 rear gears in the T56 and 3.46 rear gears in the TKO. Winding out 1st gear will get you to 70KMH, 2nd Gear over 100KMH etc. Note however the spread from 1st to 4th of the T56. They are actually a closer together than the ratios than the TKO. T56 has a taller 1st, 2nd and 3rd gears.

6th gear in the T56 is just a cruising gear. It's only good for loping along on the open road and that's what it's designed for. Note 110HMH freeway speeds tick over at a bit over 1700RPM with 3.91 gears. Good economy etc

Now look at the RPM the TKO is doing in 5th gear at 110KMH with those 3.46 rear gears: approx 2500RPM. A bit High for open road cruising. a 3.08 rear end might be a better choice.

So with the T56 you have the advantage of a close ratio 5 speed with a 6th gear for cruising on the freeway allowing you to run some nice short rear gears.

I'll post up some more graphs if you are interested. I've done them comparing Top loader wide and close ratio boxes too.

If you have a particular box and rear end ratio combination in mind let me know and I can put those numbers in the spread sheet too.

Cheers

[Aussie Mike]

With the mid shift conversions I keep trying to improve them with everyone I do. I now have a CNC mill and I've spent a fair bit of time programming up a new shifter design.

This is the latest box I built for Paul Samson, a member of the Vic club.

I spend a lot of time working on the geometry of the shifter and each one is dialled in to the box. They are adjustable for preload on the springs that centre the shifter and I dial them in so the shift always pops back over the 3-4 gate.

When going from 2nd to 3rd you just push the shifter forward and it naturally pops into the 3-4 gate and continuing to push forwards has you in 3rd gear. On the way back down from 5th to 4th, pulling back on the shifter and it naturally pops back across into the 3-4 gate. continuing to pull back has you in 4th gear.

There's a bit of fettling to get it right.

Here's the base plate of the new shifter freshly machined on the mill.



Here it is bolted up to the gearbox.



And here's Paul's shift lever modified to suit. It's the traditional top loader style. Also modified the shift knob to tidy up the look of it.





The CNC means you can have a bit of fun with making parts too. It's a great time saver as once I've written the program and made a fixture it's easy to reproduce parts. Here's the new cover plate for the old shifter position. I can knock one up in a fraction of the time it took on my old manual mill. Plus I use to just stamp a date and some initials into them...



Cheers

[Aussie Mike]

The CNC also make machining up some of the more fiddly parts easier. This is the block off plug for the old reverse lockout position. A time consuming job on the manual mill.

It uses the the original style O ring seal



Installed in place.



Machine soft jaws for the mill vice make securely holding an odd shaped piece easy.



Sorry to distract from the original post. I get a bit excited about machining stuff. Back on topic now...

[gjkrv8]

Mike that is a thing of beauty. Wish you had done my T56 conversion. Mine is a bit tricky on the 3/5th selection - e.g. you get 5th sometimes going from 4th. Quick question - do you have to take the box apart to do your conversion? Also do you move the reverse lockout forward too? cheers Gregg

[Treeve]

Very nice.

[Aussie Mike]

So if anyone is interested in the math it's pretty straightforward.

The Gear ratios are readily available on the web for most gearboxes. Lets take the Tremec TR3550 as an example

1st 3.27:1
2nd 1.98:1
3rd 1.34:1
4th 1:1
5th 0.68:1

We need to work out the output shaft speed in relation to Engine RPM.

The 1st gear ratio is 3.27:1 That means for one rotation of the gearbox output shaft the crankshaft must rotate 3.27 times. So at 1000 RPM at the engine the output is spinning at 1000 / 3.27 = 305.8 RPM.

Next we need to work out the axle speed. if the diff ratio is 3.46:1 that means the axle is running 3.46 times slower than the input. At 1000 RPM at the engine the axle is doing 305.8 / 3.46 = 88.38 RPM

Now we need to work out how far we travel for one rotation of the axle. The tyre specs are also readily available on the web. My 315/35/17 rear tyres are 652mm in diameter. To work out the circumference we multiply the diameter by Pi and get 2050mm or 2.050 Meters.

Last thing to do is work out what speed we are doing for any given engine RPM. If our engine is spinning at 1000 Revolutions Per Minute our axle rotates 88.38 times each minute. Each rotation covers 2.050 Meters distance so we would cover at 88.38 x 2.050 = 181.18 Meters in one minute. In an Hour we would cover 60 x 181.18 = 10.871 KM/ per hour.

The graph below is a comparison between the T56 and the TR3550. The T56 is coupled to the 3.91 rear gears and the TR3550 is using the 3.46 rear end.

The taller 0.68:1 5th gear in the TR3550 makes for a good cruising gear with this ratio.



Cheers

[Rob. Smith]

I've got an app on my phone called Tremec Tool Box. It has a driveline angle finder.
A vehicle speed Calculator. An RPM Calculator and a Tyre Size Calculator. It's pretty good.

[Bender]

I get the LS engine is light, easy to work on and good horsepower. I think 50% of the cobra owners would not care if it had a Chev or Ford engine. But if you want to sell your car you have just killed 50% of your market. Ford all the way for me. I have Tremec 6060 out of a Commodore for mine. It has an aftermarket shifter that mounts in the forward position closer to the box. oooops chev gearbox. lol

[fastd]

Not sure what y’all are talking about...t56 is an absolute dream...since when is have 6 gears a bad thing?

[RockBit]

another transmission out there is the LGT-700. Here is a link

Learn about Legend Gear & Transmission's LGT-700