To T-5 or not to T-5....

[Esprit]

...that is the question I'm pondering.

Now that an engine has been secured, project TR7 is now off the ground and under its own steam. I'm dumping a TVR500 RV8 into her and although subtley tweaked, she'll not be mega horsepower over standard. Now here's the kicker: Until now I'd just assumed I'd find myself a T5 gearbox as is used on the Griff to go behind it as I'd assumed it was stronger and has a better shift. All this as well as bearing in mind that down the road I want to slot a 400+bhp custom-build RV8 engine in I thought this would futureproof me.

Anyway, after doing a little research I've found that the good old LT-77 Rover box has been used in racing applications up to 500bhp and shouldn't even blink an eyelid at 300. Fair enough the shift is far notchier and requires a fair bit of shoulder to be put into it, but it's a tough box and in such a light car as the TR7, it SHOULD be up to the task. Given the replacement price and availability of the Rover LT-77 here in NZ I could afford to chew through 4 or 5 LT-77s for each T-5, never mind trying to track down the right T-5 in NZ. I've even seen some figures that suggest the T-5 is WEAKER than the LT-77 in terms of torque capacity.

I'm now leaning towards staying with the LT-77 now.. it saves me a truckload and makes the conversion easier as I don't have to fabricate mounts etc and I'm all for keeping it "standard" unless there's a damn good reason to change the parts. I can use the standard TR8-SD1 bellhousing etc and all will be sweet.

When the time comes to fit my insanity engine down the line I can either try running that through an LT-77 box too and see how I go (bearing in mind that the TR7's transmission torque capacity is always limited by wheelspin) and if it's really necessary I can mount up a T-5 behind the insanity engine and drop it in with it along with the T-5 bellhousing off the original 500 engine... fair enough the shift won't be as nice with the LT-77 but I can live with that.... and it's a box that can withstand a fair bit of shifting abuse if you put your back into it.

Any advice from you chaps out there?

Just wondering if anyone had anything to add or any information to the contrary.... anything else I haven't thought of?

Cheers!

[satman]

To me, it looks like you have asked and answered your own questions.

Hope your project goes well.

>> Edited by satman on Wednesday 15th December 08:43

[Esprit]

Heheh reading through it it DOES sound like I've made my mind up... and I guess at the moment I have.... I just want to find out as much info on the issue so as to make an informed decision..... Like I don't want to build it around the LT-77 and then find that I'm popping boxes every fortnight and then retrofitting a T-5 to cure the problem is a major... it's just me doing my homework is all

[walking hormone]

www.pistonheads.com/gassing/topic.asp?p=2&f=23&t=140879&h=0

ey up esperit, don't know if you saw one of my replies on this post , but it was the question of why gears have to be straight cut to enable quick shifts. Don't suppose you could let me know could you? Could be very useful for a project of mine at the minute.

cheers

WH

[Esprit]

walking hormone said:

www.pistonheads.com/gassing/topic.asp?p=2&f=23&t=140879&h=0 ey up esperit, don't know if you saw one of my replies on this post , but it was the question of why gears have to be straight cut to enable quick shifts. Don't suppose you could let me know could you? Could be very useful for a project of mine at the minute. cheers WH

Well I believe it's this:

If you've got straight cut teeth, it's very noisy... but if you can imagine two straight-cut gogs meshing together and then you try to slide them apart sideways, even if they're under load, they'll slip apart pretty easily.

Now imagine a helical cut gearbox as in most cars... quieter. Now if you have helical cut teeth meshing and you try to slide them apart sideways... it's almost impossible to do when the gearbox is under load... hence shifting when there's any stresses on the gearbox is hard... with straight cut teeth it matters less and hence full-power changes are an option.

Aside from that, a straight cut profile can be made more robust than a helical profile and hence you do less damage when you DO screw it up.

[walking hormone]

Esperit

YHM

WH

[B19GRR]

Or how about an entirely different route?

www.conversioncomp.co.nz/results.html?category=TVR

Stick a Toyota Supra gearbox behind the Rover. They should be relatively easy for you to get hold of in NZ and will be more than up to the job I would've thought.

Cheers,
Rob

[shpub]

Esprit said:

I'm popping boxes every fortnight and then retrofitting a T-5 to cure the problem is a major... it's just me doing my homework is all

The 520SE has been dumping 380 bhp at the wheels (slicks) through its original LT77 box throughout this years sprinting season and the end result has been no real problems. They can be strengthened which is a big help and declaring them a consumable is another big help as then the know that they have to behave... www.t-v-r-services.co.uk if you want more detail and what we've been upto!

[Esprit]

B19GRR said:

Or how about an entirely different route? www.conversioncomp.co.nz/results.html?category=TVR Stick a Toyota Supra gearbox behind the Rover. They should be relatively easy for you to get hold of in NZ and will be more than up to the job I would've thought. Cheers, Rob

Hi Rob... yeah I've looked into that route, althogh the conversion kit is pretty expensive, and Toyota prices are heading up here as the number of Supras that end up feeding the crusher are increasing... I've looked into it and it is an option there if I need it... thing is, I've got a T-5 bellhousing and a LT-77 bellhousing all ready to go. I have a suspicion that the W-series gearboxes fit okay but are similar strength to the Rover unit (although nicer shift for sure)... the R154 box is stronger again, but I don't think it fits up inside the TR Trans tunnel without cutting metal... something I'll avoid if I can Food for thought though.

[Esprit]

shpub said:

The 520SE has been dumping 380 bhp at the wheels (slicks) through its original LT77 box throughout this years sprinting season and the end result has been no real problems. They can be strengthened which is a big help and declaring them a consumable is another big help as then the know that they have to behave... www.t-v-r-services.co.uk if you want more detail and what we've been upto!

Thanks shpub... I saw some of your contributions on other posts... certainly food for thought... that's the sort of thing I've heard about. And to be honest it's what I want to hear. It's strange, most of the reputation for the LT-77 being weak on the internet seems to be coming from the 4x4 fraternity where I imagine huge torque loads and low speeds prevail.... most sports car owners seem to report that the LT is up for a bit of abuse even if it is a little rough around the edges and isn't the world's most dainty shift. The LT advantage is I can use my existing drivetrain more or less as-is. I'm looking into freshening up my old LT box as well as getting another in decent nick to keep as a spare. Mine's done 140,000 miles and is still as quiet as a kitten although the synchro rings on 2 and 3 are worn to buggery.
I was led to believe that there was no point in trying to make the Rover box even look at over 250bhp but it seems that even in racing applications they can just barely cope with TWICE that... so if I'm dealing with up to 450bhp I can possibly make it stretch.

I reckon I'll give the LT a shot... I've got nothing to lose by doing so as I can always retrofit another gearbox later on just as easy as I can now, so long as the new box doesn't involve cutting of metal (something I DON'T wanna do after I've spent 10,000 getting the chassis perfect!). And hey.. if it ain't broke don't fix it... I'm after keeping as much of the car "original" or "original in spirit" anyway.... if it was all about the best solution, I'd have slotted a Lexus QuadCam 4L in ages ago and be dialling up 400+bhp easy by now... but somehow that's not cricket is it?

Thanks for the input... still open to advice/suggestions though

[anonymous-user]

"still open to advice/suggestions though"

As much as I enjoyed my ownership of several 7's, both tin- and drop-tops, and one 8, I can't help having learned one thing from the experience - That it would have been better starting with a TVR Wedge and developing that

[Esprit]

hehe thanks dod .... duly noted :P Nah I love my "7" too much and will never let it go, it's wonderful and I love it, and despite its foibles, I'll forgive it everything :P