6-Speed box for RV8

[Transmitter Man]

Any suggestions for a relatively compact and all ali cased 6sp gearbox that can handle the torque of a mildly tuned 4.2L RV8?

Thanks.

Phil
TVR 420 SEAC

[stevieturbo]

To handle the thorque of an RV8 should be easy.

Compact probably wont be. Also consider what ratios you need.


Some of the BMW range might be half decent, or the Toyota twin turbo Supra 6 speed isnt too big..although it has an integral bellhousing. It will handle anything a RV8 could ever throw at it with ease.

T56 is an option, but rather large.

[Pumaracing]

If it's a mildly tuned engine i.e. a wide powerband why would you want a 6 speed box anyway other than for fashion? More ratios makes an absolutely negligible difference to the overall acceleration of a car that doesn't need to be kept in a very narrow powerband.

[Transmitter Man]

Hi Guys,

Yes, thec Supra had crossed my mind as I'm aware of it's power handling abilities.

I was unaware of a built-in bell-housing as I was sure I'd read somewhere of a Aussie or NZ company offering adapters for this box. Maybe they offer adapter plates?

Puma,

I'm not looking to improve accelleration but would like more effortless crusing on motorways at slightly lower rpm;



Phil

[GreenV8S]

In that case, wouldn't a taller 5th be a simpler solution? (I have no idea how hard that is to do on the LT77, by the way.)

[Roop]

Isn't there a Hollinger than can go in, or even a Corvette box...? Maybe a Borg Warner T56 would be an easier fit...?

Edited by Roop on Monday 31st August 16:45

[stevieturbo]

Transmitter Man said:

Hi Guys,

Yes, thec Supra had crossed my mind as I'm aware of it's power handling abilities.

I was unaware of a built-in bell-housing as I was sure I'd read somewhere of a Aussie or NZ company offering adapters for this box. Maybe they offer adapter plates?

Puma,

I'm not looking to improve accelleration but would like more effortless crusing on motorways at slightly lower rpm;

[/IMG]

Most conversion kits will be based around the 5 speed boxes which have a removable bellhousing. There may be adaptors to suit the 6 speed for some popular engines....but cant see why anyone would ever want to go to teh trouble of using one on an RV8.

It woule never need the strength, thats for sure.

If you want taller gearing, fit a taller diff.

Phil

[Pumaracing]

From the possibly questionable figures I've gleaned from the web the standard ratios are pretty high geared anyway. About 31 mph per thousand rpm according to my calcs (diff 3.07, 5th 0.72, tyres 225/50/15). That's only 2250 rpm at 70 mph. I can't imagine that being very intrusive. My Focus does 22 mph per thousand rpm, 3200 rpm at 70 mph, and that isn't exactly screaming its nuts off. I do however remember being driven in a Peugeot 205 1.6 Gti when they came out many years ago and that was doing about 4k rpm at the same speed and was quite unpleasant to be honest.

However if you really want a tad more gearing the easiest, and essentially free way, if there's room under the wheel arches, might just be to go to 225/60/15 tyres. Even if you just did the back ones it would obviously suffice. That would give a not inconsiderable 7% taller gearing, 33.1 mph per thousand and 2100 rpm at 70. You'd need about 3/4 of an inch of spare clearance all round the tyres to get those in i.e that's the increase in radius. I can't imagine that being a problem on most cars, especially on the rear where the tyres don't have to turn which is when larger fronts tend to foul.

A half way house would be 225/55/15. It's surprising just how much you can alter gearing with small changes to tyre spec if there's room to fit them.

As most speedos read high, about 6% to 7% is actually the average error from the several I've checked over the years, a further advantage might be it'd put that right too.

[Poledriver]

Are there any alternative ratio diffs available? This would shift all of the gears "up" a bit. The effect would be a slight reduction in 0-60 times but improved fuel consumption and lower revs when cruising. I find that in my 450i (about 255 real BHP) 1st gear is virtually redundant anyway. With more power the change in gearing would make 1st gear more useful. (The above does NOT follow if reducing the power bandwidth significantly)

[Transmitter Man]

Thanks for the suggestions.

Puma, The only time you'll see a SEAC doing 70mph is on the back of an AA Relay van

Every time I'm out on the motorway it feels like it could do with another cog or at least an over-drive.

Phil

[rev-erend]

Phil

Take a look at this speed calculator ..

You input the gear ratios and axle ratios and wheel tyre size and it tells you the speeds.

I tend to agree with others - in that the SEAC is actually long geared and does not need a 6th cruise ratio .. after all V8's have loads of torque and can pull forever.

A easy way to slightly longer gearing is to fit 16 inch wheel with a 245/45 tyre.

As far as I know it - there are no alternative ratios for the LT77 box and the only real alternative is the T5 box but that change entails a lot :

Clutch
Box (& recon) must be Sierra cosworth and not TVR
Bellhousing
Propshaft length
gearbox mountings
Speedo drive (manual)

Note - the T5 is available with some different gearings from gearbox man but these are pricey .. upwards of 1K and can be near 2K.

Rather a lot to just get a longer gearing.

[Boosted LS1]

Bare in mind also that a 6 speed box weighs some, in the case of a T56 something like 9 stone! That said, it's got 2 overdrive gears iirc.

[Transmitter Man]

Umm, forgot about the different wheel and or tyre size.

Alan, did TVR ever offer alternative diff ratio's which would be another rout when my car is restored over the winter and the body comes off?

I am considering taller wheels and could use that time to go to an overall taller tyre which as some have suggested may give me what I want in reducing the rev's a little.

Yes, the 6-sp boxes I'm aware are heavy. Also aware of the not so easy T5 conversion but am I correct in that this unit only ever came as a 5-sp? Also aware of the different T5 models in that they are still offered in I believe several V8 powered cars around the world. My friend on PH and in Aus has just fitted one of the stronger T5's behind his De Tomaso's 5.7L Ford V8.

Thanks to all.

Phil

[rev-erend]

Sorry - forgot to post the calculator link .. doh

http://www.gearboxman.co.uk/info.html

It's basically a Jag axle (IRS) and the SEAC should be an LSD too.. which is nice.

The Jag axle came with many different ratios .. probably worth calling gearbox man to see if different ratios can be used with the LSD .. the guys there know Steve Heath - so are familiar with the wedges.

[Poledriver]

rev-erend said:

Sorry - forgot to post the calculator link .. doh

http://www.gearboxman.co.uk/info.html

It's basically a Jag axle (IRS) and the SEAC should be an LSD too.. which is nice.

The Jag axle came with many different ratios .. probably worth calling gearbox man to see if different ratios can be used with the LSD .. the guys there know Steve Heath - so are familiar with the wedges.

Gearbox man?

The back of my Wedge is jacked up at the moment, fitting new suspension and brakes, now would be the right time, going for 5 litres supercharged so would like a higher diff ratio. I'm fitting a digital dash so calibration of speedo is...simples!

Edited by Poledriver on Thursday 3rd September 21:31

[russell_ram]

Not overly familiar with the back end of TVR's, but if the diff is Dana/GKN 4HU based (Jaguar/Scimitar/Aston etc) then you can have pretty much any ratio between 2.88 and 4.55:1. Commonest (easiest gears to source) are 3.1, 3.3 and 3.5 (from Series 1-3 Jag XJ) but higher ratios 3.8, 4.1 and 4.5 are also available (from XJ40s). The 2.88's (all V12 Jags) are a bit of an odd ball though and are not readily interchangable unless you use the correct carrier - you'd need a complete diff to salvage parts from . On the plus side, all 2.88s are powerlock. I do loads of re-cons of Jag diffs for the Cobra boys and ratio changes are not too tricky.

HTH

Russ

Edited by russell_ram on Friday 4th September 09:10