GT 5 speed conversion

This is an area for discussion about modifications to Vivas.

Re: GT 5 speed conversion

Postby phil dawson » Tue Jun 14, 2011 10:11 pm

Not sure what is involved but think some holes have to be drilled.
Someone will know better and keep you right.

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Re: GT 5 speed conversion

Postby jpsmit » Mon Jun 20, 2011 3:18 am

Was emailing a friend and he says that a Jensen Healey 5 speed bolts on the GT engine. Can anyone confirm this?

thanks
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Re: GT 5 speed conversion

Postby pbottomley » Mon Jun 20, 2011 12:23 pm

should do yes, as the lotus engine bolts to the normal 4 speed OHC gerabox
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Re: GT 5 speed conversion

Postby innts » Wed Apr 11, 2012 2:05 pm

Hi , Only just joined the forum and spotted this thread.

I undertook a 5 speed conversion 29 years ago, in 1983 when we competed in a Viva GT.

I spotted by chance a fire damaged Jensen Healey in a salvage yard in Liverpool...a very rare find and after a lot of haggling, persueded the yard to sell me the engine and gearbox etc.

We removed the 16 valve head from the engine with the intention of fitting it to the 2.3 bottom end and sold the Lotus bottom end to a Lotus owner who had blown his Lotus upon the M62 and got more than enough back to cover the purchase cost of the bits.

The Jenson has the 5 speed Getrag box (as has been pointed out before) + an alloy bellhousing.

Provided you swop the clutch over, this will fit any of the Vauxhall slant 4 OHC engines but the gear lever is further back plus of course, you will need the change/modify the propshaft.The starter motor and clutch bearing/lever, is a straight swop too.

We also fitted a Jaguar/Salisbury 4HA rear axle that had disc brakes and a Salisbury Limited Slip Diff and had a propshaft made by Prop Services on the Desside Industrial Estate..for £70..cracking job, dynamically balanced etc.

AP racing also made us a ceramatallic paddle clutch - I think the Getrag had a 1" - 23 spline input shaft which was much lighter and lasted forever.

When we ran a close ratio 4 speed, we used the usual performance conversion of fitting the 8.5" CF Van type cluch assembly until this disintegrated at 110mph on the New Brighton Sprint Course.

However, whilst the Getrag box is much stronger than the Vauxhall 4 speed, it really did not provide any performance advantages especially as it had a very low first gear. The Getrag box was virtually identical to boxes fitted to BMW's, except they were an integral casting with the bellhousing and the box really needed a proper set of close ratio gear...but the cost was prohibitive as only the works BMW Touring Cars used them!

The 4 speed close ratio set is actually very good for comp use (2:5, 1:76, 1:30 and 1:1) ...I think the Viva would hit 70 in second with a 3.4:1 standard diff.

You can do a very simple modification to convert a standard OHC box to close ratio....fit the VX 4/90 (FD) first motion (input) shaft.

As some members have also mentioned, if it's just an improvement in cruising mpg, noise etc, then it may be better to fit an overdrive unit...if you can find one.

My Viva GT was basically upgraded to what was then DTV spec using Magnum/Firenza comp parts...all completely interchangable.

You could also use the ZF setup from the HP Firenza but these are extremely rare and very expensive....it's the same basic box that's used in MK1 and MkII Escorts used in competition but is actually....a tractor gearbox.

I scrapped the Viva in 1987 as by then, the body shell, although it had no corrosion issues, it was very tired...the spot welds on the floor pan were going in different directions plus I had no room to store.

We had used only the best available parts, Blydenstein engine components etc and at the time (25 years ago!) sold the drive train and suspension for nearly £3000.

One useful modification if you have a tired wiring loom is to fit one from a Chevette. Our engine loom was contaminated with il etc, very brittle and we found a Chevette loom to be a straight swop apart from the instrument panel and column stalks...lighting connectors, engine bay etc, all perfect fit.

Still have the originally factory workshop manual plus the Magard/DTV Sportpart manual.
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Re: GT 5 speed conversion

Postby hbpeter » Wed Apr 11, 2012 5:04 pm

Wow, your very welcome!! Thats a lot of very helpfull and interesting info. Dont suppose you have any pictures of your GT do you? :respekt:

Peter :welcome:
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Re: GT 5 speed conversion

Postby Painter an » Wed Apr 11, 2012 8:14 pm

Great write up, looking at Jensen gearbox for my gt or any other options, nice one :D
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Re: GT 5 speed conversion

Postby jpsmit » Thu Apr 12, 2012 3:39 am

HBPeter wrote:Wow, your very welcome!! Thats a lot of very helpfull and interesting info. Dont suppose you have any pictures of your GT do you? :respekt:

Peter :welcome:


+1 thanks very much for that
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Re: GT 5 speed conversion

Postby GTpete » Sun Dec 05, 2021 10:22 pm

Old thread I know, gearbox info still relevant but the info regarding using a Chevette wiring loom in a HB is interesting...

One useful modification if you have a tired wiring loom is to fit one from a Chevette. Our engine loom was contaminated with il etc, very brittle and we found a Chevette loom to be a straight swop apart from the instrument panel and column stalks...lighting connectors, engine bay etc, all perfect fit.


https://www.ebay.co.uk/itm/185106604783 ... SwUr9haE7m
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