Replacement 5 speed Mazda gearbox now available for an MGBGTV8

.What is the Vitesse Mazda based replacement 5 speed gearbox kit like, how do the ratios compare with those of the original 4 speed box with overdrive on top gear, how does it perform, what does the installation involve and how much does it cost? Our article has the news. More

Vitesse website with details of the 5 speed Mazda gearbox for the MGBGTV8. More

Posted: 170116
Updated: 170202
Replacement 5 speed Mazda gearbox now available for an MGBGTV8
With the availability of replacement parts and original complete gearboxes for the MGBGTV8 increasingly difficult to find, many owners have looked to alternative gearboxes as replacements like LT77 and R380 boxes but they too are becoming less easy to find. So the news that Vitesse now offer a 5 Speed Mazda Gearbox Conversion Kit for the MGBGTV8 is very welcome.

In service experience
Vitesse say that since Autumn 2016 they have fitted production kits to two MGBGTV8s, two MGBV8 Roadsters, Costello MGBV8 and an MG RV8. Vitesse say the in-service feedback has been good. With the torque characteristics of an MGBGTV8 there will be torque load build up on long climbs of hills but the experience so far is the Vitesse Mazda box copes well with that and with the effects on the lay cluster.

Our comparison of the gear ratios is below.

Gears without fears
East Anglian V8 Burbler, Ashley Vane, says "you've no doubt seen all the advertising and articles in various MG magazines recently about the Mazda 5 speed gearbox conversion, well from someone who has made the "change" I can thoroughly recommend it as money well spent". Read his article on having a replacement Vitesse 5 speed Mazda gearbox fitted to his 4 litre MGBGTV8. 170202 More

Torque comparison chart

Download a copy

Update: 170127

Update on Vitesse's experience with high torque levels on other applications
In a V8BB posting on 26th January 2017 Christian Disney, Business Development Manager at Vitesse, provided some information from the other applications of their replacement Mazda MX-5 gearbox:

"BBR produce factory endorsed, warrantied turbo upgrades for the MX-5, producing 302 bhp @ 7350 rpm, and 254 lb.ft of torque available @ 4950 rpm. This conversion demands an uprated clutch, but the standard transmission is still used with no issue. We supply Caterham with their 5 speed gearboxes and they use it in their 620s (supercharged 2.0L Ford Duratec producing 310bhp, 219lb.ft) with no issue. They have done thousands of miles of road and track testing. It's a lighter car but with 215-section ZZR rear tyres it will have significantly more traction than an MGB with 185-section road-biased tyres, meaning the powertrain will be stressed more in that application despite the lower torque figure.

Morgan Motor Company take our gearbox for their 4/4, Plus4 and Three Wheeler models. The 2.0L V-twin in the Three Wheeler delivers torque in one big lump that stresses all components, but we have had no issue with the gearbox! Our own development car, a 4.0L V8, has covered a few thousand (mainly spirited) miles and we have not had a single problem with the gearbox. Safe to say, we are very confident that the Mazda gearbox is a great unit that is more than strong enough for the V8 MGB."

have tabulated the torque data provided by Christian and created a chart which shows the comparison more easily.
Torque comparison chart