A bit of history (part 19) – Thinking inside the box
- ainsworthashley
- Sep 28, 2017
- 2 min read
While Peter had my engine I figured it made sense to ask him to service my gearbox, it had been a bit awkward in 1st and 2nd, so it seemed worth checking over whilst everything was out of the car again. But, in their usual style, things soon escalated…
First up I decided to replace the stock differential, which is viscous limited slip unit, and renowned for being particularly ineffectual. I was presented with two real options: a plate (eg TRD) or a gear (eg Quaife) based replacement unit.
As usual, following lots of research I came to the conclusion that whilst a plate differential may be less prone to understeer, it was also far less progressive and as such could be tough to drive with on track when we’re trying to keep everything smooth. The Quaife differential, on the other hand, is supposed to be far more progressive, but probably less effective in straight line drag racing or drifting.
Based on these conclusions I chose a Quaife ATB (Auto Torque Biasing) differential:
I was warned by those in the know that this may promote some understeer on track, but I figured if it was a real issue I could swap it out at a later date…it also had the benefit of not requiring servicing, fit and forget- always a bonus!
So off the box and LSD went to Peter, and soon I received a call from him offering me some kit he’d had destined for Simon Hick’s drag car, which Simon was giving up on…namely an increased final drive ratio (effectively makes each gear in the gearbox a bit longer). The stock final drive ratio is 4.285, the new output shaft is 3.993, being approximately an 8% in gearing…and a suitably increased top speed if I ever feel brave enough to find out!
This is a highly desirable modification for any MR2 with significantly increased torque levels as it basically makes 1st gear useable again! Previously 1st gear was over so quickly that you were often on the limiter before you had a chance to try and pull for 2nd.
Not cheap, but I did get a good deal as Simon was looking to extract cash from his project as quickly as possible, so I caved in and went with it…
The conversion wasn’t quite as simple as we had assumed, the Quaife ATB requiring some parts from the earliest Rev1 MR2 gearbox (speedo drive ring, and diff bolts), which it took me a while to source…but shortly after the engine was complete I was in possession of a newly built, and suitably upgraded gearbox to try and contain the power my engine was going to deliver!
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