Type 9 Gearbox Ratios
Discussion
I had a similar problem - with a 3.92:1 diff ratio (shortest commonly available in a 7" diff) the type 9 ratios were way way too long in my Striker. The standard 'close ratio' type 9s (BGH etc) are all clustered around the 1:1 ratio 4th in a normal Type 9 and so suffer from the same problem.
I ended up using a Caterham 6 speed box (which has a 1:1 ratio 6th gear). Its designed to be a bolt up replacement for the Type 9 that Caterham used so dimensionally its close, uses the same bellhousing and has the same input and output spline patterns. Unfortunately Caterham use a weird version of the Type 9 that has a different length input shaft from both the common long and short shafts, but I used a short input shaft bellhousing and a small spacer and it all works. Not cheap, but cheaper than a close ratio Type 9 and a shorter ratio diff (which you didn't seem to be able to buy at the time anyway - couple of companies advertised them, but no availability).
I ended up using a Caterham 6 speed box (which has a 1:1 ratio 6th gear). Its designed to be a bolt up replacement for the Type 9 that Caterham used so dimensionally its close, uses the same bellhousing and has the same input and output spline patterns. Unfortunately Caterham use a weird version of the Type 9 that has a different length input shaft from both the common long and short shafts, but I used a short input shaft bellhousing and a small spacer and it all works. Not cheap, but cheaper than a close ratio Type 9 and a shorter ratio diff (which you didn't seem to be able to buy at the time anyway - couple of companies advertised them, but no availability).
Hi
Your best bet is to change the diff ratio. Although you may see lots of ratios listed for the Type 9, in practice they are hard to find, even the "standard" close ratio sets. I ran a Dare built G4 in sprint and hillclimbs for 10 years with a Type 9 gearbox. After breaking the so-called heavy duty gears on the start line at Debden, I had the box rebuilt by SP Developments, with Quaife semi-helical close ratio gears and the alloy case. Also had a 4.4 Quaife LSD. With that lot I could reach around 145 mph at Goodwood (shift light was on in 5th about a third of the way down the straight!), with a 2 litre Zetec and 225 bhp. Most other venues I never got beyond third gear. At 70 mph on the road (I drove it to events, and usually back) it was pulling 4000 rpm, which was tolerable. Most of the noise at that speed came from the Quaife diff, which is like having a cement mixer behind you a lot of the time.
Your best bet is to change the diff ratio. Although you may see lots of ratios listed for the Type 9, in practice they are hard to find, even the "standard" close ratio sets. I ran a Dare built G4 in sprint and hillclimbs for 10 years with a Type 9 gearbox. After breaking the so-called heavy duty gears on the start line at Debden, I had the box rebuilt by SP Developments, with Quaife semi-helical close ratio gears and the alloy case. Also had a 4.4 Quaife LSD. With that lot I could reach around 145 mph at Goodwood (shift light was on in 5th about a third of the way down the straight!), with a 2 litre Zetec and 225 bhp. Most other venues I never got beyond third gear. At 70 mph on the road (I drove it to events, and usually back) it was pulling 4000 rpm, which was tolerable. Most of the noise at that speed came from the Quaife diff, which is like having a cement mixer behind you a lot of the time.
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