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Gearbox decisions


RandyMcStab
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So I have finally decided that I am fed up with the ratios of my standard type 9 gearbox!

I have a C20XE, circa 210Bhp (limiter kicks in at 7000rpm), 3.6 rear diff with 185/69/14 rear wheels.

I use the car mostly for quick country road driving to work and I have my first trackday lined up this summer. I don't want a straight cut box as im not a fan of the noise they make. 

I would quite like to rebuild my current box with a kit.  I enjoy getting my hands dirty and as I have never rebuilt a gearbox, except for a couple of boat outboards and so I would like to give it a go! I may buy a second standard donor box to do this as my current one is in great working order. 

Budget wise, the less I spend the happier Mrs A will be! 

My questions are:

- What would be my best ratios (does anyone have the same set up as me)?

- Who would be good to buy from in terms of warranty and customer support? 

- Does anyone have a gearbox that they might sell either as a donor or one to spec? 

Many thanks!

Randy

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Not got the same setup as you with 15" wheels and a3.92 diff, but my BGH E6 is a revelation!

I used to hate the old type 9 first gear as it was useless. The car now just feels "right"  and I don't even think about the gearbox, just smile and use it. 

I have a long first and short fifth. Love it. 

 

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The best option would be to download a gear ratio calculator and have a play to find what you really want. A decent gear calculator is here https://locost7.info/gearcalc.php

General best practice is to think about how you want 1st gear to behave and your ultimate top speed and then work backwards with the remaining gears ensuring that the speed / rev drops between the gears gradually reduce as you increase the speed. Then look at what is available from different places like SPC, BGH, Quaife etc and select accordingly.

However, with the more commonly available diff ratios such as 3.6 and 3.9, an overdriven 5th is not a great option and really needs to be underdriven unless you can find a hens tooth 4.1 or 4.44 diff

 

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I'm in the same decision mode as well regarding my T9.  As a starting point i wanted to find the std ratios as a comparison, I did find various versions, but selected this as it crops up often for the car version. 

 Picture

Before I started looking into the ratios i thought a 1st of about 2.8 was not long enough, but when compared to the std it is quite a change, of course if you get it wrong and spec something too long or short it becomes an expensive hobby changing  ratios.

At the moment i'm edging towards an SPC box, Steve's boxes get good write ups and on balance "may" appear to be better built than a BGH box, although that could be because BGH sell more boxes so potentially more scope for people reporting problems.

I have also been looking at http://stores.ebay.co.uk/mkf-engineering but they are a long way from home, which for any potential problems ads extra logistical conundrums.

Cheers

Ian

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IMHO a 2.39 first is fantastic and practical. The 14" tyres you have are not great in terms of future tyre options where 13" and 15" have more choice and this will affect your gearing particularly in terms of cruising speed or top speed on track

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1 minute ago, terry everall said:

IMHO a 2.39 first is fantastic and practical. The 14" tyres you have are not great in terms of future tyre options where 13" and 15" have more choice and this will affect your gearing particularly in terms of cruising speed or top speed on track

What dif ratio is that with Terry?

 

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I'm sure you'd be able to have a really high geared first without problems.  When I fitted my zetec I mostly started off in second with a standard type 9.    But I'd say Unless then you also tweak second you'll find arch a minimum jump to 2 you'll end up short shifting to 3rd.    Mines a mkf close ratio set.  Basically 1-2-3 are modified 4th and 5th remains.    I find 5th to high and only a cruise gear.  I have a 3.6 diff at the moment but planning on fitting a 3.9 I have this winter.   195-50-15

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The description long first when used with a first gear ratio of 2.8 is not really fair. For sure its better than a std box but far from ideal with a 2L Vauxhall. 2.4 first or longer than that is better again. So description long first was used to allow many gearbox re -manufacturers to reuse existing designs or parts and make it appear like a good option. I ran a 2.04 first for road with a 3.9 and 4.1 diff and it was about perfect. And that's after using a 2.8.

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Another popular combination is a 2.39 first with a 3.92 LSD

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Thank you for all of your replies! I like the idea of of the SPC and building it myself but MKF had a good deal awhile ago...

I'll probably give them a call this week and see what they can do. I would like a longer first as advised by Arm above. 

if I went the SPC route by the time of got a second box to build on plus gaskets etc I could of bought the MKF unit. 

I'll ask if there is discount for a bulk order; perhaps find a few WSCC members who would like to buy a new gearbox. 

IMG_7252.PNG

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