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Manual gearbox question!

2003 - 2009, roadster, coupe, facelift
Steve.Eagle
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Manual gearbox question!

Post by Steve.Eagle » Thu Dec 14, 2017 9:35 pm

Out of interest, has anyone on here fitted a 6 speed box to a 2.5?

I'm finding my gearbox very short and wondered if a conversation to a 6 speed box was a solve!

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Manual gearbox question!

Post by ZedM » Thu Dec 14, 2017 9:40 pm

:? Personally I find the 5-speed perfectly matches the torque characteristics of the 2.5 M54. 3k revs at 70 mph - spot on. Happy in 5th at 1500 revs and pulls well right through the remainder of the rev range. BMW put a 5-speed with the 2.5 for good reason, although I'm sure both the 3.0 M54 and the 2.0 models both had 6-speed boxes and would think that maybe the 3.0 box would fit but might not suit the smaller engines outputs?? Someone with more knowledge will be along soon. :)
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patriot66
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Manual gearbox question!

Post by patriot66 » Thu Dec 14, 2017 10:13 pm

My Zed is a 2.5i SMG. The gearbox is the same 6 speed manual fitted in the 3.0i. Perfect ratios for the 2.5i in my opinion although 6th is quite tall and I only really use it on dual carriageways/motorways. :thumbsup: I'm not sure if the diff.ratio is the same for the 2.5i and 3.0i....maybe someone could clarify this.
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Mr Tidy
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Manual gearbox question!

Post by Mr Tidy » Thu Dec 14, 2017 10:25 pm

I know what you mean OP.

My E46 is a 325ti so has the same engine and box as your Z4 (assuming it is a pre-facelift) so it also pulls 3,000 rpm at 70 mph.

This seems a bit high to me, but does have the advantage that if you want to pick up speed quickly on a motorway you don't really need to change down.

Having said that my nephew also had a 325ti, but his was a facelift model which got the 6-speed box and it was definitely more relaxed on motorways - more like 2,500 rpm at 70 mph IIRC.

I suppose in part it depends what you use it for - track days or B-roads blasts you're never going to need 6th! :lol:
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MACK
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Manual gearbox question!

Post by MACK » Fri Dec 15, 2017 7:22 am

Not sure if it applies to the pre facelift Zed but on the 330i E46 when Bmw went from fitting a 5 speed to a 6 speed as standard the ratio's were basically the same 1-5 with 6th giving a more relaxed motorway cruise and slightly better fuel economy on a run.
Might be worth finding the stats for the zed and putting them into one of the online gear/diff ratio calculators to see what you will actually get from changing.
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Steve84N
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Manual gearbox question!

Post by Steve84N » Fri Dec 15, 2017 7:56 am

6th in my coupe is 76mph on the motorway at 3,000rpm.

The ratios are slightly shorter on the coupe than the roadster though for better acceleration, I think it's the final drive that's different.
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Manual gearbox question!

Post by brillomaster » Fri Dec 15, 2017 8:42 am

I always find this site useful:

http://www.bokchoys.com/differential/GearRatios.htm

I think generally gears 1-5 are the same, but then 6th adds an overdrive for cruising. Bear in mind also the 3.0 has a longer diff than the 2.5, which will affect how all the gears feel. and a diff swap is a relatively easy thing to do.

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Manual gearbox question!

Post by Machine monkey » Fri Dec 15, 2017 9:40 am

I think the bell housings are identical. And the engine architecture is the same. So yes it will fit no problem. I would imagine that they are the same length also. Worst case scenario you may need a 3.0l prop shaft as well.
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Manual gearbox question!

Post by GuidoK » Fri Dec 15, 2017 2:10 pm

^5 box is shorter in lenght, so def. a 3.0 propshaft needed.

Also a new clutch might be needed, the early 5 speeds are 9 spline and all 6 speeds (and later 5 speeds) are 22.
I dont know if that also requires a new dmf.
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Mr Tidy
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Manual gearbox question!

Post by Mr Tidy » Sat Dec 16, 2017 12:53 am

Steve84N wrote: Fri Dec 15, 2017 7:56 am6th in my coupe is 76mph on the motorway at 3,000rpm.

The ratios are slightly shorter on the coupe than the roadster though for better acceleration, I think it's the final drive that's different.
That's interesting - is 76 mph based on GPS? My Coupe tends to be showing almost 80 mph at 3,000 rpm!
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Steve84N
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Manual gearbox question!

Post by Steve84N » Sat Dec 16, 2017 9:54 am

I'm running 245/40/18 which is a larger circumference.

Stock speedo over reads by around 2-3mph but with these tyres it's almost bang on against GPS.
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Steve.Eagle
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Manual gearbox question!

Post by Steve.Eagle » Sat Dec 16, 2017 12:47 pm

Thanks for all the advice guys, really helpful info there.

I might look out for a six speed box to rebuild and gather the other bits up ready for a conversation.

I've got a couple of other priorities at the mo on my house so as soon as they are done I'll crack on.

Thanks again.

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Manual gearbox question!

Post by Scooba_Steve » Sat Dec 16, 2017 5:59 pm

Steve84N wrote: Sat Dec 16, 2017 9:54 am I'm running 245/40/18 which is a larger circumference.

Stock speedo over reads by around 2-3mph but with these tyres it's almost bang on against GPS.
NCS has some options for setting wheel size if the mileage is out.
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Steve84N
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Manual gearbox question!

Post by Steve84N » Sat Dec 16, 2017 9:11 pm

Good to know, I won't be playing around with it though as the car will no longer be mine by next Wednesday.
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kis
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Manual gearbox question!

Post by kis » Tue Dec 19, 2017 1:45 pm

Steve84N wrote: Fri Dec 15, 2017 7:56 am 6th in my coupe is 76mph on the motorway at 3,000rpm.

The ratios are slightly shorter on the coupe than the roadster though for better acceleration, I think it's the final drive that's different.
6th in my SMG (3.0i) sits at 2500rpm at 70mph
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1 Series - E87
3 Series - E46 Coupe, E46 M3, E90 (x3)
4 Series - F36, F82 M4
5 Series - E34 (x2), E39
7 Series - E32
X5 - E53, E70
X6 - E71

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