|
1975 was the last year the 240 was equipped with the M40, but it's likely the M45 simply took over when the M40 stocks had run out, so your's maybe one of possibly very few in the 1975 model year. The VIN won't give you any clues as the gearbox code part of it has "1" for both the M40 or the M45 (or "2" for M41 or M46). I don't know if Volvo needed to modify anything to mate the M45 to the B20, but I would expect so as it seems to me that the M45/M46 were introduced along with the (slanted) OHC versions of the redblocks.
To put things into perspective and give you an idea of rpms: I drive a 1992 245 with a 111 bhp B200F on a M47 and a 3.91:1 rear axle. On the factory 185R14 tyres, this would do an acceptable 2750 rpm at 100 km/h (62 mph) in top (5th) gear. But this isn't a fast car by any stretch of the imagination, 0-100 km/h time is 13 seconds (as specified by Volvo). Swapping to 3.54:1 would make this even worse.
A B230F on a 3.54:1 (or maybe 3.73:1) both had better acceleration (only 5 bhp more, but quite a bit more torque) and lower rpm at speed, so that engine could deal with the taller ratio.
The instruction manual lists three possible axle ratios for this model year and they were:
1) 3.54:1 (33 km/h per 1000 rpm in 4th gear, which is 1.00:1)
2) 3.73:1 (31 km/h per 1000 rpm in 4th gear)
3) 3.91:1 (30 km/h per 1000 rpm in 4th gear)
If you then calculate for 100 km/h rpm, you should have the following in 4th - and the reduction in 5th gear to:
1) 3030 rpm - 2485 rpm
2) 3225 rpm - 2645 rpm
3) 3333 rpm - 2733 rpm
So if you keep your current M45, which also has a 1.00:1 ratio in top (4th) gear, expect the rpms on the left if you swap the rear axle. >3000 rpm still sounds very "busy", but the overdrive adds quite some more reduction, as you can see.
If your B20A is only 90 bhp, like it was in my Amazon, I would consider keeping the current axle but switching - if possible - to a M46. You will need to find a shorter driveshaft too, of course.
The M47 route means cutting and welding two different bellhousings together. It can be done, but I forget if you can use your current driveshaft or not.
Edit: no you cannot. I found these pictures on a Dutch forum on mating a B20 to a M47.
The transmission mount must also be changed as the M47 is longer, but apparently the holes intended for automatic transmission mount come in handy.
|
