Board logo

Diff swap?
Nickp - 5/4/17 at 10:32 AM

After only a quick drive in my 2.8 BMW engined Haynes it seems very obvious that it'll be much better with a taller final drive ratio. It's currently got a 3.62 LSD and first gear is pretty much redundant. I can set off easily and rapidly in 2nd no bother. On the motorway I'm pulling 4krpm @ 75mph and this big engine really doesn't need to be spinning that fast when cruising. With a 3.14 I could hit 60 in 2nd, 92 in 3rd, 125 in 4th leaving 5th for cruising. I think 1st will become more useable and the gearing would be better on track.

So the question is, can I get any 3.14 CWP and fit it into my LSD diff with bolt on flanges?

I know the 3.14s go for strong money as the BEC guys want them, but if anyone happens to be converting from BEC to a normal engined CEC then I'd be up for a swap at some point.


mcerd1 - 5/4/17 at 11:16 AM

I take it you've got a standard ford 7" LSD at the moment ?

the 7" 3.14 CW&P will fit - but you'll need to rebuild the diff to swap them over


Nickp - 5/4/17 at 11:20 AM

quote:
Originally posted by mcerd1
I take it you've got a standard ford 7" LSD at the moment ?

the 7" 3.14 CW&P will fit - but you'll need to rebuild the diff to swap them over


Yeah std 7" diff. So the 3.14 will go straight in providing I set up the diff?


rodgling - 5/4/17 at 12:09 PM

I have a 3.23 ratio diff in my car (currently the E36 M3 engine, used to be a 328), with the BMW 5 speed box. For me this is about right (and felt good with the 328 engine too), it pulls hard on track up to 140 (haven't found a long enough straight to discover the upper limit) and goes off the line like a stabbed rat. Obviously you have a bit less torque but I would think something close to 3.23 should be good.

Either way, I don't think you will find much use for first though.


Nickp - 5/4/17 at 01:20 PM

quote:
Originally posted by rodgling
I have a 3.23 ratio diff in my car (currently the E36 M3 engine, used to be a 328), with the BMW 5 speed box. For me this is about right (and felt good with the 328 engine too), it pulls hard on track up to 140 (haven't found a long enough straight to discover the upper limit) and goes off the line like a stabbed rat. Obviously you have a bit less torque but I would think something close to 3.23 should be good.

Either way, I don't think you will find much use for first though.


Cheers, that pretty much confirms my thinking.
I could go for a 3.38 but if I'm going to the trouble then may as well go for the 3.14. This will hopefully give me 4 driving / track gears and a cruising one.


rodgling - 5/4/17 at 02:14 PM

You may even find that 2nd is not needed on track - I find that I have enough torque that on the exit of hairpins where I might consider 2nd, I usually can't quite be flat in 3rd anyway. At Bedford for instance, there's one hairpin where I sometimes use 2nd if it's hot and dry and I'm 100% on it, which is probably slightly faster than using 3rd, but usually I will just use 3rd - 5th everywhere.


Nickp - 5/4/17 at 02:47 PM

quote:
Originally posted by rodgling
You may even find that 2nd is not needed on track - I find that I have enough torque that on the exit of hairpins where I might consider 2nd, I usually can't quite be flat in 3rd anyway. At Bedford for instance, there's one hairpin where I sometimes use 2nd if it's hot and dry and I'm 100% on it, which is probably slightly faster than using 3rd, but usually I will just use 3rd - 5th everywhere.


Yeah, I do Blyton a lot and reckon it'd be perfect with the 3.14 just using 3rd and 4th. As it is I reckon it'll be 3rd 4th and 5th.


kitcardirect - 5/4/17 at 06:17 PM

Diffs 338 and 314 for sale here if it helps

http://www.locostbuilders.co.uk/forum/34/viewthread.php?tid=208242


mark chandler - 5/4/17 at 06:36 PM

You keep the LSD part and housing, unbolt the crownwheel and pinion from the 3.14 donor and swap onto the LSD.

Takes an hour, provided you can get the castellated nuts moving, do not hit these.

You will also need a long socket for the pinion nut, I got a short one from halfords, cut the driving part off and welded a bit of 2" tube to space it out.


Nickp - 5/4/17 at 06:51 PM

quote:
Originally posted by kitcardirect
Diffs 338 and 314 for sale here if it helps

http://www.locostbuilders.co.uk/forum/34/viewthread.php?tid=208242


Cheers, I'll bear you in mind.