running an m30 3.5 on a 4.27 open diff?

[Rav335uk]

Any body got some info on what this will be like as i haven't got a 3.46 diff as yet.I have to pick that up from theo at gaydon.If my car is ready, should i bring it tho the show !or just come in the van
Advice would be welcome

[secondtimelucky]

Well you dont wanna turn up in a van do you?? lol

[march109]

tell me what the gearbox ratios are for you and I'll do some maths.

[Rav335uk]

Gear box i'm using is the m30 3.5 from then donar car, sorry don't know the ratios, would be helpful if you could help.Cheers

[ric325i]

i drove from teesside to manc and around manc for a month on my 4:1 small case diff..... it didnt go pop because i really pushed it (exhaust was too loud in the city )

1st gear is pointless, i mean pointless 2nd is 1st - its basically like having 4 short gears. the motorway is death!

dont go nuts in it though because they have been know to go pop on hard starts.


should not stop ya though if you dont go nuts

[Rav335uk]

i drove from teesside to manc and around manc for a month on my 4:1 small case diff..... it didnt go pop because i really pushed it (exhaust was too loud in the city )

Do you mean you pushed it or didn't push it, and were you running it on an m30 3.5 gearbox????

[ric325i]

oop im trying to get ready to finnish work should have said DIDNT really push it.

the engine pulled pretty well actually. m30 box.

[Rav335uk]

What rpm was it doing on the motorway, asking as gaydon is about 40 mins drive from solihull

[jonb]

The diff will be far to low.

I had a 4.1 diff in a 3.5 conversion once. It had a top speed of 125mph on the limter. Midrange(3rd gear) excelleration was really good though. It was far to low. 4.4 will be terrible.

Try a 3.6

[Rav335uk]

I have a 3.6 but got to collect it from a zoner at the gaydon meet.Best bring the van then I suppose and hide it well

[march109]

well according to some google searches the m30 came with getrag 260/5

Assumptions
g/box ratios
1 3.83
2 2.20
3 1.40
4 1.00
5 0.81
Reverse 3.46
Final Drive 3.46

on 15 inch BBS @195 55 15

4000 RPM shift limit.

Gives:

Gearbox:-
Tyre:- Michelin all patterns 195/55 x 15
-------------------------------------------------------------------------------------------
Top Gear gives 19.567 MPH/1000 RPM and a top speed of 78.267 MPH at 4000 RPM

Engine speeds in top gear:-
30 MPH = 1533 RPM 40 MPH = 2044 RPM 50 MPH = 2555 RPM 60 MPH = 3066 RPM
70 MPH = 3578 RPM 80 MPH = 4089 RPM 90 MPH = 4600 RPM 100 MPH = 5111 RPM

Top Speed in 1 gear = 16.552 MPH
And changes into 2 gear at 2298 RPM dropping 1702 RPM
Top Speed in 2 gear = 28.816 MPH
And changes into 3 gear at 2545 RPM dropping 1455 RPM
Top Speed in 3 gear = 45.283 MPH
And changes into 4 gear at 2857 RPM dropping 1143 RPM
Top Speed in 4 gear = 63.396 MPH
And changes into 5 gear at 3240 RPM dropping 760 RPM
Top Speed in 5 gear = 78.267 MPH
******************************************************************************************

[march109]

and a top speed of 136.967 MPH at 7000 RPM

[Rav335uk]

Is that with the 4.21 diff or the 3.46 diff.Oh and the tyre sizes are 205 x 50 x 16. What would you do? I don't want to cause any damage to the mechanics if it is going to strain the engine and be on high revs.
Cheers

[march109]

Thats on the diff you have now, 4.27

Basically in first gear at 4000rpm your only doing a little over 16 mph, thats crap, as said before 1st is unusable. and 2nd becomes 1st and cruising on the motorway becomes a battle of sanity as the engine screams at you. Oh and don't think about the fuel.

I'll redo it for your new tyre sizes for both a 4.27 diff and 3.46

[march109]

4.27

-------------------------------------------------------------------------------------------
Top Gear gives 20.210 MPH/1000 RPM and a top speed of 80.840 MPH at 4000 RPM

Engine speeds in top gear:-
30 MPH = 1484 RPM 40 MPH = 1979 RPM 50 MPH = 2474 RPM 60 MPH = 2969 RPM
70 MPH = 3464 RPM 80 MPH = 3958 RPM 90 MPH = 4453 RPM 100 MPH = 4948 RPM

Top Speed in 1 gear = 17.097 MPH
And changes into 2 gear at 2298 RPM dropping 1702 RPM
Top Speed in 2 gear = 29.764 MPH
And changes into 3 gear at 2545 RPM dropping 1455 RPM
Top Speed in 3 gear = 46.772 MPH
And changes into 4 gear at 2857 RPM dropping 1143 RPM
Top Speed in 4 gear = 65.481 MPH
And changes into 5 gear at 3240 RPM dropping 760 RPM
Top Speed in 5 gear = 80.840 MPH
******************************************************************************************

[Rav335uk]

Well ,if its ready in time i'll bring it up.Better raid the kids money boxes for change then

[march109]

3.46

-------------------------------------------------------------------------------------------
Top Gear gives 24.941 MPH/1000 RPM and a top speed of 99.765 MPH at 4000 RPM

Engine speeds in top gear:-
30 MPH = 1203 RPM 40 MPH = 1604 RPM 50 MPH = 2005 RPM 60 MPH = 2406 RPM
70 MPH = 2807 RPM 80 MPH = 3208 RPM 90 MPH = 3608 RPM 100 MPH = 4009 RPM

Top Speed in 1 gear = 21.099 MPH
And changes into 2 gear at 2298 RPM dropping 1702 RPM
Top Speed in 2 gear = 36.732 MPH
And changes into 3 gear at 2545 RPM dropping 1455 RPM
Top Speed in 3 gear = 57.721 MPH
And changes into 4 gear at 2857 RPM dropping 1143 RPM
Top Speed in 4 gear = 80.810 MPH
And changes into 5 gear at 3240 RPM dropping 760 RPM
Top Speed in 5 gear = 99.765 MPH
******************************************************************************************

[Rav335uk]

What would the top speed be? not 96mph surely, or have i just read the figures wrong

[march109]

What would the top speed be? not 96mph surely, or have i just read the figures wrong

I assumed a shift limit of 4000 RPM, this means your not ragging it all the time.

Top speed (negating wind resistance) would be guestimated on max RPM's of your engine, which would depend on wether it was chipped or modded too. So whats the max RPM and I'll get you a better top speed.

The top speeds above are based on the engine only revving to 4000RPM though.

[Rav335uk]

looking at the tach on the car it's 6500rpm.

[march109]

3.46 DIFF = 24.941 * 6.5 = 162.12 MPH top speed
4.27 DIFF = 20.210 * 6.5 = 131.37 MPH top speed

assuming no wind resistance and gearbox ratios were correct of course too.

[Rav335uk]

You just made my day with those figures.

[gareth]

be careful if it's a small case, it will go pop sooner or later (probably sooner) bit it will get you about for a bit

[Rav335uk]

I'm open to your advice on this gareth, as i was toying with the idea of just replacing the internals of my diff to get the ratio right, but am a bit confused about it being a "small case" diff.What would you advise on this.
Cheers

[gareth]

guessing by the 4.27 ratio, yours is a small case diff which will not be man enough for the M30

here's what they both look like: http://www.e30zone.net/modules.php?name ... ic&t=22202

anyway, regardless of the type you have fitted, the ratios are also no good so you'll need a 3.46 or 3.64 large case diff from a 325i but it looks like you have that covered already.

[FormerMember]

I'd use 3.15 or 2.93 for diff ratio, no idea going +3,5 ratios because the torquey nature of M30 gets wasted then.

[Andy335Touring]

I'd use 3.15 or 2.93 for diff ratio, no idea going +3,5 ratios because the torquey nature of M30 gets wasted then.

Those ratios will be way to long for a normal E34/32 5 speed box, if you use the dog leg box they should be OK.

I started off with a 3.25 which was too long, then went for a 3.64 which was a tad to short and then found a 3.46 which strikes a fair balance.

Ideally i'd go back to a 3.64 to get a little bit better in gear acceleration(sp?) in 4th and 5th* but try and build a gear box with the **M20 Sports gear box** ratios so the lower gears are longer.

*Going with a longer diff like a 3.25 seems to make more of an impact on 4th and 5th(and to a lesser degree 3rd) gears, in the lower gears you have plenty enough power to pull well.

**M20 and E34/32 M30 gear boxes are supossed to be very similar internally, it's the casing/bell housing thats different**

[ric325i]

andy just use a 320 box.
its pretty much the same as a sport box. just remember the 320 box is shorter than the m30 so teh prop will need to be longer.

320 box fits to the m30
me and jaffro had a few boxes and props to play with to see what fit. bolt pattern isnt perfect but it fits

probs solved.



rav
just drive it and pray the thing doesnt go pop. like i said i actually drove mine from teesside to manc, then manc to newc and back to manc on a small case dif. 70 is about 4000rpm so keep it about 60mph and you should be fine.

i even tested the 4th and 5th gear on the motorway scared a few people with the noise

[jaffro]

320 box fits m50 not m30!! its the m10 box that will fit the m30

[Dave_M3]

Where's that "M30b35 :1. Small case diff :0" sig gone Garreth?

Seems very fitting for this thread

[gareth]

hehe, it does rather!

my small case diff.....

[nickso]

^^^ hehe nice implosion

i had a 3.46 with a 535 box on my 335. i reckon it was the best combination having driven ritchies 335 with its 3.64 i think he has.

on mine 1st, 2nd and 3rd were fabulous 4th was ok and 5th was just long enough for decent cruising.

[Rav335uk]

Will try, had to put a hold on things this week as BEEFY hasn't got any mounts in stock, but assured me I would get them for thursday/Friday next week, so far had the rocker cover and inlet manifold off to have it powder coated in black, had the throttle body of, dipped in tryc, and then went over to the NANO PHYSICS DEPT at Birmingham uni to get the thing aero washed.(Came out like brand new).
Now, maybe take of the oil filter housing and get that powder coated aswel.Time to burn until the mounts get here.

[Rav335uk]

Will a 3.64 open diff be ok as i can't get a lsd for the right price.

[e30bmlover]

i have a 3.64 fitted now(to a 320 box) and it hits 35 in 1st 60 in second and so on... happy with it.