more power

[Andy70]

I have a 3.0L M3 and want more power, before you say by an evo or an E46 I like the fact that its a bit lighter and HASN'T got electric this and automatic that, Ive come over from the TVR forum, so you probably understand that basic cars appeal to me more, any way, I was browsing on Ebay and come across a shorter ratio diff for the M3 and wondered if this could be a realistic upgrade for every day usage or is this more suited for track use? thanks for any info guys

[TheEnd]

You could try the 3.23 ratio M3 3.2 rear axle (larger diff size, so not a straight swap)
That was the ratio used on the M3 GT too, but they gave the 3.2 an overdrive 6th to give better cruising.

[Andy70]

ok cool, so what extra power would a shorter ratio give the car? there is a guy on ebay that builds shorter diffs for the 3.0 and the evo and its quite reasonable, there is also another bloke who acually sells genuine BMW shorter ratios on there own, believe it or not at 3 times the price as this bloke charges to build you one, so I thought it was worth a look but wanted some advice first, cheers!

[skeeterm5]

Andy70 said:

ok cool, so what extra power would a shorter ratio give the car? there is a guy on ebay that builds shorter diffs for the 3.0 and the evo and its quite reasonable, there is also another bloke who acually sells genuine BMW shorter ratios on there own, believe it or not at 3 times the price as this bloke charges to build you one, so I thought it was worth a look but wanted some advice first, cheers!

I believe it wouldnt change the power output, it changes the gearing and hence make it accelerate faster.

S

[Andy70]

Yeah I realise it isnt giving the engine more power but would make a difference on a rolling road read out?

[TheEnd]

It would give more torque at the wheels, but the wheels would be turning slower = power output the same.

Generally it gives better acceleration, but a lower top speed.
You'll still be able to do over 160mph, but the revs at an point will be higher.

[Andy70]

I see, so would it be much less economical over all do you know?

[Andy70]

Yeah I realise it isnt giving the engine more power but would make a difference on a rolling road read out?

[TheEnd]

It shouldn't make a difference on a rolling road.
Economy would drop a little too.

[Andy70]

Ok cool might be worth a closer look then, thanks guys!

[jas xjr]

Also look into reducing weight . Better power to weight ratio for free

[Andy70]

Thats why I got an early one, less crap on it I'll never use lol. I've already seen carbon bonnets and boots too

[TheEnd]

Carbon is a bit gucci for cars really, only used for very high level motorsport and show off kids.
Fibreglass is just behind it in weight, and a fraction of the cost.

[Andy70]

Yeah thats true, I just haven't seen fibreglass panels for these cars before

[Wills2]

Andy70 said:

Yeah I realise it isnt giving the engine more power but would make a difference on a rolling road read out?

Why would that matter, out of interest? No more power is no more power.

[Andy70]

Sharper acceleration which is what I'd like really

[Wills2]

I get that, it was the comment about whether it would fool a rolling road into showing it had more power that I don't understand.

[Andy70]

personally i have no idea about ratios and the technical side of things, but my little brian says surely if a car were accelerate quicker regardless of the method, then surely it would read more power on a rolling road, yes i'm aware top end would be sacraficed, but i never go over 100 any way, its the strong pull i like in every gear, I remember when i used to race radio control cars when i was a kid, if i put a smaller pinion gear on the electric motor, it got to the first corner before everything else, yes top end was lost, put it pulled away much quicker, if im wrong then a thickies explanation would be welcomed!!!

[Wills2]

I'm thick too mate! Hence my question,

I remember a guy on another forum changing his and he said it gave him better acceleration through the gears, I would imagine it makes the car feel quite lively and very revvy.

[isleofthorns]

I have a 3.91 in my 3.0l track car. Def feels more punchy and top end is still circa 145mph... On the road it makes the car feel more urgent as you're more regularly in the higher rev ranges more quickly. Good for a blast but a bit much for a daily driver . Perhps look at 3.73?! Fuel consumption is going to be lower. Power the same.