Rev Limits

[mattG]

How high can a modified M20B25 rev to & what mods are need?

[march109]

How many £Â£Ã‚£'s you got?

[Colonel Sanders]

in excess of 9500rpm, but that will be full work on the head.

[mattG]

I'm looking at putting a new clutch in soon, I have a good spare engine but thinking of rebuilding strengthing it for my turbo setup.

At the moment the current 170k engine seems to take 7k rpm but I guess I'm pushing my luck

May be build a safe 7.5k - 8k rpm limit, I know I should just change up a gear but there seems no noticable drop off in power at 6.5k-7k.

[Colonel Sanders]

with a standard cam theres no point goin over 7000rpm.
if you had a massive turbo a different cam, bigger valves, stiffer springs ect then it would be worth it for power.

[snoops]

my dads high comp 325i was cammed/chipped, revved like a loon up to 7250rpm

[tubby17s]

My old 2.7ltr used to go to 8,500rpm..

just have to go through your engine and make everything as light and strong as possible. some billet rockers would be a good start and if you think they are expensive its probably not worth going down the high reving idea..

[Yaninnya]

Why you want to rev turbo engine so high? The power on turbo engines is from boost not revs.
Jan

[Colonel Sanders]

bigger the turbo the higher the revs to spool it, so it will have a higher power band so if it revs to say 9500rpm the turbo wont spool till say 5500rpm, so you need the extra for the power or you would only be boosting for 1000rpm if the limit stayed low.
this only counts on real high power m20s like 600hp+

[Yaninnya]

bigger the turbo the higher the revs to spool it, so it will have a higher power band so if it revs to say 9500rpm the turbo wont spool till say 5500rpm, so you need the extra for the power or you would only be boosting for 1000rpm if the limit stayed low.
this only counts on real high power m20s like 600hp+

Are you talking about road usable engine?
Jan

[tubby17s]

Lol have a look at the old F1 BMW turbo engines....

[Yaninnya]

Lol have a look at the old F1 BMW turbo engines....

Mega lol everyone here is driving old F1 BMW turbo engines every day.
Jan

[Colonel Sanders]

bigger the turbo the higher the revs to spool it, so it will have a higher power band so if it revs to say 9500rpm the turbo wont spool till say 5500rpm, so you need the extra for the power or you would only be boosting for 1000rpm if the limit stayed low.
this only counts on real high power m20s like 600hp+

Are you talking about road usable engine?
Jan

well in this case no.
but in other cases yes, depends how much power you want....

[Yaninnya]

Have you ever drove a 500+ BHP car? I do and that why I asked a question.
Jan

[mikekean]

what do you drive yaninnya? i dont know of many 500bhp cars in jersey unless you drive some sort of super car.

[Yaninnya]

what do you drive yaninnya? i dont know of many 500bhp cars in jersey unless you drive some sort of super car.

Not in Jersey. In Poland racing group H Escort Cossie and RWD(!) RS 500. Both on slicks and still demands a lot of attention. Cars which I used to service.
Jan

[mikekean]

ahright sounds mental. ive driven the 550bhp audi s4 over here and fook me is it fast i shat myself when i drove, and it was wet so i cant even imagine driving a 500bhp e30 mines a handfull with 170.

[Colonel Sanders]

Have you ever drove a 500+ BHP car? I do and that why I asked a question.
Jan

yes, and im also in the middle of building another one

[reggid]

My old 2.7ltr used to go to 8,500rpm..

just have to go through your engine and make everything as light and strong as possible. some billet rockers would be a good start and if you think they are expensive its probably not worth going down the high reving idea..

not much point if it doesn't make any power past 7k though.........what were the specs though (e.g. cam, rockers, valve springs, head etc)?

[mattG]

Are the rockers the weakest link on the m20, how much are billet rockers?

Would uprated valve springs & a cam only make a safe 7.5k-8k rpm?

[march109]

rockers do tend to go, billet rockers are circa £500 + shipping

I've also seen some alloy rockers apparently 4x stronger than stock and half as light, I'll try find out where and post a link for you though.

as for billet pure performance do them in europe, ireland engineering in the US and theres a company on ebay based in Australia that do them too.

e21Jason was also selling forged steel ones for £250 no so long ago on here.

Billet rockers + suitable cam + stiffer valve springs would see 9k rpm withought too much trouble possibly more.

[mattG]

Billet rockers + suitable cam + stiffer valve springs would see 9k rpm withought too much trouble possibly more.

Cheers March, is that 9k rpm on a stock bottom end?

RPM with just valve springs & cam?

[march109]

http://www.carrindustries.com/catalog/b ... ements.htm
http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... =p3907.m29

[march109]

I'm not talking form experience just what I have read here and from the manufacturers of such products.
I cannot see the point in building an M20 screamer when power is made much further down the RPM anyway, that is unless your going to turbo or SC.

But then the cam suitable for high RPM is not necessarily great for FI.

http://www.e30zone.net/modules.php?name ... highlight=

[mattG]

Those rockers look sexy.

The engine is turbo charged & easy screams to 7k just want to strengthen it up a bit.

[Colonel Sanders]

unless your looking for over 500hp i wouldnt bother with billet rockers, no need to rev over 7500rpm.

[Yaninnya]

ahright sounds mental. ive driven the 550bhp audi s4 over here and fook me is it fast i shat myself when i drove, and it was wet so i cant even imagine driving a 500bhp e30 mines a handfull with 170.

Over here I have driven loads of 400+ BHP car like Audi RS6, Jag XKR, many, many TVR's (you know where I'm working), 911 Turbo, M5, etc. But these Cossies where under 1200 kg. That is making the difference.

yes, and im also in the middle of building another one

And how you can comment it? how it is on the road when till 5000 rpm nothing and then - bang! - and no traction at all?
Jan

[Colonel Sanders]

[quote="Yaninnya

yes, and im also in the middle of building another one

And how you can comment it? how it is on the road when till 5000 rpm nothing and then - bang! - and no traction at all?
Jan[/quote]
lots of fun!!!

[Yaninnya]

lots of fun!!!

So it's looks like we have different definition of fun. For me it is fun when I can drive as fas as possible without fighting with a car. The car shoud be the tool not the enemy.
Jan

[Colonel Sanders]

i like evil power.... thats just me though.

[Yaninnya]

i like evil power.... thats just me though.

Till first big crash. And remember that on Guernsey you don't have any extreme weather and road conditions (snow, ice, mountains) exept narrow roads. I'm the old grumpy and I used to drive cars like that (ie bloody RS 500 with hibrid T4 - over 450 BHP and still 205 road tyres) and there is no fun without traction.
Jan

[Colonel Sanders]

ive had my fair share of big crashes and being in hospital for months on end, my car is only a toy really.
a very very expencive toy...

[mattG]

Any way guys,

what safe RPM would be achived by uprating the valve springs & cam only?

[march109]

Any way guys,

what safe RPM would be achived by uprating the valve springs & cam only?

There are cases (and members here have experienced it!) of stock rockers breaking before the stock rev limit on normally aspirated e30s with mild mods.

If your going FI too I wouldn't go over stock rpm limit.

[mattG]

Any way guys,

what safe RPM would be achived by uprating the valve springs & cam only?

There are cases (and members here have experienced it!) of stock rockers breaking before the stock rev limit on normally aspirated e30s with mild mods.

If your going FI too I wouldn't go over stock rpm limit.

I surpose there is no option other than billet rockers then,

what can the std. bottom end take, will go for some total seal rings & have been told to use 325td bearings