Safe Rev Limits and Valve Float?

[DmcL]

old head, new rockers so float above 7k could be an issue then..

DIE 3.73 nazis DIE!! 4.10 FTMFW!!

RE: gearbox, its an 89 325is box with slightly overdriven 5th, not quite 1:1 in 5th with the 4.10.

[nando]

for a 7500rpm redline you'd need a schrick 288 or 304. no point in going much past 6500 with a stock cam.

stock (new) springs start to float past 7200 in my experience. haven't had any trouble with the rockers. if you have an original head you probably don't want to turn it that high either, as it will float earlier and break rockers.

[Mike]

try a 3.73lsd

[SpecM]

you should be able to get 60mph in second.

my m42 is chipped with a dinan and limits out a 7k, and i snatch 3rd right at 60 or so.

m42 cars had a different tranny with slightly different ratios, so that too is a "moot" point

[Farbin Kaiber]

know about shift points and all that.. just thinkint the ability to rev that little higher would be a good thing. was on a 6850rpm chip but couldnt crack 60 in 2nd with the 4.10 have a 7000rpm chip in now tho havent tried 60/2nd yet so may be a mute point but still curious.

Moot point, moot point.

[DmcL]

well then i might be ok with the current 7k chip. with a 6850rpm chip i was topping 2nd just shy of 60 which makes my 0-60 times look bad. was thinking a little more revs up top would mean better times from a dig.. well on paper anyway. if i can crack 60 in 2nd my 0-60 time should drop a good bit as its the extra gearchange that causes the 7.5 time otherwise prob be more like 6-ish. dont want a taller geared diff because that will lessen the power put to the ground in each gear. i retained the 4.10 for better acceleration so i dont want to ditch it.

car does 7.5 to 60 BUT thats including having to change to 3rd to hit 60. i can manage 2.1 60ft times too and thats on old all weather tyres that came on the weaves when i go them.. so old the sidewalls have small cracks in them so id imagine the compound has gone hard. be interesting to see my 60ft times with some sticky rubber in the back.

[xwill112x]

you should be able to get 60mph in second.

my m42 is chipped with a dinan and limits out a 7k, and i snatch 3rd right at 60 or so.

[jlevie]

Unless you are in a situation where an up shift to third would be immediately followed by a down shift to second, times would be improved by shifting up. If you can't shift up, run a lower final drive ratio.

[DmcL]

know about shift points and all that.. just thinkint the ability to rev that little higher would be a good thing. was on a 6850rpm chip but couldnt crack 60 in 2nd with the 4.10 have a 7000rpm chip in now tho havent tried 60/2nd yet so may be a mute point but still curious.

[craz azn]

with a stock head, the optimal shift point(as determined by the torque curve) for an m20b25 will be around 6100rpm. The engine will rev past that, but for optimal performance you want to stay in meat of the torque curve. A search for "optimal shift points" will be illuminating.

+1

[craz azn]

I run my car regularly up to 7000, with a stock cam and stock rockers, but the powerband is clearly not up there anymore. It is only useful for AutoX. As far as powerband goes, after 6k it drops off, and 6500+ its just making noise. When I am on track with my car, I just shift at 6k. No sense to labor it.

I personally would not rev it above 7200 on stock valvetrain.

[jlevie]

With a stock head, the optimal shift point(as determined by the torque curve) for an M20B25 will be around 6100rpm. The engine will rev past that, but for optimal performance you want to stay in meat of the torque curve. A search for "optimal shift points" will be illuminating.

To answer the OP's question, the weak point on an M20B25 head is the rockers. Billet rockers are usually safe for a 7000rpm redline, but might be iffy above that.

[iX-treame]

I was just talking to my friend John about it the m20 can turn higher speeds you just need better rockers and you can turn close to 8k

[Dirtbleed]

After a dyno run, max hp was at 5500rpm and max torque at 5000rpm. No need to rev it to 7500rpm.

[Erick]

Stick to 6500 on M20s. Rockers are the engine's weakest link.