Rocker arms & Cams

[winstontj]

I'm new to this forum. Just bought my second e30 ever....

M10 motors have really bad rockers. They fail over 7,500rpm.

How are the m20 rocker arms?

Also what cams do you guys run for street motors? Is 292 too aggressive?

[JRKOUPE]

arms go now and then on tracked cars..........over @ 6800 rpm......... not too common but a known weaker part. Newer ones are more reinforced than orig items. 292!!***???........um yup..............way over the top.......try 272 to 288

[nando]

you aren't going to be reving an M20 to 7500rpm anyway. realistically, there's not much point in going past 6500, it just runs out of breath.

M20s are more of a torque motor anyway, if you are spending all your time in the higher RPMs you are missing out on most of the useful power band.

a dual pattern cam is great for the street. I run a 284/272 and it idles pretty smooth with plenty of low end torque. a 292 would be fine for a race car but I wouldn't want one on the street..

[winstontj]

292!!***???........um yup..............way over the top.......try 272 to 288

Haha.... Well I'm used to M10's! My current motor has a Schrick 292 with 9.5:1cr.

Why so low? I'm going to have to do some digging because I have NO IDEA what is in this motor but I plan to build a 3.0L motor and thought 9.8:1cr with schrick 304 cam would do it on the street..... Am I way off base?? If so why??

EDIT: Ok so forgot that I won't be revving up to 8 grand... So you guy do what... keep duration down but increase lift?

[nando]

sure, you could use a 304 cam on the street.. if you spent $10,000 to make the head work at higher rpms. but it still wouldn't have much in the bottom end. and I don't think it would last very long, either.

[backtrail69]

Yea, M20s and M10s are totally different beasts. A 292 is a really good street cam on a 2002 and a 288 is a pretty aggressive cam on a m20..

[winstontj]

i guess since i've been driving the 2002 for so long now (e30 eta prior to that) that I forget what torque is... Guess I'll believe you guys since I asked & you answered!

Thanks!

[SA E30]

IMO, there is nothing wrong with a 292... works very well, as is actually quite streetable.

I run a 288, and IMO, it's perfect for my motor... although I've seen guys have really good results over here with 292 and also a few of them run 300deg on their M20 .

I find my car pulls strong from around 3500rpm till about 6200rpm . but is pretty dead under 3000rpm... but then who does much driving at 300rpm ?

[winstontj]

Car I bought comes with 40% lockup 4.10LSD so there will be plenty of revvs. Considering a 3.45LSD (25%) and a CR box but that too will keep the revvs up because of the final drive in the CR box. I don't want to lose too much down low and I think I can help that with proper backpressure (exhaust) and cam. Thanks for the replies. I still don't even know where redline is on these cars, heck I don't even know where they idle or what my car will cruise at on the highway.

[MrK]

The redline on an m20b25 is around 6500rpm. It will be difficult to extract any more power after the redline without a well-built head and a set of ITBs. They idle around 750rpm.

IMO, a 282 would be a great cam for street as well as track.

[nando]

I'd go for a 288, or a 284/272. a straight 272 is too mild IMO to be worth the money, and a 292 is probably a bit much for stock displacement. be sure to check for valve clearance at TDC!

if you get a decent set of long tube headers, you can gain back most of the lost bottom end. and remember, backpressure is never good, it's exhaust velocity that you are after!

[MrK]

+1 on checking for valve clearance. I had to deepen the valve pockets on my pistons for the 304 cam to avoid contact! Of course I had shaved my block, but still...

[SA E30]

I'd go for a 288, or a 284/272. a straight 272 is too mild IMO to be worth the money, and a 292 is probably a bit much for stock displacement. be sure to check for valve clearance at TDC!

if you get a decent set of long tube headers, you can gain back most of the lost bottom end. and remember, backpressure is never good, it's exhaust velocity that you are after!

Oh yeah... I dont think displacement is a such an issue, more so the CR, I think the stock CR on a M20B25 is to low for a high lift camshaft.

[Lance Racing]

Me and my buddies running Pro-3 E30s with basically stock M20 engines have done a lot of dyno runs with our cars. The power/torque pretty much fall of at 6,000 RPM... maybe 6,200rpm. For my car it is 6k, so that is were I shift. A side benefit is those extra revs to redline are when you'll bust a rocker. I've got a lot of high revving hours on my race engine, but because I shift at 6k I've not broken a rocker in a long time.

Me:


My buddies:


If you are wondering were I am in the group shot... I'm ahead of those guys. LOL.

[Massive Lee]

Rocker arms are the weak link of the M20. Their rocking ratio is 1:1.50 while it was 1: 1.25 on the M10. This means they are more stressed in the leverage aspect..

An M10 can be revved to 7200-7500 on a regular basis (mine revs to 7500 with no problem, on stock rocker arms). This is begging for trouble on an M20. We all have friends who have busted rocker arms on M20s. This rarely happens on M10s.