RACE Cam

[threlevenguy]

I have an M20 with an e block and i head conversion. Also i have headers and 2 1/2" exhaust. Sooo it's loud. This particular E30 may become a weekend car as i think im going to buy an 85 325e beater. What's a good cam to get maximum output on? I've been looking on IE at their 272 cam but have no knowledge on what numbers the cams mean.

[CarsSuck]

the 272 is regarded as a sporty "street" cam. the 288 is probably more up your alley with the dual pattern 284/2?? falling in between. The next cam up would be a 302, and is really for much more heavily modified engines, the power band would be too high for your engine.

The numbers refer to the duration that the valve is kept open in terms of degrees of crankshaft rotation. Its most indicative of powerband. Lift is also very important. This is why everyone here is going to tell you to avoid regrinds, and instead buy a fresh billet.

[Jordan]

Keep to about 11.5mm of lift, that is if your Frankenstein engine will support that much. You'll have to measure...

On a street driven car don't go past 274 on a cam. Motronic does not like 288, and will idle/run like crap in general.
302 is high even for racers, and would push the power band so far past whats usable on a m20 it would be useless.

[threlevenguy]

oo so i gota fork ovet the extra 130$ for the new one. how much power would i see outta a new 272 billet?

[SpecM]

-Probably none. Cams like compression, and your e/i hybrid has VERY low compression.

[digger]

-Probably none. Cams like compression, and your e/i hybrid has VERY low compression.

actually cams can create compression but they also lose it when you go too wild and this governs the powerband.........

[evoe46m3]

I have a super eta bottom end and an i head, intake manifold, everything else. Anyways I have a top end performance 274 cam and it idles like crap. Before I got a better ignition coil it would die accasionally at stop lights.

[digger]

probably something else wrong aswell thats exacerbating the problem of added overlap becasue i have seen other cars with hotter cams that idle quite reasonably

[PeaveyBassist]

probably something else wrong aswell thats exacerbating the problem of added overlap becasue i have seen other cars with hotter cams that idle quite reasonably

Lobe seperation.

Will

[whowhatwhere]

actually cams can create compression but they also lose it when you go too wild and this governs the powerband.........

How on earth would a camshaft create compression?

[digger]

How on earth would a camshaft create compression?

a better choice of word is "increase".

A cam increases or decreases the compression depending on when the intake valve closes relative to BDC this is the definition of dynamic compression. If the intake valve closes at BDC it will have the most compression at very low speeds because all of the stokre is used during compression and every degree after it loses compression at low speed because the air is pushed back out as the valve closes so you have effectively lost some stroke.

At high speeds is possible to use the velocity and hence inertia of the incoming air to increase the compression by clsoing the valve quite a while after BDC and this is the main reason why higher duration cams which typically close the intake valve around > 75 degrees after BDC work better at higher rpms and not so good at low rpms as they tend to push air out at low speed and at high speed use inertia filling.

There are some compression test results at bimmer.info done before and after a cam timing adjust via a adjustable cam pulley. The cam was advanced 4 degrees making it close earlier (i.e.closer to BDC) and compression went from around 175psi to around 195psi.

http://www.bimmer.info/forum/showpost.php?p=34730&postcount=1

this adjustment increased torque down low (more compression) and lost some topend because inertia filling reduced.

This is the reason why IMO the cam is ther most important part of the engine it is the primary governer of the torque curve......

[digger]

Lobe seperation.

Will

what about it?

[SA E30]

I never had a problem running a 288 Schrick... lumpy idle, but the car ran like a dream,

[nando]

what about it?

I think he means overlap.

a 272 isn't exactly a "race" cam. it's barely an upgrade over the stock cam. the reason people have problems is most likely because they put a cam into a motor that wasn't running right to begin with, and it magnified an issue that was pre-existing.

[CarsSuck]

nando, arent you running the dual pattern schrick? how is it?