Advantages of mild (284) camshaft?

[Guest Anonymous]

In recent posts there are several recommendations for an upgrade to a mild cam (284). I have experience with a 272 cam that looked pretty but did not offer any noticeable difference from the stock cam. I also used a 300 shrick, but that left me with a lopey idle making stop and go traffic more of a nightmare than it is.

I fully understand that a regrind can mean a lot of things including increased lift, difference in open duration and overlap. Given that the stock cam (264) was used in the majority of all M10's, is the extra 20 degrees in the 284 cam that significant a change as to make a night and day difference in my 32/36 9.5:1 auto (yest auto) daily driver? Can you actually get a very smooth idle as I currently have? Does anyone have any real world dyno data that might make me take the plunge again?

Thanks.

[Mike_R]

I put an IE reground 284 cam in my engine rebuild with S/S standard size valves & Schrick HD single valve springs. Works nice and has a very smooth idle & power curve. I did need lash caps and also put clamp on style rocker arm retainers for safety. It was a compleatly new engine from the clutch forward so I cannot tell you how indidual components made a difference. No before & after data except a huge smile and no oil spots. I can tell you the most economical way to go is with a reground cam for less than $175.

[Guest Anonymous]

Thanks for the quick reply. This is not an argument, but do you think a newly rebuild engine with the stock cam and new gaskets (no drips) would have left you with the same smile?

D;)

[cam1602]

... is the extra 20 degrees in the 284 cam that significant a change as to make a night and day difference in my 32/36 9.5:1 auto ....

I can not comment on these specific cams because I do not have experience with them yet. New to BMWs but not new to cars. Generally speaking, more duration moves the power band further up the RPM range. This helps the motor make more HP. But keep in mind that HP is just a mathematical function of torque in relationship with RPM. So if you move the torque curve to peak at a higher RPM, then you will make more HP. It looks nice on a dyno chart but in real life, most of us never use the upper RPM range for an extended period of time, even in some forms of racing like auto-x. Also more duration will typically take away some lower RPM torque. Therefore, for a street driven car, it is easier and more fun to drive if the torque comes in low. Also, torque is a direct function of cylinder pressure, it is very difficult to create cylinder pressure if the valves are always open. That is why American muscle cars in the 60’s with high compression ratios had big cams, the dynamic compression ration really was not that high and did not require special race gas. A motor works as a complete system, each part should complement the others. Back to the original question, a mild increase in duration with an automatic trans and no other changes would likely not see much of a difference. If you pump the compression ratio up a little, you should be able to “feel” the difference but it will not knock your socks off. And most of the bolt on upgrades commonly available will help in the high RPM range only.

[Mike Self]

with 9.5 pistons and a Weber 32/36. Since that rebuild was on a 200k+ engine that was a bit tired, I'm not sure how much new performance is the cam, but I do know that the engine seems to be much more lively in the 3000+ rpm range. Above 3000 rpm, acceleration is nearly as good in overdrive 5th as it was with direct drive 4th on the old engine.

Idle seems to be happier at around 1k vs 750-850, but that might be the legacy of an old dizzy--about the only thing I didn't replace.

mike

[mbaze]

I raised this very question a couple of weeks ago with Allen at H&B motors here in Berkeley, who have been tuning 2002s since the very beginning. He strongly advised against going with the 284, saying that my motor will never run as smooth and be tuned as nice as with a stock cam. Without going into details, he said, adamantly "It's just one of those things you learn after doing this for 35 years and trying out all sorts of different combinations.''

That's just one person's opinion, albeit soomeone who's been under the hood of a lot '02s. You'll need to weigh that against other people's real-world experiences.

I personally tend to think it's probably not worth the cost, unless this is something you can do yourself relatively inexpensively.

Good luck,

Michael

[JackF]

I don't know about the 284 but I have a 292 in my 72 with the 32/36. This was a stock motor rebuild which I then had the head P&P'd and added the 292. It's fun at the higher rpms, but how much time do I spend there? The answer is not a hell of a lot. The stock motor was incredibly smooth, idled very nicely and was delightful. It now likes 1000+rpm for idle and is just a bit loopie. Frankly, I wish I had stuck with the stock cam.

[Napes]

A few months ago I got a nice new rebuild from Eric Kerman, in Long Island, and I went w/ 9.5:1 Mahles and a stock cam in my ' 75. Runs great and love the engine. Part of the decision to go w/ the stock 264 cam is that I have an automatic and they do better that way. I also run a 38/38, ' 73 tii dizzy, tii exhaust manifold, and absolutely none of the OE smog garbage. I agree w/ the above posts that for a daily-driver I think you'd do well to stick w/ the 264 grind.

Bob Napier

[JohnC]

I don't know about the 284 but I have a 292 in my 72 with the 32/36. This was a stock motor rebuild which I then had the head P&P'd and added the 292. It's fun at the higher rpms, but how much time do I spend there? The answer is not a hell of a lot. The stock motor was incredibly smooth, idled very nicely and was delightful. It now likes 1000+rpm for idle and is just a bit loopie. Frankly, I wish I had stuck with the stock cam.

Yeah, I tend to agree. Every now and then I air it out on a freeway onramp and the 292 feels really nice, but I'm annoyed that I can't get that really smooth idle. I'm idling at about 1100, it's not too bad. I may eventually go back to a stock cam.

I'm ok with the torque curve. The 292 doesn't radically compromise the low end torque. I drove a megasquirted car with a 284 regrind, it pulled pretty well throughout the rpm range.

[boxy02]

If you are into the occasional track days, you'll be glad you installed the 284 (or 292). But, as stated above, if you are on the street 99% of the time, don't install it.

[kbmb02]

Good info above - I'm about to yank out a reground cam (*great above 5K!) and go back to stock (using the famous cam removal tool, which is a great device).

Also have a few good stock cams for sale, if anyone's interested...