17 replies to this topic

[scotty_18]

I bought a 286 cam down at L2B from MiniSpeed I believe. Pretty sure it was second hand as it didn't come in a box, and it came just as a cam. Paid £60 for it and they had a couple. 

 

Are second hand cams OK to use? My spec is going to be 85bhp+. 

[se_juggles]

I can garentee its a second hand for that price. Sounds like a steal. I used a second hand one in my old engine. Same cam and had no problems but then I could have been lucky if your not ment too.

[KernowCooper]

Your going to have to have a good head with the correct CR and a well spec engine with a low final drive and gear ratios to get the best from it, if its 85bhp your after you have the wrong cam

[scotty_18]

I'm aiming for a minimum of 85, would like to get 90-100 if I can. 

 

I've been doing my research around it, I know it's the right cam for me. 

[KernowCooper]

Whats the spec of the other components you have in mind on the build?

[scotty_18]

Close ratio gearbox, straight cut drops, metro turbo crank or 1275 crank, 286 cam and haven't decided on the head yet. 

[Gremlin]

If your happy with the choice of cam, make sure it's in good condition by posting the bearing sizes and measure the maximium lift on it, then when timing it post up any other measurements you can measure

[scotty_18]

I'll get that done soon, thanks

[Cooperman]

To get it to pull away cleanly and stay 'on the cam' when changing gear you will need a FDR of no higher than 3.76:1.

To get maximum power you will need a bottom end and pistons capable of a sustained 6500 rpm.

Not cheap to achieve and 21253 pistons may not be up to the job. In my engine, which runs a 286 I use Karl Schmidt pistons with everything accurately balanced, twin H4 carbs, a very well gas-flowed head, etc.

But it does need to really rev to get the power out of it. I generally change up at about 6600 rpm.

[scotty_18]

I was going to go for a 3.44 final drive or around that mark. I was given pistons with the block I bought but I need to have a look at them and see if I need new ones or not. 

[Cooperman]

I tried a 3.44 with a 286 and if trying to pull away up any sort of hill it really did heat up the clutch!

 

By the way, I wouldn't bother with the straight cut drop gears. They are absolutely awful, unless you want to be wearing ear plugs on any journey over about 5 miles. I'm taking my engine out soon for some routine work (with a 286 the engine needs regular stripping and re-building because of the wear caused by the very high revs) and the SC drops are coming out to be replaced by the original helical ones. My engine has c.115 bhp at 6400 rpm, but I simply can't have those horrible SC drops any more.

Edited by Cooperman, 22 May 2014 - 07:30 PM.

[scotty_18]

What final drive would you recommend? The car will be used as a toy on weekends and also track days.

[cal844]

3.76 as stated in Cooperman's first post!!

[scotty_18]

Just found this, makes so much sense now!!

 

http://www.retromini...d=19&chapter=20

[Cooperman]

The 'hotter' the cam, the more critical the gearing becomes.

The 286 is a 'top end power' cam and requires an engine which will rev safely to 7000 rpm. That really means better pistons and a fully balanced bottom end, plus some other things like a lightened steel flywheel. A really well gas-flowed head is also vital and around £500 should be allowed for this alone.

To keep it 'on the cam' when pulling away and changing gears requires a close ratio gear set and this means that 1st gear is quite high.

So, as performance is obviously the aim and this includes the ability to pull away quickly from rest, a low FDR is needed. If this is not done the clutch will have to be seriously slipped every time you pull away from rest which means frequent clutch changes.

For motorsport when using a 286 cam it is normal to fit a 3.9:1 FDR. This is predominantly for tarmac rallying.

Of course, a low FDR to optimise the cam and gain performance means that the car is revving high, as intended by such a cam, in top gear with a 3.9 giving just over 14 mph/1000 rpm in top gear. But as the engine will rev to almost 7000, that makes to maximum speed around 95 mph and a 70 mph cruise will be 5000 rpm.

In turn, that means fairly frequent engine re-building and on my Cooper 'S' which has the 286 I refresh the engine after every 8 rallies, with new rings after 16 rallies and a re-bore after around 30 events.

Personally I love the 286 for serious motor-sport, but would never fit it for a road car, or even for un-timed track days. The reason for this is the high wear rates on the engine and the need for very high revs to get the performance out of it. Also expensive pistons and a very free-flowing head will be needed to get a 286 to work well. For example, the Karl Schmidt pistons I run with my 286 cost me over £550 for a set, compared with around £160 for a set of 21253 pistons which are only good for up to around 6200 rpm sustained. But 6200 is insufficient for a cam which gives its peak power at 6400 as a 286 does and thus needs to rev well beyond this to get the best from it.

I hope this is not too confusing, but fitting a 'hot' cam without getting everything else correct is simply 'over-camming' to no good effect.