30 replies to this topic

[jaydee]

Who said Kent MD range were designed for 1.5 rollers?
And no, swapping to rollers changes the lifting speed of the valves, and alters the timing a tiny bit.
Its another thing you need to evaluate wisely while writing your engine spec.

[AndyMiniMad.]

A decent cam manufacturer will state the timing figures that you should set the cam at with both standard rockers and 1.5 ratio..Dont be put off the 286 for your engine spec, mine goes like a train with i.5 roller tip rockers and has enough torque to spin the wheels in third gear....uphill....in the dry.....but as has been said above slapping in a big cam isnt the whole story...

[miniand]

I have the same engine 1293 with a 286 It´s perfect

[ACDodd]

For all those that answer this thread with the statement that a 286 is ok and works well for them are missing the point that this cam suits your driving style. Fact is, most road engines need to pull hard from 1500rpm or so. A 286 with stock rocker will pull from 2krpm and 2.5 krpm hard. With 1.5 rockers more like 3krpm. If you like to rev the engine this is this cam to go for. If you like to keep maintenance costs low you need to keep the rpm (duty cycle down) this is where a more suitable milder cam comes into its own. A 286 has 0.090" of split overlap, lift meaning high emissions and MOT issues, not straight away but after a few miles as the valve seal drops away. That is not to say the 286 is a bad cam, in fact it is a very good cam and I have used it to very good effect when used in the right application. Regular valve seat refreshing is needed to keep the engine clean and running well. For regular daily used engines Keep split overlap figures below 0.070". The more split overlap lift you run the worse the emissions, the worse the idle quality. Incidentally 0.050" is the limit for a smooth idle in big bore A-series engines with stock rockers.

Also helpful, do not start talking about cam characteristics from duration and lift figures only is it meaningless.

To determines a cams characteristics ie how it will drive; you need to know the Duration at a known a familiar checking height, you need to know the Lobe separation angle, the intake lobe centre line angle, the total lobe lift and most importantly you need to know the split overlap lift figures.
You also need to know the engine size and the rocker ratio used.

There are other issues like intake manifiold and port sizes, but these have a lesser effect than those stated above.

Misleading information on cams is rife on forums.......


AC

Edited by ACDodd, 19 March 2012 - 04:20 PM.

[ACDodd]

No amount of ignition advance can compensate for both valves open at the same time.

AC

[AndyMiniMad.]

Yes.. but the OP did state that he has a spirited driving style...which is why I for one, posted my recomendation of the RE 13 OT cam...(very similar to the 286)...I agree that a lot of mis information can be given on the forum by people who dont understsnd cams, duration, lift and overlap figures can be quite a handfull if your a novice..but on the other hand if someone has a certain cam that works for them...then why should they not recomend it to others.. regardless of their knowlege of how it actually works..

[ACDodd]

One mans spirited drive is another man's nightmare. When selecting cams alwasy er on the conservative side, thew engine will last longer and be less fusssy to drive and save you money on rebuilds and fuel.

AC

[AndyMiniMad.]

One mans spirited drive is another man's nightmare. When selecting cams alwasy er on the conservative side, thew engine will last longer and be less fusssy to drive and save you money on rebuilds and fuel.

AC

Very true...I tend to wheek my engines out regularly anyway so its not really a problem for me to rebuild every year...but I suppose most people will be looking for a lot more reliability if the car is more than just a weekend toy..

[Cooperman]

I reckon I must have driven with almost every production cam going right back to the 60's. In my rally 'S' I have a 286 with 1.5:1 rockers and it is fairly 'evil' below about 2800 rpm when hot. When driving hard I try to keep the revs between about 5000 and 6800 as it performs best at those revs. I am thinking of building a 'softer' engine with a 276 cam to try to get it more 'friendly' in mid-range on the basis that it will be easier to drive on the limit in forests or on tarmac with smoother power delivery.
In a 1380 the big advantage should be the mid-range torque which the added 'cubes' give, so a well set-up 1380 with a 266 cam, big-valve head, CR around 10:1-ish and standard gear ratios would be an excellent road car for daily use.
With the 286 and the revs I use I have Karl Schmidt pistons and re-build the engine after every 6 or 7 rallies. My transmission is also to full comp spec, SCCR gears, SC drops, 3.9:1 FDR, X-pin diff, EN24z drive shafts.
My 1330 Innocenti Cooper has a 510 cam and a 3.44 FDR and it's just so friendly to drive, but still quick.

[ACDodd]

Thats my point chaps, both of you have said you perform regular maintenance/rebuilds, and that is fine, as that is what is required.Its just when people recommend cams, they must also bear in mind the maintenance and hence cost that goes with it.

Cooperman you might want too look at my own cam range, if you have tried most others I can guarantee you will find something different. If you like the 286, you'll love the ACD - TSR.

AC

[Cooperman]

Thats my point chaps, both of you have said you perform regular maintenance/rebuilds, and that is fine, as that is what is required.Its just when people recommend cams, they must also bear in mind the maintenance and hence cost that goes with it.

Cooperman you might want too look at my own cam range, if you have tried most others I can guarantee you will find something different. If you like the 286, you'll love the ACD - TSR.

AC

Hi AC,

I'm not doing as much motorsport as I used to due to being 71-years young now and having recently returned to flying as a hobby. However, I do still build a few engines for myself and others and I'll probably take you up on that. I usually use cams from the Kent range as they seem to be good quality again, after their QC problem a few years back, and they do time-in easily. However, I like to try different things. Thanks for that.

Peter

[MJWarren]

With the 286 and the revs I use I have Karl Schmidt pistons and re-build the engine after every 6 or 7 rallies. My transmission is also to full comp spec, SCCR gears, SC drops, 3.9:1 FDR, X-pin diff, EN24z drive shafts.

Why do you rebuild it after that short period of time? Wheres the need?

[Cooperman]

With the 286 and the revs I use I have Karl Schmidt pistons and re-build the engine after every 6 or 7 rallies. My transmission is also to full comp spec, SCCR gears, SC drops, 3.9:1 FDR, X-pin diff, EN24z drive shafts.

Why do you rebuild it after that short period of time? Wheres the need?

It's now done 32 Historic rallies, won 5 of them, and I still have the same crank journals and thrust faces. I like to change the mains, big ends, thrusts and the oil pump quite often. I changed the rings, fitting 'Total Seal' with the gapless 2nd ring, after 15 events and re-bored to 1310 cc after 30 events. It's a genuine Mk.1 'S' engine and I want it to last a long time, which it has so far.

[ACDodd]

The need comes for the accelerated wear that happens on a high power unit. As shown regular rebuilds keep the engine fresh and the power at a competative level.

AC

[Cooperman]

The need comes for the accelerated wear that happens on a high power unit. As shown regular rebuilds keep the engine fresh and the power at a competative level.

AC

Have you tried the 'Total Seal' replacement rings with a gapless 2nd ring? They are made in Phoenix, Arizona. Not cheap, but very effective. My friends in the USA who are involved in air racing put me onto them and they do a ring set for the Kark Schmidt pistons I use.