1.5 :1 rockers

[sagalout]

1.5:1 roller rockers are available for various engines, including the old Mini A-series.
Now I know these increase the lift in the same way as a high lift cam, but they won't increase the overlap or change the timing etc. Are they a good idea or do they simply increase the loading on the valve train to a unacceptable level with little power gain?
Anyone out there with any experience?

[Marquis_Rex]

I don't know much about the Mini A Series, I guess I would suggest that you read or looks up artciles that Mister Vizard has written perhaps?

I know that My project engine, the BMW M20 has an average of 1.55 :1 ratio rockers (with a high of 2:1!)as standard and the cam runs in seven bearings , the bearings are of generous diameter (40 mm plus) and the camshaft is hardened cast iron. How many bearings does the Mini cam run with? 3? It is pushrod there is alot more valve system mass and inertia to think about. Peak revs will also have an influence:
A 4 bearing camshaft version of the above M20 BMW engine was made with the same ratio rockers and similar cam lift, but much shorter durations-so the flank accelerations were much greater, and the only thing that changed was that the engine was now limited to about 4750 rpm.

[Justin S]

I stuck a set of 'overlised' bushings on my A series 1340 cc.This gave as near as 1.5 to 1 ratio.It didnt make a great deal of difference to the bhp.Roller rockers are good tho.The use of a high lift cam and increasing the ratio,does put a side load on the valve guides,but the rollers stop that.It is also easier to set the tappets.