Quote:
1200rallycar wrote:
is there any other advantages?, do they put mose stress on any parts?, which way does the ratio work?, 1mm of pushroad lift = 1.5mm of push on valve???
Thats right, at 1.5 to 1 ratio, 1mm of tappet lift - 1.5mm of valve lift.
If the ratio is higher than stock, then the pressure from the valve spring has more leverage against the cam & applies more force against it. Ratio improvements are usually gained by moving the adjusting screw closer to the rocker shaft. It doesn't take Einstein to figure out that there is only a limited scope for realignment here, but even a little can mean a lot.
With a higher ratio, the valve opens at the same time as before, but lifts a little quicker, & opens a little further than previously with the same cam. It stays open at a lift figure that is equal to, or greater than the previous "full open" figure, for a little longer. Finally it reseats itself at the same time as previously.
This means that it idles the same as before, but the head has better flow characteristics.
What do you pay for all of this?
Well, apart from the extra money it takes to buy them, the extra pressure exerted on the lobes would theoreticly increase the wear rate, but if the increase in pressure is relatively minor, & top quality parts are used, like stock Datsun stuff or better, then you will probably blow it up before you wear out these related parts.
If the rockers are roller types, there is a minor[?] reduction in friction at these roller points [rocker tip & shaft, as applicable] This may be enough to counter the additional load at the cam face in terms of total internal friction loads.
If you already have a high lift cam, it may be necessary to make absolutely sure that the valve springs don't coil bind, or that the collets don't bottom out on the valve guides. Thats when it gets expensive.
Again, if you have a high lift cam, you had better check the valve to piston clearance too, particularly if it was marginal before.
Depending on the engine, & the ratio increase, it may be necessary to enlarge, or elongate the pushrod holes in the head.
So that's the deal, a hotter cam without changing the cam, or the cam specs.
Depending on price, it could be an affordable & discrete improvement to your engines output.
It costs nothing to ask.
P.S. You may need to add a "thou" to your tappet setting.
Transfer
