Roller Rockers/Ford x-Flow

[Bullman]

Ford roller rockers std ratio 1.54:1 or high lift 1.69:1 ratio.What does that mean?How can I be sure which ones I have?Is there some where I can measure to confirm?They are made by Titan Motorsport.What are the advantages of using roller rockers over a steel set up,of rocker shaft,pedestals etc.Any advice would be greatly appreciated.Which camshaft would you recomend to go with which roller rocker ratio?Many thanks Bullman.

 

Bullman

[Morls]

I think,

 

The ratio refers to the linear valve movement up and down when compared to the lift of the cam (the difference between base circle diameter and the top of the lobe.

 

For example:- A DOHC engine would give a 1:1 Ratio. A rocker with the pivot midway between cam follower(or pushrod top) and valve to would give 1:1. A rocker with the pivot nearer the cam(or pushrod top) would give increased lift to the valve for the same cam lift.

 

The theoretical advantage of a high ratio rocker is high lift for a tame cam.

 

The theoretical disadvantage of a high lift rocker is the increased force exerted on the cam face by the follower as the valve spring rate has been magnified by the increase in ratio.

Another possibility is the new lift of the valve may need pocketed pistons.

 

The theoretical advantage of the rockers is to remove losses through the exertion of side force as the rocker end moves trough an arc.

 

The theoretical disadvantage is the increased polar moment of inertia due to a "heavier" end moving further (in a given period of time), at a greater distance from the pivot. This would reduce the effective limit (in theory).

 

I seem to recall the original use for high ratio rockers was to give high valve lift in classes where camshaft mods were not allowed, but this might just be the cynic in me.

 

Sorry, can't help with the cam, I only remember the above from youthful A Series days and a theoretical valve train redesign at college.

 

 

 

Mark

[cdg]

Cam choice really depends on what you expect to be doing with your car.

 

For standard ratio roller rockers, any camshaft may be fitted to suit your application. With high ratio (1-1.69) you need to be more careful on cam. selection. A friend of mine used a Kent 244 with hi-lift rockers in his hillclimb Striker (with a Phil Jones head) and it made 141bhp at the wheels and very good torque figures. However, at nearly 1/2" of lift the valve gear had a hard time, and it made a terrible racket!

 

I have used high-ratio rockers with both a Kent 1FR4 and a Burton BLF18 and both 1700cc engines made about 140 at the wheels with excellent midrange and driveability, which I thought was important for Speed events. These cams have longer duration than more modern profiles, but the lift at about 10.5mm is not excessive. This gets uprated by the rockers to about 11.5mm.

 

I know of many racers, particularly in historics, who use older Cosworth profiles such as the A6 or A8 with high-ratio rockers. Bottom end and mid-range is non existent, but once over 6000rpm the the way the power comes in can only be likened to that of a turbo installation.

 

You pay your money etc.....

[Roger King]

I haven't much to add to Mark's explanation.

 

The 1.69 ratio rockers give higher lift. The rockers are stamped either SL (standard lift - 1.54) or HL (high lift - 1.69).

 

Do not try to use the high lift version with modern high lift cams such as the 234 family. On the other hand they work well with older low lift profiles like the A2, A6, A8, etc.

 

Cynical Mark is dead right about the high ratio rollers adding lift to older type cams.

 

The real concern lies with the increased inertia of the roller set up which can cause the valve spring to lose control of the valve train. This can happen even with the standard lift version and is the reason that we don't use rollers with the 234 family cams. I know that plenty of people will say that they have had no problems, but we see enough engines to feel that the likelihood of problems is unacceptable.

 

This is a classic case of a component working brilliantly in one set-up, but causing problems in another.