11 replies to this topic

[087dave]

Hi all does anyone have a set of 1.3 roller rockers on their 998
are they any good,is there any real difference

Thanks

[Bungle]

Standard ratio is around 1.25 to 1 not sure you will notice 0.5 extra lift

[Cooperman]

Roller rockers do reduce the side loading of the valve stems on the valve guides. There will be no noticeable performance, although in theory it is possible to shorten the guide intrusion into the inlet tract which will improve gas flow into the combustion chamber.

[087dave]

Thank for the replys and 1.5 ones are these a no no on a 998??

[Bungle]

too much lift on a 998

[bmcecosse]

All you will do is wreck the valve stems/guides/followers/cam lobes...... Changing rockers is not a cost effective way of getting more power.

[TimmyG]

To the original poster, if your 998 is otherwise standard there is no reason why you could not fit 1.5 ratio rockers as anything that will get the tiny valves open more will help. Problems are likely to happen when the head already flows well through bigger valves and then 1.5 rockers are fitted. Too much valve area too quickly for the small cylinder size which reduces gas speed and running problems can result.
However, if you are going to pay 200 odd quid for roller rockers, your'e better off continuing to save and get the head modified, or, cheaper still, fit an unmodified 1275 cylinder head, preferably MG metro (with suitable mods to allow it to fit)
Incidently the standard sintered rockers do not give anything like the ratio that is quoted, atleast not the ones i measured. They weren't even making 1.21 ratio at full lift, (i didn't measure through the cycle so i can't comment on that). So even a 1.3 ratio rocker is going to give you a fair chunk of extra lift.
If you do fit higher ratio rockers you should not use stronger valve springs, and the valve clearances need to be opened by the same proportion as the rocker ratio increase. Rapid wear may result otherwise.

[KernowCooper]

1.3 roller rockers on a std 998 are money which could be used a lot more efficiently elsewhere, what tune is the motor? and a point on the 998 will standard springs allow more lift on 1.5s ? Didn't think 1.5s are recommended for 998s? better of with a cam change

Money wasted in my opinion lots of places to spend it on before roller rockers come on the list

[jaydee]

Std sintered rockers are about 1.21 on a lucky day, its very common to find these fitted with wrong geometry.
1.3 rollers are about 1.27 and, if fitted properly, they'll make a difference.
Wasted money if they come on a 'vintage' engine, good idea if its a brand new build.

[Vipernoir]

Old style pressed steel rockers have a better lift ratio than the sintered type, and can also be rebushed to prolong their life.

[Cooperman]

Old style pressed steel rockers have a better lift ratio than the sintered type, and can also be rebushed to prolong their life.

Yes, and they are lighter too. If you want to use the old pressed rockers at high revs the trick is to run a line of weld across the top face where the two sides are pressed together. That stiffens them without much increase in weight. Grind the weld back and they are very strong and still extremely light.

[Spitz]

I believe it was a Calver article I read in which the different varieties of standard rockers were measured. Pressed steal, as stated, were the best. I seam to recall sintered being bad, but the worst were the original S type.

I've not used 1.3 rollers....but if I had money burning a whole in my pocket, I'd buy a case of Guinness and a set of 1.3 rollers

Edited by Spitz, 29 January 2013 - 09:29 PM.