15 replies to this topic

[Bam]

What are the advantages of fitting roller rockers, i've heared that they improve prformance and the equivilent of fitting a new cam shaft and also that the just reduce were in the engine. Are they any good?

[Sprocket]

Less side load on valves reducing valve guide wear( not much point if your guides are already worn) and if fitting the 1.5:1 items( which you should if buying them) increase the valve lift there by increasing power. usualy fit these when you fit a modified head to get the full benefit. By no means the best mod, pound/ bhp, on a bog standard engine but still increases power

[Bam]

i have a stage 2 head and am considering 1:5:1 thank you for youre help.

[stormduck]

Don't fit them if you are considering replacing your cam at any point. The rockers have to match the cam profile otherwise the valve springs could crunch together if too much lift is generated, resulting in a broken rocker shaft, screwed springs and possibly other damage. Just to let you know - they're a lot of money those rockers.

[minimanclive]

I've heard the 1.5 rockers are quite good with the milder cams. Does anyone know how well they work on the MG Metro cam?

[Guess-Works.com]

As Sprocket has said they are 'kinder' to the top of the valve stem and also are less prone to wear, when compared to the standard rockers. But, and a big one, 9 times out of 10, this is not the reason they are being fitted, but rather to gain extra lift from the cam by changing the cam to valve lift ratio.

As standard the ratio of the rockers is about 1.25, this does vary depending on manufacturing tollerances, but it's a nice number to work with... roller's are generally available in 1.3 and 1.5 ratios, but I'm sure I've also heard of 1.7's.

With the increase in ratio, you are increasing the valve lift, but you also increase the stress which is placed on the rocker assembly, pushrods and cam.

So taking a std MG cam profile, which has a .250" cam lift, this would translate to 0.313" valve lift at std, 0.325" with 1.3 and 0.375" with 1.5's, this obviously increases the ability to flow, both in and out of the combustion chamber. What it does not do is change the duration of the lift, nor the opening time of the valve, so you're still stuck with a 252 degree duration cam..

So using a MG metro cam with 1.3 ratio rockers, is very close to the profile offered by the Kent MD256 using std rockers, which is considered the tamest of the Kent range... Using 1.5's on a MG cam would bring you nearer the lift of a 276, but the duration increase offered by the Kent adds considerably more...

IMO, unless you don't have the equipment, time or desire to remove the engine and change the cam, then the rocker ratio is the ONLY way you are going to increase the valve lift, but, pound for pound, it's much cheaper and effective to change the cam.

[Karl]

You know what, that`s one of the first posts that I have learnt something from in a LOOOOOOOOONG while, cheers GW

[The Matt]

... roller's are generally available in 1.3 and 1.5 ratios, but I'm sure I've also heard of 1.7's..........

Yep you can deffo get 1.7:1 roller rockers. From Minisport (IIRC).


There is a certain point at which opening the valve further doesn't necessarily increase flow, they may offer maximum flow when open at say 0.4" so there is no point opening them past there (it is better to have them open for a longer time to get more air/fuel in and exhaust out).

The maximum flow rate will obviously depend on head/valve spec too.

I reckon roller rockers are a simple bolt on piece of tuning equipment that offer reasonable gains, but as GW has already said, there are alot more options when tuning a motor!

P.S. I have a set of 1.5:1 roller rockers from Minisport (I got buying fever and went and got them) but now I deem them un-necessary due to my change of cam spec as they would make the car unusable below about 3000RPM!!! I now wish to change to 1.3:1 as this will be much more usable and will be kinder to my valves

Don't buy them if you are considering further mods as it may prove to be a waste of money!

[Bam]

I might just go for the 1:3:1 set up and keep the modifications low to start with.

[twincarb1275]

So a 1.5 ratio would be a sound fit to a standard 1275 then?
Or would it be better to fit a 1.3 ratio?

[JamesRance]

So a 1.5 ratio would be a sound fit to a standard 1275 then?
Or would it be better to fit a 1.3 ratio?

any one know the answer tho the question above? ^^^^

also if i changed my standard rockers on my 1275, to 1.5's do i have to adjust the vavle timing??


thanks for your time

James

[AzMaN]

i fitted 1.5's to my standard head (not double valve springs) and 10 miles down the road it snaped a valve at the top of the spring, so this time its gona be a stage 3 head

[minicb]

imo go for 1.3's

[Alastair Kirby]

I ran a standard 1275 cooper engine on both standard 1.3 and 1.5 lift rockers...Here's what I found:

I changed the standard rocker gear on my standard head (apart from double valve springs).
I did find that the engine did 'breathe' ever so slightly more easily but i had to fiddle with the timing and the mixture to get any real difference from it.
After a week I was fed up with the loss of low down pick up and power, constantly having to push the revs even in light traffic just to get the engine respond in any meaningful way. So I changed back to the standard rockers and I was much happier, as was my engine.

What I found more interesting is that I now have 1310cc bloc with stage 2/3 head and Kent 266 camand I tried it again. Same thing happened. I still run the standard rocker 1.3 rocker gear from my original 1275 with all the joy of low end power (2k up) with no noticeable restrictions of power or revs up to around 7000rpm in 1st, 2nd & 3rd.
#Note: my engine can rev higher but there's no power up there so I choose not to

In my personal opinion and personal experience I have found hight lift rockers to be a bit of a non-event; not quite a 'waste' of money, but I do honestly feel that the money could be better used elsewhere i.e Camshaft, headwork etc.
I do know that on much hotter bigger bore engines you would certainly see a marked improvement with high lift rocker gear.

[Cooperman]

With my Mk.1 Cooper 'S' which has a 286 cam and 11.2:1 CR and big valves, I tried it both with standard lightened 'S' rockers and with offset 1.5 roller tips. With the roller tips I gained 2 bhp, which is less than 2% at over about 5700 rpm, but nothing below that. It also seems even more lumpy at the bottom end, below about 3000 rpm with the 1.5's as opposed to the standard ones. If racing a couple of bhp are worthwhile, but not, IMHO, for a road car.