18 replies to this topic

[sprite72]

Good day
My question is I was thinking of putting a kent 266 cam in my 1275 engine or would I be better off putting some 1.5 roller rockers on instead.
I have a stage 3 head on at the moment and a stage one kit done .
Any help would be great .
Thanks

[Carlos W]

What do you use the car for?

[sprite72]

General road only in the summer it only covers about 2k max

[Carlos W]

266 or 276 cam

[sprite72]

I was going to put a 266 one in

[racingbob]

yes cam not 1.5 rockers my mg metro is good cam

has a stage 3 head on as well

ideal road use

[mini stephen]

Sorry to hi jack but what would the roller rockers be good for

[Dusky]

Sorry to hi jack but what would the roller rockers be good for

Nothing major. Less wear on the valve stems, but they'll wear the camshaft out... 1.3 rollerrockers are your best option.

[mini stephen]

Sorry to hi jack but what would the roller rockers be good for

Nothing major. Less wear on the valve stems, but they'll wear the camshaft out... 1.3 rollerrockers are your best option.

Am sorry if this is a silly question but would the 1.3 roller rockers add much bhp or would they just make it lift more down low or up top

[Cooperman]

The only measurement of roller rockers I have done was on my 'S' engine which has a very good head (I never use the 'Stage x' expressions as they are meaningless).

I have a 286 cam and after fitting 1.5:1 roller rockers I gained 2 bhp at 5700 rpm and above, nothing below that and I lost a bit of bottom end power & torque, although this was not measured.

On a road car this is no improvement at all. On my rally car it is probably not in any way useful either.

[Mini Manannán]

If you're using it for 'normal' road use torque is your friend. So, go for the 266 or a SW05-07. (Other high-torque camshafts are available!)

[nz_seamless]

Rockers with a higher ratio "can" be helpful if your cam is one that will benefit from what they offer. And what they offer is threefold.

First, they lift higher. Standard arms take the motion of the pushrod and multiply it by 1.3-ish to give you your valve travel. So a 1.5 will give you more travel, meaning the valve face will be further from the seat. How does that help, well if you think about air flowing through an open valve the aperture it gets to flow through is constrained by the valve seat, and the valve face. Move them further apart and air will be able to move more freely. Do most of our road going motors benefit from that? No, not really. A Miglia build would though. At very high revs (which is not a 266s sweet spot, nor much fun on the road) with intake duration extremely quick, if you can get a bit more air in, you can make more power. Cylinder filling at high revs with a mini head can be a problem, but a road going motor with a mild cam, not anything to care about.

 

Secondly, because of the increase of valve travel distance in the same period, the speed at which the valve moves, increases. That means the time from the valve starting to open to a point where it flows a given cfm will happen quicker with a higher ratio set. Is that useful to us? Maybe. Depends on the cam. On stock cams, or mild cams, it helps. It really is worth it on cams that already have good table manners. A 266 is fairly mild and would benefit from higher ratio rollers because the time from totally closed to flowing 50% will happen quicker.

Cams with bad table manners at low revs do so because there is quite an overlap between intake and exhaust (both are open at the same time). If you open that intake valve faster you are just making it a better exhaust. So if as Cooperman above had, you have a worked head and a high duration high overlap cam like a 286 then at low revs, high ratio rockers will lose you power as it exacerabates an issue the 286 already has. Once there is enough air momentum at higher revs, the intake doesn't run in reverse any more and the faster rate of valve opening and higher overall lift helps make power.

 

The third thing worth mentioning is spring tension and in your case is no issue at all but this post may help someone doing a more aggressive build. High ratio rockers give more leverage to the rocker arm, which means when the spring is closing the valve it too can use this leverage to control the rocker arm and pushrod assembly. When you hear of valve float at very high rpm, it is less about the spring not being able to pull the valve onto the seat because of the weight of the valve, more about the weight of the rocker/pushrod assembly presenting to much inertia. More leverage means more control for the same spring pressure and less need to use crazy powerful springs.

 

So that was long. What is my personal recommendation? Well a cam is 153 pounds and will make you go a bit faster. A set of 1.5 roller rockers are 473 pounds and will make you go a bit faster.

If you want the most bang for your buck, cam.

If you can afford it, cam and rollers.

 

I used to have a 272 with 1.5 rollers and it was lovely, now I have the same rollers and a SW5 which is a wonderful setup.

[Dusky]

Sorry to hi jack but what would the roller rockers be good for

Nothing major. Less wear on the valve stems, but they'll wear the camshaft out... 1.3 rollerrockers are your best option.

Am sorry if this is a silly question but would the 1.3 roller rockers add much bhp or would they just make it lift more down low or up top

more lift is generally more bhp.
Bit its really an improvement over the factory high manifavturing tolerance rockers

[mini stephen]

The only thing putting me off the cam is taken the engine out but weirdly am happy enough to get the head ported and polished and ma stage one kit but scared to take the engine out as my brothers has bn lien for months waiting for the bloke to be skimmed and rebuilt the prob is when ya take them out everyone says well its out now so ya might as well do this and this which means weeks of saveing which leads to months of no mini

[ACDodd]

The question really is what cam do you have now?

Ac