29 replies to this topic

[fwdracer]

Thanks for the replys all

Nicklouse so you'd recomend for my use to stick with 1.3 ratio ?

 Use your 1.5 rockers and make sure the followers are decent. Most destroyed cam lobes I've seen have been because the follower has worn prematurely and the cam has taken the hit.

[hhhh]

 

I think that would depend on spring tension, lift, and even zinc content in the oil. The cam can't "know" what the rocker ratio is. It will have forces acting on it which can be equalized between 1.5 and 1.3 rockers by properly adjusting spring load. If springs designed for 1.3s are used on 1.5s, it will almost certainly increase cam wear.

Springs are not designed for the rockers they are designed to control the valve so you don't get bounce. And so you don't get coil bind. That could be from a high lift cam and standard rockers or a short lift cam with high lift rockers. The Spring will be the same but the loads seen by the cam will be more.

 

 

But with high lift rockers, the valve train up to the rocker moves through less distance and therefore has lower reciprocating forces which in turn require less spring pressure to control. It's when the inertia of the lifter side of the valve train overcomes the valve's spring force that valve float occurs. Higher ratio rockers give more mechanical advantage when returning the valve train to the closed position and therefore lighter springs should be used to achieve the least power losses and least wear.

[nicklouse]

And there you are changing a parameter. The cam has nothing to do with the Spring. Valve lift does.

High lift rockers put more force on the cam fact.

A longer leaver exerts more force.

Same valve lift from different cams one operating through standard rockers and one operating through 1:1.5 rockers with the same Spring the high lift rockers will put more force on the cam.

I think that would depend on spring tension, lift, and even zinc content in the oil. The cam can't "know" what the rocker ratio is. It will have forces acting on it which can be equalized between 1.5 and 1.3 rockers by properly adjusting spring load. If springs designed for 1.3s are used on 1.5s, it will almost certainly increase cam wear.

Springs are not designed for the rockers they are designed to control the valve so you don't get bounce. And so you don't get coil bind. That could be from a high lift cam and standard rockers or a short lift cam with high lift rockers. The Spring will be the same but the loads seen by the cam will be more.

 
But with high lift rockers, the valve train up to the rocker moves through less distance and therefore has lower reciprocating forces which in turn require less spring pressure to control. It's when the inertia of the lifter side of the valve train overcomes the valve's spring force that valve float occurs. Higher ratio rockers give more mechanical advantage when returning the valve train to the closed position and therefore lighter springs should be used to achieve the least power losses and least wear.

What you trying to do? Get valve bounce?

Mad.

[gazza82]

OK ... Semi-synth not a problem for for me as my gearbox is separate and runs in its own 20W50 ...

Edited by gazza82, 15 October 2015 - 09:01 PM.

[hhhh]

And there you are changing a parameter. The cam has nothing to do with the Spring. Valve lift does.

High lift rockers put more force on the cam fact.

A longer leaver exerts more force.

Same valve lift from different cams one operating through standard rockers and one operating through 1:1.5 rockers with the same Spring the high lift rockers will put more force on the cam.

 

 

I think that would depend on spring tension, lift, and even zinc content in the oil. The cam can't "know" what the rocker ratio is. It will have forces acting on it which can be equalized between 1.5 and 1.3 rockers by properly adjusting spring load. If springs designed for 1.3s are used on 1.5s, it will almost certainly increase cam wear.

Springs are not designed for the rockers they are designed to control the valve so you don't get bounce. And so you don't get coil bind. That could be from a high lift cam and standard rockers or a short lift cam with high lift rockers. The Spring will be the same but the loads seen by the cam will be more.

 
But with high lift rockers, the valve train up to the rocker moves through less distance and therefore has lower reciprocating forces which in turn require less spring pressure to control. It's when the inertia of the lifter side of the valve train overcomes the valve's spring force that valve float occurs. Higher ratio rockers give more mechanical advantage when returning the valve train to the closed position and therefore lighter springs should be used to achieve the least power losses and least wear.

What you trying to do? Get valve bounce?

Mad.

 

 

It's the laws of physics. Overspringing your valves is mad because it's simply a waste of horsepower and valve train life, no matter what rockers are used. What's exactly required to control the valves, plus a little for a safety factor (to accommodate accidental over revving) is the route to maximum horsepower and long equipment life. That's a fact. I think the stories of people wiping their cams with high lift rockers are simply because they've oversprung their valves by not taking the physics of the situation into account as outlined above.

 

I would also add that the cam profile does affect spring choice because a pointier cam profile means faster valve train acceleration and therefore higher loads which require stronger spring force to control. Your first few lines above agree with my assertion that higher lift rockers mean that weaker springs can be used because the additional leverage better controls the valve train.

Edited by hhhh, 15 October 2015 - 09:18 PM.

[Dusky]

You've cheered me up... 1.5:1 and a 266 is my spec.

Tell us more about your oily experience ... maybe a new thread?

 Oil - done to death. Basically Semi Synth doesn't protect the box as well, and finds every exit path. Good Mineral 20w/50 all the way - even in my race motor.
 
My road car is a 1293cc + MG metro cam (266 equiv), 1.5 ratio rockers, Rob Walker head and it gargles through a 45 DCOE!  Pulls like a train between 2-7k. That is exactly where you need the performance in a road engine.

Performance at 7 k in a road engine? I rather have the power between 1-6k. Wich is more likely with that cam by the way, 7k seems very high to me.

[fwdracer]

Dusky - yeah, you must be right, I clearly don't know what I'm doing. That same MG cam makes 9K rpm in a fully prepped Mini Se7en race engine. I've had loads of experience with that cam and its timing makes a big difference (yourself?)  . When the rolling road is done I'll bang a plot up for the naysayers.

 

Quite a few advocate its usage in variety of small and large bore A-series - and you can track the cam lineage back to the 1960's 2A948 profile. It has stuck around because it works.

 

Back on topic - What has the Original Poster decided on?

[Dusky]

Im not a nay sayer, im just astonnished that your cams makes top bhp at around the same rpm as my dads fully prepped racecar (7.3k rpm).
But very intrested in rollingroad graphs, just out of a healthy young curiosity ;)

[imaparana]

Cheers for the input all, I think by the looks of it the performance benefit doesn't out way the possible increased wear will be putting the standard ones back on

Cheers all

[hhhh]

Vizard had very little bad to say about 1.5 rockers in his blue book, other than they're too much for a small bore with already good lift if I remember right. I haven't read the later yellow version. Did he retract any of it?

[fwdracer]

Im not a nay sayer, im just astonnished that your cams makes top bhp at around the same rpm as my dads fully prepped racecar (7.3k rpm).
But very intrested in rollingroad graphs, just out of a healthy young curiosity ;)

This what 1.5 ratio rockers can achieve on an MG Metro cam-1293cc with a decent head, Weber 45 on a 5 inch manifold and Maniflow exhaust. Close attention to clearances, and cam timing on the build.

The engine is mapped on a mega jolt and will pull top gear from under 2k without fuss.

Attached Files

•  image.jpg   52.5K   50 downloads

[firstforward]

Close attention to the TURBO!

[Dusky]

 

Im not a nay sayer, im just astonnished that your cams makes top bhp at around the same rpm as my dads fully prepped racecar (7.3k rpm).
But very intrested in rollingroad graphs, just out of a healthy young curiosity ;)

This what 1.5 ratio rockers can achieve on an MG Metro cam-1293cc with a decent head, Weber 45 on a 5 inch manifold and Maniflow exhaust. Close attention to clearances, and cam timing on the build.

The engine is mapped on a mega jolt and will pull top gear from under 2k without fuss.

 

Peak power at 5.9, you'll rev to 6.2-ish to get the best out of it. 
Thats far from the 7k, like I said. 

Nevertheless , a very impressive curve.

[mini13]

with the RE13 you should have little int he way of issues, the nose of those cams is very very rounded and they are rather good at not wearing out.

 

 

 

 

Ive got minispares 1.5 roller tip rockers and a claver RE13OT Cam, Ive got a fully worked head with double valve springs which are up to the job

[MRA]

Cheers for the input all, I think by the looks of it the performance benefit doesn't out way the possible increased wear will be putting the standard ones back on

Cheers all

 

Firstly what condition are the pads on your standard rockers ?  what kills cams more than a little offset is too big a clearance, Ihave seen clearances stated on here for 1.5:1 at 22 though !!!  you only need about 14 to 16 thou and any more will kill your cam in a short while.

10W40 works in my 1380 turbo (180bhp) and it revs to 7500 no issues at all...

I use semi synthetic less friction.

 

and I use 1.5:1 rockers from Minispares with no issues except the normal high mileage wear you would expect.