13 replies to this topic

[Alice Dooper]

Anyone any experience with these on an MPI?
Do they need stronger springs than standard ones?
They’re not roller rockers, will that make much difference to the valve train wear?

Thanks.

[Ethel]

Any higher ratio rocker increases the effect of the spring rate on the cam side. You might get a bit more side load on the valve stem compared to a roller tip.

[brivinci]

A better solution would be a proper head and cam combo, then maybe a set of Calvers 1.4 rockers. It has been discussed that 1.5 is really not ideal and the nearly undetectable "gain" from going to 1.5 is nothing compared to the strain it puts on the head parts. John Cooper and the likes used the 1.5 rockers as a way to get some performance gains without having to pull the motor to do the cam. Before I had my custom head done, I started with a SW5-07 cam and it was a nice change in the drivability of the car. HP gains, no idea BUT the car had better power, more of the time.

[johnv]

but doesn't swiftune recommend that you use 1.5's with the SW5-07?

[hhhh]

As alluded to above, the whole valve train needs to be treated as a system. A cam can be ground to give the same effect as higher ratio rockers by increasing its maximum lift without increasing duration. But if the cam is intentionally short on lift, higher ratio rockers may be required to achieve the desired result. Combining an already high lift cam with high ratio rockers could very well lose power to excessive lift beyond what the RPM limit of the engine dictates. Spring pressures need to increase with higher RPM and/or lower ratio rockers.

[Wazzah]

I purchased some Swiftune 1.5's and they made a noticeable difference through the mid range. No difference in top end or top speed. I have their super sport big valve head and a SW5 on the way. A SC ECU is also on the way. Must be all on the Endeavour as they are taking their time.

[brivinci]

Wazzah, that should yield a very nice motor once tuned. Please post your results and thoughts. 

[Steve220]

I purchased some Swiftune 1.5's and they made a noticeable difference through the mid range. No difference in top end or top speed. I have their super sport big valve head and a SW5 on the way. A SC ECU is also on the way. Must be all on the Endeavour as they are taking their time.

SC don't do anything in haste. I've been waiting 2 months to reply to my emails as I currently have an ecu with no map that they promised they'd send.

[racingbob]

1..5 rockers have bad reputation on wearing your mpi cam as in short as just 10.000 miles

[nicklouse]

MPI cams wear faster than other cars as the FDR is such that not as much oil gets thrown at the cam as the gears are not rotating as fast. using 1.5 rockers would just enhance the wear.

[hhhh]

If the valve springs are derated in accordance with the change of ratio (as the geometry and valve train dynamics allow without increasing valve bounce) I don't see how the rocker ratio can have any effect on cam wear.

[Fastorq]

If the valve springs are derated in accordance with the change of ratio (as the geometry and valve train dynamics allow without increasing valve bounce) I don't see how the rocker ratio can have any effect on cam wear.

Hi
Can you explain that a bit more please.
Setting the VT geometry is essential with any performance engine but can you explain what you mean about derating valve springs
Certainly incorrect VT geometry will destroy a camshaft quite quickly.

Thanks
DavidR

[nicklouse]

 

If the valve springs are derated in accordance with the change of ratio (as the geometry and valve train dynamics allow without increasing valve bounce) I don't see how the rocker ratio can have any effect on cam wear.

Hi
Can you explain that a bit more please.
Setting the VT geometry is essential with any performance engine but can you explain what you mean about derating valve springs
Certainly incorrect VT geometry will destroy a camshaft quite quickly.

Thanks
DavidR

 

what is being disused/suggested is the spring rate that is needed to control the cam followers. that is to say if you have the correct spring poundage with standard/1.3 rockers when you change to 1.5 rockers there will be a greater force on the said cam followers. i imagine there was something similar needed to be done with the flat 4s if you changed rocker ratios or the cam profiles?

[hhhh]

The rocker forms a simple lever arrangement. If you consider the valve spring extending as the force acting on the lever,  the higher the rocker ratio, the less force it needs to keep the inertia of the pushrods and followers from overcoming the valve at high RPM. I think a lot of the bad reputation high ratio rockers have of destroying cams is due to their installation mistakenly perceived as being a quickie "bolt-on" modification without considering appropriate valve spring rate.

 

The issue is compounded by the fact that the original springs are being compressed further than they originally were, resulting in greater peak original force being applied to the pad on the rocker, which is then amplified by the higher rocker ratio. The ideal spring for high ratio rockers would likely be a beehive which is capable of providing high enough force with the valve closed, but then increasing in a non-linear fashion so that peak force is actually less than typical.