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Duration/Lift : Power Guideline on RB26.

25K views 26 replies 11 participants last post by  R32 Combat 
You can run 9.15 without mods.

The max duration of camshaft for a 6 cylinder with emissions in mind is 240deg (the std duration). Hence any longer duration, overlap starts becoming an issue and mpg goes right out the window.
 
Ti retainers are a total waste of money. You will never be able to measure the difference unless you are revving 10K+ rpm.

I run JUN 272 10.5 cams with the STD springs and retainers.

Higher lift is usually related to cam duration due to the ramp angle. You can't have 11.5 lift on a 240deg cam because the ramp angle would be too high.

264 cams will easily produce 500@hubs.

The smaller the lift, the harder you need to blow through the hole, but 2530 will work admirably.
 
^^^^ Ditto

I used 3.8-4.2mm thick shims and slightly modded retainers to accept the larger diameter. The base circle is smaller on my cams. JUNAUTO display the base circle on there cams so you know roughly how this the shims will need to be.
 
I have not seen ramp rates quoted, but can recall a conversation many years ago with the engineer that developed the Metro 6R4 engine for BL Motorsport, where they spent some considerable time trying on the engine dyno trying to sort out the best compromise on lift, duration and ramp angle.

As a check at what they thought was the end of the process, they asked for a set of Cosworth profiles to be ground on to some blanks and the engine torque and power jumped noticeably.

There is also nothing that I can think of that would suggest the need for the angles to be the same, although they generally do.
If the angles are the same, then are you sure the steeper the ramp rate the more torque is required to turn the camshaft?
 
Yup, as you increase the camshaft ramp angle you will increase the speed that the valve opens and therefore the work being done while the valve is opening, so inevitably increasing the torque required to turn the cam.

Bit like walking up a steep hill compared to walking up a gentle slope hill
This is counter acted completely by the valve pushing the cam lobe up?
 
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