Machining Head For High Lift Cams (rb26dett)

[Mik]

Everyone knows that Tomei PONCAMS drop straight into an RB26 without the need for any clearancing. These run a standrard base circle (32mm) and 9.15mm lift. This means that the lobe height from the centre will be 25.15mm (16mm+9.15mm).

Now Tomei PROCAMS with 10.25mm lift run a base circle of 30mm. This means that the lobe height will be 25.25mm. Does this mean that the head will not need to be clearanced?

[BU5TER]

Mik the difference in the base circle has more to do with lifters/shims and the clearances with the lobe in the head has more to do with what lift the cams have

[Mik]

Mik the difference in the base circle has more to do with lifters/shims and the clearances with the lobe in the head has more to do with what lift the cams have

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Of course with the 2mm smaller base circle, you need an extra 1mm lifter height, but unless I'm totally missing something, the head clearance should increase as well.

The only thing is, the clearance will be 0.1mm less than it is with PONCAMS and I'm wondering if there will be enough.

[proengines]

You wont need to machine the head to fit those cams, that's why they make them with a smaller base circle.

If the base circle diameter is 2mm smaller and the distance from the centre of the cam to the top of the lobe is the same, you will have 1mm more lift without increasing the height of the lobe.

You will have to use shims 1mm or so thicker as the clearance is set between the bucket and the base circle of the cam.

[Mik]

You wont need to machine the head to fit those cams, that's why they make them with a smaller base circle.

If the base circle diameter is 2mm smaller and the distance from the centre of the cam to the top of the lobe is the same, you will have 1mm more lift without increasing the height of the lobe.

You will have to use shims 1mm or so thicker as the clearance is set between the bucket and the base circle of the cam.

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Thanks mate...thought as much