calculation for valve lift
Turbo Mini Forums

I wrote a rather long first post and it somehow went missing so I'll try again.

I am trying to calculate the total valve lift for a piper 285 scatter cam, plus 1.5:1 roller tip rockers and was wondering if someone could confirm my maths

Total lift as quoted by the piper website is 10.16mm or 400" for both inlet and exhaust

So i'm assuming total valve lift is 1.5 x 10.16 = 15.24mm or 599.9"

p.s I hope this makes sense as currently i have had 3 litres of cider!

Thanks
James

You have to subtract tappet clearance and that also assumes that the rockers are a genuine 1.5:1 lift ratio. Depending on height etc. the rockers will probably be working at less than 1.5:1

On 12th Nov, 2009 Paul S said:

I think Gary OS has taken over my role as the forum smart arse

Thanks

What/does the expansion of the metal account for then for the tappet clearences?

The rockers are minispares 1.5:1's

I always set tapet Clerence hot so expansion acounts for nout

Yes i moved to the darkside

Instagram @jdm_brett

It depends on the cam I normal set any cam with a LSA of less that 106 deg to 018" and any more that 108 deg to 014"

on the higher duration cams I have always fount that a little more valve clearance seems to produce the best power rather than a little less the down side is a noise valve train never bothered me or any of the race folk.
There is also the add bonus of less side loading on the valve by the larger tappet clearance.

I think that the lift advertised by Piper is the valve lift with standard rockers.

Hence you need to divide by 1.3? before you multiply by 1.5.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I did think the lift was high, I will try that again with the adjusetd figures, still theres gonna be a fair old slab of lift there.

ahh, 11.7mm thats ok I did think 15mm was mental.