tr4a rocker arm ratio

[terry]

Can anyone tell me the Rocker Arm Ratio for the tr4a please.

i need this to check and verify the valve lift for my new Piper cam TR3BP285 Ultimate Road.

Terry

[AndyR100]

I believe std is 1.55:1

...... Andy 

[terry]

Thanks Andy much appreciated for that quick reply...will use that.

kind regards Terry

[Allan Westbury]

I have looked up rocker arm ratio so now know what is is but can anyone please tell me why it is important & how you use it?

thanks,

Allan

[AndyR100]

I'm sure someone will provide additional info, but my simple brain thinks of it as a simple translation of camshaft lift to valve lift - eg. the valve will be moved by 1.55mm for every 1mm of lift at the camshaft.

..... Andy

[terry]

Hi Allen.

this is how i used it....i measure with calipers the Nose to Heel of the cam which is 1.394 inches then i measure the Base Circle of the cam which is 1.109 then i subtract 1.109 from 1.394 and get 0.298",....for the actual valve lift in the engine i multiply 0.298 by rocker arm ratio 1.55 and arrive at 0.466" lift.which is very very close to the manufactures spec.

i did this check after a engineer from Castrol made a comment about the size of the lobes

 

  

[terry]

22 minutes ago, terry said:

the base circle reading should be 1.096 and not 1.109"