Frank, Ted, thanks for the explanation, I didn't think there would be much [street] advantage in it other wise everybody would be doing it. The thing you have to do to get a scrubs to run properly!!!, although I did think to myself now those 1.4,s off the spare motor in the cupboard, I could.........

Pete, one of the Aussie mob. Beechworth, Victoria60 F100 Panel Van, Y-block. 65 Galaxie Country Sedan 390

Here’s simply adding to what Frank said.

Varying  the rocker ratios between the exhaust and intake valves is common practice on racing engines and is done as a compensation for a camshaft that isn’t exactly what the engine is wanting.  There is no set rule as it varies from engine to engine depending upon head flow, intake manifold design, camshaft specs, exhaust sytem, etc.  I’ve seen where a 1.2:1 ratio was beneficial because the camshaft was such a mismatch in its partiuclar application so it just depends upon the individual combination as to what the engine likes.  What works for a higher ratio on the intakes on one engine may end up being a higher ratio on the exhausts on another engine.  Every combination is subtly different.

 

You can experiment with the 1.43 and 1.54 rockers and potentially find an advantage depending upon your combination but these changes are typically small and usually found on a dyno, not seat of the pants testing.  Most cams for the Y will like as much ratio on both valves that you can throw at it though due to most camshafts for the Y being on the mild side.  Another item to check is to measure the actual lift at the valve to insure that the ratio is as advertised as there is some error or tolerance in the rocker ratios and also some variability in the ratios depending upon where the adjuster is residing once the valves are set.  As a rule, a ‘high’ adjuster is a higher ratio while a ‘low’ adjuster is a lower rocker ratio so you could in effect simply change rocker ratios by changing the length of the pushrods.

 

And it’s way too early in the morning to be this deep in thought.

Lorena, Texas (South of Waco)

Pete,

                   This is usually done to avoid replacing a cam that's too small on on lobe or the other. If the motor needs more exhaust lift/duration, you simply put a higher lift rocker on that side. If you do it, watch out for Coil bind  unless you change springs. Might want to check the piston to valve clearance too. This is not usually a problem since you don't really gain all that much. What happens is obvious, the valve moves further with the higher lift rocker arm.   

Frank/Rebop

Bristol, In ( by Elkhart) 

Was reading an engine build-up article [chebbie] the other day and the builder was going to use two different rocker ratios, 1.6 inlet and 1.5 out. Is this common? why would this be done and what are the advantages, if any? would a special cam be needed to match this set up? If there is an advantage could a Y run 1.5-1.4? 

Pete, one of the Aussie mob. Beechworth, Victoria60 F100 Panel Van, Y-block. 65 Galaxie Country Sedan 390