[JUDGE3]

I recall a test in hpp via Pete Mcarthy where an engine improved a lot using 1.5 on the intake and 1.65 on the exhaust.

[Skippy597]

Do you remember if it was a single or dual pattern cam.

I would think that on a single pattern cam you would not use 1.65 only on the int, but on either both or none or possibly just the exhaust. Especially on lower flowing heads to.l make up for a poor int/exh flow ratio.

[Jay S]

Originally Posted by Skippy597

Do you remember if it was a single or dual pattern cam.

I would think that on a single pattern cam you would not use 1.65 only on the int, but on either both or none or possibly just the exhaust. Especially on lower flowing heads to.l make up for a poor int/exh flow ratio.

Just chasing after HP or ET swapping rocker ratios often do not work out how you think it would. You don’t know what the engine wants until you try something different. Sometimes you pick up or loose HP by a rocker change because something else in the combo is the driving factor, and goes completely against what the E/I splits of the heads and cam would indicate. For example one of the guys on this board was running a reverse split cam (249* intake, 233*@.050” exh) on some highly ported 340CFM round ports with 1.65s on the intake and 1.5s on the exhausts. On the dyno he tried a 1.6 rocker on the exhaust and lost 20+ HP on the top end. I am not sure what caused that, but he would have never caught that if it wasn’t tried on the dyno. They obviously thought they were going to gain power, or they would not have tried it.

I like mechanical cams where you can adjust the lash and get an idea of what the combo is wanting. If it picks up HP or ET with tighter lash on intakes, exhaust or both, it probably will like bigger rockers. . Not to often do you find an engine that responds to tight lash on the exhaust side, but finding HP with loose lash on the exh, it likely will respond well too a smaller rocker on the exh.

[1968GTO421]

My thanks to Skippy597 for starting this informative thread and thank you to all who have posted here. I have several different cams on my garage shelf and now think I should also carefully think about rocker arms and their ratios in determining which cam to use.

[Schurkey]

Originally Posted by 64speed

I am running 1.7 BBC Chevy Rockers on mine. Seem to be doing ok. Made that 60919 Crower a little rowdier

I'd have expected geometry problems.

Stamped-steel OEM rockers? Roller-tip aftermarket rockers? Full-roller aftermarket rockers? What brand/model?

Contact at the valve tip reasonably centered?

What pushrod length did it need?

What heads are those on? Need to grind the pushrod hole for clearance?

[Skip Fix]

Since BBC rocker bodies are 0.120 longer trunnion to rocker stud hole than a Pontiac I would also. I have Crower 0.090 offset 1.8 rockers on my pump gas motor and I had to use a lash cap and a 0.200 shorter pushrod than the HS rockers to get a decent pattern on the valve tip.