[big_gto]

Anyone mixing rocker arm ratios between intake & exhaust? HPP, HO Enterprises had an article on this back in the `90's. Installing 1.65 on the intake & 1.5 on the zaust. seems like the 400 didn't need the added zaust lift.

[Steve C.]

I have 1.65 ratio on the intake side and 1.6 ratio on the exhaust side on my T&D shaft system. It was set up that way years ago for the cam choice on a 700 hp combo. Today it's installed in my 505 street motor and it was left as is. The intake and exhaust lobes on the cam have the same .4300" lobe lift, thus less lift on the exhaust.

Interesting comment.......

"If you are going stupid high lift on the intake it doesn't make sense to do the same thing on the exhaust. The intake valve wants the max lift at the max port depression and velocity, so it makes sense to give it more there. The exhaust on the other hand has peak pressure at low lifts when the valve is open so high lift exhaust flow really doesn't do too much for you."
http://speedtalk.com/forum/viewtopic.php?f=1&t=2183

And on the Performance Trends Engine Analyzer program it suggests the input for the exhaust cfm flow be input at a lower valve lift than the cfm input for the intake side. The amount is based on a percentage of the intake inputs lift. I'll try and look it up to be sure, unless someone here can comment.

I looked- The prograns exhaust input is at less lift but it has to do with the valve lift (and corresponding CFM flow) as close as possible as practical to one fourth the valve head's diameter.


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[Skip Fix]

I have 1.8 Crowers on the intake and 1.7 HS on the exhaust of my pump gas motor.

I also have a reverse split cam(more intake duration and lift) in my RAIV motor that does similar and added a little more duration it liked.