Rocker ratio for 399 stroker?

I'm looking for some opinions on which ratio rockers to use for a 399 stroker I'm gathering parts for. It's a 351w with a 3.85 crank, 5.596 rods, .060 over Hyper pistons, Edelbrock Performer RPM manifold and 750 carb,self ported smog heads with 1.94/1.60 SS valves, full length headers, and a hydralic flat tappet cam:Speed-Pro CS1231 -adv. dur. 290 int./ 300 exh., dur @.050 214/224 w/ 112 lobe sep. I can get a deal on some 1.6/1.7 ratio rockers, but I'm not too sure about that with a split cam. Not much $ diff between them, the 1.6's and the 1.7's though, so which of the 3 would be best for this streeter?

That's a fairly mild cam for a 399, but I would check your retainer/guide, coil bind and piston/valve clearances to verify what you can handle before smacking stuff together at speed. You might mock it up with stock rockers first, measure, then choose based on that.

David

I actually have a set of roller rockers that can be set to 1.6 or 1.7 , but they are steel and I don't like the looks of them, so I would only use them for mock-up or dyno runs. I'm too far away from putting this thing together to do a mock-up right now or I wouldn't need to ask. I'm not too worried about coil bind and I don't have any pushrod guides, so the main thing is piston clearance. With as small a lift as it is, I don't think that would be an issue either, but I don't know.

Lift dopes not affect the piston to valve clearance, the duration does. With those heads just run the stock ratio rockerarms, because it wont make any differance anyhow.

JOE SHERMAN RACING ENGINES

Originally Posted by BIGJOE

Lift dopes not affect the piston to valve clearance, the duration does. With those heads just run the stock ratio rockerarms, because it wont make any differance anyhow.

JOE SHERMAN RACING ENGINES

Ouch- Point taken. Thing is I keep finding 1.70, 1.72 and even 1.6/1.7 rockers more often and usually cheaper than the 1.6's, but I think I may buy some 1.6's from a FM member.

Originally Posted by BIGJOE

Lift dopes not affect the piston to valve clearance, the duration does. With those heads just run the stock ratio rockerarms, because it wont make any differance anyhow.

JOE SHERMAN RACING ENGINES

I don't think I will ever get you to build a race engine for me.
You must have failed geometry and maths at school.

with a cam lobe lift of 0.318
1.5 rockers gives you 0.477 valve lift
1.6 rockers gives you 0.509 valve lift
1.7 rockers gives you0.541 valve lift
Of course it changes the piston to valve clearance and gives you more power

Originally Posted by gordon

I don't think I will ever get you to build a race engine for me.
You must have failed geometry and maths at school.

I think his point is that duration of high performance cams has more effect on the relationship of the valves to piston clearance than lift, and you can run as much lift as you want as long as the piston is far enough away from TDC when the valve opens. Given no change in duration, higher lift would have to decrease the distance from valve to piston and I'm pretty sure he would agree with that. BTW-Gordon's math is correct, but I'm not sure what the point is. I think Joe's main point was that my heads were crap- which they are, but just like a bad kid- they're mine and I gotta love 'em and they probably won't be that bad for what I'm building.

the numeric duration only stays the same if you don't consider the amount of opening. Cams today are rated by the SEA duration spec of duration at .050" lift. The duration at .050" will change and so will the overlap. Since the valve lift is higher it will open further, sooner, and stay that way longer.
Finaly some one got it right, From one retired mechanic to another, thank you.