Roller rocker ratio

[Bill D]

I will be buying the heads (Edelbrock Victor Jr) and the roller rockers soon. Would there be any benefit to going with a higher ratio on the exhaust to improve exhaust flow? My cam specs are .373 lift at the lobe. With a 1.6 rocker, my valve lift is .598. If I go with a 1.7 on the exhaust, the valve lift becomes .634. Duration is 230 intake and exhaust at .050. Induction will be 48IDA Webers.

Thanks
Bill D

 

[Chris Duncan]

IMHO .634 is pushing the limits of dependability. You need such a strong spring to return from that height it's hard on the valve train and seats. You'll need solid lifters and it will be even worse with a roller cam.

Another thing I ran across was a geometry discrepancy with AFR heads, not what you have but maybe something to look at on any brand. The geometry gave an effective ratio of 1.7 with a 1.6 rocker.

With any custom hi-po setup it's better to measure than just taking the specs for granted.

 

[Sandy]

Bill -

If the heads are ported see what the big gain might be from the lift change, i.e., at .600 and at .635.

The duration is not affected by rocker ratio, so just the lift difference would be the change in flow. Good to get the 1.6's as they are the "stock" and most cam grinds are good for them, get the cam that you want instead of patching it with rockers.

I would say the most important thing is making sure all the components are able to support it as Kalun mentioned, spring coil bind, piston to valve, etc. One of most important thing that is overlooked is the rocker geometry and using incorrect lengthed pushrods, especially with the aftermarket heads.

I have a set of 1.6 Comp Cams stainless 1.6 rockers with little use that you can try if you want, they are collecting dust.

Sandy