I'll be using a set of heads for next race season with 1.94 /1.50 valves. The heads I used this year had 1.84/1.50's. I'm planning on installing some roller rockers this winter, and was considering putting 1.6's on the exhaust and 1.5's on the intake. The reason being as to make up for the small exhaust valve since the new heads have 1.94 intakes.

What do you guys think about this.... I dont want to go into whether roller rockers are worth the $$ or not, but rather if the 2 different sizes will be good/bad/indifferent.

 

It will help alittle, what cam are you going to use?

 

If you can spare the lift, I would just toss 1.6's on both sides (assuming nothing radical for the cam).

 

Hey, I would only use the 1.6/1.5 combo if you are running a single pattern cam (IE. LPE cam or a TPIS ZZ-409). I had a 355 with a split duration cam and tride that combo, I later got some 1.5 rr's for a good price and picked up an extra 2/10's on my et with the switch, I was runing heads with 1.90 int and 1.50 exh. Any how, good luck with your engine.

 

I have a pretty mild cam. .442/.465 214/224@.50 Its the same one that took the car to the 8.34 pass with the 305 heads.

I had thought about running all 1.6's but wasn't sure if I'd have some power left to gain since the exhaust lift/duration would still be equal to the same ratio as it would be with all 1.5's. (if that makes any sense lol)

But then again, the split duration cam might make up for it by itself anyways possibly?

 

No that makes no sense, but i know what your talking about. 1.6 ratio will increase the lift and also the duration, making the valves think that a more radical cam was installed.

 

I'm with stupid ^^^

In all seriousness though, what he said is exactly true.

 

The duration will really only change ~2-3* @.050" lift. That's not enough to make that cam act very different. The overlap will also increase a tad, but not enough to effect things with 112* LSA, which I suspect that cam has based on the common specs you've given.

The lift will only help though, if you have the clearance. But as said, 1.6 on both would help more than 1.5 on all, and more than a 1.5/1.6 combo.