johhnymopar!thanks,just wondering if the extra lift can also help in the low end to some degree?,and what difference to the overall torque/h.p. figures they would make percentage wise?i know this is a broad band here but just curious if someone has some ballpark figures.
Be Carful!ON pontaic's you can't just stick 1.6
in where 1.5 were, to much angle and holes in head do not accomadate angle without work before hand. Don't know about chevy's for sure . Ron
where are you?Bet he knows.Look forward to following this
The larger ratio rocker will primarily affect the amount and not the timing of the valve opening. It will be noticeable at that crossover point where the lower lift rocker begins to suffer from lack of air volume. The larger valve opening allows for deeper breathing. Having said that, it acts like a cam with a longer duration, particularly on a motor which suffers from lack of good flow at higher rpms. I think you would get better hp from the larger rocker, but may not feel much at the lower end. Maybe some but not like at higher rpms. You can't just use them without doing the math however because some heads will not support the added lift for a cam sized to the max already for 1.5 rockers, so be careful.
f1rodder,howdy! ihear you, and the rest of you guys too!thanks.pontiacman,the rockers will clear on the 350 chevy,no sweat.the heads are gm stock castings with some valve/port/polish action, and should benefit from a little additional time to breathe.are they worth it?maybe to small a difference to matter,jimm
Jim: if you are asking if you should port your heads, you need to tell us what heads you have. For instance, if you were to port GM fast burn aluminum or L31 Vortec heads, you would acutally hurt the flow....
f1rodder,howdy!, the heads are gm castings w/155cc runners ,76cc chambers,gasket match intake and ehaust with add'l porting and polishing on the exhaust.the cam is neither wild nor mild [226/[email protected],480/498 lift].am i correct in my thinking that 1.6vs1.5 will yield approx. .030 more lift? also what is the math?as you put it, regarding use of one ratio vs another? thanks a million,jimm
One thing I didn't see mentioned above is you need to make sure your springs can handle the added lift. Coil bind will ruin your day and your cam. Since it is a 350 Chevy I doubt you will have any valve to piston clearance problems. I also agree 1.6 rocker will not help low end (if anything it might slightly suffer), you basically just put a larger cam in the engine by switching to the higher ratio rockers. I run 1.6's on my set-up but it was built with that in mind. If they are going to help it is going to be in the mid to upper rpm range.
Remember to check for coill bind on the inner and outer spring as well and the dampener. Also check for retainer to guide clearance.
Typically the exhaust port on SBC heads are the weak spot, so it in normal to see people run 1.6 on the exhaust side and 1.5 on the intake. This is to help get more flow out of the exhaust. This serves the same purpose as a split pattern cam (more exhaust lift and/or duration). It can help power output IF the exhaust port is the bottle neck. It really depends on the combination of which works best. Sometimes trial and error are the only way to see what works and what doesn't.