adding 1.7 rockers will add more lift. If you want to know how much take the lift of your cam devide it by 1.6 example .500 (Lift) / 1.6 (rocker) = .3125 now take
.3125 x 1.7 = .53125 <---thats the new lift..... so you go from .500 lift to .531 lift. this is just an example as I do not know what lift cam you have. Everything basically stays the same but youll gain some power. Make sure that the valve springs are rated for the amount of lift youll achive.
don't really have anything yet, just trying to get an understanding of the relationships with lift before I start deciding on cams, heads, pistons, valve train, etc.
Stock springs are good to around .500 lift if you go beyond .500 you should upgrade your springs. You have to be cautious of Valve to piston clearance with high lift cams. My cam is the comp cams nx264 hr it is rated .512 with 1.6 rockers and .544 with 1.7 rockers. I have all stock bottom end and I run the 1.7 roller rockers. I have had no problems. I think the duration also plays a role in vtp clearence also because the piston is chasing the valve as it closes so its always a good Idea to use clay and measure the vtp. Hope this all helps
OK - just did some quick research so here's a scenario with info I got from Summit:
E cam with the 1.7 roller rockers - duration would remain constant at 220 (.050), but lift would increase to .529 from .498.
F cam with stock 1.6 non roller rockers - duration more than the E at 226 (.050) and lift at .512.
Questions: (Simple - assuming all other components equal and springs can handle up to .530 lift? in a carbed engine)
1. First, would the power band change by changing the lift specs with rockers?
2. Is it the same as having a cam with said increased lift?
3. Would it be benneficial in any way to have the above scenario?
The August 2004 5.0 Mustangs and Super Fords magazine that I just got in the mail last night has a very extensive article on this exact subject. I haven't read it all yet, but if you pick it up I think it'd answer all your questions and then some.
Great article from newcovenant. I will get the one from 5.0 Mustangs and Super Fords magazine and read it too. I just could not find exactly what I was looking for searching through older posts. From what I gather so far, changing the lift with rocker arms will not change the power band. Depending on the max flow for the head, raising the lift could help or harm the performance, but the power band would still remain across the same rpm's. So if there are no flow numbers for the heads, they should be tested. It seems that if one cam made up the lift to equal another that uses larger ratio rockers and the first one did not increase it's duration, there would be a greater tendancy for it to float due to higher ramp angles, thus it would have a lower usable top rpm. And if that is true, why don't we see more 1.7 rocker arms used with lower lift cams to achieve a target overall valve lift?