Stupid question about roller rockers

60Impala4Dad

60Impala4Dad

Well Known Member
First of all, I originally posted this as a stupid question about ROLLER rockers. What I meant to post was "Stupid question about higher ratio rockers". I have never went beyond stock ratios with roller rockers, and I know I must be missing out. Obviously by going with something with a higher ratio you will increase your valve lift across the board, but what are the drawbacks? Sure, you don't want to go too high if the combination doesn't match your engine. I imagine if you went mild with your cam and your heads/intake/exhaust can take more then it would be easier to increase your rocker ratio than swapping to a higher lift cam..... but what about when you are building a hot motor from the beginning? In that case, why would you go with higher ratio rockers instead of getting the cam grind that you want? Is it so that you can bump down to lower ratio rockers some day when you want to tone the motor down a bit?

Help me out here. I have some experience overhauling engines so I know what all the parts do, but I just think I am missing the boat when it comes to combining a cam change with higher ratio rockers at the same time.

Thanks.
Doc
 
cheap1

cheap1

 
Supporting Member 1
I asked the same question to a Comp Cams rep at a car show a couple of weeks ago. He told me that you would not see a noticable increase in power by making the switch even though you are increasing valve lift:dunno. He was probably just trying to sell me another cam. I'm curious to see what some of the other guys think.
 
Ronnie Russell

Ronnie Russell

Well Known Member
Supporting Member 2
Doc, There is some advantage to the quicker opening of the higher ratio rocker, but you would only see that on a dyno. Your logic is good. Decide what ratio you want to use ( 1.70 or 1.75 ) and then order the cam lift you need. JMO, maybe others have a different view.
 
Skip FIx

Skip FIx

Well Known Member
It all depends on the motor, heads and cam. My pump gas 455 Pontiac motor consistently picked up HP and TQ swapping from 1.5s to 1.65s to 1.8s on the intakes. About 5-8 hp a pop.Even used 1.33 break in rockers to not have to just use outer valve springs since it was a flat tappet.

A higher ratio rocker keeps the same seat timing because you are still on the no lift part of the lobe but amplifies the lift as it hits the ramp and lobe because you multiply the lobe lift by the ratio. In doing so it also makes the cam act as if it has slightly more duration at 0.050. Usually about 2 degree per 0.1 ratio as you go up.

Since stock for a W is 1.75. swapping to a 1.8(Comp,HS and Crower have some for 7/16 studs) or a more common BBC 1.7 may or may not have much effect since the ratio change isn't that much different.
Lots of the Super Stock guys are using 1.9-2.0 ratios. Newer GM LS series motors use a 1.8 and have 1.85 aftermarket rockers.

Down side you need to check for spring coil bind or retainer hitting guide or seal with more lift. Depending on the head the pushrod may hit the head at full lift. On SBC there is even a tool for cutting a deeper slot for that. Pontiac non RAIV iron heads and Edelbrock heads need to be clearanced for the increased ratios also. The reason it does that is the ratio is increased by moving the pushrod cup closer to the stud.
 
60Impala4Dad

60Impala4Dad

Well Known Member
Thanks

Thanks guys. I'm not in the middle of a new build at the moment, but it was one of those things that I needed information on to close the gap on rocker selection, etc. All good info.
Thanks again,

doc
 
jim_ss409

jim_ss409

Well Known Member
Supporting Member 5
It seems like higher rocker ratios help most on a fairly mild cam but if you have an aggressive cam that's designed for let's say 1.70's and you move up to 1.85's you may run into valve control issues at higher rpm's.
Unlike the small block Chevy with it's 1.50 rockers our engines have a good rocker ratio. (1.75) If you make sure everything's in order you can step up to 1.80's like Skip is doing but you also won't loose much if you stick with 1.70's or 1.75's.
By the way I notice that a lot of top engine builders often use a more aggressive rocker ratio on the intake and a less aggressive ratio for the exhaust.
 
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