rocker ratio

[Anonymous]

Can someone tell me in simple terms what changing rocker ratio's does. I kinda have an idea but how do you measure it. On a stock cam if I go from 1.5 to a 1.6 , what does that really do to my stock cam. This is not on a 300 motor either. Hence the wrong ratios. Does it just turn you cam up a notch? And will you have to re-time the motor. How do you know how much there as well.

 

[Anonymous]

The rocker ratio acts as a multiplier on the lift ground into the cam lobes. The bigger the ratio, the more added lift.

Example- if a cam lobe has 1" of lift at the cam, a 1.5 rocker ratio translates to 1.5" lift at the valve. A 1.6 ratio would increase that lift to 1.6". Obviously, nobody uses a cam that big, but 1" makes the math easy.

You can alos work the math the other way. If you know the lift at the valve, and the rocker ratio, you can calculate the lift gorund into the cam.

By changing ratios, you effectively increase the lift on your cam. It will behave like a bigger cam without actually performing a cam swap. I don't know anything about re-timing the motor or not. I haven't made this mod to my 200 yet, but it's on my list.

Some more information can be found on Fordsix.com or on the tech descriptions at Fordsixparts.com. It probably does a better job of explaining it, too.

--mikey

 

[Anonymous]

i just bought an 89 Isuzu Trooper and it has a 2.8 chevy v6. 60 degree motor. Instead on putting in a bigger cam for now. I can get a 1.6 rocker over the stock 1.5 rocker. I know it would be cheaper and cost less than the cam change. just valve cover gaskets and the new rocker arms. Where as in a 60 degree motor, you have to remove the heads and all to pull the cam. So later if I still wanted to change cams I would have to buy a smaller cam because the ratio would already enhance it.

 

[Anonymous]

Make sure to check things like valve clearance, coil bind on the valve springs, & push-rod length. i don't know if any of these would jump out to bite you, but it's smart to check.

There's something nagging at my mind that thinks it's not _that_ easy, but i could be mistaken. Check everything out before you buy parts. Old man Murphy lurks in strange places.

And, if it ever has to be smogged, the increased lift will probably increase emissions, too.

--mikey

 

[Anlushac11]

8)

Another way to think of it in case your still confused?

A cam lobe might measure .235". You then multiply that times 1.5 for the mechanical ratio of the rocker. At the valve you now have .352" of lift. If I now decide I want more lift at the valve I can install 1.6 ratio rockers. Now multiply .235" times 1.6 and you get .376" lift at the valve.

On a V8 higer ratio rockers are a little bit more expensive. For our inlines sixes they are an arm and a leg.

 

[Anonymous]

for this 2.8 they are $120 . Which is what the cost of a good cam is. But you don't have to tear into the motor. What all do I need to check into to see if this is gonna work. I mean it is a stock cam. I am sure its an economy grind. the valve springs in my ford 2.8 were rated to .0450" stock. So you would think this chevy 2.8 would be close to the same.

 

[StrangeRanger]

The problems you encounter are going to vary from engine to engine. What causes trouble on a Ford 300 may not be an issue on a C***y V-6 and vice-versa.

Things to look out for in general:

1) either overcompressing or binding the valve springs. The first will lead to reduced life, the second to destruction.

2) Peening of the valve stems and keepers due to the higher loads.

Both of these are solved with aftermarket components: high lift springs and hardened keepers.

3) Pull out of pressed-in mounting studs. Cured by replacing with screw-ins

4) Binding of the pushrods in the guide slots in the head. Caused by relocating the upper end of the pushrod. Requires machine work to open up the slots and/or add pushrod guide plates.

5) Different length pushrods required to maintain the desired valve train geometry.

6) Overstressing the timing chain/gears due to the increased loads. Cured by substituting aftermarket parts.

7) Oiling problems if the high-lift rockers are not designed specifically for your engine

Did I miss anything?