Rocker Arms Ratio

[jikelly]

I've got a set of roller rockers on my 351w that are a bit worn with like 80 thousand miles on them. They need to be replaced and I'm thinking about replacing them with a set of 1.7 ratio roller rockers.

Do you think I will have clearance issues?

Is it worth the gain in lift?

 

[D.Hearne]

The difference in lift is .030. Only if your springs are maxed out in lift now will you have a problem with coil bind. Ditto on the valve to piston contact if you have a really big cam.

 

[jikelly]

My springs should be fine. I know they worked with a much higher lift comp 268x cam before.

I went with the Trick Flow Stage 1 cam that gives .499/.510 with 1.6 roller rockers.

The higher ratio rockers will open the valves quicker and bump up the lift to what?

 

[D.Hearne]

Add .030 to the lift you listed. .499/.510 goes up to .529/.540 You're running a roller 351W right ? If so have the pushrods ever been replaced ?

 

[jikelly]

Add .030 to the lift you listed. .499/.510 goes up to .529/.540 You're running a roller 351W right ? If so have the pushrods ever been replaced ?

I bought new pushrods when I put that motor together. Yeah it's a roller block. It idles fairly well. This time around I wanted to go with a milder setup looking to increase my mileage. Didn't really improve much though.

If I were to mill the heads I bet I could bump up my mileage and power output. Don't know about that though. I'd like a set of aluminum heads, but money is going to be tight tight from here on out. I can't even make this month's SCCA autocross. Not without my wife beating me.

 

[bnickel]

my calcs show the new lift would be .530/.542, basically no change from D.Hearnes but slightly more precise..... also the 1.7 rockers will have a small effect on duration too so you may notice a slightly more burbley idle too.

milling the heads will have an effect on power and mileage because of a bump in compression. however i'm not sure how much you could ump the compression and not have detonation issues. generally you'll be good with a 10:1-10.5:1 or so on pump gas, though with your iron heads i'd shoot for closer to 10:1 or so. you might be able to get away with 11:1 or so on pump premium with aluminum heads. if we could just get E-85 around here you could get away with 11:1 or even higher with iron heads

 

[D.Hearne]

If you really want a mileage increase, a switch back to the factory roller cam that engine came with is what you want. Combined with the 1.7 rockers, it's an outstanding cam for smooth power and mileage and the closest you'll come to having EFI performance with a carb.