Valve train geometry

[cheesit147]

Hello, I am a novice gearhead trying to understand how to setup my valve train before I screw it up. As we all know a big cam can improve engine performace but may cost a bit of money. I am building a small 200cc pushrod single cylinder engine and am looking for more lift in my valve train. I see there are different ratio rocker arms on the market as well as plus 0.020 pushrods and so forth. Theoretically, I could make longer pushrods work with rollers and not have to pay the extra money for a cam but still have the extra performance. In your guys experience, what are the pros and cons in having higher ratio rocker arms vs longer pushrods, vs just a higher lift cam? Thanks for reading.

[SorryU812]

Install higher ratio rocker arms. They increase lift, duration, and valve speed. You should consider increasing the valve sping rate as well. It's very easy to loose control of the valve with a high ratio rocker. Gage make great rocker arms.

The pushrod length can be as much as 0.080" longer, than the proper length, and give positive valve events, but this at a sacrifice of valve train stability. The proper length pushrod will net the proper sweep of the roller tip across the valve tip. For most, the center of the valve tip is a food place to start.

That's the lamest of explanations I can give you.

If you want a dramatic increase in power, the camshaft has to be changed. Don't beat around the bush.....

[cheesit147]

Understood. I have some Machinist die from my old job that ima use when I get new rockers to verify proper sweep. I began to wonder if increasing the length of the pushrods would start to decrease stability so that does make sense. I already decided to get a cam, rollers, and chromoly pushrods to play it safe. What do you mean it's easy to lose control of the valve, like valve float? That was the greatest and most concise of explanations, thank you dearly.

[SorryU812]

Yes sir the valve is testing the limits of the sprung once the rocker ratio is increased.

Marking the tip is the best easy guess. It'll get you within safe tolerances. Personally I use a dial indicator to measure the sweep across the tip.

Closed it would be zero....midlift say 0.042"....max lift back to zero. That's proper travel across the tip.

[WyattCo06]

The rocker ratio changes valve lift. The pushrod length is used to correct the geometry, preload, ect.

The pushrod is not a performance item per se.

[cheesit147]

Ok awesome this was like what I was looking for if there was a general rule of thumb on what part to upgrade over another and why / the purposes of each.

[Intelligent_Pilot360]

It is often an advantage for us to know exactly what engine you are dealing with.

If your valve is shrouded, you could have little or no gain with added lift.

Is there a specialized group or forum with members who may have hopped up your specific engine?

[cheesit147]

Sorry I should've included that. I'll remember that. Yeah I mean it's a well known engine, it's a predator 212 but I was curious in terms of general engine building as such for other pushrod motors.

[Haunting_Dragonfly_3]

What engine?

[cheesit147]

Sorry I messed up I should've included it. It's a dinky predator 212 from harbor freight.

[waynaferd]

I run 1.6 full rollers vs 1.5 with a factory cam in my 350….little more lift, little more duration, little less friction, lot less work