Questions for the Cam Grinders Hydraulic Rollers

[Ron Miller]

This question is for aftermarket ground, not OEM SB & BB Chevy hydraulic roller cams. Is their a limit on an increase in rocker ratio? It looks like most cams are ground for 1.5 (sb) & 1.7 (bb) ratios. With an SB, can you use a 1.8 - 1.7 rocker combo? With a BB, can you use up to 1.9 ratios? I've always wondered about this. Can cam or lifter damage happen or accelerated wear? Fire away good or bad.

Thanks for looking,

[PackardV8]

Too many variables for an answer:

Steel billet or iron cam?

What RPM?

What profile?

What spring pressure?

Whose lifters?

[Stan Weiss]

The velocity and acceleration of the lifter / lobe is known at design time. The velocity and acceleration of the valve will increase with RPM but it will also increase at the same RPM with an increase in rocker arm ratio. At 7500 RPM with a 1.65:1 rocker arm ratio you will see the same peak velocity as a 1.8:1 rocker arm ratio at 6875 RPM. How does that change the spring needed to run the same RPM with the higher ratio?

Stan

[Geoff2]

The cam lobe doesn't know what the rocker ratio is at the other end, the lobe only knows the force generated by the spring/rocker ratio. If the spring tension is sufficient to maintain valve train control at max rpm, don't see a problem with high[er] ratio rockers. I understand nascar engines are running 2+ rocker ratios.

[Walter R. Malik]

When using a HYDRAULIC roller lifter and lobe combination in any application, it is better to get as large a cam diameter as you can get for the most lobe lift and use the lowest ratio rocker arm you can use for the end valve lift you want.
You are not always able to do that so, testing THAT particular application can be the only way to go.

[CamKing]

Not only can you not increase rocker ratios with some Hydr roller profiles, some Hydr roller lifters can't handy an increase in to let ratio. The higher the force put on the Hydr lifter, the quicker the Hydr unit will collapse. Force on the lifter plunger is mass and acceleration, and both are increased with an increase in rocker ratio.

[Ron Miller]

Guys,
Thanks for the replies and info. So, increasing the rocker ratio on hydraulic roller cam should not be a big deal whether its a cast or steel core. This will be a catalog grind, not a max effort deal nor did I even consider using a stock lifter. I have a set of Comp Cams 1.8 & 1.7 I want to use on my next build with a hyd roller cam. This will be a street beater that might see 6800 rpms max.

Thanks Again,

[Walter R. Malik]

I understand nascar engines are running 2+ rocker ratios.

They never used HYDRAULIC lifters in NASCAR ... that is where the issue lies with using higher ratio rockers and multiplying spring force more to the lifter button and hydraulic mechanism.

[KnightEngines]

Tried it, doesn't work!
Lifters bleed down too early.
Only way I can see it working is with a light valve train (Ti valves etc) so you can back off the spring pressure to keep the lifters bled up.

Just run a street solid roller.

Or, if you already have the hyd roller cam run solid lifters on it at tight lash (like .006-.008" tight)

[CGT]

I have done a decent amount of rocker ratio dyno testing with hydraulics on the dyno. Its definitely a balancing act...lobe intensity, spring pressure, and weights. Increasing ratio is mulitplying spring force to the lifter plunger also.(collapse)..adding spring pressure to stabilize things can make this even worse. Like Knight mentioned, lighter stuff and less pressure (or less rpm) is what it takes if your serious about it.

I've run heavier components to 7500 with 1.7 ratio on a hydraulic roller sbc, but thats with some farely calm cam lobes. But I could have probably gotten to the same place rpm wise and "area" wise with less ratio and more agressive lobes truth be known. And regardless of ratio, just because something revs up and doesn't audibly miss doesn't mean your valve is seeing all the cam lobe...especially with hydraulics

[Walter R. Malik]

I have done a decent amount of rocker ratio dyno testing with hydraulics on the dyno. Its definitely a balancing act...lobe intensity, spring pressure, and weights. Increasing ratio is mulitplying spring force to the lifter plunger also.(collapse)..adding spring pressure to stabilize things can make this even worse. Like Knight mentioned, lighter stuff and less pressure (or less rpm) is what it takes if your serious about it.

I've run heavier components to 7500 with 1.7 ratio on a hydraulic roller sbc, but thats with some farely calm cam lobes. But I could have probably gotten to the same place rpm wise and "area" wise with less ratio and more agressive lobes truth be known. And regardless of ratio, just because something revs up and doesn't audibly miss doesn't mean your valve is seeing all the cam lobe...especially with hydraulics

Exactly !!!
When using high ratio rockers with roller hydraulic lifters in competition it is standard practice to use much more spring pressure than needed and then set the lifter plunger at .010" less from bottoming out.
I sure wouldn't want to do that on an everyday application.

[smeg]

The cam lobe doesn't know what the rocker ratio is at the other end, the lobe only knows the force generated by the spring/rocker ratio. If the spring tension is sufficient to maintain valve train control at max rpm, don't see a problem with high[er] ratio rockers. I understand nascar engines are running 2+ rocker ratios.

Sorry, it isn't as simple as that, as TK say's the lifters bleed down all hell breaks loose, seen it many times on the pump. You can shim the Hyd rollers to around .020" travel, that helps a lot.

[MadBill]

The cam lobe doesn't know what the rocker ratio is at the other end, the lobe only knows the force generated by the spring/rocker ratio. If the spring tension is sufficient to maintain valve train control at max rpm, don't see a problem with high[er] ratio rockers. I understand nascar engines are running 2+ rocker ratios.

Sorry, it isn't as simple as that, as TK say's the lifters bleed down all hell breaks loose, seen it many times on the pump. You can shim the Hyd rollers to around .020" travel, that helps a lot.

Many speculate that the often-reported short life for high lift solid rollers on the street is largely due to the stop/start rotation resulting from lash. Seems like using an ultra-fast bleed near-bottomed out/short travel hydraulic on a solid roller cam would address the issue. (Or maybe, a hybrid lobe combining short/no ramps of a hydraulic lobe with the overall aggressive very high lift profile of a serious race roller..)