Difference between a HYD and SOLID Cam

[mcfly94 169]

Hey guys so what are the main differences?

Like what do you need to run a solid or why would you even go solid?

[gerg 10,871]

Hydraulic: street

Solid: race

 

There's an overlap between the two where you could have a racy hydraulic cam or a street solid, but the general rule is that solids are for higher rpm levels that hydraulics won't handle. Conversely, hydraulics are used on street engines because they are zero maintenance, quiet and are gentle on the valvetrain, sort of like a shock absorber. They normally last the life of an engine if used in mild applications.

 

If you want to know the reasons for either then you'll have to go right back to the start.

 

The valvetrain needs clearance between the rocker and the valve to allow for its expansion due to heat. If it was set up at zero cold, under heat the valve (especially the exhaust) would actually hold itself open, allowing gases to escape and you'd eventually burn out valves and seats. So to allow for the expansion, the clearances are often set when cold (some may be hot-set) and almost always the exhaust is looser than the inlet. An example might be 0.008" inlet and 0.014" exhaust. This is on a mechanical or "solid" valvetrain. This has to be checked and adjusted at regular intervals to allow for wear in all of the valvetrain components, eg every 20,000 km.

 

A hydraulic setup gives effectively zero clearance as the gap is taken up by oil pressure feeding into the lifter and filling a tiny cylinder inside. It also allows for wear on the valvetrain. As the cam comes onto lobe, a tiny valve inside the lifter shuts off and oil is trapped inside, and the lifter becomes pretty much solid. You might ask why the valves don't stick open when hot, due to the zero clearance... Well the litters have a very small amount of leakage so that they're always constantly pumping up and leaking back down to maintain the zero clearance.

 

Which brings us to why they don't like big rpm. At high speed, the lifter can actually start to leave the back of the cam lobe due to the valve spring not being able to push back enough and keep them in contact. The hydraulic lifter now sees that split second of no load as a clearance, and oil is pumped in to take it up. Then you have negative clearance.... And valves stuck open. That's what you call lifter pump-up. Ever thrashed your hydraulic-cammed engine for a while and noticed it running like a hairy goat afterwards, then come good again? That's the symptom right there. Pumping up and slowly bleeding back down again.

 

So then you install heavier valvesprings to cope with the rpm but there's a point where the internals of the hydraulic lifter can't cope with both the higher spring pressure and the high rpm loads.

 

Enter the solid lifter... It solves all those problems at the price of higher maintenance and (slight) noise.

 

Hydraulic cams can have a more aggressive ramp because the lifters have a fluid cushioning effect. Solid cams need a more gentle ramp because there is no cushion. What you give at one end, you get at the other. For this reason, neither type can interchange, unless a very particular application requires it.

 

Hope it all makes sense after all that.

[Clevo120Y 815]

Hyd is less maintenance, pretty much a set and forget. Solid requires regular lash setting checks, they perform better, allow a more aggressive cam profile to be used and in turn allow an engine to hit higher rpm. You can't be lazy with a solid if you want the engine to last. Hyd is more forgiving, as long as you have some preload on the lifter it will be fine, a hyd lifter runs on a pocket of oil in the lifter which absorbs the shock somewhat between the cam and the valve spring, that is why you don't have a lash setting, the rocker arm is always in contact with the valve, this makes them run quiet, a solid makes noise as there is a gap "lash" between the rocker arm and valve so it "taps" the valve every time it is opening making the "ticking" sound you hear with a solid cam. You can still get great performance from a hyd cammed crossy and not have to worry about it.

[Clevo120Y 815]

Typing at the same time LOL

Your explination is better than mine

[gerg 10,871]

Typing at the same time LOL

Your explination is better than mine

 

Yeah freaky! Nah yours is nice and short... I tend to crap on a bit. Explaining this shit is like therapy for me

[Clevo120Y 815]

At least we said the same thing, that would have been awkward hahahaha

[bear351c 10,273]

Yeah.........what they said. ^ ^ ^ ^

 

Great explanation guys.

[xeeclipse 37]

SOLID: Skitzo engine that doesn't get driven

 

HYDRAULIC: Daily run around and the logical choice.

[slydog 7,873]

Some basics are a solid cammed engine doesnt like to sit around idleing as it destroys the camshaft and lifters,enter the EDM lifters with oil squirters in the contact face.But basically a hyd cammed engine = every day and a solid is weekend toy but a roller cam does both worlds better.

 

Just throwing it out there...

 

P.S another way to look at solid v hyd is about $500 or so.

[Thom 6,654]

Solids can be used in daily applications (most cars ran solid cams up until the mid 60's) but a hydraulic is more maintenance friendly, now days I wouldn't use a solid cam in a daily unless I wasn't doing many k's (even then I would still think hard about it before I did so)

[bear351c 10,273]

Mmmm.............Roller cam.