mushroom lifters

[lyonsy]

ive herd a bit about these latly of old school guys.
apparently they allow you to run lots more spring presure with out choping cam's out due to increased surface area.
anyone herd of them?
drift

 

[addo]

Many older motors ran mushroom-headed tappets. Y-blocks are one I can think of straight away, also the Ford sidevalve four used in Tens and such.

They greybeards are sort of right - pressure is force divided by area, so increasing the area allows you to increase the force without so much pressure the metal gets grated away. But you'll still need over-duty valve springs...

 

[rickwrench]

They let you run a much steeper cam profile, not quite roller cam profile, but close. The wider lifter head lets the steep cam ramp roll underneath without the lifter edge gouging into the cam lobe face. They were the hot ticket, right up until roller cams. They are a pain to load into the bores. Cam out, engine inverted, load lifters, re-install cam.
Rick(wrench)

 

[StrangeRanger]

Standard equipment on a Ford "Kent" 1.6 litre

 

[lyonsy]

so does anyone do them anymore for clevland/250xflow or are the xflow lifters the same as log 250 as well?
so with mushroom lifters id be able to have a faster opening soild cam then say a regular soild cam which is better again over a hydrolic cam?
drift

 

[80broncoman]

I don't have a clue who runs this combnation.
Hyd or solid has nothing to do with the rate of lift.
Just the dia of the bottom of the lifter determines the max rate of lift.

 

[worken2much]

The greybeards also developed them for another reason. The larger diameter lifter on the same lobe profile opens the valve earlier and closes it later. Much like having a higher performance cam without changing the camshaft. The total lift doesn't change, just the duration. In a class racing situation an engine equipped with an approved cam and mushroom lifters would have an advantage over an engine with "stock " diameter lifters and the same cam profile.

Worken2much

 

[Lazy JW]

There is a limit though. Stock lifters on air-cooled Volkswagens have such a large mushroom that the outer portion of the lifter never gets touched by the cam. Never could figure why they made them that way.
Joe

 

[addo]

Inertia? Might have been to dampen potential harmonics, or reduce the chance of valve float. Wondering about cooling, too.

 

[80broncoman]

There is a limit though. Stock lifters on air-cooled Volkswagens have such a large mushroom that the outer portion of the lifter never gets touched by the cam. Never could figure why they made them that way.
Joe

Maybe it was a real pain to bore the holes for the lifter Exactly where they were supposed to be.

 

[Anonymous]

Lifters used in NASCARS, AKA Freak cars, are Mushroom styled.
Ken

 

[80broncoman]

Nascar outlawed them in the 80's In the early 90"s they let all teams run a max dia of .875 lifter.

 

[Anonymous]

"The larger diameter lifter on the same lobe profile opens the valve earlier and closes it later"

No, doesn't affect the duration at all. What will increase the duration is if the new tappet has a larger contact radius. A longer surface with the same radius = no change. A longer surface with a smaller radius = reduced duration.

"pressure is force divided by area, so increasing the area allows you to increase the force without so much pressure"

No, the contact area is exactly the same.