turbo SBC's... was RE: Thanks for the EFI! (off topic)

[Greg Hermann]

At 9:34 AM 12/17/01, Mark S. Riley wrote:
>They were legal. Rollers never have been in the "CUP" series. Problem with
>mushroom lifter camshafts are that they don't last very long. If you put an
>aggressive grind that will need valve spring to maintain control, then
>lifter and lobe life is very much shortened over "Normal" flat tappet cam
>grinds. Also the bottom of the block "must" be spotfaced to prevent one
>point of the lifter touching a casting tit or bump which breaks the foot off
>the lifter. Perhaps lifter float cause you were trying to run the lightest
>springs to cut down on drag and wear. Then the driver does something bright
>like turn it 9600 on a restart. Also they have to be shimmed front to rear
>against cam walk cause the opposite lobe will lift the wrong valve with very
>little aft to fore movement. Used to see pallets of Crane, Competion Cams,
>Cam Dynamics, Reed, and Crower Cams mushrooms at some of the local "CUP"
>shops. They couldn't run a cam and lifter but once. Wouldn't make two races.
>I use to buy the used cams and lifters and  run them in short track engines.
>Valve action with a mushroom can be more radical than a roller ever dreamed
>about. They just don't last long because of the loading. Oh, the lobes are
>thinner to help with the "crosslift problem" because of the big foot. The
>"CUP" stuff was cut for a 1" foot lifter. When Nascar outlawed the mushroom,
>they all went to the ford lifter size, .850" I think. Precisioneering in
>Asheville, NC does most of the lifter boring and registering for the teams.
>They have a factory type lifter boring machine.
>Duh, that's probably more than anyone would want to know about that "old"
>stuff. later, Mark

My thought is that with a turbo engine, get the power with boost and don't
turn it all that fast. MUCH more durable that way, overall, so long as you
avoid any sign of the devil detonation. Thus, the valve springs can stay
more like normal "hi-po" valve springs, since spring requirements vary with
the square of the rpm. This ought to cure the wear problem. Another thought
is to run a "hi-rev" spring kit in the valley--thus allowing slightly
lighter valve springs, and keeping some of the necessary spring force off
of the valves and rockers, at least.

No doubt, the thinner lobes contribute mightily to the wear problem, too.

There are plenty of HD diesels which use mushroom lifters, stock, without
wear problems. So did the IHC "Red Diamond" engines. (404/450/501 I-6's).
They all do it to improve BSFC under load. Of course, none of these are
high rev items, so the springs are reasonably mellow.

Point is that the wear/durability problem comes from the spring force used
trying to squeeze out the last few rpm, not  from the mushroom design
itself.

In my particular case, 1.375" diameter lifter feet will fit without any
cross lift problems, even with stock width (about 5/8" wide) lobes, and the
cam is properly and precisely located fore and aft in its stock condition.
5-3/8" bore centers on a V-8 and good basic design will do that sort of
thing for you !! :-)

Greg
>
>----- Original Message -----
From: "Shannen Durphey" <shannen at grolen.com>
>To: <diy_efi at diy-efi.org>
>Sent: Tuesday, December 15, 1998 10:44 PM
>Subject: Re: turbo SBC's... was RE: Thanks for the EFI! (off topic)
>
>
>> Greg Hermann wrote:
>>
>> > Don't know if they are still doing it for a "cheat", but I know some
>NASCAR
>> > guys were running mushrooms for a while. Rollers were against the rules,
>> > and the tech check was to stick something down the pushrod hole to see
>if
>> > the lifters would rotate. Mushrooms rotate ! :-)
>> >
>> Last engine I saw had Ferd lifters.  It's been a few years.
>>
>> Mebbe them lifters is like the gauges, they is either open or close and
>nothing
>> in between. ; )
>> Shannen
>>
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