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

clayb clayb at sbcglobal.net
Thu Dec 20 02:39:49 GMT 2001


> 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)

> I spoke to the place in Maryland today. He did not think that the mushroom
> cam/lifters was an idea he would like to see in my car. He suggested that I
> use a flat tappet cam. Guess he thought the $$$$ for a roller would not pay
> very big dividends. Had some interesting ideas about many things, many of
> them seemed directly apposed to what I have come to feel is the norm. One
> thing for sure, I need to make things as sure as possible with this part of
> my upgrade. Toooo many benches full of parts. Toooo many new changed and
> untried systems on vehicle.
> 
> Anyone have opinions of roller cams vs. flat tappet?
> 
> Other than the dollar figure, I thought rollers had thing covered hands
> down!

Rollers are great, especially if you want high RPM and a broad
powerband. Downsides are: high spring pressure, wear, and semi-regular
replacement of the roller lifters. If you want the last ounce of power,
and are willing to replace lifters every couple years, you'll get power
out of them.

For long life and good performance, a mechanical flat tappet is the way
to go. Mushroom lifters aren't real practical in a block not designed
for them. The .850" Ford lifter would be a reasonable try at improving
lift rate, if you could get the machining done cheaply enough (not!)

As you're doing a turbo engine, the flat tappets make even more sense.
The more conservative cam timing dictated by a turbo will limit your RPM
anyway. Turbo engines (at least non-VVT) make power with boost, not RPM.

- Clay

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