Hey guys. Wanted to get some insight from those who have done it or done similar or just know - will I "have" to get +size pushrods for a ZZ4 cam install into my stock '87 L98 350 with stock heads (heads are having K-motion springs/10 degree retainers/10 degree locks/guides milled/studs screw-in/seals postive). Also, same goes for the stock rockers - any problems anyone has seen? Wanted to get some insight and experience, preferebly, from those who have done and/or know - would be great. Thanks!



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1987 Trans am GTA
5.7 liter TPI / 700R4
Aus 9-bolt + 3.70 gear

 

Ammendium: Also wanted to ask - If I really do need longer pushrods/rockers - what are the cheapest +.050 (or +.100 ?) sbc roller-pushrods I can buy and what are the cheapest long-slot rockers I can buy? Aside from the ZZ4 cam (and head work to accomodate them) I wont be blasting this thing at high rpms very much (stock tranny/stall/stock TPI intake)... for now. Thanks again!



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1987 Trans am GTA
5.7 liter TPI / 700R4
Aus 9-bolt + 3.70 gear

 

You shouldn't need longer pushrods unless you swap heads... Cam doesn't have anything to do with pushrod length. The geometry is affected by deck height, not lift/duration.

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1984 z28 w/ a 357 cu in. monster engine which is looking like the posterchild for Edelbrock with the exception of the Holley 750vac... all the suspension stuff... 9-bolt posi disk is in...

-=ICON Motorsports=-

 

Ray:

That is not correct at all.

In order to make a cam "bigger", you can't keep making the lobes actualy taller. Eventually they would become so tall that they won't fit through the bearings, and then it would not be possible to install it. Instead, since lift is the difference between the low side of the lobe and the tip, what they do is make the short side smaller. When you do that, if the push rod length doesn't change, the lifter (and therefore the push rod) sinks farther into the block. Eventually you get to a point where the push rod is so low that the rocker is tipped so far back that it pushes partly sideways on the valve stem during the early part of its motion; the rocker may even hit the retainer; and the push rod moves closer to the rocker stud when at its "rest" position, wnich requires lengthening the slot in the head or the guide plate.

Longer push rods put the rocker back into its correct range of travel. The rule of thumb I use for a stock SBC is to add .050" of push rod for every .050" of lobe lift above .430", all else being equal. But with valve trains that are far from stock, an adjustable push rod and a test fit is the only way to be certain that it's right.

My favorite way to measure for perfect geometry is to put some gear marking compound on a valve stem, and rotate the engine through one complete cycle (2 turns of the crank); and adjust the pushrod length for the smallest pattern of movement of the rocker tip across the valve stem. That point obviously corresponds to the minimum side loading on the valve in the guide. I usually check one intake and one exhaust on each side.

IMHO the ZZ4 cam is big enough to probably require longer push rods. IIRC it has lobe lift somewhere around .350", while a typical stock cam has lobe lifts of .300" or less. So even though stock push rods will work, for optimum results, they really should be longer.

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"So many Mustangs, so little time..."
ICON Motorsports

[This message has been edited by RB83L69 (edited September 24, 2001).]

 

I used the stock pushrods with my ZZ4 cam, and my LT4 hot cam. But it all depends on the valve train geometry, which needs to be checked every time you change the cam.

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1991 Camaro Z28
5.7L 5-Speed (originally 305)
317 RWHP, 418 RWTQ
13.23 @ 107.62 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Member: SoCal F-Bodies
-=ICON Motorsports=-

 

Well guys, thanks for your input so far. Its valuable. Anyone else have experience with a ZZ4 cam? I would interested in seeing as much as anyone wants to post... Thanks!!



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1987 Trans am GTA
5.7 liter TPI / 700R4
Aus 9-bolt + 3.70 gear