Ok, I'm a dumba$$, what needs to be done to go from 1.5 to 1.6 rockers? I always thought you just switched them out, but now I realize that may not be so... Do I need to get longer pushrods, if so by how much? Also do I need to enlarge the pushrod holes? (thats what sdpc said I neeed to do.) I was thinking of getting vortec heads and realized my stock cam would be pretty mismatched, I figured 1.6s could hold me over. What would a stock L98 cam ('89) be with 1.6s? Thanks!

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-='89 Iroc-Z=-
-= 350 TPI =-

 

You may need longer pushrods, but to be sure you need a pushrod length checker, cheap tool from summit or jegs. I didn't have to enlarge the holes on my aluminum l98 heads, but I could see why that may be necessary on a different set.. Just check the whole range of motion as you crank the engine to see if the pushrod is going to have decent clearance.

 

Maybe you should save your money and not get the 1.6's, they're not going to give you much over the 1.5's.

 

as a rule i go to .100 longer push rods when i increase lift by .150. you won't be gaining .050 lift on a stock cam so the longer push rods aren't need. you shouldn't have to make any changes in the heads as well. in short you can just swap them out and not have any major problems come up. it's always good to think about all the little related things when you do something like this so you don't find you self i na bind , breaking other parts, or having to buy other parts to make something simple work.

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ICON Motorsports
1st & 3rd
MM Black Diamond 538 F&AM

 

Think how rocker ratio works...

It is the ratio of 2 distances. The first is the distance between the fulcrum (center of the stud) and the valve stem. Obviously that one doesn't change when you bolt on new rockers. The other is the distance between the fulcrum and the push rod seat. That's the one that changes.

It changes in the direction of getting shorter. That is, the push rod moves toward the stud. The slot in the head often is not long enough for where the push rod needs to end up. So you often have to lengthen the slot at that end to keep the head from pushing the push rod out of the place in the rocker where it belongs. That's what the guy at SDPC was telling you about. Around half of the heads I have ever put 1.6 rockers on had to have their slots lengthened.

You don't need longer push rods. The reason you need longer push rods is because when you make a cam "bigger", it does not in fact get bigger. The peaks of the lobes are almost always very nearly as tall as they can be and still go through the bearings. I.e. if you made them any taller you wouldn't be able to install the cam. A minor detail yet it can't be ignored. So, since lift is the diference between the tip of the lobe and the back side, they make the back side smaller and smaller as they make bigger cams; and as they do that, the push rod sinks farther down into the block, and the rocker tips farther back, until eventually you get to a point where it's totally out of kilter. So when you change cams, you need to evaluate the optimum push rod length for your specific parts. Changing the rockers has nothing to do with that.

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

[This message has been edited by RB83L69 (edited October 14, 2001).]

 

Thank for the great info guys. Do you think the "high performance" vortec heads would need the holes legthened? Or should I just forget the 1.6s and put that money toward a better cam?

 

Bitchin, are you planning to get the tpi base that fits the Vortec's as they have a differant port location and bolt pattern. The standard Vortec's will work up to around .450 lift. You probably could use them without any rework. I had to grind the pushrod holes in mine as was mentioned toward the rocker stud to be used with 1.6 Crane rollers. By the way the spring retainers hit the valve seals on mine at .465 requiring the use of .050 shims and .050 offset keepers to get proper clearance for a .480 lift cam. Good luck.