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351 cj rockers
#1
Wrench 
351 Cleveland Cobra Jet 4v Help


Hey everyone I am building a 351 cleveland right now I sent the motor to a machine shop here were I live told him what I wanted and my price engine cam back bored 30 over heads ported new cam springs all the good stuff crank all redone motor balanced . Now my question for you guys is I am running a comp thumper cam here is the part number cl32 601 5 he matched the springs valves everything but the rockers and push rods , he told me my stock rockers would work fine but it has me worried because my stock rockers only lift 419 from what I have read and the cam is 519/503 would someone please shine some light on this for me maybe I am missing something , also he told be that I wouldn't have to run headers that I could run stock exhaust manifolds on the motor now it's going in a 1954 ford f100 and there's not much room at all for headers thanks everyone's

 
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#2
Unless you have rockers with increased lift ratio (like 1.6 or 1.7 roller rockers), I would think the rockers would lift however far the cam & pushrods shove them open. I could be wrong, though.

Are you sure it wasn't the stock cam that had the .419" lift rating, and not the rockers themselves?

Eric

[Image: mach1sig2.gif]
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#3
It could have been I just got off the phone with a good mechanic that I should have took it too in the 1st place and he said max lift on intake was 525 so I am good to go
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#4
Glad you got the information you needed. thumb

Hopefully however, someone with a better grasp on stock rocker arm functionality can weigh-in so we'll know for sure.

Eric

[Image: mach1sig2.gif]
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#5
The stock rocker ratio on a 351c is 1.73:1. The numbers you're referencing from your cam card should be either at lobe or at valve. The cam card should list the rocker ratio assumed for the at valve values.

In order to get accurate lift measurements at the valve, you have to use solid lifters or you can use very light test springs on the valves. If you go the solid lifter route, you need to set the rockers to zero lash relative to the valve tip. This will allow you to check cam timing and lift numbers.

I suspect you used hydraulic lifters and they collapsed, resulting in a lower gross valve lift measurement.

Hope this helps
BT
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