Magnum heads convert to sbc rockers?

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gregsdart

gregsdart

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I want to run a Voodoo 712 hydraulic roller cam in a 408 build, and would like input on reasonably priced sbc 1.6 ratio rockers to use. Also any input on how well this conversion works using the 5/16x3/8 stud conversion kit available.
 
gregsdart said:
I want to run a Voodoo 712 hydraulic roller cam in a 408 build, and would like input on reasonably priced sbc 1.6 ratio rockers to use. Also any input on how well this conversion works using the 5/16x3/8 stud conversion kit available.
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It's the hot set-up. The SBC rocker swap is one of the most common conversions, and the thicker studs aid in reducing deflection. The stud girdle kits will then also fit. Take a look at the Jomar girdles.
 
It's only blasphemy with genuine Chevy trash in there. Aftermarket trash is ok.

Right?
 
I'd look real hard at the Hughes magnum rocker setup, it pairs 2 rockers together on a shaft, kinda like a jessel setup....very sweet
 
No need to use rocker arms listed for Chevies :realcrazy:just replace the AMC designed magnum rocker setup with some roller rockers for an AMC:thumbsup:
 
I have this set up & I am pleased to date with it. Hughes supplied the tech & parts (1.65 ratio arms, pushrods, guide plates, matched up studs) and it has been working well in my 408.
 
I used SBF rockers... milled down the Magnum rocker stands and used Comp rocker studs.
 
Thanks for the input everybody, I will consider the Hughes deal , as it looks to be about the best considering cost versus what it offers. One possible change though on cam choice. Two reliable sources are using other brands, less radical ramps allow more stable rpm before lifter pump up is what I was told. The dyno operator I plan to go to said the Voodoo cams have fairly radical lobes which on some of their dyno sheets show them having less rpm potential due to lifter pump up. He said they saw instability as low as 5500 rpm. So,, A Muther thumper looks like a winner. The right .050 specs for what I want, and ought to be stable.
 
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Here are a couple of picsof my heads. I used push rod Guide plates which aren't on the mock up pics. It's been 2 years now with no problems. I don't really push the motor that hard, it runs nice. They are slightly noisy, I've heard it described " sewing machine sound".

WP_20140625_16_38_01_Pro.jpg


WP_20140625_16_39_55_Pro__highres.jpg


WP_20140625_16_39_55_Pro.jpg
 
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Robbie, what brand rockers are those? Also, whose guide plates?
 
gregsdart said:
Robbie, what brand rockers are those? Also, whose guide plates?
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I really don't know, the machine shop picked them out. I got the guide plates from Edelbrock If I remember right. We used 7/16th studs for the rockers, the machinist thought it was a good idea. It's a mild roller cam but the open spring pressure is 320#s. I hope that helps. I used the regular rockers, not the self centering. The self centering looked too close to the retainers. These are the stainless rockers, not aluminum. I think they are fairly cheap. I would use them on a street motor but not on a race motor. I have a few aluminum ones I used for mock up and these are heavier and use needle bearings. I don't rev over 5500, the cam is out of breath above that.
 
The Chevy rockers work fine. I would use the Comp steel rockers with the roller tip. Very durable and affordable.
 
gregsdart said:
Thanks for the input everybody, I will consider the Hughes deal , as it looks to be about the best considering cost versus what it offers. One possible change though on cam choice. Two reliable sources are using other brands, less radical ramps allow more stable rpm before lifter pump up is what I was told. The dyno operator I plan to go to said the Voodoo cams have fairly radical lobes which on some of their dyno sheets show them having less rpm potential due to lifter pump up. He said they saw instability as low as 5500 rpm. So,, A Muther thumper looks like a winner. The right .050 specs for what I want, and ought to be stable.
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Hold the phone there...... this really bothers me. Did they explain why the lifters pumped up? (Do they even understand why?) The ramps are a contributor but not the real casue. Float happens only because the other valve train parts are too heavy or the springs are too weak or instable to keep the valves from floating a bit at those RPM's. OR the rocker geometry is such that is is causing large speed variations in the valvetrain acceleration or deceleration. I am have to ask if the dyno operator ever explored that or recommended any corrections. (And some dyno operators are just that... operators..... not builders.)

The correction to this is NOT to change cams from what is best for the application, but to fix the valvetrain issues.

I don't think much of the mutha thumpr line; it is for the noise, not the go.
 
And if you were looking at the Voodoo 20200712, that does not look all that challenging for lift or rate..... Did the dyno operator make the Thumpr recommendation?
 
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gregsdart said:
Thanks for the input everybody, I will consider the Hughes deal , as it looks to be about the best considering cost versus what it offers. One possible change though on cam choice. Two reliable sources are using other brands, less radical ramps allow more stable rpm before lifter pump up is what I was told. The dyno operator I plan to go to said the Voodoo cams have fairly radical lobes which on some of their dyno sheets show them having less rpm potential due to lifter pump up. He said they saw instability as low as 5500 rpm. So,, A Muther thumper looks like a winner. The right .050 specs for what I want, and ought to be stable.
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Comp cams has a new asymmetrical line of roller profiles that claim to have a slower ramp profile on the closing side for better rpm ability. You can get a similar deal from Mike Jones cams. I would use the latter.
 
Brooks James said:
Did you get them to quiet down ??
Anyone reading this have a similar issue ?
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They are still a little noisy compared to regular rockers. I'll be adjusting them next week and see if that makes any difference. You only really notice them with the hood open and it idling. The engine seems to like the combo, it has a ton of torque and revs well.
 
jbc426 said:
It's the hot set-up. The SBC rocker swap is one of the most common conversions, and the thicker studs aid in reducing deflection. The stud girdle kits will then also fit. Take a look at the Jomar girdles.
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Are you saying that the SBC Jomar girdles will work on the magnum heads, the rocker spacing is the same ???
 
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