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What head, cam and springs do you have now?

If you're talking about 40 year old stock heads and original springs, the answer is "not much" ...

Also the valve guide has to be cut down for any lift over about .470 (I think).

-Charles
 
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Stock head over .550 will need the guides shortened to prevent the retainer from hitting it. Cut the guide to us the PC style teflon seal.

Don.
 

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You might find this page with valve, valve lift, and spring data of interest. Look how little load is available even when those springs were new! I wouldn't try and run those with any kind of performance cam.
Imperial FSM page

If you're going to the trouble to buy and install a cam and lifters, changing the springs isn't that much more work. Even with the heads on the engine, with the right tools it can be done pretty easily. Of course if your guides and valve seats are shot, and you're going to rebuild the heads, you've got a lot more options. Is the engine together and running?

I did a cheapy-rebuild once on a '67 383 with the stock springs and guide heights, so I used the smallest Direct Connection "RV" cam (260/.434 hyd). No interference or coil bind. It didn't make power past 5500 anyway so float wasn't a problem even with the old springs.

-Charles

ps Don are you sure you can go all the way to .550 without cutting the guides?
 

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Discussion Starter · #8 ·
Resurrecting an oldie. SO I can run the single springs up until .550" lift? Am getting ready to fire this beast and may be getting a cam swap before I do. Just trying to cover my bases. Thanks in advance.
 

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413_Dart said:
Resurrecting an oldie. SO I can run the single springs up until .550" lift? Am getting ready to fire this beast and may be getting a cam swap before I do. Just trying to cover my bases. Thanks in advance.
I would buy a new set of valve springs. Cheap insurance...
 

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Discussion Starter · #10 ·
Yeah I will be replacing the springs but want to go as big a cam as I can without removing and milling the heads.
 

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.509 is the biggest lift you can go on average. Remember you have to allow for about .050 clearance at full lift, so .559 coil bind is really .509 (or so) max safe lift.

I have run the .509 cam on a set of untouched 906 heads with just changing the cam and lifters. In reality we changed the valvesprings out a month later so longterm reliability is unknown.

My buddy tried that on the .528 cam and the heads couldn't take it - coil bind, retainers hitting, etc.
 

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speedymopars said:
.509 is the biggest lift you can go on average. Remember you have to allow for about .050 clearance at full lift, so .559 coil bind is really .509 (or so) max safe lift.

I have run the .509 cam on a set of untouched 906 heads with just changing the cam and lifters. In reality we changed the valvesprings out a month later so longterm reliability is unknown.

My buddy tried that on the .528 cam and the heads couldn't take it - coil bind, retainers hitting, etc.
Sometimes I wish I would've just gone with the .509 and saved a few hundred on machine work.
 

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.430 lift was on factory 413s in 65.
You need to cut down the guides and get better springs.
 
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