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valve float?


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Here is the deal

350 chevy

.40 overbore

9.5-1 flat top 4 valve relief pistons

stock crank

plain ole basic.

Crane cam .333 at the lobe, 500 at the valve with 1.5 rocker

373454 casting heads (stock chevy p/u) 76cc chamber. Nothing done to them

halfway down the straight, at about 5000rpm the engine has missing/loss of power

stock valve springs with spacers.

Question. If you have limited time and very limited money to spend, do you put on stronger springs?

Mill .30 off the heads first? What about coil bind? Stock rocker arms also.

I have no access to other heads that would be legal.

Any input on improvement would help me.


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Putting a stronger spring would help with valve float, what you want is a stronger open spring pressure if you don't want to exceed what your rules say on seat pressure .Milling the head .030 will do nothing to help with valve float it will increase compression. Far as coil bind the new springs that you will install will give you all the ratings [ max. valve lift,opening and closing pressure, coil bind ]

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The cam card calls for spring loads of closed 105 @ 1.700

and open 288 @1.220

So I guess that is the rating springs I would get and then check for coil bind.

What affect does milling have on the prospect of coil bind? Does it increase the likelihood?

How much would milling .030 increase the compression. I am running composition head gasket.

Should I move to a shim at say .022 or .018 thousandths?



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Milling the heads will not have an effect on valve float unless the problem is actually not valve float. If what you're feeling is pre-ignition or detonation, milling the heads will make it worse. If your heads have not been milled, you may be able to run a thinner head gasket, but it really depends more on your deck height (how far in the hole your pistons are at TDC.)


If you think your valve springs are causing the problem, remove a few of them and have them checked on an accurate spring rater. If they are too far below the recommended seat pressure for your cam, replace them.


Your problem may not be valve float, however. That's only one of a few things that I've seen cause the problem you described. Some other things to check may be: water in the fuel, float level (too high or too low), power valve, timing, electrical problems (in the tach or ignition or poor ground), weak battery, or sticky valve guides (soon to be a big problem.)


Good luck diagnosing this one. Most of the stuff I mentioned can be checked for pretty easily.



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Well, last first. I am running 5.38 final drive gearing


Started in on it and found 1 broken valve spring on exhaust.

The other springs rated pretty weak.

Replaced those with stronger, taller springs and offset retainers.

thought about the electrical last saturday, replaced coil, cap and wires and ran without a tach for the main.

I guarantee you I am double checking everything.

Concensus is that with the weak springs and ending up with a broken spring (lucky I didn't poke a valve thru the piston) we had a bad case of float.


Thanks guys.


Now, anyone got any low buck performance tips to help the horsepower?


One other thing, did GM make a larger water pump pulley that I can use to underdrive the waterpump?

I am running the stock 2nd gen camaro pulley now.

I hate to spend money (70.00) on pretty pulleys if I can get one at the salvage for 5.00 :rolleyes:

Thanks guys

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