Well Im gonna upgraded cam and already have 650 duals for my previous cam....my new cam has 643 lift....woul I be safe with theese (650)burly clearing the 643 lift on new cam??

My heads will not fit 700's
And the 660 is almost the same as my 650's I think

Lmk what u all think....opinions very much welcomed...thanks in advance...

Monch

 

I run .595 lift on PAC 1218 that rated for .600 lift.

 

What are the specs of the springs? do you have a part number?

You will most likely be fine with what you have.

 

What kind of springs are they? How many miles on them and what were the specs on your previous cam? Any idea what your piston to valve clearance will be?

All these things will play into effect IMO. That would really be pushing the springs close to coil bind. You might be safe on the exhaust valve which is lighter and easier to control. The intake valve I think I'd step up the a better spring.

Mike

 

Not necessarily. We really need the spring specs to determine that.

 

I'm probably wrong on this one, but I have my opinion that I'm going to share anyways. Experts please chime in, I'm always trying to learn more about valve spring tech.

All springs have memory, including coil springs, including valve springs. Let's say you've been running your old .650 springs for 30K miles at .551 lift, through thousands of heat cycles. They have a memory.

Now you install your new cam, with .643 lift. I think everything will be fine, at first. But I also believe that valve spring failure is imminent, so new springs would be recommended, IMO.

I think with a .643 cam, most .650 rated springs would be just fine. But if the lobes are aggressive enough, a .660 or better spring would be advisable. Need more info to make a recommendation about what springs you "should" run with your cam.

 

Technically yes you are right. But, I tend to error on the safer side of things. Given the limited info and already having xxxxx miles on them.

In the end its all going to depend on the actual measured existing spring pressures at open/closed and whether or not a shim is required to bring them back into specs at installed heights. If a shim is required then chances are good that if they're rated at. 650 lift then the springs will be very close to coil bind with a cam having. 643 lift. Not worth risking that IMO. A couple over revs and some valve float would push into coil bind very easily.

If it were mine I'd test actual spring pressures and coil bind heights first then go from there or just buy some better springs and be done with it. Or, choose a cam with less lift.

Mike