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Old 06-24-2009, 06:44 PM
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piston to valve clearance

well to get started i HAD a 350 4 bolt with 9.1 to 1 CR crate engine with 64cc/170cc vortecs and then i put a lunati roller cam..520/540 lift 110 lsa/106 icl 300/310 duration, 242/252 @ 50 i believe...with the same heads...horrible setup up i know(long story)

my question is if this setup up was ok for piston to valve clearnace would this next setup be ok?...i have a smaller cam with bigger heads, same 64cc though.

197cc/64cc aluminum heads 2.055/1.60 in/ex
comp roller 510/520 lift 282/288 duration 230/236 @ 50 110 lsa/106 icl

the way i see it is that theyre both 64cc, and my combo now has a smaller cam so why would it not be ok if the 64cc worked with a bigger cam?.....i would just like to get some insight on the situation, mabey im completely wrong, i dont know. i do know i can get checking springs or solid lifters the same size and find out clearance this way but id rather not have to do this

thanks for any help!

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Old 06-24-2009, 07:24 PM
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Any time you swap out parts and go with different heads with different springs you always need to check for piston to valve clearance. I went with the pushrods that was recommended by the cam company when I got there cam and on my new build I had the block just decked .010 and long story short I had to get pushrods that was longer then what they recommended. So you always have to check things when swapping out parts from one thing to another.Tolerances on one head may be different on the other heads etc. Sounds like a nice build man good luck on it.
Eric
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Old 06-24-2009, 07:24 PM
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Theres only one way to know how much p - v clearance you have.You gotta check it,theres different ways of doing this,but using the clay method will give you a ballpark figure.Valve timing,lobe seperation angles,piston shape ,etc., all have an impact on p - v clearances.This isnt the area to be going on guesswork.
Guy
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Old 06-24-2009, 07:32 PM
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Yeah, what they said, plus, unless you measure it, you have no idea what the distance is from the valve seat to the surface of the head on either one. The new heads could have the seat closer to the head deck, which would decrease the p/v clearance.

What's the static compression ratio of the motor?
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Old 06-24-2009, 11:30 PM
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well i talked to a few different tech on the phone and they all said id be fine....but according to all of you i should check....so i guess i might as well do it...i dont want to buy soild lifters, and i dont have the tools to put checking springs on so it looks like i have a couple trips to the machine shop to put them on and take them off
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Old 06-24-2009, 11:32 PM
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Quote:
Originally Posted by techinspector1
Yeah, what they said, plus, unless you measure it, you have no idea what the distance is from the valve seat to the surface of the head on either one. The new heads could have the seat closer to the head deck, which would decrease the p/v clearance.

What's the static compression ratio of the motor?


im not to sure on that...i dont know the deck height or how much the piston is dished to calculate that
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Old 06-24-2009, 11:46 PM
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OK, so without knowing the static compression ratio, what criteria did you use in choosing the cam?

Without knowing the SCR, you can't figure the DCR, so you don't know what the cylinder pressure will be, so you don't know if the motor will be a player or not.

That's not particularly how I would want to spend my money.
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Old 06-24-2009, 11:49 PM
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well i just new it had 9.1 to 1 CR when i bought the motor with the vortecs...and that cam seemed like a good match and it says needs 9 to 1 CR, also i know it will have slightly more now because of the aluminum heads
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Old 06-24-2009, 11:51 PM
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Just going from the 1.94" valve in the Vortecs to the bigger 2.055" valve is enough to put you into possible trouble. The fact that the chamber size is the same has virtually nothing to do with it. The previous posters have given you sound advice- Check it!

Compression doesn't change just because they are aluminum, they are both 64cc chamber, the compression ratio will be the same.
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