Too close are

General engine tech -- Drag Racing to Circle Track

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Newold1
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Re: Too close are

Post by Newold1 » Mon Mar 05, 2018 2:56 pm

You put a +.040" to .060" thicker head gasket there and his compression is shot to hell.

1972ho
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Re: Too close are

Post by 1972ho » Mon Mar 05, 2018 3:37 pm

I talked with the machine shop this morning and they told me it’s something that they do,but they farm it out to some aero type machine shop because of the machine’s that they have that can slowly grind on them to keep from overheating the valve.Im going to use my old CV valves that have less margin already ground into them.

stealth
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Re: Too close are

Post by stealth » Fri Mar 09, 2018 11:30 am

1972ho wrote:
Mon Mar 05, 2018 3:37 pm
I talked with the machine shop this morning and they told me it’s something that they do,but they farm it out to some aero type machine shop because of the machine’s that they have that can slowly grind on them to keep from overheating the valve.Im going to use my old CV valves that have less margin already ground into them.
Interesting concept considering the environment they operate in...
The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man.

mag2555
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Re: Too close are

Post by mag2555 » Fri Mar 09, 2018 12:39 pm

Low lift Exh flow wise you do not want to be shaving .030" off the face of the valve/ margin!

liqu
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Re: Too close are

Post by liqu » Fri Mar 09, 2018 1:07 pm

Isky makes a Piston notcher just for this.

CGT
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Re: Too close are

Post by CGT » Fri Mar 09, 2018 4:52 pm

Retard the cam a couple degrees, it would be enough to get that out of trouble. It wont be the .050 to .060 thousandths someone else mentioned, most likely .020 to .025. But should be enough.

hoodeng
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Re: Too close are

Post by hoodeng » Sat Mar 10, 2018 6:32 pm

You would typically want to see .060" clearances built into all relating components which was it appears done on the original build , that said , any swarfe from the combustion chamber will drop your compression as has been stated by others. If your engine will not tolerate compression loss the following is pretty much how it goes,,, apart from new pistons if you don't want compression loss and want to keep the cams new timing.

The least amount of material removed to achieve clearance would be to valve chamber face profile cut into the piston crown , leaving the center of the piston valves relief as high as possible, the cc gain will be the arc area volume removed.
Next would be If the valve is a deep tulip on the combustion side and you have a reasonably thick margin, cutting the od of the valve chamber side face will give clearance but the cc gain in the chamber will now be the diameter of the valve band area loss volume.
Cutting a deeper flat valve relief in the piston is the next greater cc gain in the chamber .
Next, dropping the valve on the seat will be a chamber cc gain of the area of the valve head x amount dropped.
Worst would be fitting a thicker head gasket as we now chamber cc gain the total volume of the gaskets bore x height addition volume.

As has also been stated ,re dialing the cam to achieve clearance would be easiest if you would still be happy with the performance.

Cheers.

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