Cams - Valve/Piston spacing

53BigDog

Active Member

May 22, 2001

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Palm Harbor, FL

Mar 8, 2008

#1

• Mar 8, 2008

• #1

I have a 97 GT naturally aspriated with PI Heads and I am planning putting in flat top head pistons with no relief valves inlets. I am trying to decided between Comp Cams XE268H (part # 102200) or XE270AH (part #102600). The major difference between these two cams are the valve lift. The XE268H's have a valve lift of .500 which is more similar to the non-PI stock. The XE270AH's have a .550 lift and I am concerned whether or not I will need clearance or valve reliefs in my pistons.

Anyone able to answer?

 

CobraRed_96_GT

Active Member

May 20, 2006

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UCSD/La Jolla

Mar 8, 2008

#2

• Mar 8, 2008

• #2

Unless im mistaken you already have flat top pistons stock. 268H's are designed for NPI heads, hence less lift. I dont think you'll have a problem with 270AH's as long as you degree them

 

53BigDog

Active Member

May 22, 2001

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Palm Harbor, FL

Mar 8, 2008

#3

• Mar 8, 2008

• #3

no, my stock pistons are dished ??

 

R

rugster

New Member

Aug 31, 2004

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Mar 9, 2008

#4

• Mar 9, 2008

• #4

NPI pistons do not have a dish, thats why those motors are higher compression than PI motors.

 

CobraRed_96_GT

Active Member

May 20, 2006

1,421

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UCSD/La Jolla

Mar 9, 2008

#5

• Mar 9, 2008

• #5

rugster said:

NPI pistons do not have a dish, thats why those motors are higher compression than PI motors.

Click to expand...

96-’98 Non-PI Heads have a 49.77cc combustion chamber and the pistons have a .153cc dish relief.

’99-’04 PI Heads have a 42.45cc combustion chamber and the pistons have a deeper dish at .188cc dish relief.



guess i'd stick with a .500 lift over a .550 then

 

J

Jim@CMS

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Jan 5, 2008

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Mar 9, 2008

#6

• Mar 9, 2008

• #6

The 270 will be scary close....if it clears at all.