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Small Block & Big Block Chevy Specific Mouse & Rat Motor Discussion & Conversions

Valve overlap problem.

   
Old Jun 8, 2009 | 12:26 AM
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Default Valve overlap problem.
Current specs :
Block: 454 March IV Bored .60 over
Heads:Stock cast iron ported&polished. 230Intake valve / 188 Exhaust.
Tranny: 2 Speed Powerglide on Throttle stop (Supergas).
Camshaft: .720 Lift Lunati Roller. Dont have exact specs atm but will dig them up when I can find them..

It seems like the intake valve is opening really early creating tons of overlap.. Just wondering what would help this situation.
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Old Jun 8, 2009 | 01:49 AM
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Originally Posted by AnthonysAuto
Current specs :
Block: 454 March IV Bored .60 over
Heads:Stock cast iron ported&polished. 230Intake valve / 188 Exhaust.
Tranny: 2 Speed Powerglide on Throttle stop (Supergas).
Camshaft: .720 Lift Lunati Roller. Dont have exact specs atm but will dig them up when I can find them..

It seems like the intake valve is opening really early creating tons of overlap.. Just wondering what would help this situation.
You can retard the cam timing to open the intake valve later, but your exhaust valve is going to close later too, which could affect you ptv clearance. You cannot change the amount of overlap though. It's ground into the cam. The answer there is a new cam.
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Old Jun 8, 2009 | 01:11 PM
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Originally Posted by fast01
You can retard the cam timing to open the intake valve later, but your exhaust valve is going to close later too, which could affect you ptv clearance. You cannot change the amount of overlap though. It's ground into the cam. The answer there is a new cam.
What do you think would be the best thing to change to help this problem?
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Old Jun 8, 2009 | 03:16 PM
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The only thing you can do to change the amount of overlap is change the cam. Look for something with a wider LSA (ex.112 as opposed to 110). Here's a link that'll help you calculate the overlap on any given cam.

http://www.empirenet.com/pkelley2/Overlap.html
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