valves size question..
03-16-2008, 09:05 PM
#1
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valves size question..
ok heres the deal, i have heard that going with larger valves can help greatly. however, i have also heard the exact opposite. i figured that they would help a whole lot since the valve size that i have decided to go with are the ones in the lt4. 2.0 and 1.56. my question is, since i am doing some port matching and some smoothing, will these valve sizes work really well with a cc503, and the head work im planning on?
03-16-2008, 10:50 PM
#3
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I don't recall but I do believe that there is a ratio for exhaust to intake sizes for the street. I believe the best ratio was around 75% from exhaust to intake valve sizes. It was from an SA Designs book called "HP Chevy Cylinder Heads".
http://www.jegs.com/i/S%20A%20Design...SA125/10002/-1
2.00 is about the largest you can go with a stock seat. If you opt for a 2.02 then you should change your seats. It is more cost and effort than the benefit you'll typically gain from the extra 0.02.
http://www.jegs.com/i/S%20A%20Design...SA125/10002/-1
2.00 is about the largest you can go with a stock seat. If you opt for a 2.02 then you should change your seats. It is more cost and effort than the benefit you'll typically gain from the extra 0.02.
Last edited by Wild1; 03-16-2008 at 10:51 PM. Reason: Added info about seats
03-17-2008, 09:15 AM
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You can't just pick a valve diameter out of the blue and go with it. The ports have to support the valve diameters. The combustion chamber has to be cleaned up to prevent valve shrouding. When GM designed the LT4 head, they significantly changed the port, and altered the combustion chamber slightly. ASSuming that the LT4 valve size will improve flow in a stock LT1 head may not be correct.
Here's the site that identifies the differences between the LT1 and LT4 engines. Take the time to read the section on heads.
http://www.grandsportregistry.com/lt1vslt4.htm
Here's the site that identifies the differences between the LT1 and LT4 engines. Take the time to read the section on heads.
http://www.grandsportregistry.com/lt1vslt4.htm
REVISED HEAD DESIGN
The big difference in the heads is the intake and exhaust ports. Both are larger with bigger radius bends. The "short side" radius of the LT4's exhaust port in particular has been increased to reduce back pressure at higher RPM's. A throat cut just past the exhaust valve seat also opens up the exhaust port. (Unshrouding valve). The Intake port volume has increasd by 25cc. Increased from 170cc on the LT1 to 195cc for the LT4. The flow through the heads have been increased from 212CFM (Cubic feet per minute) @ 28" (711mm) (LT1) to 240CFM (LT4).
The roof was slightly lowered and the walls were moved back slightly from the valves for better breathing, undercutting next to the exhaust valve thereby "unshrouding the valves." Revised port contours enhance air flow into and out of the engine resulting in increased fuel burning efficiency.
The big difference in the heads is the intake and exhaust ports. Both are larger with bigger radius bends. The "short side" radius of the LT4's exhaust port in particular has been increased to reduce back pressure at higher RPM's. A throat cut just past the exhaust valve seat also opens up the exhaust port. (Unshrouding valve). The Intake port volume has increasd by 25cc. Increased from 170cc on the LT1 to 195cc for the LT4. The flow through the heads have been increased from 212CFM (Cubic feet per minute) @ 28" (711mm) (LT1) to 240CFM (LT4).
The roof was slightly lowered and the walls were moved back slightly from the valves for better breathing, undercutting next to the exhaust valve thereby "unshrouding the valves." Revised port contours enhance air flow into and out of the engine resulting in increased fuel burning efficiency.
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