Benefits of larger valves
10-30-2002, 09:24 AM
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Benefits of larger valves What is the real benefit of having larger valves? Does this increase low lift flow, high lift, or both? Is it better for long duration cams?
This is for a set of 5.3 heads. Heads came with 1.89" instake and 1.55" exhaust valves stock. Heads are having minor port work and polishing done on the runners. Heads will be used with a relatively low lift cam (Comp 212/216 .522 .529 114). The seats should support up to a 2.02" intake, but I was thinking of just using a set of stock 2.00" LS1 valves. I need to have a valve job done anyway, so going to a 2" intake valve shouldn't be that big of a deal.
Anyone have an opinion or info for me? Anyone have a set of new stock LS1 valves?
This is for a set of 5.3 heads. Heads came with 1.89" instake and 1.55" exhaust valves stock. Heads are having minor port work and polishing done on the runners. Heads will be used with a relatively low lift cam (Comp 212/216 .522 .529 114). The seats should support up to a 2.02" intake, but I was thinking of just using a set of stock 2.00" LS1 valves. I need to have a valve job done anyway, so going to a 2" intake valve shouldn't be that big of a deal.
Anyone have an opinion or info for me? Anyone have a set of new stock LS1 valves?
10-30-2002, 09:35 AM
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Re: Benefits of larger valves Its not only the larger valves, but the larger valveseat opening that can be used if you go with larger valves. Just a bigger cross-sectional area, so yes they should flow more given the same port work.
The larger valved heads (2.055/1.60) setups have had the stock valveseats machined out and replaced with larger diameter seats which can be opened up. Smaller valves are said to help out port velocity and lower rpm torque, larger valves tend to favor higher rpm flow.
-Tony
The larger valved heads (2.055/1.60) setups have had the stock valveseats machined out and replaced with larger diameter seats which can be opened up. Smaller valves are said to help out port velocity and lower rpm torque, larger valves tend to favor higher rpm flow.
-Tony
10-30-2002, 09:53 AM
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Re: Benefits of larger valves </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Nine Ball:
<strong>... Smaller valves are said to help out port velocity and lower rpm torque, larger valves tend to favor higher rpm flow.
-Tony</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Thanks Tony. This makes some sense to me. These heads are for a 5.3 truck. Would I be better off sticking with the stock valve size just for the torque? I need all the torque I can get.
Richard
<strong>... Smaller valves are said to help out port velocity and lower rpm torque, larger valves tend to favor higher rpm flow.
-Tony</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Thanks Tony. This makes some sense to me. These heads are for a 5.3 truck. Would I be better off sticking with the stock valve size just for the torque? I need all the torque I can get.
Richard
10-30-2002, 01:42 PM
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Re: Benefits of larger valves PAUL J, Since these heads are for a 5.3 truck, I need the smaller chambers to keep up the CR. Compression is 9.5:1 stock, so if I moved to LS1 heads, I'd end up with less compression even if I did have them milled. As is, I plan on having these milled ~.030 to get my CR to about 10:1.
If a larger intake valve will increase my low end, I'm interested.
If a larger intake valve will increase my low end, I'm interested.
10-30-2002, 08:34 PM
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Re: Benefits of larger valves stock valves rule! Just don't run a to aggressive cam and spring pressure with them they will snap. you can use larger valves but the cylinder head must be ported correctly to use them.
10-31-2002, 12:05 AM
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Re: Benefits of larger valves The only reason to use 4.8/5.3L heads is for a smaller combustion chamber. LS1 5.7 heads use the same intake and exhaust ports as the 4.8L heads but have a larger combustion chamber (68 vs 64 cc)
You will lose flow with the smaller 1.900" intake valve compared with the 2.00" LS1 5.7L, although the 4.8L intake seat can accomodate up to a 2.02" intake valve. This will require substantial work with enlarging the seat and unshrouding the chamber to fit in the 2.00" valve.
I would use a 5.7L head and mill the surface .030-.040" to bring the chamber down to 64-65cc. To answer your question, yes, larger valves will improve flow, particularly in the low to mid lift range (Up to .15 times valve dia.) Larger valves will not improve flow in the higher lift range if the port is not also enlarged. In this case, the 5.7 and 4.8L ports are the same.
Paul J.
You will lose flow with the smaller 1.900" intake valve compared with the 2.00" LS1 5.7L, although the 4.8L intake seat can accomodate up to a 2.02" intake valve. This will require substantial work with enlarging the seat and unshrouding the chamber to fit in the 2.00" valve.
I would use a 5.7L head and mill the surface .030-.040" to bring the chamber down to 64-65cc. To answer your question, yes, larger valves will improve flow, particularly in the low to mid lift range (Up to .15 times valve dia.) Larger valves will not improve flow in the higher lift range if the port is not also enlarged. In this case, the 5.7 and 4.8L ports are the same.
Paul J.
