which spec produces better numbers
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TECH Enthusiast
Joined: Nov 2001
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From: Henderson, NV
which spec produces better numbers Lift or drations specs??
I ask because i was reading an old issue about how they got the 20 horses out of the new LS6 in GMHTP. And then that got me asking ?s. So i went to summit to look at cam specs. All these cam had looooooong duration with lift in the 400's, maybe low 500's. But i read that long duration is what causes overlap, which is low emissions, which is why the new LS6 has .525 lift with somethng like a 206 duration.
I have always been set on a cam like 222/222 .563/.563 112. But then there is the 221/221 .558 112. With thousands other!!!!! <img src="gr_emb.gif" border="0"> I dont kno where to start. It amazes me how ou guys on here know so much and that there is sooo much to learn about a little 2 foot rod in a motor!
I ask because i was reading an old issue about how they got the 20 horses out of the new LS6 in GMHTP. And then that got me asking ?s. So i went to summit to look at cam specs. All these cam had looooooong duration with lift in the 400's, maybe low 500's. But i read that long duration is what causes overlap, which is low emissions, which is why the new LS6 has .525 lift with somethng like a 206 duration.
I have always been set on a cam like 222/222 .563/.563 112. But then there is the 221/221 .558 112. With thousands other!!!!! <img src="gr_emb.gif" border="0"> I dont kno where to start. It amazes me how ou guys on here know so much and that there is sooo much to learn about a little 2 foot rod in a motor!
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Joined: Nov 2001
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From: Nawf Carolina
Re: which spec produces better numbers Think of duration as the coach of the engine. Its not the only component to the cam or engine, and the other parts are very critical, but it determines the "plays" (the valve timing events, when the intake and exhaust valves open and close). It determines the characteristics of a motor.
A cam with more duration (everything else held equal) will make more power, but it will typically make it at a higher rpm. So if you put a hydralic cam with 250@.050" in your 346 LS1, it would make more power, but you'd have to rev it to like 7500 or something (just a guess). From idle to maybe 5500 you'd be making less power. So you need to match the cam to how high you want to rev. Another trade off is more duration will idle worse, and the emissions will become worse (if you have to pass the sniffer).
So when choosing a cam, you need to decide where you want to shift at, if emissions matter to you, is it a daily driver (idle quality), etc.
I've never heard of less lift making more power, lift is just a measurement of how far the valves open. But more lift will decrease valve spring life.
edit - You really cant compare cams from one motor to another, every engine is different. But, when you look at Jegs or Summit, see if the duration is advertised duration or .050" Typically we (most EFI ppl) look at duration at .050, while many cams in Summit and Jegs are listed in advertised duration. Advertised duration will always be greater than at .050.
J.
[ January 22, 2002: Message edited by: Crazyquik ]</p>
A cam with more duration (everything else held equal) will make more power, but it will typically make it at a higher rpm. So if you put a hydralic cam with 250@.050" in your 346 LS1, it would make more power, but you'd have to rev it to like 7500 or something (just a guess). From idle to maybe 5500 you'd be making less power. So you need to match the cam to how high you want to rev. Another trade off is more duration will idle worse, and the emissions will become worse (if you have to pass the sniffer).
So when choosing a cam, you need to decide where you want to shift at, if emissions matter to you, is it a daily driver (idle quality), etc.
I've never heard of less lift making more power, lift is just a measurement of how far the valves open. But more lift will decrease valve spring life.
edit - You really cant compare cams from one motor to another, every engine is different. But, when you look at Jegs or Summit, see if the duration is advertised duration or .050" Typically we (most EFI ppl) look at duration at .050, while many cams in Summit and Jegs are listed in advertised duration. Advertised duration will always be greater than at .050.
J.
[ January 22, 2002: Message edited by: Crazyquik ]</p>