Why do most people go with a cam that has more exhaust duration?
03-31-2006, 12:42 PM
#3
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Ive always kinda wondered why there is a bias toward the traditional split cams too, almost all setups include LT headers, no cats, and free flowing exhaust, often times people are using cutouts. Is it the exhaust port design, the exhaust port flow characteristics, or is it because it looks good on paper?
03-31-2006, 01:07 PM
#4
From the flow numbers I've seen for various heads, the intake usually outflows the exhaust by quite a bit. Maybe that's got something to do with it. Longer exhaust duration to compensate for less flow from the exhaust port. Or I could be totally retarded for all I know! 
03-31-2006, 01:44 PM
#6
It's a touchy subject. Some believe in shutting the exaust valve sooner (reverse split) to build more pressure in the cylinder, and some don't. I for one don't like reverse splits because they have never shown me anything spectacular. I prefer to go by results instead of theory, and traditional split cams have always out powered reverse splits, so that's what I stick with.
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03-31-2006, 02:02 PM
#8
Traditional splits are fine with me, but I'm a fan of leaving the exhaust valve closed for as long as possible (when running a good exhaust with a naturally aspirated motor). You tend to get better torque production. This ususally means smaller splits between intake and exhaust or narrower LSA cams.
Early exhaust openings are better when running restrictive exhaust (like stock manifolds) or when running nitrous (because n2o burns so much faster). Wider LSAs or wider splits are the norm here.
Early exhaust openings are better when running restrictive exhaust (like stock manifolds) or when running nitrous (because n2o burns so much faster). Wider LSAs or wider splits are the norm here.
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2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
2023 Corvette 3LT Z51 soon to be modified.
Custom LSX tuning in person or via email press here.
2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
2023 Corvette 3LT Z51 soon to be modified.
Custom LSX tuning in person or via email press here.
03-31-2006, 02:39 PM
#9
My TR230 reverse split was awesome... I'd run another reverse split and "go against traditional thoughts" again... As for traditional splits, I'd say its b/c the intake flows more and the added duration/lift on the exhaust will help expel all the exhaust gases 
03-31-2006, 02:49 PM
#10
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Our MTI X1 (230/227) put down 385rwhp/386rwtq through a 3400/2.2 STR converter, with the standard bolt-ons (LT, ORY, Ported TB, SD Tune-no MAF, etc.) on the initial tune.
Not too bad IMHO. YMMV
Not too bad IMHO. YMMV
04-20-2006, 11:41 AM
#11
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My 228/222 588/581 Comp put down 389rwhp/365rwtq through a Yank 2800 stealth converter with standard bolt ons (headers w/cats, ported TB, UD pulley, intake) on my Goat.
04-20-2006, 02:37 PM
#12
I'm surprised no one has mentioned that exhaust gas is under pressure in the cylinder before the valve opens. Even though intake and exhaust ports are flow tested at the same depression, exhaust under pressure is going to flow faster through a port than the intake charge does with a vacuum. Add a good flowing exhaust system with headers that actually scavenge and longer exhaust duration - and increased overlap - isn't really necessary. In theory, the reverse split should produce the same amount of power as a cam with similar intake duration, but with less overlap at the same lobe separation. That way, you can tighten up the lobe sep for more torque, without the extra 8 - 12 degrees of exhaust duration.