Explain wide duration cams?
02-01-2008, 11:17 PM
#21
Her thoughts completely disregard another big question. Why do the OEM's favor intake head flow over exhaust flow so much? The L92 heads are a glaring example. The old school ideas of intake vs exhaust percentage of flow seem to be thrown out the window. I still contend that it is EPA related.
02-01-2008, 11:19 PM
#22
Her thoughts completely disregard another big question. Why do the OEM's favor intake head flow over exhaust flow so much? The L92 heads are a glaring example. The old school ideas of intake vs exhaust percentage of flow seem to be thrown out the window. I still contend that it is EPA related.
02-02-2008, 07:48 AM
#23
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To say the least...
Thoughts? I can't get past her avatar. No offense to Jess, but she may look no more like her avatar than I do like mine. More's the pity!
Jon
Originally Posted by ArcticZ28
So do you care to share your thoughts?
Jon
02-02-2008, 02:21 PM
#25
I was thinking Jessica was nothing more than a Parrot,just agreeing with the smarties but IF that is her BOOBIES I LOVE HER....I like to think out of the box,why do what everone else does just because they say its GOD...
I'm pretty sure Jenkins and Garlits didnt
I WANNA KNOW WHY GM USES THESE DARN SPECS NOW ANSWER OLDMAN....
I'm pretty sure Jenkins and Garlits didnt
I WANNA KNOW WHY GM USES THESE DARN SPECS NOW ANSWER OLDMAN....
02-02-2008, 09:08 PM
#26
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Hey Jon is it easier, or more effective, to create a pressure differential by squeezing(exhaust) than it is by sucking(intake)? Or is delta p simply delta p, anyway you get it.
Could this explain the differences in intake/exhaust flow?
Could this explain the differences in intake/exhaust flow?
02-02-2008, 11:46 PM
#28
The scoggins dickey post answers the original question nicely, but I'm more curious about what has led head design in such a different direction in recent years. I have always thought that intake should be maximized at all costs, because you only have so much atmosphere pressurizing the intake, and you have almost unlimited pressure available to evacuate the exhaust. However, old school thinking did NOT agree with this. Nowadays (think L92 heads) it seems the OEM's are using my line of reasoning. On older motors, or on modern race motors, exhaust scavenging during overlap would explain needing X% exhaust flow. On OEM motors with little to no overlap (necessitated by emissions concerns), it seems the flow is HEAVILY biased to the intake. Am I off-base here?
02-03-2008, 02:26 AM
#29
1998 - 2000 Fbody
202/210 int/exh @ 0.05" duration
0.496" / 0.496" int/exh lift
116 LSA
2001 - 2002 Fbody
197/207 int/exh @ 0.05" duration
0.467" / 0.479" int/exh lift
116 LSA
For reference, overlap on the first cam has -26* overlap... second one has -30*.
02-03-2008, 02:11 PM
#30
Guess I'll throw in my .02 cents, basically the exhaust split it to compensate for the lack of flow on the exhaust side.
Do to current designs and limits of valve sizes and volume of cylinder head exhaust ports, the increase in exhaust duration would be to compensate for this lack of flow compared to the intake flow.
Since engine are limited to certain bore sizes and combustion sizes, you have to split available space for intake and exhaust valves, from an engineering stand point it isn't practical to have the same size exhaust and intake valves because the smaller intake valve would suffer a greater power loss than a smaller exhaust valve.
Also the size of the volume of the port also effects the need for greater exhaust splits, but keep in mind, valve size is very important on flow, adding a few more cc of intake or exhaust volume will not effect power as much as the actual increase in valve size.
In layman's terms, running a larger valve will net you a great gain in power than running a slightly larger port size.
On average the intake valve is about 1.25 times larger than the exhaust valve.
I am not 100% certain so don't jump on my for it, but an average head would flow about 65-70% on the exhaust as compared to the flow of the intake in cfm.
Another reason to have more duration on the exhaust size would be to compensate for increased exhaust flow that is created from nitrous oxide and super charged applications.
Right or wrong, just my .02 cents, and time for beer and super bowl
Do to current designs and limits of valve sizes and volume of cylinder head exhaust ports, the increase in exhaust duration would be to compensate for this lack of flow compared to the intake flow.
Since engine are limited to certain bore sizes and combustion sizes, you have to split available space for intake and exhaust valves, from an engineering stand point it isn't practical to have the same size exhaust and intake valves because the smaller intake valve would suffer a greater power loss than a smaller exhaust valve.
Also the size of the volume of the port also effects the need for greater exhaust splits, but keep in mind, valve size is very important on flow, adding a few more cc of intake or exhaust volume will not effect power as much as the actual increase in valve size.
In layman's terms, running a larger valve will net you a great gain in power than running a slightly larger port size.
On average the intake valve is about 1.25 times larger than the exhaust valve.
I am not 100% certain so don't jump on my for it, but an average head would flow about 65-70% on the exhaust as compared to the flow of the intake in cfm.
Another reason to have more duration on the exhaust size would be to compensate for increased exhaust flow that is created from nitrous oxide and super charged applications.
Right or wrong, just my .02 cents, and time for beer and super bowl
02-04-2008, 09:21 AM
#31
Thank you 
Old school thinking made less HP, did it less efficiently, and with more emissions.
Old school thinking made less HP, did it less efficiently, and with more emissions.
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02-22-2008, 01:28 AM
#32
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the bigger the duration the more time valve is open basically... and the lower the lsa the more valve overlap you will have making idle rough, but will increase power at higher rpms.....
