Let me see if I've got the whole intake/cam/heads/header thing figured out.
06-27-2004, 11:24 AM
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Staging Lane
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Let me see if I've got the whole intake/cam/heads/header thing figured out. Please bear with me because I'm not entirely familiar with all the terminology...
from reading one of the threads, for a stock bore and stroke, any head that flows more than 280CFM is pretty much overkill (unless you're also looking at the low-lift flow numbers).
now the exhaust stroke... I'm guessing here as I haven't finished reading up on it, but... if the head doesn't allow the ehaust gasses to flow out at some max flow rate (280CFM?), then the piston will be forcing the air out rather than letting it "flow out" and cause back pressure within the cylinder resulting in power loss.
With the heads, what's mainly limiting it's achievment of max flow is the intake and headers, intake effecting how fast it fills up the cylinder, and headers effecting how efficiently the gasses are expelled.
am I correct so far?
so what I'd want to do when selecting a cam would be to have one which gives the maximum lift for the entire duration of the down stroke (intake), and the same for the exhaust stroke.
Now... pretend that I have a stock bore/stroke and a set of heads that flow at 300CFM- a little over kill but the low-lift flow numbers are a little higher. If I wanted to save some wear N tear on my engine, could I have the valves open a little early to give a slower slope before hitting maximum lift, and a similar closing slope that would have a little over lap so that my valves wouldn't be slamming shut so harshly.
If I went to a custom cam manufacturer and got a cam with those properties, would that be considered a "good" cam? or do I have the concepts wrong?
Also, the intake and Headers effect the flow of the heads, so it would be worth my while to go with a high-flowing intake like an LSX or to stick with my plan of the LS6 intake. Along similar lines would I be mistaken to go with open headers to minimize backpressure in the exhaust and maximize the rate at which the heads flow exhaust? My goal is around 420HP/400TQ range and my finished car will be a dedicated track/weekend driver, so things like mufflers and cats aren't really a neccesity
from reading one of the threads, for a stock bore and stroke, any head that flows more than 280CFM is pretty much overkill (unless you're also looking at the low-lift flow numbers).
now the exhaust stroke... I'm guessing here as I haven't finished reading up on it, but... if the head doesn't allow the ehaust gasses to flow out at some max flow rate (280CFM?), then the piston will be forcing the air out rather than letting it "flow out" and cause back pressure within the cylinder resulting in power loss.
With the heads, what's mainly limiting it's achievment of max flow is the intake and headers, intake effecting how fast it fills up the cylinder, and headers effecting how efficiently the gasses are expelled.
am I correct so far?
so what I'd want to do when selecting a cam would be to have one which gives the maximum lift for the entire duration of the down stroke (intake), and the same for the exhaust stroke.
Now... pretend that I have a stock bore/stroke and a set of heads that flow at 300CFM- a little over kill but the low-lift flow numbers are a little higher. If I wanted to save some wear N tear on my engine, could I have the valves open a little early to give a slower slope before hitting maximum lift, and a similar closing slope that would have a little over lap so that my valves wouldn't be slamming shut so harshly.
If I went to a custom cam manufacturer and got a cam with those properties, would that be considered a "good" cam? or do I have the concepts wrong?
Also, the intake and Headers effect the flow of the heads, so it would be worth my while to go with a high-flowing intake like an LSX or to stick with my plan of the LS6 intake. Along similar lines would I be mistaken to go with open headers to minimize backpressure in the exhaust and maximize the rate at which the heads flow exhaust? My goal is around 420HP/400TQ range and my finished car will be a dedicated track/weekend driver, so things like mufflers and cats aren't really a neccesity
Last edited by Biomechanoid; 06-27-2004 at 03:50 PM.
06-27-2004, 10:16 PM
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Sounds like the cfm required thread confused you more than helped,I think some guys on here like to play with calculaters TOO MUCH!First you want a head that flows good numbers low lift to high lift,if you are building a race only set-up then you can use bigger heads with larger ports.I still don"t know where the 280 cfm came from!!Your heads will make or break your motors HP.I think the new AFR head with its small 205 cc port is a good example of a small port with great flow numbers.On the exhaust side the flow numbers are lower than the intakes thats because its easier to push the spent gases out of the cylinder than to suck it in.Usually an exhaust flow of 70 to 85 % of the intake flow is plenty.Get a good flowing head with a modest size intake port, then match the cc in the chamber to get the CR you want.
Now on the cam question,the cams that are making the most power open the valves at a very rapid rate and close at a rapid rate too,don"t worry about being easy on the valvetrain just get good parts that are matched to the cam, lifters, etc.Your cam and related components should be selected for the CID that you have and the RPM that you want to turn,also many other things enter such as car wt, automatic or manuel trans,rear gear ratio and it goes on.Cam selection is a place where you can screw-up if you don"t know what you are doing,ask questions,talk to guys that have done some cam swaps,ask the vendors that you are going to buy the parts from, they don"t mind answering questions if your buying the parts from them.
How about the intake?Seems like you don't have that many choices,ls1,ls6,FAST,CUSTOM MADE??GMPP(WAR)?Seems that the FAST INTAKE is making the most power ,if you don"t want to spend that much then use the ls6.Sounds like the new ls2 intake may be a good intake,may be available soon,can"t what to see a comparison to the ls6 and the FAST!Again get advice from the guys that have tried some different intakes,TB"s etc.On the headers,most cars use 1.75 diameter big motors or high turning stock CID can use1 7/8 headers, the only way you can run OPEN headers will be at the track as this will be VERY LOUD!!!And illegal!!Look at the motors that are run on this thread,look at the numbers they put down,notice their times at the track,you will learn ALOT more about what you want and need than some of these technical threads that
you most of the time. 
:
Now on the cam question,the cams that are making the most power open the valves at a very rapid rate and close at a rapid rate too,don"t worry about being easy on the valvetrain just get good parts that are matched to the cam, lifters, etc.Your cam and related components should be selected for the CID that you have and the RPM that you want to turn,also many other things enter such as car wt, automatic or manuel trans,rear gear ratio and it goes on.Cam selection is a place where you can screw-up if you don"t know what you are doing,ask questions,talk to guys that have done some cam swaps,ask the vendors that you are going to buy the parts from, they don"t mind answering questions if your buying the parts from them.
How about the intake?Seems like you don't have that many choices,ls1,ls6,FAST,CUSTOM MADE??GMPP(WAR)?Seems that the FAST INTAKE is making the most power ,if you don"t want to spend that much then use the ls6.Sounds like the new ls2 intake may be a good intake,may be available soon,can"t what to see a comparison to the ls6 and the FAST!Again get advice from the guys that have tried some different intakes,TB"s etc.On the headers,most cars use 1.75 diameter big motors or high turning stock CID can use1 7/8 headers, the only way you can run OPEN headers will be at the track as this will be VERY LOUD!!!And illegal!!Look at the motors that are run on this thread,look at the numbers they put down,notice their times at the track,you will learn ALOT more about what you want and need than some of these technical threads that
you most of the time. :
06-27-2004, 10:59 PM
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Staging Lane
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Originally Posted by FASTONE
Sounds like the cfm required thread confused you more than helped,I think some guys on here like to play with calculaters TOO MUCH!First you want a head that flows good numbers low lift to high lift,if you are building a race only set-up then you can use bigger heads with larger ports.I still don"t know where the 280 cfm came from!!Your heads will make or break your motors HP.I think the new AFR head with its small 205 cc port is a good example of a small port with great flow numbers.On the exhaust side the flow numbers are lower than the intakes thats because its easier to push the spent gases out of the cylinder than to suck it in.Usually an exhaust flow of 70 to 85 % of the intake flow is plenty.Get a good flowing head with a modest size intake port, then match the cc in the chamber to get the CR you want.
Now on the cam question,the cams that are making the most power open the valves at a very rapid rate and close at a rapid rate too,don"t worry about being easy on the valvetrain just get good parts that are matched to the cam, lifters, etc.Your cam and related components should be selected for the CID that you have and the RPM that you want to turn,also many other things enter such as car wt, automatic or manuel trans,rear gear ratio and it goes on.Cam selection is a place where you can screw-up if you don"t know what you are doing,ask questions,talk to guys that have done some cam swaps,ask the vendors that you are going to buy the parts from, they don"t mind answering questions if your buying the parts from them.
How about the intake?Seems like you don't have that many choices,ls1,ls6,FAST,CUSTOM MADE??GMPP(WAR)?Seems that the FAST INTAKE is making the most power ,if you don"t want to spend that much then use the ls6.Sounds like the new ls2 intake may be a good intake,may be available soon,can"t what to see a comparison to the ls6 and the FAST!Again get advice from the guys that have tried some different intakes,TB"s etc.On the headers,most cars use 1.75 diameter big motors or high turning stock CID can use1 7/8 headers, the only way you can run OPEN headers will be at the track as this will be VERY LOUD!!!And illegal!!Look at the motors that are run on this thread,look at the numbers they put down,notice their times at the track,you will learn ALOT more about what you want and need than some of these technical threads that you most of the time. :
Now on the cam question,the cams that are making the most power open the valves at a very rapid rate and close at a rapid rate too,don"t worry about being easy on the valvetrain just get good parts that are matched to the cam, lifters, etc.Your cam and related components should be selected for the CID that you have and the RPM that you want to turn,also many other things enter such as car wt, automatic or manuel trans,rear gear ratio and it goes on.Cam selection is a place where you can screw-up if you don"t know what you are doing,ask questions,talk to guys that have done some cam swaps,ask the vendors that you are going to buy the parts from, they don"t mind answering questions if your buying the parts from them.
How about the intake?Seems like you don't have that many choices,ls1,ls6,FAST,CUSTOM MADE??GMPP(WAR)?Seems that the FAST INTAKE is making the most power ,if you don"t want to spend that much then use the ls6.Sounds like the new ls2 intake may be a good intake,may be available soon,can"t what to see a comparison to the ls6 and the FAST!Again get advice from the guys that have tried some different intakes,TB"s etc.On the headers,most cars use 1.75 diameter big motors or high turning stock CID can use1 7/8 headers, the only way you can run OPEN headers will be at the track as this will be VERY LOUD!!!And illegal!!Look at the motors that are run on this thread,look at the numbers they put down,notice their times at the track,you will learn ALOT more about what you want and need than some of these technical threads that
you most of the time. :
I've decided that I want to go with 300CFM intake heads for the high low-lift flow numbers. and as you said, ask vendors about what they'd reccomend for cams when I've got everything decided. I know that open headers are loud- I have 6" of exhaust after the turbo on my turbo minivan 
but that is pretty much a dedicated track/rice eater, and my LS1 powered car is going to be the same in use.Right now my biggest problem with getting things done is $$$ until my girlfriend moves in and we start splitting the cost of rent, I can only put away about $350 a month towards the engine- but that should double in a month or two.