Intake Manifold flow vs Head flow
06-23-2003, 09:39 AM
#1
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Intake Manifold flow vs Head flow
I was thinking about this the other day.
Lets suppose your heads flow 275cfm@.550lift but your LT1 intake only flows 235cfm@.550 lift.
What's the point of having heads flow that much if your manifold is flowing considerably less than that?
Wouldn't you only get 235cfm flowing through the head with the intake on?
Or are there people out there getting their intakes to flow as much as their heads?
Lets suppose your heads flow 275cfm@.550lift but your LT1 intake only flows 235cfm@.550 lift.
What's the point of having heads flow that much if your manifold is flowing considerably less than that?
Wouldn't you only get 235cfm flowing through the head with the intake on?
Or are there people out there getting their intakes to flow as much as their heads?
06-23-2003, 11:07 AM
#3
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I am almost positive the intakes flow well into the 300s? And if not, its pretty simple that you can only flow as much air as the weakest flow point.
Which is why i never understood a 3" ypipe and the 4" mufflex exhaust system.
cause if you put a garden hose and mate it up to a fire hose, you wont be able to flow more water than if you just kept a straight gardenhose instead of the firehose attached on.
Which is why i never understood a 3" ypipe and the 4" mufflex exhaust system.
cause if you put a garden hose and mate it up to a fire hose, you wont be able to flow more water than if you just kept a straight gardenhose instead of the firehose attached on.
06-23-2003, 11:26 AM
#4
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You gotta understand two things:
1) Just because a particular orifice, like a manifold, is said to flow "235 CFM", that doesn't mean that this is an absolute limit; rather, it just describes the rate of flow at a given pressure drop. If you've got 235 CFM at 28" of H20, then you can flow 470 CFM at 112" of H20, or you can flow 127.5 CFM at 7" of H20.
2) Flowbench numbers assume constant rates of flow. That doesn't happen in the intake runner. If you can sacrifice a bit of "flow" (i.e. increase the static pressure required for a given flow rate) but pick up a significant amount of pressure in the running from resonant tuning effects, it'd be a good compromise - but the flow bench would tell you differently.
thewinner,
Keep in mind that the resistance of an orifice increaes with length, so your analogy isn't exactly correct. You also need to keep in mind that the exhaust gases cool and lose velocity as they get further from the combustion chamber, so it's natural that they'd like to "see" a larger cross-sectional area as they get further away from the head.
1) Just because a particular orifice, like a manifold, is said to flow "235 CFM", that doesn't mean that this is an absolute limit; rather, it just describes the rate of flow at a given pressure drop. If you've got 235 CFM at 28" of H20, then you can flow 470 CFM at 112" of H20, or you can flow 127.5 CFM at 7" of H20.
2) Flowbench numbers assume constant rates of flow. That doesn't happen in the intake runner. If you can sacrifice a bit of "flow" (i.e. increase the static pressure required for a given flow rate) but pick up a significant amount of pressure in the running from resonant tuning effects, it'd be a good compromise - but the flow bench would tell you differently.
thewinner,
Keep in mind that the resistance of an orifice increaes with length, so your analogy isn't exactly correct. You also need to keep in mind that the exhaust gases cool and lose velocity as they get further from the combustion chamber, so it's natural that they'd like to "see" a larger cross-sectional area as they get further away from the head.
06-23-2003, 12:09 PM
#6
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Originally posted by thewinner
I am almost positive the intakes flow well into the 300s? And if not, its pretty simple that you can only flow as much air as the weakest flow point.
Which is why i never understood a 3" ypipe and the 4" mufflex exhaust system.
cause if you put a garden hose and mate it up to a fire hose, you wont be able to flow more water than if you just kept a straight gardenhose instead of the firehose attached on.
I am almost positive the intakes flow well into the 300s? And if not, its pretty simple that you can only flow as much air as the weakest flow point.
Which is why i never understood a 3" ypipe and the 4" mufflex exhaust system.
cause if you put a garden hose and mate it up to a fire hose, you wont be able to flow more water than if you just kept a straight gardenhose instead of the firehose attached on.
My $.02
Last edited by OldSStroker; 06-23-2003 at 12:19 PM.
06-23-2003, 12:47 PM
#7
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Funny how a 320cfm LS1 head with a LS1 intake on it flows 220cfm and still puts the car in the low 10's, look at Judd's car from S.A.M. There is something odd about this.
Now if you had 300cfm out of the intake with 320cfm heads then you are going to get much more power.
Bret
Now if you had 300cfm out of the intake with 320cfm heads then you are going to get much more power.
Bret
06-23-2003, 02:51 PM
#9
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Originally posted by thewinner
I am almost positive the intakes flow well into the 300s? And if not, its pretty simple that you can only flow as much air as the weakest flow point.
Which is why i never understood a 3" ypipe and the 4" mufflex exhaust system.
cause if you put a garden hose and mate it up to a fire hose, you wont be able to flow more water than if you just kept a straight gardenhose instead of the firehose attached on.
I am almost positive the intakes flow well into the 300s? And if not, its pretty simple that you can only flow as much air as the weakest flow point.
Which is why i never understood a 3" ypipe and the 4" mufflex exhaust system.
cause if you put a garden hose and mate it up to a fire hose, you wont be able to flow more water than if you just kept a straight gardenhose instead of the firehose attached on.
i thikn you are thinking of "bottle necking?" which holds true to a cetrain degree- but not 100% of thec case. you cant figure out the flow of an entire system based on the weakest link or else no one with a cat would ever get an aftermarket catback
06-23-2003, 08:47 PM
#12
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How would an LT1's performance change if you cut out the divider between each runner in the intake, effectively shortening the individual runners to each cylinder? Does this make a narrower or broader torque curve? Earlier torque of high rpm torque? What other parameters would a change like this alter? Seems like there would be less time for the flow to develop (streamlines to straighten themselves out) due to the shorter length, but would this be good? I guess not since nobody does it but a good explanation would be nice.
H
H
06-24-2003, 01:47 AM
#13
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Originally posted by 96TAWS6
How would an LT1's performance change if you cut out the divider between each runner in the intake, effectively shortening the individual runners to each cylinder? Does this make a narrower or broader torque curve? Earlier torque of high rpm torque? What other parameters would a change like this alter? Seems like there would be less time for the flow to develop (streamlines to straighten themselves out) due to the shorter length, but would this be good? I guess not since nobody does it but a good explanation would be nice.
H
How would an LT1's performance change if you cut out the divider between each runner in the intake, effectively shortening the individual runners to each cylinder? Does this make a narrower or broader torque curve? Earlier torque of high rpm torque? What other parameters would a change like this alter? Seems like there would be less time for the flow to develop (streamlines to straighten themselves out) due to the shorter length, but would this be good? I guess not since nobody does it but a good explanation would be nice.
H
Bret
06-24-2003, 01:49 AM
#14
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Originally posted by Gripenfelter
So would you see a large gain in putting a Hogan manifold on ported LT1s? Or is it best left for blower and large stroker applications?
So would you see a large gain in putting a Hogan manifold on ported LT1s? Or is it best left for blower and large stroker applications?
If I'm going with big dollars for a custom intake, either I'll make one myself out of Carbon Fibre or go to Wilson Manifolds. That or just adapt a Single Plane intake like I'm doing now.
Bret