Intake Manifold flow vs Head flow
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Originally posted by Gripenfelter
Do you have a link for Wilson?
Do you have a link for Wilson?
This is a good example http://www.wilsonmanifolds.com/smform5.html
Here is Wilsons Site
http://www.wilsonmanifolds.com/
I do sell their stuff too just as a disclaimer, but I only retail stuff that I would use.
Bret
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Oh sweet they are 30 minutes from me, i might have to use them or at least swing by and check them out. 
Edit: Hmm maybe not as they quoted me ruffly $3500 for an intake
Edit: Hmm maybe not as they quoted me ruffly $3500 for an intake
Last edited by kmook; Jun 25, 2003 at 11:26 AM.
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So back to the original topic...
Would you see a big gain going from heads that flow 250cfm@.550 lift to heads that flow 265 or 270cfm@.550 lift with the stock crappy manifold?
Would you see a big gain going from heads that flow 250cfm@.550 lift to heads that flow 265 or 270cfm@.550 lift with the stock crappy manifold?
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It's all relative Jordan.
I work with single planes that flow 288cfm on a 293cfm runner (for example) right out of the box with a port match. Going to a 260cfm intake on a 290cfm runner is not very good IMHO. Longer runners giving a ealier higher tuning pressure with more flow is worth about 40hp.
Bret
I work with single planes that flow 288cfm on a 293cfm runner (for example) right out of the box with a port match. Going to a 260cfm intake on a 290cfm runner is not very good IMHO. Longer runners giving a ealier higher tuning pressure with more flow is worth about 40hp.
Bret
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Originally posted by JordonMusser
brett-
I was under the assumption that a ported LTX intake would flow more than most LTX cylinder heads.
brett-
I was under the assumption that a ported LTX intake would flow more than most LTX cylinder heads.
Bret
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From: Michigan's left coast
Originally posted by Gripenfelter
Would you see a big gain going from heads that flow 250cfm@.550 lift to heads that flow 265 or 270cfm@.550 lift with the stock crappy manifold?
Would you see a big gain going from heads that flow 250cfm@.550 lift to heads that flow 265 or 270cfm@.550 lift with the stock crappy manifold?
1) The stock manifold is not necessarly crappy. Static flow ain't everything.
2) Yes, you'd tend to see an improvement from the increased head flow, especially in regions of operation where manifold tuning came into play.
I'm still waiting for someone to confirm or dispute what I said in my first post.
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From: Upstate NY
Originally posted by Eric Bryant
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.
Yep, flow varies by the square root of the pressure drop ratio. BTW, that's 117.5 isn't it? FWIW why was 28 " H2O selected as the de facto standard for comparing port flow?
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.
Isn't the LTX manifold's short runners the tuning problem for rpm below 7k+?
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.
Why would you want to slow exhaust down with larger pipes? Doesn't that mean that the pressure would rise per Bernoulli? My take is that to keep exhaust flow somewhat steady, the cross-section of the system should steadily decrease as the flow temp and therfore volume decreases.
I'm still waiting for someone to confirm or dispute what I said in my first post.
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.
Yep, flow varies by the square root of the pressure drop ratio. BTW, that's 117.5 isn't it? FWIW why was 28 " H2O selected as the de facto standard for comparing port flow?
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.
Isn't the LTX manifold's short runners the tuning problem for rpm below 7k+?
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.
Why would you want to slow exhaust down with larger pipes? Doesn't that mean that the pressure would rise per Bernoulli? My take is that to keep exhaust flow somewhat steady, the cross-section of the system should steadily decrease as the flow temp and therfore volume decreases.
I'm still waiting for someone to confirm or dispute what I said in my first post.
My $.02
Last edited by OldSStroker; Jun 26, 2003 at 08:23 AM.
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I think the important concept in Eric's post was the fact that most people have no idea what they are talking about when they start talking about "flow". If he hadn't said it, I would have.
There seems to be a huge number of people who post (not on this forum, of course ) here that feel that if you have a 4" exhaust system, and somewhere in that system you add a 3" diameter pipe, the entire system can NEVER flow more than a 3" pipe is capable of. They have no concept that a flow number is totally meaningless if you don't accompany it with a pressure drop. They have no concept of "looking at the system as a whole". Yes, an undersized single component will "affect" flow, and that affect will be in the direction of reducing flow for a given pressure drop, but that single component does not determine the flow capacity of the system all by itself.
The comment about:
...displays the level of knowledge. What it so hard to understand about flowing the exhaust from each bank of 4 cylinders in a 3" pipe, and then going to a 4" pipe when combining the flow of 8 cylinders? Yet the question suggests that because there is a 3" pipe somewhere in the exhaust system, it is somehow going to cause the 4" pipe to be useless, and restricted to the capacity of a 3" pipe.
Throw in the complications of non-steady state flow and changing temperatures, and it becomes overwhelming for the average person. Actually, its not all that easy, even with the "basic" training.....
There seems to be a huge number of people who post (not on this forum, of course
) here that feel that if you have a 4" exhaust system, and somewhere in that system you add a 3" diameter pipe, the entire system can NEVER flow more than a 3" pipe is capable of. They have no concept that a flow number is totally meaningless if you don't accompany it with a pressure drop. They have no concept of "looking at the system as a whole". Yes, an undersized single component will "affect" flow, and that affect will be in the direction of reducing flow for a given pressure drop, but that single component does not determine the flow capacity of the system all by itself.The comment about:
Which is why i never understood a 3" ypipe and the 4" mufflex exhaust system.
Throw in the complications of non-steady state flow and changing temperatures, and it becomes overwhelming for the average person. Actually, its not all that easy, even with the "basic" training....
.
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From: looking for a flow bench so Brook and I can race
Originally posted by Injuneer
I think the important concept in Eric's post was the fact that most people have no idea what they are talking about when they start talking about "flow". If he hadn't said it, I would have.
There seems to be a huge number of people who post (not on this forum, of course ) here that feel that if you have a 4" exhaust system, and somewhere in that system you add a 3" diameter pipe, the entire system can NEVER flow more than a 3" pipe is capable of. They have no concept that a flow number is totally meaningless if you don't accompany it with a pressure drop. They have no concept of "looking at the system as a whole". Yes, an undersized single component will "affect" flow, and that affect will be in the direction of reducing flow for a given pressure drop, but that single component does not determine the flow capacity of the system all by itself.
The comment about:
...displays the level of knowledge. What it so hard to understand about flowing the exhaust from each bank of 4 cylinders in a 3" pipe, and then going to a 4" pipe when combining the flow of 8 cylinders? Yet the question suggests that because there is a 3" pipe somewhere in the exhaust system, it is somehow going to cause the 4" pipe to be useless, and restricted to the capacity of a 3" pipe.
Throw in the complications of non-steady state flow and changing temperatures, and it becomes overwhelming for the average person. Actually, its not all that easy, even with the "basic" training.....
I think the important concept in Eric's post was the fact that most people have no idea what they are talking about when they start talking about "flow". If he hadn't said it, I would have.
There seems to be a huge number of people who post (not on this forum, of course
) here that feel that if you have a 4" exhaust system, and somewhere in that system you add a 3" diameter pipe, the entire system can NEVER flow more than a 3" pipe is capable of. They have no concept that a flow number is totally meaningless if you don't accompany it with a pressure drop. They have no concept of "looking at the system as a whole". Yes, an undersized single component will "affect" flow, and that affect will be in the direction of reducing flow for a given pressure drop, but that single component does not determine the flow capacity of the system all by itself.The comment about:
...displays the level of knowledge. What it so hard to understand about flowing the exhaust from each bank of 4 cylinders in a 3" pipe, and then going to a 4" pipe when combining the flow of 8 cylinders? Yet the question suggests that because there is a 3" pipe somewhere in the exhaust system, it is somehow going to cause the 4" pipe to be useless, and restricted to the capacity of a 3" pipe.
Throw in the complications of non-steady state flow and changing temperatures, and it becomes overwhelming for the average person. Actually, its not all that easy, even with the "basic" training....
.
A lot of what you just said is common sense imho. And I dont mean that in a negative way towards you, Its hard to get the tone right with a keyboard so I wouldn't want to offend you.
I have never taken any class involving flow of any kind.
Common sense tells me that a 4'' pipe with a 3'' section in the middle will not flow as well as a 3'' pipe all around...
As for the y pipe comment, even "more common" sense-
think of it this way (and i know its isn't 100% accurate due to several factors but its a good visulization)
2 three lane highways merge into a 3 lane highway.
2 three lane highways merge into a 4 lane highway.
I really dont have much to contribute to this thread but i have been keeping up with it trying to figure it all out. I'm glad Fred confirmed my "common sense" theory.
It seems like there is a "general" discussion in this thread and an advanced one. The pressue drops and all that stuff is really beyond me. One is scaring me while the other is confusing me... I'll let you figure out which one is which.
Last edited by treyZ28; Jun 26, 2003 at 08:36 AM.
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Originally posted by Injuneer
What it so hard to understand about flowing the exhaust from each bank of 4 cylinders in a 3" pipe, and then going to a 4" pipe when combining the flow of 8 cylinders?
What it so hard to understand about flowing the exhaust from each bank of 4 cylinders in a 3" pipe, and then going to a 4" pipe when combining the flow of 8 cylinders?
Bret
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Trey:
I'm not sure what your point was.... are you agreeing, disagreeing, or just trying to confuse me
.?
The 2-3" pipes vs 1-4" pipe has been explained already. When comparing pipes of relatively similar size, a quickie method of comparing pressure drop, accounting for both cross-sectional area and wetted perimeter is to compare diameter to the 2.5 power, rather than squared. Using that approach puts 2-3's even closer to 1-4.
Who's common sense? The answer actually depends on how long the overall system is. If you had a very long system, and a length of 3" pipe in the center, assuming you used tapered transitions, rather than "butt" connections, the 4->3->4 would produce a greater flow for a given pressure drop, or a lower pressure drop for a given flow, than the same system utilizing all 3" pipe. Even without the tapered transitions, the 4-3-4 system will flow more for the same pressure loss.
In a very short system, the losses resulting from the "transitions" between diameters might be large enough to cause the "all 3" system to flow better. But in the length of the typical exhaust system, this isn't going to happen.
Huhh? what is the analogy to an exhaust system? You lost me.
If you merge the cars from two 3-lane roads into a single 3-lane road, the traffic on the single 3-lane road needs to move twice as fast as the traffic on the two 3-lane feeders, or there will be a huge backup. They will only need to travel 1.5 times as fast on the single 4-lane road. The faster the exhaust moves, the more pressure loss in the pipe. So the 2 3-lane into 1 4-lane exhaust pipe produces the least pressure loss.
I think you're just trying to confuse me....
I'm not sure what your point was.... are you agreeing, disagreeing, or just trying to confuse me
.?The 2-3" pipes vs 1-4" pipe has been explained already. When comparing pipes of relatively similar size, a quickie method of comparing pressure drop, accounting for both cross-sectional area and wetted perimeter is to compare diameter to the 2.5 power, rather than squared. Using that approach puts 2-3's even closer to 1-4.
Common sense tells me that a 4'' pipe with a 3'' section in the middle will not flow as well as a 3'' pipe all around...
In a very short system, the losses resulting from the "transitions" between diameters might be large enough to cause the "all 3" system to flow better. But in the length of the typical exhaust system, this isn't going to happen.
2 three lane highways merge into a 3 lane highway.
2 three lane highways merge into a 4 lane highway.
2 three lane highways merge into a 4 lane highway.
If you merge the cars from two 3-lane roads into a single 3-lane road, the traffic on the single 3-lane road needs to move twice as fast as the traffic on the two 3-lane feeders, or there will be a huge backup. They will only need to travel 1.5 times as fast on the single 4-lane road. The faster the exhaust moves, the more pressure loss in the pipe. So the 2 3-lane into 1 4-lane exhaust pipe produces the least pressure loss.
I think you're just trying to confuse me....