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?

anybody have a real figure of exactly what the LT1 and LT4 intakes flow?

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.

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.

seems to me that the exhaust gases will contract upon cooling, therefore not requiring a bigger catback, and a 3"
pipe would actually keep velocity up.:confused: :confused:

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.

The inside area of a 4 inch outside dia. tube is about 91% of the inside area of 2 tubes 3 inch outside dia. Flow depends primarily on cross-section area and amount of wall surface. The 4 in. tube has only about 2/3 of the surface area of 2 3 inch tubes, so effectively, the flow of 2 3 inch tubes would be close to that of one 4 inch tube.

My $.02

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

So what do our intakes in fact flow? Ported and stock.

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.

umm i dont know about you, but my garden hose is only about 1'' thick.... i'm confident its a bit of a restriction...

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 :o

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?

Originally posted by treyZ28
i thikn you are thinking of "bottle necking?"

ya pretty much what i was thinking.

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:)

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:)

Basically you are shortening the runner and causing odd tuning in some cylinder pairs, namely the 5 and 7 pair. None of this is a good idea. There were old aftermarket intakes back in the day that had this but they didn't work either.

Bret

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?

A stock intake is fine on a blown setup, it's the NA tuning pressures where the stock one really sucks.

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

Do you have a link for Wilson?

Originally posted by Gripenfelter
Do you have a link for Wilson?

Yeah, none of it's cheap though but for stuff that's about a work of art and Wilson's expertise it's worth it on a uber setup.

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

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 :eek:

Someone needs to make a plastic intake manifold with slightly longer runners. :p

Originally posted by kmook
Hmm maybe not as they quoted me ruffly $3500 for an intake :eek: Ouch. Hogan's did mine for $2,850 with direct port nitrous bungs installed. :)

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?

yes, you will see gains. the stock intake is NOT crappy.

not great, but not a huge restriction.

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

brett-
I was under the assumption that a ported LTX intake would flow more than most LTX cylinder heads.

Originally posted by JordonMusser
brett-
I was under the assumption that a ported LTX intake would flow more than most LTX cylinder heads.

It would have to be very well ported. Almost all the time you see some CFM decrease, there are some setups where it gets better but they are a very well worked out package.

Bret

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?

IMO:

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.

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 did ask for opinions.

My $.02

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:

Which is why i never understood a 3" ypipe and the 4" mufflex exhaust system.

...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.... :).

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.... :).

Fred-
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.

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?

Really what is so hard about that? 2 3" pipes flowing into 1 4" pipe

Bret

Trey:

I'm not sure what your point was.... are you agreeing, disagreeing, or just trying to confuse me :D :D.?

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...


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.


2 three lane highways merge into a 3 lane highway.

2 three lane highways merge into a 4 lane highway.

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.... :eek:

Originally posted by Injuneer
I think you're just trying to confuse me.... :eek:

Tis the nature of confused people to confuse those around them.... this could become a real problem. And Albert Einstein is likely rolling in his grave 13.88 times a day.:o

-Mindgame

Originally posted by Injuneer
Trey:

I'm not sure what your point was.... are you agreeing, disagreeing, or just trying to confuse me :D :D.?

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.... :eek:

I was agreeing fred ;)

and you basically agreed with me agreeing to you :confused:

And yes, the 4--->3--->4 would be a smooth transisiton, not a "butt" - i'm sure thre a bazillion variables we could include

so 4-------------->3--->4------------> will more than likely have more flow than

3 all the way acorss (but then there are issues with how the 3'' meets the 4'' and stuff.


and the highway was in agreement again with "duh think about it for half a second"

2 three inch collectors meeting a 3 inch catback vs 2 three inch collectors meeting a 4'' catback


my basic agreement point was "think about it for a second"
but guess it wasn't all that clear :o


Let me summerize-

I agree fred :)

Originally posted by Mindgame
Tis the nature of confused people to confuse those around them.... this could become a real problem. And Albert Einstein is likely rolling in his grave 13.88 times a day.:o

-Mindgame

ROFL here.

"Men who borrow their opinions can never repay their debts."---George Savile, 1633-1695

LOL

"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former." - Albert Einstein;)

-Mindgame

alright, enough picking on Trey here.

On the manifold topic, there is easily alot of power to be found in LT1's through the intake IMHO. I would easily take another 20cfm and longer runners on a LT1 vs another 20cfm, both would be even better. The TQ gain would be worth it more than the HP gain, but the additonal TQ you would really feel.

Bret

Originally posted by OldSStroker
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?


Oops, I made another math error. Let's be honest - I never learned to count past 10 :(

I have no idea where the standard of 28" H20 comes from, but it's damn close to 1 PSI so I imagine that has something to do with it. Either that, or the first flowbench designer had a broken-off yardstick sitting around.


Isn't the LTX manifold's short runners the tuning problem for rpm below 7k+?


Yep, but I'm guessing that tuned runners would require more plenum volume, and that of course would have made the packaging issues worse for the 4th-gen F-body. If you believe what Lingenfelter had to say on the topic, the Accel Superram was a big improvement over the stock LT1 intake (but I'd be making the same claims if I was trying to sell you a $1K intake, too).


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.


It's not that I want to slow down the exhaust gases; it's that they're naturally going to loose velocity as they cool, and therefore they're going to require a larger cross-sectional area. At least that's the way I understand it; hopefully someone can correct me if I'm wrong.


You did ask for opinions.


That's because I like it when guys like you speak up and either tell me that I'm right, or inform me that I need to lay off the crack pipe :)

Originally posted by Eric Bryant

It's not that I want to slow down the exhaust gases; it's that they're naturally going to loose velocity as they cool, and therefore they're going to require a larger cross-sectional area. At least that's the way I understand it; hopefully someone can correct me if I'm wrong.


As the gasses cool down, they become more dense, occupy less volume. To get the equivalent pressure drop with the smaller volume, you would use a smaller pipe as the gasses cool. If you just leave the pipe size alone as they cool down, they will just naturally slow down and produce less pressure drop. Can't think of a reason why they would need a larger cross-sectional area.

I don't think Bernoulli is relavent to this.... isn't that the theory that tells you the pressure perpendicular to flow direction is reduced as velocity increases.... not a "pressure drop" issue?

I always go back to George's car.... 1,125HP, Hooker LT's into a 3" Y-pipe into a 4" Mufflex cat-back, with a single 4" pipe out of the exhaust. But George likes the "stock" look, so he cuts the little tiny tip off the 30th SS's original SLP 2OTL exhaust and welds it to the end of the 4" pipe out of the muffler. Looks stock. Still make good HP. But it also pushed the gas velocity way up, as demonstrated here. (http://cjcfo.fbody.com/members/injuneerzz@aol.com/PhotosF/DCP02505.jpg)

From what you said Trey, it seemed like you read it completely backwards. A 3" pipe is going to provide more resistance than a 4" pipe, so even if a 3" coupler in the midst somewhere , the rest of the exaust at least is free flowing.

What I think Fred was getting at though, is if we are using a Hooker LT example, you have two 3" collectors going into a hopefully dual 3" to 4" Y pipe hooked up to your 4" exaust.

Originally posted by Dr.Mudge
From what you said Trey, it seemed like you read it completely backwards. A 3" pipe is going to provide more resistance than a 4" pipe, so even if a 3" coupler in the midst somewhere , the rest of the exaust at least is free flowing.

What I think Fred was getting at though, is if we are using a Hooker LT example, you have two 3" collectors going into a hopefully dual 3" to 4" Y pipe hooked up to your 4" exaust.
wow-

I just re-read what i wrote-

I thought 4-3-4 > 3-3-3 but for some reason i wrote will NOT flow as well:confused:

now i see where all the confusion is coming from (and jokes at my expense:o ) I re-read it twice quickly but i guess i read what i thought i wrote over again, not the actual words.

I was sitting here trying to figure out why everyone was disagreeing. I just couldn't picture the 3-3-3 flowing as well as a 4-3-4

I REALLY need to be more careful and I feel rather stupid right about now...:(

my appologies:cry:

Is there a way of measuring velcocity of air after it goes through the cylinder head and into the chamber? I don't mean cfm. Maybe Swirl Velocity or Swirl RPM??

Originally posted by Gripenfelter
Is there a way of measuring velcocity of air after it goes through the cylinder head and into the chamber? I don't mean cfm. Maybe Swirl Velocity or Swirl RPM??

We are getting off this topic, but yeah there are swirl meters for flow benches.

Bret

Originally posted by OldSStroker
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?

My understanding gives credit for this std. (28") to S. Yunick. The reasoning was that using this std. to compare head port flow, would result in a more accurate comparo to actual/usable gains experienced on a dyno. :shrug:

Originally posted by Mindgame
"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former." - Albert Einstein ;)

-Mindgame

Da mind is a terrible ting.

Originally posted by arnie
My understanding gives credit for this std. (28") to S. Yunick. The reasoning was that using this std. to compare head port flow, would result in a more accurate comparo to actual/usable gains experienced on a dyno.



I'll go along with that. Smokey claimed that at less than about 26-28 in H2O he couldn't find small changes, and above that it didn't make much difference.

Also, 28 in H2O is just about 1 psi, which is near what a max. performance engine pulls around hp peak.