boost psi vs head flow for 427
03-09-2009, 11:39 PM
#21
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That's true I suppose. I guess it depends alot on power goals as well. If you arent looking to set records, you probably dont need big money spent on heads and its better spent elsewhere...
03-10-2009, 01:53 AM
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Think about this way....at some point if you put pressure to a garden hose....at some point the hose can only pass so much weather that 20psi or 50psi the out put will be the same...it just back pressure with no out put gain.. I have seen 3 lt1 car with more turbo then the heads can flow can in general the rwhp is around 1100 regardless of how much you turn it up..thats it! It's all it can pass through.. That way im going to a dart block with brodix heads. They will be able to pass more volume/air.
When i use to play with the 5.9Cummings diesel engines . They would just keep making more and more power as boost went up. Ive seen over 80 psi of boost pressure on them and they made alot more power at 80 then when it was run at 50 psi.
Yes they run on different fuel but they work in the same manners /acting as just a big air pump? SO as long as the fuel is there more boost pressure should make more power.
What was the port flow on the lt1 heads? What was the exhaust pressures before the turbo? What was the boost psi going in?
Im sorry guys i just cant seem to fully understand this.
Last edited by BigRich954RR; 03-10-2009 at 02:14 AM.
03-10-2009, 07:05 AM
#25
wouldn't in theory the engine with the least amount of boost and the best flowing heads make the most power ?
even if the IAT are the same.
The exhaust (turbocharger) backpressure of the higher boosted engine will be higher and therefore limit the power and would lower rpm at which max power occurs.
At least my personal experience seems to dictate the lower boost + higher flowing head likes more rpm's, making more power but at the cost of torque in midrange compared to high boost + worse flow heads
You could even take it a step further and use a bigger a/r ratio on the engine with the high flow heads as this engine produces more power N/a and thus more exhaust gasses at the same rpm and can benefit from a higher flowing compressorwheel + turbine
even if the IAT are the same.
The exhaust (turbocharger) backpressure of the higher boosted engine will be higher and therefore limit the power and would lower rpm at which max power occurs.
At least my personal experience seems to dictate the lower boost + higher flowing head likes more rpm's, making more power but at the cost of torque in midrange compared to high boost + worse flow heads
You could even take it a step further and use a bigger a/r ratio on the engine with the high flow heads as this engine produces more power N/a and thus more exhaust gasses at the same rpm and can benefit from a higher flowing compressorwheel + turbine
Last edited by jeejee; 03-10-2009 at 07:17 AM.
03-10-2009, 10:02 AM
#26
Turbos will be different than superchargers because with turbos, they are managed by a certain boost pressure. So obviously 15psi of pressure with high flowing heads will make more than 15psi with low flowing heads. With a supercharger, you are spinning it with a belt and it will flow whatever cfm it is going to flow with no regard to how much boost its making. apples to oranges comparo there.
And as far as the compressibility of air goes, at the levels discussed here (30psi and less) the air is barely compressed much at all. That is an invalid point when discussing fluid flow with air at that level.
Furthermore, in regard to the garden hose analogy, i can promise you that a garden hose at 50psi WILL be flowing more than a garden hose at 20psi. (That is, unless the flow is completely blocked off and capped at one end). The math is not that difficult.
Assuming laminar, negligible compressibility flow with negligible friction, head, or thermal losses.. From the Bernoulli equation...
V = (2P/d)^0.5
V = velocity
P = differential pressure
d = air density
area = A = pi(dia^2)/4
flowrate = Q = V*A
There is a direct relation in flow rate with increased pressure. In short, more pressure correlates to more cfm given the same system.
And as far as the compressibility of air goes, at the levels discussed here (30psi and less) the air is barely compressed much at all. That is an invalid point when discussing fluid flow with air at that level.
Furthermore, in regard to the garden hose analogy, i can promise you that a garden hose at 50psi WILL be flowing more than a garden hose at 20psi. (That is, unless the flow is completely blocked off and capped at one end). The math is not that difficult.
Assuming laminar, negligible compressibility flow with negligible friction, head, or thermal losses.. From the Bernoulli equation...
V = (2P/d)^0.5
V = velocity
P = differential pressure
d = air density
area = A = pi(dia^2)/4
flowrate = Q = V*A
There is a direct relation in flow rate with increased pressure. In short, more pressure correlates to more cfm given the same system.
03-10-2009, 10:12 AM
#27
I understand the garden hose theory. But water doesnt compress so your are not compressing more into the same space forcing it to take up less room just forcing it harder thought a hole. Which still adds to the flow but not as much lets say a garden hose flows 12 gpm with a 1/2 hole at 40 psi This is a avg but close. Now my water jet flows 8.8 gpm at 60K psi though 1/16 hole
When i use to play with the 5.9Cummings diesel engines . They would just keep making more and more power as boost went up. Ive seen over 80 psi of boost pressure on them and they made alot more power at 80 then when it was run at 50 psi.
Yes they run on different fuel but they work in the same manners /acting as just a big air pump? SO as long as the fuel is there more boost pressure should make more power.
What was the port flow on the lt1 heads? What was the exhaust pressures before the turbo? What was the boost psi going in?
Im sorry guys i just cant seem to fully understand this.
When i use to play with the 5.9Cummings diesel engines . They would just keep making more and more power as boost went up. Ive seen over 80 psi of boost pressure on them and they made alot more power at 80 then when it was run at 50 psi.
Yes they run on different fuel but they work in the same manners /acting as just a big air pump? SO as long as the fuel is there more boost pressure should make more power.
What was the port flow on the lt1 heads? What was the exhaust pressures before the turbo? What was the boost psi going in?
Im sorry guys i just cant seem to fully understand this.
Btw...air takes up space, and can back up in the intake and be unbenifisal to making power...instead just building heat.
03-10-2009, 10:17 AM
#28
Turbos will be different than superchargers because with turbos, they are managed by a certain boost pressure. So obviously 15psi of pressure with high flowing heads will make more than 15psi with low flowing heads. With a supercharger, you are spinning it with a belt and it will flow whatever cfm it is going to flow with no regard to how much boost its making. apples to oranges comparo there.
And as far as the compressibility of air goes, at the levels discussed here (30psi and less) the air is barely compressed much at all. That is an invalid point when discussing fluid flow with air at that level.
Furthermore, in regard to the garden hose analogy, i can promise you that a garden hose at 50psi WILL be flowing more than a garden hose at 20psi. (That is, unless the flow is completely blocked off and capped at one end). The math is not that difficult.
Assuming laminar, negligible compressibility flow with negligible friction, head, or thermal losses.. From the Bernoulli equation...
V = (2P/d)^0.5
V = velocity
P = differential pressure
d = air density
area = A = pi(dia^2)/4
flowrate = Q = V*A
There is a direct relation in flow rate with increased pressure. In short, more pressure correlates to more cfm given the same system.
And as far as the compressibility of air goes, at the levels discussed here (30psi and less) the air is barely compressed much at all. That is an invalid point when discussing fluid flow with air at that level.
Furthermore, in regard to the garden hose analogy, i can promise you that a garden hose at 50psi WILL be flowing more than a garden hose at 20psi. (That is, unless the flow is completely blocked off and capped at one end). The math is not that difficult.
Assuming laminar, negligible compressibility flow with negligible friction, head, or thermal losses.. From the Bernoulli equation...
V = (2P/d)^0.5
V = velocity
P = differential pressure
d = air density
area = A = pi(dia^2)/4
flowrate = Q = V*A
There is a direct relation in flow rate with increased pressure. In short, more pressure correlates to more cfm given the same system.
I know its a bit off the topic, but in a perfect motor ..turn it up, might work...but other force are also at play ..so really it not the case with our motors....but I would like to know more about this.......
Last edited by otherwhitemeat; 03-10-2009 at 10:48 AM.
03-10-2009, 11:48 AM
#29
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a given size motor with a s/c or turbo will always make more power with better flowing heads and less boost.Making boost costs hp and creats heat.To make higher boost the compressor has to work harder to do that.
On a turbo setup building more boost means building more exhaust backpressure-which costs hp.on a s/c making more boost takes more hp from the crankshaft.Plus more heat means higher iat's which means you cant be vas aggressive on the tune.
So what i'm saying is that if you have to move a certain amount of air-it's going to alot easier with a smaller amount or restriction-it's like trying to blow through a coffee stir compared blowing through a drink straw.
On a turbo setup building more boost means building more exhaust backpressure-which costs hp.on a s/c making more boost takes more hp from the crankshaft.Plus more heat means higher iat's which means you cant be vas aggressive on the tune.
So what i'm saying is that if you have to move a certain amount of air-it's going to alot easier with a smaller amount or restriction-it's like trying to blow through a coffee stir compared blowing through a drink straw.
03-10-2009, 11:48 AM
#30
Yes.. add friction, heat air and fuel mix, plus port and volumes and dissigns in the mix....And if we are trying to TURN IT UP.... psi is going to be well past 30 psi...and most likely past 40 or 50 psi....Why would a racer spend 10-15k on high flow cfm heads.. if they can just turn it up???
I know its a bit off the topic, but in a perfect motor ..turn it up, might work...but other force are also at play ..so really it not the case with our motors....but I would like to know more about this.......
I know its a bit off the topic, but in a perfect motor ..turn it up, might work...but other force are also at play ..so really it not the case with our motors....but I would like to know more about this.......
What I think a lot of ppl dont understand is that if you are flowing 1500cfm for example into the front of the TB opening on a manifold, all that air WILL get divided up into the 8 cylinders and the engine will be forced to consume it. Hence the whole term "forced induction". There is nowhere for any excess air to go BUT the cylinders. It is a closed system. This is not a difficult concept to grasp.
03-10-2009, 07:38 PM
#31
Yes, heat, and friction will be a small factor, but not nearly enough to totally compromise the equations above or skew the results significantly at all. Oh, and port geometry is included in the equations. That is simply cross sectional area.
What I think a lot of ppl dont understand is that if you are flowing 1500cfm for example into the front of the TB opening on a manifold, all that air WILL get divided up into the 8 cylinders and the engine will be forced to consume it. Hence the whole term "forced induction". There is nowhere for any excess air to go BUT the cylinders. It is a closed system. This is not a difficult concept to grasp.
What I think a lot of ppl dont understand is that if you are flowing 1500cfm for example into the front of the TB opening on a manifold, all that air WILL get divided up into the 8 cylinders and the engine will be forced to consume it. Hence the whole term "forced induction". There is nowhere for any excess air to go BUT the cylinders. It is a closed system. This is not a difficult concept to grasp.
03-10-2009, 08:45 PM
#32
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a given size motor with a s/c or turbo will always make more power with better flowing heads and less boost.Making boost costs hp and creats heat.To make higher boost the compressor has to work harder to do that.
On a turbo setup building more boost means building more exhaust backpressure-which costs hp.on a s/c making more boost takes more hp from the crankshaft.Plus more heat means higher iat's which means you cant be vas aggressive on the tune.
So what i'm saying is that if you have to move a certain amount of air-it's going to alot easier with a smaller amount or restriction-it's like trying to blow through a coffee stir compared blowing through a drink straw.
On a turbo setup building more boost means building more exhaust backpressure-which costs hp.on a s/c making more boost takes more hp from the crankshaft.Plus more heat means higher iat's which means you cant be vas aggressive on the tune.
So what i'm saying is that if you have to move a certain amount of air-it's going to alot easier with a smaller amount or restriction-it's like trying to blow through a coffee stir compared blowing through a drink straw.
so your saying if u had 406 sbc 23* cylinderheads made 1000 fwhp with a gt4788 ,then swapping the cylinderheads for 15* cylinderheads you would make 1000 fwhp with less boost with the same turbo??? maybe with a different turbo/turbine but not with same turbocharger.
03-10-2009, 09:26 PM
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Thats not exactly what I was trying to disagree with....but answer this...so you think you can put a turbo on a car and keep turning it up till it maxxes the turbos cfm rating and the motor will just make the power that applies to the turbo/cfm rating......cause thats where I have trying and it doesn't work.
corect me if i am wrong
03-10-2009, 11:41 PM
#34
if the air gets stuck int the intake manifold or the intake runers in the head then your only building boost ( restrection ) and no CFM ( air flow ) is going to the pistons and thus no more power , again it dipends on the cam and were is it geting in full song
corect me if i am wrong
corect me if i am wrong
03-11-2009, 02:27 AM
#35
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if the air gets stuck int the intake manifold or the intake runers in the head then your only building boost ( restrection ) and no CFM ( air flow ) is going to the pistons and thus no more power , again it dipends on the cam and were is it geting in full song
corect me if i am wrong
corect me if i am wrong
How could the air get stuck in the intake track ? Thats all boost is a way of forcing it passed any restriction. Im not saying better head wont make it easier to build more power at lower psi. there has to be a point where it doesnt matter much ?
As we sit here reading this post we are breathing the air at 14.7 psi around sea level this reads on a boost gauge as 0 a base Now add 14.7 of boost your at double the amount of air. 28.6 psi 3 times the amount at base
ok heads the flow 350 cfm at base 0psi
heads at 14.7 psi 700cfm Right ?
heads at 28.6 psi 1050cfm of air ?
VS heads That flow
250 CFM at base
500CFm at 14.7
750CFM at 28.6
Yes there a different amount But at what point will it not matter much
piston at BDC with 0 psi fill cylinder to 80% with 350 cfm head.
piston at BDC at 14.7 fills to 12 psi with 700cfm head
piston at BDC at 28.6 fills to 28.6 psi cause we are trying to force 1050 CFM of air into a 1cbf of space and has enough time and force for intake pressure to equal cylinder pressure.
I know as you compress air it heats up which makes the tune less aggressive but let take that part out. Im not trying to talk about heat change of the air that can be kept the same in other ways. Like I just installed a huge intercooler with meth injection which keeps the air temps the same.
03-11-2009, 06:59 AM
#36
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that is not geting into tourqe , then this another story
03-11-2009, 12:41 PM
#37
as soon as the intake valve into the cylinder opens, whatever pressure that is in the manifold will equalize into the cylinder. If the manifold was choking the intake track like you guys are trying to say, then that would cause cavitation and be detrimental to the blower itself. This would almost be the equivalent of closing the throttle really fast and having no BOV or BPV to let the excess boost buildup escape, so it forces its way back thru to the blower and causes severe damage.
03-11-2009, 01:55 PM
#38
as soon as the intake valve into the cylinder opens, whatever pressure that is in the manifold will equalize into the cylinder. If the manifold was choking the intake track like you guys are trying to say, then that would cause cavitation and be detrimental to the blower itself. This would almost be the equivalent of closing the throttle really fast and having no BOV or BPV to let the excess boost buildup escape, so it forces its way back thru to the blower and causes severe damage.
