LS7 head flow numbers
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Joined: Feb 2003
Posts: 2,639
From: Mooresville, NC
Re: LS7 head flow numbers
i was wrong! turns out they are in the 220-230 range... 
http://members.***.net/jason99ta_2/stockLS1.jpg
http://members.***.net/jason99ta_2/stockLS1.jpg
Registered User
Joined: Sep 2002
Posts: 655
Re: LS7 head flow numbers
Still amazing to get that sort of power from the head and cam figures.
The 0.500" numbers don't even get touched.
Are you telling me the LS1 slams out 300+ HP with a peak flow of 222 CFM @
0.500" lift? Even then, how much duration does that valve see at 0.5"?
Someone please find the valve timing for the stock LS1 camshaft (IVO, IVC, EVO, EVC).
I can't find them anywhere.
< 220 degrees @ 0.050" Damn...
The 0.500" numbers don't even get touched.
Are you telling me the LS1 slams out 300+ HP with a peak flow of 222 CFM @
0.500" lift? Even then, how much duration does that valve see at 0.5"?
Someone please find the valve timing for the stock LS1 camshaft (IVO, IVC, EVO, EVC).
I can't find them anywhere.
< 220 degrees @ 0.050" Damn...
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Joined: Oct 2002
Posts: 6,518
Re: LS7 head flow numbers
Looking at those flow numbers, valve sizes and the supposed cam specs the motor is really well balanced.....
Initially looking at a 348cfm intake and a 219cfm exhaust at peak lift you think.... dam that's way off at 63% E/I ratio. A lot like most high end 2 valve NA heads (Pro Stock, NASCAR etc...) This is due to the valve sizes.... We are talking about a intake valve on a OEM production motor that is 53% of the bore! That's amazing and following the lead of most high end NA race heads. At the same time you see a exhaust valve that is small in comparison, but still 73% the curtain area/diameter. They could have moved that exhaust valve over a little more and squeezed a bigger intake in there but it really wasn't needed.
The 211/230 cam with probably a LSA in the 118-120 range is pretty fitting to this as well. I would say that's the LSA range due to a few things.... the first being GM likes to have -16 to -20 overlap at .050 in a OEM HO engine like this today. The second being that at a 118 ICL you are looking at a DCR of 8.5 and 8.3 at 120 ICL.
When you combine the cam lobe area with the valve sizes and the flow you end up with what is considered a perfect 75% E/I ratio.... It's not easy to come up with since you need to calculate the lobe area of the cam lobes in deg/sq in. Gotta love computers.
To the whole bigger valve thing....
Valve size is basically a limiting factor in a cylinder head. I've seen Darrin Morgan or Reher-Morrison describe it the best, but esentially the valve diameter and valve lift are what limits flow. You then can look at the L/D (lift/diameter) ratio of a valve (This is calld the Discharge Coefficent once you throw the flow in there.) and determine when it starts to get out of it's own way. This happens at a L/D of 25% so in the LS7 it's .550 lift. Basically that's what Larry was getting at here too. Now in terms of software and how this effects everything it all relates to how sophisticated the program is. The simple engine programs out there will reward you with more power when you increase the valve size because it takes into account that you will gain flow with that. A program that thinks you are smart enough to change the flow numbers when you change the valve size and therefore how it would actually work in the real world will punish you if you throw more valve at it, because you are not getting any more flow and in turn you are increasing the Discharge Coefficient of the motor. In reality a motor with a 2.00" valve and a port designed around it can't out flow or keep up with a port with a 2.08" valve and a port designed around it. If you kept the port flowing the same cfm say 300cfm @ .600 you would have a significantly higher discharge coefficient on the small valve.... 2" valve =79.6 D/C and a 2.08" valve = 76.5 D/C, if you kept up the 79.6 D/C you would end up with a head that flowed 312cfm and therefore probably more power.
Bret
Initially looking at a 348cfm intake and a 219cfm exhaust at peak lift you think.... dam that's way off at 63% E/I ratio. A lot like most high end 2 valve NA heads (Pro Stock, NASCAR etc...) This is due to the valve sizes.... We are talking about a intake valve on a OEM production motor that is 53% of the bore! That's amazing and following the lead of most high end NA race heads. At the same time you see a exhaust valve that is small in comparison, but still 73% the curtain area/diameter. They could have moved that exhaust valve over a little more and squeezed a bigger intake in there but it really wasn't needed.
The 211/230 cam with probably a LSA in the 118-120 range is pretty fitting to this as well. I would say that's the LSA range due to a few things.... the first being GM likes to have -16 to -20 overlap at .050 in a OEM HO engine like this today. The second being that at a 118 ICL you are looking at a DCR of 8.5 and 8.3 at 120 ICL.
When you combine the cam lobe area with the valve sizes and the flow you end up with what is considered a perfect 75% E/I ratio.... It's not easy to come up with since you need to calculate the lobe area of the cam lobes in deg/sq in. Gotta love computers.
To the whole bigger valve thing....
Valve size is basically a limiting factor in a cylinder head. I've seen Darrin Morgan or Reher-Morrison describe it the best, but esentially the valve diameter and valve lift are what limits flow. You then can look at the L/D (lift/diameter) ratio of a valve (This is calld the Discharge Coefficent once you throw the flow in there.) and determine when it starts to get out of it's own way. This happens at a L/D of 25% so in the LS7 it's .550 lift. Basically that's what Larry was getting at here too. Now in terms of software and how this effects everything it all relates to how sophisticated the program is. The simple engine programs out there will reward you with more power when you increase the valve size because it takes into account that you will gain flow with that. A program that thinks you are smart enough to change the flow numbers when you change the valve size and therefore how it would actually work in the real world will punish you if you throw more valve at it, because you are not getting any more flow and in turn you are increasing the Discharge Coefficient of the motor. In reality a motor with a 2.00" valve and a port designed around it can't out flow or keep up with a port with a 2.08" valve and a port designed around it. If you kept the port flowing the same cfm say 300cfm @ .600 you would have a significantly higher discharge coefficient on the small valve.... 2" valve =79.6 D/C and a 2.08" valve = 76.5 D/C, if you kept up the 79.6 D/C you would end up with a head that flowed 312cfm and therefore probably more power.
Bret
Banned
Joined: Oct 2002
Posts: 6,518
Re: LS7 head flow numbers
Originally Posted by Joe Brodman
Are LS7 heads just "as-cast" or are they CNC'd / other work done to them as well?
God it would be nice to get some of those without the CNC... That would be great for the guys who use them on the race teams or whoever is going to need to modifiy these animals.
Bret
Registered User
Joined: Jul 2001
Posts: 752
From: Double Oak TX
Re: LS7 head flow numbers
Originally Posted by SStrokerAce
Looking at those flow numbers, valve sizes and the supposed cam specs the motor is really well balanced.....
Initially looking at a 348cfm intake and a 219cfm exhaust at peak lift you think.... dam that's way off at 63% E/I ratio. A lot like most high end 2 valve NA heads (Pro Stock, NASCAR etc...) This is due to the valve sizes.... We are talking about a intake valve on a OEM production motor that is 53% of the bore! That's amazing and following the lead of most high end NA race heads. At the same time you see a exhaust valve that is small in comparison, but still 73% the curtain area/diameter. They could have moved that exhaust valve over a little more and squeezed a bigger intake in there but it really wasn't needed.
The 211/230 cam with probably a LSA in the 118-120 range is pretty fitting to this as well. I would say that's the LSA range due to a few things.... the first being GM likes to have -16 to -20 overlap at .050 in a OEM HO engine like this today. The second being that at a 118 ICL you are looking at a DCR of 8.5 and 8.3 at 120 ICL.
When you combine the cam lobe area with the valve sizes and the flow you end up with what is considered a perfect 75% E/I ratio.... It's not easy to come up with since you need to calculate the lobe area of the cam lobes in deg/sq in. Gotta love computers.
To the whole bigger valve thing....
Valve size is basically a limiting factor in a cylinder head. I've seen Darrin Morgan or Reher-Morrison describe it the best, but esentially the valve diameter and valve lift are what limits flow. You then can look at the L/D (lift/diameter) ratio of a valve (This is calld the Discharge Coefficent once you throw the flow in there.) and determine when it starts to get out of it's own way. This happens at a L/D of 25% so in the LS7 it's .550 lift. Basically that's what Larry was getting at here too. Now in terms of software and how this effects everything it all relates to how sophisticated the program is. The simple engine programs out there will reward you with more power when you increase the valve size because it takes into account that you will gain flow with that. A program that thinks you are smart enough to change the flow numbers when you change the valve size and therefore how it would actually work in the real world will punish you if you throw more valve at it, because you are not getting any more flow and in turn you are increasing the Discharge Coefficient of the motor. In reality a motor with a 2.00" valve and a port designed around it can't out flow or keep up with a port with a 2.08" valve and a port designed around it. If you kept the port flowing the same cfm say 300cfm @ .600 you would have a significantly higher discharge coefficient on the small valve.... 2" valve =79.6 D/C and a 2.08" valve = 76.5 D/C, if you kept up the 79.6 D/C you would end up with a head that flowed 312cfm and therefore probably more power.
Bret
Initially looking at a 348cfm intake and a 219cfm exhaust at peak lift you think.... dam that's way off at 63% E/I ratio. A lot like most high end 2 valve NA heads (Pro Stock, NASCAR etc...) This is due to the valve sizes.... We are talking about a intake valve on a OEM production motor that is 53% of the bore! That's amazing and following the lead of most high end NA race heads. At the same time you see a exhaust valve that is small in comparison, but still 73% the curtain area/diameter. They could have moved that exhaust valve over a little more and squeezed a bigger intake in there but it really wasn't needed.
The 211/230 cam with probably a LSA in the 118-120 range is pretty fitting to this as well. I would say that's the LSA range due to a few things.... the first being GM likes to have -16 to -20 overlap at .050 in a OEM HO engine like this today. The second being that at a 118 ICL you are looking at a DCR of 8.5 and 8.3 at 120 ICL.
When you combine the cam lobe area with the valve sizes and the flow you end up with what is considered a perfect 75% E/I ratio.... It's not easy to come up with since you need to calculate the lobe area of the cam lobes in deg/sq in. Gotta love computers.
To the whole bigger valve thing....
Valve size is basically a limiting factor in a cylinder head. I've seen Darrin Morgan or Reher-Morrison describe it the best, but esentially the valve diameter and valve lift are what limits flow. You then can look at the L/D (lift/diameter) ratio of a valve (This is calld the Discharge Coefficent once you throw the flow in there.) and determine when it starts to get out of it's own way. This happens at a L/D of 25% so in the LS7 it's .550 lift. Basically that's what Larry was getting at here too. Now in terms of software and how this effects everything it all relates to how sophisticated the program is. The simple engine programs out there will reward you with more power when you increase the valve size because it takes into account that you will gain flow with that. A program that thinks you are smart enough to change the flow numbers when you change the valve size and therefore how it would actually work in the real world will punish you if you throw more valve at it, because you are not getting any more flow and in turn you are increasing the Discharge Coefficient of the motor. In reality a motor with a 2.00" valve and a port designed around it can't out flow or keep up with a port with a 2.08" valve and a port designed around it. If you kept the port flowing the same cfm say 300cfm @ .600 you would have a significantly higher discharge coefficient on the small valve.... 2" valve =79.6 D/C and a 2.08" valve = 76.5 D/C, if you kept up the 79.6 D/C you would end up with a head that flowed 312cfm and therefore probably more power.
Bret
Also wasn't considering the impact of widening the lobe seperation on that cam. Ya.... with wider lobe seperation it probably does what GM wants. Again, the engineers at GM are no dummies. Well..... most of the time anyway.
Registered User
Joined: Oct 2002
Posts: 2,931
From: Upstate NY
Re: LS7 head flow numbers
Originally Posted by Denny McLain
... Again, the engineers at GM are no dummies. Well..... most of the time anyway.
A few who left on their own accord (long ago) were Herb Adams, Don ***, Lee Dykstra, Terry Satchell. Not a dummy in the lot! Exactly the opposite. All found homes in motorsport, and motorsport has been much the better for it.
FWIW, GM doesn't let production cars get released if they have a government "Gas Guzzler Tax" (GGT) attached. Z06/LS7 has to abide by that, I believe. Probably the ONLY 500 hp car to not have the GGT.
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Joined: Oct 2002
Posts: 6,518
Re: LS7 head flow numbers
Originally Posted by OldSStroker
Herb Adams
Originally Posted by OldSStroker
Don ***
Originally Posted by OldSStroker
Lee Dykstra
Originally Posted by OldSStroker
Terry Satchell
All of these guys actually went to the same college around the same time too. GMI or what is now known as Kettering University. If you ever wonder why I get testy when someone who is not a engineer uses "Engineering" in their company title especially when it has to do with racing, it's due to guys like these. These guys are real race engineers, and they even have the BSME on top of it all.
Bret
Last edited by SStrokerAce; Mar 1, 2005 at 03:21 AM.
Re: LS7 head flow numbers
Registered User
Joined: Nov 1999
Posts: 2,801
From: Nashville, TN
Re: LS7 head flow numbers
2 points.
The gas guzzler tax....the GTO automatics get hit with the guzzler tax, so its not a 100% hard rule by GM. But I suspect 6th gear will give the Z06 enough legs to beat the tax.
Second, on intake to exhaust ratio, quit looking at just the peak numbers. The ratio is much better from .400 and down, right at 70%, which is what I thought the magic number was, not 75%
The gas guzzler tax....the GTO automatics get hit with the guzzler tax, so its not a 100% hard rule by GM. But I suspect 6th gear will give the Z06 enough legs to beat the tax.
Second, on intake to exhaust ratio, quit looking at just the peak numbers. The ratio is much better from .400 and down, right at 70%, which is what I thought the magic number was, not 75%
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Joined: Oct 2002
Posts: 2,931
From: Upstate NY
Re: LS7 head flow numbers
Originally Posted by Chris 96 WS6
2 points.
The gas guzzler tax....the GTO automatics get hit with the guzzler tax, so its not a 100% hard rule by GM. But I suspect 6th gear will give the Z06 enough legs to beat the tax.
The gas guzzler tax....the GTO automatics get hit with the guzzler tax, so its not a 100% hard rule by GM. But I suspect 6th gear will give the Z06 enough legs to beat the tax.
http://www.pontiac.com/sp/specs/spec....jsp?brand=gto
They missed it by 1.5 mpg highway on the A4. Pity.
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Joined: Feb 2004
Posts: 584
From: Wildwood, MO
Re: LS7 head flow numbers
Originally Posted by 94FBIRD
.595/.588
Just thought I'd throw that out there since they are different than what everyone else is saying.
