Calling all l92 cam GURUS ?????
08-19-2008, 09:02 PM
#21
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My heads flow 340 cfm and the engine in question is a pump gas 454 w/ 11.1:1 compression and a hydraulic roller with an LS7 intake.
Port speed is determined by HP and port cross section regardless of displacemnt. Ever notice that everybody's big L92 head engines seem to make about the same max HP?
The engine seems to be sensitive to exhaust valve timing with regards to carrying the HP curve i.e.- the valve needs to open at a certain time in order to a certain HP, but port flow seems to have virtually no effect on HP.
The intake, with it's big cross section has relatively low port speed (in the runner) so hanging the valve open too long WILL cause intake reversion. Close the valve a little earlier to trap the cylinder and let the large port carry the HP.
The problem with the intake is that when you start making, say.....630 fwhp, the port speed at the bowl is so high the air stream will not stay attatched to the floor as it turns toward the valve. This causes the air stream to tumble and spill entirely out the far side of the valve seat area instead of some air going out the far side and some going out the near side. The valve is a crucial component of directing the air through the seat area and when you open it too far, it's no longer in a good position to guide the air stream through at higher speeds so the stream goes turbulent and VIOLA!..... no more air flow.... no more HP!
Port speed is determined by HP and port cross section regardless of displacemnt. Ever notice that everybody's big L92 head engines seem to make about the same max HP?
The engine seems to be sensitive to exhaust valve timing with regards to carrying the HP curve i.e.- the valve needs to open at a certain time in order to a certain HP, but port flow seems to have virtually no effect on HP.
The intake, with it's big cross section has relatively low port speed (in the runner) so hanging the valve open too long WILL cause intake reversion. Close the valve a little earlier to trap the cylinder and let the large port carry the HP.
The problem with the intake is that when you start making, say.....630 fwhp, the port speed at the bowl is so high the air stream will not stay attatched to the floor as it turns toward the valve. This causes the air stream to tumble and spill entirely out the far side of the valve seat area instead of some air going out the far side and some going out the near side. The valve is a crucial component of directing the air through the seat area and when you open it too far, it's no longer in a good position to guide the air stream through at higher speeds so the stream goes turbulent and VIOLA!..... no more air flow.... no more HP!
Im suprised the airspeed is as high as you have seen. I have not seen that air seperation happen even on my outlaw sprint engines with all pro 265cc 15 degree heads and they flow 400+ cfm with the same volume/cross section as these L92 that means the airspeed is even higher so it must be supersonic at the bowl. It must be really detaching on those heads im suprised they make the 850hp. they do. technically I should shorten up my intake lobes on them too ?
08-19-2008, 09:11 PM
#22
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The only reason HP can dictate air speed is the more HP you make of course the airspeed will be higher it takes more air to make more power. and they all do make about the same but at different rpms depending on cubic inches. I know a 408 and a 454 both making say 700hp will both have the same airspeed to make the same HP but the 408 will make it a higher rpm...
No thats wrong thats why your 454 will make more power at any given rpm than a 408 will with the same head. The larger cubic inch moves more air at a lower rpm correct ? yes, so that means the cubic inch is increasing the air speed making more power, hp is not increasing air speed cubic inch is. The only spot they can be equal is at the peak hp reading wich will be at different rpm's. because why ? cubic inch difference, right.
08-21-2008, 10:17 AM
#23
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Yes
Wrong.... the avg. intake port air speed will be about the same in the 408 and the 454 at the RPM which they make the same power BUT that power level will occur at a different RPM in each engine because of their different displacements.
Air speed will vary with cubic inch OR engine speed.... you need to know both to determine velocity, but knowing ONLY the power can give you velocity as well, regardless of displacement or RPM.
Wrong.... the avg. intake port air speed will be about the same in the 408 and the 454 at the RPM which they make the same power BUT that power level will occur at a different RPM in each engine because of their different displacements.
Air speed will vary with cubic inch OR engine speed.... you need to know both to determine velocity, but knowing ONLY the power can give you velocity as well, regardless of displacement or RPM.
I agree thats true, I also feel dynos vary so alot of the testing done on these L92 combos can vary too. There is alot of similarities reguardless to cam changes on these so people are moving in the right direction non the less.
08-21-2008, 02:20 PM
#25
Since you all are on the subject. I have a 86 s10 with a lq4 want to do the l92 swap what would you guy recomend for a cam. th350 4000 conv. 9inch w/411 gears. mostly a weekend truck. also carbed.
08-23-2008, 12:29 PM
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My heads flow 340 cfm and the engine in question is a pump gas 454 w/ 11.1:1 compression and a hydraulic roller with an LS7 intake.
Port speed is determined by HP and port cross section regardless of displacemnt. Ever notice that everybody's big L92 head engines seem to make about the same max HP?
The engine seems to be sensitive to exhaust valve timing with regards to carrying the HP curve i.e.- the valve needs to open at a certain time in order to a certain HP, but port flow seems to have virtually no effect on HP.
The intake, with it's big cross section has relatively low port speed (in the runner) so hanging the valve open too long WILL cause intake reversion. Close the valve a little earlier to trap the cylinder and let the large port carry the HP.
The problem with the intake is that when you start making, say.....630 fwhp, the port speed at the bowl is so high the air stream will not stay attatched to the floor as it turns toward the valve. This causes the air stream to tumble and spill entirely out the far side of the valve seat area instead of some air going out the far side and some going out the near side. The valve is a crucial component of directing the air through the seat area and when you open it too far, it's no longer in a good position to guide the air stream through at higher speeds so the stream goes turbulent and VIOLA!..... no more air flow.... no more HP!
Port speed is determined by HP and port cross section regardless of displacemnt. Ever notice that everybody's big L92 head engines seem to make about the same max HP?
The engine seems to be sensitive to exhaust valve timing with regards to carrying the HP curve i.e.- the valve needs to open at a certain time in order to a certain HP, but port flow seems to have virtually no effect on HP.
The intake, with it's big cross section has relatively low port speed (in the runner) so hanging the valve open too long WILL cause intake reversion. Close the valve a little earlier to trap the cylinder and let the large port carry the HP.
The problem with the intake is that when you start making, say.....630 fwhp, the port speed at the bowl is so high the air stream will not stay attatched to the floor as it turns toward the valve. This causes the air stream to tumble and spill entirely out the far side of the valve seat area instead of some air going out the far side and some going out the near side. The valve is a crucial component of directing the air through the seat area and when you open it too far, it's no longer in a good position to guide the air stream through at higher speeds so the stream goes turbulent and VIOLA!..... no more air flow.... no more HP!
