243/799 or L92 Heads?
06-25-2013, 09:16 PM
#62
What's the velocity at .300" and .400" if the cathedral head has a 2.08" valve and the square port head has a 2.16" valve, and they both flow the same amount of air?
Which head would then make more power on most combinations when using a stock style, long runner intake?
Which head would then make more power on most combinations when using a stock style, long runner intake?
To me the long runner intake plays such an integral part in what the air-
pump truly sees. The Sperry brothers designed the LS1 heads AND intake
together as a complete package where the cross sectional area starts large
and gradually gets smaller as it approaches the valve...carefully blending
tumble AND swirl (but not 2 much of either) to promote mixture atomization
This technology enhances BSFC and reduces emissions until direct injection
comes along and now the runner doesn't have to efficiently suspend the fuel
droplets anymore.
06-26-2013, 12:04 AM
#63
I'm not impressed with them in stock form anymore (4.030 and smaller).
Maybe with a 4400+ converter and an intake that can handle more than 5800-6K in most cases.. Possibly.
If you can get them to stay above 4500 RPMs and breathing into the 6500 range... I see them performing awesome.
I had a 3500 (little small since I was going to hit it with 200)... And it REALLY showed how much it lacked in the mid-range. Once I got in 3rd gear a little bit and the RPMs stayed up without shifting, it started pulling hard... But again it fell off pretty quick as well.
However, for a street car... That isn't necessarily something that most are looking at.
In that perspective, it is easy to beat an untouched square port for the smaller bores (especially the 364/370 guys). I had give or take 700-800$ in my l92 heads. For another 800$ or so I'm in the ball park of an as cast head that can be later touche up to really shine.. And the as cast would out perform the l92 combo for the smaller bore guys.
I was pretty strongly against square ports and the more and more I read the more I wanted to believe some of the posts I read in the l92 threads.
I changed my complete outlook and was behind them and supported them.
After I got the car running and got to compare it to some cathedral setups, I can't back them anymore.
On paper/dyno/theoretically, they looked great.. Real world, I was let down.
You guys are a little over my head with some of it but great info and reading!
Maybe with a 4400+ converter and an intake that can handle more than 5800-6K in most cases.. Possibly.
If you can get them to stay above 4500 RPMs and breathing into the 6500 range... I see them performing awesome.
I had a 3500 (little small since I was going to hit it with 200)... And it REALLY showed how much it lacked in the mid-range. Once I got in 3rd gear a little bit and the RPMs stayed up without shifting, it started pulling hard... But again it fell off pretty quick as well.
However, for a street car... That isn't necessarily something that most are looking at.
In that perspective, it is easy to beat an untouched square port for the smaller bores (especially the 364/370 guys). I had give or take 700-800$ in my l92 heads. For another 800$ or so I'm in the ball park of an as cast head that can be later touche up to really shine.. And the as cast would out perform the l92 combo for the smaller bore guys.
I was pretty strongly against square ports and the more and more I read the more I wanted to believe some of the posts I read in the l92 threads.
I changed my complete outlook and was behind them and supported them.
After I got the car running and got to compare it to some cathedral setups, I can't back them anymore.
On paper/dyno/theoretically, they looked great.. Real world, I was let down.
You guys are a little over my head with some of it but great info and reading!
06-26-2013, 12:13 AM
#64
Jst figured I would post up, I made peak power @6,500 with my rectangle port setup. The "porting" on my ls3 intake consists of cutting out the bridges only. This is a great read and lemons I am going to pm you as I have done questions for you!
My dyno graph and thread https://ls1tech.com/forums/dynamomet...454-425-a.html
My dyno graph and thread https://ls1tech.com/forums/dynamomet...454-425-a.html
06-26-2013, 07:49 AM
#65
I don't agree that you have disproven anything. You've shown what the heads are like on a flowbench at 28" and steady state, but as the saying goes, "we don't race flowbenches".
If you were to take the same heads and calculate airspeed for a 364ci engine at various RPM points, it paints a completely different picture. Here is what I got:
2.165" valve x 1.97" throat
3000 - 201ft/sec
5000 - 337ft/sec
7000 - 472ft/sec
2.040" valve x 1.86" throat
3000 - 226ft/sec
5000 - 376ft/sec
7000 - 527ft/sec
I used the same formula as this LINK, so feel free to check my math.
Exactly^^^^
But if we are talking about stock untouched 241, 799, 862, 317, 243's vs. the LS3/L92's squareports, the proof is in the pudding. As said the squareports are tough to beat for the price and out the box.
I can pretty much garuntee, you are going to have to close that valve pretty damn late with more duration in order to achieve certain cylinder fill volume with your stock cathedrals as proof in KCS's combo.
But if we are talking about stock untouched 241, 799, 862, 317, 243's vs. the LS3/L92's squareports, the proof is in the pudding. As said the squareports are tough to beat for the price and out the box.
I can pretty much garuntee, you are going to have to close that valve pretty damn late with more duration in order to achieve certain cylinder fill volume with your stock cathedrals as proof in KCS's combo.
Again, my 241's got a valvejob and has the 2.02"/1.60" valves. Not what I would call stock or untouched, but definitely minimal work was done. I blended in the bowls in one evening during commercial breaks. I did all the work myself, but for the average Joe to duplicate it, it would be cheaper than a set of LS3 heads.
06-26-2013, 10:58 AM
#66
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WOW! Thanks for all the input guys! There is definately a lot of guys with some great experience and knowledge on this board! i believe i am going to go with the good ole cathedrals and a fast setup! Along with a good custom spec'd cam i think i will be in the chips! lol Thanks again for all who took their time out to discuss, this has turned out to be a great thread! 
06-27-2013, 09:13 AM
#67
Foolhardy? For what reason? It's not like the slipping clutch is inflating the numbers or anything lol.
I don't agree that you have disproven anything. You've shown what the heads are like on a flowbench at 28" and steady state, but as the saying goes, "we don't race flowbenches".
If you were to take the same heads and calculate airspeed for a 364ci engine at various RPM points, it paints a completely different picture. Here is what I got:
2.165" valve x 1.97" throat
3000 - 201ft/sec
5000 - 337ft/sec
7000 - 472ft/sec
2.040" valve x 1.86" throat
3000 - 226ft/sec
5000 - 376ft/sec
7000 - 527ft/sec
I used the same formula as this LINK, so feel free to check my math.
My 235 duration intake with a 109 ICL puts the IVC @ ~46* ABDC. Martin's 230 on a 110 ICL puts the IVC @ ~45* ABDC.
Again, my 241's got a valvejob and has the 2.02"/1.60" valves. Not what I would call stock or untouched, but definitely minimal work was done. I blended in the bowls in one evening during commercial breaks. I did all the work myself, but for the average Joe to duplicate it, it would be cheaper than a set of LS3 heads.
I don't agree that you have disproven anything. You've shown what the heads are like on a flowbench at 28" and steady state, but as the saying goes, "we don't race flowbenches".
If you were to take the same heads and calculate airspeed for a 364ci engine at various RPM points, it paints a completely different picture. Here is what I got:
2.165" valve x 1.97" throat
3000 - 201ft/sec
5000 - 337ft/sec
7000 - 472ft/sec
2.040" valve x 1.86" throat
3000 - 226ft/sec
5000 - 376ft/sec
7000 - 527ft/sec
I used the same formula as this LINK, so feel free to check my math.
My 235 duration intake with a 109 ICL puts the IVC @ ~46* ABDC. Martin's 230 on a 110 ICL puts the IVC @ ~45* ABDC.
Again, my 241's got a valvejob and has the 2.02"/1.60" valves. Not what I would call stock or untouched, but definitely minimal work was done. I blended in the bowls in one evening during commercial breaks. I did all the work myself, but for the average Joe to duplicate it, it would be cheaper than a set of LS3 heads.
When CFM is a constant as it is in the equation you used and CSA is shrunk, of course air speed will increase. That's simple mathematics and it is the point Brian made with his 2.08" intake valve versus 2.16" intake valve question he posed to me. They both move the same amount of air, but one has a smaller cross section.
My argument here is when you have a cylinder head that flows as much as a well ported square port head can, the added diameter that the larger intake valve carries is negated by that increase in CFM. In this instance airspeed is increased!!!
Combine that with a very early intake valve close event and you have massive low speed torque and mid range power. As Brian said though, it's hard to put the right cam in these set-ups due to P to V. To achieve the IVC event that would be optimal there would not be enough P to V clearance at TDC for the intake valve to clear. Since I've begun to do more and more square port cams, my intake valve close event has gotten earlier and earlier with no loss of peak power, only to gain large amounts of low end torque each time.
It is what it is and I still prefer cathedral's over square port heads unless the engine has a 4.070" bore and larger.
Last edited by Sales@Tick; 06-27-2013 at 09:47 AM.
06-28-2013, 04:38 PM
#69
I will also say that flow is not everything. Cross sectional area is more important for your intended application.
When we have a long runner intake such as the stock intake from GM, or even a Fast intake, the length of the runner will dictate where the engine can operate efficiently and make peak power. You can stuff all the cross section you want under that long runner intake and you're still stuck with sub 7000rpm capabilities. When you can carry torque further into the rpm range without it dropping off as fast as it does after 6000rpm with a OEM LS intake it will always make more horsepower. This is the limiting design of a LS engine the way the OEM intended it.
Until that intake is taken out of the equation, all of that added cross section that the square port heads carry is pretty much useless for the RPM range we are stuck with. When you're looking at cylinder heads you have to determine what RPM range your motor will operate most efficiently in and make the most power in that given RPM range. Since we're pretty much stuck with 4000-7000rpm we must choose our cross sectional area of our cylinder head choice wisely.
This is really why the smaller cathedral port heads make so much more under the curve power than the square ports. I just felt like some of the velocity myths needed to be cleared up for educational purposes.
When we have a long runner intake such as the stock intake from GM, or even a Fast intake, the length of the runner will dictate where the engine can operate efficiently and make peak power. You can stuff all the cross section you want under that long runner intake and you're still stuck with sub 7000rpm capabilities. When you can carry torque further into the rpm range without it dropping off as fast as it does after 6000rpm with a OEM LS intake it will always make more horsepower. This is the limiting design of a LS engine the way the OEM intended it.
Until that intake is taken out of the equation, all of that added cross section that the square port heads carry is pretty much useless for the RPM range we are stuck with. When you're looking at cylinder heads you have to determine what RPM range your motor will operate most efficiently in and make the most power in that given RPM range. Since we're pretty much stuck with 4000-7000rpm we must choose our cross sectional area of our cylinder head choice wisely.
This is really why the smaller cathedral port heads make so much more under the curve power than the square ports. I just felt like some of the velocity myths needed to be cleared up for educational purposes.
06-28-2013, 05:45 PM
#70
What would you say if I told you my car, with 241 heads and an LS1 intake made almost 430ft-lbs at 3000RPM? On a Mustang dyno even.
430rwtq on a stock stroke, mild worked 241s and LS1 intake
06-29-2013, 07:51 AM
#74
The cam timing is not quite the same thing. Different lobes, different timing, etc.
I like the during commercial break thing.
I don't think anyone is questioning your knowledge or ability as I think you are solid from the post you ve made. It was a great thread.
The only thing that causes a squint in the eyes is the fact that you had clutch issues or other issues while testing(dynoing) and the process of using different calculations/formulas to calculate torque production is a science. Same with velocity, port volume, cylinder volume etc. Most of us just did not go to MIT to figure this sh^t out.
To me, the test was inconclusive as you could not make clean pulls. The results look to all over the place. I bet it was mean on the street though, I like single pattern cams.
Your graph reminds me of the ol peanut port BBC heads.
I like the during commercial break thing.
I don't think anyone is questioning your knowledge or ability as I think you are solid from the post you ve made. It was a great thread.
The only thing that causes a squint in the eyes is the fact that you had clutch issues or other issues while testing(dynoing) and the process of using different calculations/formulas to calculate torque production is a science. Same with velocity, port volume, cylinder volume etc. Most of us just did not go to MIT to figure this sh^t out.
To me, the test was inconclusive as you could not make clean pulls. The results look to all over the place. I bet it was mean on the street though, I like single pattern cams.Your graph reminds me of the ol peanut port BBC heads.
Coefficient of discharge is what I was calculating in my equations which includes CFM where as your equation does not. To calculate velocity you need to be able to determine the area of the throat and how much air moves through it, not just the cross sectional area. You left out a very key portion to the velocity equation which is why your numbers showed much higher for the smaller valve. If you took into account CFM in your equation at those various RPM points the square port would be ahead.
When CFM is a constant as it is in the equation you used and CSA is shrunk, of course air speed will increase. That's simple mathematics and it is the point Brian made with his 2.08" intake valve versus 2.16" intake valve question he posed to me. They both move the same amount of air, but one has a smaller cross section.
My argument here is when you have a cylinder head that flows as much as a well ported square port head can, the added diameter that the larger intake valve carries is negated by that increase in CFM. In this instance airspeed is increased!!!
When CFM is a constant as it is in the equation you used and CSA is shrunk, of course air speed will increase. That's simple mathematics and it is the point Brian made with his 2.08" intake valve versus 2.16" intake valve question he posed to me. They both move the same amount of air, but one has a smaller cross section.
My argument here is when you have a cylinder head that flows as much as a well ported square port head can, the added diameter that the larger intake valve carries is negated by that increase in CFM. In this instance airspeed is increased!!!
I will also say that flow is not everything. Cross sectional area is more important for your intended application.
When we have a long runner intake such as the stock intake from GM, or even a Fast intake, the length of the runner will dictate where the engine can operate efficiently and make peak power. You can stuff all the cross section you want under that long runner intake and you're still stuck with sub 7000rpm capabilities. When you can carry torque further into the rpm range without it dropping off as fast as it does after 6000rpm with a OEM LS intake it will always make more horsepower. This is the limiting design of a LS engine the way the OEM intended it.
Until that intake is taken out of the equation, all of that added cross section that the square port heads carry is pretty much useless for the RPM range we are stuck with. When you're looking at cylinder heads you have to determine what RPM range your motor will operate most efficiently in and make the most power in that given RPM range. Since we're pretty much stuck with 4000-7000rpm we must choose our cross sectional area of our cylinder head choice wisely.
This is really why the smaller cathedral port heads make so much more under the curve power than the square ports. I just felt like some of the velocity myths needed to be cleared up for educational purposes.
When we have a long runner intake such as the stock intake from GM, or even a Fast intake, the length of the runner will dictate where the engine can operate efficiently and make peak power. You can stuff all the cross section you want under that long runner intake and you're still stuck with sub 7000rpm capabilities. When you can carry torque further into the rpm range without it dropping off as fast as it does after 6000rpm with a OEM LS intake it will always make more horsepower. This is the limiting design of a LS engine the way the OEM intended it.
Until that intake is taken out of the equation, all of that added cross section that the square port heads carry is pretty much useless for the RPM range we are stuck with. When you're looking at cylinder heads you have to determine what RPM range your motor will operate most efficiently in and make the most power in that given RPM range. Since we're pretty much stuck with 4000-7000rpm we must choose our cross sectional area of our cylinder head choice wisely.
This is really why the smaller cathedral port heads make so much more under the curve power than the square ports. I just felt like some of the velocity myths needed to be cleared up for educational purposes.
I guess I'm doing something right then. Lol
07-01-2013, 12:06 PM
#77
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Foolhardy? For what reason? It's not like the slipping clutch is inflating the numbers or anything lol.
I don't agree that you have disproven anything. You've shown what the heads are like on a flowbench at 28" and steady state, but as the saying goes, "we don't race flowbenches".
If you were to take the same heads and calculate airspeed for a 364ci engine at various RPM points, it paints a completely different picture. Here is what I got:
2.165" valve x 1.97" throat
3000 - 201ft/sec
5000 - 337ft/sec
7000 - 472ft/sec
2.040" valve x 1.86" throat
3000 - 226ft/sec
5000 - 376ft/sec
7000 - 527ft/sec
I used the same formula as this LINK, so feel free to check my math.
I don't agree that you have disproven anything. You've shown what the heads are like on a flowbench at 28" and steady state, but as the saying goes, "we don't race flowbenches".
If you were to take the same heads and calculate airspeed for a 364ci engine at various RPM points, it paints a completely different picture. Here is what I got:
2.165" valve x 1.97" throat
3000 - 201ft/sec
5000 - 337ft/sec
7000 - 472ft/sec
2.040" valve x 1.86" throat
3000 - 226ft/sec
5000 - 376ft/sec
7000 - 527ft/sec
I used the same formula as this LINK, so feel free to check my math.
If you read through the website you linked, you will see what you posted is not actually port velocity, but instead something called "limiting port velocity". Limiting port velocity is an empirically derived theoretical calculation from a textbook published in 1985, and the formula has been picked up by recent popular software packages.
Calculated theoretical flow velocity through the valve throat of a 364 cid engine based on swept volume and engine speed at 100% VE is below:
1.97" throat = 3.05 sq in
3000 - 249 ft/sec
5000 - 415 ft/sec
7000 - 581 ft/sec
1.86" throat = 2.72 sq in
3000 - 279 ft/sec
5000 - 465 ft/sec
7000 - 651 ft/sec
If you wanted to achieve theoretical valve throat velocities which are equal to the limiting port velocities, then the valve throat diameters and areas would need to become 2.190 in (3.88 sq in) and 2.068 in (3.36 sq in). Note the valves would be larger than the throat areas. This obviously isn't going to work well.
I suspect the intent of your post was to say that volumetric demand of the engine is less than the volumetric supply of the heads, and therefore, given supply is greater than demand, port velocity will be determined by demand, and the additional supply will drive demand (velocity) down. The only problem with this type of hypothesis, is that it does not take into account for optimal valve timing and variable VEs.
