408 vs. 346 flow needs
06-13-2008, 07:17 AM
#1
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408 vs. 346 flow needs So im having a disagreement with a buddy *famous last words*
my lq4 had GTP Stage 2 heads and a tsp 231/237 cam, fast 78mm intake.
The arguement is that he feels that I will LOSE power with these same parts (minus the intake, im going to a ported 92) on a 408 versus a stock cubed ls1 or my iron 6.0.. anyone?
my lq4 had GTP Stage 2 heads and a tsp 231/237 cam, fast 78mm intake.
The arguement is that he feels that I will LOSE power with these same parts (minus the intake, im going to a ported 92) on a 408 versus a stock cubed ls1 or my iron 6.0.. anyone?
06-13-2008, 11:16 AM
#4
OK I'll bite. I'm the buddy.
My stance was that they are still pulling in the same amount of air because the heads will only flow so much. Since they are pulling in the same amount of air, the smaller engine would be able to use it more efficiently and effectively. Much like a turbo. On an ls1 a smaller turbo might make a certain amount of power but that same turbo on like a honda might make more power at the wheels. All because the smaller engine uses the incoming air more effectively.
My stance was that they are still pulling in the same amount of air because the heads will only flow so much. Since they are pulling in the same amount of air, the smaller engine would be able to use it more efficiently and effectively. Much like a turbo. On an ls1 a smaller turbo might make a certain amount of power but that same turbo on like a honda might make more power at the wheels. All because the smaller engine uses the incoming air more effectively.
06-13-2008, 11:36 AM
#5
OK I'll bite. I'm the buddy.
My stance was that they are still pulling in the same amount of air because the heads will only flow so much. Since they are pulling in the same amount of air, the smaller engine would be able to use it more efficiently and effectively. Much like a turbo. On an ls1 a smaller turbo might make a certain amount of power but that same turbo on like a honda might make more power at the wheels. All because the smaller engine uses the incoming air more effectively.
My stance was that they are still pulling in the same amount of air because the heads will only flow so much. Since they are pulling in the same amount of air, the smaller engine would be able to use it more efficiently and effectively. Much like a turbo. On an ls1 a smaller turbo might make a certain amount of power but that same turbo on like a honda might make more power at the wheels. All because the smaller engine uses the incoming air more effectively.
Here's how I see it: Say the cylinder head flows 300cfm----the 346 is going to ingest 43.25 cubic inches of air into each cylinder during the intake stroke whereas the 408 will ingest 51 cubic inches. They are not pulling in the same AMOUNT of air (bigger cylinder = more volume), they're just ingesting the air at the same RATE of 300cfm.....(cfm = cubic feet per minute).
06-13-2008, 11:42 AM
#6
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Not quite. The 408 is absolutely going to make more power than the 346....adding displacement always = more torque. My explanation may not be 100% accurate number wise, but the theory is what matters. Here's how I see it: Say the cylinder head flows 300cfm----the 346 is going to ingest 43.25 cubic inches of air into each cylinder during the intake stroke whereas the 408 will ingest 51 cubic inches. They are not pulling in the same AMOUNT of air (bigger cylinder = more volume), they're just ingesting the air at the same RATE of 300cfm.....(cfm = cubic feet per minute).
Here's how I see it: Say the cylinder head flows 300cfm----the 346 is going to ingest 43.25 cubic inches of air into each cylinder during the intake stroke whereas the 408 will ingest 51 cubic inches. They are not pulling in the same AMOUNT of air (bigger cylinder = more volume), they're just ingesting the air at the same RATE of 300cfm.....(cfm = cubic feet per minute).
06-13-2008, 11:54 AM
#7
I did a little looking in the Advance Tech section to see what people WAY smarter think and found this:
Torque is more directly related to displacement. This is because it's a more a factor of cylinder fill rather than cylinder fill * speed. The same cam heads intake (assuming that this is the limiting factor, not strength of parts or knock or float) will usually produce the same (similar) max power within a wide (but limited, i.e. don't use a 1 c.i. engine compared to 400 c.i.) range of displacements. The torque (at lower RPM than peak power) will always be greater with more displacement. The intake system has more of a %efficiency factor for obtaining torque, but a max flow limit for obtaining power at high speeds.
Harmonics and component mass and friction will fight this theory a little, but it's more of a generality.
In general with the same heads, cam, intake:
Big engine will have greater torque, obtain peak hp sooner, and keep a flatter peak hp curve. Also will have more area under the curve.
Small engine will have lower torque peak, and peak hp late and peak in a sharp manner, but can achieve about the same peak power.
Makes sense.....
Torque is more directly related to displacement. This is because it's a more a factor of cylinder fill rather than cylinder fill * speed. The same cam heads intake (assuming that this is the limiting factor, not strength of parts or knock or float) will usually produce the same (similar) max power within a wide (but limited, i.e. don't use a 1 c.i. engine compared to 400 c.i.) range of displacements. The torque (at lower RPM than peak power) will always be greater with more displacement. The intake system has more of a %efficiency factor for obtaining torque, but a max flow limit for obtaining power at high speeds.
Harmonics and component mass and friction will fight this theory a little, but it's more of a generality.
In general with the same heads, cam, intake:
Big engine will have greater torque, obtain peak hp sooner, and keep a flatter peak hp curve. Also will have more area under the curve.
Small engine will have lower torque peak, and peak hp late and peak in a sharp manner, but can achieve about the same peak power.
Makes sense.....
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06-13-2008, 12:16 PM
#9
If I'm understanding everything I'm reading, it seems we were both kind of on the right track though. More displacement with the same top end will produce similar (probably a little more) peak HP as the smaller motor, but the peak occurs at a much lower rpm and produces more torque throughout the power band. Check out some of the threads in the advanced tech section, there's some good interesting reading on this subject there......
06-13-2008, 01:04 PM
#11
OK I'll bite. I'm the buddy.
My stance was that they are still pulling in the same amount of air because the heads will only flow so much. Since they are pulling in the same amount of air, the smaller engine would be able to use it more efficiently and effectively. Much like a turbo. On an ls1 a smaller turbo might make a certain amount of power but that same turbo on like a honda might make more power at the wheels. All because the smaller engine uses the incoming air more effectively.
My stance was that they are still pulling in the same amount of air because the heads will only flow so much. Since they are pulling in the same amount of air, the smaller engine would be able to use it more efficiently and effectively. Much like a turbo. On an ls1 a smaller turbo might make a certain amount of power but that same turbo on like a honda might make more power at the wheels. All because the smaller engine uses the incoming air more effectively.
The air is not getting pulled. It is flowing from a higher pressure to a lower pressure. May seem like it doesn't matter, but it does.
06-13-2008, 03:30 PM
#12
If I'm understanding everything I'm reading, it seems we were both kind of on the right track though. More displacement with the same top end will produce similar (probably a little more) peak HP as the smaller motor, but the peak occurs at a much lower rpm and produces more torque throughout the power band. Check out some of the threads in the advanced tech section, there's some good interesting reading on this subject there......
06-14-2008, 01:13 AM
#15
One thing to note here... heads and pistons.. if your running a 59cc head and have a 408 built for the proper compression (correct dish piston) for that head and then switch heads to say a L92 that has like a 75 cc chamber.. your compresion isnt going to be what you want.. you cant shave that head to 59cc's althought I guess you can have it welded. You need to plan it out. One thing effects another with an engine build and if you start doing things without a plan you end up spending more money that need be.
06-16-2008, 05:39 PM
#16
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One thing to note here... heads and pistons.. if your running a 59cc head and have a 408 built for the proper compression (correct dish piston) for that head and then switch heads to say a L92 that has like a 75 cc chamber.. your compresion isnt going to be what you want.. you cant shave that head to 59cc's althought I guess you can have it welded. You need to plan it out. One thing effects another with an engine build and if you start doing things without a plan you end up spending more money that need be.
I think ive got this step taken care of. TFS heads arent too big that they cant be easily milled to match the chamber size of the ls1 castings that im using now.
06-17-2008, 03:16 PM
#18
But you are correct in what you are saying on a ET 11 degree or LS7, because they are totally different.
BTW, a turbo or blower have limited displacement, and a naturally aspirated engine has an unlimited supply of 14.7 PSI of air. This is why turbo and blower cars suffer more from making the same power no matter what the engine displacement they are on.
If your 6.0L heads are a little oversized (230+cc and big valves, 2.055-2.08) on a 5.7, then they can make quite a bit more power when coupled with the bigger 408 bore (which the 6.0L heads work better on) and a Fast intake. Conversly if you have a 210cc-220cc LS1 head with 2.00-2.02 intake valves and small exhaust valves and keep the LS intake, then you could very well make exactly the same peak power, just like was stated above.
Last edited by Brian Tooley Racing; 06-17-2008 at 03:24 PM.
