A
Anonymous
Guest
When looking at a custom manifold one has too consider what the engine/car is going to be used for. Factors like where power use will occur and RPM range desired play a large role in the manifold design. A manifold that takes away from mid range and works very well on top might not be the ideal for street use. Then again a manifold that works exceptionally well in the mid range might not be ideal for drag use or long circuits where all the power is need up top.
Runner diameter, length and plenum size is very important when it comes to manifold design. Air flow is important but just as important is the velocity or the speed at which the air flows. It does not help if a manifold flows very well (lots of CFM) but the air speed is so slow that it can not fill the cylinder in time. (especially in the mid range or low valve openings) This situation is daily seen when cylinder head porters hog out the ports too much. The car makes power up top but it’s a dog low down.
If an open port (port without valves in it) flows for example 280 CFM with airspeed of 320 feet per second and with valves in, flows 265 CFM at airspeed 345 feet per second the manifold that flows higher CFM but at a lower airspeed will make more power upstairs but will be a lot less affective down stairs but a manifold that flows slightly less than 280 CFM but match the 345 air speed or slightly better will do well threw out the range. Example of this is the manifold I built for David Lashbrooks MR2 that made 755 HP with 550 plus foot pound of torque. Runner diameter was 1.870 with a length of 11 inches. Mid range on this car is not poor due to manifold design but due to turbo size. T78’s are very lagy on a 2.0 L engine.
Too much airspeed can also become a problem and in a turbo car can be eventually the cause of compressor surge and or poor cylinder fill.
My manifolds are not one size fits all but custom hand made for each individual’s requirements with an emphasis on power at low boost levels and even more at the higher levels. (No Bling bling just functionality)
The question was asked at what HP level does it becomes necessary to change the manifold. It is my opinion that there is a direct benefit at any HP level, even air distribution and unobstructed flow is beneficial to any engine no matter what the HP level
Runner diameter, length and plenum size is very important when it comes to manifold design. Air flow is important but just as important is the velocity or the speed at which the air flows. It does not help if a manifold flows very well (lots of CFM) but the air speed is so slow that it can not fill the cylinder in time. (especially in the mid range or low valve openings) This situation is daily seen when cylinder head porters hog out the ports too much. The car makes power up top but it’s a dog low down.
If an open port (port without valves in it) flows for example 280 CFM with airspeed of 320 feet per second and with valves in, flows 265 CFM at airspeed 345 feet per second the manifold that flows higher CFM but at a lower airspeed will make more power upstairs but will be a lot less affective down stairs but a manifold that flows slightly less than 280 CFM but match the 345 air speed or slightly better will do well threw out the range. Example of this is the manifold I built for David Lashbrooks MR2 that made 755 HP with 550 plus foot pound of torque. Runner diameter was 1.870 with a length of 11 inches. Mid range on this car is not poor due to manifold design but due to turbo size. T78’s are very lagy on a 2.0 L engine.
Too much airspeed can also become a problem and in a turbo car can be eventually the cause of compressor surge and or poor cylinder fill.
My manifolds are not one size fits all but custom hand made for each individual’s requirements with an emphasis on power at low boost levels and even more at the higher levels. (No Bling bling just functionality)
The question was asked at what HP level does it becomes necessary to change the manifold. It is my opinion that there is a direct benefit at any HP level, even air distribution and unobstructed flow is beneficial to any engine no matter what the HP level
