6-71 blower on a 340
Hi there, Are you sure about this?
I have never run a 6/71 first hand but know they displace approx 411" every revolution (360 crank degrees)
a 340 mopar engine motor inhales 340" every *second* revolution. (or 720 crank degrees)
Therefore hypothetically it be would trying to cram 822" into a 340" motor at 1:1 drive ratio.
Now to relate this to "boost" pressure.
A good hypothetical for figuring out the maths involved is to use Atmospheric pressure at sea level, which is approx 14.7psi from memory. It's this pressure that causes air to fill your cylinders when naturally aspirated.
Adding "boost" increases this pressure, adding an additional 14.7 PSI of boost would DOUBLE an engine's power output. (everything else being equal. heat etc)
This would become 29.4PSI absolute pressure at sea level. (atmospheric pressure + boost pressure combined)
Now back to our 340 with a 6/71 and a 1:1 drive ratio
822" blower output divided by 340" engine input = a ratio of 2.417
Now if we multiply our atmospheric pressure by 2.47 we get an absolute pressure of ~35
Boost pressure = absolute pressure minus atmospheric pressure.
35 - 14.7 = boost pressure of 20.3PSI at sea level.
But wait, we're not done yet!
Blowers aren't 100% effecient like that.
Let's be a bit realistic and consider that these blowers are not race units, a 10% reduction in volumetric efficiency to compensate for leakage past the seals. Bringing it to a factor of 0.90 (90% efficiency)
20.3 x .90 = 18.27 PSI boost at 1:1 drive ratio
As with everything, real world scenarios are subject to a lot of variables relating to engine configuration and efficiencies.
Here's a chart I found for those who hate maths. It suggests that a 340 at 1:1 would be about 16.5PSI
So it's good to know I wasn't too far off!
Hi there, Are you sure about this?
I have never run a 6/71 first hand but know they displace approx 411" every revolution (360 crank degrees)
a 340 mopar engine motor inhales 340" every *second* revolution. (or 720 crank degrees)
Therefore hypothetically it be would trying to cram 822" into a 340" motor at 1:1 drive ratio.
Now to relate this to "boost" pressure.
A good hypothetical for figuring out the maths involved is to use Atmospheric pressure at sea level, which is approx 14.7psi from memory. It's this pressure that causes air to fill your cylinders when naturally aspirated.
Adding "boost" increases this pressure, adding an additional 14.7 PSI of boost would DOUBLE an engine's power output. (everything else being equal. heat etc)
This would become 29.4PSI absolute pressure at sea level. (atmospheric pressure + boost pressure combined)
Now back to our 340 with a 6/71 and a 1:1 drive ratio
822" blower output divided by 340" engine input = a ratio of 2.417
Now if we multiply our atmospheric pressure by 2.47 we get an absolute pressure of ~35
Boost pressure = absolute pressure minus atmospheric pressure.
35 - 14.7 = boost pressure of 20.3PSI at sea level.
But wait, we're not done yet!
Blowers aren't 100% effecient like that.
Let's be a bit realistic and consider that these blowers are not race units, a 10% reduction in volumetric efficiency to compensate for leakage past the seals. Bringing it to a factor of 0.90 (90% efficiency)
20.3 x .90 = 18.27 PSI boost at 1:1 drive ratio
As with everything, real world scenarios are subject to a lot of variables relating to engine configuration and efficiencies.
Here's a chart I found for those who hate maths. It suggests that a 340 at 1:1 would be about 16.5PSI
So it's good to know I wasn't too far off!
