New Whipple 2.9L compressor, 175AX
Oct 21, 2008 | 10:52 AM
#31
If both the engine and the blower were 100% efficient air pumps, the engine would be pumping 248 cubic inches per revolution and the super charger would be moving 140 cubic inches per its revolution. It isn't simple math to determine how much boost you get out of this, you have to consult one of these charts and figure from there.
Oct 21, 2008 | 09:23 PM
#37
Yes.
Oct 22, 2008 | 01:47 AM
#39
Looks like the 8100's most efficient RPM is at about 3800. We'll use 4000 at 100kPa since that has the highest peak VE. (Sea-level air pressure is actually a little over 101kPa) That can be rounded to 89% efficient.
8100cc devided by 2 since a 4-stroke is 4050cc per rotation at 100% VE, so multiplied by 89 = about 3600cc per rev of air going in assuming 1 atmosphere in the manifold. (Actual kPa in the manifold during WOT you'll find will be less, between 90-95, but forget about that for now.)
Now go back to the other data we know and can presume. We know the pulley setup is spinning the blower 3.16 times faster, so about 12500 is close enough for blower input RPM @ 4000 engine RPM. We know the manifold was seeing 7psi boost at best. (100kPa = 14.5psi) 7 psi of boost is about 150kPa, or 1.5 bar. There's no VE number for that value but plotting a curve using existing numbers we can presume it's about the 91%. (If the VE table continued on based on real flow data you'd see it almost levels off rising less and less with each subsequent column of kPa.) Multiply the 4050cc at 100kPa conveniently by 1.50 for 7psi (50kPa) boost, multiply by 91% and 5500cc of air pumped per revolution at 4000RPM with 7psi boost. Multiply that by itself.
5500cc x 4000RPM = 22,000,000 cubic centimeters (22 cubic meters) per minute.
Now go to the chart for the 2300 compressor. (Keep in mind that is a Lysholm map and not a Whipple map which is why I'm rounding everything anyway here for clarity. The Whipple designed compressor is more efficient slightly.)
Look up 22 m3/min. Chart says the needed blower RPM should only be between 10,000 and 10,500RPM, (depending on backpressure) in other words about a 2.7/8" pulley. Because air volume is measured at the inlet, pressure is constant regardless of the outlet pressure.
10,500 suggested RPM versus 12,600RPM. Why the 20% difference? 5% error factors in data and 15% RESRICTION!
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You want to know how big of a blower and what pulley for the boost you need.
How about 10psi. It's a big block with intercooler. 10psi would be fun. We'll say 170kPa. To find maximum requirements use the maximum engine RPM. I will use 4800RPM since I know an 8.1L stock can't do more than that.
VE is less at 4800 then at 4000 by about 4 points, so I will use 87% VE. 4050 x 87% x 1.70 (kPa divided by 100) = 5990cc x 4800RPM = 28.75 cubic meters per minute. Call it 29 just for good measure. At a 1.8x pressure differential a 2.3L supercharger at 4800 engine RPM with absolutely no inlet restrictions would need to be turning 14000RPM and need about a 2.5" pulley. Factor in the restrictions int he real world and you're off that chart just like that. Note how far to the right of the blower's sweet spot that is. The 2.3L compressor most efficiently turns torque into boost around 8000 RPM, according to Lysholm's chart.
Now check out a 1.8x pressure differential at 29 cubic meters per minute with the 3.3L compressor. Only 9500 RPM! (at 100% no restriction) Factor in the 20% error and restriction and you're still only at 11,400RPM for the blower at 4800 Engine RPM, and that's about a 3.1/8" pulley. Remember I said a 3" 6-rib is about minimum pulley size for a 3300cc compressor?
How's that
Tired... will fix typos tomorrow
8100cc devided by 2 since a 4-stroke is 4050cc per rotation at 100% VE, so multiplied by 89 = about 3600cc per rev of air going in assuming 1 atmosphere in the manifold. (Actual kPa in the manifold during WOT you'll find will be less, between 90-95, but forget about that for now.)
Now go back to the other data we know and can presume. We know the pulley setup is spinning the blower 3.16 times faster, so about 12500 is close enough for blower input RPM @ 4000 engine RPM. We know the manifold was seeing 7psi boost at best. (100kPa = 14.5psi) 7 psi of boost is about 150kPa, or 1.5 bar. There's no VE number for that value but plotting a curve using existing numbers we can presume it's about the 91%. (If the VE table continued on based on real flow data you'd see it almost levels off rising less and less with each subsequent column of kPa.) Multiply the 4050cc at 100kPa conveniently by 1.50 for 7psi (50kPa) boost, multiply by 91% and 5500cc of air pumped per revolution at 4000RPM with 7psi boost. Multiply that by itself.
5500cc x 4000RPM = 22,000,000 cubic centimeters (22 cubic meters) per minute.
Now go to the chart for the 2300 compressor. (Keep in mind that is a Lysholm map and not a Whipple map which is why I'm rounding everything anyway here for clarity. The Whipple designed compressor is more efficient slightly.)
Look up 22 m3/min. Chart says the needed blower RPM should only be between 10,000 and 10,500RPM, (depending on backpressure) in other words about a 2.7/8" pulley. Because air volume is measured at the inlet, pressure is constant regardless of the outlet pressure.
10,500 suggested RPM versus 12,600RPM. Why the 20% difference? 5% error factors in data and 15% RESRICTION!
----------------
You want to know how big of a blower and what pulley for the boost you need.
How about 10psi. It's a big block with intercooler. 10psi would be fun. We'll say 170kPa. To find maximum requirements use the maximum engine RPM. I will use 4800RPM since I know an 8.1L stock can't do more than that.
VE is less at 4800 then at 4000 by about 4 points, so I will use 87% VE. 4050 x 87% x 1.70 (kPa divided by 100) = 5990cc x 4800RPM = 28.75 cubic meters per minute. Call it 29 just for good measure. At a 1.8x pressure differential a 2.3L supercharger at 4800 engine RPM with absolutely no inlet restrictions would need to be turning 14000RPM and need about a 2.5" pulley. Factor in the restrictions int he real world and you're off that chart just like that. Note how far to the right of the blower's sweet spot that is. The 2.3L compressor most efficiently turns torque into boost around 8000 RPM, according to Lysholm's chart.
Now check out a 1.8x pressure differential at 29 cubic meters per minute with the 3.3L compressor. Only 9500 RPM! (at 100% no restriction) Factor in the 20% error and restriction and you're still only at 11,400RPM for the blower at 4800 Engine RPM, and that's about a 3.1/8" pulley. Remember I said a 3" 6-rib is about minimum pulley size for a 3300cc compressor?
How's that
Tired... will fix typos tomorrow
Oct 22, 2008 | 02:02 AM
#40
One more thing before I run off for the evening, meant to mention...
BELT SLIPPAGE
Do you find belt dust stuck to the front of the supercharger? I used to run a 2.5" pulley on the smallblock with at least 30 degrees more of belt wrap around the pulley than the 8100 kit gets and had belt-slippage problems from hell most of the time.
Slipping belt goes a long way to explain less-than-expected boost levels.
BELT SLIPPAGE
Do you find belt dust stuck to the front of the supercharger? I used to run a 2.5" pulley on the smallblock with at least 30 degrees more of belt wrap around the pulley than the 8100 kit gets and had belt-slippage problems from hell most of the time.
Slipping belt goes a long way to explain less-than-expected boost levels.
