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Join Date: Jun 2020
Location: West Virginia
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How much HP gain removing PS and AC?

As the title says... how much HP gain will I get by removing the PS and going to a full manual rack, and I am contemplating removing the AC compressor since the AC doesn't work anyway.

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Old 07-10-2020, 07:31 PM
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It won’t make more HP but you will release maybe about 5hp max to the rear wheels. Thing is those systems don’t draw power from the engine all the time. The AC only draws power when the clutch is engaged and even when it’s on the clutch cycles it on-off anyway. Power steering only really draws real power from the engine when turning.

Folk don’t really remove those systems primarily to release power, they do it to make things simpler, more reliable and to remove weight.
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1986 944 (Street); 1986 944 (Track); 1986 951; 1989 951 (3.0L 8V); 2000 996 Cab.
Old 07-11-2020, 02:15 AM
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AC only sucks power when it's running. Otherwise the pulley is a freewheeling bearing like a giant idler.

PS doesn't have much drag either 99% of the time, it only really takes meaningful power when you are cranking the wheel to full lock while standing still.

Would you believe that a 100 amp alternator at full load might only eat about 2HP, even after accounting for belt efficiency?
Old 07-11-2020, 04:28 AM
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I have been thinking of deleting these two items also... because one doesn’t work and the other tends to leak.

So, if these don’t draw much HP, where is the loss from crank to the wheels? Is the transaxle any more HP draining than the usual car?
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Old 07-11-2020, 06:08 AM
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4 driveshaft bearings
??? bearings and gears meshing inside the transaxle
90 degree turn of power from pinion to ring gear
24 CV joint balls
wheel bearings
minor brake pad friction

AFAIK nobody has come up with the actual number of 944 drivetrain loss. people like to throw around a percentage but its not really a percentage, it's a fixed amount for a given setup (you would have to do a back to back engine dyno and chassis dyno to approximate, or use a special kind of dyno to run up and coast down to measure friction).

the friction loss rises proportionally with RPM but it is a pretty gradual slope when you look at other cars that have actually measured that loss. made up numbers but for example you might lose 10hp at 2000rpm, 15 at 4000rpm, 20 at 6000rpm.

when i did some dyno testing years back my bone stock early NA made 121whp on a dynojet, SAE corrected. Porsche rated that engine at 143 crank. so apparently 22hp lost through the drivetrain. i have heard that an 86-88 non-S 944 turbo, crank rated 217hp will usually dyno around 190whp, so about 27 down which is in the right ballpark (since it uses all the same drivetrain bearings etc that my NA did).

and no matter what a vendor says, underdrive pulleys and lightweight flywheels will NOT add any power to an engine. they are not increasing combustion efficiency in the engine at all; no more power is being made, but the marginally less mass will accelerate easier (change RPM) so an inertial dyno might show it as a HP gain based on how they work. it's a lie.

Old 07-11-2020, 06:20 AM
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