924Board.org

[daveo]

qestion,,,haw much air duz a NA 924 draw on full chat 6500 RPM ?
Need to know as trying to sort out what size electric motor (rpm) we will need, as we r trying to make a SC using a garet turdo as the fan unit
A) to fill the normal volume of air & B) to be able to boost on top of that
any hints will be good
thanks
Dave

[WEASEL149]

Using the formula ((Max RPM/2)*Displacement in CI)/1728...

I get 229cfm at 6500rpm. This is probably optimistic as it assumes 100% volumetric efficiency, and that is more likely to be 85%.

195cfm is probably a more realistic figure.
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1979 UK 932

[daveo]

THANKS thats what i needed,,,,had one compant trying to sell me a SC (£175) that would push 130 cfm,,, with clames of more pawer,,just shows whats out there
thanks for your reply

[Euro924S2]

Have you searched on this topic? I'm sure i remember someone who was better at math's than I am doing some calculations about the energy, in watts needed to move that volume of air, and then the extra load that would put on the alternator, and therefore the BHP that uses. As far as all the previous discussions have concluded - there was no milage in electric superchargers. I'm all in favour of inventive solutions and I seriously hope you document your endevours (good or bad) but there must be a reason the major car manufacturers don't use such systems??

Don't forget if you do generate boost, you will need to alter the fuel and ignition just as you would with conventional boosted systems.

Best of luck
John
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UK spec '83 N/A with 931 motor with Eaton MP62 'charger @ 15psi. EFI - 565cc inj. Standalone Adaptronic ECU. 951 FMIC. Ally rad. Twin throttle. Recirc valve. Custom manifolds and CAI. 232bhp

[PorscheDrift]

Actually if your trying to run a electric supercharger or something of the sort, using a turbo cold side is bad idea. You would need a incredible motor to move the kind of volume that would be required for positive pressure. Their designed for exhaust systems and spin at 10k plus rpm.

Essentially you could use a 20volt capacitor like a blast cap for a car stereo and a high amperage relay to turn the unit on and off without too much of a tax on the battery but your still going to have to tax the alternator recharging it because it will drain a 2 farad blast cap fairly quick. Your not going to really see much gains out of it. The only good thing is the CIS will adjust the fuel for you as it moves the plate up with the extra air flow. However unless you completely seal up the stock air box, revamp the intake piping, and run silicon couplers or even hard pipes your not going to gain anything out of it and you may actually loose power due to heatsoak from the metal pipes.

Believe me, i know first hand about electric superchargers or e-turbo whatever their calling it......

[simsport]

I did wonder if for a supercharged car an electric blower might help by 'priming' the roots blower and make it more efficient?

cheers
simon
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Blown is always best!

[PorscheDrift]

It might, but it would be doubtful. I tired something similar with a turbo car and a rpm switch right before the turbine started to spool to try and reduce the lag. Also tried it with just a killswitch next to the shifter to try and keep the turbo semi-spooled inbetween shifts...... the answer is a solid Mmmmnope.

If your running a very small supercharger its a possibility that it may help with the preload of the unit if you can pinpoint the exact rpm the charger beings to engage and ran it for about a second and couple 100 rpm or so before but anything thats crank driven like that really changes depending on the load of the engine as well. On the straits it might engage a couple 100 lower than on a hill or vice/versa know what i mean? It would be easier to just run a killswitch and try to feel it out, or if you had a engine management program that ran off the load of the map and the rpm to signal a relay but is that really worth all the extra nonsense just to run a e-turbo or a bilge blower to try and get a quicker response out of a real charger?

All it does is sound like a shop vac. Once upon a time i had 2 hooked up to a piece of lexan mounted to the front of my cis distributor. It sort of made a difference and i got a boost in afl readings on the safc2 when i ran 1 in front of my maf on my fc but in retrospect wouldnt say they did too much.

Later on down the road, I had made one up out of a old garret coldside and a cut up starter motor off a minitruck and it moved a decent amount of air, but it really wasnt too justified having that kind of nonsense sitting under your hood and the power drain was HUGE its like starting a car while at full throttle going 80mph everything dims badly and on a efi thats not a good idea cause of, you know, injectors and computers..... Really didnt do too much flow wise unless you would of sealed the back tight with rtv and mounted it right at the throttle body and would of caused a massive restriction when not spinning.... Plus finding a way to brace it so that it doesnt want to flop all over the place when the starter motor is engaged.... But with the twister/e-rams at least they sound cool

Easiest way to actually test if it works..... put it on a pipe same size as your intake piping, put your hand over it, turn it on (watch fingers, darwin applies here) and feel how much vacuum it pulls now go to your car, take off the air box (obviously not a 924 im talking about here) rev it up to 6 grand and feel how much air its sucking through the pipe. If the bilge blower, dinky electric motor, e-whatever can double the velocity of what the engines sucking through the pipe, then maybe you might see some notable gains.

The only reason a cis system MIGHT be a better candidate for this is because it is purely run off engine vacuum and isnt sensitive to voltage/current spikes. But you would need to redesign the whole intake piping on the car to see any kind of gains.

But again your going to need some kind of a reserve power supply that is SAFE for use under the hood to power the unit so that your not taxing your battery and charging system. I ran a 20volt 2 farad cap inside the cabin with dual 80amp relays and 8 gauge wiring to each unit when it was on the 924 that was activated by a switch ghetto rigged to my shifter in its *final stage* before i took it apart cause the engine went poof on me....again.... Really would of liked to see some numbers on what it did as far as afl or even a map sensor readings on that setup with the cis airbox to see if there was any change in pressure. Maybe once i get the megasquirt hooked up on the car i will throw them back on and fab something up again.
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80 euro
82 usdm
and all kinds of rice