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Wo ist die Rennstrecke?
 
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Quote:
Originally Posted by kenikh View Post
Now we're talking. Can the ECU datalog more than one cylinder?
Yes, but the sensor installation would be a nightmare. It would be much easier for me to log EGT for each cylinder - in fact I have the fixtures, but not the motivation right now. At this moment, I am looking up the calibration numbers for the stock CHT sensor from Porsche to get it to work with my ECU.
Old 08-09-2009, 07:49 AM
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Some thoughts to put in you tool box (most you should already have).

-thermal coatings of piston top, combustion chamber, valve tops, exhaust port.
-check you fan speed against you rpm limit, do not want it to caveate.
-get the oil cooler off the motor and divert that air to the cylinders.
-Porsche seemed concerned w the exhaust valve cooling and added additional oil flow to them.
-use Nickie's instead of factory cylinders.

I think you are building a small displacement motor (under 2.5 with very high rpm). If you are not going much 400hp and do not over-spin the cooling fan should be ok. Using the above thoughts should be ok through 500hp+ on the track if you can keep the heads on the motor and the rods from turning into mush.

Good luck.
Old 08-09-2009, 08:50 AM
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Good advice. I am doing all of the above. Coatings and Nickies are major cooling benefits. Also, a 3.6 fan is a great add, too. I am selling my early 11 blade to get one and may even fabricate a flat fan shroud like the one earlier in the thread for it. I really like the corvair-like tensioned belt idea to get even cooling.
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Old 08-09-2009, 10:50 AM
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Double check, I think the old fan might blow more but the 3.6 is quieter. I suspect you know but the Corvar style fan drive is prone to the belt jumping and failure.

Get rid of the motor oil cooler like Porsche did and maximize what you have and it should be as good as anything that would be fabed.
Old 08-09-2009, 12:05 PM
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Quote:
Originally Posted by kenikh View Post
Also, a 3.6 fan is a great add, too. I am selling my early 11 blade to get one and may even fabricate a flat fan shroud like the one earlier in the thread for it. I really like the corvair-like tensioned belt idea to get even cooling.
The 3.6 fan is more quiet than the 3.3 fan, but also moves less air.

From the Porsche specs:

3.0L - 1:1.81 drive ratio - 1380 l/s @ 6000 Crank RPM
3.3L - 1:1.68 drive ratio - 1500 l/s @ 6000 Crank RPM
3.6L - 1:1.60 drive ratio - 1010 l/s @ 6100 Crank RPM

The 3.6 has a slightly higher drive ratio and still moves less air. Seems like the stock 3.3 fan is the best.
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Old 08-09-2009, 12:24 PM
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Originally Posted by 911st View Post
Get rid of the motor oil cooler like Porsche did and maximize what you have and it should be as good as anything that would be fabed.
I also like Goran's (BeepBeep) idea of overdriving the fan about 20% and remote mounting the alternator. For those of us without A/C, the Alt. could be mounted in place of the compressor and driven off of the compressor crank pulley, with a custom pulley to get the proper ratio. You could also use a smaller, more modern Alt, like a small Hitachi.
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Old 08-09-2009, 12:28 PM
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That is what I thought about the 3.6 fan.

This guy plans on pulling 8K rpm so overdriveing the fan would just get it to where is goes ineffecent quicker.

However, that can be a good idea on a normal 930 that goes to 6500rpm.
Old 08-09-2009, 12:54 PM
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3.6 fan is made to be quiet but it moves less air. There is a reason why Porsche used straight-blade 930 fan on turbocharged 3.6 and curved-blade fan on N/A engines.

20-30% overdrive won't cavitate the fan, tip speed is still way below mach 1. But it will eat belts and generators unless you move the generator out and gear it down.

It's not the speed that kills the belt but accelleration. Generator rotor weights a lot. If you increase speed by 30% you increase amount of energy in generator with 69%! If you use lightweight flywheel and "flip the throttle" you will cause major belt-slippage when trying to accelerate 2kg rotor from 1500 to 9000-ish RPM in fraction of a second.

Moving the generator might be a good idea even if you don't plan to overdrive the fan but do want to rev to 8000 RPM.
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Last edited by beepbeep; 08-09-2009 at 12:57 PM..
Old 08-09-2009, 12:55 PM
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Interesting info on the 3.6 fan. Being larger and with curved fan tips, I expected it to push more air. Very interesting indeed.
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Old 08-09-2009, 01:09 PM
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One read was that Porsche added to pop up wing on the C2 was to make up for some fo the cooling loss, not so much for down force.

Porsche was mostly in-search of lower noise to meet some of the euro countries noise requirements which is why they also installed the under tray/diaper.
Old 08-09-2009, 01:59 PM
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Interesting read on thermal loading properties using FEA on aluminum cylinder heads in a diesel motor:

http://www.gacsolucoes.com.br/pubs/STRUCTURAL_ANALYSIS_ALUMINUM_CYLINDER_HEAD.pdf

There are some interesting nuggets in there.
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Old 08-09-2009, 02:15 PM
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The back curved blades of the 3.6 fan would reduce the efficiency, but that alone would not account for the lower air flow. I suspect that fan needed to be designed for a lower flow rate to prevent stall. The 3.6 had the engine mounted oil cooler removed so the total air flow area is reduced and the flow resistance would be greater.

Most modern automotive fans have forward swept blades to reduce noise, but not lose as much efficiency as the backward swept blades.
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Old 08-09-2009, 03:21 PM
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Blade curavature design is based on the speed at which the efficiency of the fan is desired to be greatest. Current automotive fans have the S curve design. This is good with electric motors running them at very high speed, where it is desired to have the best efficiency.

For an engine driven fan, (no longer used in new automobiles), you need to produce the target airflow, pressure, and efficiency at a range of speeds, and at a lower speed, which makes such a design less suitable. Also, a Porsche fan is actually a ducted axial fan, in which case I would think the backward curvature is better for efficiency, especially with variable speeds. It seems Porsche also reached that conclusion. Also, noise and efficiency are really the same thing really. Acoustic energy is wasted fan energy.

None of that really matters though. What makes anybody think that more airflow is going to produce more cooling? Think on it a little more.
Old 08-09-2009, 09:32 PM
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Quote:
Originally Posted by Speedy Squirrel View Post
None of that really matters though. What makes anybody think that more airflow is going to produce more cooling? Think on it a little more.
Interesting thought; there has to be a heat transfer threshold at which the inneficiency of air to draw heat from the aluminum plateaus. More air won't overcome the inability of metal to let go of heat into a medium as inefficent as air. The question is: where is that threshold and can it be exceeded given the volume of a 911 fan?
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Old 08-10-2009, 08:40 AM
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Quote:
Originally Posted by kenikh View Post
Interesting thought; there has to be a heat transfer threshold at which the inneficiency of air to draw heat from the aluminum plateaus. More air won't overcome the inability of metal to let go of heat into a medium as inefficent as air. The question is: where is that threshold and can it be exceeded given the volume of a 911 fan?
Looking at Porsche's product offering and some racing engines, roughy 400Hp on the 930 based engine and roughly 500HP on the M64 based engines. The M64s higher due to the benefits of ceramic exhaust port liners.
Old 08-10-2009, 09:19 AM
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If building an 8000rpm small bore turbo, might want to use the 1500 cfm as a starting point and recalulate the ratio needed to turn the fan at the same speed as the 930 turns is at 6000rpm.
Old 08-10-2009, 09:41 AM
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Just for arguments sake, is reliability the only reason no one considers going electric? Here's an example:

http://www.derale.com/single-rad-fan.html


2200CFM @1670 RPM w/ 23.4 amp draw

I am wondering if these fans are rated for a 100% duty cycle...
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Old 08-10-2009, 10:15 AM
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I think there is at least 12" between the intake tracts.

This wouldn't be too hard to make a shroud to fit. Of course, How would your alternator like that current draw? I suppose a new efficient version wouldn't care.

My $0.02... I think the largest limitation is the excess combustion heat and its ability to saturate the heads. This means there is a fundamental requirement to keep the combustion chamber as cool as possible. The ceramic thermal barrier coatings have already been mentioned. Why not mill out two rows of fins off the sides of the head and weld a section of aluminum square tubing down each head. Tie the tubing together and pump some water through. A small radiator would work fine connected to an electric water pump. Now go crank up the boost with your water-assist, air-cooled heads. Of course, Grady Clay's "rubbermaid" solution would be much easier and cheaper to implement.
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Old 08-10-2009, 10:25 AM
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Quote:
Originally Posted by kenikh View Post
Just for arguments sake, is reliability the only reason no one considers going electric? Here's an example:

http://www.derale.com/single-rad-fan.html


2200CFM @1670 RPM w/ 23.4 amp draw

I am wondering if these fans are rated for a 100% duty cycle...
I made a mistake, factory fans are not rated in CFM. I suspect that would not blow anywere near the amount of air needed but could be mistaken again.
Old 08-10-2009, 10:33 AM
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The electric is putting out 1038 l/s at no back pressure.
Given the amp draw, and assuming 80% efficient motor, and 80% efficient fan, it is capable of generating .3 air horse power.

The 1500 l/s turbo fan opperating against 17 inches of water pressure is generating 6.65 air horse power.

To duplicate that with an electric fan would require over 500 amps.
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Old 08-10-2009, 11:12 AM
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