i've been experiencing weaker and weaker performance from my alternator over the years and i suspect it may be nearing time for a rebuild (more and more of the dim glow..having to turn down stereo volume or reduce a/c fan speeds when stereo just quits..little signs like that), so this may be a good time to pull it out and inspect for signs of debris that i may not be seeing beneath THE CIS..;) grady has also mentioned the thermostat issue..i'll do a search and find out what i need to do to pull it and get it tested. personally, i will be amazed to find that i have much debris on my motor..i tend to keep a close check on the obvious.
ryan

My data from a week ago is similar to Ryans;

"""""I did some testing today with my car just for fun. It is hot here. 89F, 62% humidity, 13 mph breeze, feels like 99...Feels hotter to me but this is what the local weather says.

I drove the car at an indicated steady 60 mph 3rd gear at 4600, 4th gear at 3600, and 5th at 2900. The car seemed to run the coolest in 5th (again indicated by the oil temp guage). I am talking the difference between about 215F and 220F.

After the highway cruise, I tried different gears and rpm around town at 40 MPH. Obviously the car had less load that at 60 and as such ran cooler, right around 210F. I didn't see any noticeble difference on the guage but the car seemed most at ease around 3000 rpm.

I also tried some stationary "cooling" buy letting the car car sit with the cold idle throttle at different settings. There was no question that at 3000 rpm more air is passing through the fan and over the jugs. However, the car stayed a little cooler (again about 210F) at about 2200 rpm."""""

My car by the way is a 2.4T, no aux cooler, 11 blade fan, Mobil-1 15W50, and a confirmed clear air path from the fan to jugs and engine mounted cooler. How many blades does a turbo fan have? Photo?

My informal test seemed to indicate that I got the most effective oil cooling in the 2000-3000 rpm range and that maybe, just maybe the sweet spot (where increased revs produces no better cooling) is in the 2500-3000 rpm range (of course for my car in my enviromental conditions).

There is little doubt in my mind that the 1:82 turbo fan ratio will help cooling. However, it looks to me that based on the data we have received here, that in an early 911 system with no aux oil cooler the car simply generates more heat from combustion with increasing RPM (above some point) than increased fan flow can cool. This is exacerbated by 90F ambient/60% humidity. Therefore, if we really want to keep our indicated oil temps in the 180-210 range, we need to extract more heat via external oil cooling.

Here are some additional thoughts. There are a couple things that we have not considered in this testing. 1) the amount of cooling cpacity in the ambient air and 2) the efficiency of the airflow at highway speeds. Referring to point one, assuming that we have the same temperature and humidity in two cities, I should have more cooling capacity (relative to air density) at sea level than Ryan does at 3000 feet (or whatever Arkansas is). There are some pilots here who can probably share a density altitude chart, aren't there? A counter to that though is that if the air is indeed less dense in Arkansas, his car requires less power to overcome wind resistance. Where that trade off is requires a better engineer than I.

Secondly, does anyone really know what the airflow is doing around our cars at 60 or 75 MPH? Is it coming in the rear deck, or is the boundary layer effect causing is to sail right by? Where does the waste heat form the heat exchangers go? Is it getting sucked back in to the fan intake? If so, lower RPM might promote better oil cooling. What about the airflow around the oil tank? Is there any? Is the waste air from the heat exchangers being blown on the oil tank excaerbating the problem?

Any other ideas are welcome.

Don

don,
i actually was a professional pilot for many years..few hundred feet above sea level here..density altitude is a few thousand though..
ryan

IIRC correctly there is not much change in convective heat transfer coeffs. with the air density between 0 and say 8,000 ft. altittude. You can look in Kreith or Karlekar & Desmond tho (beginning course heat transfer texts). Plug the changes in the tables in the back into the conv. coeff. eqns.

Speaking of airplanes, the back of a 911 is like a wing and lift is created at speed which means there is a low pressure area at the grill at speed.

So, I'm curious as to how much cooling is improved by the use of a spoiler for highway cruising.

When I had a spoiler on the back of my car w/ the 2.7 engine it ran about 15F cooler on the highway than w/o the spoiler.
My current 3.2 runs about 15F hotter on the highway in 4th gear than it does @ the same speed in 5th.
I have never had a spoiler on the car w/ the 3.2.

I think we need to keep the tail as a constant.....
I have an early turbo tail...
i prop my decklid an inch and the thing seems to run cooler (or maybe im just crazy)
dont take that as "Fact"

Wow, that is substantial. My 73' Targa has a 3.2 with a Carrera cooler and fan up front, no tail, and an engine grill mounted A/C condenser. I've seen some hot temps lately without the A/C running. I would speculate that it is starving for air with that grill mounted condenser. Maybe it's time to ditch it.

I believe that is how this whole series of threads started, regarding the A/C condenser in the decklid. When you start getting 130F condensing temperatures, the air going into the decklid opening becomes really warm. Now, this really warm air is still much cooler than the cylinders, heads, etc., but still degrades the heat exchange performance...it effectively raises the operating temps of the engine by the difference between ambient and condensing temp.

The decklid condenser is definitely a restriction to airflow. If you don't want A/C, ditch it. I don't think you can get by solely on the underbelly or front condenser for A/C purposes. A/C is a "quality of life" issue.

Don,

Good points.

Yes, the “Turbo Fan” has 11 blades same as your ’72. The
difference is in the pulley. The 1.82:1 fan has a smaller (84 mm)
pulley part to the fan than your 1.3:1. The fan itself appears to
be exactly the same. The other part of the equation is the larger
(134 mm) crankshaft pulley.

The atmosphere has a great deal to do with the cooling. It is
mass air flow that is important, not volume flow. The higher the
air density the better. High humidity reduces air density partially
because water vapor (H2O atomic mass = 18) displaces the
Nitrogen gas (N2 = 28) and Oxygen gas (O2 = 32) in relative
proportion. High atmospheric pressure causes higher density
(and is usually dryer weather.) High altitude dramatically lowers
the density as does higher temperatures. While I am at 5280’
altitude, I wouldn’t expect the Arkansas Valley to be much over 100’.

The reason the “Rubbermaid Solution” works so well is the heat
of vaporization of the water going from liquid state to vapor
state absorbing heat, not the introduction of water.

Of course the lower the air temperature the greater the “delta T,”
the difference in air temperature before the heat transfer device
(radiator, cylinder & head fins, etc.) and after. The difficulty is to
get the largest delta T without having the high temperature
surfaces get too hot.

I don’t know if the shape of the 911 and the air flow over the
intake grill has a great effect. It must have some because the
air flow causes lift. That would indicate higher velocity and
consequently lower pressure just like above an airplane wing.
The best place to intake air would be at the base of the
windshield where there is high pressure air.

I think the waste air from the heat exchangers may be an issue.
It is exceedingly high temperature coming off red-hot exhaust
headers. It is wasted above and along side of the transmission,
ahead of the engine. The critical issue is to make sure the
engine seal is properly split around the engine tin. This prevents
reversion of the very hot air getting back in the engine
compartment. This is difficult with an old hard seal. With a
pliable seal it is done during engine installation with a cord
similar to installing a windshield & gasket.

When Porsche dyno an engine, the waste heater air is restricted
to simulate the heater control flaps and is directed down under
the engine (red arrow). Porsche even specifies a 30 mm thin-
edge orifice as the restriction. If you just open up the outlet of
the heat exchanger, too much air escapes to the detriment of
the engine cooling.
IMAGE DynoFactory01a.jpg “
http://forums.pelicanparts.com/uploa...1120858795.jpg "
© 1965 Dr. Ing. h.c. F. Porsche K.G.


On my dyno, I did the same thing.


One of the reasons I’m concerned about keeping the engine at
higher rpm is to maintain oil circulation. The heat can’t get to an
oil radiator if little oil is flowing. The flow is in direct proportion to
rpm.

As the engine heats up the alloy crankcase expends faster than
the steel crankshaft and the clearance between the crankshaft
and the main bearings increase. This allows a lot more oil to
flow in this path and reduces the oil pressure. Anyone who has
disassembled a 911 engine knows the main bearings usually
appear perfect. This is from the high oil flow. Many are tempted
to re-use them and some do. Porsche addressed this issue with
the cast iron bearing carrier in the 996, 997, and others.

I think this is the reason Porsche has the piston cooling nozzles
close below 3-4 bar (42-56 psi) so there is enough oil for the
connecting rod bearings. The trade off (engineering
compromise) was to allow the piston to run hotter with
consequent increased wear as opposed to a rod bearing failure.

I think the restriction in the oil flow to 993 cams & rockers was for
the same reason. Better to wear out a cam lobe or rocker arm
than loose a rod bearing.
IMAGE OilRestrictionCam993a.jpg "
http://forums.pelicanparts.com/uploa...1120858983.jpg "
© 2003 Wayne Dempsey How to Rebuild & Modify Porsche 911 Engines p. 83.


I prefer the other approach; increase the oil flow capacity with a
big Turbo oil pump (3) compared to standard (4).
Ignore Wayne’s yellow arrow.
IMAGE OilPumpTurbo01 “
http://forums.pelicanparts.com/uploa...1120859146.jpg "
© 2003 Wayne Dempsey How to Rebuild & Modify Porsche 911 Engines p. 77.

I also use both center oiling cams and the normal spray bar as in a 935.
IMAGE OilCenterCam935a.jpg “
http://forums.pelicanparts.com/uploa...1120859342.jpg "
© 1996 Bruce Anderson Porsche 911 Performance Handbook Second Edition, p. 59.

This requires a center oil cam and the chain housing cover
designed to hold the seal and fittings. This pumps a huge
quantity of oil to the cams lubricating and cooling the cam-to-
rocker friction surface, rocker bushings, and the ever important
valves & guides.

I don’t understand why Porsche didn’t use this approach with the
air/oil cooled engines. They successfully fought those battles in
the mid-‘70s with the race cars. Add the 1.82:1 fan and
substantial front oil cooler and these engines become long life
bullet proof again. We do it after the fact with 20-20 hindsight.

Best,
Grady

Here's something for the curious - the change to about 7,000' is only about 30%.

http://www.engineeringtoolbox.com/air-altitude-density-volume-21_195.html

As always, the methodology is important - temperature and absolute humidity are important also. That's why you need to measure things for yourself.

grady,
if i understand you now, i already have the 245 mm fan that was also on the turbo (i tried to measure my diameter yesterday..eyeballing with a ruler graduated in inches and converting mathematically to mm's i got roughly 240..so close enough i think). so what i need are different pulleys - both of them..the double pulley off the crank of 134 mm and also the pulley end associated with the fan of 84 mm's, plus i guess i would need 6 new shims..what does my stock '74 have now?

also are you also suggesting to possibly upgrade to the turbo oil pump as well? would it be interchangeable on my car? also, this is the first i've seen or heard of these racing cam oilers.
ryan

74's came with the early style setup. 11 blade 245mm with 1.3:1 ratio.

You can replace your hub with a either 1.8:1 (76' to 77') or a 1.67:1 (80 up) ratio hub.

guys,
forgive my ignorance..i think i understand that i would need the double pulley that goes to the crankshaft (134 mm), but what about the fan end of the belt? do i need a different diameter pulley where the shims go? i understand that i have the proper fan (245 mm). if this is the case and i don't need the actual fan, then this doesn't sound like a too expensive conversion. and as i mentioned to grady, i could switch back to my original pulley in winter when i'm trying to get the engine warmer. :)
ryan

Ryan,

You will need the large 134 mm crank pulley from a ’78-’79 911SC with the A/C pulley. You need the fan from a Turbo or ’80 and later 911 (SC or Carrera) with the small (84 mm) fan pulley. You will also need six shims, a hub, and the outer pulley half from an ’80 and later 911. Use new parts here. I’ll see if I can get the part numbers for you.

You can drill out the attachment of your steel hub to your magnesium fan and fit the steel part salvaged from a 5-blade fan with some flat-head Torx bolts and steel lock nuts. However, I encourage you to keep all your original parts intact. You may want to install them in the cool weather or just save them for a future restoration.

No, I wasn’t suggesting you change oil pumps, cams, etc. That is the fun kind of stuff that keeps everyone interested – including me. You can do that at your rebuild in 90k mi.

After your fan conversion you should start beating the bushes for the right set of pieces for a front cooler system.

Keep it up – the revs that is.

Best,
Grady

EDIT for spelling

grady,
according to the following pelican list i must already have the 245 mm fan? when i rough measured mine's diameter yesterday i was closer to 245 than 226 mm. i thought you said the turbo fan was also 245 mm..is there another difference in the two i'm missing? i'm hoping my fan is fine (clearly the biggest $$) and that all i need are the pulleys and shims (hoping)? somehow my density must be showing here..:)
ryan



Cooling Fans
11-Blade Fan (245mm Dia), 3.75" Dia Pulley, 911 (1974-75)
A-106-010-03 $641.05
11-Blade Fan (245mm Dia), 3.25" Dia Pulley,(also replaces 5 bladed fan)
911 (1980-89), 911 Turbo (1977-89) [Photo]
H-106-012-00 No Longer Available
11-Blade Fan (226mm Dia), 3.125" Dia Pulley (1978-79)
H-106-011-01 $317.50
5-Blade Fan, (1976-77)
C-106-028-00 $327.75
Outer Pulley Halves
Outer Pulley Half (3.75" Diameter), 911 (1974)
A-603-421-01 $21.05
Double Outer Pulley Half (3.75"/96mm Diameter), 911 (1975 CA Model)
C-106-207-02 $58.95
Outer Pulley Half (3.75" Diameter), 911 (1975 49-state)
C-106-207-00 $62.15
Double Outer Pulley Half (3.125"/82mm Diameter), 911 (1976-79)
C-106-208-00 $48.70
Outer Pulley Half (used when upgrading to 11 blade fan on 1976-77 911, 3.125" Diameter), 911 (1980-89), 911 Turbo (1976-89) [Photo]

70 oF, cloudy and raining in Oregon - split up some pinot noir -- great weather...

Ryan, the problem is that one side of the fan pulley is built into the fan, so you cannot get the smaller 80/83mm pulley on your fan. There is a larger pulley half rivetted on. Grady mentioned you could drill these out and replace but you may want to save for cooler weather or just not deal with the hassle. Call around to some dismantlers and you can hopefully score a 245mm fan w/ the correct upper pulley half for cheap money (definately cheaper than new). Its on my to-do list as well, but I've already ordered all the parts to install a front mount trombone cooler. If that doesn't keep the heat down, on goes a new fan and pulley set up (arguably a good idea anyway to keep head temps down, etc, but the excess income only comes in so fast).

klaucke,
thanks for your reply..i had a feeling that's what the deal was, but didn't know how to articulate it. the fan/pulley on mine isn't correct - the fan is the right size, but wrong pulley..gotcha. sounds like the best deal is what you're doing and look for the right fan cheap. doesn't look like pelican carries the 134 mm crank pulley though..
ryan

Parts Heaven dismantlers quoted me $35 for a 134mm fan pulley yesterday. I would think that the project would run in the $250 range once you got the fan. Just a guess, hopefully it's not more than that or I'll have to wait longer to upgrade!

EDIT: I should have also mentioned, you can add just the crank pulley and get about a 1.5:1 ratio, but you'll also need a non-Porsche belt, i.e. 735x10 (Continental makes one of these I believe). So if it takes a little while to find a good deal on a fan, you can use your fan with the bigger crank pulley and still be better than stock, just not as good as it could be. This was mentioned in a previous thread.