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Caveman Hammer Mechanic
 
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Clewett Alternator/Crank pulleys

Like it says, I decided to get the Clewett Serpentine belt kit. I had the exhaust system off, and the kit was on the bench openly mocking me. I embarked on the install, like all the Clewett stuff, the instructions were top notch. Got the kit installed, and decided to make a run from Boulder Creek to Livermore for some parts.
Absent the knowledge that it was there, it was/is mostly invisible. While running at 70mph and OAT at 80, my oil temps came up to 200, with the stock pulleys they almost never got off the 185 peg. Was wondering why, it seems that the Clewett crank pulley is about 4.5” and alt is about 3.25”. The stock crank pulley is about 5” and the alt pulley is about 3”. I do like the increased belt contact on the pulleys.
The change in ratio means the oil is almost always at 190ish and when running uphill in a hurry it hits 220. It comes back quickly, I am thinking that the oil will be in a happier range and the sludge in the oil tank might not form. When the rpms go up the cooling comes right down, so this summer will be the test, the Calif Central Valley is a regular run, so we will see. I do know that running an engine too cool is not as bad as too hot. I have always thought that my 3.2 ran too cool on the oil temps.
Thoughts?

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1984 Carrera El Chupacabra
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"Easy, easy, this car is just the right amount of chitty"
"America is all about speed. Hot,nasty, bad ass speed."
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Last edited by ClickClickBoom; 06-01-2019 at 11:34 AM..
Old 05-31-2019, 06:03 PM
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I also have one (yet to be installed). I'm interested to see what others have experienced.
Old 06-01-2019, 05:31 AM
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I too have admired the Clewet belt drive, thinking it to be more robust than the stock v belt.
At 220 is the thermostat fully open? If so, I think you will see higher oil and engine temps, when the air warms with summer/harder driving.
Even a bigger cooler may not keep it under the "too damn hot" 240.
You might still be ok with the aluminum 3.2, but I'd be worried with my 74 mag case.
Give Clewett a call to discuss??
Chris
Old 06-01-2019, 07:07 AM
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I'd suggest asking Richard Clewett directly. He's an expert, why not get an expert opinion ?
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Old 06-01-2019, 07:07 AM
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Almost a 20% decrease in fan speed. Yeah, that's a big difference, especially when ambient temps climb.

The stock 'stat opens at 185, so it's probably worse than at first blush, as in stock form the t-stat is probably only sporadically opening, whereas with the underdrive pulleys, it's wide open.

It probably frees up enough horsepower to feel the difference though.

Is there an option to retain the stock diameter pulleys?
Old 06-01-2019, 08:40 AM
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Quote:
Originally Posted by dannobee View Post
Almost a 20% decrease in fan speed. Yeah, that's a big difference, especially when ambient temps climb.

The stock 'stat opens at 185, so it's probably worse than at first blush, as in stock form the t-stat is probably only sporadically opening, whereas with the underdrive pulleys, it's wide open.

It probably frees up enough horsepower to feel the difference though.

Is there an option to retain the stock diameter pulleys?
My 3.2 in the central valley running at 80 MPH with the OAT at 100F, would only hit 190F, When climbing the Santa Cruz Mountain hill climb at a sporty speed, never went over 200-210F. I had always wondered why the thermostat was almost never open for the front cooler. My car has spent 90% of its existence with me, at 185F. My 2.7 without a front aux cooler ran from really hot to smoking hot, I saw 250F on the hillclimb.
3.2 operating temp
Oil cooler details?
Oil Cooler Baffling!
As you can see oil temp has been a quest on both my cars, one too hot, one too cool. One 2.7 v. 3.2 the quest for oil temp control is neverending.
I recognize that Porsche has to design for all environmental possibilities. As I mentioned earlier, my car has always ran cool, almost too cool. The closest analogy for aircooled engines is the aircraft world where temperature control is exercised with air control.
Lycoming Aircraft suggests oil temps between 165F-220F for cruise, and cylinder head temps below 400F for cruise as well. After doing some reading on oil temps, too cool is to be avoided as well as too hot. Too cool doesn't allow the additive package to activate properly, too hot causes the base stock to break down. I guess the final analysis is going to be determined this summer. I will be watching my temps like a hawk until I am satisfied that they remain in the correct range for my application. Cylinder head temp control is a fine art in the aviation world.
I am wondering if Clewett designed this ratio intentionally. The crank pulley area has room not only to fit the original size pulley, but since the flat ribbed belt has a lower profile, the possibility of even an increased crank pulley seems possible. The alt side of the equation is not size limited, except for smallest diameter. Methinks this might be an intentional design result.
From the website:
911 Serpentine Fan Belt Kit for 2.0-3.3 is back!
http://www.clewett.com/index.php?main_page=page&id=19
“After being discontinued for over a year, we are bringing back our 2.0-3.3 Serpentine Belt Kit. The belt tensioner has been redesigned, making it smaller and lighter. The kit is easier to install & adjust, and provides better air flow to the engine.”
Install instructions:
http://www.clewett.com/instrux/20-33serp.pdf
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1984 Carrera El Chupacabra
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"Easy, easy, this car is just the right amount of chitty"
"America is all about speed. Hot,nasty, bad ass speed."
Eleanor Roosevelt, 1936

Last edited by ClickClickBoom; 06-01-2019 at 11:38 AM..
Old 06-01-2019, 09:44 AM
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Quote:
Originally Posted by dannobee View Post
Almost a 20% decrease in fan speed. Yeah, that's a big difference, especially when ambient temps climb.

The stock 'stat opens at 185, so it's probably worse than at first blush, as in stock form the t-stat is probably only sporadically opening, whereas with the underdrive pulleys, it's wide open.

It probably frees up enough horsepower to feel the difference though.

Is there an option to retain the stock diameter pulleys?
What I didn't factor is the measurement of flat ribbed vs v-belt pulleys. I measured the simple outside diameters. Flat pulley is easy, v-belt, not so much. https://www.usarollerchain.com/identifying-v-belt-pulleys-s/5963.htm
The devil is in the details. It appears that I may have been crying wolf on the operating temps, being too critical. I will still be following the operating temps more closely. I may replace the engine mounted thermostat as a precautionary repair item. They use an expanding wax capsule and they can lose wax in use, and this will cause them to not open fully, passing the cooling duties to the front mounted cooler.
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1984 Carrera El Chupacabra
1974 Toyota FJ40 Turbo Diesel
"Easy, easy, this car is just the right amount of chitty"
"America is all about speed. Hot,nasty, bad ass speed."
Eleanor Roosevelt, 1936
Old 06-02-2019, 09:55 AM
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They never fully "open" anyway. The t-stat casting obstructs the oil cooler passage in the case. You can clearly see this if you remove the oil cooler and look through the drilled passage with the t-stat installed. The t-stat obstructs about 1/4 of the hole.
Old 06-02-2019, 10:58 AM
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Quote:
Originally Posted by dannobee View Post
They never fully "open" anyway. The t-stat casting obstructs the oil cooler passage in the case. You can clearly see this if you remove the oil cooler and look through the drilled passage with the t-stat installed. The t-stat obstructs about 1/4 of the hole.
By “fully” I mean’t the design intent. It seems that the “new” parts are not the quality of the original Porsche parts. Planned obsolescence....sell more parts.
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1984 Carrera El Chupacabra
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"Easy, easy, this car is just the right amount of chitty"
"America is all about speed. Hot,nasty, bad ass speed."
Eleanor Roosevelt, 1936
Old 06-02-2019, 01:15 PM
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I would be concerned if the last setup had lower and more consistent oil temps. The higher oil temps and more readily changing oil temps means the cylinder head temps are also not as consistent.
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Old 06-02-2019, 02:24 PM
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Quote:
Originally Posted by manbridge 74 View Post
I would be concerned if the last setup had lower and more consistent oil temps. The higher oil temps and more readily changing oil temps means the cylinder head temps are also not as consistent.
I am trying to be a little more objective. In measuring the pulley diameters and comparing them to the OEM stuff, the difference is not as great as it first appears. I did replace the engine thermostat when I first got the car, given the lack of durability of "new" parts, I am wondering if the heating difference might be coming from the "new" thermostat. I am ordering a "new" thermostat and will compare. In the meantime I will be doing some drives of very familiar composition to compare "old" datapoints to the new configuration. Driving on the flat, highway is not a normal datum for me and the car.
I took El Chup, up the hillclimb when the temps were close to the normal data points. The new fan pulleys were very close to the old normal temps and conditions. I am going to retract the original chicken little screetch, and replace it with a thumbs up on the install. I also measured the belt tension and found it to be slightly loose as well, it seems that a 120 mile trip at temp, it loosened/settled in. I will adjust the tension with my nifty Gates tension meter and get everything tip top shape. Further reporting to follow.
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1984 Carrera El Chupacabra
1974 Toyota FJ40 Turbo Diesel
"Easy, easy, this car is just the right amount of chitty"
"America is all about speed. Hot,nasty, bad ass speed."
Eleanor Roosevelt, 1936

Last edited by ClickClickBoom; 06-02-2019 at 07:01 PM..
Old 06-02-2019, 02:46 PM
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Fan speed vs delivered cfm??

A 20% fan speed reduction sounds significant.
Does anyone have an RPM/CFM delivery graph.
I worry about engine,(head), temps and corresponding oil temps.

Porsche engineers calculate thermal loads to be dissipated by head and cylinder fin surface area, then specify the air flow to get rid of the heat. There needs to be some margine of safety for altitude, heavy load, tuning deficiencies.

IMHO, one of the best ways to provide a Significant margine of safety, in terms of thermal dissipation, is to provide a comfortably bigger oil cooler than is needed at maximum expected load, THEN control oil Flow with a thermostat to maintain oil temps at sufficient levels to boil off condensates and prevent destructive viscosity loss due to elevated temps.

Similarly, I hope to provide enough air over the head and cylinder fin area to maintain safe thermal operation, (within design parameters), for the bits and gubbins- guides, pistons, valves, cylinders.

Brakes are a very good analogy here. Thermal load needs to to be managed, or performance and more importantly, component life will be seriously limited.

This is easy, install a bigger oil cooler than you think you might need and control it with a quality thermostat. DONE. A good margine of safety.

Similarly, make sure the fan/belt drive set up gets enough air flow/stock designed CFM standard.
A few thoughts,
chris
Old 06-02-2019, 03:10 PM
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Another way to measure it is to mark the fan when the crank is at Z1, then rotate the engine one revolution and note how far the fan moved.

Serpentine belts usually grip really well compared to a v-belt. If you think your fan is loose, try to turn the fan blade and see if the belt slips on the fan. If it's tensioned correctly, it should move the crankshaft.
Old 06-02-2019, 07:17 PM
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Quote:
Originally Posted by chrismorse View Post
A 20% fan speed reduction sounds significant.
Does anyone have an RPM/CFM delivery graph.
I worry about engine,(head), temps and corresponding oil temps.

Porsche engineers calculate thermal loads to be dissipated by head and cylinder fin surface area, then specify the air flow to get rid of the heat. There needs to be some margine of safety for altitude, heavy load, tuning deficiencies.

IMHO, one of the best ways to provide a Significant margine of safety, in terms of thermal dissipation, is to provide a comfortably bigger oil cooler than is needed at maximum expected load, THEN control oil Flow with a thermostat to maintain oil temps at sufficient levels to boil off condensates and prevent destructive viscosity loss due to elevated temps.

Similarly, I hope to provide enough air over the head and cylinder fin area to maintain safe thermal operation, (within design parameters), for the bits and gubbins- guides, pistons, valves, cylinders.

Brakes are a very good analogy here. Thermal load needs to to be managed, or performance and more importantly, component life will be seriously limited.

This is easy, install a bigger oil cooler than you think you might need and control it with a quality thermostat. DONE. A good margine of safety.

Similarly, make sure the fan/belt drive set up gets enough air flow/stock designed CFM standard.
A few thoughts,
chris
In my original chicken little squawk, I fired a little early. I didn't think through the pulley sizing, I used an apple vs apple, when it should have been apples vs pears. The effective pulley diameter for v-belt pulleys is measured differently than serpentine belt pulleys. Tomorrow I will hit the shop and break out the calipers and perform a more effective measurement of the stock pulleys. As well as the Clewett pulleys, I originally used a tape measure, not the most accurate method of measuring v-belts. For this disservice I apologize.
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"Easy, easy, this car is just the right amount of chitty"
"America is all about speed. Hot,nasty, bad ass speed."
Eleanor Roosevelt, 1936
Old 06-02-2019, 07:45 PM
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No worries. The stock ratio on your car is 1.67:1. That is, the fan turns 1.67 times for each turn of the crankshaft.

Measure the new setup as it sits right now as I outlined above.
Old 06-02-2019, 08:20 PM
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The Clewett does turn the fan/alternator slower than stock. I discussed this with him two years ago. He told me that he couldn't make a pair of pulleys which would have the same ratio as stock - there wasn't room, and there is a minimum diameter for pulleys, which limits how small you can make the fan pulley. Clewett didn't chose the pulley sizes in order to increase horsepower. Reliability was the goal.

The slower turning does add some horsepower. Not a lot, but enough to measure. Porsche did this on some race motors. JWE, it seems, did some testing on fan speeds vs HP for a customer (using some custom pieces from Clewett?), who found the biggest HP boost/slowest speed didn't cool enough. But that was slower than what Clewett stocks and sells, which seems to have met expectations.
Old 06-02-2019, 08:56 PM
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Went out and put a measure on the stock pulleys:
4.4375/2.750=1.613 ratio calculated.
4.500/3.250= 1.384 ratio calculated.
At first blush a 15% reduction in drive ratio.
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1984 Carrera El Chupacabra
1974 Toyota FJ40 Turbo Diesel
"Easy, easy, this car is just the right amount of chitty"
"America is all about speed. Hot,nasty, bad ass speed."
Eleanor Roosevelt, 1936
Old 06-03-2019, 09:22 AM
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Well,
Called Clewett and talked to the designer. A multitude of reasons for the ratio design change. In the context of design belt size availability was foremost in the process. Area in the lower engine mount around the pulley was the other reason, the smaller engines had less real estate to work with. We also discussed volumetric efficiency, pumping losses(oil), and CHTs as they relate to the operation of engines. It was evident I was discussing things way above my paygrade with a guy who has far more engineering expertise than I do. It was an enlightening and informative conversation. I am now entirely comfortable with the installation.
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1984 Carrera El Chupacabra
1974 Toyota FJ40 Turbo Diesel
"Easy, easy, this car is just the right amount of chitty"
"America is all about speed. Hot,nasty, bad ass speed."
Eleanor Roosevelt, 1936
Old 06-03-2019, 10:47 AM
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In past threads concerning Clewett's serpentine fan belt innovation, several people argued that it is a solution looking for a problem to solve. I found such comments a bit unconvincing. Clewett has a well-deserved reputation for making carefully engineered products, so he doesn't need to make questionable products that serve no purpose. Further, just because Dr. Porsche's original design works well, that does not mean that it cannot be improved upon. Another of the things that confirms Dr. Porsche's genius in his design of the 356 and 911 is that so many brilliant people around the world are working to make small but significant improvements on them. No one is trying to do that with the Ford Fairlane.

It is significant that every car maker in the world has now adopted the serpentine fan belt configuration. So, perhaps this is a good time to look at the evidence for its use in the 911.

So, ClickClickBoom, even though it is above your pay grade, could you share the evidence concerning volumetric efficiency, pumping losses of oil, and cylinder head temperatures with respect to the serpentine fan belt that not only made you feel comfortable using it, but convinced you it was a genuine improvement in terms of reliability and cooling efficiency?

You might not be able to relate everything the engineer shared with you, but your insights would be helpful to us. ClickClickBoom, thank you for being so diligent on this issue!

Cordially,
Greg
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Old 06-03-2019, 04:44 PM
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Greg - I reiterate the fact that Clewett did not come up with this to improve cooling efficiency. He did it to deal with the issues some have had with V belts coming off.

The trade off is less air gets moved.

My experience is with these used in race cars. Until the rules for a specific class were explained in words of no more than two syllables, some racers were using these when they shouldn't - because you get a HP gain. Not enough, really, to spend the money on, but a horsepower is a horsepower. They were using them because either they had once lost a V belt, or had heard others had and were fretting. I didn't hear from anyone that these guys were having overheating issues with the serpentines, at least not more than they were used to. Race engines spend maybe 90% of their lives at WOT? I've never calculated it. Most have added extra oil cooling, so their experience may not translate well to a street car on that score.

A quick look at fan characteristics showed that, at least as a first approximation, CFM rate changes are linearly proportional to fan RPM: CFM2 = (RPM2/RPM1)*CFM1. I didn't see mention of a fall off at some point, but if the stock fan isn't going supersonic at redline, a slower fan isn't affected by some such effect.

Efficiency might be complicated. Sources point to ease of maintenance and installation as perhaps the main benefit of the serpentine. On newer cars, using one belt to drive a lot of systems is a benefit, though it does not appear that this reduces parasitic losses as such, but that's not applicable to our air cooled cars (though you could convert your AC too, maybe, and actually have a serpentine and not just the multi grooved flat belt. One source suggests V belts are 95-98% efficient when new, but that this slips to around 93% when worn. The spring tensioner system might reduce this fall off? I am a bit dubious that any gain in energy efficiency from the belt type itself is more than de minimis.

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