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Quote:
Originally Posted by kenikh View Post
Bottom line, keep the engine cool. Best mechanism? Water.

Does this mean a water jacket around the head? No. There are 911 racers in the SouthWest that use water misters behind the fan that blow misty air down around the heads, using the heat transfer capability to cool the engine in a open circuit (vs. closed circuit of a water cooled head), keeping temps way down. Also the use of alcohol and water in the intake tract keeps charge temps down, mitigating heat.

Even an air cooled motor can be water cooling assisted.
Check my recent 2.4L TURBO install and you'll see I agree but these are solutions and we are still digging for details to get an understanding.

Ok, here is some information that may be relevant. If so, we need to do some real digging to find the “limit” for our Porsches.

An old “How to HOTROD Volkswagen Engines” from 1970 book:

“We do not know of any published figures for the VW cylinder-head temperatures (sound familiar?) but some Corvair figures may be of interest. A Chevy dealer bulletin advised cylinder-head temperatures for the turbosupercharged Spyder models as: 200 to 300 degrees at idle, 350-475 at 30 to 60 MPH cruise, and 460 to 575 degrees from 3,000-5,000 RPM at full throttle.”

I’ve never owned a Corvair but according to this book they had a CHT overtemp limit switch that lit an idiot light at 575 degree. They were on Spyders(Turbo), 140HP motors and those with A/C. P/Ns 1993599 or 1993547.

Last edited by copbait73; 08-03-2009 at 05:23 PM..
Old 08-03-2009, 05:21 PM
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Quote:
Originally Posted by copbait73 View Post
Yes yes yes but Porsche knows a location(s) they can place a sensor and based on controlled lab testing and racing of other 911/930 based engines, often to destruction, know when this particular engine is overheating or not. That's what we are after here.
I think that is not correct. We are not talking an average wall temp here, which is tough enough to measure. We are talking about transient temps during the 15 degrees or so of combustion.

Porsche probably learned that their hot spot is the exhaust valve, from trial and error. They might not know how hot it is. They just try to reduce it as best they can.

Here are my suggestions:

1. Weld up the combustion chambers so that they have squish areas like the current production Chrysler Hemi. This will improve the end gas detonation problem.

2. Twin plugs are a must.

3. If we could find a way to smooth the the fins, and I mean really smooth, like a mirror (some sort of external extrude hone?), that would help the cooling efficiency.

4. Flat fan. Cylinders 3 and 6 get screwed for airflow. A flat fan would help a lot.

5. Improved efficiency fan. You can tell our fan is crap because the blades are straight. Every engineer knows that the tips should be curved backward for better efficiency. It would be quieter too.

6. Air to water intercooler. Stop dumping the hot intercooler air into the engine. The air going into the tail should just be for the engine.

7. Direct injection. The vaporization of the fuel cools the combustion air. There are turbo motors out there running 10:1 compression and 1.5 Bar boost with direct injection!

Of course you can run on tolulene, spray liquid N2 into the fan, and all kinds of wild stuff, but these are things that are practical, and we would have them today if Porsche could have stuck with air cooling.
Old 08-03-2009, 07:59 PM
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Quote:
Originally Posted by Speedy Squirrel View Post

Here are my suggestions:

1. Weld up the combustion chambers so that they have squish areas like the current production Chrysler Hemi. This will improve the end gas detonation problem. Search "peanut head" on this forum

2. Twin plugs are a must. Yep

3. If we could find a way to smooth the the fins, and I mean really smooth, like a mirror (some sort of external extrude hone?), that would help the cooling efficiency. One word: Nickies. Oh, make it two: Xtreme Cylinder Heads

4. Flat fan. Cylinders 3 and 6 get screwed for airflow. A flat fan would help a lot. What's a repop flat fan cost these days?

5. Improved efficiency fan. You can tell our fan is crap because the blades are straight. Every engineer knows that the tips should be curved backward for better efficiency. It would be quieter too. Like a 993?

6. Air to water intercooler. Stop dumping the hot intercooler air into the engine. The air going into the tail should just be for the engine. Laminova, the only way to go.

7. Direct injection. The vaporization of the fuel cools the combustion air. There are turbo motors out there running 10:1 compression and 1.5 Bar boost with direct injection! Hold tight on this. There are some prototype direct injectors, integrated w/ spark plugs in R&D with some of the big auto parts manufacturers. Imagine twin plugging a head with a set of DFI/spark plugs w/ ion sensing for knock! It's coming.

Of course you can run on tolulene, spray liquid N2 into the fan, and all kinds of wild stuff, but these are things that are practical, and we would have them today if Porsche could have stuck with air cooling.
..
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Old 08-03-2009, 08:18 PM
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Why would smooth fins dissipate heat better?

I am thinking that roughness adds surface area and promotes a turbulent boundary layer to bring more air into contact with the metal and draw heat away.
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Old 08-03-2009, 11:33 PM
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I will also add ceramic thermal barrier coatings to the piston crown, head chamber, valves and exhaust ports. I applied them to my 3.2SS NA and can really see a difference in overall engine temperature compared with stock despite the >45% increase in power. I do not have CHT measurements but I am certain that the heads run cooler as well.
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Old 08-04-2009, 05:02 AM
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There also this:

Quote:
Originally Posted by beepbeep View Post
I just found a thread on another forum with nice pictures of home-made flat fan....on a VW bug.

I like the corvair-style belt drive and nicely made injector housings. This engine will probably make a lot of power.





Quote:
Originally Posted by stevemfr View Post
Funny, I was just about to post this pic of a 3.2L (!!!) type4



This motor belongs to a friend of mine over here. This motor only runs to 6kRPM's, but fan (belt) reliability has not been an issue since he added the 2 gold tensioners.

Funny too, we had talked about using a flat multi-rib belt vs. V-belt that his motor has. We also discussed adapting this setup to a flat 6. Non-original, but for better cooling...
Anyone who'd be seriously interested? Wouldn't be extremely cheap, but it would be nowhere near the price the guy from South Africa (?) wants for his copy of the Porsche flat fan setup.
Source tread: http://forums.pelicanparts.com/newreply.php?do=newreply&p=4646140
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Old 08-04-2009, 07:27 AM
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All great pictures however we are gavitating toward solutions with no understanding of the limits.

I'll give you two examples:

1) I just built this killer BWM turbo motor. Power is doubled. On the track the waste heat load added to the cooling system overwhelms the the exisiting system. Water temp gauge pegs.

2) I just built this killer Porsche 911 turbo motor. Power is doubled. On the track the waste heat load added to the cooling system overwhelms the the exisiting system. ?????????
Old 08-04-2009, 10:00 AM
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Quote:
1) I just built this killer BWM turbo motor. Power is doubled. On the track the waste heat load added to the cooling system overwhelms the the exisiting system. Water temp gauge pegs.

2) I just built this killer Porsche 911 turbo motor. Power is doubled. On the track the waste heat load added to the cooling system overwhelms the the exisiting system. ?????????
Oil temp gage pegs.
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Old 08-04-2009, 10:04 AM
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There are a few folks here on the board that use CHT gages from the aviation world which makes sense for the application.
You see oil temps rise after a boost run. I would assume that anything near the thermol limit of the cylinder would result in audible detonation.
Extreme racers such as Juan or Eddie B will have insight for you.
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Old 08-04-2009, 10:09 AM
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Quote:
Originally Posted by RarlyL8 View Post
Oil temp gage pegs.
Thanks Brian but I was looking to bring the discussion back to the CHT.

Oil systems have too much thermal inertia to give you usefull information about head temperatures. The first example could still have reasonable oil temperatures when pegging the water temp, same as can our 911s.

Yes, still looking for those who push their 911 and monitor CHT.
Old 08-04-2009, 10:41 AM
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I use a CHT on my VW motor. You just tap and thread the cooling fins one one of the heads (or all 6 should you so desire). I believe it is a VDO sensor - the gauge is definitely VDO. This set up should work fine with our heads and should pipe fine into any one of the standard data logging systems that most EMS now have. This would be the way to go after it.
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Old 08-04-2009, 10:44 AM
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The aviation world would have more info on this than the air cooled Porsche world. Oil temps are all we get, any other monitoring system would be custom therefore not an approved method and not standardized.
Your 2.4L heads are steel right? If so then heat would be a grater issue for the case than the heads I would think.
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Old 08-04-2009, 11:16 AM
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All Porsche heads are aluminum, including 2.4 heads.

I finally get the point of this thread - knowing head temps is a black hole that should be filled and how to lower temps is only interesting after we know what to measure against.

Might be interesting to cross post to the technical forum to see if anyone there has run head temps sensors.
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Old 08-05-2009, 08:46 AM
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eng. cooling

my 2 cents. I built Juan Ruiz car/ engine and one thing I like to do is add some fuel on decel / overrun this help with engine cooling , that why you see some flames out the exhaust. also shield the air filter or turbo inlet from eng. bay heat.
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Old 08-05-2009, 08:57 PM
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So again, anyody running a CHT on their car?
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Old 08-06-2009, 12:58 PM
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Quote:
Originally Posted by kenikh View Post
So again, anyody running a CHT on their car?
Not me, but I have all the hardware and software (ECU) to monitor. I think this might be a good Saturday afternoon project.
Old 08-06-2009, 06:10 PM
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Quote:
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Not me, but I have all the hardware and software (ECU) to monitor. I think this might be a good Saturday afternoon project.
Now we're talking. Can the ECU datalog more than one cylinder?
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Old 08-06-2009, 10:34 PM
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I don't monitor CHT either - couldn't find a "good" spot. I now use EGT and so far seeing ~1550degF as max temp. My sensors are ~1" from the exhaust port poking into the headers type.
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Old 08-07-2009, 06:44 AM
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Quote:
Originally Posted by Turbo Werks View Post
my 2 cents. I built Juan Ruiz car/ engine and one thing I like to do is add some fuel on decel / overrun this help with engine cooling , that why you see some flames out the exhaust. also shield the air filter or turbo inlet from eng. bay heat.
He knows what he's saying!

The other Juan
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Old 08-07-2009, 12:15 PM
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Quote:
Originally Posted by Turbo Werks View Post
my 2 cents. I built Juan Ruiz car/ engine and one thing I like to do is add some fuel on decel / overrun this help with engine cooling , that why you see some flames out the exhaust. also shield the air filter or turbo inlet from eng. bay heat.
Any pics of the shielded air intake? Don't most cut fuel on decel for economy?
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Old 08-08-2009, 08:19 PM
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