Heat source

What is the source of warm air that the warm up regulator (?) on the back of the injection pump uses on MFI engines? What is it's mode of force? is it just hot air rising?

bruce

My experience with Bosche CIS systems is that, while the WUR is bolted to the engine and this will get them warm, there is usually an electrical plug on the regulator that supplies electricity the unit to heat it. I suspect there's one of those bi-metal strips in there, like auxilliary air regulators, only the WUR warms up more slowly. Sometimes when the heating element fails, warm-up fuel pressure going from the WUR to the very top of the fuel distributor is good on startup, then gets poor as the engine warms but the WUR does not, then things get fine again when the WUR get to engine temperature. As warm-up pressure is basically the car's choke, the car will run rich during this in-between time. My experience with Porsches is just beginning (I should have been driving these all along), but I believe the Bosch k-basic CIS system is very similar on all cars. My '83 911, my dad's '84 M-B 500 SL and my '84 VW Rabbit all work the same.

And here's my $.02. I've heard all about Webers and I suspect they are the thing to use when changing cams. CIS systems are made to match the airflow characteristics of the engine and changin cams changes that. But if you're not changing major engine parts, I am very convinced, that no carburetor system can match the accuracy and gas atomization of an injection system that is running right. They are usually very reliable and straightforward to troubleshoot.

The heat exchanger, constantly under pressure from a 2 1/4" air duct off the rear cooling shroud, supplies hot air to the 'thermostat' through a 1" hose on street engines ... it is removed and a block-off plate covers the access port on racing engines.

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Warren Hall
1973 911S Targa

Is there a rigid section of pipe comming from the heat exchanger that feeds the hose that goes to the injection pump? The reason I ask I am setting up an MFI with headers I want to keep the warm up part of the pump. My plan is behind the fan on the fan shroud i have there is a 25mm nipple, I think it fed air to the air cleaner box. I plan on running a line from there to a fabricated box on the header then go from the box up to my pump. I'm thinking this will supply the needed hot air. I've been thinking though about what type of material I could use for the hose that could withstand the temperatures I would expect to see at that box on the header. I'm thinking that it would get pretty hot and really test any hose I run to it. So if there was a rigid section that I could run off the box at both entry and exit points i figure the temp. at the end of that section would be cooler also i could then just use the stock hose for this aplication. what kind of temperatures do you think I would see on the header? 300, 400 500 degrees? does My idea seem sound as far as getting that pump to work correctly? jus to be clear this is not the CIS but the earlier MFI belt drivven of the cam, and that is the pump I am talking about.

Bruce

[This message has been edited by mackgoo (edited 03-29-2000).]

I have that same nipple in the shroud, and right on top in the air box there is a same 25mm nipple. Should this be connected? If not, what are they for?
2.7L cis...

MM I saw the F1 race on TV sunday, did you make it?

Bruce

Yes, I was at IBM´s paddocks. Very nice, too bad the brazilian racer got out on the 23rd lap.
Its amazing the tecnology on these cars. At the end of the strait, 300 km/h, and they start braking after the 50m marks. And the motor sound is stupidly loud, very exciting.

The hose from the heat exchanger to the 'elbow' at the sheet metal juction is a heavy rubber 3 or 4 ply hose. The hose from the junction to the thermostat is a paper/foil/plastic flex hose.

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Warren Hall
1973 911S Targa

Would you care to speculate as to the temperature at the heat exchanger?

Bruce

Isn't the nipple on the shroud behind the fan for the pipe for the charcoal canister in the trunk. I think it then goes to the back of the air box. I do not have mine connected, would this be a problem?. I don't have to work about smog test as it's a '70. The car seems to work fine without it.

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Any one have any ideas what kind of temp.'s I might see on the surface of the collector part of a header at normal operating temp?
I read in another post someones exhaust was cherry red. How hot does carbon steel need to get to be cherry red?

Bruce

The exhaust system on an MFI engine NEVER gets anywhere near 'cherry' red!!! A thermocouple probe reading I just took with a Fluke Model 52 thermometer after shutdown, having warmed up the oil to 180 F idling for 15 minutes was 323 F at the shroud by the outlet to the injection-pump thermostat.

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Warren Hall
1973 911S Targa

Thank you Warren. I apreciate you taking the time to do that expirement.

Bruce