Intake Air Temperatures

[Lawrence Coppari]

I did a test this morning. The ambient temperature was 77-78 F. I installed a thermocouple just in front of my mass flow intake - conical filter assembly crammed in just behind headlight. At 59 mph and at 74 mph the thrmocouple read about 2-3 degrees F higher than the ambient. I had to use a different thermometer to measure outside temperature but later compared it to the thermocouple for calibration purposes and corrected for the slight difference. With the 77-78 F ambient, the air temperature at the cone intake filter was in the 79-81 F range with the car moving.

Secondly, I placed the thermocouple in the hole where the snorkel would normally go. The readings were within a degree F.

The biggest difference in the two locations was the temperature rise when the car is not moving. When the thermocouple is at the cone filter, within several seconds it rises to over 110 F when the car is not moving. I suspect it goes much higher if you wait for it. With it in the position where the snorkel gets its air, the temperature rise is much slower and less.

Lastly, my car has brake ducting which significantly channels incoming air from one vent to the brakes. Without the ducting, more air could be getting into the engine compartment and might reduce the temperature difference (which does not seem to be much when the car is on the highway).

This is better than I would have thought. Think I'll concentrate on my driving skills rather than cutting a hole in the front of the car to get a wee bit more oomph. I admit that there are slower cars with better drivers that have lower lap times than I.

PS - Since I was on the highway, I could not flog the car a lot to get the turbo really exercised. Therefore one heat load under the hood, the intercooler, was missing. However, I did floor it in 3rd gear and ran it from 50 to 100 without the temperature changing. The thermocouple has little temperature lag because it is small. Last time I floored it, a half shaft came off at the tranny.

[hoff944]

What happened when it came off? How fast were you going?

[Lawrence Coppari]

When it came off I was driving on I-81. I had just replaced the exhaust header that had been leaking and lessening boost. I was returning from Road Atlanta PCA Driver's Ed. About 20 miles from home there appeared a long streach of clear highway, no where for police to hide, no cars to pass at extreme speed. So, off I went. Had been doing about 75 and just finished passing some SUVs that were crawling due to gas consumption, I suppose. Boost came up (pegged), the grin on my face was there - sides of my mouth just about touching my ear lobes, just passed 100 when WHAM and tinkle, tinkle. Instinctivly, I let up on the gas, pushed in the clutch, and put it in neutral. Coasted off on the apron. Looked in the rearview as I slowed - no smoke. OK engine did not blow. Blipped throttle, tach shows engine OK. Sounds OK. Got out and looked under car. Half shaft came completely off at tranny. Can't believe my eyes. All bolts are missing.

CV joint broke off the speedo sender unit and took a big gouge out of stiffening ridge on tranny. Other than that, it is OK. Darn lucky that did not happen on track. It would have wrecked me.

Only thing I noticed on way home was cruise control pulsating when going downhill. I think that was from slop in loose drive train.

From now on I check the 24 bolts on the CV joints before a track event. Used to do that during wheel changes at the events but had quit doing it.

[hoff944]

Had you replaced them recently? I've never heard of a half shaft popping off like that. Your lucky it sounds.

[1.2gees]

If you're talking CV joint coming off the transaxle, (and the shaft in the control arm, but not someting coming off the tranny, or the control arm)

I've heard, AND seen that happenning on quite a few 944s, AND a 911...

I'd make it usual practice to check bolt tightness often...
Ahmet

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It's all the driver...

[1.2gees]

Oh, also, I don't check it now, but I checked it periodically for a few days when I repacked my CV joints last year, they worked their way loose, I took the bolts off, sprayed a good amount of brake cleaner in there, wiped the bolts off, put back on, and retorque, they've been fine for about 35k since than.

Ok, two more tips, if you're replacing/repacking CV joints, make sure you use the exact size tool for it, and clean the bolt before inserting, or it'll strip.

The other is to check the boots for the CVs often, they won't go bad, if the boot is intact. The one above the exaust is usually first to go, some "header wrap" works really good to avoid this common prob.
Ahmet

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It's all the driver...

[Lawrence Coppari]

I had had the CV joints rebuilt in January of 1999 and installed them myself without cleaning the bolt holes and without using Loctite or some equivalent.

This time, before installing the new shaft, I cleaned the bolt holes by cramming a brake cleaner soaked rag through each hole in CV joint and flange, using cleaner rags as I progressed. I also bought a 12 point bolt driver that fits properly. I also took care in torquing them to the 31 ft-lbs specified. I did not take this kind of care when I installed the rebuilt axles in 1999.

I have learned my lesson. The rebuilt axles only lasted about 12-13K miles. Don't know what was used for the joints. The replacement for the right half shaft I am going to do myself. I think I was lucky regarding what could have happened with a shaft coming off. Thanks for advice, Ahmet.

[lm6y]

WOW,
You're a lucky man Lawrence. Sounds like we all should get a tube of loctite, and make sure it doesn't happen to us.

[1.2gees]

I wouldn't exactly use lock-tite, those bolts are easy to strip already!

Just make sure you clean, AND dry them, and torque them right, keep an eye on them, just like brake lines/pads, spark plug wires, tires whatever, if you're running the car hard...
Ahmet

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It's all the driver...

[cyclemike]

When mine sheared off at the tranny flange I drilled out the broken off bolts and used new 14mm(head) bolts of the same stength and medium loctite.(I think blue) This makes gripping them a hell of alot easier than those crappy 12point hex-head bolts.(In my opinion of course.)