Why superchargers fail

[WCP]

Interesting, Nels - raises some questions. Any information regarding drive torque, blower output, and output air temp. comparisons before and after the change. Lower temp. has to indicate less frictional heating of the balls, races and ball driver. If there is no impact on the output, then it should be all plus.

[nels]

Bill, no specific info on temp measurements, just seat of the pants checks but easily noticed to anyone who has checked fluid in a hot blower. As for the blower prep, most were higher pressure plate loads, Erb impeller and tight scroll to impeller clearance.

[BobPalma]

quote:Originally posted by nels

I'll bet I've burned up fifteen blowers in my day. All fifteen or so were with standard trans fluid. All ran so hot during a road trip that you could not check the fluid with out burning your fingers. I switched to a full synthetic about ten years ago and have never failed a blower since. Heat is the enemy and the first thing I noticed after using synthetic is a drastic drop in blower temp. I could check the oil without burning my fingers. I do add a teaspoon of STP to the mix to insure oil hangs on the output race after cool down. That is something I do as it seemed to make sense. I don't care what everyone has heard, this is what I have done and I am absolutely sold on it.

Good testimony, Nels. Which synthetic fluid do you use; brand and type? BP

[gordr]

I seem to remember reading about stuff called Santotrac, a synthetic fluid that was custom-made for planetary ball-and-race drives such as those used in Paxton (and McCullogh) superchargers.

Supposedly, one of its properties was that under extreme pressure, it became very tacky, and allowed the balls to transmit more torque without slipping. You could get more boost without adding extreme pressure to the spring pack.

Anybody here had experience with it?

Gord Richmond, within Weasel range of the Alberta Badlands

[nels]

Bob, I think I last used Mobil synthetic but I really don't think it would make a difference which you use. Gordon, I remember Sonatrac and Paxton's knock off that was Paxtrac I think. I think the intro of those products and the continued blower problems led me to try full synthetic trans fluid. I would imagine full synthetic oil would probably also work. The older units, in the 50's, often plumbed engine oil to the blower to cool it

[jlmccuan]

nels, I'll take your direct experience over my "a guy told me or I read this somewhere, so that's the way I do it" Thanks for weighing in.

Does anyone know what part of the SC is responsible for the bulk of the heat? The belt drive, bearings, ball drive, tranfer of the heat from compressing gasses? I have always assumed that most comes from the ball drive, but have not quantitatively tested that theory.

Jim

____1966 Avanti II RQA 0088_______________1963 Avanti R2 63R3152____________Rabid Snail Racing

[WCP]

It's possible that we could talk KoolR2 to do some comparison runs here in Ontario. If someone was prepared to offer up a working MS-SN60, I'm prepared to disassemble the unit to clean it out and set it up for a fluid change, check cold turning torque and give to Peter for a run. His data logger records max boost and the rpm. We could check oil temp with a thermocouple at the end of each run. There would be a week between runs, weather permitting in order to repeat the cleanout and fluid change. It will be a few weeks before I can talk to him. Maybe we can establish some hard data.

[okc63avanti]

John</div id="left">

<div align="left">'63 Avanti, R1, Auto, AC, PW (unrestored)</div id="left">

[grobb284]

Are you gentlemen going to install a filter inline with your dipstick cooler to catch contaminants?

Any pressure sensors to monitor the pump?

Why not also install a temperature sender to monitor real time heat build up, rather than a thermocouple check after a run?

[jlmccuan]

Cundracing sell the kits and I believe Paradise Wheel as well. I've made a couple, but my initial tests will be with a dipstick Paxton used and misc. parts. I have a remote filter boss I had planned on using, but some folks are using clear fuel filters. I will be logging fluid temps as well as the air charge temp. Should be interesting to see any differences, especially if the air entering the carb bonnet is significantly cooler. But I believe most of the heat gain to the intake air is from the compression rather than transfer from the mechanicals. Another neat feature is being able to pump the fluid from the supercharger for fluid changes. Since the stick doesn't go all the way down into bottom of the sump, I thought I would change as much as I could pump out and increase the frequency.

Jim

____1966 Avanti II RQA 0088_______________1963 Avanti R2 63R3152____________Rabid Snail Racing

[nels]

Jim, the results of the test you are planning will be very interesting. I'm glad you're taking this on. I've often wondered what the delta T was through a typical Paxton. I am curious as to how much of the temp rise can be attributed to compressing the air and how much is from air shear between the impeller and the scroll. Who knows, maybe a tight clearanced impeller fit putting out higher boost may exhaust cooler than a lower boost unit with wide clearances?

[grobb284]

Is "delta T" like Long Island Tea?

[Dan Timberlake]

A 100% efficient compressor would increase air temp (Rankine, which equals Fahrenheit + 460) by the ratio of absolute pressures (Pressure out/pressure in) raised to the .283 power.
A 14.7 psi boost (absolute pressure ratio = 14.7 atmospheric plus 14.7 boost = 29.4/14.7 = 2) would result a temp increase of ~ 115 F.
A real centrifugal compressor could be as good as 70% efficient, and that would increase the outlet temp to ~ 165F instead of 115.

7 psi boost would heat the air an additional 64 F ( 100% efficient) or in the real world more like 92 F.

Tight gaps or a shrouded impeller could add a few percent of efficiency, but that's only worth about 5 degrees in the 7 psi example, compared to over 60 degrees just from squeezin'.

[jlmccuan]

Thanks for the theoretical numbers. I was just going to ask for input on that to make sure I used the right resolution sensor for the air charge. Right now, my SC case runs at around 185 at cruise. Sounds like the heat gain is in the ball park for the sensor I ballparked. The bad news may be that the SC may not be adding all that much heat to the air charge and that cooling the fluid may not give much benefit to cooling the air. But one would think it would increase service life.

Jim

____1966 Avanti II RQA 0088_______________1963 Avanti R2 63R3152____________Rabid Snail Racing

[nels]

Is "delta T" like Long Island Tea?

Gene, not Long Island but Louisiana ice tea.