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Why superchargers fail

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  • jlmccuan
    replied
    I don't have any direct experience, but have been told and read that engine oil and regular ATF do not have the correct friction modifiers needed at higher RPM's and boost pressures to efficiently operate the ball drive SC's, hence the specification of the type "F" ATF by Paxton. I'm not sure, but weren't Paxton and McCullough the only ones using the ball drive? I also have a Procharger with an intercooler (more correctly, an aftercooler). It is a gear drive unit and recircs engine oil for lube and cooling, similar to other currently made brands.

    Jim

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

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  • jlmccuan
    replied
    That's the dipstick and pump exactly, but my heat exchanger is different. The dipstick is the hard part, the pump is FLAPS available and a variety of heat exchangers can be used. As I said earlier, I bought one of the dipsticks, but I think one can be built for less if you're handy. I've been logging temps coming from the air charge and the SC oil temps and it looks as though the bulk of the heat is from the compression. Possibly, more heat is going into the oil from the heat of the air being compressed than from the mechanical operation of the SC. Probably why most SC manufacturers concerned with heat going into the engine use intercooling or aftercooling rather than trying to directly cool the SC. But it's still too early for any conclusions.

    Jim

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

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  • okc63avanti
    replied
    quote:Originally posted by jlmccuan

    John, I'll be testing out one of the dipstick coolers in the next week. I should be able to get temps of both the SC case as well as the air charge temps with and without the cooler. Although this information will not give direct evidence of extending SC life, one would think that if the dipstick cooler does in fact reduce the operating temp of both the SC and the air the SC delivers, it would be a good thing.
    Jim,

    I found a picture of a dipstick cooler for Paxton SC by a company called JC Performance in Grover Beach, CA. Is this the one you are trying out or something similar to it. If so I definitely would like to hear about your results.


    <div align="left">John</div id="left">

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

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  • packardclipper
    replied
    You really need a direct oiling system that was installed in many cars in the 50's with superchargers where engine oil was pumped into the unit. A drain hole was made half way up on the side of the case and when the oil reached that hole drained back to the oil pan or oil adding tube. I have this setup on my 57 Packard Clipper and it has worked great. On my 58 Packard Hawk I will not do it because it is not "correct". So when not showing the car I remove the belt and put it the belt on for shows. The superchargers are getting harder and harder to find and more and more expensive. I have a 7 of them and paid hardly anything for them because years ago they were worthless.Cubic inches put the last nail in superchargers coffin besides its failure rate. Getting back to direct oiling. At my shop every late model Camaro,Firbird and Mustang I have seen with an aftermarket supercharger set up absolutely used a direct oiler system.No ands,buts or maybes about it. If Paxton Superchargers were so great more manufacturers would have installed them.

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  • Thomas63R2
    replied
    Nels, no belt driven supercharger, centrifugal ball drive or gear drive or otherwise, is 100% efficient. I'm not sure what Paxton had rated the SN60, but I believe it was significantly less than 70%.

    Turbos are the most efficient way to boost an engine. On real high end turbo setups the magic word is "crossover" - which is when the power created is in excess of theoretical. The simple theory is based on atmospheres of boost (every 14.7 psi is one atmosphere, or 1 bar). So an engine at 1 bar of boost could in theory have double the non boosted horsepower (14.7 psi atmospheric, plus 14.7 psi boost equals the engine breathing as though it were twice the displacement).

    Thomas

    Long time hot rodder
    Packrat junk collector
    '63 Avanti R2 4 speed

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  • nels
    replied
    Dan, I'm not sure I understand the 70% efficiency part. Is the loss in efficiency from the impeller clearance or something else? Trying to understand.

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  • nels
    replied
    Is "delta T" like Long Island Tea?

    Gene, not Long Island but Louisiana ice tea.

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  • jlmccuan
    replied
    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

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  • Dan Timberlake
    replied
    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'.

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  • grobb284
    replied
    Is "delta T" like Long Island Tea?

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  • nels
    replied
    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?

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  • jlmccuan
    replied
    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

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  • grobb284
    replied
    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?



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  • okc63avanti
    replied
    John</div id="left">

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

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  • WCP
    replied
    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.

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