Ladies and gents,
One extraordinary document I have been able to lay my hands on (with thanks, Ed) is a copy of a thesis written in November 1985 - Rotary Vane Compressors, Testing and re-design of a sliding vane compressor for supercharging. The thesis was authored by Mark Hammond and Edward Vieusseux at the NSWIT. Hammond and Vieusseux’s project evaluated the suitability of a Norman to supercharge engines up to 2,000cc capacity. The work undertook extensive bench testing, including analysis of alternative vane materials. The test mule for this work was one of Mike’s 200 Normans, casing number 2000002S, as shown below:
The test rig drove plain air (and in some cases lubricant spray) through the Norman, using a waterbrake dyno driven by a BMC 1800cc engine. Different casing liners were used to give different port timings (0% compression, the standard 16% compression, and a higher 32% compression), along with two rotors (3- and 4-vane).
Some learnings from the thesis:
• The Norman supercharger has an adiabatic efficiency of 45-60% for 2-10psi boost. This lines up pretty well with the numbers I have used earlier in this post when we modelled the Norman. I had assumed 60%, whilst other resources indicate 70% (Eldred) and 50-65% (Corky Bell).
• At 4000rpm (typical operating range for a wide-open early Holden Norman), the volumetric efficiency starts at around 80% at 2psi boost, and drops to 70% at 10psi. Increasing pressure ratio lowers the efficiency due to the increased internal pressure recirculating gas within the supercharger. This is a little lower than the values I used in the modelling – I assumed 90%, compared to literature values of 82-90% (William Lyons), 90% (Royce Brown) and 85% (C.F. Taylor).
• The 200 Norman casing was measured (using the modern method, not Eldred's method) to give 115ci/rev (very similar to the Type 65). The 16% internal compression ratio of a standard Norman was close to optimal (i.e. increasing or decreasing internal compression was not beneficial).
• Four vane materialss were tested: Bakelite, Feroform F31 (similar to the Feroform F57 I have discussed earlier), Tuffclad Moly (a self-lubricating thermoplastic) and Nylacast Moly (a self lubricating thermoplastic filled with nylon). Of note:
a) vane wear for the Bakelite was very similar to that noted by Mike Norman – about 4-5mm per 20,000km of driving. One of the reasons for this is that Mike’s design has a very high vane tip speed due to it’s large casing diameter – some 49m/s at 6000rpm, which is nearly four times faster than a grey motor piston at redline.
b) using water alone as a lubricant for Bakelite vanes lead to liner scoring. Oil is required.
c) water can be used as a lubricant for the Feroform and Tuffclad Moly materials. It removes frictional heat far better than oil, probably by partial vapourisation.
c) friction power loss was not noticeably different for the different vane materials. However, the Nylacast Moly vanes tended to pick-up in the vane slots (even with water lubrication) and hence are not suitable.
d) Both the Nylacast Moly and Tuffcast Moly were more susceptible to delamination or cracking than Bakelite. The slots cut out for the vane spring carriers act as a stress riser.
• Vane rattle was examined, and found to be due to:
a) too much clearance between the vane and slot. This stops once operating temperature is reached. Note that a clearance of 0.005” was recommended for Bakelite vanes (this is perhaps a little more accurate than Eldred’s “flop fit” specification), and is a useful number for anyone milling down their own replacement vanes.
b) low speeds (<1500rpm) where the small centrifugal forces are unable to overcome slot friction and the weight of the vanes. This is where the vane springs are useful. Of note, there was no discernible power loss from using the vane springs (i.e. they do not increase friction, as the centrifugal forces on the vanes far exceed the spring tension).
• Whilst four-vane rotors are more efficient and do not increase shaft power, they are not a simple swap-in for the exiting Normans. Four-vane rotors were tried, but delaminated over 2000 pm as the vane stroke was too high in the existing casing. A word to the wise – if replacing the rotor in one of Mike’s Normans, do not be tempted to use a 4-vane design unless the end-plates are remanufactured to give less vane stroke.
• The seal between the end-plate and casing was effected through the use of a synthetic sealing strip (I have yet to find one of these in a Norman… they tend to get discarded, and replaced with a line of sealant like Sikaflex
• Just like Roots superchargers, the positive displacement Norman delivers a pulsing flow at the discharge ports. Four-vane rotors delivered smoother flow than three-vane rotors. The attached graph shows how the discharge pressure changes over time. Note that a Norman running at a nominal boost pressure of 10psi has the discharge port oscillating between 7 and 11 psi (albeit over a very short time frame).
• The nature and surface finish of all sliding surfaces have to be very hard and smooth to reduce friction and vane wear. A surface finish of <16µinch is recommended, as per the red line in the chart below. As a comparison, a rough turned item with visible toolmarks is about 500µinch, a smooth machined surface around 125µinch, bearing surfaces are around 32µinch, and fine lapped surfaces are around 1µinch.
The document also contains a compressor map for the 200 Norman – this is the only Norman compressor map that I am aware of:
Cheers,
Harv (deputy apprentice Norman supercharger fiddler).
327 Chev EK wagon, original EK ute for Number 1 Daughter, an FB sedan meth monster project and a BB/MD grey motored FED.