Good stuff, Matt!

BTW, I would suspect that the "abradable coating" is one that allows plastic deformation, rather than one that has chunks that come off. Then again, maybe the MINI can tolerate a little fiber in its diet.

 

I am pretty sure that the M62 will not fit, plus new mounting positions would need be fabricated. The idea's been raised before, as has been said, so that probably is enough empirical evidence that it isn't feasible. I personally think that a complete replacement for the SC [with another non-Roots SC thank you! ] is the way to go, if you want dramatic changes in power.

 

There are really only two viable other solutions, a cetrifugal and a twin-screw. The first is more effecient, but acts more like a turbo and won't keep our nice flat torque curve (but since the BP valve is there, it doesn't really matter below 3000 RPMs) and the twin-screw isn't cheap. Whipple has some listings for small twinscrews on their site, but the links go to pages under construction.

I'm not sure that the M62 is the way to go, it seems like a big PTIA to get stuffed into our cars. The twinscrews are a nice compact package, so one could get better efficencies without trying to stuff a rather large square peg into a small round hole!

As for sourcing, try wrecking yards and eBay!

Matt

 

what is the difference between out Roots-style Eaton & the Twin Screws?

thanks!

-jac

 

I’ve had a good look at five assembled MINI superchargers one of them being a 05 model, also two completely disassembled 03 build units, only one 02 build high mileage unit had no flaking of the rotor coating other than the usual wear scuffs. The low mileage 05 model interior case had polished surface swipes and corresponding marks on the rotors without the characteristic shiny lobe scuffs of the early models. That is why I conclude the case surface is being scraped by the later build rotors to a greater extent than the early type of coating.

I don’t think one should lose sleep over the occasional minor bits of glued on rotor coating or case material that may find there way out of the SC but for some really scary looking pictures look here http://www.theoldone.com/articles/damaged%2Dblower/. This is an old example and not representative of the current generation of Eaton’s products.

For some pictures and one manufacturers propaganda you can see the twin screw here http://www.whipplesuperchargers.com/....asp?PageID=65. A Google search will reveal more.

 

And they're related. The roots is known as a posative displacement air pump. Fancy language to say it moves air, but doesn't compress it.

The twin screw compresses as it pumps. this leads to greater effeciencies, but also requires closer tolerance machining.

So the twin-screws are more expensive to make. They also create heat by compressing the charge all the time, even at low engine loads.

It's extra credit for those that want to thing about what this means in day to day driving....

Matt

 

Ooohh, me! me! . Means more power down low but also higher wear and tear because of higher IAT. Right?

 

higher IATs out of the SC at lower revs, and when the bypass valve is open, and there's no boost. Since the motor isn't under laod, detonation won't be a problem, but one has to watch the charge temp.

Matt

 

Without disagreeing with any of the Dr's statements above, I think the boost pressure reaches steady state less due to leakage (3.1 and 3.2) than air compressibility, which is implied but not stated in 3.3. The compressibility of air is what allows the cylinders to be filled with a greater quantity of air molecules under boost vs atmospheric pressure. For example, if the working fluid here were water rather than air, increasing the pressure would change the number of molecules in the cylinder a miniscule amount, since water is nearly incompressible.

Since the roots SC simply moves air without compressing it, it seems as if the thermal efficiency should drop considerably as the pressure on the downstream side increases. Anyone with info on this? If so, it seems that the best way to increase SC efficiency would be to improve the flow thru the valves & head & exhaust to lower the boost pressure and thus the improve thermal efficiency.

 

what really helps the output temp of the SC is to feed it with greater than atmospheric pressure...like the twin charger rigs do. very low IAT's with 20+psi boost, as they have found

 

The fact is that the Roots design gets much worse as a function of higher boost and RPM. http://automotive.eaton.com/product/...argers/M45.asp
This shows the behaviour of the M45 vs RPM for temp, drive power etc.

And for the relative contributions to steady state boost levels, I've read (but haven't measured) that rotor-case leakage is a bit less than 5%, reversion is a bit less than 10%, and the rest would be flowing into the head. Since I live a science life, I guess I forget that most people don't think of the ideal gas law any time pressures of gasses are discussed, but I guess I should keep this in mind, as most discussions are about boost (pressure) and not molecular density (absolute pressure divided by absolute temp), which tells you how many molecules are available to burn.

So, the "conventional wisdom" about heads not mattering with boosted motors is just wrong. Anything that gets more air into the combustion chamber has the potential to create more power. Head work definantly falls into this category.

jlms point is right on, if you want the best bang for the buck, run each item at it's most efficeint point. And for the Roots blowers, that isn't at it's redline or at very high pressure deltas.

For those interested in pros vs cons of different SCs, here's a very short description....
http://www.automotivearticles.com/12...Choices_.shtml

If you want to see what a twin-screw has to offer, check this out....
http://www.kennebell.net/techinfo/ge...REWvsROOTS.pdf

Matt