LaserMark4 said:
So I think I've come full circle back to either ESS or VF Engineering-- and installing at the factory is a huge plus is I can get the car in that vicinity.
I once made a post on e46fanatics regarding someone who wanted to build his own supercharger on his m54b30 (so e46 330i) based on the eaton m45/62/90 series where I gave him an example of calculations on various compressormaps where he would end up in terms of range.
Mind you, these are coarse calculations as there has been no temperature change taken into account (even intercooling doesnt get your temps back to room temperature), so the exact place of the points I dotted is different from where I put them.
But taking temperature into account gets very difficult.
This is that topic (and my conclusion was that he should definately take the m90 for a 3L engine).
https://forum.e46fanatics.com/showthread.php?t=1192081
In that topic I also plotted my twinscrew compressor with the amount of boost ESS gave it for the TS2+ pulley, which is quite a good match but if I want to fit an even smaller pulley, my compressor can easily take that and will become even a little bit more efficient (I now work at 8,5psi but 10 would be very interesting provided it wont detonate...
The meaning of the dots is where the pressure and air intake is in the efficiency graph at maximum rpm and maximum boost, so where you have the maximum power usually (generally speaking).
For a twinscrew you can draw a horizontal line from that point to the left and that describes how efficient the compressor works throughout the revrange (because a twinscrew is a volumetric compressor and that always gives the same amount of boost from ~1000rpm)
For a centrifugal compressor its way more difficult, as the boost gradually builds up. So that is a somewhat upsweeping line in a curve from 0 to that point.
Now, I did those same calculations for the c38-81, where I gave 2 dots: the red one is the same red dots as the ones in the e46fanatics topic (so based on 5psi boost and 6500rpm redline) and the green one is based on the Active Autowerke specs, so 7k redline (watch out, this is pretty high for an engine with hydraulic valve adjusters), and 8psi boost.
You can immediately see that the c38-81 is a very potent compressor (that is not necessarily a good thing!)
For example its way to big for a 3L engine that revs to 6500rpm and has 5psi for boost.
For 8psi and 7000k rpm its a whole lot better. So its not a complete mismatch that AA did (ok they wouldnt do that as they've been making supercharger sets for over 2 decades now....
But I cant say that if it would be better than a vortech 3sci, or even if its better than a rotrex c38-71 or c38-61.
Maybe for top horsepower its the best rotrex, but for mid power range a smaller one might be better. Lots of tuners choose the top power one because that gives the highest horsepower range and that sells the best.
The reason I say this is that the c38-81 has been used in a lot of m3 setups. but that engine is bigger (0.2L) and revs higher (8,5k versus 7k for the AA tune) so that needs more air. In the past for the m54b30 engine a smaller size (C30-94) has been used and thats the size rotrex themselves are referring to (but for all I know that one might be on the small side, I havent looked at the data or done calculations)
But for example Gpower (a geman supercharger tuner) has in a lot of their kits the tendency to focus more on midrange power. Might be down on top power but gives a different (more aggressive) feel to the engine/car.
I suspect that the high horsepower Gpower sets might not be available anymore for the m54b30 engine. When I informed 8 years ago they had them, but back then they only had factory install and that made the kit expensive. I only wanted diy install, as that is what I do for a hobby.
Even though the info above gives some pointers, it doesnt contain all info. For instance how much rpm the pully from the compressor has to turn can also be a decision factor, if that has to be really high, you need a very small pulley. A small pulley has very little grab on the belt and can only relay very little power. If the compressor needs more power than that, you get belt slip. That means loss in power, more belt wear etc. But I guess that's not a real issue on these kits, looking at stock pulley sizes rotrex suggests.
A Twinscrew is not necessarily the best supercharger. If you only need top power, a centrifugal supercharger is more efficient, so on a drag strip that will be faster depending on how close your gear ratio's are.
However a twinscrew gives boost all the time, so at 1500rpm it already pulls much harder than the stock engine whereas the centrifugal supercharger will drive the same as the stock engine (depending on the choice of supercharger, a centrifugal one will start to build up real boost at 3-4,5krpm and will continue to increase till redline)
Another advantage of a centrifugal supercharger is that because its more efficient and only builds up boost in the high range (so you dont have boost all the time) it also generates less heat (the air leaving the supercharger is of lower temperature with the same boost,
if the size of the supercharger is well matched to the engine size/needs.
That means that if you want to build a cheap supercharger set you can get away with no intercooling on low boost setups (5psi etc).
With a twinscrew (and certainly a roots, that has a way lower efficiency than twinscrew) I would never recommend that. Always use some sort of intercooling with those type of superchargers.
With my setup I'm very pleased although my car is loud (headers) and the tuning runs a bit rich (you smell that, but thats better for preserving the valve seats). As for tuning, on my first setup (no camshafts) it had the strange tendency to get into emergency mode on high altitude (above 1500m). With camshafts, headers and specific tune for that that was gone. Now it only sometimes pulls the timing every other second in specific situations (which you feel in acceleration and total power) and sometimes not.
That is something I hope to solve with an aftermarket ECu and custom tuning.
The e46 ESS tuning doesnt have that problem (There are people that convert their z4 specifically to e46 ECU and wiring loom etc to solve this). So this also shows that a well renound tuner, who can perfectly tune e46'es (both 330i and also m3's they had a car that held the nordschleife record for years) also has problems tuning a Z4. And one of the tuners in norway even drove a z4 himself with TS2 setup.
So that shows that tuning, once you get into the higher HP's with the stock ecu gets really really difficult to get 'factory driving smoothness'
