Quote:
If we say the supercharger makes 7PSI boost at 7k RPM, you will have less than 1.5PSI of boost until the turbos are pushing out all 14.5PSI or whatever they provide. So 99.9999% of the time, the supercharger would actually cost you horsepower due to parasitic drag. You'd see a benefit from idle to 1500rpm in first gear.
Now the follow up argument is that the supercharger will increase throttle response and to a point it will. But with MDM enabled, the N54 uses the wastegate to keep the turbos spooled up for quick response.
Unless you plan on increasing the turbo size and introducing more lag into the system (and can't utilize the MDM wastegate tuning), the s/c isn't going to pay off for the added complexity. And the same thing applies, once the turbos are spooled the charger provides little benefit.
First off the supercharger makes whatever boost it's displacement and rpm will allow so if it's 7 psi at 1,000 rpm it will be 7 psi. at 8,000 rpm...
It does not rob HP when compounded since the presure out put from the turbo offsets the parasitic losses and helps to spin the blower... There is no free ride but if you want instant throttle responce and zero turbo lag this is the only way to go....
There is no 1.8ltr gasoline engine making 420 ft tq at 3,800 rpm that I know of on 91 octane.
You can not get the power from small turbos alone, if you want big power you need a larger turbine housing to rid the exhaust gas pressure and heat and with that you get lag.... Unless you keep your foot planted you will always have lag in the real world with a big turbo setup alone...
It is the superchargers instant pressure and the exhaust heat and pressure that will spool the larger turbo....
My car at 70 mph cruises at 3,000 rpm if I touch the throttle I get an instant 16 psi.of boost by the time it hits 3,700 rpm I have 35 psi. I have never been in any car with this kind of responce..
Remember it's only 1.8 ltr and pulls like a freight train al the way to it's 10,000 rpm redline in any gear....
Compound charging works and it works better than any turbo alone setup...
Oh yeah my charge temps are never more than 10*f above ambient at 35 psi. due to my chargecooling setup... Here is a 27 psi.pull on 91 octane