Quote:
Originally Posted by Bee Pee
It says a lot about stock turbo B58 v N55 when Mx40i autos with decat DP and OTS p/back map are hitting high 7's to low 8's on pump fuel and low 7's with decat & Jb4 on pump fuel and WMI !!!!
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N55 PS2 PWG on WMI and pump gas (no need for ethanol) does 7s flat 100-200 all day, can do sub 7s on good condition. Keep in mind given same car my numbers seem to be 0.5s more conservative than British numbers.
Speaking of B58, compared to N55 EWG, it has a bigger turbo from factory - 10% bigger compressor and 6% bigger turbine, according to BMW. N55 PS2 is definitely more than 10%/6% bigger.
Below I also have attached a picture of B58 turbine housing (4.5" outlet). The blade pitch seems just as conservative as N55 stock.
I tend to believe all N55 STG2 turbo (PS2,GP500,TTE460) flows better than B58 stock turbo and thus will make more power, everything else being equal.
What's more is that B58 has a higher compression ratio, which is much more octane sensitive under high boost. Alongside with its very incapable W2A IC, B58 is in desperate need for WMI, albeit its freer flow turbofold (than N55) greatly helps ignition timing.
That being said, I have no doubt B58 on hybrid turbo has 600+whp potential, with enough octane from WMI+ethanol+race gas.
In BMW's way, S58 should have a bigger W2A IC, twin turbo with a freer flow turbofold and, as I suspect, a lower compression ratio to allow for higher boost on pump gas.
The same thing also happen with Merc's M177/M178 twin turbo V8. When they use bigger turbo and increase boost for higher-end variants, they lower compression ratio.