MotoMan_YZ400

Hey I have a few questions. I was studying the mini cooper site, can saw some specs for the standard and S models. The bore and stroke are VERY close to ours, just proportionally bigger in each to make it a 1.6L. BUT the only diff between the 115HP (wow thats close to ours) to the S with 168HP (could be fun in our cars) is the diff in compression ratio. I know the standard mini and the xb have close to the same CR, but the S is running 8.5:1 to be more happy on boost.

Now heres my question. If one could lower the xb's comp ratio to close to 8.5, could they run say 6? 8? 10? PSI reliebly? Or is all forged parts needed? If thats not the limitation, what is? what will break first on boost?

Now please, if you really dont know what your talking about, please dont pollute this thread with false info. I'm looking for someone with a good background on turbos. Thanks


David

UV7

ZPI has created an xB running more than 180hp without leaving internals on the concrete. Based on some of their prior posts, it appears that the drivetrain becomes the weakest link at 200+.

Simplyscion

I ran 6-13 psi on stock internals...its all in the fuel delivery and tune. I ran it everyday on 6 psi and that was fine for daily driving. If you plan to run big boost then yea, forged lower compression pistons would be a good idea

JSosa

lowering compression ratio is key in a forced induction automobile. The less compression the more boost you could push into the cylinder. Its all about space inside the cylinder. When you have high compression and air being fored into the cylinder at the same time thats when you break engine components. Unless you figure out some way around it with proper tuning and alot of knowledge.

TuningIsLife

You have to figure, when you figure out compression + boost, you are accually increasing the compression ratio. So a 10:1 + 6 PSI is accually like 16:1 compression. So if you lower the compression of the pistons, increase block to head gap to cause a bigger area for the stroke, you can increase the boost potential. A lot of STR4 Guys run 18lbs on a stock motor.

Prototype_xB

Alot of Stage III mopar srt4 guys are running 22+lbs on stock motors and with a larger turbo.

lastlookcustoms

Thats because those motors were built to handle the boost from the factory... Just like the 2JZ turbo motor that I am running 28psi through...


As for the xB motor, I along with Simplyscion were a couple of the first people to boost these cars. With some extra fuel and a good tune you can safely run boost into these motors. I ran my kit for about 6 months peaking 14psi at times. Wow, what a surprise, that same motor is still in my car and still running...Now boosted by a supercharger. ANyways, these motors can safely be boosted. You just need half a brain when you do it. Just dont slap a kit on it and not do any fuel or tuning...

Simplyscion

Hey Stu, I dont know if you heard or not but the guy who bought my box blew the thing up 6 months after he bought it from me
Best thing was it was while he was doing a 3 gear standstill burnout...or so he says? I was never able to get my box to do a 3 gear burnout lol.....it was an auto for christ sakes...he fried the piston rings, lost a lot of compression, drained the oil and overfilled it with an extra qt then brought it up to the Ford dealer, cleared the codes in the parking lot and traded it in for an 06 Mustange GT