rpm - psi mapping

[boostm3]

You guys running megaboost on your GNs.....What rpm level do you usually hit at, say, 20 psi?

On my M3, for instance, on a WOT run, 5 psi usually occurs somewhere around 5000 - 5500 rpms; and 6 psi is about 6000 rpms. Since, unlike you guys, I have a Centrifugal Vortech supercharger, my boost levels skyrocket above that...As you can see, Im making 6 psi at 6000 rpms, and my redline is 7000 rpms, and I make 11 psi at redline, which means Im going from 6 psi at 6000 rpms to 11 psi at 7000 rpms.

 

[BoostKillsStres]

full boost before 3000 depending on wether or not we're leaving on boost or off idle. Thats why the cars are so deadly out of the hole and start frying the tires halfway across the intersection

 

[boostm3]

full boost before 3000

Wow...NO wonder you guys can spray so much so early! Your torque curves probably peak sharply around 3000 rpms, and then slowly table downward. That should allow you to spray a large amount as earlyl as 3K without bogging..If I did that, Id gurgle my way to a quick stall, almost. Youre at full boost, or like over 20 psi between 3 and 4K probably, whereas Im only making about 3 psi there. For me to get good effect I have to delay spraying til about 5psi, which is near 5000 rpms. That only allows me a 2000 rpm band over which to enjoy the cooling effect of the spray. And I dont even hit 5 psi unless Im on the floor, so part throttle running never even sees the water/alky. I bet you guys regularly are using your water/alky at part throttle, right? Which is why my tankfuls of fluid last sooo long.

I know that I could be effectively using more fluid at an earlier point if I graduated to the 2C system (aquamist) from my current 1s. The 2c kit plugs into the fuel injector wiring, so that you spray the fluid amounts according to the injector pulse. This allows you to spray a little down low, and max up high, which is ideal for a centrifugal SC like mine. Only thing is I like the simplicity of the 1S kit. I find that you need to be testing and monitoring the system quite a bit, and the last thing I want to do is increase the complexity. Since I never have an EGT problem, ie, EGTs rarely exceed 1300 degrees F, and only even see 1300 when above 6000 rpms, I guess I really dont need to start spraying much below my current 5000 rpms which translates to approx. 5 psi.

Which just goes to show that water/alky injection can benefit a vast number of applications, but often in a very different way.

 

[Chuck Leeper]

Linear boost??

Sounds to me as tho the system has a problem in that the boost on a belt system should be fairly linear and this 1 definately is not.. to rev to 5000 to get 5psi, then go 1000 more to gain only 1 additional psi, then see a near doubling of boost,[6 to11] in the next 1000 rpm, does not seem correct.
I'd look at the belt drive system and see where the belt may be slipping, etc..
Having said that, I assume you are not running external boost controls, but controlling w/ pulley sizes??

Exhaust sytem problems?? Low flow at hi revs?? Exh back pressure hi??

 

[YGETV8]

Also, no two turbos will spool the exact same on two different cars. Timing, fuel mixtures, exhaust leaks, humidity, etc. can and will vary the spoolup greatly from car to car. It would be difficult to "map" psi rise vs. RPM. Your belt drive, if operating corectly, should be much more linear than ours. And, as Chuck stated, our boost is usually all in at very low RPMs, that is why we get killer torque numbers!

 

[boostm3]

Sounds to me as tho the system has a problem in that the boost on a belt system should be fairly linear and this 1 definately is not

No, this is absolutely not true...Its anything BUT linear on a centrifugal blower...Typically, at the halfway boost point, where youre rpms double to redline, the boost will be cubed! ie, at 3500 rpms, I'll be making like 2.2 psi, which at redline, will be 2.2*2.2*2.2 or near 11 psi. This is wnat a centrifugal supercharger is all about, and is why PD blowers absolutely kill them off the line. PD blowers, and many turbos, will make their boost down low to mid...But CF blowers always make their max boost at redline, which is why some guys prefer them on the track, where you want to really wind it out...Because of its boost curve, many guys say it drives more like an NA engine. But, its anything but linnear, except in the sense that the higher the rpms, the higher the boost, on a WOT run.

Maybe youre thinking of a Positive Displacement blower...Thats why I said in my post Im using a Centrifugal blower; ie, the Vortech or Paxton variety, not the Roots type.