I am still trying to iron out what size turbo to buy and I am looking at compressor maps. So my question is about calculating lbs/min for my motor. What modifications can I make to increase lbs/min for a given pressure ratio? Which value changes in the equation (does porting change the 2.6L value? or the VE value? etc.) I have a BR built 13b with their mild street port. I was hoping for 58lbs/min at a 2.2 pressure ratio to hopefully land somewhere around 400whp. The SXE362 doesnt plot that using 7500rpm 2.6L and 90% VE. I feel like I'm missing something?

 

porting will change the VE. pretty much everything affects the VE (intake, exhaust, turbo), displacement stays the same.

 

How do we know what to change the VE value to based on changes in porting/intake manifold/exhaust?

 

what are you using to do these calculations...

 

I'm just using the recommended stuff from the compressor map illiterate sticky post and another thread that said the 13b flows about 30-40lbs/min depending on porting. So 2.6x7500x2.2x90/5660. I am no expert and am enjoying learning from some of the big honkin brains on here. I admittedly have a lot of questions.

 

You seem to be on the right track, although I think you may be neglecting the pressure drop in the plumbing.

I'm pressed for time right now so I can't type a more comprehensive response: the short story is that 56 to 58 lbs/min at around 2.6PR (or better) is achievable; the exact PR will depend on losses present in the system including, but not limited to, the IC, plumbing and, of course, VE (which encompasses porting and EMAP, among other things).

Anything you do to increase density (i.e., lower temp, higher pressure) will increase lbs/min vs cfm. Dry air at sea level weighs about 0.076lb per cu ft at 68 deg F (20 deg C.) Therefore, 58# at 68 deg F equals ~763cfm.

Common reference temps for compressor maps are 15 deg C., 20 deg C., and 85 deg F; so corrections for mass flow and mass vs volume (CFM) may need to be made when comparing maps or conditions. Mass is also commonly measured as kg/sec and volume often seen as M^3/sec, so be sure to check the conditions carefully. (You may see both of the latter scales as the X axis on some maps--be very careful about this as the numerical values are so close they are often confused and they have very different meaning.)

 

Thank you sir! That makes perfect sense. I had planned on making a ducted SMIC out of the 2.5in core from cxracing(another person used this in their build thread and it seemed to work well) and I am going to get a vented hood. Hopefully this will bring those intake temps down a bit. I really do not want to use a water/meth injection system if I can help it, but maybe it is something to reconsider with the cooling it provides? I am starting to want to make a 2.2 pressure ratio as dense as possible on sx/sxe362 and if that nets me 350-375 then so be it, because I really like those turbos based on their maps. Not to mention an rx7 with that power is pretty stinking fast for a sunday afternoon car.