If your street trim means 93 octane and no alcohol/water injection then you will need 50's at least and maybe a little bigger. That's how I run and I was way out of injector at 12.58/107 with red-stripes (base fp was 60+ psi), with poor 2.0 60's. Traction and a converter would have gotten me to low 12's, but if you compensate for the fp I needed 46-48 lb/hr injectors already. I went up from a TE34 to a PTE54 turbo, and 72's, and have run lots of 12.30's at 109-110 and a best of 12.18 at 110.5 with a 1.8 60' on a cool evening (at 4020+ lbs total
). Yes, the 72's are overkill for me - I'm only running about 80% duty cycle at 36 psi base fp but I wanted to play with making chips
. The injector sizing charts, like the nice table that Joe Lubrant put together at gnttype.org, assume a bsfc of 0.5 which basically means lots of timing and lots of octane. For 93 octane and 18-20 degrees of advance a bsfc of 0.6 or even 0.65 is more realistic and will keep you from leaning out or buying injectors twice.
People like the 50's because they are well behaved and easy to make chips for, they are the biggest high impedance injectors that are available, and they are big enough in race gas/race chip trim to get you to low 11's/high 10's which is where most people stop trying to go faster on a stock block
. They are made by Delphi and sold by msd and everyone else. If you add the $100-150 cost of modifying the ecm to the price of larger, low impedance injectors like the 55's or 72's, the total is not much different.
Pick an et target and a total racing weight with fuel and you in the car, and use the formula rwhp=197*weight/(et*et*et) to get an average rear wheel horsepower requirement. For example, 12.18 at 4020 lbs requires 438 rwhp. Now inflate this with whatever fudge factor you like to compensate for the "hp loss" of the automatic trans, say 20% or 438/0.8=548 flywheel hp. With a bsfc of 0.65 lb/hp-hr this means 548 hp * 0.65 lb/hp-hr = 356 lb/hr total, divided by 6 injectors = 59.4 lb/hr at 100% duty cycle. If the bsfc is 0.5 you only need 46 lb/hr injectors at 100% dc - see why I say you need at least 50's with pump gas? And, of course, you want some headroom so plan for a max of 85-90% duty cycle so that 59.4 becomes 66-70 and that 46 becomes 51-54 lb/hr. See
http://www.turbobuick.com/forums/showthread.php?s=&threadid=19799 for more discussion on this, including the feeling by Joe that the extra 20% from trans losses doesn't really need to be included.
