facboy

hi all,

anyone know what the 951 BSFC is? i been playing around with the RC Engineering injector calculator http://www.rceng.com/technical.htm#WORKSHEET.

According to Danno (https://rennlist.com/forums/showthre...6&page=2&pp=18) the stock injectors are 34.6lb/hr @ 3bar. i've seen the number 36lb/hr around as well.

anecdotal evidence suggests that the stock injectors @ 3bar on a stock turbo-S car will max out between 270 and 300rwhp (depending on who you ask). Being pessimistic, let's assume 270rwhp and 12% drive-train loss. this gives us 306hp at the flywheel.

let's continue to be pessimistic and assume the injectors have their max flow at 95% duty cycle. we'll also be pessimistic and go with the 36lb/hr rating for the injectors.

if you plug these numbers into the calculator you'll find that the BSFC is around 0.44.

plug a BSFC of 0.44 back with stock S specs (247hp, 2.5bar = 36psi) and you get around an 83% duty cycle which doesn't sound unreasonable. assuming the regular non-S has the same BSFC (217hp), the duty cycle is 73% which also seems ok.

so, it seems the 951 BSFC is in the 0.44 range if the car is in good condition. this number could be lower (or higher) if you assume

• 270rwhp is a bit low (or high) for maxed-out injectors on a stock S.
• 12% drive train loss is a bit low (or high) to convert to flywheel hp.
• 95% duty cycle is a bit high (or low) for the injectors to hit their maximum possible flow
• 36lb/hr is a bit high (or low) for the stock injector rating.

this is just a 'napkin' (world of theorycraft for you geeks) calculation. thoughts?

EDIT: mucked up the fuel pressure values.

Rob

The only thing I would say is I think you made an error by adding in the boost pressure to your fuel pressure. While the FPR adds fuel pressure at a 1:1 ratio with boost, this is to maintain the same differential pressure between the fuel line and the intake. In other words, the fuel pressure increase doesn't add more fuel for a given duty cycle it maintains the fuel flow into a pressurized intake.

333pg333

Well, if nothing else, it's good to see two guys from Melbourne getting together at least? Just different countries IIRC.

anders44

yes, math has some errors as rob points out.

has anyone got stock injector size for turbo and turbo S, and duty cycle in their head? if so I could do some math as well, but it's likely that this has been by someone before.

I ordered and payed for my new 95lb delphi injectors yesterday

facboy

oic. that makes the BSFC even lower...i wasn't sure about that part of it. i'll edit it.