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BSFC of 308QV?

Discussion in 'Technical Q&A' started by zff, Jan 6, 2004.

  1. zff

    zff Karting

    Nov 1, 2003
    145
    Hawaii
    Full Name:
    Ken
    I've been doing some research into aftermarket EFI, and there's a lot of talk about Brake Specific Fuel Consumption. I was wondering if anyone had an idea of what the BSFC value of a stock 308QV was and how much one can hope to improve that number.

    Thanks
    Ken
     
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  3. ricrain

    ricrain Karting

    Nov 1, 2003
    195
    Dallas Area
    Full Name:
    Ric
    This is all from memory, but here goes...

    BSFC is about 0.45 on most modern normally aspirated engines. It is a measure of overall efficiency for the power produced. BSFC is the amount of fuel used divided by the HP.

    What you really want to know is "How big should my injectors be?".

    Long story short: HP * BSFC / Cylinders = lbs/hr per injector.

    Example: 255 HP * .45 / 8 = 14.3 lbs/hr.

    BUT, you need to figure an 80% duty cycle on the injectors, so take 14.3 / .8 = 17.9 lb/hr.

    ...and you end up with a normally aspirated requirement of about 18 lbs/hr per cylinder on pump gas. 19 lbs/hr is a fairly common injector (mid 90's 5.0L Detroit motors), and you won't hurt anything by going a little large. If you go too large (>25 or so), you might not get a good idle. Choose a high impedence (12 ohm) injector for most EFI systems.

    FWIW, I got a good solid 900 RPM idle on my turbocharged 308 with 26 lb/hr injectors, with enough room to safely flow 375 HP. If you aren't going to breath on the motor, then go with 19's or 21's.
     
  4. mk e

    mk e F1 World Champ

    Oct 31, 2003
    11,538
    The twilight zone
    Full Name:
    The Butcher
    Yeh, what rick said....although to pull 375 hp from 26 lb injectors must have require pretty high fuel pressure, non-linear rising rate regulator maybe?? I was running about 360 hp on 36 lb injectors with a linear regulator.

    I don't know what the stock BSFC is. I know my QV got about the same milage before and after conversion, but I added a blower too so...I would guess the earlier cars without feedback in the FI use more and the carb cars more yet, probably closer to .47 or .48
     
  5. ricrain

    ricrain Karting

    Nov 1, 2003
    195
    Dallas Area
    Full Name:
    Ric
    Yep, I had one of Corky Bell's rising pressure regulators. At peak boost, it was set to go up to around 70 PSI. I never ran the car at full boost though, only 8 PSI.
     

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