Fuel system sizing

So, I’ve finally got a break since starting work at 06:30, so I thought I’d jot down the fuel system sizing I need. I have taken lots of sizing information from this zetecinside.com article and injector specifications and ratings from witchhunter (weird name).

I have 4 injectors (Weber IW-31) and desire 215bhp minimum with an option to size up to 250bhp later when I supercharge it (ahem). According to the Weber website, I need to flow 269 cc/min and my IW-31s are rated at 274 cc/min. This isn’t good, because it implies a 98% duty cycle. As such, my injectors will be flowing nearly full flow (and therefor full duration) whereas most people aim for a 80% duty cycle. This is a bummer because it means (potentially) 4 new injectors at £80 each. I will need to sell mine on though which will offset the cost.

Next I need a fuel pump. Now I know I’m flowing 1076cc at full chat, I need a fuel pump (internal) that can deliver the goods. The Walbro GSS 342 can flow 255 litres per hour, which translates to 4250 cc/minute. It seems adequately over spec for my needs.

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