Quote:
Originally Posted by NorCalRider
I find it hilarious when people ask about fuel mileage on a turbo/sc kit. The mileage is dictated by you right foot. If you stay out of boost it will be as good as stock and in some cases better then stock. The minute you go in to boost you will be using more fuel. Forced induction forces more air into your engine and requires more fuel to complete the burn process to create more power. Mileage is all up to you as a driver.
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Continuing the off-topic discussion. Consider the average 86 buyer. They want power (jdm powah if possible), but don't want to get 20 mpg during highway cruising.
If the AFR is proper (on and off WOT), and the system uses DI effectively (major assumptions)... a "big turbo" kit won't be capable of running into boost if you drive like a grandma (< 3000-3500 rpm). Generally, you'll see a slight improvement in fuel economy. I'd guess this is because the slight spin of the turbo relieves pumping losses and air temperatures are higher.
When you hit the rev range (really it's an exhaust flow rate) that boost is available, you effectively turn on an extra row of cylinders. You don't necessarily have to use the available torque, but it's there.
A "small turbo" kit is the same... but you add on less cylinders at lower engine speed (exhaust flow rate). If you're cruising down the highway, it's pretty likely that you're atleast at half of your max boost pressure. This means you've got more available torque and the potential for worse fuel economy.
Fuel economy is really about air flow and AFR. If you keep RPMs and LOAD low, air flow is low. If you're tune is in an efficient zone (and closed-loop mode is operational), AFR will stay high.
Can any of the gurus classify these kits as "big" or "small" for us? FBMv2 is fairly big, AVO is fairly small, right?