[Isaac Zachary]

Originally Posted by ps2fixer

Of my understanding it's to reduce pumping losses to achieve higher max air flows.

Bingo!

Reducing intake pumping losses are to improve MAX air flow. Unless you're at max throttle then it doesn't matter what the restriction is.

You can increase efficiency if you reduce pumping losses in the:

• Exhaust system
• Oil system
• Coolant system
• and Intake system

But three of those don't have much of an effect on immediate power output whereas the last one does.

Imagine if your throttle were controlled directly by the engine's own oil pressure or coolant flow. Maybe you have some sort of electric oil pump or water pump that you control its speed. You couldn't just turn down the pump to reduce pumping losses without affecting your throttle if cars were built like this.

The easiest way to reduce intake pumping losses is to floor it. That or remove the throttle valve all together.

Clogged or restrictive air cleaners don't have much of an effect on fuel economy except in two situations.

1. On older engines with carburetors since a clogged air filter can cause the engine to run richer.
2. On any engine that the air cleaner is so clogged you have to make the engine run at full throttle causing high load enrichment.

But just having a restrictive or clogged air cleaner in itself doesn't hurt fuel mileage as the throttle simple is opened slightly more to compensate.

The total air restriction has to remain the same to maintain a constant speed on a flat grade, and that's the sum of the air filter, the throttle and rest of the intake design.

• If you make it flow better but cruise at a constant speed the throttle just closes a bit more making the restriction the exact same again.
• If you make the intake manifold or air filter more restrictive the throttle just opens a bit more making the total restriction the exact same.

Intake pumping losses are not fixed with changes to the intake design unless we're talking about trying to get more power at full throttle, or a diesel engine. The biggest restriction is the throttle. If you can't keep the throttle wide open or remove it then there's no benefit from a less restrictive intake.

Put it this way, most of the time the only true restriction is the throttle. It's like having three or four good eco drivers in the car and one terrible driver. It doesn't matter how good the eco drivers are if you put the terrible driver in the driver's seat. You have to get him out of the driver's seat and put a good driver there if you want better fuel mileage.

The same with the throttle. As long as it's creating "the restriction" there's no point in opening everything else up. First design a car without a throttle and then we can discuss reducing intake pumping losses.

The only real way of reducing pumping losses in the intake is to design the engine to run with a throttle that's more open. Smaller engine, higher gearing and EGR all accomplish that. Those techniques make the throttle tend to stay more open. More open throttle means you're lowering "the restriction."