s10_xtreme

iTrader: (6)

Okay, I was really board so hear ya go, my thought.

Just a guess but the reason you were able to get better fuel economy from those two modifications could be due to a lower IAT. Having a lower IAT allows your engine to advance the spark without inducing detonation. This nets you a higher cylinder pressure with the same amount of fuel (meaning a higher efficiency). You get more heat out of the fuel pushing down on the piston rather than coming out the tailpipe.

Even if the ram air provides a pressure increase in the intake it your MAP would remain the same, your Throttle blade would just be closed a little more to compensate. To cruse at a set speed you vehicle has a certain torque demand. This is directly related to manifold pressure. Say you need 30kPa to maintain a set speed. It doesn’t matter if you have a 2” bent pipe of an intake, a super ram air capable of 20,000CFM of airflow, or a leafblower. You still need 30 kPa after the throttle to maintain speed. If you have any more you will be accelerating seeing as how you are providing more torque than what is required to keep the system in equilibrium. The Throttle is what will regulate the pressure in your manifold, if you replace your 76mm TB with a 90MM one it won’t give you any fuel economy benefits, you just won’t have to open it as far to get the same result.

As far as airflow is concerned, it’s a beautiful thing for power, but your enemy (for engines that need to run stoic that is) for fuel economy. All the air that enters your engine needs fuel to be added to prevent running lean. Simply put more airflow means more fuel flow. Thus a throttle body to regulate the amount of air into your engine.

Diesels are the exception here. The more air flow you throw at them the more efficient they will be. This is because (last time I checked, I know the duramaxes have a throttle body now but I think it is emissions related) diesels are fuel regulated not air regulated like gas engines. By allowing more airflow into a diesel you lower the pumping losses of engine, gaining you efficiency (I'm not sure by how much) it's a very similar concept to cylinder deactivation on the gen IV smallblocks.

Of all the stock intakes (on N/A motors) I have seen, none have produced more than 1/2 a psi of vacuum with a clean airfilter. Granted that’s a 3% drop, still, stock intakes aren't as bad as people make them out to be.

I have seen an airfilter so dirty it actually got sucked in, breaking the seal around the edge of the filter element. After replacing it there was less than a 1psi increase (I think it was 4 kpa but I'm not sure) in MAP at high RPM WOT. And no the clogged filter did not affect part throttle operation of the engine AT ALL, the only effect was lowered crankcase pressure and a little loss of power at the top end.



p.s. “let it run wide open just idling” think about that statement, then explain how it is possible/impossible.

Bullitt347

p.s. “let it run wide open just idling” think about that statement, then explain how it is possible/impossible.[/QUOTE]

Easy: Diesels do it all the time!

engineermike

Yes! And, unlike gasoline engines, Diesels will actually gain mpg's when you improve the air intake!

s10_xtreme

iTrader: (6)

read FULL post, theeeeen comment

richard head

iTrader: (2)

it seems like pulling a significantly larger amount of air would lean out the combustion to one degree or another, and in an application such as mine (SD) the computer is only able to compensate using the short term o2 readings which are narrowband and not particularly accurate anywhere except stoich. So, I get a leaner acceleration mix and it does in fact benefit me to have ram air and a good, clean filter. Cruising, right around stoich, the sensors keep the mix at the same level so it uses the same amt of gas. There are certainly circumstances (such as PE) where having an available supply of airflow absolutely helps improve gas mileage and there are circumstances (cruise) where my car which is a stalled automatic always gets about the same 24.2 mpg on the highway. It got 24.2 stock, it got 24.2 with airlid and tb bypass, it got 24.2 with the cutout open and it got 24.2 after the stall. go fig.

engineermike

Some people apparently have no idea what a "throttle valve" does and how it works.

Green69firebird

Been lurking around Ls1tech for awhile now, so I thought I'd finally say something.

While I completely agree that the obstructions in front of the TB have no effect on engine efficiency, I have to bring up their effect on the driver. Could it be that in the "real world tests" the driver is using less power during acceleration because they perceive it to be the same or faster? How about changing gears earlier with an manual? Most people that I've known tend to drive loud cars slow and quiet cars fast.

*edit most CAIs that I've seen have made the vehicle a bit louder.