It could only hurt mileage, here's why:

the ECU keeps a precise stoichiometric ratio of fuel and air, now the K&N filter, if anything, is less restrictive than the stock filter, therefore more air comes through, and as a result, the ECU adds more fuel to keep this ratio correct.

Make sense?

 

lol more air doesn't magically come in, the engine (being NA) only draws in what it can via vacuum.

Reducing restriction increases overall efficiency. This is why manufacturers don't use 1" intake/exhaust tubes on a 4L engine. By what you're saying that would dramatically reduce the amount of fuel used. In reality it would just be horrifyingly inefficient (if it worked at all.).


If you have some numbers to back up what you're claiming though, and not just anecdotal advice, I would like to see it.

 

the amount it will draw in via the natural vacuum is limited by the restrictiveness of the air filter/intake design in the case of the LS400 and most vehicles


No, it doesn't, and I am disappointed to see you of all people fall into this mode of thinking.

An engine design is a balance between the holy trio of power, fuel efficiency and emissions. - If fuel efficiency was the only consideration, they would use a smaller, more restrictive intake.

Not saying that a less restrictive design wouldn't possibly yield more power, but it comes at an unacceptable cost in fuel efficiency and emissions.

Toyota spent nearly 1 BILLION dollars on the design of LS400, and part of that went into finding the optimal air intake design, shape, size and filter restrictiveness - you, me, or some little Mickey Mouse company like K&N et al, is not going to out-engineer Toyota/Denso/Aisin

the are very few true improvements that can be made in the original design engineering of the LS400, via aftermarket products, even after all of these years - oil and tires are the primary two things you can truly improve from what came on the car, without massive redesign such as dropping in the LS460 powertrain, etc.

 

they spent ~$1 billion to create a compromise of efficiency, power, and emissions using technology from the early 1980s.

There is always room for improvement.


I'm still waiting on numbers or actual evidence, yet all I'm seeing are more anecdotes.

 

I think if anything, headers have shown pretty significant increase in exhaust flow. They claim 20 HP. I would not be be surprised if it was close to that or more. The LS400 and 430 exhaust manifolds are not particularly free-flowing.

I'm not comparing my old Mustang GT to my LS430 or Ford vs Lexus but (on my 07 GT) a custom tune, intake with a K&N huge filter, Kooks headers, full catback exhaust with Borla mufflers was good for over 85 HP. Pretty impressive numbers. We all know Ford is not as refined but their 4.6 V8 is not a poorly designed engine.

 

do you guys really think that free flowing exhaust and less restrictive intakes were not available to Toyota engineers in the 1990's? - there has been zero technology improvement in headers, oil-able air filters etc. over the last 25 years, those are like 1950's technology!

you also have to consider the 4th factor of quietness, if I wanted my LS400 to sound like a hopped up Camaro rather than a refined, nearly silent ultra luxury car, then I would have just bought a hopped up Camaro!

there is NO aftermarket technology or mod that will improve your intake or exhaust, that doesn't compromise one or several of the following: mileage, power, emissions, quietness

 

I have had a K&N in my 92 LS for about 1000 miles. I think I am going to switch back to the OEM style filter. I just don't see how the K&N could flow the same expecially better with that round rubber/plunger piece in the center.

 

especially since your AFM is designed for the OEM filter and its unique aerodynamics!

 

Yeah, I am going to pick up a OEM filter tomorrow. LOL

 

you can get the original Denso filter from RockAuto.com for $16, and the WIX or Hastings or FRAM are fine as well, as they are virtually identical to the original Denso part.

 

Good to know, Thanks!

 

If lexus could charge another 1-2k per car and throw caution to the wind in regards to emissions, yes i''m relatively confident they would have gone with fully scavenged equal length SS tubular exhaust manifolds.

As they had to reach a compromise in order to meet packaging, environmental, and economic requirements, while still providing (for the time) adequate power, yes I'm relatively confident in my statements.

Also "zero technology improvement"? Really? I encourage you to go to your nearest university library and start going through the engineering and physics journals. Fluid dynamics and behavior is still a very intense and growing field, and companies (both OEM and non-) are advancing every day with everything from variable length EXHAUST manifolds as well as tubing, as an example. Granted the K&N cotton gauze filters haven't changed too much, there are many other oil and non-oiled filters that have been intro'd to the market in even the past 10 years (such as the RP Foam series, though I'm not a huge fan myself).