You will notice 20-30whp, and that's a huge gain for the IS 350. I'm probably only getting 10-15whp more from intake and full catback exhaust, and my times on the drag strip definately improved even factoring in the environment. But, 20-30 whp from an intake though, not likely.

 

your 350 has 12 injectors that fires on cold start.

 

I disagree. Will you see results? Yes (minimal). Will you actually feel it? Unlikely.

When I had my WRX, mind you the car weighs about 700lbs less, I had the car tuned and jumped 25whp on a Mustang Dyno. I couldn't tell the difference in power. I went from 254whp to 279whp... the car felt more responsive, but that was because of a tune.

Either way the intake would not be a "night and day" difference.

 

On my intake I notice a huge dirence in my acceleration

 

You really don't.

You imagine one, but it's just your imagination.

If you actually measured your acceleration times you'd see no significant difference.

An intake, by itself, won't provide more than about 5 rwhp.

Which is not noticable at all, let alone a "huge difference"

The electronic snake oil I mention might give you another 5-10 until the ECU tunes it back out... which again won't amount to a "huge difference"

Short ram intakes such as yours can add a huge amount of noise though- and many people confuse that with horsepower.

 

Can i go ahead and ask? How old are you, IS350Rock? How much experience with cars do you have?

And really, take the best advice given by the forum and remove your intake to try and resolve your problem. Even the "imaginary huge gains" your intake gives, i doubt is worth 3.6mpg.

 

OP - are you refilling your tank after driving 40-50 miles? B/C that's what would have to happen if you got 3.5 mpg. If that's the case, revert back to your stock intake set up and see if that resolves the problem. If not, then maybe you need to bring it to the dealer (with stock set up in place) and have them evaluate things.

I find it hard to believe you get 3.5 mph and there is no engine warning light, etc. B/C with that crappy of mileage there would certainly have to be something wrong with the car.

 

I really don't understand the gibberish in the original post.

It sound to me that the car has a non-stock intake and the displayed mpg (current and or tank) is fluctuating greatly.

So...lets find out what your actual MPG is.

1) fill tank
2) reset one of the trip odometers
3) drive the car normally until you are just about empty
4) fill tank again.
5) take note of how many gallons it takes
6)Check the miles on the trip odometer you reset in step 2)
7)Divide (this is the math part) the miles from step by the gallons in step 5. MPG = Miles/gallons

What is the answer? Somewhere around 20?

 

I got more than that at the track, thats crazy... like some have said.. just try driving a whole tank and look at the tank avg. city you should get at least 16 and hwy you should get low to mid 20s considering you dirve pretty agressive