i was driving my friends xB the other day and he has the aem intake and i noticed that in 5th gear goin like 75 mph's his rpms were only at like 3000 - 3100.

now i dont have the intake and when i am at 75 mph, my rpms are at like 3900-4000.

are his rpms lower because he has the intake? or is my car just weird?

thanks

Does he have bigger wheels on his car, like 17,18,or 19's?

no, he had the stock hub's on his

Manual or auto? An intake can't change the rpm's at X mph. That's determined by 1st through 5th gears and final drive ratio in the trans. Different size wheels will change it, small wheels turn faster and big wheels turn slower at X mph.

So if you have bigger wheels your RPMs will be higher because more power is needed? That would mean shorter engine life possibly? Hmmmm. Now I wonder if I should get 17s?

RPM vs speed is a math function of engine speed, gear ratio and over all tire diameter (NOT WHEEL SIZE). I have 17" wheels and 215/45 tires on my Xa and they are .25" shorter in dia. than the stock tire/wheel combination. Not noticeable at all.

Power does not make a car cruise at a lower RPM, it does make it cruise with less throttle opening at the same RPM.

ken

prolly going up a slope the time without the intake, so yer steping steeper and pulling the rpm up to maintain speed.

Sorry, I should have said overall tire diameter.

A taller tire will turn less RPMs at a certain speed since it has to roll longer to complete 1 revolution. Think of it this way: If you cut a tire across at one place and laid it out a 225/50/16 tire would be longer than a 205/40/16 (just used those sizes as an example). If you look an www.tirerack.com at the specs page of a certain tire. It'll show you overall diameter and revolutions per mile for all the sizes offered.

prolly going up a slope the time without the intake, so yer steping steeper and pulling the rpm up to maintain speed.


No, if the speedo says X mph the rpm will always say Y rpms in a given gear. uphill, downhill, or thrown off a cliff!

and bigger wheels will change hte ACTUAL speed, in a given gear at a given rpm, but NOT the indicated speed. Your speedo will just now be wrong.