CAI - lower revs?

[engsr]

i installed an AEM CAI w/bypass valve about a month ago. now, i've noticed that my car at lower speeds revs a bit higher than with my stock intake system (about 400 rpm difference). the rev difference isn't there at highway speeds, or while idling, just in slower city driving. i did reset the ECU and even hooked up the stock oxygen sensor. so, did i install the CAI wrong, or is this a common occurence? thanks for any help.

[VTECseoul]

R U sure UR not driving faster? at startup when engine is cold i noticed it idles higher, but after warming it settles down to normal.

[b16a3sol]

the question is what kind of tranny do you have? no matter what you do to the motor, if you leave the tranny the same nothing will change with the speed to rev ratio, as long as you have a manual. with a stick, the tranny is attached to the engine directly meaning that the speed is directly related to the gear ratios and the revs of the engine. if the gear ratios and the tranny are untouched, the spped will always be the same for every point in revs. if it is an auto, it is close to the same, but no always, especially at lower speeds.

[Rice-Rocketeer]

Originally posted by VTECseoul
at startup when engine is cold i noticed it idles higher, but after warming it settles down to normal.

In continuation to this, if you somehow mess up or don't reconnect the AIT sensor, the engine will stay at warm up rpms (higher rpms) until the intake manifold itself warms up which could take 15 - 20 minutes of driving. You might also get rpm spiking where it goes up and down continously at idle until it warms up.

[engsr]

put it this way:

stock intake: 5th gear, 70km/h = 2000 rpm
AEM CAI: 5th gear, 70km/h = 2400 rpm

after the engine warms up, the idle settles at 800 rpm, like it always did. no spiking either. any speed higher than 100km/h there is no difference in rpm.

[ivymike1031]

Originally posted by engsr
stock intake: 5th gear, 70km/h = 2000 rpm
AEM CAI: 5th gear, 70km/h = 2400 rpm

Since you've got a 5th gear, I assume you've got a 5-spd manual transmission.

This means that one of the following is most likely the problem:
1) your tach has never given consistent readings
2) you've accidentally messed up the wiring for the tach, resulting in an error
3) your speedometer doesn't give consistent readings
2) you moved your seat, and the apparent position of the tach has changed
3) you changed to smaller tires and thus changed the overall drive ratio (and didn't tell us about it)

As was previously mentioned, in a manual transmission there is a fixed ratio between tire speed and engine speed for each gear. There's no way to change this ratio without changing internal transmission/differential components (unless you count slipping the clutch). If your tires are turning at the same speed (same size, same vehicle speed), and you read a different value from the tach than you used to, either you or the tach has made a mistake. Since you're using the speedometer to judge vehicle speed, you can add another possible source for your measurement error.

[Spunkymonkey]

Originally posted by ivymike1031


Since you've got a 5th gear, I assume you've got a 5-spd manual transmission.

This means that one of the following is most likely the problem:
1) your tach has never given consistent readings
2) you've accidentally messed up the wiring for the tach, resulting in an error
3) your speedometer doesn't give consistent readings
2) you moved your seat, and the apparent position of the tach has changed
3) you changed to smaller tires and thus changed the overall drive ratio (and didn't tell us about it)

As was previously mentioned, in a manual transmission there is a fixed ratio between tire speed and engine speed for each gear. There's no way to change this ratio without changing internal transmission/differential components (unless you count slipping the clutch). If your tires are turning at the same speed (same size, same vehicle speed), and you read a different value from the tach than you used to, either you or the tach has made a mistake. Since you're using the speedometer to judge vehicle speed, you can add another possible source for your measurement error.

I agree.

I haven't had any problems with my CAI.

[Spunkymonkey]

Originally posted by VTECseoul
at startup when engine is cold i noticed it idles higher, but after warming it settles down to normal.

Thats normal dude.

[fritz_269]

I agree with Ivy Mike entirely. With a manual tranny, the engine RPM to the MPH is a fixed ratio, no engine part can possibly change it.

[engsr]

hey guys, thanks for the help, much appreciated. i guess i must be going crazy