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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > NA Engine (non-turbo) / Drivetrain / Exhaust Modifications > Rev drops



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      05-22-2012, 10:39 PM   #1
e9012345
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Rev drops

How fast do your revs drops? I feel as if I have an air leak in the intake as the rectangular rubber hose does not fully seal and clamp around the snorkel duct.

My rev's SHOOOT down extremely quickly - I drove a friends 350z and was amazed at how long they stayed floating and how long before they dipped.

(I have a K&N Drop in, Cyba scoops and a charcoal delete)

Whats normal?

Thanks
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      05-23-2012, 11:03 AM   #2
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Well your driving a totally different car.....
Go out and
Drive a similar thrn compare
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      05-24-2012, 02:47 PM   #3
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I assume 6MT? Mine drop very fast and at first it took some learning to be able to shift fast enough to catch the revs.

With AC on its impossible to be smooth. They drop stupid fast with the AC on.

The devil is the dual mass flywheel....



Quote:
Originally Posted by e9012345 View Post
How fast do your revs drops? I feel as if I have an air leak in the intake as the rectangular rubber hose does not fully seal and clamp around the snorkel duct.

My rev's SHOOOT down extremely quickly - I drove a friends 350z and was amazed at how long they stayed floating and how long before they dipped.

(I have a K&N Drop in, Cyba scoops and a charcoal delete)

Whats normal?

Thanks
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      05-24-2012, 04:09 PM   #4
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Quote:
Originally Posted by RupertPupkin View Post
I assume 6MT? Mine drop very fast and at first it took some learning to be able to shift fast enough to catch the revs.

With AC on its impossible to be smooth. They drop stupid fast with the AC on.

The devil is the dual mass flywheel....
wait til u get lightweight single mass, it will drop faster! did u get rid of the CDV? also OP u need find out if you have 6mt and need chop the CDV, it will help tranny catch those dropping rev faster.
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      05-24-2012, 05:53 PM   #5
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Yea ditched the CDV the first week and have the performance SSK. You have a single mass? Im going to need a new clutch soon I fear and have been looking in to options. What do you have?




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wait til u get lightweight single mass, it will drop faster! did u get rid of the CDV? also OP u need find out if you have 6mt and need chop the CDV, it will help tranny catch those dropping rev faster.
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      05-24-2012, 06:07 PM   #6
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The speed at which the revs drop (assuming everything is working correctly) is a factor of engine tuning and rotating mass in the engine and flywheel. This car has very low rotating mass for being stock so it spins down fast. The fact that's it's dual mass doesn't really make it spin down faster. In fact, most dual mass flywheels are heavier than their single mass counterparts. Cars will heavy flywheels get better gas mileage since the flywheel can keep the car rolling longer because of it's rotating mass. Cars with light flywheels are harder to drive smoothly and harder to get moving from a stop. Since then engine has no rotating mass, it has a tendency to stop spinning lol.

That floating or "rev hang" you felt in your friend's 350z is all engine tuning. Whenever you snap the throttle closed, you end up with excess fuel which ends up in your exhaust unburned. Not so good for emissions or your cat. Some cars will advance the timing or keep the throttle open until the fuel is reduced. Tuning companies are able to remove that rev hang. If you have a loud exhaust, you will hear the raw fuel burble and pop as it explodes in the cat (or out the tail pipe if you don't have a cat).
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      05-24-2012, 06:13 PM   #7
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Quote:
Originally Posted by RupertPupkin View Post
Yea ditched the CDV the first week and have the performance SSK. You have a single mass? Im going to need a new clutch soon I fear and have been looking in to options. What do you have?
I still got OEM, thinking ditching it too after my warranty is up. I had lightweight single mass flywheel on my GTI 1.8t before, it made big difference in 2nd gear and i like the way rev drop faster cuz it u get more engine brake.

bad part is the clutch chattering, but i am already getting slight chatter on my 328i now on a hot day.
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      05-24-2012, 06:19 PM   #8
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Yea My buddy has a soutbend stage 2 on an mk6 gli stage 2 tune and it chatter ssooooo bad, turn ac on and it sounds horrible.

My current original OEM one chatters pretty bad. Anyone with 6MT every get a slip feeling coming from a stop in first?





Quote:
Originally Posted by jc5988 View Post
I still got OEM, thinking ditching it too after my warranty is up. I had lightweight single mass flywheel on my GTI 1.8t before, it made big difference in 2nd gear and i like the way rev drop faster cuz it u get more engine brake.

bad part is the clutch chattering, but i am already getting slight chatter on my 328i now on a hot day.
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      05-24-2012, 06:23 PM   #9
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Can the OEM clutch be adjusted? Is it a DIY? Mine only gives me this slipping feeling in first gear, never any others. I can bog it down in a higher gear up a hill and gun it and no slipping at all.




Quote:
Originally Posted by jc5988 View Post
I still got OEM, thinking ditching it too after my warranty is up. I had lightweight single mass flywheel on my GTI 1.8t before, it made big difference in 2nd gear and i like the way rev drop faster cuz it u get more engine brake.

bad part is the clutch chattering, but i am already getting slight chatter on my 328i now on a hot day.
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      05-24-2012, 08:04 PM   #10
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Quote:
Originally Posted by e90pilot View Post
The speed at which the revs drop (assuming everything is working correctly) is a factor of engine tuning and rotating mass in the engine and flywheel. This car has very low rotating mass for being stock so it spins down fast. The fact that's it's dual mass doesn't really make it spin down faster. In fact, most dual mass flywheels are heavier than their single mass counterparts. Cars will heavy flywheels get better gas mileage since the flywheel can keep the car rolling longer because of it's rotating mass. Cars with light flywheels are harder to drive smoothly and harder to get moving from a stop. Since then engine has no rotating mass, it has a tendency to stop spinning lol.

That floating or "rev hang" you felt in your friend's 350z is all engine tuning. Whenever you snap the throttle closed, you end up with excess fuel which ends up in your exhaust unburned. Not so good for emissions or your cat. Some cars will advance the timing or keep the throttle open until the fuel is reduced. Tuning companies are able to remove that rev hang. If you have a loud exhaust, you will hear the raw fuel burble and pop as it explodes in the cat (or out the tail pipe if you don't have a cat).

Thanks. I have both my CDV deleted and my muffler deleted and I get INSANE amounts of burble and pop when I get off the throttle as well as the quick rev drops. What could that mean together?
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      05-24-2012, 08:07 PM   #11
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There's always a little be of overrun in everycar, but BMW might just have it programmed not to burn off the excess fuel or at least not as much as other cars.
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      05-24-2012, 08:25 PM   #12
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Quote:
Originally Posted by e90pilot View Post
The speed at which the revs drop (assuming everything is working correctly) is a factor of engine tuning and rotating mass in the engine and flywheel. This car has very low rotating mass for being stock so it spins down fast. The fact that's it's dual mass doesn't really make it spin down faster. In fact, most dual mass flywheels are heavier than their single mass counterparts. Cars will heavy flywheels get better gas mileage since the flywheel can keep the car rolling longer because of it's rotating mass. Cars with light flywheels are harder to drive smoothly and harder to get moving from a stop. Since then engine has no rotating mass, it has a tendency to stop spinning lol.

That floating or "rev hang" you felt in your friend's 350z is all engine tuning. Whenever you snap the throttle closed, you end up with excess fuel which ends up in your exhaust unburned. Not so good for emissions or your cat. Some cars will advance the timing or keep the throttle open until the fuel is reduced. Tuning companies are able to remove that rev hang. If you have a loud exhaust, you will hear the raw fuel burble and pop as it explodes in the cat (or out the tail pipe if you don't have a cat).
I learn something new every day

Now I get why my exhaust pops/gurgles when I let off, thanks!
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      05-24-2012, 09:00 PM   #13
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here is some info, the "burbling" sound actually consider to be part of the performance power kit to BMW....


"• “Exhaust Burble” sound during engine overrun conditions (new feature only applicable to Power Kits installed on 135i and 335i vehicles with the N55 engine using ISTA/P 2.43 or higher). "
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      05-24-2012, 11:36 PM   #14
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Audi uses an small fuel injector after the cats to make their burble.
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