I'm fairly certain its the throttle body being commanded to slowly close. I don't believe it can be changed with HPTuners. If you have a way to log PCM parameters take a look at commanded ETC and it should reflect what I'm saying. I'll check later tonight if I can get some free time.

 

I as well think it's the throttle body. As far as the flywheel goes, our flywheel may not be "lightweight", but it was lightened for the 2.0 supercharged engine from what I have seen.

 

would it be right to assume that if the TB was commanded to close as quickly as possible, the revs would drop quicker, BUT then the rev drop would be limited by the flywheel/ rotating mass

 

im gonna say its some of both

 

Yes, but HPTuners doesn't really have a conventional way of commanding how quickly it can close. You may be able to trick it into closing quicker or bringing down the rpms easier by either changing the idle scalar area of the throttle body or editting coastdown spark to drop the engine speed. However, I'm fairly certain you would run into nasty drivability issues.

Edit: I have to do something similar to this when I tuned for my cams. It allows commanded rpm at idle and actual rpm to match up a little bit better but creates a rougher idle. Its the only way I can tune the cams since we don't have access to our idle airflow tables.

 

Flywheel weight and balance have a direct affect on driveability and acceleration/top end speed as you know. The flywheel is probably close to the normal weight of most 4 cylinders, but may be a little light than the other Ecotecs which don't have to drag a supercharger.

I don't know for sure.

Edit: Integra Type Rs have a flywheel in them with a weight of 16 lbs. as compared to 18 lbs. in the GSR. The lightened flywheels from Fidanza for the Cobalt claim them to weigh around 7.5 lbs which is an approx 10 lbs reduction in weight from the stock flywheel; this would make the stock flywheel roughly 17.5 lbs. I think the flywheel is just about normal 4 cylinder weight as I previously stated and they use the TB for slow decel.

 

i thought the LSj was supposed to have a lightened flywheel accually, which is part of what makes it hard to launch

 

I think I read somewhere that the pcm is programed to keep the revs up after you let off the pedal.
So I would think you could some how remove this with a tune.

I personnelly find it annoying and also not having any engine braking.

Man I ive got to learn to type faster ,type my post and theres 10 more 1

 

I have read that in an article that said the flywheel was lightened. But, it didn't say compared to what. It could just be lighter than the 2.2 and 2.4L flywheels or it could be lighter than most flywheels that cars use. In that same article it mentioned that you needed to give the engine a little more gas because of the lightweight flywheel. Who knows if they knew the truth or not, that's why I always make sure I don't say things as facts.

Edit: It was a Motortrend article that said these things.

 

ya know. sometimes, just sometimes. im not talking out of my ass.

witt, mikey, thanks.

 

Its all about the compression, and your cam lobe. When you here Muscle cars, rev up and right back down to 800 rmps, it is because of their compression. In our cars our compression is very low, when we are not under a load "boost". so there for when you let off the gas, the compression is low and not putting any resistance on the engine. Hope this helps.

by the way no need to rev to show off, just mod the **** out of it and beat everyone on the street, except ls1's of course. lol

 

What

The

Hell?

Where did you hear this crap?

I'm sorry but that made 0 sense.

 

WTF?

LS1 : 10:1
LSJ : 9.5:1

 

It has to do with the rate of the electronic throttle closing, nothing to do with effective or static compression.

 

compression and lsa does have effect on de-rev.... his statement about muscle cars is true also.. my first reaction to this post was compression and what not... however i know we run 9.5:1 so its more of a tb/electric issue for us....

no need to flame the guy b/c he is old school thinking... doesnt make him less knowledgeable.. just in a different field.. hell im still learning this new tech stuff

 

Maybe Angel you're right, I myself don't know much about the "old days" but I know about cars with EMS's.

 

nod.. its cool man.. thats why we get alot of heated debates on this boared i noticed since i been here.. alot of old school guys bought these cars along with former import ownerns and some of the build concepts contradict themselves like hell... lmao..

im still fightinging this whole 10:5:1 head + 15 lbs on these cars.. to me thats freaking crazy.. but some people here are like no thats fine... just 2 different build generations..

 

15 lbs is one thing but it depends on the compressor it's coming from. If you're talking about the M62...yeah...you know that answer LOL

 

Yeah, higher compression does cause faster engine decel. On a diesel if you rev it the rpm will immediately drop, and if you downshift prepare to eat dashboard. In a Mercedes diesel when the automatic transmission downshifts and the car decels the ECM commands the throttle plate almost fully open so that full compression cannot be built. This is similar to what is happening on our cars, but instead of them doing it so you don't have a jerky downshift they are doing it to help emissions.

Until I believe the 07 model year we don't have pulsed air injection, which is used to burn excess fuel on decel as well.

 

The difference is, thats when you are using the engine's compression to provide braking and also removing fuel. In that case does compression have to do with engine deceleration, however the OP's questions was revving in neutral, in which case compression is countered by a power stroke.

Most GM PCMs use transient fueling tables to take care of any excess fuel as well as anticipate additional fueling on throttle changes.

 

Witt/NJHK.. you guys are crazy smart. It scares me some times.

 

Oh yeah, I know he was talking about in neutral. I was just saying, in that guys defense what he was saying made sense to me, but does not apply to this situation.

Edit: I thought you were saying that they slowly close the throttle plate to take care of excess fuel? Yeah, I could see why they would use fuel tables to take car of excess fuel and anticipate changes, I've never really experienced any hesitation in my Cobalt from decel to accel in any scenario I've been in.

 

Yah, I gotcha there.

I'm really not sure why it closes the plate so slowly, it may be to burn fuel since we lack transient tables, or at least don't have support for them.

Speaking of weird TPS behavior... on my car the TPS will start commanding strange values due to my custom cams after about 30 seconds of idle of which I'm forced to correct with a custom idle adaptive spark table. I still can't explain that one although I have a feeling it has something to do with us not being able to edit Base Running Airflow parameters.

Or crazy bored.

 

Man, tuning can be a pain in the ass sometime, and it's usually because of something like you're experiencing where you can't adjust certain parameters due to lack of access. That's why I like standalones, but on the other hand standalones have their own set of problems, especially if they don't support all of the stock sensors.

I'm sure you're right about the cams; I honestly don't have a clue as to what I would do. As long as you have it under control I guess it doesn't really matter how you fixed it.

 

As a small thread jack...don't be surprised if you see a company such as Hydra support us for a standalone solution. It could happen one day.