TOPIC: 2008 Chevrolet Cobalt 2.2L

Last vehicle in the driveway to be done (better half's)

Engine cowling required the loosening of two hose clamps, one to the air-box and the other on the TB, and the spring clamp for the PCV hose on the plenum (air intake) side.
There is also a hold down retainer and post on the right side, you can release the center pin on this by lifting it as you would a coin.









This throttle body has the contoured venturi, the design allows the throttle plate to follow the wall of the venturi with minimal air flow until it begins to open out beyond the venturi walls.


The throttle plate follows the arc of the wall to approximately 30 degree angle where the bottom of the venturi wall straightens out.




As noted in the above drawing, I placed the groove just at the point the throttle plate met the edge of the vertical wall. It probably could have been placed a little higher as the opening would have been maintained but the angle would probably have to be adjusted.

I used the Large bit on this without any issues.

Initial results
Pre-Groove 24mpg avg.
EPA published numbers for this vehicle 22city, 26 average, 31 highway

Post-groove
26+ city / 35+ highway

ecu reading
pre-groove
Load % 20.4
ShrtFT1 -2.3
LongFt1 3.9
MAF .444
TP 20.4

post-groove
Load % 19.6
ShrtFT1 -4.7
LongFt1 0.8
MAF .421
TP 18.4

The way the intake manifold is designed on this engine, there are four distinct air paths occuring between the TB and each cylinder.

Not sure but this may or may not influence the effects of the Groove to some extent.
(Just a theory)

Karl Fortner
Tacoma, Wa.
Gadgetman Tacoma

<strong>From Gadgetman:
To you all:
The pictures you are posting are confusing to the new guys, displaying the angle incorrectly. I want you all to start using 20 degrees as the base. Here's what 20 degrees actually looks like:



Please be aware that if The Groove is too steep, you will not be getting the best waveform. So, in the future, please take more care in your illustrations, in the interest of accurate dissemination.</strong>

nicey documented. What else did you do more then the groove? any vacuum tubes blocked or moved?
saludos MOB

Hi Markus,

no, only thing I did was Groove the TB. As I noted it could have been placed a little further up into the Venturi and possibly a little more effective at the same time.

There are several vehicles that I have looked at where the vehicle manufacturer actually routes the PCV to the intake air by default, this Cobalt was one of them.

I'm going to try and document any further mod's the same way, I want to make sure the details are there to look back on, for anyone else to review before going forward with their mod and of course allow others to critique one way or the other.

I prefer to go forward knowing what others have learned already rather than repeating the same mis-steps experienced by others to obtain the end result.

Hopefully others will follow.

Cheers

Karl Fortner
Tacoma, Wa.
Gadgetman Tacoma

Got back to this vehicle and regapped the spark plugs

Originally .035", opened them up to .049"

Took it for a 12 mile run out on the highway and rechecked the numbers.

Post groove
Load 19.6
SHrtFt1 -4.7
LongFt1 .8

After some run time and a recheck I found not much change in the Load or ShrtFt1 but the LongFT1 had shifted to 7.5.

After regapping the plugs and the highway run
(with some local streets to get back home)
LOAD 13.3 / 14.1
SHRTFT1 -2.3 / 2.1
LONGFT1 2.3
*MAP 8.0 / 8.3

* The MAP prior to the plug regapping was at a consistent 9.7

The plugs on these vehicles are the Iridium tipped... a bit different from what I'm used to.



Also you can't gap these the old fashioned way without damaging the tip so a pair of bull nosed pliers from one side is very helpful in the adjustment.

Karl Fortner
Tacoma, Washington

The gap on this engine can probably go to at least .060.
When regapping, to see the fastest changes, you will need to clear the ECU. This was done on a Honda Accord recently and it took 1/2 tank to realize a gain from 29.5 to 34.5.

I was considering it... seen the video

Found one of the plugs had degraded. 45,000 miles on the vehicle.

Since this is my partners car, when she buys the new plugs for it, I'll gap them at .060" before I put them in.

Karl Fortner
Tacoma, Washington