GMPD Tech Presentation on '08 Cobalt SS and Direct Injection overview
08-10-2008, 09:34 AM
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GMPD Tech Presentation on '08 Cobalt SS and Direct Injection overview
I was doing some research on a couple things and ran across a couple documents on the GM Performance Division web site. I haven't seen them posted/linked here before, but there's a few interesting tidbits of info in them. Both documents look like they were originally developed for internal GM presentation/briefings.
2008 Cobalt SS Overview (technical presentation)
http://www.gmperformancedivision.com..._SS_Owners.pdf
Some various points of interest and things I noted from the presentations:
- GM sees the Caliber SRT-4 and Mazdaspeed3 as key competitors.
- GMPD rated performance numbers of 0-60: 5.7 sec, quarter-mile: 14.2 @ 103, 60-0 braking: 118 ft, lateral acceleration: .90g.
- Launch Control designed not only to work as a two-step (hold revs at ~5100) but apply a selective traction control algorithm during launch.
- No-Lift Shift keeps throttle open to maintain boost while retarding spark and uses fuel cut-off to hold redline. No mention of cam phasing changes like some press media coverage has reported. GMPD says it improves acceleration 0.07 seconds per up-shift when used.
- Spring rates increased 20% front, 30% rear (unsure if they are talking over base Cobalt or old SS) with re-valved strut/shocks providing more damping.
- EPS (electronic power steering) amperage also increased to 61A vice 58A on base system in addition to the controller recalibration that's been previously reported.
- Besides just having a faster 14.8:1 ratio steering rack, the new rack was designed to work with the new short steer arm knuckle geometry and also has a higher required driver torque (i.e. turning effort at the steering wheel) which is the rack force and rack-and-pinion ratio (or C-factor). Probably one reason the EPS system has increased capacity.
- ESC (electronic stability control) was tuned at the Nürburgring.
- ETC (electronic traction control) disabled in Competitive Mode. The ESC allows more aggressive driving before intervention in Competitive Mode.
- The Brake Limited Differential (standard electronic diff vice optional mechanical limited slip) is active any time TCS (traction control system) is not (“TCS OFF”, “Comp Mode”, “ESC Off”). I read that to mean it does not work in normal, full traction/stability control mode.
- The engineers have implemented torque management using data from the ABS/ESC controller to detect and prevent "powerhop" (i.e. wheel hop).
- The stabilizer bar geometry was the primary factor in reduction of torque steer.
- The new SS was not only tested at the Nürburgring, but also at the GM Milford Proving Grounds, Virginia International Raceway, Phoenix International Raceway, Barber Motorsports Park, Firebird Raceway, Buttonwillow Raceway, and the GM Vehicle Dynamics Road Course.
- Presentation includes better pictures of the Reconfigurable Performance Display. Looks to be able to adjust shift light on a per gear basis and turn additional indicators for comp mode/launch control/ESC-active/TCS-active on and off. Can present boost, air-fuel ratio, cam phaser angle and overlap, spark advance and knock retard, and engine power and torque in gauge-type displays. Sidebar can display tire pressure at each wheel, barometer, outside temp, battery voltage, coolant temp, intake temp, fuel pressure, or a shift/gear indicator. A lateral g-meter with digital speed is also available in place of gauge display.
2.0L Ecotec Direct Injected Turbo Engine (direct injection overview)
http://www.gmperformancedivision.com..._Injection.pdf
- The LNF pistons are still a cast aluminum design. I've seen some people keep speculating they are forged units (probably still made by Mahle along with the rods like the LSJ).
- Normal boost is between 15-18 psi but can go as high as 21 psi.
- Primary benefit of SIDI (spark ignition direct injection) is increased power with minor fuel economy gains. Increases efficiency and reduces knock sensitivity.
- Secondary benefits are that the direct injection is less sensitive to fuel properties and doesn't have to run as rich.
- Uses "split injection" where fuel is injected during intake stroke as well as during compression stroke for rapid catalyst heating (vice normally injection during the compression stroke just prior to ignition). Probably why the direct injection has a faster ticking on cold startup before settling to the slower lope.
- GMPD recognizes "tunability" of direct injection is concern and that there will be ways to increase power, just like on diesels.
2008 Cobalt SS Overview (technical presentation)
http://www.gmperformancedivision.com..._SS_Owners.pdf
Some various points of interest and things I noted from the presentations:
- GM sees the Caliber SRT-4 and Mazdaspeed3 as key competitors.
- GMPD rated performance numbers of 0-60: 5.7 sec, quarter-mile: 14.2 @ 103, 60-0 braking: 118 ft, lateral acceleration: .90g.
- Launch Control designed not only to work as a two-step (hold revs at ~5100) but apply a selective traction control algorithm during launch.
- No-Lift Shift keeps throttle open to maintain boost while retarding spark and uses fuel cut-off to hold redline. No mention of cam phasing changes like some press media coverage has reported. GMPD says it improves acceleration 0.07 seconds per up-shift when used.
- Spring rates increased 20% front, 30% rear (unsure if they are talking over base Cobalt or old SS) with re-valved strut/shocks providing more damping.
- EPS (electronic power steering) amperage also increased to 61A vice 58A on base system in addition to the controller recalibration that's been previously reported.
- Besides just having a faster 14.8:1 ratio steering rack, the new rack was designed to work with the new short steer arm knuckle geometry and also has a higher required driver torque (i.e. turning effort at the steering wheel) which is the rack force and rack-and-pinion ratio (or C-factor). Probably one reason the EPS system has increased capacity.
- ESC (electronic stability control) was tuned at the Nürburgring.
- ETC (electronic traction control) disabled in Competitive Mode. The ESC allows more aggressive driving before intervention in Competitive Mode.
- The Brake Limited Differential (standard electronic diff vice optional mechanical limited slip) is active any time TCS (traction control system) is not (“TCS OFF”, “Comp Mode”, “ESC Off”). I read that to mean it does not work in normal, full traction/stability control mode.
- The engineers have implemented torque management using data from the ABS/ESC controller to detect and prevent "powerhop" (i.e. wheel hop).
- The stabilizer bar geometry was the primary factor in reduction of torque steer.
- The new SS was not only tested at the Nürburgring, but also at the GM Milford Proving Grounds, Virginia International Raceway, Phoenix International Raceway, Barber Motorsports Park, Firebird Raceway, Buttonwillow Raceway, and the GM Vehicle Dynamics Road Course.
- Presentation includes better pictures of the Reconfigurable Performance Display. Looks to be able to adjust shift light on a per gear basis and turn additional indicators for comp mode/launch control/ESC-active/TCS-active on and off. Can present boost, air-fuel ratio, cam phaser angle and overlap, spark advance and knock retard, and engine power and torque in gauge-type displays. Sidebar can display tire pressure at each wheel, barometer, outside temp, battery voltage, coolant temp, intake temp, fuel pressure, or a shift/gear indicator. A lateral g-meter with digital speed is also available in place of gauge display.
2.0L Ecotec Direct Injected Turbo Engine (direct injection overview)
http://www.gmperformancedivision.com..._Injection.pdf
- The LNF pistons are still a cast aluminum design. I've seen some people keep speculating they are forged units (probably still made by Mahle along with the rods like the LSJ).
- Normal boost is between 15-18 psi but can go as high as 21 psi.
- Primary benefit of SIDI (spark ignition direct injection) is increased power with minor fuel economy gains. Increases efficiency and reduces knock sensitivity.
- Secondary benefits are that the direct injection is less sensitive to fuel properties and doesn't have to run as rich.
- Uses "split injection" where fuel is injected during intake stroke as well as during compression stroke for rapid catalyst heating (vice normally injection during the compression stroke just prior to ignition). Probably why the direct injection has a faster ticking on cold startup before settling to the slower lope.
- GMPD recognizes "tunability" of direct injection is concern and that there will be ways to increase power, just like on diesels.
08-10-2008, 09:54 AM
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