loose control under acceleration?
- Thread starter Steve Schneider
- Start date
While boost by gear can be done routinely with turbos, not sure I have ever seen any control or mechanism to do this with a SC.... so I wonder how you have achieved?? Boost control is possible in a turbocharger becuase you can divert (via wastegates) the "drive force" but you are not controlling boost by any kind of regulation or valving of manifold pressure. Can you share more of the overall concept for how this could be achieved?
BlackICE
GT Owner
One way would be to modulate the bypass valve instead of it working as an on/off switch.
Fubar
Totally ****** Up
BlackICE
GT Owner
Superfly
HERITAGE GT OWNER
I think you need to start a new thread and tell us more about this. Wow, sounds VERY cool.
Fubar
Totally ****** Up
Fish is doing most of this on my GT. The only feature that will not be included on my project is a new fuel cell. It was one of those things I didn't think I would need, as a full methanol fuel is not one of my objectives. I am a little sorry I didn't go that route now, his new fuel cell added about 5 gallons of additional fuel capacity.
Fish is really good about taking pictures along the way and I will post up a really detailed explanation. Right now there isn't a lot to see. We are waiting on the motor from John at Accufab. The fuel system was the first things we had to tackle, and you have seen that work. Once the fuel system was upgraded we could add power (the car was making around 800 when we maxed the stock fuel system). At that point it was just a matter of saving my pennies until I could figure out my next move. MoTec or motor... I decided you couldn't do one without the other. Knock sensors and DBW turned out to be a little icing on the cake. If Fish could talk me into a MoTeC dash we could add cruise control and a few more driver information queues but I just can't bring myself to chop up the look of the stock interior (or exterior for that matter).
I will post up the build progress in this thread: http://www.fordgtforum.com/forums/showthread.php?23526-Fubar-s-GT-Build
sahlman
Ford GT Team Alumni
I will try to add to and reinforce rather than reiterate many of the good statements and cautions here.
Traction and Stability Control- this was not required by law when the GT was designed and built. The requirement for these controls I believe happened late in 2008. The MoTec project looks very interesting- I hope it goes well!
Vehicle Physics- the laws of physics remain constant regardless of the vehicle…the REGION of physics and resultant behavior changes depending on driver control usage, the vehicle (including tire condition), ambient conditions and road surface. A vehicle’s balance depends on 5 major categories:
1- Load (vertical load on each of the 4 tires)
2-Slip Angle (the angle between the heading and the path/trajectory of the tires- typically about 3 degrees at the 4 tires at the limit on cars like the FGT) before grip flattens or falls off.
3-Slip Ratio (by percentage how much faster the contact patch is moving longitudinally versus the ground at the contact patch- 6-8% slip ratio is a typical region of max grip before it starts falling off)
4-Camber
5-Tire Properties- and how they react to the first 4 as well as weather conditions and road surface.
The vehicle’s inherent design AND the driver’s behavior with the controls (steering, throttle, brake) dictate the region the first 4 are operating and the resultant vehicle behavior.
Pass Car Balance- Understeer for sure-
Understeer (sliding the front before the rear) is stable and much more intuitive/easier. You lift off the throttle and you will regain front control- no drama.
Oversteer (sliding the rear before the front) is unstable and regaining control is much tougher and counterintuitive because lifting off the throttle transfers weight forward reducing rear grip further and making it worse- known as trailing throttle oversteer- do it over a rise, as noted in this thread, and it will be much worse due to even more vertical load off the rear tires.
However, ALL cars will oversteer with specific combinations of steering, throttle, brake, weather and road surface- hence stability control laws to try to save our ass when we venture into bad combinations of these items.
FGT chassis design understeer examples- Bruce (cobra498) noted the roll understeer at the rear on the GT- this increases rear slip angle (adding rear grip) more than the front as you push it harder (chassis rolls more). In addition, the GT has more camber gain at the rear than the front to also add more rear cornering grip as you push it harder. However, most importantly, the tire sizing and resultant properties relative to the car’s weight distribution dominates the car’s balance in a car like the FGT (especially on a steady state corner like a skid pad). We specified the tire sizing and behavior specifically to work well with the FGT inherent properties including like weight distribution.
Combined Cornering and Accel or Decel (Friction Elllipse)- A car has more pure cornering capability than it does when you add accelerating or braking. Add more throttle and your cornering ability goes down more. Opposite tradeoff for straight-line and then adding cornering.
High Horsepower but not Equal- FRONT engine, big HP cars like the GT500 have 59% front weight (vs FGT 43%) with good sized rear tires so the car has tons and tons of understeer inherently and have way less capability (acceleration and handling). You spin rear tires much earlier and easier under acceleration on a car like the GT500, so it is easier for the average person to deal with wheel spin on the GT500 with the very high understeer at much lower speed when it is breaking rears loose.
DBK’s line including “the car is deceptively fast”- I agree with this note. You are going faster and cornering harder than you think in the FGT. The car and tire properties are very forgiving at the limit, but its capability is very high. We noted this track testing with the F360 Modena. Everyone would always comment how much “faster” the F360 felt on the handling track and how much harder you felt like you were working than the FGT. However, the FGT was consistently 2 sec per lap faster than the F360 on our tiny little handling track where HP is not much of a factor. Side note- exceed the limit on a F360 Modena (with OEM tires) and you will spin faster than any other car we tested by a large margin.
Temperatures- as many noted here- below 40 deg F the tires lose considerable grip- be very careful in this region of temps or below.
Always roll into the throttle!
Scott
Traction and Stability Control- this was not required by law when the GT was designed and built. The requirement for these controls I believe happened late in 2008. The MoTec project looks very interesting- I hope it goes well!
Vehicle Physics- the laws of physics remain constant regardless of the vehicle…the REGION of physics and resultant behavior changes depending on driver control usage, the vehicle (including tire condition), ambient conditions and road surface. A vehicle’s balance depends on 5 major categories:
1- Load (vertical load on each of the 4 tires)
2-Slip Angle (the angle between the heading and the path/trajectory of the tires- typically about 3 degrees at the 4 tires at the limit on cars like the FGT) before grip flattens or falls off.
3-Slip Ratio (by percentage how much faster the contact patch is moving longitudinally versus the ground at the contact patch- 6-8% slip ratio is a typical region of max grip before it starts falling off)
4-Camber
5-Tire Properties- and how they react to the first 4 as well as weather conditions and road surface.
The vehicle’s inherent design AND the driver’s behavior with the controls (steering, throttle, brake) dictate the region the first 4 are operating and the resultant vehicle behavior.
Pass Car Balance- Understeer for sure-
Understeer (sliding the front before the rear) is stable and much more intuitive/easier. You lift off the throttle and you will regain front control- no drama.
Oversteer (sliding the rear before the front) is unstable and regaining control is much tougher and counterintuitive because lifting off the throttle transfers weight forward reducing rear grip further and making it worse- known as trailing throttle oversteer- do it over a rise, as noted in this thread, and it will be much worse due to even more vertical load off the rear tires.
However, ALL cars will oversteer with specific combinations of steering, throttle, brake, weather and road surface- hence stability control laws to try to save our ass when we venture into bad combinations of these items.
FGT chassis design understeer examples- Bruce (cobra498) noted the roll understeer at the rear on the GT- this increases rear slip angle (adding rear grip) more than the front as you push it harder (chassis rolls more). In addition, the GT has more camber gain at the rear than the front to also add more rear cornering grip as you push it harder. However, most importantly, the tire sizing and resultant properties relative to the car’s weight distribution dominates the car’s balance in a car like the FGT (especially on a steady state corner like a skid pad). We specified the tire sizing and behavior specifically to work well with the FGT inherent properties including like weight distribution.
Combined Cornering and Accel or Decel (Friction Elllipse)- A car has more pure cornering capability than it does when you add accelerating or braking. Add more throttle and your cornering ability goes down more. Opposite tradeoff for straight-line and then adding cornering.
High Horsepower but not Equal- FRONT engine, big HP cars like the GT500 have 59% front weight (vs FGT 43%) with good sized rear tires so the car has tons and tons of understeer inherently and have way less capability (acceleration and handling). You spin rear tires much earlier and easier under acceleration on a car like the GT500, so it is easier for the average person to deal with wheel spin on the GT500 with the very high understeer at much lower speed when it is breaking rears loose.
DBK’s line including “the car is deceptively fast”- I agree with this note. You are going faster and cornering harder than you think in the FGT. The car and tire properties are very forgiving at the limit, but its capability is very high. We noted this track testing with the F360 Modena. Everyone would always comment how much “faster” the F360 felt on the handling track and how much harder you felt like you were working than the FGT. However, the FGT was consistently 2 sec per lap faster than the F360 on our tiny little handling track where HP is not much of a factor. Side note- exceed the limit on a F360 Modena (with OEM tires) and you will spin faster than any other car we tested by a large margin.
Temperatures- as many noted here- below 40 deg F the tires lose considerable grip- be very careful in this region of temps or below.
Always roll into the throttle!
Scott
Fubar
Totally ****** Up
This thread is epic. It has tremendous educational value. Thank you for taking the time to flesh out those explanations Scott.
Question for the pros... From a pure vehicle dynamics perspective, if the suspension was modified with stiffer shocks etc would a crown in the road or uneven asphalt exaggerate the vehicles response under acceleration? What about lowering the GT?
twobjshelbys
GT Owner
sahlman
Ford GT Team Alumni
Glad the post was worth while. Thank you for the kudos guys.
Stiffer shocks and crown and uneven ashphalt- for the most part I would say it should not have a noticeable impact on acceleration response unless it is bumpy and starts producing some velocity at the shock (standard street shocks and the ones on the GT create force due to velocity, not travel/displacement. Offroad/dirtbike and some of our race cars also change force with displacement, but this does not apply to the GT OEM shocks or any of the after market shocks I am aware you guys are using). However, increasing rear compression damping (especially low speed) will tend to break the rear free earlier if it is bumpy (straight line or cornering) or you are making an evasive maneuver like a hard lane change, running the Esses or a slalom.
Lowering the GT- if you return the GT to stock static camber and toe like T&A Shocks recommends for the street then lowering would not have an effect on acceleration response on a crownded or uneven road. However, if you do not re-align (camber- I assume you will realign toe) to stock settings and leave more static camber, then the response of the car will definitely change under acceleration on crowned or uneven pavement for the worse. Camber creates camber thrust, which is a lateral force...more camber and more rut following and moving around with uneven pavement. Therefore, lowering the car and leaving the camber alone (increased from stock due to camber gain with travel) will definitely make it harder to keep the GT going straight under hard acceleration on crowned, rutted and uneven road. More cornering grip, but harder to drive on the street and obviously wears the inside tire edge more.
A quick note on weight distribution for mid-engine cars like the GT and many of these cars ending up around 43% front. This heavily comes down to the big engine/high HP mid-engine car architecture and for the GT A LOT of focus on getting weight forward from very early on. I ran initial calculations with packaging and found we could easily have ended up at 41% front weight (even with the GT's long wheelbase), so we put a huge push on from the beginning to move as much weight forward as possible. 41% front weight would have been even harder to match tires to the weight distribution and hit all of our vehicle dynamic and performance targets. We put everything in the front end we could. This is the main reason you don’t have much for luggage space- weight distribution and the GT’s cool looking radiator outlets.
Have a Merry Christmas guys and drive smart!
Scott
Stiffer shocks and crown and uneven ashphalt- for the most part I would say it should not have a noticeable impact on acceleration response unless it is bumpy and starts producing some velocity at the shock (standard street shocks and the ones on the GT create force due to velocity, not travel/displacement. Offroad/dirtbike and some of our race cars also change force with displacement, but this does not apply to the GT OEM shocks or any of the after market shocks I am aware you guys are using). However, increasing rear compression damping (especially low speed) will tend to break the rear free earlier if it is bumpy (straight line or cornering) or you are making an evasive maneuver like a hard lane change, running the Esses or a slalom.
Lowering the GT- if you return the GT to stock static camber and toe like T&A Shocks recommends for the street then lowering would not have an effect on acceleration response on a crownded or uneven road. However, if you do not re-align (camber- I assume you will realign toe) to stock settings and leave more static camber, then the response of the car will definitely change under acceleration on crowned or uneven pavement for the worse. Camber creates camber thrust, which is a lateral force...more camber and more rut following and moving around with uneven pavement. Therefore, lowering the car and leaving the camber alone (increased from stock due to camber gain with travel) will definitely make it harder to keep the GT going straight under hard acceleration on crowned, rutted and uneven road. More cornering grip, but harder to drive on the street and obviously wears the inside tire edge more.
A quick note on weight distribution for mid-engine cars like the GT and many of these cars ending up around 43% front. This heavily comes down to the big engine/high HP mid-engine car architecture and for the GT A LOT of focus on getting weight forward from very early on. I ran initial calculations with packaging and found we could easily have ended up at 41% front weight (even with the GT's long wheelbase), so we put a huge push on from the beginning to move as much weight forward as possible. 41% front weight would have been even harder to match tires to the weight distribution and hit all of our vehicle dynamic and performance targets. We put everything in the front end we could. This is the main reason you don’t have much for luggage space- weight distribution and the GT’s cool looking radiator outlets.
Have a Merry Christmas guys and drive smart!
Scott
2112
Blue/white 06'
BlackICE
GT Owner
sahlman
Ford GT Team Alumni
You are welcome guys. Glad to try to help when my background applies.
Very close on location- Verona is just southwest of Madison...about 20 minutes from downtown.
Very close on location- Verona is just southwest of Madison...about 20 minutes from downtown.
Sinovac
GT Owner
No run flats on the GT. Goodyear makes an EMT F1 Supercar tire but the GT didn't have them.