Re: Vorshlag 2011 Mustang GT 5.0 - auto-x/track build
Project Update for January 29, 2013 : We have a lot of ground to cover on the S197 Mustang thread. so look for several updates over the next week or two. Our last real S197 thread update was in November, and a LOT has happened behind the scenes since then - with respect to future competition in our 2011 and 2013 GT's in SCCA Solo ESP for 2013, plus several track events. We will also cover the new NASA TT3 classing and our first 2013 competition (with a track record + double-win), a track event in December with both of our S197s, the whole Watts Link/SCCA debacle, a new shock/spring set-up we've been testing on S197s, and then the BFGoodrich Rival tire launch event that I attended, where I got to test with four different types of cars and seven types of tires at the NOLA Motorsport park, including FR500S Mustangs (former Miller Cup cars). This set of updates will be broken up into multiple thread posts over the next several days, otherwise it will be too long and I won't get any sleep - and I've been on the road, racing various cars for four of the last five days, then sick with a stomach bug, so I'm beat. Let's back up and start with the preparation on the 2013 GT before the December track event first...
2013 GT Coilover Shock Install
The last time we took the 2013 Mustang to ECR, it was on the OEM shocks and springs and the handling was "frightening", to say the least. The car was hopping and flopping around, like a fish out of water. Lots of lean, roll, dive, and all that bad stuff we are used to on OEM sprung/damped S197s. Our long term plans at the time still included SCCA E-Street Prepared class preparations, but we would still do a track event or two before we got too far down the rabbit hole of autocross-only modifications.
Obviously a big improvement we could tackle that worked for both autocross and track use was to add our normal monotube adjustable coilover upgrade. Since Vorshlag sells AST and Moton monotubes, plus some others, we had several options that would work. We picked up some AST double adjustable coilovers with remote reservoirs for an S197 (AST 4200-RR), a custom test set made by AST-USA for a former employee. These were built with racing style "eye-to-eye" rear shocks, just like the Motons on our 2011 GT. On this car, however, I wanted to keep them "pin" style on top, to allow for the rebound knob to be located in the trunk for easy rebound changes (see above, left). An eye-to-eye shock tends to have the rebound knob located under the trunk floor and, like in the case of our Moton CS shocks on the 2011 GT, we have to remove a rear wheel to adjust rebound. It is a hassle, and that adjustment almost never gets tweaked. so we end up using the same setting for street and track use (which is a shame). So we asked AST-USA to re-work the rear shock shafts to have a traditional top pin and used it with the OEM style shock mount. They swapped out the shafts and adjusters to our favored eye lower/pin upper style and now the rebound knob is easy to access.
Once these were built to our liking, Vorshlag fabricator Ryan fashioned some reservoir mounts for the rear shocks, and cut holes in the trunk floor "spare tire well" to route the reservoirs through without disconnecting the hoses (which is a PITA) - just like on the 2011 GT. I asked him to tweak the angle of the reservoirs to be able to see the knobs easier from behind, which he did. The reservoirs were mounted into the spare tire well using the 2-piece "Seals-It" brand grommets to make this hole water tight. He mocked-up the seals with temporary Clecos, then used small machine bolts and nuts to hold them in place. If the shocks need to be removed from the car, the 2-piece grommets can be unbolted then the reservoir can slide right through the now open hole... no mess, no fuss. The other mounting/routing option for shock reservoir hoses is to drill much smaller holes/grommets and add (very costly) quick-disconnects on each shock line. Even then you still have to bleed off the Nitrogen charge before disconnecting the hoses, and re-fill the N2 when reinstalling. We feel this "big hole/2-piece grommet" arrangement is easier to deal with in the long run, and it is less expensive - but there are a dozen ways to skin this cat.
The front struts were not that unusual, being a typical non-inverted 22mm shaft monotube with rebound knobs on the strut shaft top and the compression knobs on the remote reservoirs (just like the rears). The hoses were long enough to route underneath the inner fender structure and mount the reservoirs just about anywhere in the engine bay. Ryan made some additional reservoir brackets for the front struts, but unlike our 2011 GT this car still had the factory airbox in place (everything is still bone stock under hood, for the lower 380 whp output). This meant we couldn't mount the reservoirs in the same place as on the '11 (which was blocked on this car by the giant OEM airbox), so we thought about it and placed them vertically in the airstream behind the headlights.
Shock reservoirs need to shed heat when they are working (they turn motion into heat), so we always try to keep them cool. Mounting them so that they get cool air from the front end seemed like the best idea. This location doesn't "show them off" as well as elsewhere, but so be it. I've seen some racers place remote shock reservoirs near the worst sources of under hood heat - like above a turbocharger (I've even done this myself) - but you really have to think about where you mount these things to keep them cool. A boiling hot reservoir will not allow the shock to perform nearly as well as one that stays closer to ambient temperature.
As you can see in the "Before and After" shots above, the ride height on the 2013 GT is significantly lowered, with the front dropping 1.25" and the rear dropping nearly 1.75". This gets ride of the huge front-down rake these cars come with and lowers the CG significantly. The spring rates we used were somewhat mild, with 450#/in in front and 225 #/in in the rear. This makes for a very decent ride on the street, but still a sizable bump in spring rates over stock, for better track handling (well, at least the front rates). See the updated spring charts below for the base 2013 GT OEM springs, the 2011 "Brembo GT" OEM springs, and the '07-08 Shelby GT spring rates (equipped with the FRPP M-5300-P springs).
Click the charts above for larger image... LEFT: 2013 Base GT. CENTER: 2011 "Brembo" GT. RIGHT: M-5300-P/'07-08 Shelby GT.
Since I first posted several OEM S197 Mustang spring rate tests, we noted two problems: first, we weren't compressing the springs nearly far enough. We were barely getting them compressed enough to even approach static ride height. So we upgraded our digital spring rater to a new "ram" to allow for 15" of spring compression vs the 4.5" it came with, which let us test over a wider range. These newly tested Mustang spring rates then become much more linear as we tested them over a wider displacement range. Second there was an error in our calculations for "rate at compressed height" that has also been fixed in our default spreadsheet. The measured force numbers never changed, just how we were showing them (rate of rate change vs rate at position). Sorry for the confusion.
So as you can see, we've upped the front spring rate considerably more than the rear on this car once again, which we have found - from a lot of coilover testing - works better with an S197, both on track and on the street. The bigger rate increase up front cuts down on brake dive, body roll and camber loss under cornering forces. It also reduces understeer caused by bottoming out of the front suspension. This 450#/in spring also makes the car transition much faster than with the ~100 #/in rates. Luckily the adjustable AST monotubes do a fine job of managing the 4.5 times increase in front rate. You won't see OEM-lowering springs in this spring rate range because the typical shocks these are used on (OEM style) cannot deal with those spring rates.
(continued below)
Project Update for January 29, 2013 : We have a lot of ground to cover on the S197 Mustang thread. so look for several updates over the next week or two. Our last real S197 thread update was in November, and a LOT has happened behind the scenes since then - with respect to future competition in our 2011 and 2013 GT's in SCCA Solo ESP for 2013, plus several track events. We will also cover the new NASA TT3 classing and our first 2013 competition (with a track record + double-win), a track event in December with both of our S197s, the whole Watts Link/SCCA debacle, a new shock/spring set-up we've been testing on S197s, and then the BFGoodrich Rival tire launch event that I attended, where I got to test with four different types of cars and seven types of tires at the NOLA Motorsport park, including FR500S Mustangs (former Miller Cup cars). This set of updates will be broken up into multiple thread posts over the next several days, otherwise it will be too long and I won't get any sleep - and I've been on the road, racing various cars for four of the last five days, then sick with a stomach bug, so I'm beat. Let's back up and start with the preparation on the 2013 GT before the December track event first...
2013 GT Coilover Shock Install
The last time we took the 2013 Mustang to ECR, it was on the OEM shocks and springs and the handling was "frightening", to say the least. The car was hopping and flopping around, like a fish out of water. Lots of lean, roll, dive, and all that bad stuff we are used to on OEM sprung/damped S197s. Our long term plans at the time still included SCCA E-Street Prepared class preparations, but we would still do a track event or two before we got too far down the rabbit hole of autocross-only modifications.
Obviously a big improvement we could tackle that worked for both autocross and track use was to add our normal monotube adjustable coilover upgrade. Since Vorshlag sells AST and Moton monotubes, plus some others, we had several options that would work. We picked up some AST double adjustable coilovers with remote reservoirs for an S197 (AST 4200-RR), a custom test set made by AST-USA for a former employee. These were built with racing style "eye-to-eye" rear shocks, just like the Motons on our 2011 GT. On this car, however, I wanted to keep them "pin" style on top, to allow for the rebound knob to be located in the trunk for easy rebound changes (see above, left). An eye-to-eye shock tends to have the rebound knob located under the trunk floor and, like in the case of our Moton CS shocks on the 2011 GT, we have to remove a rear wheel to adjust rebound. It is a hassle, and that adjustment almost never gets tweaked. so we end up using the same setting for street and track use (which is a shame). So we asked AST-USA to re-work the rear shock shafts to have a traditional top pin and used it with the OEM style shock mount. They swapped out the shafts and adjusters to our favored eye lower/pin upper style and now the rebound knob is easy to access.
Once these were built to our liking, Vorshlag fabricator Ryan fashioned some reservoir mounts for the rear shocks, and cut holes in the trunk floor "spare tire well" to route the reservoirs through without disconnecting the hoses (which is a PITA) - just like on the 2011 GT. I asked him to tweak the angle of the reservoirs to be able to see the knobs easier from behind, which he did. The reservoirs were mounted into the spare tire well using the 2-piece "Seals-It" brand grommets to make this hole water tight. He mocked-up the seals with temporary Clecos, then used small machine bolts and nuts to hold them in place. If the shocks need to be removed from the car, the 2-piece grommets can be unbolted then the reservoir can slide right through the now open hole... no mess, no fuss. The other mounting/routing option for shock reservoir hoses is to drill much smaller holes/grommets and add (very costly) quick-disconnects on each shock line. Even then you still have to bleed off the Nitrogen charge before disconnecting the hoses, and re-fill the N2 when reinstalling. We feel this "big hole/2-piece grommet" arrangement is easier to deal with in the long run, and it is less expensive - but there are a dozen ways to skin this cat.
The front struts were not that unusual, being a typical non-inverted 22mm shaft monotube with rebound knobs on the strut shaft top and the compression knobs on the remote reservoirs (just like the rears). The hoses were long enough to route underneath the inner fender structure and mount the reservoirs just about anywhere in the engine bay. Ryan made some additional reservoir brackets for the front struts, but unlike our 2011 GT this car still had the factory airbox in place (everything is still bone stock under hood, for the lower 380 whp output). This meant we couldn't mount the reservoirs in the same place as on the '11 (which was blocked on this car by the giant OEM airbox), so we thought about it and placed them vertically in the airstream behind the headlights.
Shock reservoirs need to shed heat when they are working (they turn motion into heat), so we always try to keep them cool. Mounting them so that they get cool air from the front end seemed like the best idea. This location doesn't "show them off" as well as elsewhere, but so be it. I've seen some racers place remote shock reservoirs near the worst sources of under hood heat - like above a turbocharger (I've even done this myself) - but you really have to think about where you mount these things to keep them cool. A boiling hot reservoir will not allow the shock to perform nearly as well as one that stays closer to ambient temperature.
As you can see in the "Before and After" shots above, the ride height on the 2013 GT is significantly lowered, with the front dropping 1.25" and the rear dropping nearly 1.75". This gets ride of the huge front-down rake these cars come with and lowers the CG significantly. The spring rates we used were somewhat mild, with 450#/in in front and 225 #/in in the rear. This makes for a very decent ride on the street, but still a sizable bump in spring rates over stock, for better track handling (well, at least the front rates). See the updated spring charts below for the base 2013 GT OEM springs, the 2011 "Brembo GT" OEM springs, and the '07-08 Shelby GT spring rates (equipped with the FRPP M-5300-P springs).
Click the charts above for larger image... LEFT: 2013 Base GT. CENTER: 2011 "Brembo" GT. RIGHT: M-5300-P/'07-08 Shelby GT.
Since I first posted several OEM S197 Mustang spring rate tests, we noted two problems: first, we weren't compressing the springs nearly far enough. We were barely getting them compressed enough to even approach static ride height. So we upgraded our digital spring rater to a new "ram" to allow for 15" of spring compression vs the 4.5" it came with, which let us test over a wider range. These newly tested Mustang spring rates then become much more linear as we tested them over a wider displacement range. Second there was an error in our calculations for "rate at compressed height" that has also been fixed in our default spreadsheet. The measured force numbers never changed, just how we were showing them (rate of rate change vs rate at position). Sorry for the confusion.
So as you can see, we've upped the front spring rate considerably more than the rear on this car once again, which we have found - from a lot of coilover testing - works better with an S197, both on track and on the street. The bigger rate increase up front cuts down on brake dive, body roll and camber loss under cornering forces. It also reduces understeer caused by bottoming out of the front suspension. This 450#/in spring also makes the car transition much faster than with the ~100 #/in rates. Luckily the adjustable AST monotubes do a fine job of managing the 4.5 times increase in front rate. You won't see OEM-lowering springs in this spring rate range because the typical shocks these are used on (OEM style) cannot deal with those spring rates.
(continued below)
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