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Discussion Starter · #41 · (Edited)
Here is my car on a first "road test" of the Stance Aircups on the Ridetech 3-way racing coilovers. Great for street - track test next!

 

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Discussion Starter · #42 · (Edited)
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Back on track, this time at the Thunderhill 5 mile course (w Crows Nest). The car ran like a champ!

There were appr 20 changes done to the car since the previous shakedown I did in February, therefore this was more or less a new shakedown, with a bit more confidence since I've been able to put some street miles on the car these last months. The main performance changes were the installation of aero parts, swaybars and different coilovers/springs, plus much needed Borg delrin offset bushings for the front LCAs.

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The good:
- The math worked out right wrt to swaybar wheel rates, the balance was pretty much perfect, as it was on the initial shakedown without the bars. Same exquisite agility, just a lot less roll now which is awesome!

For a GTM doing only track duty only I would increase the spring rates to make it act like a racecar but the current rates are a good blend for street/track. A firm ride on the street but acceptable. If you have adjustable shocks you can cheat a little bit and firm them up a little when on track to keep the mass in check during transitions.

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Room for upgrades:
- This is almost silly but turned out to be the main gripe: I need to remove the driver door armrest! It kept limiting my left arm downward movement when turning left. Also limits quick oversteer corrections when turning right. It was a bit like driving one handed. That's never ideal, especially without any powersteering to muscle the 305 wide front tires. It wasn't as bad the way I sat before, but in the week leading up to this track day I bought a Kirkey seat which bolted lower on the floor with more layback. In total that was a huge relief to get full helmet clearance being 6'3", but obviously it resulted in the armrest needing to go as well. Oh well, easy one.

- G50 rear rubber mount needs help. The transaxle moves too much left and right during cornering, making it difficult to get to the correct shift gate with confidence (3rd/4th gate vs 5th/6th gate for example). I think some kind of clamp to keep it fixed at the track, but removable to just have the rubber mount for street, is the answer.

- The rear diffuser angle is still too steep for my liking. Going to work more on that to reduce drag and add downforce.

Other notes worth mention: The car pulled some pretty impressive lateral Gs already after a few steps of shock absorber tuning, so luckily the oil pan baffles from Improved Racing kept their promise. The oil pressure stayed steady in the mid to high 30s up to around 1.4G. When I ran with sustained (~5 seconds) cornering force higher than that, the oil pressure went as low as 26psi but it still held steady there. Thankfully never ran dry...

Speaking about the motor, the LS1 does good work but a GTM on good shocks can definitely handle a lot more, as many GTM builders have already proven. Doing something about that soon.

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Although I was basically driving one handed, and still working on small setup changes as I ramp up the level of attack, times were good. The AiM logger started at 3.14, then along with shock adjustments 3.12 on repeat, then 3.10,5 and then 3.10,2 in bad traffic (solid 3.08 without traffic). This step by step grip and detailed handling improvement by gradual changes to the shock settings kept going on even as the ambient tempartures progressed from mid 70s up to 97 degrees.

Bottom line, a GTM is a quick animal when done right. Can't wait to go fine tune some more, get that arm rest taken care of and hit the track on a cool day.
 

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Discussion Starter · #43 · (Edited)
One thing I did BEFORE the last track day that I forgot to mention was to shim up the forward mount on each front upper control arm. This adds dynamic caster and increases camber gain. Another effect is reduced anti-dive.

So far I shimmed just about 1/4" as an experiment but it already seems to be doing something.

PLEASE NOTE: Both sides of this bushing has shims, in the photo the left one is just blocked from view. You can see some flex in the rubber from the slant, to relax that I will be adding extra shim(s) to the foremost one (blocked from view) to keep the angles of the bushing and arm aligned.

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The added camber gain means more grip when turning the wheel.
The anti-dive turned out to improve brake feel (as many chassis books say it will), a welcome bonus.

Where did I get this from? I saw some extreme control arm angles on an unbelievably fast 2020 GT3 racecar and it made me think about why, so I did some thinking and read up on what it might do more that I may have missed and I realized this is huge untapped territory on the GTM for gaining speed and even better driving feel.

This play with shims is just baby steps so far to tailor the geometry to my liking. I'll be evaluating this more, but even this small 1/4" stack feels like a good start. Easy, ultra low cost mod for anyone wanting to try it out.

On another topic; out of curiosity ahead of next track day I got a temp meter wired up with 4 individual probes. Will be moving these around throughout the day and look for the best future position to catch cold air to the intake, check shifter cable temp, where oil cooler hot air goes, evaluate where and if brake ducts would be most effective etc.
 

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Discussion Starter · #44 · (Edited)
Speaking of temps, the DBA C5 Z51 rotors have color markers on them that change to a different color when the core temp reaches a certain level. Thanks to those markers I was able to establish brake temps at the last track day.

FRONT:
Green has turned white (not on photo) = passed above ~460
Orange has turned yellow = passed above ~550
Red still red = did not pass ~630

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REAR
Green has turned white = passed ~460
Orange still orange = did not pass ~550
Red still red = did not pass ~630

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These are good operating temps for the Ferodo DS2500 pads, good margins for the rotors and the Endless RF650 brake fluid.

It was almost 100 degrees out, so pretty much as high ambient as I will see.
Of course, if I add 10-20mph at the end of any given straight with more power, and giving the brakes a shorter time to cool down due to expediting the straights, these temps will likely go up some, and a bit of added cooling will be the first step to keep it in a good temp window.

This is all commonly known stuff, just good objective data to have with no real effort with brake temp sensors installed in the pads or anything like that.

The DBA C5 Z51 rotor kit proved to be a great minimal cost upgrade vs stock C5 brakes.
 

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Discussion Starter · #45 · (Edited)
Went to another track day last weekend at Buttonwillow Raceway Park. The track character is vastly different from Thunderhill's sweeping flow. Buttonwillow is rugged, cutting kerbs is a must for any sort of good laptime, and the surface has become pretty bumpy over the last couple of years after many years of being very nice from a resurface. The track layout and character is a true challenge to the damper setup and an excellent track to fine tune handling.

Yet again, the Stance Aircups set the tone of the day with super easy unloading thanks to the 2" front lift. Sweet. It just works.

Staged and ready to roll.
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The key changes to share with GTM owners and builders were increased swaybar stiffness front and rear, as well as a clamp to fix the transaxle in position.

The GTM front swaybar kit comes standard with black aluminum arms with a single hole/no adjustment. Adjustment is done by replacing the bar with different wall thickness. The black arms have a curve/offset to them, like shown here in the QRP kit photo. This offset is there to clear the damper. It puts the droplink pretty close to the tire which becomes a challenge when using very wide wheels and tires. I mounted the swaybar in front of the front axle instead of behind it, as shown in an earlier post, and last week I replaced the curved black arms with straight ones since they don't have a shock to clear when pointing back toward the droplink from the front of the car.

Straight arms allow almost full steering angle with very wide wheels while also allowing some freedom of arm length and adjustment holes, which translates to adjustability without replacing the bar itself. I'll have to grab a photo.

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The result of the increased stiffness is that I now have an even better handling version of my GTM, the way it turns is much more precise, the weight transfer is more controlled, the tire use much better without excessive roll defeating the negative camber. There is still a need for more roll stiffness though so I look forward to making the next adjustment/upgrade in that area.

Subjective observation from the track photos reveal that the current gen Acura NSX rolls more than my car, a sample of stock looking to tuned 991 GT3 RS roll a little less, and the very fast McLaren 720S rolls even less.
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The other key item for me was the rear transaxle mount and a couple of shift cable cooling ducts.
First: The stock rubber mount allowed way too much lateral movement which made shift selection really difficult. Using C-shaped shims to fix the transaxle took care of this and it's truly a night and day upgrade, shift precision is great now. The car also feels like one unit of mass without the drivetrain mass moving about a little. There is no detectable increase of engine vibration when cruising.

Second: Added a Naca duct to the floor access plate that directs airflow to the shifter cable where it's the closest to the headers. This seems to aid the shifter cables from getting too heated up and changing friction, they felt the same all day no matter the driving circumstance.

Overall it's starting to feel really solid. This was the 3rd day on track without having to stop for any other reason than tires.
This photos shows evidence of too much roll, as was the case especially at Thunderhill before the added swaybar stiffness. Temps were much better across the tires at Buttonwillow. Static camber should be enough once the roll is taken care of. More to come...

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361133
 

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Discussion Starter · #48 ·
Hit first real snafu but it had nothing to do with the car. Gambled on a LS7 engine out of an SLC and it’s been in the shipping crate until last week when I had it out to dress before pulling my LS1 out.

Unfortunately best use of that LS7 bottom end will probably be under glass for a coffee table. So my motor update will get an undesired delay. Heads can be serviced so if someone has a good LS7 shortblock let me know! Longblock is good too, these heads can be sold.

One of the main bearings here.
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361168
 

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Sorry to hear about the engine.

Love seeing this beast out on track!

With all of the track time and the brakes looking like being at proper temperatures, have any additional work been done for brake cooling?

Thanks.
 

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Discussion Starter · #52 ·
Thanks guys appreciate the sympathy! I evaluated a number of various paths forward and have a different LS7 straight from GM on the shopfloor ready to get dressed. Just marked out all the harness parts and about to power up and connect to the ECU with my HP Tuner sw and check everything looks good for standalone operation.

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Also, something about the front swaybar: I had mentioned I went to straight arms and added some adjustment, but it wasn't enough, the car needs more roll stiffness. I realized I can easily switch left/right side swaybar bushing mounts, this simply puts the swaybar about 1.25" rearward, while using the same bolt holes, and that means I can cut those straight arms by the same amount.

Benefits:
  • Takes off material from these heavy arms so reduces unsprung weight
  • The shorter arms will mean my new adjustment holes will all be in the stiffer direction, which I am seeking.
  • The shorter arms mean that the front bar will "switch on" at less roll, which will match the rear bar better. The rear already has a pretty short arm.

More on chassis + mild aero upgrades to come once the new motor is in place.
 

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Discussion Starter · #53 ·
Embarking on standalone ABS install as well, to be documented here:
 

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Discussion Starter · #54 · (Edited)
Sorry to hear about the engine.

Love seeing this beast out on track!

With all of the track time and the brakes looking like being at proper temperatures, have any additional work been done for brake cooling?

Thanks.
I haven't done anything with brake cooling, hopefully don't have to either. The additional material of the Z51 rotor upgrade proved to be a great performance injection in terms of feel and thermal capability.

That said, with my motor plans underway to 475 rwhp as we speak up from 330, then possibly headed towards 620+ rwhp at some point I am going up in brake size now.

The stateside Essex Parts/AP Racing engineer went for a deep dive into the GTM data and came up with this brake combo to ensure they are stout enough while also not running too cold on either axle.

Rotors
372mm front
355mm rear

Calipers:
AP Racing 9660 front
AP Racing 9661 rear

New master cylinder bore: 0.875 both front and rear
Pads: Ferodo DS 3.12

Those calipers have a lot more natural venting by design, and the sets are lighter than the Corvette brakes.

The master bore increase is calculated to keep the pedal travel and pressure similar to what I have.
 

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Discussion Starter · #55 ·
Front AP Racing 9660, 372mm.

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Rear AP Racing 9661, 355mm. No ebrake drum, considering options. Dry sump tank for LS7 visible in the background.

361981
 

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Discussion Starter · #57 ·
WhT is your plan for your e brake?
Test fit some mechanical ebrake calipers. Viper ebrake said to work for this rotor size but that’s a pricey one.
 

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Thank you, this is a great write up! Do you have any pictures for us of where you mounted your oil cooler in the rear?
 

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Discussion Starter · #59 ·
Thank you, this is a great write up! Do you have any pictures for us of where you mounted your oil cooler in the rear?
Engine oil cooler. Setrab 25 row. This went in during the resto-mod and works very well so far.
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Transaxle cooler and pump. Setrab 19 row cooler. Pump was something I had sitting around. Pumps oil from bottom of transaxle, drops it at the top off the cooler and then it runs back to the transaxle.
362295
 

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Discussion Starter · #60 · (Edited)
G50-20 rear mount wedges. Prevents left/right motion of the drivetrain. Without these, when the gearbox moves due to cornering, the shifter inside the cabin moves left right and right and it even moves when moving the shifter left/right itself. The issues compound to a point where you're not sure what gate you're going into, risking mis-shifts, or even a condition where you just got to not shift and wait for a straight line. This upgrade went in a while back and made a night/day difference both on track and on the road. Perfect precision now.

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