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The reason I asked is because all of the Gen II GTMs that we've built here with the factory FFR fiberglass vent inserts installed have all run pretty hot.....
 

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Discussion Starter · #22 · (Edited)
I’ve heard that’s the case. The outside coolant pipe routing adds a lot of volume and also dissipates heat in a relatively open environment vs the tunnel and may be part of the solution. Also I have the Setrab 25-row oil cooler. Will report back when temps hit 90-100 in the summer.
 

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Discussion Starter · #23 ·
Man I love this car, how it drives, Rock steady. Great dampers are truly key for uneven roads. And for those who didn’t already know this, the Kooks exhaust note is nothing short of glorious. I return home only thinking about when I will get a chance to go for another drive.

Lots of little stuff to do though for comfort, sealing little gaps, adding sound deadening in the right places, then splitter, diffuser and more camber for track duty. Lovely project. And she’s still in primer.

357322
 

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Discussion Starter · #24 ·
Shane, I forgot to mention on more thing: I have placed my radiator more flat (rear is higher than original position by ~2.5" and I have a curved aluminim guide seamlesly connecting from the bottom front of the radiator box to the back / bottom of the radiator in a nice wide curve shape.

The (unproven) theory I have is that the airflow now gets curved up and through the radiator as a flow, rather than hitting the radiator in shear and possible stalling in the back of the radiator box with potential aero chaos and pressure build up.. If there's resistance in the box it can of course go through the radiator however it has to fight new air coming in as well, basically just adding a more pressurized zone that in turn would make some air choose a path other than the grille inlet instead of into the grille.

If this theory is correct it'd mean there is more air flowing into the grille and up through the radiator and no stalled air or pressure build up except the resistance of the radiator fins. I imagined trying to flow water at high rate through the grille and out the hood to come up with something that'd make the best flow with least resistance, but CFD simulation would prove this right or totally wrong. Anyway, as mentioned before I will follow up when the summer comes around.
 

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Discussion Starter · #26 · (Edited)
359626


Long since I posted, and actively worked on the car apart from a few things:
Polycarbonate hatch "glass" - quick and dirty, too wavy so will do again
Headlight covers
Z51 brake rotor upgrade.
Borg lower control arm offset bushings (for more negative camber at the front).
Camera based rear view mirror
All LED lights incl DRL/turn indicators
Adjustable rear diffuser rods, the original angle is too step to generate good downforce/low drag

The big step came today though. Sacramento did decide that the car has to visit the BAR for a thorough smog exemption process (called SB100 in CA). After a lot of paperwork collection and virtual meetings and calls with the BAR, I finally got invited to an in person vehicle inspection. I can't thank Jack (cob427sc) enough, he originally built this GTM and helped provide testimonial of assembly and references to the yards that sold him the donor parts. Without the build history it would likely not have been possible to complete the CA registration. Today's lunch appointment at the BAR was supposed to be the last step but they took photos, checked that the car matched the paperwork from the virtual meetings. Then said "Now a manager has to review it. He'll call in a few days, and if not then you have to call us back."

Oh no another go around.... but believe it or not they called me only 2 hours later and said it's been approved. Great stuff. I still have to return for the actual label to get affixed in the engine bay but that should be it. A good excuse for another drive and the station is very close to my house.

With just below 100 degrees outside the cooling system seems fine, stays at 175-180 all the time. Got to sit at a few stop lights and it doesn't seem to cause any issues. I do need to properly pull vacuum and fill the AC though, only put a pressurized can on it when I reassembled the car and that seems to have proved it's leak free but it's (OBVIOUSLY) not as effective as it should be. Easy job on the To Do list.

Next up is side skirts, front splitter, some kind of door handles. I DO NOT LIKE POPPERS, to me it's a HUGE nuisance at a track day to have to go dig in the pocket for the remote every time I want to open a door, or if the window is open lean in and drag on the inside door handle. I want a proper way to grab and open the door. It's the first interaction with the car before you drive. It should feel solid. Maybe a cutout under the hips shape of the door and a push button that I can kill with a remote to lock the car. Also have a couple of low mileage 997 handles that feel superb but not sure how they'd look on the door. Also inside I want to switch to the interior door handles of a 997, or just the GT3 RS type straps. The semi flexing interior Corvette handles just don't do the solid driving characteristics justice. You can't have a rock solid car when driving and then when you touch it to get out, or get in, it's flimsy or annoying.

The car is performing very well. It is nice to work on comfort items for a bit, and it's soon time to get help to fix the body gaps and get it painted.

I worked out the engine items I discovered at the shakedown. It had a bad tune with torque limiter that depowered the car in every gear, and the coolant temp sensor wire was grounding to the block intermittently telling the motor sometimes it was at 278 deg F, which pulled crazy timing and made it run weak. With those items solved the car gained around 125hp on the dyno, feels quick, and the Kooks exhaust sounds absolutely glorious. Absolutely glorious! It made 330 rwhp on 91 pump gas which is nice and easy to drive with. Bone stock LS1 with the LS6 manifold and Kooks. I do have a 555rwhp LS7 ready to drop in sometime, but probably won't be until this fall or winter after enjoying the car this summer.

Loving this car more and more the less I need to do hard work on it, and the more I can just drive and play with it.
 

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Discussion Starter · #27 ·
I had more oppo in 95 deg temp to push the cooling system in day to day driving conditions. Already confirmed it to be great at the track. Did 2x40 min drive with a 25min stop and some parking movement inbetween, drives had lots of stop lights, idling, low speed. After that I just let it idle for 20 min. Needle lands at 191. Fans kick in, cools it, fans turn off. Then takes 1-3 minutes before fan kicks in again. Repeat. If it was 105 I don’t think it’s going to be much different. Plus cockpit doesn’t need much AC to stay cool. Bottom line; rear mount reservoir and outboard coolant pipes work just as great on a street car as a racecar.
 

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Discussion Starter · #28 ·
Installed the QRP swaybar kit today. Had to run it in fwd position bc the coolant side pipe solution takes up the spot the bar normally go into. Driving notes below.

359702
 

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Discussion Starter · #29 ·
I was debating w myself whether to install the swaybar or not. Balance was absolutely perfect on my track shakedown so adding front bar generally induces push which will require a rear bar or spring rate change. So why add weight, work, to create more work? The answer is, pictures! There was a lot of body roll visible from my track shakedown. And a lot of uneven tirewear from not enough camber combined with excessive bodyroll. Springs are hardcore already. So bar on to reduce roll (or sway).

Results: Insanely good steering response. Super 7 meets racecar. On top of that a more composed ride on uneven roads. The coupling of left/right took down bump steer by 70-80%, the steering wheel doesn’t jog left rig left right anxiously along some of the vineyards. I can just drive and hold it lightly on really uneven roads, before I had to keep the car actively from the ditch or oncoming unless the road was pretty smooth. Game changer. In regards to comfort, bumps that used to feel like extremely harsh impacts are now feeling a bit rounded, this is a known swaybar effect in OEM car development when it comes to ride tuning.

359703
 

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Discussion Starter · #30 · (Edited)
Still not painted but added splitter, and put on APR C7 wing stands that are slanted rearwards more. This generally results in less drag, better overall downforce. Did a number of under the body jobs too incl Z51 caliper brackets and rotors. Adds rotating mass but more rotor material is the wise choice since I have a cammed LS7 ready to drop in this winter, adding appr 200 rwhp. Looking forward to take it to another track day soon.
360208


Here's a clip of the LS7 I got that's going to get a new intake, stronger cam. Motor came out of this SLC.
 

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Discussion Starter · #32 · (Edited)
Hey Taz, hopefully can get something with enough quality, like a 100ft distance shot when on track, since it's not painted.

Important (to me) GTM update: Installed a rear swaybar using 2 welded tabs/mounts on the rear frame, and by placing the bushings at the exact same spread as on a C5 made it possible to source any rear bar that fits a C5. This lets me rely on existing data for those bars when calculating overall wheel rates. I found that Hotchkis adjustable rear C5 bar offers the most suitable one for a GTM that has been fitted with QRPs front swaybar kit.

Having bars on each axle is inexpensive and makes the car much better on a track day without the need for super stiff springs, so you can retain some of the street manners. You can also keep more moderate camber settings that are also suitable for the street and less tire wear.

I also added Stance Aircups on the front axle, to be able to have a great performing and nice looking low rideheight while keeping the FFR carbon fiber splitter. The cups raise the car by appr 2" and makes it possible to deal with steep driveways and speedbumps. Stance's 110mm diameter cups work well with most coilovers and springs. In my case with Ridetech 3-way adjustable shocks and Swift Springs which are proven on the PDG4 racecar to be very hard to beat and extremely durable.

To minimize weight I went for the Stance tankless system. This means it takes about ~5 seconds for the air compressor to lift the nose fully. If you opt for a tank, it will contain pre-pressurized air and your car basically snaps up almost instantly (as fast as your rebound settings allow). I located the compressor low behind the steering rack, more or less side by side with the Vintage Air unit.

The ability to lift the nose 2" is a huge benefit. 2" lift at the coilover translates to a bit more out at the splitter. Also, the Stance aircups when deflated are nothing but 2 metal discs with no air in between them = effectively this is your new spring perch. This makes them suitable for track use as opposed to many types of kits for car shows such as airbags, some airsprings, hydralic lifters etc.

More work was done and the car is pretty much ready to hit the track again. Will post when I have more photos.

The photo shows the nose in raised position. Controlled by a flick switch on the dashboard.

360621
 

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Ive been looking for a lift system for my GTM. This one looks awesome! Thanks for sharing. I really like the looks of this one and glad to know you have verified fitment and operation on a GTM. Thanks for sharing the info.
 

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Discussion Starter · #34 ·
ChevyChad, I'll grab some photos as soon as I have a chance.

Shocks need to have the shock body up, piston down. The cups fit upside down near the bottom/lower A arm, there is plenty of room. Trying to fit them around the upper A-arm won't work, the space is a little tight.

For you to be able to utilize the full lift, the shocks themselves need to have at least 2” droop available from standing at rideheight. It is easy to check your droop by lifting up the front up with a floor jack and measure the gap between the tire and fender when the shock is fully extended and compare to the gap when the car is standing. If the difference is 2" or more you'll get the full value/lift out of the aircups.
 

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Shocks need to have the shock body up, piston down.
That is a problem with the black Koni shocks. They can not be mounted piston-down....they won't work that way. The yellow Koni's will run fine that way, but not the black ones.
 

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Thanks for the heads-up, Shane. I have the black Koni's on mine still. My car only has 2,600 miles on it, but it was originally built in 2008 and it was a dedicated race car while it was in Malaysia for a few years. May be time to upgrade shocks and springs.

@RR46 can you give some more specific info about which shocks and springs you are using? I know you said ridetech & swift, but can you be more specific with part numbers, or even links would be better! If not, maybe the required info such as shock length & mounting style and spring rate, length, diameter so that I can find the right parts?
 

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RR46, your car looks sweet! It looks pretty darn good even unpainted.

Can you show us a little more on the cup ride adjuster install and also the front sway bar?

Thanks!
 

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Discussion Starter · #38 · (Edited)
360705


Right front photo with Stance Aircup in upside down position. Note: A maintenance item to blow it clean in case any dust or debris gets in there after a trackday.

This is the link to the Ridetech TQ triple adjustable shocks (note: the preview says single adjustable but click and it goes to the triple):

The ear style mount is a direct bolt-on fit that requires no mods or fabrication
5.2” length is what we use on the racecar, suitable for low rideheight cars and track dedicated cars.
I chose 6.3” since it offers more wheel travel, good for street car, uneven and undulated roads, canyon roads etc. For the rear I actually had to use drop belts to limit excessive droop so maybe 5.2" would have been ok for the street too but I will rather have long vs short travel on the road, and the 6.2" still can compress to the shortest possible length I calculated I would ever need.

The springs are 60mm inner diam from Swift, both for main and helper springs. We use 65mm on the racecar but 60mm works better on a GTM with the standard kit rear axle CV boot diameter, and clears the front upper A-arm better at max droop. Link:
Metric Coilover Springs | Swift Springs USA
Click the ID 60mm tab for selection. More about length and rates below.

Helper springs:
Click the Helper Springs tab for selection.
Choices are few here: 1.5kg front and 3.0kg rear fits the GTM (they stay compressed most of the time and provides good force on the inside wheels while cornering hard). For a heavier GTM such as an endurance racecar with big fuel load, stout rollcage structure, airjacks, ballast awarded for being too fast :) you can go to the Assist Springs instead of Helper Springs and pick out 4kg front and 6kg rear. There is more to helper spring selection that has to do with unspring weight but let's not go too crazy.

For main springs: 8" length springs are a good ballpark without air cups but DO YOU OWN MEASUREMENTS AND MATH based on your desired resting rideheight. With aircups and helper springs I went for 7" mains for my car. It seems to have ended up ok with a bit more than 1" left of threads on the shock body.

When it comes to main spring rates, this is definitely a matter of preference, expectations and use case choice. You can get the car well balanced whether you go with a soft setup, firm setup, or race setup. Softer is enjoyable to cruise but obviously becomes more sketchy as you increase speeds. Firm is great for track days but too firm can become detached from the road if you are driving on bad roads. In between you might not be happy with either cruising or track days so pick wisely. Of course, the better the shock is the more it can help increase usability for most reasonable springs except really hard ones.

When choosing rates, it is important to understand how spring rates translate to wheel rates. The location and angle of the shock changes how the spring truly performs when installed. Once you have your wheel rates, you can calculate wheel frequencies and use those as metrics to understand how firm your car is, as well as determine the spring combo's effect on the overall mechanical balance of the car.

I opted for track bias but definitely not hardcore racing: 6kg front, 12kg rear. This is intended to be very agile when using 305 wide front tires and 325 rear tires. The actual wheel rates end up much less and this is where the swaybars step in and nearly double the wheel rates when cornering to make the car more racey and responsive. The good thing with swaybars is that they don't add any ride harshness when riding straight down a highway or around town. Having adjustable settings on at least one of the bars allow for final tuning of the balance; the needs for more or less oversteer/understeer can change depending on the specific track for example, or when changing tire combo (for example from 305/325 to 305/345 or 285/325).

Photo of the right side rear drop belt setup below, to limit excessive droop. Belt length is adjustable. Here you also see the end of the rear C5 Hotchkis adjustable swaybar (anti-roll bar).

360704
 

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RR46, I was really hoping you would say the sway bar didn't really make any difference in steering feel and handling. Reading your post totally changed my mind and now I need one.

Sway bar on order. Thanks a lot. 😆
 
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