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Discussion Starter #1 (Edited)
This story starts with a rainy 25 Hour race, a subsequent phone call, a test day, racewins, a championship then two, love for the midengined no compromises rawness and beauty of the GTM, the awe and excitement over it’s inherent potential, and a crying baby at 5am on a Christmas eve that lead to a 6am plunge into GTM ownership.

So a moderately wrecked GTM got loaded onto a truck at a cold winter yard on the East Coast. The truck trundled through New Years Eve on the vast plains of Nebraska, and after clearing the Sierras, #82 finally arrived to a new home in sunny California, parked up next to the most race winning GTM on planet Earth no less. That particular PDG4 offers almost a decade of lessons learned that focus on performance, serviceability and reliability.

Let the good times begin!

RR46 is not new to the world of GTM's I know he has some experience driving one. I met him a couple times and don't exactly why he chose me to fix it, but I always try to give a hand when I can!
Fast fwd appr 6 months: To start off, Richard has done A LOT more than lend a hand on this one! So even though racing, travel and kids have limited my number of days and nights available to go enjoy this GTM rebuild, magically this car is basically only a brake bleed (and zipties to hold harnesses) from a gocart test drive. Result: Chassis is straight as an arrow, majority of the permanent sheet metal is on, racebred coolant system re-engineering is complete and pressure tested, suspension and steering is in place.

20/20 Given the amount of disassembly needed to replace even ever so slightly bent front frame bits that were discovered as we dug deeper, we established that if we would have just cut loose the whole front frame clip from the cockpit and put on a new clip we’d have ended up with fewer welds in total. But having done the full repair work, it actually feels great to know we had full control over the exact symmetry of the car without any tension in the structure. It also gave full insight and hands on feel for the true strength of this chassis design, and how to best fit some of the front end systems.



I played with a three radiator setup Pcar style to have a proper boot in the front - this will be a great upgrade but a future one since I want to drive this car soon and sort out the handling per experience from the PDG4 racecar.

Coolant pipes on the outside is a relatively straightforward mod with major payoff. Fluid volume, cockpit temp management, and less heat transfer to clutch, brake and AC lines are main benefits. Also positioned the radiator more flat to allow a curved lower part of the radiator box, to flow air upwards through the radiator instead of air hitting it in shear. It should be noted that idle water pump flow was excellent and it bled immediately with no trapped air, we just raised the front while filling and running motor warm.

Currently she sits with stock brake calipers and mix of original and borrowed shocks, with 3-way adjustable shocks going on next: The extraordinary laptime improvement we saw from installing Ridetech 3-way adjustable shocks on the PDG4 car made this an easy decision on where to invest. Great shocks on a street/track car aren’t just for speed but also for chassis compliance with varying quality roads with drops, bumps, split crowns in canyons and more. This actually equates to big improvement to relative comfort, safety, predictability and oh yeah speed again because wheels don’t grip when bouncing away from the surface, and going quick in a well setup car is easy.

Also on that note, a stiffly sprung front isn’t great on cars with light noses, so a front swaybar kit is going in along with the shocks to make it possible to drop front rates yet maintain balance and (adjustable) roll stiffness up front. This is needed along with a bump steer kit to have sweet behavior in canyons, on tracks, and freeways.

Once the car rides like a fast flying carpet with agility and the ability to keep each tire in touch and flowing with any surface shape, fine tuning of caster and camber using parts from ”crash” myraceshop.com will make this a fantastic performer, using the GTM racecar PDG4 as a performance reference and inspiration.

Brakes need a comment, these will have to prove themselves incapable of coping with this low weight car before upgrade is considered. Endless fluid is all I use (also for clutch) and with Ferodo track oriented pads there is no weakness left but rotor size, brake cooling or caliper flex left to look for. I will report whether I can hover near the top of Cali laptime charts with these brakes or not. Note: A brake bias adjuster cable is a requirement on ANY non-ABS car in my opinion.

Now onto some photos from the chassis repair.
 

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Discussion Starter #2
Before resorting to cutting out bent pieces from the front clip, we made attempts at straightening them using load straps, chains and a portapress. The chassis design is WAY to strong for that, every bar is supported by another which is supported by another so there's no meaningful movement to be had. Going straight to cutting bent pieces would have saved us a day - good reminder/learning.



Richard lending a hand. Looking at the progress, he's got a lot of hands!!!


Assessing the situation after clearing out bent parts, this is a great moment when you can see straight again so to say.
 

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Discussion Starter #3
Pass side coolant routing mockup. I HIGHLY recommend this mod, if you like me plan to drive your GTM a lot. Driver side looks appr the same.

 

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Thanks for updating us! I'm sure I'm not the only one who is jealous you found that insane bargain! Keep us posted! When are we going to get to buy posters of the PDG GTM with the new livery? Or upload some hi res shots?
I also am running coolant outside the cockpit, but from the water pump down, slightly forward, and to the sides just in front of the firewall. Then made insulated covers where it's in the cockpit along the firewall.
I did dual radiators too, but Dave Fraser pioneered it.







 

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Discussion Starter #5
Thanks for updating us! I'm sure I'm not the only one who is jealous you found that insane bargain! Keep us posted! When are we going to get to buy posters of the PDG GTM with the new livery? Or upload some hi res shots?
I also am running coolant outside the cockpit, but from the water pump down, slightly forward, and to the sides just in front of the firewall. Then made insulated covers where it's in the cockpit along the firewall.
I did dual radiators too, but Dave Fraser pioneered it.







That is a cool way to route - no conflict w seat position? This path might be a good idea for offering more room in front of the heads, For example, still trying to see if it is possible to relo either alternator to the top or set a compact AC compressor in front of one of the heads in order to fit a dry sump pump down below, then one coolant line would need to be moved out of the way.
 

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Discussion Starter #6
Gocart drive(s) done! Loving the open convertible feel on a hot Cali day.

Put a Dewitts radiator in for good measure.
Brandwood shifter cables seem to need a little fine adjustment and rerouting away from hot exhaust, slightly inconsistent resistance on shifting, esp after a bump on the road.

Can’t wait to put in the 3-way shocks, running on three kit shocks and a right front raceshock was still good but not ideal. 😉

The C5 brakes felt very very solid vs expectation and the Supercar 3R tires delivered massive traction both during hard braking and heavy accel.

Very quick car, didn’t expect that with the LS1 and I was already planning for a LS3. Disclaimer don’t know yet what if any headwork or cam swap that has been done to this LS1 but it propels the GTM very swiftly even compared to the racecar. The Kooks exhaust goes from a civilized idle and cruise rumble to a seriously angry scream above 5krpm. Couldn’t ask for more.

Definitely for a street car of this caliber, ensuring it has good suspension travel and excellent shocks is absolutely vital.

Back to the to do list, still a lot left to do.
 

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Discussion Starter #8 (Edited)
Between family, work, racing schedule and travel, 4 months have gone very quickly but finally with Richard’s help I have gotten a little more done.

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Doors are prepped for primer, going on soon after body has been primered.

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Glassfiber prep is dusty work! This blue is growing on me but probably still won’t be the final color for this car.

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That is indeed a bubble wrapped APR wing.
Wheel offsets were too conservative in the rear and required spacers to fit well.
 

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LOVE that coolant routing... I've long wondered why it isn't done that way from the start! If (and hopefully when!) I ever manage to cobble together the funds for a GTM build, that will be the first mod I make! (The second would be glassing the firewall to the body to seal the engine bay from the cabin-- but this thread isn't about my dreams)
 
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