Coupe 378 - Mod Thread

Somone asked if I had posted a mod thread, and I hadn’t as I avoided mentioning doing anything to my car as long as it was on warranty. No reason not to post now.

I bought my GXP manual transmission coupe (one of 281) on August 20, 2009. That means that my warranty has now expired and I am able to talk about my upgrade process with the car without endangering any coverage, so I thought I’d post a synopsis of my development path on this car. Long and potentially boring, so avoid if tech isn’t your thing.

Background: I have been building road racing and streetable sports cars since 1973 when I took my daily driver, an MGA, off the road and outfitted it for competition use, and bought a trailer. That was about a two year learning curve where I ran a dozen races a season, and in between races I figured out why any part that had broken had failed and fixed it in a way that was intended to prevent that particular DNF mode from recurring. Along the way, I got in a lot of track time and became a smoother and competitive driver, while sorting out my then 15 year old car (which I still own).

I’ve owned between 70 and 80 cars over the intervening years and have probably modified 90% of them to improve performance, so I developed a pretty good sense of what made a difference and what was just window dressing. I also got good enough at wrenching to be able to avoid most potential problems in advance, rather than fixing things after they went wrong (my transplant of a GM 3.4 V6 and T5 gearbox into another 1956 MGA that had a Fiberfab Jamaican body on it, worked so well that it started the first time I turned the key and nothing at all failed to work except the tach which needed an amplifier unit and the speedo, which wasn’t getting a signal from the GM sensor in the trans.

I was driving the 1988 Fiero GT that I had built with a 3.2 stroker motor and a turbo (c. 300 bhp) in the early 90s and was thinking that after 20 years it might be time to move on to something else. I’d joined the Solstice site back in 2007 when the GXP provided enough power to interest me, but at that point the looks of the convertibles didn’t really attract me enough to make me think of buying. Then in the summer of 2009 I happened to drop by the local dealer for something and saw a coupe and fell instantly in lust with them.

I called around and found a dealer that actually had some for sale (they brought about 80 into Canada and maybe a dozen to BC), and the next day went over to look at them. They had a black with no air, a lovely blue (the only one to come to Canada), but an automatic, and a couple of others but only one manual trans with air, a gray car, number 378. I bought it on the spot and made an appointment to pick it up the next Saturday. I was happy to get it and though it wouldn’t have been my first choice for colour, with only 46 manuals coming into the country I took what was available.



Performance improvements:

In the intervening week after ordering the car, I gave myself an intensive course in the technical end of the Solstice, reading four years of posts on a couple of sites to see what did and didn’t work on the cars. Before I had even picked it up, I’d put in an order for the GMPP kit to bump the power. It was installed the week after I received the car, which gave me enough time to appreciate the difference.


I added on a high flow CAT from Solo and an exhaust system (which was another story – the Street Race was much too loud on a coupe – mine was the first coupe they’d sold one for – and I swapped out for a Mach which sounds nice without giving you headaches Good deal available on a Street Race with maybe 200 km. on it!). No added power from the system, but nicer sound. I also stuck in a GMPP intake, not for performance (there isn’t any to be had there either) but to avoid issues with broken tubing elbows on the stock plastic assembly and to clean up the engine bay. I added DDM intercooler tubes and a larger Werks intercooler in preparation for future performance increases (they do nothing with a stock or mildly tuned set up).

I also researched what could be done to safely increase power beyond the GMPP stage. I bought a Trifecta tune after talking to Vince Geglia (he was more readily available in those days). I asked him if he would agree to retune if I swapped turbo units later and he agreed, and said they hadn’t done any Solstices yet with larger turbos but that there should be no problems. The tune went in shortly after I bought the car and the big wheel turbo followed in the Spring of 2010, tuned with maybe five different data logs being exchanged to get it just right. It was now putting out around 26 psi and was an impressive step above the standard Trifecta tune. The exact same set up was getting high 12.9 sec. 1/4s and dynoed at 324 hp/347 Tq at the wheels with another member I corresponded with (obviously dyno readings vary, but that gives an idea of the results). Any other larger/different turbo would have been a red flag if there had been any warranty claims so I opted to stick with this one until warranty ran out.



Handling mods:

Once I got the car, I took it out and started investigating the handling. I found a couple of flaws. The shocks and springs were predictably middle of the road choices calculated not to cause complaints about harshness by people just using their cars to drive to the mall. There was an annoying unsettled period near the apex of a hard corner (most people probably wouldn’t notice unless they corner very hard) where the car seemed to give a little lurch and lose grip. The stock brakes sucked as far as initial grip and stopping distance were concerned. I researched and talked to some of the guys running slalom competition and ordered up the ZOK bars front and rear (for solo competition they often use a stock front, but for street the ZOK front is my preference) as well as a Backbone and Probeam from DDM. All that went in within a month of me getting the car. I also added a complete set of adjustable BC Racing shocks and uprated springs within a short time, which cured the handling issues. I later added a front brace as well for a smaller but worthwhile improvement. We aligned the car a bit aggressively, and for fun I also corner weighted it, although that is something I normally reserve for the race cars.


Other mods:

I was annoyed that the factory brochure showed the twin spoke Q9Y wheels but you couldn’t buy the car with them, an error on the Canadian brochure. An early mod for me was picking up some NOS Q9Y wheels on Ebay. I eventually swapped out brake pads for EBC Reds and am much happier with them. I also added a good on board Radar/Laser detector (the new Passports had just come out and the old model – SRX – was available at around half price on Ebay, new in the box. I also added, quite early, a sonic back up alert, a proximity alarm to deal with the horrid rear visibility of the coupes when backing up.

I had early on bought a plate to obscure that annoying air bag light, and I’d ditched the plastic engine cover for a painted cam cover that actually made it look like you have an engine under the hood instead of a Tupperware collection, but otherwise I had lived with and largely ignored the various interior aspects that were awkward or displeasing – badly placed window switches, tunnel covers you couldn’t lean on without cracking, gauges located at the bottom of dark tunnels that preclude you actually reading them in bright sun and such.

So I’ve driven the car in stock form, with GMPP tune, with Trifecta tune, and with Trifecta retune with big wheel turbo, four stages in all. I’m sure you can guess which way is the only way I’d want to own it! The result is a great combination of performance and economy (once I got over the initial fun factor and started driving without the accelerator always heading for the floor), and the handling is really excellent – I was driving a local winding highway at what felt like about 8/10ths (you can’t see the speedo on a Solstice in bright sun, see above) and looked down while in a patch of shade and saw that I was doing 100 mph in a broad turn without even drawing a comment from my passenger, She-who-must-be-obeyed (and she is quick to ‘comment’ if she feels one is driving too fast!).

There are a lot of mods out there that don’t do much (or anything) for performance, but I stick to things that I get some pay back from and have been very happy – I am now considering one final modification, a larger turbo, but want it to be consistent with a stock engine. Seriously looking at the EFR 6758 for that. And a new set of tires as the stock ones have hardened over the last five years, although with only 8,000 miles on them they haven’t worn much yet!