2.4 or 2.0 Solstice/Sky? A talk with Bill Hahn Jr

2.4 or 2.0 Solstice/Sky? A talk with Bill Hahn Jr

I’ve seen an interesting comparison/recommendation made on social media pages regarding the viability of turbocharging a base model 2.4 Kappa versus selling that base and purchasing a GXP/Redline. I’ve also seen a fair amount of disparagement leveled at the base models in terms of their performance potential. I’d like to add some perspective to this. As via my company, Hahn Racecraft, I’ve worked with both iterations of the vehicle as long as both have been in production, I feel I can bring an expert and objective point of view to the matter.

First let’s examine “upgrading”. We should start with the essential comparison of vehicle value. Using KBB values for both as a uniform basis, we see the following, using standard equipment, average mileage, and the most prevalent condition for these cars of “very good”. Of course, the GXP’s typically come with more goodies, so there were a few “upsell” aspects I added:
2007 Solstice Base: $7860 - $10,829
2007 Solstice GXP: $8227 - $11,282

Now, these numbers may or may not reflect real values, as the market is swinging upwards, and the GXP/Redline models are indeed commanding a premium. So, for the sake of a comparison based in actuality, let’s call the essential difference in value somewhere between $1K and $2K. We must also consider the effort and cost of selling the existing car, as that has value, as well as sales tax/licensing/title on the new sale. As most tax values are about 7%, these costs will add approximately $1200 to the purchase. Also of note is that some insurance companies will charge a premium for the performance model. Another aspect of great interest here is that the GXP/RL is much more likely to have been driven hard, as that’s its nature, whereas the base is much more likely to have led a sedate life. This can have a huge bearing on the cost of future repairs, especially as old as these cars are by now…that’s a lot of years of hard use, and a lot of things to go wrong on cars of this “vintage”. Certainly, there are other aspects of GXP/RL which are of note, insofar as suspension and options, but to be quite honest, the differences between the cars other than engine are slight, primarily because the base Solstice/Sky was already a pretty sporting proposition to begin with.

So what are we really working with, not counting the time spent, as well as the inherent risk in buying an unknown entity versus sticking with your known car?  For the sake of our comparison, I am placing the cost to upgrade from base to GXP, IF all goes well, at $2500 - $3500. Results will obviously vary, but in terms of establishing a baseline, I feel this is a valid and objective comparison.

So we can now move to the respective performance potential and costs of each. I am going to use my company’s turbocharging products for each in this comparo. If we consider the baseline of the GXP/Redline as 260 HP, and the result of a turbocharged base 2.4 as the same, it’s a dead heat, and the GXP/RL is at this point leading the way in terms of cost, as it will cost a base owner approximately $3500-$4500 to add similar power to their car. But as we can see, the cost margin enjoyed by the GXP/RL is slight. There is, however, much more to this story.

The turbocharging system we sell for 2.4 base is, as it comes, capable of up to 500 HP. It consists of a Precision turbocharger and very tunable Precision external wastegate, massive upgrades over the rather limited and not-very durable KO4 on GXP/RL. That K04 also won’t provide much more than about 350 HP, at least not if one wants it to last for any period of time. KO4 is also limited by its internal wastegate and bypass valve, which are rather small and concessions to OEM cost savings. Our 2.4 Base system also includes an external blow-off valve, and amply sized piping/air intake in 2.5” and 3” sizes. It also comes standard with an intercooler that will absolutely smoke the stock GXP/RL unit. So while the essential comparison of turbocharged 2.4 base vs. GXP/RL shows the GXP/RL marginally ahead in cost, the same can’t be said for value or capability.

Now wait a minute, you may be saying. That stock 2.4 engine can’t take what the GXP/RL can. Well, you’re kind of right…at least, in certain years. GXP/RL engines, if modded with external upgrades, can dependably deliver up to 400 WHP and still return decent engine longevity. The base engine in 2.4 from mid-2007 on will safely contain 300 WHP. But there’s an outlier: the 2006-mid 2007 2.4’s will go well past that thanks to forged connecting rods which preceded the later version’s powdered-metal rods. To that end, we established the veracity of the early 2.4 engine over a decade ago, routinely taking them to 400 WHP and carding 11-second timeslips at the dragstrip, using the bone-stock engine and our off-the-shelf Hahn RaceCraft turbosystem.

So, now we can see that a 2006-mid 2007 base 2.4 with our turbosystem can actually run and hide from a GXP/RL. But that’s not a fair comparison, is it? After all the 2.4 base with our turbosystem has all the excellent advantages noted above, in better turbo, wastegate, blow-off valve, intake, charge air piping and intercooler, right? Now you’re starting to see the whole picture. Let’s even things back up.

So make it fair again. Take that GXP/RL. Add our Precision Turbo upgrade, charge air piping, external blow off valve, the intake of your choice, a bigger intercooler, and the tune needed to support it all. Add it all up, and now we must add about $4000 dollars in parts alone to have a comparable system as the lowly base with our turbosystem added. Don’t forget to add labor unless you’re going to put it all on yourself. Suddenly, the price comparison is getting rather skewed.

To this end, across several car lines we have for some time offered turbosystems for base models as well as upgrades for factory turbo equivalents. In every case, the above conditions were in play, and by the time the factory turbo owner ditched all the rather limited OEM turbo parts for our upgrades, he/she had essentially purchased two complete turbosystems, except one (the OEM one) was laying in pieces under the bench in the garage. So we’d coyly (but seriously) quip: Why buy two complete turbosystems just to chuck one? Buy the base and add the turbo components you wanted in the FIRST place!

Now, there are a couple more important details. The GXP/RL uses direct injection, which is by any analysis AWESOME. It is full of failsafes and capabilities that were unprecedented upon its debut, and as someone who’d already been turbocharging vehicles for decades when it came out, I was dazzled at what a quantum leap forward it was. But with that sophistication comes a cost. Upgrading it is limited and expensive as compared to the more conventional port fuel injection (PFI) base 2.4. DFI is also more complicated to diagnose and repair when things go south, whereas the 2.4’s well-established and understood tech is a breeze in comparison. PFI as on 2.4 is also easier to tune and modify; there is just exponentially more knowledge and parts available to support PFI.

Last, but not least is the difference in displacement, which is actually quite substantial, and the old maxim holds true: there’s no substitute for cubic inches. 2.4 is a full 20% larger than 2.0 GXP/RL, equivalent in V8 parlance to the difference between a 350 and a 427 (for you old school folks!). That’s a lot more torque, and more power per pound of boost, as well as a faster spooling turbo due to the displacement advantage. To that end, the diminutive K04 when installed on 2.4 is actually too responsive and will even make undesired boost pressure at cruising speeds. It’s that much of an engine displacement difference.

2.4 is a fine pedigreed engine, and for a “base”, it’s actually pretty high-tech, more so than the base engines in many other cars. As it comes, in addition to its VVT and decent normally-aspirated power output, it also boasts coated piston skirts, oil cooling jets under the pistons, floating wrist pins and beefy pistons, just like its 2.0 LNF stablemate. It is most suitable for performance increases as a result. We’ve torn them down and scrutinized them after years of severe turbocharged abuse, and seen nothing of concern inside insofar as wear or damage.

Now all you base folks, I just wanted you to get some respect. Your engine, and your car, is VERY viable. I’m only trying to make that evident. You GXL/RL people, man I love you too, and I have all kinds of goodies for you as well. It’s just that I’ve seen the base 2.4’s getting, well – bullied a bit online of late, and I saw the need for some equal time.

Thanks for your time, and if you’d like to discuss any of these points with me, have at. Let’s just save everyone the time of nitpicking; this is intended to be an overview comparison and clarification, not an exhaustively detailed treatise. Have at. I’m not shy, and I’m here to help!

- Bill Hahn Jr.
Hahn RaceCraft, Inc.

Pictured is our 2006 base 2.4 Solstice, a 400 WHP, 11-second ¼ mile performer!


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