Photography by Chris Tropea
Is it really possible to do it all with one car?
We’ve asked that question in every update about our daily-driven Mk7 VW GTI, and the answer has always been yes… with an asterisk.
What’s the catch? After multiple hot laps on track, the car loses power. It doesn’t enter limp mode, light a CEL or misbehave, but lap times slow and the throttle does less as the car gets warmer.
We’ve experimented with 100-octane race fuel to find slight improvements, but the writing has been on the wall since our first track day: Our GTI needs a bigger, better intercooler. So let’s give it one.
Why do we need an intercooler in the first place? Our GTI is fast thanks to its turbocharger, which compresses air to force more of it into the engine.
But air gets warmer when its compressed, sapping power. That’s why most modern turbocharged engines have an intercooler. In theory, this heat exchanger keeps the pressure but removes the heat, generating the holy grail: Cool, compressed air for the intake.
So what’s wrong with the factory intercooler on our GTI? Well, OEM intercoolers are usually sized for street driving, meaning a priority is placed on throttle response, so the ideal use case is closer to a spirited drive on a twisty road than it is to back-to-back laps on track.
An oversized intercooler can make the car worse on the street, increasing turbo lag. Plus it’s heavier, more expensive to build and potentially less aerodynamic. So it’s no surprise that the GTI’s intercooler was undersized for our use.
Could we have solved our problem by passing more airflow over the factory intercooler? Probably, but that would have gone against this project’s goal: We weren’t about to remove the a/c condenser, cut holes in the hood, or hack up the bumper on our daily driver.
Instead, we ordered an upgraded intercooler from 034Motorsport. At $850 this is pricier than universal options found on eBay, but promised an easy installation with zero zip ties and zero compromises.
034Motorsport intercooler on the left, our VW's OEM intercooler on the right.
034 Motorsport claims a 63% increase in volume vs. the factory part, plus higher efficiency and less pressure drop. It also has all of the little factory nubs/clips/tabs/etc. to make it a drop-in replacement that mounts with all of the factory hardware. It’s also completely invisible when installed, hiding neatly behind the a/c condenser.
Intercooler in hand, we threw the GTI up on the lift and went to work. This is a big project, but we were once again surprised by how easy the GTI is to work on.
As the pile of bolts on the bench grew, our car lost its grille, front bumper, headlights, a/c condenser, core support, and finally its factory intercooler.
VW helpfully left enough slack in the a/c hoses for us to leave the condenser dangling, which meant we didn’t have to open the system or replace the refrigerant.
Then we had to do the only irreversible part of the installation: Some minor trimming to the plastic core support, which amounted to basically squaring off the opening to make room for the larger intercooler. Then the pile of hardware began shrinking, and after a few hours we had a running, driving GTI again.
But had we fixed the car’s heat management issues? To find out, we went back to our official test track, the Florida International Rally & Motorsport Park, on a sweltering 85-degree Florida day.
Normally, the car would slow after about two laps at pace. But with the new intercooler, the GTI behaved like a completely different car. Throttle response was unchanged, with lap two passed at full speed. As did laps three and four before the street tires began to overheat around our fifth lap and we backed off.
In short: We fixed the problem, and there was now lower-hanging fruit preventing our GTI from a future in endurance racing. Success!
I always assumed bigger intercoolers were for more power. It never occurred to me that they would improve heat management. As a matter of a fact, I'd have thought just the opposite. More air means more squish/bang and more heat. This means I can call the bigger intercooler on my supercharged C230 Kompressor a reliability upgrade. This is interesting. Thank you.
In reply to Olsenkj06 :
It's not the engine coolant temp that goes up and causes problems, it's the intercooler heatsoaking so intake temps go up. This means the ECU pulls timing to prevent detonation.
On the Mazdaspeed Miata, we'd see a considerable drop in power when doing 3 back-to-back dyno runs with the stock IC because the air intake temp kept climbing. Put in a bigger intercooler and it would stay consistent run after run.
There's a trade, though, right? On another forum, a powertrain engineer said that you lose responsiveness when you go with a big, high-volume intercooler.
Certainly if it's on a supercharger and the IC is throttled volume. On a turbo...it's harder to make that claim. It WILL make it harder for the engine to cool itself, as it'll do a better job of preheating the air going through the radiator.
On these cars, you can make power in two ways: lots of timing or lots of boost.
Boost will make more power. Most off the shelf tunes are like this (catered to street), with only one company that is pretty well known for having crazy timing with minimal boost. It's also a bit "safer" [adding boost instead of timing] generally speaking if not pushing the knock thresholds.
I personally prefer getting more aggressive (but not on the ragged edge) with timing, and dialing back the boost a bit will run cooler in sustained heat (track) situations.
The ECU has tables that compensate for higher IATs and reduce timing as necessary. There is no such table for boost based on temps*. Timing will still get pulled to avoid knock based on IATs, but trying to cram 29psi peak tapered to 21psi on an overspun IS20 turbo near redline will continue generating a TON of heat, and retarding the ignition to avoid knock actually makes temps HOTTER because you're delaying the combustion event, and it'll be more inefficient making more heat in the cylinder. I run 25psi tapered to 17 on my GTI, even with a high flow downpipe. It's "weaker" than most stage 1 tunes. I'll see about 6-7 deg of timing on track near redline when it's 70F outside with IATs within 20-25F of ambient.
Y axis is degrees Celsius for IAT, X axis is RPM. Table is degrees of spark timing removed based off temp and RPM. Stock logic actually ADDs more timing in really low temperatures for reference.
Stock for my .bin for reference:
*In the STOCK ECU logic, there are MANY tables for torque reduction. Two of which include turbocharger speed turbocharger outlet temp - both of which are MODELED without real sensors... so as a result when you tune the car for more power, these things need pushed out of the way. Without doing so, you can't make more power (or at least nowhere near what any stage 1 tune makes). There's not anything inherently wrong with that, but when you're pushing these cars to the ragged edge on track with a street tune, you need to help them in any way possible via lowering IATs. Torque reduction is accomplished in the stock ECU by lowering boost in most cases, and in severe cases by closing the throttle body.
Adding an intercooler *might* make more heat in the cooling system, likely due to more restricted airflow or the more efficient removal of heat from the intake charge air (with that hot air going back directly into the radiator, lowering the delta-T), but most people do an IC + tune at the same time so it's hard to get truly good data.
https://www.datadrivenmqb.com/drivetrain/coolingdata
By and large the GTI has a MUCH easier time dealing with heat than the larger turbo IS38 equipped Golf R.
Upgrading the cooling in general is a good idea for a car used on track, radiator, oil cooling, intercooler, brakes.
I would never have thought to consider an intercooler anything but a reliability upgrade. The most powerful forced induction spark ignition engines in the world are not intercooled, after all.
Throttle response should not be affected much by I/C volume, unless you have a crazy blowoff valve that throws away all of your boost between shifts. The larger concern with big intercoolers is pumping loss due to internal drag.
034 did some tests on intercooler core design and core layout and they are pretty enlightening. As for layout, generally speaking a long core forces all of the air through a small amount of tubes, for higher pressure drop. Higher pressure drop means you have to run the turbo harder for the same manifold pressure, so you have more exhaust manifold pressure, which means more hot exhaust residuals in the chamber during the next go-round and more likely to have detonation.
A wide core forces all of the air through more tubes, for less pressure drop, but the downside is they are more difficult to package for a given core area because the tanks are necessarily larger. Also more expensive due to core design.
Those airflow rules sound a lot like how you design a water radiator as well :) More shorter tubes and the fin density in between becomes very important. Thickness is less important.
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