The airflow path by design for the 718 Cayman is to have the air exit the radiator and go downward through four openings in the bottom of the front bumper. You can see how the support bracket seals up against the top of the radiator.
I wanted more airflow through the radiator and also airflow out the top of the front bumper, hence the GT3 vent. So, I cut out most of the plastic while leaving enough material around the mounting flange locations to maintain strength. I also wanted to cut something with the 3” hole saw I bought for the oil drain modification, so I added three holes to get more airflow. I would say these holes only add an incremental amount of airflow, so maybe we say we got a few grams of weight reduction too.
Here you can see the new airflow path going out the top of the radiator. The back surface of the bracket is a bit offset for the bracket mounting flange plane, so there’s a little bit of space for air to exit the three holes I cut and go up or down to exit the area.
Plenty of space for air to exit out the bottom per the Porsche design intent.
A rectangular plastic bracket snaps to the radiator. This bracket is what an air duct piece snaps into.
I prefilled the radiator with the hoses rotated upwards with 100% distilled water. I also tiled the radiator a bit to help air escape. Why didn’t I use 50/50 mix? Because water ethylene glycol at 50/50 mix has a freezing point of -35C. I’m never going to be driving this car in -35C weather. Even if the mix is only 30% ethylene glycol, the freezing temperature is -14C. Again, I’m not going to be driving this car if it’s -14C outside. Going to a 70/30 mix, water/glycol, improves the specific heat capacity about 10% too for better cooling. It seems the coolant system capacity is in the ballpark of 5 gallons and I only added maybe a quarter gallon to fill the radiator which would have changed the mixture roughly 5%, so I’m in the ballpark of a 55/45 mix. I partially attached the radiator duct to the mating bracket to straighten out the plastic a bit as it got crushed in shipping.
11 comments
What a cool mod!
That’s not punny. You’re going to get punished by being sent to the punintentary.
Cool and rad. Nice article. I think I’ve accepted the fact that I will never be cool enough to understand Porsche life.
Just modding for more cooling for better track reliability like my other cars. Just happens Porsche has more factory parts to use!
Nice! I’m surprised you didn’t just buy the replica or OEM GT4 front bumper! You get the top vent, larger lower vent openings, and a more aggressive front splitter for maybe more front downforce. Plus you wouldn’t have had to hack up the stock front bumper. AFAIK, a GT4 front bump is pretty much a plug and play solution. Can’t wait to see even more progress on this build!
Maybe it’s just me but I would not want to put an aftermarket fiberglass bumper on a Porsche daily driven street car. An OEM GT4 bumper is pretty spendy. This is a nice compromise.
The reason for not doing a GT4 front end is that it would get destroyed around where I live. Lots of steep driveway entries in shopping plazas, gas stations, parking lots, etc. As it is, I scrape the air strake in front of the front tire every time I leave my complex. A couple people have done the full GT4 frontend conversion.
The center vent really looks factory – great job!
Great job and beautifully documented!
Fantastic final result.
It’ll be interesting to compare temperatures with a stock car with common “control” ambients and driving, at a track day.
I 100% agree with the perfect compromise of repurposing the stock bumper, on the grounds of cost and ground clearance. I have a 981 GT4 and conscious of the limited approach angle.
I live in the UK where local town councils instal traffic speed calming with “sleeping policemen”, which I negotiated at an angle and crab over.
Hotels in Europe tend to have underground car parks and on road trips I check if they are ok for low sports cars!
The 997 GT3 vent looks pretty good on the 718. But, why not just use the actual GT4 radiator kit instead of the GTS?
To do the GT4 center radiator right, either have to do the full GT4 front end conversion or make a custom center section to go from the base bumper opening geometry to the GT4 radiator. Neither are easy or low cost options.