My temps were getting a little out of control in 90+ degree weather after 15 min of hard laps. I already have dual R1 coolers. If I could only choose one, would a bumper upgrade (like a GT-C) or a oil cooler upgrade (sakebomb coolers) help more in this case?

 

Sakebomb coolers + 99 Spec front end... lookup username: thewird

 

Do the coolers first, and DUCT THEM WELL (sealed).

 

I'm running the 99 spec front bumper (much larger openings than 93) along with R-Magic ducts (which seal very well) and have had zero oil cooling issues on track. I'm running my original R1 oil coolers that were re-furbed about three years ago.

When/If I exceed the limits of the R1 coolers, I plan to call up my buddy Peppy Lopez and order a Sakebomb kit pronto

 

The water temps on a stock FD get out of control very fast even when running around in the country on a hot day so for track use it's a must to open up the front bumper by either cutting up the bumper or using the shark tooth mod and then installing custom ducting on either side of the bottom undertray and making sure the rear flap on the undertray is pressed against the bottom of the radiator and making a good seal. Rarely will the seal on the undertray still be working unless the undertray is fairly new so you'll have to get some hvac type insulation and stuff it in between the radiator and the undertray.

Upgrading the oil coolers will help a little bit if they are properly ducted but if you remove the stock coolers and ducts and put in massive coolers but don't duct them you'll have worse problems.

For best results I'd recommend the GTC front bumper and have a professional fab/race shop put in ducting for both the radiator and the oil coolers. Dual stock oil coolers have been proven to work fine the problem is the twin turbos heating up the water and the radiator being suffucated with a small opening, poor factory ducting and the AC condenser sitting in front of it.

 

I agree with Fritz. Simply put, proper airflow will solve most cooling issues.