Just added a second oil cooler...
 

Finally bit the bullet and decided to add a second oil cooler (in parallel, not in series).
Temps are not a problem even on hot days going hard on the open road.
But... on a monthly rally day dirt circuit in summer, by the end of 4 or 5 hard laps, the oil and water temps start to get very ugly.
Effectively the engine is at or near the redline in third for the entire run, and even on the short straights will "flair" up to redline in fourth due to wheel spin... so actual road speed is not super high.
I've maxed out the (realistic) cooling options on this build, with a PWR radiator, Spal fans, and cut through side garnish (does not do very much...) along with a HKS unit (with fan) mounted in place of the fog light area on right hand side...venting into the wheel well.
I dont want to draw attention to the car, so hood vents are not an option for me...and the car has a large alloy sump guard, so there is limited scope for venting the engine bay from below.
So went down the Harrop path, primarily because the cooler vents directly out beneath the car and has a minimal impact on the existing cooling packs.
My initial concern was the aftermarket sump guard, but it actually fits beautifuly.
Its mounted, but waiting on a Greddy sandwich adaptor
to replace the HKS unit, which will allow running two coolers in parallel.
I will also be fitting 3 x 80mm fans units, blowing through from the top ,but fitting inside the alloy air "scoop".
And I'm making a mesh screen to protect its underside.

What made you add a second unit instead of just getting a larger cooler? Does your other oil cooler have a fan? Is your radiator fully ducted? Would an even larger radiator be of interest to you?

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Yeah, first oil cooler has open air inlet, fan and venting. Headers are fully wrapped.
Increasing size of oil cooler creates mounting position issues, as opposed to additional oil cooler allows flexibilty of positioning.
PWR water radiator is already a significant upgrade over standard radiator, and Spal fans are largest/strongest that I can physically fit.
A physically larger radiator also starts to create extra packaging/intake/venting stresses that are expensive to solve...and begin to impact on the external appearance of the car (which I would prefer to avoid).
Radiator is not fully ducted and also has supercharger intercooler and aircon packs.
Main problem is the specific use that causes the temp issues is consistent high revs with low road speeds (ie. lower than ideal airflow), with a supercharger running at max (pulley) capacity, on E85.

Can you expand on how a larger radiator core requires expanded venting and packaging requirements?

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Wider or deeper core would take some serious effort/money to make fit .
The existing apurture would need to to be changed/enlarged and the extra airflow in would need to exit...and I dont want to add hood vents.
If you mean a thicker core, then this PWR core is already a thicker (and much more efficient) core than standard (and most other aftermarket radiators)...and I am at maximum (realistic ) fan capacity to draw air through, and vent.
All in all, an additional oil cooler that doesnt vent into the engine bay is an easier and cheaper solution.

Is buying a second hood and swapping for events an option?

I wasn't trying to suggest that your route was inappropriate. This has simply caught my attention because I developed a double pass radiator intended for LS swaps, but it will fit the FA20 application as well, with different hoses of course. It will be on the market early next year if you find yourself needing even more cooling. It fits the stock radiator location and is the largest/greatest cooling capacity radiator on the market for the twins

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That sounds really clever and interesting, I’ll keep an eye out for it!
Do you have any installed pics yet?
Most of my cooling issues are a result of stubborn self inflicted compromises.

That’s a great idea, I hadn’t considered that! That could end up as an option if I’m still sailing too close to the edge after this mod.
(But I’m also a lazy bugger… so any extra and repeating work causes severe emotional trauma 😂)

I do not. I should soon though. I have a slightly different version installed on my car currently. PM me and I'll get some to you when my partner gets his installed

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So much of that location looks scary, But if it works.

Actually its not as bad as the photo makes it look, the lowest point of the cooler is probably still about 8-10cm above the base of the sumpguard.... and about 5cm above the (scrapped) lower front lip.
The plastics surrounding the cooler are clear of any witness marks from before the install (unlike the lower front lip which looks like its been attacked with a grinder!)
I'm about to put a mesh guard over the cooler to protect against road debris, and the other bonus is the plastic panel it is mounted in can actually deflect upwards to a fair degree if it does struck something solid.
But yep... I'll be interested to see how it goes too!

Probably a good idea to add a little WRX hood(style) scoop over it. The A&A Corvette supercharger intercoolers are mounted like this and they claim it only works using a scoop

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Do you have a picture from inside the grill? Just curious.