As you may remember, I'm putting an A-12 with a turbo into a Birkin S3 Lotus Seven replica. My question for all you forced induction A-series dudes is: Is a B-210 (120Y) radiator going to be enough to cool this beast with the intercooler in front? The engine has been bored for .040" over A-14 pistons netting a total displacement just shy of 1300cc, if that matters. I will be running a stand alone ECU from Simple Digital Systems so I can tune it to the fat side if necessary. Also I'm thinking about running a heater core external to the cockpit as an additional cooler. Thoughts?

If they're the same as the Aussie models, the 120Y has a slightly larger rad than the 1200, which is a good thing for a normally aspirated A series, and may be OK for a turbo road car (which is not on boost most of the time) depending on your climate, but I imagine it would be marginal.

I'd go for something bigger so that you don't have to worry about the temp climbing on long hard runs - eg a fun drive up a mountain. If the temp starts to climb when you are driving it hard, the likelihood of detonation increases. And that is very bad news for forced induction engines. I'd go for something a bit bigger for the safety margin.

If space is an issue in the nose of the clubman, you can always get a taller core fitted to the 120Y tanks and mount it on an angle.

Scrap the heater core idea, they won't really be capable of flowing enough coolant or dissipating enough heat to really be worthwhile. Plus it will be adding more weight than getting a rad with the same extra capacity, because of the extra mounting requirements, hoses etc.
A mate of mine (who's reknowned for dodginess) used a heater core to help keep his 1200 cool on track days. It still overheated, but you couldn't convince him it didn't work.

Since you are going blowthrough, use the heater core to build a water to air intercooler. These can literally have four times the temprature drop of an air to air job.

Ooh! I hadn't thought about an air to water intercooler. I'll look into that since it will remove the air to air unit from in front of the radiator as well. As for bigger tanks on the 120Y rad, I'm already leaning the stock guy back as far as I can to get it in there. I have priced aluminum radiators from Ron Davis and I think I might just go with that. Along with the air to water intercooler, now that you mention it! Thanks!

A amte of mine, (who builds intercoler for a job) Is buidling himself a water to air for his MR2. He did an experiment where he filled the boost cooler with water. (Stagnant) And got a heat gun and a didgital thermometer. The heat gun was maknig heat around 200c. Then he blew the gun through the core. The post cooler temp was around 20-30c. There are two ways of doing it. It impeads flow and causes a slight boost drop if you have the boost passing through the fins with water going through the cores. But the temp drop is far greater than if you blow the air through the cores, and have a water jacket cooling the fins externally.
Cool air =free horsepower. All these wallys going around in their riced up Sh1tboxes, with massive front mounts, are pulling themselves. Water to air needs more plumbing ,and a bit more weight, but the power gain is well worth it.
I read that for every 17 degrees F that the charge temp drops, you gain like 1% of your horsepower.

We had a look at it last night. the intercooler I have is from a Saab and was probably going to be a tad small anyway. I think I'm going to have it converted by boxing in the fins that used to be open to the airflow and cooling that with the water. I just re-read what you said and I'm basically doing the latter of the two options you describe, the slightly less efficient method. I think it will fit better in my chassis that way.

all thoes dudes with big front mounts dont realise that bigger is not always better if its to big you will have a huge lag problem unless rectifiyed with anti-lag (not efficant for a road car) thats where heaps of ppl go wrong sucked into buying somethin shiny and huge lol

It's worse than that! My aforementioned mate was telling my that knob jockey boy racers come in and buy intercoolers, when their cars are NA!
They're like" orr, I'm gunna turbo it later. But I like how a big frontmount looks"
WHAT F***ING LOSERS!!!!!!!!!!