Radiator for Track, M30 E34 or M30 E28

[rob0r]

I've currently got fitted a new M535i radiator fitted in my setup, with twin P38 range rover fans, for normal duties this is working perfectly. Recently I went on a normal Snetterton track day and the car was creeping over the halfway mark up to 3/4, much quicker than I liked and I had to do cool down laps until it got back to halfway.

My car is a prefacelift 320i which lacks holes in the valance and lip spoiler, so the only actual direct airflow to the radiator occurs through the grill. With the E28 radiator that is about 2/3s of the radiator not in direct air flow.

I've also noticed on dual carriageways at 70mph, my car runs slightly cooler with the electric fans on, another indication of poor airflow to the radiator.

I've now holesawed my lower valance to provide airflow through the valance, and I have bought thick plastic sheeting to mould and fit direct air ducting to the radiator as a whole.

I'm also contemplating switching to the E34 M30 3.5 radiator (manual, non air con). This is distinctly shorter than the E28 radiator but is a bit thicker. The idea being that the fans will practically cover the whole radiator rather than partially on the E28 rad. It would also be easier to knock up the plastic ducting.

Though obviously the E34 M30 radiator was good enough for an E34 535i, does it lack cooling capacity in comparison to the much taller E28 M535i radiator?

Which radiator is best for track work? Or are there any other suggestions?

[DanThe]

The E28 rad fills the hole better so I would go with that, use foam tape or rubber to seal the rad to the front panel which will stop air escaping around the rad.
Some fans will slow the airflow through the rad too so this could also be adding to your problem