I'd call myself a track-day junkie, rather than an actual bike racer. I get around a track certainly fast-enough to go racing if I wanted to, but racing is an expensive "hobby", as I'm sure you're aware. Even half the guys who fill the grid at the national superbike level here in Australia are basically paying their own way. It is suggested that this is what makes Australians so successful at bike racing in the international scene, because we're all so hungry, and many riders are having to compete with inferior machinery in order to prove themselves against the big boys. I digress though.

So yeah, while my bike is little more than a race-bike with lights, it's still stock in terms of the radiator, and I've never had a problem with it overheating. The engine is probably at around 160-165hp at the crank though (1000cc engine), whereas the really tweaked 1000cc race bikes are up around 210hp at the crank, and the international superbikes up around 220hp at the crank.

I've often heard/read about the restrictors thing in high-powered engines, and to be honest I couldn't answer as to why that would be the case. It might even be a function of the water pump? If the pump impeller is spinning too quickly, cavitation may be occurring when there's inadequate back-pressure, resulting in a reduced flow-rate, and adding in some restriction may be the solution to this.

I'd seriously like to stick a flow-rate sensor onto some of these car-engines where it is reported that unrestricted flows leads to overheating. I personally think that something else is occurring, and as above, I think it'd be related to how the pump is behaving.


Back to the world of PC radiators, and the PA160.1.

When you report 3.2gpm, how are you metering the flow? You are aware that pump heat dump is a significant factor at higher flow rates. Up to a certain point extra flow through a radiator does nothing to increase performance, and indeed performance will even plateau. At even higher flow rates the pump will dump even more heat into the system (even if using a restrictor this happens), and this eventually overcomes the tiny performance improvement you got from those higher flow rates. It's not that the radiators start performing worse, it's cos the pump is dumping more heat with the higher flow rate than the benefit you get from the higher flow rate.

When you say you can achieve higher flow rates with multiple radiators, that actually backs up my assumption above. With more radiators, they can deal with the extra pump heat better, and so you can reach even higher flow rates before pump heat starts to overcome the benefits again. Throw on a third or fourth radiator, and the limit will be even higher again.

Reference this thread for a detailed discussion on this effect.

Don't worry about TN. I can handle myself just fine. I think she, and others, get a little overly defensive about their choice and accuse me of criticising their choice when really I've done no such thing. I support their choice if it suits their needs, but I sit in the scientific middle of the whole debate and approach it with a fairly impassionate eye towards what are the real impacts of what's going on, and leave everyone else to squabble over what's important to them. Some just make the mistake of thinking that I have a "side", when really I don't. I've been attacked by both high-flow and low-flow afficiandos in the past, because they don't realise that I really don't have a side, and so both camps like to paint me as suits their prejudice.

As for 12v or 24v pumps in the 8-10gpm mark, your choices are very limited. Best to first identify how much back-pressure we're expecting to operate against at that level, and then we can construct a solution for the problem. It is unlikely that there's a single pump that will do what you want, but a pair of pumps, such as 2 x Iwaki RD30's in parallel would get you pretty close. I'm not really aware of any stronger DC pumps than the RD30's that are easily available to the general consumer.