Some months ago in Fan-Forcing Your Intercooler, Part 1 we covered the fitting of an intercooler fan – a device that forces air through the intercooler either when it is getting over-heated or when the car is moving slowly and so there is little outside air being pushed through it. It’s an especially effective approach for underbonnet intercoolers.

Making that particular design even better was the use of a very powerful centrifugal blower. The blower – salvaged from the tip – was a VW/Audi cabin ventilation fan from a Kombi. And it sure moved a helluva lot of air!

Unfortunately, despite my disassembling the motor and greasing the (plain) bearings before it was put into service, after a few months of hard work the blower failed. Delving inside it (again!) showed that the top bearing was completely stuffed – not only was the bearing surface badly worn, but the shaft was also pitted and scarred. Given the rubbish tip origin of the blower, perhaps it was already well on the way out – although I don’t remember there being much of a problem the first time I looked inside it.

Anyway, this particular unit needed to be retired. Or the electric motor part of it did, anyway. That thought prompted another – could I retain the compact centrifugal blower and its associated housing, but use a new electric motor? I tried a few different ones but none had the power of the original – not surprising, when that bugger drew no less than 15.5 amps!

But did the motive force even have to come from an electric motor? What about instead using another fan on the other end of a common shaft, and driving this second fan with a nozzle connected to a turbo boost source? Kind of like a mini turbo but using a bleed of boost off the plenum and spinning a fan that pulled air through the intercooler? Such a system would need no maintenance or control, and would increase in speed as boost also went up. The downside would be that it wouldn’t operate when the car was off-boost (say stopped at the traffic lights), but that was possibly not too great a downer, particularly if when on the boost the thing worked like a Trojan.

Hmmmm. The first thing that was needed was a steel shaft supported in high quality roller bearings. Normally, this kind of demand would stop a project in its tracks – but not if you know something about VCRs. Huh? Well, inside every discarded video cassette recorder you’ll find a shiny silver video head. Pull apart the assembly and there is a superb hardened steel shaft, two very high quality sealed ball bearings – and it’s all supported in perfect alignment by an alloy housing!

I’ve been salvaging VCRs for years so I went to my video head collection and soon had the bearing and shaft assembly sorted. Next I mounted the centrifugal compressor wheel from the deceased VW/Audi blower on one end of the shaft and a similar centrifugal blower (from a Toyota cabin fan) on the other end. A mounting plate was made for the VCR bearing support to bolt to, and on this I placed a small brass fitting to act as a nozzle, aiming it at the Toyota fan.

Before even thinking of mounting all this under the intercooler I wanted to see how well it could work. That meant being able to see it in action. Not having an air compressor, that meant doing it in a turbo car under load!  I grabbed some large diameter hose and found an unused connection on the intake manifold of my Maxima V6 Turbo. I then fed back into the cabin the hose, connecting it to the proposed intercooler turbine/fan assembly. With an assistant to do the driving, I sat in the passenger seat, initially with my finger over the end of the nozzle so that the car would start and run with this big intake manifold leak.

As the car came up on boost I took my finger off the end of the nozzle (if the system did work successfully, you’d use a one-way valve to perform this function!). With an ululating wind that soon rose to a siren-scream, the speed of the rotating assembly took off. By adjusting the nozzle angle I was able to alter the pitch of the scream (and so probably the speed) until it was going like a mad thing.

But was the driven fan spinning fast enough to pull lots of air through the intercooler?

To find out I returned home and installed a proper shroud around the centrifugal fan end of the assembly, then went back testing. Unfortunately, when loaded in this way, the rotational speed dropped considerably. The fan was still moving air, but it wasn’t the gale that I wanted. I altered the nozzle, tried various other fans (both axial and centrifugal) on both ends, played with housings – and even tried a turbo compressor wheel and its cover – but to no avail. (If you do the same, remember that all fans are directional – your turbine and compressor need to be designed to spin in the direction you want them to!)

But with the ~6 psi that I had available, I couldn’t get the speed high enough for the system to be a clear-cut step ahead of a similar, electric-powered design. And remember, the boost-powered fan wouldn’t ever work with the car stationery.

However, I have a very strong feeling that if (say) 15 or 20 psi was available, the story would have been very different…

Incidentally, despite the bleeding-off of metered air, the on-boost air/fuel ratios of the car (being monitored with a MoTeC air/fuel ratio meter) changed very little – perhaps 0.2 of a ratio.

I am sure that I have read of some turbo diesel trucks using boost-powered intercooler fans (although I have no details on the design, the boost level used, etc) so it’s certainly possible. There might also be an industrial application using a low-pressure turbine – not air tools though, their working pressure is too high. If the turbine side of the system can be sorted, I think pretty well any common-design fan (axial or centrifugal) would work on the other end of the shaft.

A boost-powered intercooler fan – it’d be pretty neat, wouldn’t it?