Club 80-90 Forums

This is like watching porn at thirteen... exciting yet confusing!

Managed to pick up another little bit of the puzzle via eblag: a Jaguar V8-S vacuum actuated bypass for the blower. This little device diverts airflow from the supercharger outlet/chargecooler plenums back into the inlet plenum, so at cruise (high vacuum) the blower makes no boost, thereby reducing parasitic losses dramatically and saving fuel

This is where it lives, its the Y-shaped housing
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On the polo g40 it was vented back into the charger inlet via a butterfly operated by a linkage from the throttle butterfly so it closed as the throttle opened which worked well.

Duncan: what is considered a reasonable inlet temp for a forced induction petrol engine?
A.Graham Bell hints at around 45 Celcius in one worked example for charge density.

That being the case, if my compressor is causing the same kind of inlet charge ▲T as the Jag system (circa 100-110 *C) - albeit at 12 or 13 psi not 7 or 8 - then it needs to dump at least 80*C at 2/3 of the inlet air flow rate i.e. 190 litre/sec vs 285 l/sec, based on an ambient of 21*C.

I could possibly find out the dimensions/tube count of the Jag secondary heat exchanger but without a pump flow rate its kind of meaningless and I think its a bit of a leap to assume that a 2/3 sized secondary will shed 2/3 of the heat extracted by the engine primary exchangers at the lower flow rate.

The maths would be all wrong there, I suspect, because none of this is linear.

FWIW A.G. Bell suggests a coolant flow of 20litres/min for full load and a use of a resistor to drop the pump speed when cruising off boost (and to stabilize inlet temps generally, once up to operating temps)

Ian, a new calculation based on 12 psi boost and 185 l/s flow reduces the heat to be removed to 3.14 kw per 10 C temperature reduction.
The Bosch 002 pump does indeed flow 0.33 l/s which is what was recommended and works against a reasonable pressure drop.
I don't know what an ideal maximum charge temperature should be except the 1.8T management system starts to back off at 50 C so that ties in with what you have found.
There are some other factors to take into account;
1) we have assumed a requirement now for around 16 kw of cooling but this is at maximum continuous power which will not happen in the real world.
2) the vaporisation of the fuel from the injector will have a significant adiabatic cooling effect. If you can work out the flow rate we can derive the extra cooling this will give as well.
At this point an assessment would suggest that a smaller system but running continuously would be able to deal with the peak loads and build a buffer at part load. To maintain the charge coolers at our notional 50 C max we need the cooling fluid to be maintained below this in a reasonable summer ambient with a 0.33 l/s flow. Next job then is to reverse engineer the Mocal cooler for water/glycol using your 200 l/s fan. The fan may be the Achilles heel here as it will produce a face velocity of a little over 4 M/s with your cooler which is quite low looking at the Mocal charts and works out to a 10 mph air stream.
I will try and conclude as far as we can tomorrow as I have to head off to La Sarthe Tuesday for a week so keep posting and I will look in when I can.

Should of mentioned: find out what you can about the original jag system as it will be relevant.

Many thanks! I will do some more digging...

I suppose the easy way out would be to get a Jag secondary exchanger and pump, run hoses up the front and be done with it, but that's lazy and heavy.
The TDI boys seem to do ok with rear intercoolers, suggesting appreciable airflow down the D post, so maybe using a fan is unneccessary (more of a low-speed/offroad syncro oil cooler requirement)
I think its time to rig up my Kestrel in the back of someones bus and get some real-world air velocity readings at various road speeds.

Ok the Mocal data is for engine oil and without data for water we can only make an educated guess at the increase in performance using water/glycol. Typical data suggests between 30% and over 100% increase in thermal performance depending on a huge number of factors so to complete the loop we could conservatively assume 50% until better data is available. I wont add pages of calculations here but the end result using the 20 l/m pump flow and assuming 45C fluid flow and 25C air onto the cooler we get;
5 M/s air flow = 3.75 kw = 12 C charge air temperature drop
10 M/s air flow = 6.0 kw = 19 C temperature drop
15 M/s air flow = 6.375 kw = 20.3 C temperature drop
20 M/s air flow = 6.75 kw = 22 C temperature drop
As the average heat flow from the supercharger will be much less than the peak 16 kw full power a continuously running system with a small header tank will buffer and smooth out the peak temperatures and your 25 row cooler should be adequate with reasonable air flow.
Once we get some more accurate data this will now be fairly easy to refine.

Well done Duncan. As soon as I have co-opted a willing volunteer I will get some D-post air velocity figures.
I am more than confident that the primary coolers will give an effective buffer, being as they are from a much bigger engine that puts a lot more heat into the inlet charge.
Going to try and get Think Auto on the phone shortly.

PS I am quite prepared to duct the bottom of the D post into the rear light panel, to take advantage of the LP zone behind the bus and increase airflow

PPS when I said Kestrel, I meant this...



...and not Kes

I rang Mocal lunchtime and spoke to their technical department. Nice people but they are worryingly non-technical ( maybe I was expecting too much). I hope you have better luck, in fact Serck may be a better bet.

They are all about oil cooling to be fair, I will save the phone call.
Could we take a stab at it using the difference in specific heat capacity for oil vs water/glycol or again, too much of a leap?

Just remembered that the Jag secondary is around 600mm wide, 250 tall (tubes long dimension) but only E D I T 32mm thick and 0.85 litre capacity, presumably including header tanks.
A bit of reading suggests that the system is pretty well at capacity on the 4.0 s/c AJ V8, so any pulley mods to increase the blower overdrive just result in more heat and spark retardation (which can even occur on a standard car in hot weather)