Supercharged coolant system woes

[Dirk73]

Hi folks,

I'm all geared up with great anticipation for the Angouleme centenary race on Sunday, after some hectic weeks getting the car finished it's now tested on the road and goes well apart from cooling issues. 

Are there any racers out there with pumped cooling systems and might be able to advise me on flaws in my layout? 

The car flies along, and will stay at 70-80 degrees C on a level road at 30-40mph. But as soon as you use the throttle any more (like accelerating up a hill) it quickly boils. 

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The engine has an Aisin supercharger, a waterpump (suzuki gsxr I think) driven at engine speed & a W.H repro head with dry deck and a solid copper gasket. This was done with the intention of avoiding blown head gaskets. The blower is geared for 7-8psi.

Coolant goes from the bottom of the rad to the pump, out the pump into the front of the cylinder block on the valve side, out the back of the block, back into the rear of the cylinder head, out the front of the head in the normal place and up to the top of the radiator. 

The radiator is a repro midget 1275 aftermarket aluminium job and the coolant header tank is a modernish (1980s) plastic one with a pressure-vent style cap. The fittings added to take the coolant into the block and out the rear back to the head are quite small (16mm internal). 

If anyone has experience with similar cars (pigsty/750mc racers?) and could drop me any hints that would be a great help. Otherwise I fear I'll be on the sidelines watching the rest of the race after overheating on lap 1! 

Regards to all & if anyone else is heading to Angouleme then see you there. 
Sam Archer (aka Dirk) 

[Ian Williams]

So silly question maybe, is the pump running in the right direction? How have you made the pump housing, could it be that it is cavitating as revs increase? Some picture of the pump set up could be informative. What sort of flow rate are you getting from the pump?

[Dirk73]

Hi Ian thanks for the reply,
I briefly tested the pump in a water butt with a makita drill, at the drill's max speed of 1500rpm there was a fair torrent of flow, but had no way of measuring flow accurately. Yes it's definately going the right direction.

To begin with i had the pump 0.7 underdriven, then after the first few runs (when it was overheating on hills) i then swopped the pulley to 1:1
I'd read articles about cavitating and so was starting off slow. It stays cool for longer on the 1:1 but still runs into the 90-100 degrees on hills.

The snail housing was integral to the gsxr pump, i've made an extra bearing housing on the shaft to support the pulley drive setup. Tried to look up GSXR specs but couldn't find info on the pump's original drive speed (mind you they rev to 12k whereas i'm not going much over 6000)

As my Dad often says "why d'you have to go fiddling around trying to make them go faster!"

[Colin Reed]

HI SAM,
I am a little confused if you have a header tank the top outlet from the head goes to the header tank which has a radiator cap fitted then to the top of the radiator .
Secondly you need to block of what appears to be an outlet from the head for a heater.
the rad cap fitting  should have an outlet for the overflow which will release at the cap pressure and ether go to ground or an overflow tank.

Hope that is of some help
Cheers Colin

[Cliff Ringrose]

A shot in the dark, but worth a try.
Put a restrictor in the top return hose.
I had this problem some years ago on a highly tuned and very quick engine, (un-blown), and it turned out to be that the pump was pushing the water though the block too quickly for it to obsorb all of the heat. Placing a restriction in the top hose causes a permanent back pressure, which gives the coolant time to do its job.
Hope you get it sorted in time.
Cliff.

[Mark Dymond]

How confident are you the head gasket is not leaking?
Ideally you should measure and record the water temperature coming out the bottom of the radiator as well as going out the head. If its a water flow issue, the radiator outlet temperature will stay relatively cool. if the radiator is not shedding enough heat the inlet and outlet temperature will track upwards together as the load increases.

[Sneezerap]

I like Cliff's idea that the pump is pushing the water thru the radiator to quickly. Also, I do
not see a cooling fan.

[Ian Williams]

It looks like you have water going into the waterway above the valves rather than the cavity around the bores. I,e into the small core plug rather than the large one. If so you may not be cooling the bores very well, the two waterways are connected internally but often corrosion clogs the very narrow connections. This may restrict flow as well. I would disconnect the return to the radiator, put a hose into the rad to keep it full then run the engine to see how much water you have coming out. That should tell you if its not enough water getting through the system. if you have a huge flow then try a thermostat in the top hose to slow down circulation. My gut feeling is not enough water circulation for some reason, possibly as a result of a plumbing loop such as to the header tank, maybe an air lock, or a restriction in the water ways.

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A cooling fan is not necessary in this situation unless sitting in slow moving traffic.

[Dirk73]

Hi Ian, Colin and others, many thanks for the replies. 
I will test it with an open top hose  to view flow and then move forward from there. 

The rad doesn't have an integral header tank and cap, hence the plastic one, which is plumbed from the side of the head and isn't a part of the flow/return loop. 

The block/head mating is dry so that the gasket could blow without affecting (or pressurising) the coolant (all deck coolant holes blocked & solid gasket) 


Thanks again for all the helpful suggestions

[Henry Harris]

Porous bore? Has the block been bored more than +0.060 inches oversize?