Firstly, thanks for all the replies.

It should be noted that my motor/cooling system does not suffer from any overheating problems.

I guess I just wanted to know if I could close the heater valve off without suffering any longterm consequences whilst trying to lower in car cabin temps when I'm in stage. I will be going back to my state scrutineer for clarification on the heater box/demister issues because if I can get rid of the heater box I will do so just for the weight saving alone. I asked the scrunineers about bypassing the heater core but they were not that keen on the idea but like most things to do with rallying I guess its just one mans interpretation of the CAMS manual compared to anothers.

Feral - my motor has been through the building prep steps you mentioned above, unfortunately I am a perfectionist with access to a large machineshop and I can be my own worse enemy so I was maticulous when doing all the work to my A series. Reg Cook was the one who informed me about the simple water pump tests you have mentioned. I have performed similar tests some time ago after I modified the water pump vanes to prevent cavitation problems.

It looks like it's another visit to the scrutineers to find out more.

Thanks again to everyone who has helped,

Paul.

Running it through the heater should not be necessary if the cooling system is set up correctly with no problems. Running the coolant through the heater is usually just a band aid for a faulty cooling system. It usually indicates another problem is there but doing this masks it up.

I am including some cooling system thoughts that may make unserstanding what happens in your cooling system as bit easier.

When building any "Serious" engine you should hot caustic tank the block and head. This process helps remove scale and oil from the cooling system. Drill all the water gallery holes on the block deck to clean them of any corrossion.

If the head has been serviced correctly and there is no corrosion in the water jackets, you have a fighting chance of survival in a race engine.

The next most important thing is to keep the coolant pressure sufficiently high so steam bubbles do not form around the coolant galleries. This means that you must run a thermostat and give the coolant enough residence time to absorb as much heat as possible without being able to form steam bubbles.

The following is a simple diagnostic cooling test any one can do at no cost. It is suitable for A series, L series, CA FJ or SR's etc.

On the inlet side for coolant flow back into the block/head, fit the cap end of a 1.25 or 2 litre coke bottle into the hose on the block inlet side. Cut out the base of the coke bottle to make it like a funnel and fit the heater return line into the top of the funnel section. You may have to make an extension hose up to carry these tests out.

Half fill the funnel with water, then holding the bottle up, remove any air from the radiator cap. There should be sufficient water in the funnel so the coolant level remains relatively stable with the engine running. Top the coolant level in the funnel up with additional water to maintain the coolant level in the funnel at a constant level.

Bring the engine to a constant operating temperature. To test water pump pressure raise the coolant delivery hose into the funnel so the coolant from the heater return line falls in an arc into the top of the funnel. At approximately 800 rpm idle, the hose should be able to be raised 450 -600 mm before coolant flow stops. This indicates a coolant pressure of approximately 1 psi. If the flow level falls below 300mm before flow stops, the pump is not providing sufficient pressure for the system and the pump must be replaced.

Next look for pump cavitation by running the engine at 2000 rpm and looking at the changes that happen to the coolant. If it goes opaque or cloudy like the head on a freshly poured beer, you have some cavitation. If the cavitation is bad, large bubbles will appear in the funnel rather like the aerator bubbles in a fish tank.

If you have either symptom you should look at the water pump type you are using and the pump drive speed.

Often by slowing the pump or removing some pump blades or cutting them back, these symptoms will dissapear.

The tests were shown to me by "The Professor" John Bennet of Perfectune Engineering (Yella Terra) fame for those of you old enough to remember.

Hope the info helps.

Good thought!

Get some 12v hairdryers with a cigarette lighter plug. less weight, and not getting too hot.
win,win.

1200coupe, I've just read the CAMS manual for 2004, have look on page 11-55 (road events) section 3.10 cockpit (vi) "The original heating system may be removed but an electric demist or similar must be retained"
Bypass the heating radiator (or better still remove it, it weighs 2.5kgs) and keep the "electric fan" ie. "electric demist or similar must be retained" (a fan blowing over you windscreen is demisting it)
I don't know if this comes down to interpretation but the way I see it (and many others) if you do as mentioned above, all should be sweet, I would ring CAMS on this issue or talk to your chief scruteneer in your State

Edit:
To answer your question, my theory would be that yes if you did keep the heater box in the car and used it, it would lessen the risk of any hot spots in the rear of the motor. Why, because you are creating another avenue for water to flow from the back of the head via the hotbox down to the suction side of the water pump,SO my point is as described as above, simply remove the hotbox radiator (or bypass it) run the hose from the back of your head down to the inlet from the original heater hose and you have permantly created more flow from the area around the back of your head, the motor is not solely relying on the water jacket at the rear of the head the recirculate water.

I run my racecar with a working original heater, with no problems......

Simply buy 2 brass T pieces and a second heater tap or a plain old ball valve, a length of coolant hose and 8 hose clamps.
Put 1 T piece in the coolant line to the heater core before the tap, and the second T piece in the line after the heater core. Then run a coolant line from one T piece to the other and put the second tap in the middle.
Close the first heater tap and open the second and coolant continues to flow, bypassing the heater core. Open the first tap and close the second and the heater will work like normal.

Converted,
I have to rally with a working heater because the national rally code states that the car must have a working demister. I wanted to know because it gets very hot in the cabin when rallying in summer especially if I have the heater valve open to circulate water through the back of the head. Cabin temps are unbareable and I was looking for a way around the problem without hurting my A series. But it looks difficult if I am to meet the nat rally code and pass scrutineering etc etc.
I will have to give the problem more thought

yes definately.... run your rear heater pipe outlet to the lower front of where the lower radiator hose would have normally connected to.

I have heard the same story from several engine builders over the years in regard to a worked A-Series......

Benny