Are any of you using a Restrictor instead of a Thermostat?
Restrictor instead of Thermostat
- Thread starter SpyderMike
- Start date
David Garton
Supporter
Mike,
I don't believe in using a restrictor in place of a thermostat because of the way a thermostat functions. It is normally closed until it reaches the temperature then it opens . While it is closed the water is not flowing and is stored in the radiator which the fan is cooling by pulling air a crossed it. When the thermostat opens it moves the hot water out of the block and once the cool water enters the block and touches the thermostat it closes again allowing the cycle to happen again. I have seen when the thermostat is removed the water never stays in the radiator long enough to cool and the cars overheat. Hope this makes sense. David
I don't believe in using a restrictor in place of a thermostat because of the way a thermostat functions. It is normally closed until it reaches the temperature then it opens . While it is closed the water is not flowing and is stored in the radiator which the fan is cooling by pulling air a crossed it. When the thermostat opens it moves the hot water out of the block and once the cool water enters the block and touches the thermostat it closes again allowing the cycle to happen again. I have seen when the thermostat is removed the water never stays in the radiator long enough to cool and the cars overheat. Hope this makes sense. David
Howard Jones
Supporter
Its all about the heat load/time your are trying to regulate. This is best expressed as total BTU's in a given length of time. Ill expand on this in the following manner. We have two cool guys and their cool GT40s. Both have the same engine and the same remaining powertrain so they potentially can generate the same amount of heat. They also have a coolant system that is adequately designed to cool that heat load. Fans, ducting, radiator size and pump capacity. All are sufficient designed to cool the maximum amount of heat the power train can generate. lets say 400Hp.
BUT............Bob only drives his car on the street in a generally legal manner nearly all the time, and Rob has a track car and most of the time the car is run on the track.
So we have Bob drive his car for an hour Sunday morning sunday/funday outing. He leaves the house and nearly all the time he is moving the engine is making much less than 25% of its maximum power with a 20-30 sec blast once in a while. While at constant speed on the highway or moving on the surface streets he is at the speed limit of slightly above it but at very small throttle openings and making what is really very little power. His car will go 70mph at constant speed and it only really needs to make 50Hp to do it. Over the hour he is at something like 10-20% power 80% of the time. That would be something like 20Hp at idle 50-100hp for most of the hour with a few 30 sec blasts at 300-400hp. His average power output could be as low as less than 100Hp for the hour. I would guess less than that.
Rob on the other hand is going as fast as he can nearly the entire hour. In reality that would be two 30 min session but you know what I mean. His minimum throttle setting is about 10-20 % of the time at the apex's but quickly rises to 100% for at least 50% of the time and in the 40-60 % range the rest of the given lap. Over the hour he sees at least 200-400Hp most of the time.
You can see the problem. Widely different heat loads to control over the same time frame.
So to your question. I have found that a restrictor works very well in a track car. Once you arrive at a orifical size. My SLC has a 3/4 inch diameter restrictor place instead of a thermostat. Airflow is generally constant through the radiator and the fans are not used until I have to move at very low speed coming off the track back to my paddock location. Since I have a electric water pump, its controller regulates the flow rate to cool the coolant to the programed temp with ease. It runs 190F all day long even in Texas in August,
My GT40 has a mechanical water pump in the standard location and when I ran it at the track I used a restrictor .5/8 hole, Worked much like the SLC but it was a huge amount of trial and error getting the pullies to drive the pump in a efficient range and at the same time not cavitate so bad as to spin the impeller on the pump shaft. I went through 3 pumps due to this problem. The problem is the engine rev range 2000-6000. That is very wide for an impeller that cannot be spun much above 3500 RPMs or it cavitates.
I can write a very long diatribe on why not to run a mechanical pump on a track car but not for now.
So the thermostat has a place on a street car because it has to control a LOT less heat and has generally a much longer time to do it and that's the key to your question. Track cars really only need to establish the constant flow rate needed and then maintain it without failure, thermostats are just a unnecessary point of failure on a track car.
Along with all this is oil temp control/cooling. Can be nearly not necessary on a street car and absolutely required on a track car.
I hope this helps.
Note: use a electric pump and save yourself the grief of mechanical pumps.
BUT............Bob only drives his car on the street in a generally legal manner nearly all the time, and Rob has a track car and most of the time the car is run on the track.
So we have Bob drive his car for an hour Sunday morning sunday/funday outing. He leaves the house and nearly all the time he is moving the engine is making much less than 25% of its maximum power with a 20-30 sec blast once in a while. While at constant speed on the highway or moving on the surface streets he is at the speed limit of slightly above it but at very small throttle openings and making what is really very little power. His car will go 70mph at constant speed and it only really needs to make 50Hp to do it. Over the hour he is at something like 10-20% power 80% of the time. That would be something like 20Hp at idle 50-100hp for most of the hour with a few 30 sec blasts at 300-400hp. His average power output could be as low as less than 100Hp for the hour. I would guess less than that.
Rob on the other hand is going as fast as he can nearly the entire hour. In reality that would be two 30 min session but you know what I mean. His minimum throttle setting is about 10-20 % of the time at the apex's but quickly rises to 100% for at least 50% of the time and in the 40-60 % range the rest of the given lap. Over the hour he sees at least 200-400Hp most of the time.
You can see the problem. Widely different heat loads to control over the same time frame.
So to your question. I have found that a restrictor works very well in a track car. Once you arrive at a orifical size. My SLC has a 3/4 inch diameter restrictor place instead of a thermostat. Airflow is generally constant through the radiator and the fans are not used until I have to move at very low speed coming off the track back to my paddock location. Since I have a electric water pump, its controller regulates the flow rate to cool the coolant to the programed temp with ease. It runs 190F all day long even in Texas in August,
My GT40 has a mechanical water pump in the standard location and when I ran it at the track I used a restrictor .5/8 hole, Worked much like the SLC but it was a huge amount of trial and error getting the pullies to drive the pump in a efficient range and at the same time not cavitate so bad as to spin the impeller on the pump shaft. I went through 3 pumps due to this problem. The problem is the engine rev range 2000-6000. That is very wide for an impeller that cannot be spun much above 3500 RPMs or it cavitates.
I can write a very long diatribe on why not to run a mechanical pump on a track car but not for now.
So the thermostat has a place on a street car because it has to control a LOT less heat and has generally a much longer time to do it and that's the key to your question. Track cars really only need to establish the constant flow rate needed and then maintain it without failure, thermostats are just a unnecessary point of failure on a track car.
Along with all this is oil temp control/cooling. Can be nearly not necessary on a street car and absolutely required on a track car.
I hope this helps.
Note: use a electric pump and save yourself the grief of mechanical pumps.
Bill Kearley
Supporter
No No, not for street use. Your engine will take for ever to warm up plus with different loads all the time you will never have control over coolant and water temps.
Interesting! Thanks for the inputs.
The fans cycle on and off to regulate the heat too,n no? Is this not a major factor? They react faster than a thermostat I suspect. Just curious...
The fans cycle on and off to regulate the heat too,n no? Is this not a major factor? They react faster than a thermostat I suspect. Just curious...
Bill Kearley
Supporter
Depending where you live, Roughly speaking, a 185/190 deg stat and a 205 deg fan switch. Give the rad a chance to do it's job before the fan comes on .
Howard Jones
Supporter
