TRD radiator cap
)
(j/p of course) 
09-26-2005, 02:05 AM
#11
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Here's what a high pressure cap does: it decreases the size of the steam bubbles that form in the head on the other side of the combustion chamber.
"So what?" you ask. It means that under heavy load the coolant will be in better contact with the metal surface, so it will move more heat away from the metal than if larger steam bubbles were allowed to form. So the surface will be able to move more heat into the coolant than if a lower pressure were used.
"So what?" you ask again. Great question! For the tC, nothing. It runs just fine on 87 octane with the standard cap, so there aren't any real heat transfer issues to overcome.
"What about if I run a turbo or s/c?" Now we're getting somewhere. If the engine is making more power than stock, then there is more heat to remove from the head, but our cooling system hasn't been changed in any way to help this process. A high pressure cap is a good place to start. It will allow more heat transfer with the same configuration than a lower pressure cap.
A FUNDAMENTAL MISCONCEPTION - the engine needs to be cool to run well.
This is such a common misconception, I could make a post longer than the clutch flywheel post about why it is so wrong and fundamentally flawed, but I'll distill it into a few sentences.
When you burn fuel, you generate heat. The heat is absorbed by all the materials surrounding the event. This would be the piston, head, and valves. Those materials will absorb heat until they are fully heat soaked. The amount of heat that you need to keep them heat soaked is a complete loss.
Ideally, all the heat would be transformed to kinetic energy by pushing the piston down, but in fact, about 1/3 of the heat is absorbed by the engine and needs to be removed by the cooling system, 1/3 of the heat is blown out the exhaust port, and 1/3 of the heat actually turns into kinetic energy.
How is the heat distributed? The engine materials take its share first. Any energy needed to heat up the engine parts comes off the top. When there is excess, then the next share goes into moving the piston down the bore, where our universal gas law also takes a bit off the top, because as the piston moves down the bore the volume increases, so the temperature and pressure drop. The exhaust gets the leftovers. An excellent engine would have an ambient temperature exhaust (or an IDEAL engine would have a cold exhaust).
Understanding that the engine materials get first dibs on the heat; it makes sense to keep them as hot as possible without compromising their integrity or strength. That's the cooling system's job. Take away just enough heat to keep the integrity and strength of the engine's materials AND prevent the intake charge from autoigniting and causing detonation. Take away too much, and you are pulling heat away from pushing the piston down the bore. So it's a careful balancing act. Keep the heads as hot as possible for best efficiency, but cool enough to discourage detonation and basic material failure.
Why do I know all this stuff? Because my Supra ran great on 93 octane when I bought it in '94. Then Tosco reduced all the premium in California to 92 octane and the car pinged mercilessly while getting the poorest gas mileage I'd ever seen. It went from 18.x mpg to 14.x mpg. So I did a couple of things to the cooling system: I changed the ratio of water to coolant from 50:50 to 80:20. Water carries more heat per unit volume than any coolant, including NPG, so reducing the "antifreeze" and increasing the amount of water (and including Red Line Water Wetter for anti-corrosion) and using a 1.3 kgf/cm^2 cap instead of the OEM 1.1 kgf/cm^2, got my mileage back to 18.x mpg, and stopped the pinging completely. Two small changes that made big performance differences.
Then they went to 91. Nothing has fixed it since, and even with my mods, I only get 12.x mpg around town. Too much ignition retard, not enough cooling action going on to prevent detonation.
Anyway, I had to learn all about this stuff to understand why those two small changes restored my economy and power.
So the moral of the story is, if you are going to run a turbo or s/c, you will be doing your engine a favor while you are on the boost if you run a high pressure cap. It will be better prepared to deal with a load that the factory never anticipated. You might also want to experiment with coolant, but that's only for advanced tuners. You need to know a bit about what's really going on and what it really means before you should play with coolant ratios and ignition timing.
"So what?" you ask. It means that under heavy load the coolant will be in better contact with the metal surface, so it will move more heat away from the metal than if larger steam bubbles were allowed to form. So the surface will be able to move more heat into the coolant than if a lower pressure were used.
"So what?" you ask again. Great question! For the tC, nothing. It runs just fine on 87 octane with the standard cap, so there aren't any real heat transfer issues to overcome.
"What about if I run a turbo or s/c?" Now we're getting somewhere. If the engine is making more power than stock, then there is more heat to remove from the head, but our cooling system hasn't been changed in any way to help this process. A high pressure cap is a good place to start. It will allow more heat transfer with the same configuration than a lower pressure cap.
A FUNDAMENTAL MISCONCEPTION - the engine needs to be cool to run well.
This is such a common misconception, I could make a post longer than the clutch flywheel post about why it is so wrong and fundamentally flawed, but I'll distill it into a few sentences.
When you burn fuel, you generate heat. The heat is absorbed by all the materials surrounding the event. This would be the piston, head, and valves. Those materials will absorb heat until they are fully heat soaked. The amount of heat that you need to keep them heat soaked is a complete loss.
Ideally, all the heat would be transformed to kinetic energy by pushing the piston down, but in fact, about 1/3 of the heat is absorbed by the engine and needs to be removed by the cooling system, 1/3 of the heat is blown out the exhaust port, and 1/3 of the heat actually turns into kinetic energy.
How is the heat distributed? The engine materials take its share first. Any energy needed to heat up the engine parts comes off the top. When there is excess, then the next share goes into moving the piston down the bore, where our universal gas law also takes a bit off the top, because as the piston moves down the bore the volume increases, so the temperature and pressure drop. The exhaust gets the leftovers. An excellent engine would have an ambient temperature exhaust (or an IDEAL engine would have a cold exhaust).
Understanding that the engine materials get first dibs on the heat; it makes sense to keep them as hot as possible without compromising their integrity or strength. That's the cooling system's job. Take away just enough heat to keep the integrity and strength of the engine's materials AND prevent the intake charge from autoigniting and causing detonation. Take away too much, and you are pulling heat away from pushing the piston down the bore. So it's a careful balancing act. Keep the heads as hot as possible for best efficiency, but cool enough to discourage detonation and basic material failure.
Why do I know all this stuff? Because my Supra ran great on 93 octane when I bought it in '94. Then Tosco reduced all the premium in California to 92 octane and the car pinged mercilessly while getting the poorest gas mileage I'd ever seen. It went from 18.x mpg to 14.x mpg. So I did a couple of things to the cooling system: I changed the ratio of water to coolant from 50:50 to 80:20. Water carries more heat per unit volume than any coolant, including NPG, so reducing the "antifreeze" and increasing the amount of water (and including Red Line Water Wetter for anti-corrosion) and using a 1.3 kgf/cm^2 cap instead of the OEM 1.1 kgf/cm^2, got my mileage back to 18.x mpg, and stopped the pinging completely. Two small changes that made big performance differences.
Then they went to 91. Nothing has fixed it since, and even with my mods, I only get 12.x mpg around town. Too much ignition retard, not enough cooling action going on to prevent detonation.
Anyway, I had to learn all about this stuff to understand why those two small changes restored my economy and power.
So the moral of the story is, if you are going to run a turbo or s/c, you will be doing your engine a favor while you are on the boost if you run a high pressure cap. It will be better prepared to deal with a load that the factory never anticipated. You might also want to experiment with coolant, but that's only for advanced tuners. You need to know a bit about what's really going on and what it really means before you should play with coolant ratios and ignition timing.
09-26-2005, 02:29 AM
#13
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Hullo lo_bux_ Thank you for a fine technical essay. That was a lot of work to translate know how into text. 
I would quibble with only a few details. Please don't take me wrong. I am not an expert. I will state what I understand to be factual in summary form:
-Installing a higher-pressure cap only raises the operating temperature of the engine by some few degrees and -only at the limits of high temperture. The higher pressure cap is not going to -cause- the engine at partial throttle to be running at any higher temperature until the load demands so much more fuel (heat) that the cooling system becomes taxed to some degree.
-It won't make much difference in the operating temperature if we run higher concentration of glycol coolant than say, 70 percent.
-If you really want/think that high temperature is best for the overall performance then there are systems which dispense with water. These methods use pure glycol and will raise the operating temperature very high without boiling. However, the science behind such ideas is lacking and in general it is a very dicey thing to do, for glycols decompose at a little more than 300F into acetic acid and also turn to solid gel when overheated. And syrup when chilled. Special radiator, water pump and luck are needed to do such cooling.
Sir Harry Ricardo made a surprising determination many decades ago: there is no benefit to engine operation by running it hotter than, say 180F. The explosion temperature is in the thousands of degrees. What, then, is the benefit to heat conservation by running the engine at say, 40 degrees hotter? This alteration makes very little difference to the heat adsorbtion of the parts.
Principally, higher opperation temperature aids in the vaporization of the gasoline's heavier ends with resultant less washing of fuel residue into the crankcase oil supply.
The IC cycle operates at such rapidity that the heat soakage loss per cycle, comparing a "cold" engine" to a "hotter" engine, is of no consequence to thermal efficiency.
There is another detriment to super-high temperature operation (a pure glycol coolant scenario here now): that is this: the running clearance of the parts tend to alter with temperature. Aluminum pistons always expand much more with heat than the cast iron bores they run within. Thererfore, unless the piston is properly skirted and well lubricated, high temperature of say, 240F coolant is much more likely to result in piston skirt galling at high speeds than would be an engine with walls cooled to lower temperature.
The gain in carburation efficiency of high temperture is mitigated in other ways by the additional pre-heating of the mixture. And so, it is possible that no gain in thermal efficiency (mpg for the practical minded) will come about by running hotter than design center.
If it were so simple as to alter a cap's pressure relief in order to make the engine run better, would not Toyota know this very well? And would they not institute such a cost-less change in order to make the engine measure better and run better?
I have run on too long after promising to keep it short. Must sign off for my lads have spotted a set of spinners on a tC. We plan to nick them tonight and throw them from Tower Bridge in to the Thames.
cheerio,
Sid
I would quibble with only a few details. Please don't take me wrong. I am not an expert. I will state what I understand to be factual in summary form:
-Installing a higher-pressure cap only raises the operating temperature of the engine by some few degrees and -only at the limits of high temperture. The higher pressure cap is not going to -cause- the engine at partial throttle to be running at any higher temperature until the load demands so much more fuel (heat) that the cooling system becomes taxed to some degree.
-It won't make much difference in the operating temperature if we run higher concentration of glycol coolant than say, 70 percent.
-If you really want/think that high temperature is best for the overall performance then there are systems which dispense with water. These methods use pure glycol and will raise the operating temperature very high without boiling. However, the science behind such ideas is lacking and in general it is a very dicey thing to do, for glycols decompose at a little more than 300F into acetic acid and also turn to solid gel when overheated. And syrup when chilled. Special radiator, water pump and luck are needed to do such cooling.
Sir Harry Ricardo made a surprising determination many decades ago: there is no benefit to engine operation by running it hotter than, say 180F. The explosion temperature is in the thousands of degrees. What, then, is the benefit to heat conservation by running the engine at say, 40 degrees hotter? This alteration makes very little difference to the heat adsorbtion of the parts.
Principally, higher opperation temperature aids in the vaporization of the gasoline's heavier ends with resultant less washing of fuel residue into the crankcase oil supply.
The IC cycle operates at such rapidity that the heat soakage loss per cycle, comparing a "cold" engine" to a "hotter" engine, is of no consequence to thermal efficiency.
There is another detriment to super-high temperature operation (a pure glycol coolant scenario here now): that is this: the running clearance of the parts tend to alter with temperature. Aluminum pistons always expand much more with heat than the cast iron bores they run within. Thererfore, unless the piston is properly skirted and well lubricated, high temperature of say, 240F coolant is much more likely to result in piston skirt galling at high speeds than would be an engine with walls cooled to lower temperature.
The gain in carburation efficiency of high temperture is mitigated in other ways by the additional pre-heating of the mixture. And so, it is possible that no gain in thermal efficiency (mpg for the practical minded) will come about by running hotter than design center.
If it were so simple as to alter a cap's pressure relief in order to make the engine run better, would not Toyota know this very well? And would they not institute such a cost-less change in order to make the engine measure better and run better?
I have run on too long after promising to keep it short. Must sign off for my lads have spotted a set of spinners on a tC. We plan to nick them tonight and throw them from Tower Bridge in to the Thames.
cheerio,
Sid
09-26-2005, 02:47 AM
#14
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In english, for those of us with a C in thermodynamics:
The TRD cap wouldn't create more of a perfomance improvement vs stock, than day driving vs. night driving.
But it is a cheap way to make your engine look nicer!
The TRD cap wouldn't create more of a perfomance improvement vs stock, than day driving vs. night driving.
But it is a cheap way to make your engine look nicer!
09-26-2005, 03:47 AM
#15
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A high pressure cap has zero effect on operating temperature until the limits of the system's ability to move heat are approached, then it actually reduces operating temperature. I could run a 5 kgf/cm^2 cap on my car, and the operating temperature would not budge one degree. The only time it does anything useful is when there are steam bubbles developing in the water jacket above the combustion chamber (or around the exhaust ports). Other than that, one would never know there is anything changed at all, except the system components would be more prone to failure since they are not designed for that kind of pressure.
I chose a higher pressure cap for my Supra to regain boilover protection because I changed the water to coolant ratio, not to change my operating temperature. I changed my coolant ratio to gain thermal capacity. I could have changed the pulley on the water pump and achieved something similar, or I could have taken the head off and modified the pistons and combustion chambers to be more detonation resistant, all with the same end result. Changing the coolant ratio was the simplest, and cheapest approach that solved the problem, so it won the competition for best solution to the problem.
If you want to change operating temperature you must change the thermostat. No other device in a properly designed and executed cooling system will change operating temperature.
I am keenly aware of Evans Cooling Systems and Jack Evans is quite the clever man, having been the guy who figured out how to do reverse flow cooling for General Motors. His Non-aqueous Propylene Glycol cooling systems have been proven over and over again in all kinds of applications, but I really didn't want to open that can of worms, it's a completely different discussion.
I seriously beg to differ with your assertion that cold cycle operation and operation at normal temperatures have the same thermal efficiency. Try driving short trips (<10 miles) for an entire tank of fuel. It will not matter what speed you drive, your economy will be in the toilet for a number of reasons. The manufacturers didn't choose to install 195F (89C) degree thermostats on a lark. They did it because they needed to meet emissions standards AND fuel economy standards.
I am confident the research shows hotter engines have both better emissions profiles and better thermal efficiency. As an anecdotal example, a tC owner at YSTC.com installed a 210F (99C) thermostat in his car in hopes of improving fuel economy. He immediately saw a 10% improvement.
Again, all the concerns you mentioned are serious concerns: the parts should be sized to work at the new operating temperature, the oil must be of a superior quality so it doesn't coke and completely varnish the internals, etc., etc., and I discussed these things with the guy planning to do this. He was still willing to take the risk for the 10% annual fuel cost reduction because it made economic sense for his case.
I still have many concerns about service life for unmodified engines run hotter than design specification, but the high pressure cap does not do this, it only improves the upper bound of the system's ability to shed heat.
I chose a higher pressure cap for my Supra to regain boilover protection because I changed the water to coolant ratio, not to change my operating temperature. I changed my coolant ratio to gain thermal capacity. I could have changed the pulley on the water pump and achieved something similar, or I could have taken the head off and modified the pistons and combustion chambers to be more detonation resistant, all with the same end result. Changing the coolant ratio was the simplest, and cheapest approach that solved the problem, so it won the competition for best solution to the problem.
If you want to change operating temperature you must change the thermostat. No other device in a properly designed and executed cooling system will change operating temperature.
I am keenly aware of Evans Cooling Systems and Jack Evans is quite the clever man, having been the guy who figured out how to do reverse flow cooling for General Motors. His Non-aqueous Propylene Glycol cooling systems have been proven over and over again in all kinds of applications, but I really didn't want to open that can of worms, it's a completely different discussion.
I seriously beg to differ with your assertion that cold cycle operation and operation at normal temperatures have the same thermal efficiency. Try driving short trips (<10 miles) for an entire tank of fuel. It will not matter what speed you drive, your economy will be in the toilet for a number of reasons. The manufacturers didn't choose to install 195F (89C) degree thermostats on a lark. They did it because they needed to meet emissions standards AND fuel economy standards.
I am confident the research shows hotter engines have both better emissions profiles and better thermal efficiency. As an anecdotal example, a tC owner at YSTC.com installed a 210F (99C) thermostat in his car in hopes of improving fuel economy. He immediately saw a 10% improvement.
Again, all the concerns you mentioned are serious concerns: the parts should be sized to work at the new operating temperature, the oil must be of a superior quality so it doesn't coke and completely varnish the internals, etc., etc., and I discussed these things with the guy planning to do this. He was still willing to take the risk for the 10% annual fuel cost reduction because it made economic sense for his case.
I still have many concerns about service life for unmodified engines run hotter than design specification, but the high pressure cap does not do this, it only improves the upper bound of the system's ability to shed heat.
09-26-2005, 07:01 AM
#16
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Moral of da story...
Runnin it @ stock ain't gonna help much and perhaps not be benificial (however i don't think it'll harm performance)...
Forced induction/S\C would help substantially being @ higher operating tempz...
Its all up to U the Driver.
Runnin it @ stock ain't gonna help much and perhaps not be benificial (however i don't think it'll harm performance)...
Forced induction/S\C would help substantially being @ higher operating tempz...
Its all up to U the Driver.
09-26-2005, 05:08 PM
#17
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Your car's gas mileage will be in the toilet because on cold start, the ECU is dumping in more fuel.
This is the best discussion over the worst topic I've ever seen. There will be no difference unless you put your engine togather with no head gasket.
Just because an engine is blown or turbo does not mean it's going to run hotter.
This is the best discussion over the worst topic I've ever seen. There will be no difference unless you put your engine togather with no head gasket.
Just because an engine is blown or turbo does not mean it's going to run hotter.
09-26-2005, 05:28 PM
#18
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No, but it does mean there is more heat to move out of the engine under boost, and it's directly related to issues with detonation and basic tuning. Higher pressure in the cooling system is one inexpensive place to start corrections for additional power.
09-26-2005, 10:43 PM
#20
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You're not going to have higher pressures in the cooling system unless you blow a head gasket. The overflow tank is there for a reason, to allow for expansion under heat. Yes, technically, more heat is higher pressure, but it's so negligent it's a moot point. Negligent, as in, you'll never produce any tangible results testing for it. A stiffer or looser spring is not going to change a damn thing, except when the overflow fills up.