TRX250R.ORG
Workshop => Engine and Bottom End => Topic started by: rablack21 on April 06, 2015, 10:45:21 AM
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Does anyone know for certain if any other water pump impellers from a cr250 or cr500 will work on a 250R? Has anyone successfully used one? Just curious.
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Perhaps even one from a 4 stroke might work. If that was found to be the case, maybe one of the high flow impellers would work.
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I considered attempting to design a new water pump impeller. One that would flow more than the stock one does now.
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I considered attempting to design a new water pump impeller. One that would flow more than the stock one does now.
excellent idea!
John
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I may pursue this idea. I have an extra clutch cover. I may have to enlist the help of others to come up with another water pump shaft and impeller. I would set up a bench test and measure the flow of the stock impeller. Then model up a few different designs and have a friend machine them and then test them.
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Basing it off the 89 would be the easiest because than you could use the 89 shaft & not have to worry about splines. You'd only need to redesign the impeller that way.
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Guys, I need a little help. I need some pics of an 89 impeller, particularly the back side. Broken answered one question for me. 89 has no splines. I need to see if the rest of the back and the inner part look like my 85-88 impeller. I'm gonna start modeling up a new one tomorrow.
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A couple pics of my first idea.
(http://forums.trx250r.org/vbulletin_imports/100_5059_2017-04-18_9565.jpg)(http://forums.trx250r.org/vbulletin_imports/100_5060_2017-04-18_8129.jpg)(http://forums.trx250r.org/vbulletin_imports/100_5061_2017-04-18_1609.jpg)
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This one was modeled similar to the fins on Boyesen's super cooler kit.
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here is how dasa made a high flow impeller for a SxS. left is stock, right is high flow
(http://i49.photobucket.com/albums/f259/Sand_Junkie/Upgrades/Upgrades014.jpg)
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Thanks for the pic, Jesse.I considered trying something like that as well. Yeah, I believe as you straighten out the fins, you are pushing more volume towards the out port. That pic helps a lot with ideas though. I may consider something like that as well.
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was doing some reading, perhaps the 90 degree elbow at the back of the head is turbulent restrictive spot also. it makes sense.
(http://themotogiveth.com/wp-content/uploads/2013/09/9-16-2013-7-51-19-AM.png)
also, here is a side by side comparison from a yz450f stock impeller vs. its high flow boyesen counterpart. it seems they use the impeller to fully utilize the water pump cavity as much as possible
(http://imagizer.imageshack.us/a/img202/7408/20130419161826.jpg)
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I was talking to a local engine builder o e time and he mentioned why not use a cr shaft, but didn't go I to details about it. Maybe I'll swing out there sometime an ask specifically.
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If he knows that a cr shaft would work, that would be very helpful. I personally don't know. If you find out, let me know. Otherwise, I might go out to my local shop and see if he has any cr shafts laying around.
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rumor has it that fast water speed and a smallish cooling system capacity works best. huge volume in the head is no good. seems like kevin cameron has talked about it
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I talked to Sam (Sameltoe) yesterday. He is going to send me an 89 impeller and shaft to use. So my intention will be to test a new high flow impeller (more flow than stock) and also to produce a new impeller shaft, as the 89 shafts are getting less common, out of stainless steel. Thanks Sam, for continuing to push this idea.
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What do we believe is the limiting factor here? Is it the speed of the water or the capacity of the system?
How do you calculate the optimal flow rate to dissipate the maximum amount of heat? I'm no engineer which is why I ask, sure is an interesting subject though
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Check out 'splitstream' for some ideas too. It looks like they use a spacer to move the cover outwards, to fit a taller impeller in there, on some thumpers. Could be some adaptable ideas for you there.
Cool idea you have here!! LOL
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Both can be a limiting factor. You are right, the trick is to "balance" the cooling system. Increasing the coolant flow rate will lower the radiator inlet temperature but raise radiator outlet temperature. There can come a point when the temps are so close together that it doesn't help the system. The major players when it comes to cooling are:
1. surface area across the radiator
2. air flow
3. coolant flow rate
4. specific heat of the fluid used.
To improve #1, you have to go to a larger radiator
To improve #2, you have to either ride faster, use a fan, or use shrouds that force extra air into the radiator fins
To improve #3, you have to increase the flow rate by a beneficial amount
To improve #4, you have to use a fluid that has a better specific heat than water/coolant mix. This one is difficult to change.
Right now, I am addressing #3. When I get time, I will move on to #2
With all of the rough cast surfaces in the clutch cover and cylinder jug, I see a lot of room for improvement to flow.
What do we believe is the limiting factor here? Is it the speed of the water or the capacity of the system?
How do you calculate the optimal flow rate to dissipate the maximum amount of heat? I'm no engineer which is why I ask, sure is an interesting subject though
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Check out 'splitstream' for some ideas too. It looks like they use a spacer to move the cover outwards, to fit a taller impeller in there, on some thumpers. Could be some adaptable ideas for you there.
Cool idea you have here!! LOL
Thanks for the idea! That is exactly what Boyesen does as well, but in a different way. The spacer idea would be very easy to do and would provide room for longer fins on the impeller. The longer fins would provide additional improvement.
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With all of the rough cast surfaces in the clutch cover and cylinder jug, I see a lot of room for improvement to flow.
dont forget about that hose bung on the back of the cylinder, the machining on the inside of that thing is stopping up flow terribly. it is basically shaped like a "T" but outletting only coming in and going out the bottom and one side of the "T".
... on the ESR cylinders i mean, i dont know about cp water outlets.
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Is it possible the coolant is going too fast to actually pull heat from the exhaust side. Possibly put an exopy in the head and drill holes like a stock gasket.
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Is it possible the coolant is going too fast to actually pull heat from the exhaust side. Possibly put an exopy in the head and drill holes like a stock gasket.
That would actually not be possible. There's no way that the flow could be fast enough not to pull "some" heat from the area. With that said, the flow on these pumps have never been a great deal. Which is why they produce almost zero flow when at idle. Yes, the flow is better as the revs go up, but it is still very slow. If you feel the inlet hose to the water pump when you have the engine revved up, you will still barely be able to tell that draw is taking place. You also can't notice any liquid movement in the radiator. In vehicles where you can visibly see down into the radiators, you will notice that when you rev up the engine, you will see the liquid moving. Obviously this is not a quantified measurement but give you some observations.
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Another option could be an electric pump and just do away with the shaft bearing and impeller
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lets say the rad had 10 large rows. what about 20 smaller rows instead and increase the water speed
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lets say the rad had 10 large rows. what about 20 smaller rows instead and increase the water speed
The row size is generally not the customizable variable, it's the air fin pitch and shape. Unfortunately, we don't have any control over this and this is at the discretion of the cooler manufacturer. You can go with a smaller fine pitch which will increase cooling capability, but will also increase the possibility of clogging. Debris will not flow through the fins as easily. You can also change the fin shape, but going to a more efficient fin shape will also increase clogging probability. Those that never ride in the woods could probably get away with this change without issues. The fin pitch on my CBR radiator already appears to be fairly small. Not sure you could go any smaller without making it difficult to clean out mud and debris. That is why I am moving on with something that I can change. :topsecret:
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The row size is generally not the customizable variable, it's the air fin pitch and shape. Unfortunately, we don't have any control over this and this is at the discretion of the cooler manufacturer. You can go with a smaller fine pitch which will increase cooling capability, but will also increase the possibility of clogging. Debris will not flow through the fins as easily. You can also change the fin shape, but going to a more efficient fin shape will also increase clogging probability. Those that never ride in the woods could probably get away with this change without issues. The fin pitch on my CBR radiator already appears to be fairly small. Not sure you could go any smaller without making it difficult to clean out mud and debris. That is why I am moving on with something that I can change. :topsecret:
I think we could have impellers and pump covers made pretty easily (by NPM perhaps?). That would keep the cost down and still improve flow. Especially at slow speeds
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I think we could have impellers and pump covers made pretty easily (by NPM perhaps?). That would keep the cost down and still improve flow. Especially at slow speeds
I contacted Jeremy just yesterday. I will be getting a quote from him along with maybe one or two others about making a prototype and then on to producing them after that, if there is a demand for them. How do I setup a survey in this thread? I wanted to see how many might be interested in one of these when I get through with them.
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The row size is generally not the customizable variable, it's the air fin pitch and shape. Unfortunately, we don't have any control over this and this is at the discretion of the cooler manufacturer. You can go with a smaller fine pitch which will increase cooling capability, but will also increase the possibility of clogging. Debris will not flow through the fins as easily. You can also change the fin shape, but going to a more efficient fin shape will also increase clogging probability. Those that never ride in the woods could probably get away with this change without issues. The fin pitch on my CBR radiator already appears to be fairly small. Not sure you could go any smaller without making it difficult to clean out mud and debris. That is why I am moving on with something that I can change. :topsecret:
mylers can make most anything you want, so theres plenty of customization available. they also have a supercool series that is supposed to be condiderable improved over stock. never used one but thats what they claim. besides the improved pump and radiator ideas, im a believer in fans. alot of people simply dont generate sufficient airflow for the system to work properly. even with the best pump and most efficient rad, without air the whole system is useless.
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mylers can make most anything you want, so theres plenty of customization available. they also have a supercool series that is supposed to be condiderable improved over stock. never used one but thats what they claim. besides the improved pump and radiator ideas, im a believer in fans. alot of people simply dont generate sufficient airflow for the system to work properly. even with the best pump and most efficient rad, without air the whole system is useless.
I agree. The hardest one of the three to control is the airflow. Unless you're using a fan, it has a condition. You have to go fast to get good airflow. I believe in the use of fans as well. But I just haven't seen a good way to hook a fan up to a cr 250 ignition, which I am currently running. But yes, more airflow would be ideal. Just hard to get it. lol.
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you don't want the coolant moving too fast or it will be counter productive.
john
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you don't want the coolant moving too fast or it will be counter productive.
john
That is true but almost impossible. The rate at which the heat transfers is far faster than the coolant can ever flow in this system.
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That is true but almost impossible. The rate at which the heat transfers is far faster than the coolant can ever flow in this system.
thats good. ryan, i know you did your homework,
john
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Another great way to increase end suction centrifugal pump efficiency is to have the proper suction clearance. You should measure the stock, and space the impeller outward to take up the clearance. You want as little clearance as possible. This will create more head pressure and increase the flow rate by reducing internal recirculation of the pump.
I work with end suction centrifugal pumps for a living. If you have specific questions, I may be able to help.
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That's a good idea, Kyle. I thought about this as well. However, this appears to be an area that Honda did quite well with. These clearances are already very close. I don't think the benefit of the additional suction would be worth the super tight clearances it would take to move the impeller any closer than it already is now.
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i dont keep up on some of this stuff but last i heard service honda was working on a new and improved cr250 ign that would run lights. maybe it never got completed or they scrapped the idea ? something like that would power a fan i would think
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well its called suction clearance, but its not about creating more suction. Anyways. What is the current clearance. I would take it down to .005 if its not already there.
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The shaft will grow approximately .0025 total length going from 75 to 200 degrees. so setting it at .005 would give you about .0025 clearance.
I dont know what honda sets it at, it would be cool to know.
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Another option could be an electric pump and just do away with the shaft bearing and impeller
An electric water pump flow rate is not proportional to the engine RPM and engine heat output. I do not think that you have enough electrical power coming out of the stator to power a water pump with the needed flow rate. I have not done any flow test on the 250s but the flow rates on the early 80s RM 125cc engine was in the neighborhood of 32 liters per minute at 10,000 engine RPM. these engines had power levels in the low to mid twenties hp range. My guess is you would need a flow rate of at least 15 gal/min with a pressure drop of a few psi for a 250 making 50 plus hp
V8 engines will have water pump flow rates in the 50 to 100 gallons per minute range.
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I think that there will be a lot more gains made removing / improving the flow restrictions in the cooling system than trying to redesign the water pump.
The inline temp gages, and billet finned inline coolers reduce the coolant flow through the hoses.
The billet elbow inlets as well as some of the die cast OEM elbows on the cylinders are horrible. Liquid does not like all of the sudden 90 deg corners with all of the sharp edges. 3 minutes with a small porting tool could possibly improve the flow more than the best power robbing high flow rate water pump. All of my testing points to improving the air flow through the radiator will be much more rewarding than spending time building high flow water pumps There was a period where guys were spending/wasting money on the high flow impellers for the Banshees. The Banshees needed an impeller that did not slip on the shaft when it got hot not a big power robbing water pump.
In the mid 1980s we used a Rotax model 256 road racing engines in the 250 shifter karts. We used the same engine on the micro-sprint dirt track cars. These 250cc twin cylinder engines made 75 to 80 hp. We had these 250s running 157 mph at Daytona. The radiator in the shifter kart was 5" high 12" wide and 2" thick and the engines never ran over 140 deg.f. The micro sprint cars used an automotive radiator that was about 24" x 24" x 2" thick and they would run 200 deg F. with a lot of heat related engine failures. The micro-sprint guys put their radiator behind the roll cage, drivers shoulders and head blocking much of the air flow. I could not make these guys understand the importance of getting airflow through the radiator.
The majority of the heat transfer occurs within the water jacket by a process called convective heat transfer. The heat transfer relies on velocity. As the velocity of the coolant over the surface increases, the heat transfer increases. Convective heat transfer is also what cools an air cooled engine. Increase the velocity of the air through the fins...cooling increases. The water passageways through the jacket do not need to be a mile wide and a mile deep just like the air moving through the fins on an air cooled engine only needs to moving fast over the surface of the fins.
I do not think that higher coolant flow rates are necessarily needed but only higher coolant velocities over the surfaces within the engine that need to transfer heat to the coolant. Higher velocity of the coolant over the surfaces, requires coolant passageways that are designed to be conducive to good flow with out turbulence as the coolant turns corners. Were turbulence or cavitation occurs heat transfer will be hindered.
As stated in an earlier post, increasing the volume of coolant in the water jacket or head does not have any effect on improving the heat transfer rate. It only increases the thermal inertia of the cooling system.
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makes you wonder why coolhead keeps using them fins on the back side of the chamber. not to mention the jacketing likely has the water volume increased. other than the fact that you can take a blank dome and machine it to nearly infinite chamber shapes and locate the spark plug where ever desired but other wise i see no value in the cool head style of head. other aftermarket heads look to be just copy cats of the coolhead more or less. maybe these aftermarket heads are part of the problem why people have heat issues
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makes you wonder why coolhead keeps using them fins on the back side of the chamber. not to mention the jacketing likely has the water volume increased. other than the fact that you can take a blank dome and machine it to nearly infinite chamber shapes and locate the spark plug where ever desired but other wise i see no value in the cool head style of head. other aftermarket heads look to be just copy cats of the coolhead more or less. maybe these aftermarket heads are part of the problem why people have heat issues
There is nothing in these billet heads mentioned above to direct the coolant between the fins on the domes. The fins fill up with steam bubbles and do not escape at the rate they are being formed on the surface of the fins. The steam bubbles keep the coolant from coming in contact with the hot surface of the dome. When this happens this will not cause the engine to have high coolant temperature if the radiator is of adequate size and getting the right amount of air flow through it.
We have design errors like this plaguing the aftermarket performance industry. These guys have the skills and equipment to make just about anything if they are handed a blueprint that is the result of using basic engineering principles and testing. The unfortunate part is they do not understand thermodynamics, fluid mechanics and heat transfer well enough to design parts that do what they are advertised to do.
Moto-cross engines, woods engines, and cross country engines do not usually run at max load for long enough periods of time for the symptoms of ill designed heads and coolant passage ways in the cylinders to ever raise their ugly head. These engines are plagued with bumpers with number plates, bumpers with air stopping grills, bumpers with cow catchers on them, shock reservoirs, designer radiator grills, and ill designed air scoops that keep sufficient air flow from getting through the radiator.
The symptoms of ill designed heads and coolant passage ways in the cylinders of salt flat racers, road racers, enduro type shifter karts and other applications that spend long periods of time at wide open throttle will show up very quickly even though the coolant temps may be below 140 deg. F. Improperly designed coolant passageways will show up as hot spots within the engine and will raise their ugly head when coolant temperatures are low.
If you are experiencing high coolant temps, this is not a symptom of needing more water flow or higher velocity coolant flow through the engine. The engine is getting rid of the heat but the radiator is not. This is a symptom of needing more air flow through the radiator or a radiator with the ability to dissipate more heat to the atmosphere.
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some of the aftermarket stuff seems to have very little thought put into the design. rather than a bunch of fins and a spark plug encased in thick material with hardly a chance of being cooled down, why not do something more like this, surely it would be far better
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some of the aftermarket stuff seems to have very little thought put into the design. rather than a bunch of fins and a spark plug encased in thick material with hardly a chance of being cooled down, why not do something more like this, surely it would be far better
The big question is, what are you trying to accomplish with a new head design?????????
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im not making a new head but if i were, it would be in a similar direction as the pic above. i wouldnt waste my time with coolhead or any of its copycat variants (wont mention any company names). most oem heads ive seen are designed well but unsuspecting people get sucked into exagerated sales pitches by aftermarket companies, so the oem parts get tossed on the shelf or sold. i think very few of these aftermarket companies actually have real engineers employed
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im not making a new head but if i were, it would be in a similar direction as the pic above. i wouldnt waste my time with coolhead or any of its copycat variants (wont mention any company names). most oem heads ive seen are designed well but unsuspecting people get sucked into exagerated sales pitches by aftermarket companies, so the oem parts get tossed on the shelf or sold. i think very few of these aftermarket companies actually have real engineers employed
Anytime I am designing something new, I have to have a list of things that are wrong with the old design before I can target the problematic areas with possible solutions to the problems. If there are not problems with the old design that need improving, then there is not any need to spend time and money developing a new mouse trap.
Most of the OEM heads have room for improvement in improving the combustion efficiency. I do not know of any of the OEM heads that need the cooling ability improved. I have not seen any of the billet heads with removable domes that address the real issues I am concerned with.
I have CNC equipment that could make billet heads but have not done so because I do not think that it would improve the power or the reliability on most cases. If I build a part it has to have an advantage in power and or reliability over the OEM part. I will let the guys that do not really understand engines continue to make all of the bling parts and spend a ton of money trying to market them to the customers that do not really understand engines.
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if you want to see a perfect example go on ebay and look at aftermarket banshee heads. theres 4 or 5 different companies making them and basically all they did is take a coolhead finned dome then made their own proprietary outshell around it. so pretty much all the aftermarket heads use the same coolhead dome :disgust:
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No one is disputing the need for more airflow. I have said this from day one. I also said early on that almost every shroud I have seen for the 250R is ill designed and not actually helping with air flow. Since we can "manufacture" air flow, we only have two options when it comes to obtaining more of it. We can either use a fan,(which I don't want to discuss in this thread) or to design better shrouds (which I will design after I get done with the new impeller).
Yes, we also mentioned earlier in this thread that there are several areas of poorly designed bottlenecks and rough casting areas. Since this requires multiple parts to be modified that are that way from their manufacturer, I don't find this idea to be as beneficial. If you increase the flow in the system by the impeller, it will help the system regain some or all of the flow it lost because of the rough castings and imperfections.
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No one is disputing the need for more airflow. I have said this from day one. I also said early on that almost every shroud I have seen for the 250R is ill designed and not actually helping with air flow. Since we can "manufacture" air flow, we only have two options when it comes to obtaining more of it. We can either use a fan,(which I don't want to discuss in this thread) or to design better shrouds (which I will design after I get done with the new impeller).
Yes, we also mentioned earlier in this thread that there are several areas of poorly designed bottlenecks and rough casting areas. Since this requires multiple parts to be modified that are that way from their manufacturer, I don't find this idea to be as beneficial. If you increase the flow in the system by the impeller, it will help the system regain some or all of the flow it lost because of the rough castings and imperfections.
If the deta T between the radiator inlet and outlet temp is more than 10 deg it is time to improve the coolant flow rate. If the delta T is less than 10 deg it is time to improve the heat exchange between the radiator and the atmosphere.
What is your delta T at 10 mph, 30 mph, 50 mph? If you do these simple test, I think that you will find that you are wasting your time pursuing more coolant flow through the engine and radiator.
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If the deta T between the radiator inlet and outlet temp is more than 10 deg it is time to improve the coolant flow rate. If the delta T is less than 10 deg it is time to improve the heat exchange between the radiator and the atmosphere.
What is your delta T at 10 mph, 30 mph, 50 mph? If you do these simple test, I think that you will find that you are wasting your time pursuing more coolant flow through the engine and radiator.
Every system design and requirements is different, so what technical information or background research do you base your magical 10° off of? Just for clarity are you speaking of 10°C or 10°F, because there is a very big difference. And when you say it needs to be more than 10° delta T in order to be beneficial, to what speed are you speaking of? 10mph? 30 mph? 50mph? or are you speaking of at any given time? I think that you will find that throwing out a blanket statement like that is a little presumptuous and ridiculous.
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A higher flow water pump will also slightly raise the pressure in the system which helps prevent "hot spots" and "steam pockets" caused by poor water jacket design and poorly designed passage ways.
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Every system design and requirements is different, so what technical information or background research do you base your magical 10° off of? Just for clarity are you speaking of 10°C or 10°F, because there is a very big difference. And when you say it needs to be more than 10° delta T in order to be beneficial, to what speed are you speaking of? 10mph? 30 mph? 50mph? or are you speaking of at any given time? I think that you will find that throwing out a blanket statement like that is a little presumptuous and ridiculous.
10 deg is not a magical number but a ballpark number that is an observed trend seen over 40 years of designing and modifying two stroke engines.
I have made and studied the test results of around 150,000 dyno runs and field test. I see a lot of trends that are common on engine cooling systems. I am a mechanical engineer. I use theory to guide my design work. I use test results to guide changes and make refinements to the original design. We are taught theory in the engineering colleges around the world and learn how to use it as we gain hands on experience as we apply our education and past experience to real world projects.
The Deta T is in deg.F.
Heat transfer is proportional to the delta T. The speed at which the delta T is measured allows one to match the cooling system to the application.
My goal on this forum is to share my experiences and failures with the members. If I prevent them making expensive failures I have accomplished my goal.
We can get into the engineering that this topic is centered and display equations, graphs and other test results, but is probably beyond the scope of the majority of the members. I try to communicate in layman's terms on this forum.
I was just trying to save you some time and money going down a road that I have been down many times on different engine development projects. If you think that is ridiculous then take that journey. I hope you arrive at a different destination than the Honda engineers and myself arrived.
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10 deg is not a magical number but a ballpark number that is an observed trend seen over 40 years of designing and modifying two stroke engines.
I have made and studied the test results of around 150,000 dyno runs and field test. I see a lot of trends that are common on engine cooling systems. I am a mechanical engineer. I use theory to guide my design work. I use test results to guide changes and make refinements to the original design. We are taught theory in the engineering colleges around the world and learn how to use it as we gain hands on experience as we apply our education and past experience to real world projects.
The Deta T is in deg.F.
Heat transfer is proportional to the delta T. The speed at which the delta T is measured allows one to match the cooling system to the application.
My goal on this forum is to share my experiences and failures with the members. If I prevent them making expensive failures I have accomplished my goal.
We can get into the engineering that this topic is centered and display equations, graphs and other test results, but is probably beyond the scope of the majority of the members. I try to communicate in layman's terms on this forum.
I was just trying to save you some time and money going down a road that I have been down many times on different engine development projects. If you think that is ridiculous then take that journey. I hope you arrive at a different destination than the Honda engineers and myself arrived.
While I appreciate you putting things in layman's terms for us simple folk, but I happen to be a mechanical engineer as well that happens to study, design, and spec cooling systems for a living. I also use theory to guide my design work and use test results to guide changes and make refinements to original designs. I also was taught theory in the engineering college that I went to and have traveled around the world with my work due to the engineering experience and capacity that I have.
You are right about the heat transfer being proportional to the delta T at the rated rpm (not speed), at a given airflow, that the engine produces it's highest heat rejection requirement, and the cooling system is balanced to meet this heat rejection based on this value. So, something we agree on.
While I appreciate you trying to save me money and time with your 40 years of engineering experience and testing on this exact situation, I respectfully disagree with your theoretical outcome and will continue to pursue this and do some actual testing. A destination that you and Honda arrived at? Again, quite presumptuous. Honda spec'd this cooling system for a 246cc engine, not anything larger. So I'm reasonably sure (not completely sure, because I don't want to be presumptuous) that Honda didn't study this specific application.
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One thing I noticed about every billet o ringed sealed head that I have scene is the coolant passages are all the same size. You would think this is a good design while actually the OE designed head gasket with the different sized passage ways that force more coolant to the front of the cylinder is best. The only o ringed head that has the OE design that I know of is the cast Pro-X ones.
I like the idea of trying to improve the cooling system as much as possible and just the fact that someone may re produce the 89 250R style water pump shaft is great. Honda still sells the 89 impeller but not the shaft, go figure. I don't think you can even get the 85-88 style water pump parts anymore.
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While I appreciate you putting things in layman's terms for us simple folk, but I happen to be a mechanical engineer as well that happens to study, design, and spec cooling systems for a living. I also use theory to guide my design work and use test results to guide changes and make refinements to original designs. I also was taught theory in the engineering college that I went to and have traveled around the world with my work due to the engineering experience and capacity that I have.
You are right about the heat transfer being proportional to the delta T at the rated rpm (not speed), at a given airflow, that the engine produces it's highest heat rejection requirement, and the cooling system is balanced to meet this heat rejection based on this value. So, something we agree on.
While I appreciate you trying to save me money and time with your 40 years of engineering experience and testing on this exact situation, I respectfully disagree with your theoretical outcome and will continue to pursue this and do some actual testing. A destination that you and Honda arrived at? Again, quite presumptuous. Honda spec'd this cooling system for a 246cc engine, not anything larger. So I'm reasonably sure (not completely sure, because I don't want to be presumptuous) that Honda didn't study this specific application.
I'm no mechanical engineer, but it seems delta T is the difference in temperature between the radiator and the engine. In a zero air movement environment, your delta T should be theoretically zero, no matter what speed above a trivially low rpm you run the engine at. It is in the heat exchange provided by the radiator that delta T increases.
What Jerry is saying is the water velocity's impact on the engine temperature is proportional to the difference in temperature between the radiator and the engine. The MPH-only situation might be overly simplistic, and there would be a major difference between say 10krpm 2nd gear at 30 and 2krpm 6th gear at 30, but the speed of air passing by the radiator is an important component.
At these different speeds, if the "delta T" is zero, then a new impeller is pretty pointless. If your delta T is 50, then it's probably worth it. 10 sounds like a decent ballpark figure.
This data, at different speeds, is exactly what I'd think any engineer would do before designing a "better" component.
Unless you just want your mouse trap to have death spikes and some mouse poison just to make extra sure.
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One thing I noticed about every billet o ringed sealed head that I have scene is the coolant passages are all the same size. You would think this is a good design while actually the OE designed head gasket with the different sized passage ways that force more coolant to the front of the cylinder is best. The only o ringed head that has the OE design that I know of is the cast Pro-X ones.
I like the idea of trying to improve the cooling system as much as possible and just the fact that someone may re produce the 89 250R style water pump shaft is great. Honda still sells the 89 impeller but not the shaft, go figure. I don't think you can even get the 85-88 style water pump parts anymore.
All esr billet heads have always had more flow to the ex side then the intake side. Look at all of the passageway cutouts in the shell and you will see it. It has changed over time but there has always been something in theirs, but not always in others like you said.
edit=without making another post v v v v v, thanks z.
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I don't mean to hijack your thread Ryan but since this came up I thought I'd post on it. Red=Old ESR Black=New ESR
(http://forums.trx250r.org/vbulletin_imports/103_4721_2017-04-18_2106.jpg)
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I got the shaft modeled up this morning. Am working on making the drawings. Going out for quotes pretty soon. I'm gonna get these made in 304 SS. I'm gonna start another thread to see if other are interested in the shafts or the impellers to see how many to get quotes for.
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(http://forums.trx250r.org/vbulletin_imports/100_5098_2017-04-18_630.jpg)