Yes, my Fluidyne cooler should easily do the job of cooling my current engine. But I am building a P-port 20B to replace this motor downstream, so I need to design for 375hp (375 x .8 = 300). The Fluidyne cooler is 297 cu in (core size is 9 x 11 x 3). Close enough for government work.
On Mon, Dec 14, 2009 at 5:48 PM, George Lendich
<lendich@aanet.com.au> wrote:
Sorry Mark,
It's hard to keep track of who's running what, on a 20B or say 300 +hp, two would still be too much, but you know that already, as you said your running too cool. One of your coolers is more than a stock 13B cooler by about 14 cu"
Do you or anyone know the size of the stock 20B oil cooler?
Just playing with the figures, I guess I could use .8 or .85 cu" per Hp for oil cooling, just as a linear calculation. Using .8 , Mark's need for 300hp is only 240cu", however each oil cooler is 189cu" ea. This area required may need to increase incrementally with increased HP.
Anyone with any suggestions in regard to this?
George (down under)
George,
Keep in mind that I have a 50% greater cooling requirement than a 13B.
Mark
On Mon, Dec 14, 2009 at 3:51 PM, George Lendich
<lendich@aanet.com.au> wrote:
Mark/ Jeff,
I hadn't bothered to check the size before as the Mazda oil cooler is known to be more than adequate. If your using over the Mazda size in cu" then your over sized. Both your cooler areas are well over sized. I seen one chap used two Mazda coolers when taking off on water using NOs, but he admitted it was over cooling.
George ( down under)
George,
I'm not at the hangar today, but off the top of my head, they are about 4 1/2 x 18 x 2. I had considered using two RX-7 coolers arranged in a wedge configuration. But I ended up going with a large rectangular unit which I chose because the air would not have to change directions to get through the core. Hopefully, that would provide lower cooling drag.
Mark
On Mon, Dec 14, 2009 at 1:50 PM, George Lendich
<lendich@aanet.com.au> wrote:
Mark /Jeff,
What is the Mazda cooler size., in comparison?
George ( down under)
----- Original Message -----
Sent: Tuesday, December 15, 2009 3:34 AM
Subject: [FlyRotary] Re: Oil Cooling
Jeff,
I doubt an air lock is/was the problem as it was oriented with the inlet/outlet on the side. If there was an air lock, I would think that at least part of the other end tank would get warm (which it doesn't). Good suggestion though.
This single cooler is almost twice the size as one of your coolers. So, it should be up to the task at hand. This is assuming that it is working as designed.
Mark
Oil is a poor conductor of heat. It does not absorb heat readily and once heated does not give up heat readily. So, compared to a water radiator the oil cooler must be much larger than one would think.
The rotor exposes a huge amount of iron to the fires of combustion. From that stand point the piston engine, with just the piston crown involved starts to look pretty clever.
The rotor is cooled by the incoming fuel air mixture which expands violently when it "sees" the straight line infr-red 350 to 400 degrees of the rotor face. This expansion slows the incoming charge and in effect reduces the displacement of the engine. This is why the turbocharged engine works so well. The losses
in charge volume are overcome by the turbo.
So, the remaining cooling is by spraying hot oil into the rotor through those jets in the crank. The hot oil picks up some additional temperature and is whipped into a Mirical Whip like foam and it then drops into the pan through the center iron drain back cavity.
Most oils do not give up those air bubbles (foam) very readily. And that air is an insulator, and that
(in effect) makes your oil coolers smaller.
This also affects oil pressure. As the oil is heated, non multi grades become thinner and develop higher leak rates, so the oil pump becomes just a bit less effective, and oil pressure drops a bit from the cold oil or cool oil numbers.
The milti grade oils contain polymers (long strings of plastic) that link up when heated and this overcomes the thinning effect seen in straight weight oils. So you will see oil pressure increase with oil temperature. For a while. Over time the strings will be chopped up so many times the linking effect will become less appearant, and peak oil pressure will be lower. The polymer chains linking up makes foamed oil hold the air bubbles longer, and increases oil temperatures.
If you have a margenal oil cooling system, you can control oil temps with the throttle. Less throttle = less temperature. More throttle = more temperature. The closer to the cooling limit you operate the more obvious the effect. Once heated it takes longer time wise to get back to a lower temperature.
Plain bearings rely on an oil wedge that forms just in front of the loaded side of a bearing. Since combustion is only on one side of the engine, the oil wedge in the rotary and most engines is generally in one place on each main bearing. The oil temperature in the wedge is very much higher than the oil temperature gage will report to you. So the most important oil temperature is never reported.
Oil pressure is used to move this superheated wedge oil off of the bearing, so as to keep the soft silver bearing stuff out of the oil filter and oil pan. This is why racers jack up the oil pressure. It has almost no affect on lubrication, just cooling the bearings.
Oil weights are a measure of how fast they drain out of a little funnel. This has almost nothing to do with how good any particular oil will be at protecting bearings.
Rotaries are difficult to start when cranking speeds are low. So a multigrade oil in very cold weather is helpful in this regard.
The smaller number in a multi grade oil is the pour rate of the base stock oil. Like 5W-50. The big number is what the oil acts like (pours) when at operating temperature. The polymers in oil take up volume, so there is less oil in each can of a multi grade.
Street oils have chemicals that neutralize acids generated from sulfer compounds in combustion. So sulfuric acid will not gobble up the bearings and aluminum stuff in you engine. Some oils have so much of this stuff that they claim you can go 7,000 miles between changes. So those cans have even less oil in them.
Racing oils have few such chemicals but do have more anti scuff (zink compounds) and anti foamng compounds. Racing oil cans in straight weights have lots of oil in each can. Nonsynthetic racing oils are cheap and can be changed often without breaking the bank.
So, high oil temps endanger bearings. Produce even more foam, leading to more overheating. Oil temps above 160 degrees cost HP on the dyno.
The very best oils for film strength and lubricity are the synthetics.
There is no such thing as excessive cooling capacity.
Lynn E. Hanover