Hijacker's Paradise - the Grooved Housing edition...
 

so does the water jacket milling help with cooling? great build so far!

You must be new to Rotary engine :)

Racing Beat has been doing it for years.

I was thinking of sending my Turbo housing to RB for modification, but now I think I might send it to BDC (along with lots of other stuff) :)

Which part? Adding the grooves on the sides or removing the splitters? In theory, both. As has been said, Racing Beat has been doing the grooving on the water jacketting walls forever. The removal of the splitters in the jacketting was my idea based on what I saw being done factory on some Renesis rotor housings. Figured I'd give it a try.

B

Heat transfer is (for the most part) all about surface area and flow rate. The grooving about doubles the surface area and removing the splitters decreases the flow resistance. You lose some surface area from removing the splitters, though if you are seeing lower temps then the increase in flow must be making up for the loss of area.

yeah i am new to rotaries and what type of tools will be needed to do this? if this will help with cooling i might want to do this to mine since living in a very hot area (las vegas). thanks...:icon_tup:

Interesting. Thanks for the explanation.

B

An increase in flow would reduce cooling capacity. The purpose of the grooves is to create turbulence and slow coolant flow, giving it more time to absorb heat from the housing.

Also I would recommend against using aluminum foil to isolate that trigger line. My car (when I ran a Haltech) had to have the *worst* trigger problem in the history of haltechs and nothing short of putting it on a bench with a new harness would do the trick for isolating the trigger and keeping it noise free.

If you have issues, get quality trigger wire and replace the whole chunk of garbage one end to the other. Otherwise the day will come when a misfire trashes a few apex seals, and you'll be scratching your head wondering why the foil from your christmas turkey didn't do the job.

Actually, um, no. Any convective heat transfer is dependent on the surface area and the temperature differential between the surface and the fluid. The faster the fluid is moving, the less time there is for any particular 'packet' of that fluid to collect heat. This corresponds to a lower bulk fluid temperature -> higher temp differential -> higher energy transfer rate. The same is true for the radiator. In order to radiate more heat, you need to move more air through it.

The heat transfer coefficient is dependent on the physical properties of the system and the flow dynamics. On the inside of the engine, the flow is always going to be in the turbulent regime, unless the water pump isn't working at all, in which case you have bigger problems.

As a Chem-E I'm less familiar with electrical dynamics, but the shielding I've seen in most cables is essentially just foil wrapped inside the outer insulation jacket. I know in A/V systems, there are issues with grounding both ends of the shield and causing ground loops, but I'm not sure if that applies to cars since the whole damn thing is pretty much a ground.

You know, the one thing that I think would put some of this water jacketting mod stuff to bed would be CHT gauges. Of course, none of us run 'em. I don't even know if it's possible or not.

so are you saying there should be more flow through the block or less? I think through the radiator you need maximum flow, because it has an unlimited external supply of cool air. Within the block, the fluid takes time to heat and cool, so lower flow rates are better. Im sure its more like a bell curve though, since flow rates too slow will not cool either

In an absolutely perfect world you would have infinite surface area with infinite flow. The radiator example is actually a really good one. In a way, you have in unlimited supply of coolant, since it is constantly being cooled by the radiator and it's constantly being supplied to the motor. In order to maintain the best heat transfer you want the largest difference possible between the coolant ant the engine. "giving the coolant time to heat up" is bad, since there's always more, cooler coolant on the way.

You can approach this another way too. If you wanted to slow down coolant through the passageways, why wouldn't you simply put on a larger pulley on the water pump to slow it down instead of taking the time and energy to machine the ridges in the coolant passageways?

You're on the right track, but you have the ins and outs backwards. The engine block can be looked at as a general energy source. Energy transfer(heat flow) is caused by a temperature gradient(hot -> cold). The temperature of the engine is determined by how big the temperature differential needs to be to remove that amount of energy that is being created by the engine. The full system is 2 steps. First, heating the water inside the engine, then cooling the water with the radiator.

Looking at just the engine, the driving force for heat transfer is the differential between the metal and the water. (If we wanted to get really complex, we'd evaluate the conduction through the metal and the convection on the surface independently.) The convective heat transfer only occurs at the interface between the metal and the water. At any decent flow rate the fluid will be fully turbulent. Due to the mechanical mixing of the water from that turbulence, the temp of a given 'slice' of the water perpendicular to the flow direction will be roughly uniform. The temp of the water will increase in the direction of the flow as energy from the engine moves to the water. The faster you pump the water through the block, the cooler the water will be throughout because it does take time to heat up the water. Cooler water overall will increase the energy transfer rate.

Looking at the radiator is slightly more complex since the transfer is from one fluid to another instead of from a solid to a fluid. The goal here is to remove as much heat from the water and transfer it to the air. Here the rate is limited by the temp of the air. The maximum temp differential is from the water temp down to ambient temp. As far as air flow is concerned, it's the same case as water flowing through the engine. The faster the air flows, the lower the bulk temperature, the faster the transfer rate. The complexities come in with the water flow Here we start to run into the trade-offs that make heat exchanger design difficult. If our goal is to cool the water as much as possible, we want to leave the water in the radiator longer to give it more time to approach ambient temp. This however decreases the actual energy transferred due to the lower temp differential at the outlet of the radiator. To move as much energy as possible, we would maximize the flow to make the entire surface of the radiator hotter, even though the outlet temp of the water will be higher.

At the limit of infinite flow, all of the water in the system will be the same temperature. That temperature will be defined by the differentials necessary to move a given amount of heat from the engine to the water and then from the water to the air. I can't say for sure, but I'm pretty sure that temp would actually be much higher than what we see in the real world, due to the differences in conductivities.(air=shitty) At infinite flow, you would also need an infinitely large radiator in order to bring that temperature down to ambient. Here in non-textbook land, there will be an optimum flow to get the engine temp where we want it. Flow too little and the engine gets too hot, flow too much and the radiator gets too hot(seriously, think about it for a bit).

I can't say for sure what the optimum flow is for the system as a whole, due to the behavior of the radiator. But if an increase in flow corresponds to an increase in system temp, that means you are limited by the capacity of the radiator, which is a little easier to adjust for than the capacity of the cooling passages in the engine.

Sorry about that whole wall of words. I hope is helps someone out. :blush:

Edit: sorry scrims, didn't see your post at first. Yeah, that's pretty much it. :)

Thanks. I could've done a better job with the cutting on the jackets. I'm not using a long enough carbide ball bit and the tool jumped around more than I'd like. Next time I might try it on a drill press instead and see if I have any success with sliding the housing left and right. /shrug

B

ive seen pictures of rotary race engines where cooler water flowed into those areas from a hole that was tapped in the general vicinity.

Had an idea like that w/ a buddy of mine a few months back -- drilling and tapping 1/4" to -6AN adaptors in front of the leading plug bosses and running a pair of -6AN water lines from post radiator. Kinda dismissed it as being overkill, though. Really, I'm not sure if anybody can quantify differences in plug temperature or not with all of this stuff. I'm a numbers guy and I like seeing the hard data so this sort of bugs me a bit even though I spent a couple of hours screwing with the water jackets on these housings.

B

Well, well, well....
 

Enjoy the new home, fellahs... ;)

:cool:

Heh, heh. Thanks Mario. I thought this looked familiar...

You can have ground loops between head units and amplifiers. It isn't common but there have been a few occasions I had to use a ground loop isolator on the RCA's, but thats like 3 times out of 1000 cars.

The first couple cars I did audio in had horrible wiring, so I just got in the habit of using ground loop isolators on all of my signal wiring. Not sure if it's necessary, but it's not hurting anything.