water jacket weave porting
 

i'm going to attempt to resurrect this seemingly dead art by giving it a new name!

since these days rotaries have been going onward and upward exponentially over the past few years i thought this would be a good time to attempt porting the water jackets and try to get a comprehensive result on if they help or do anything at all. keep in mind this will take some time to actually prove whether it is worthwhile or not at all.

https://img413.imageshack.us/img413/2439/dsc00155oc.jpg

the point of the modification is to slow water flow across the surface and increase the surface area in the hottest part of the engine(the combustion area durr!). by increasing the surface area and slowing water flow it increases heat exchange and increases cooling efficiency in that area. the spark plug bosses have a tendency to crack, meaning the engine is running far too hot in that area so cooling it more would be beneficial.

the other reason i see for doing this is to help ignition breakup and additional apex seal cooling through the housing, the hotter the housing gets the less the apex seal can cool itself and can flex(too much flex can cause it to catch the exhaust port opening). increased internal temperatures also increase the possibility of a detonation cycle to occur.

this modification is nothing new to rotaries, the last i heard about it was about 5 years ago and doing a recent search leads to that being the end of the discussion here on this forum.

now i don't foresee myself trying to sell this service because it takes a gross amount of labor hours(about 15 hours per housing..) to do a meticulous job, as i do it all by hand so as not to dig too deep into the rather thin walls of the spark plug castings. but if tendinitis permits i could probably do a pair of housings for around $500(both leading and trailing spark plug passages). i know other shops do it for less but they also don't put up pictures of how well they do the portwork or where the focus is made...

after the porting is finished and cleaned up i will treat the raw aluminum surface to help prevent electrolysis from eating away at the hot spots(around the spark plugs).

on another side note, mazda did attempt to cool the rotor housings more in this area on the S6(FD3s) rotor housings by cutting deeper towards the rotor around the spark plugs but they did not bother to recast the housings for more improvement beyond that. S4 and S5 housings had 0 improvements in this area that could be benefitted from.

these housings will be used in an S5 FC that will be making ~500-550WHP, it made 450WHP on the dyno with the old turbo @17psi and the engine lasted approximately 30k miles until it died due to injector fouling(i built the engine about 3 years ago and last tuned it about 1.5 years ago. test results showed the leading secondary injector output 15% low which resulted in a dead front rotor). it has always had temperature issues with the front mount IC.


anyways, i'm curious if anyone else has used this type of modification and have noticed beneficial or negative results. the key to progress is making sure you move forward, the more we can do to make more reliable power from the rotary engines the better to prove the others wrong.

It doesn't slow the water flow down at all... speeds it up quite a bit actually where it counts - the surface.

it may not slow it down......but the fact that it is a rougher area makes it less easy for the water to pass by (much like cooling fins on a radiator or IC)...which could possibly help cool the motor. I'm interested to see the outcome...

the important thing is that the surface area is increased, this allows the heat to be transfered more quickly, the same reason air cooled Harleys have fins on the cylinders, or like heat sinks on computer processors.

That's cool stuff Karack. I've been reading about Meth/Water injection as a way to enhance cooling also. I bet they could be used together as a double hitter.

The purpose is to increase turbulence, so that more of the water flowing through the water jacket will contact the walls.

Remember, the whole point is for the water to make contact with the surfaces. Fast, turbulent flow is the goal. You don't make radiators with three or four huge tubes, and for the same reason.

i figured that this car was a good test for this modification due to it's purpose. the only thing it has removed is the a/c, has full trim and more additional weight from upgrades and stuff in the bins(full trim weight is probably ~2800lbs dry) and is using ~500whp for sustained periods in canyon runs going uphill as well. since we are not going to the v-mount i wanted an additional safety buffer to aid in combustion cooling since it is going to be turned up to 20psi or so on pump fuel/AI.

sub

I never understood this mod.

The flow of the cooling medium is at 90* to those ridges. So I would think that when fluid flows over/through it, I would think the same thing would happen there as when water flows over a set of ridges on the beach - flow slows, water flow becomes turbulent and bubbles form.

When looking for performance in the intake tract, you replace accordion style intake piping for smooth piping. That makes sense to me. This does not but I'm not expert.

"Bubbles" can mean two things in a fluid: 1) air or other gas suspended in the fluid and 2) fluid is momentarily transformed into a vapor, aka cavitation.

There should be very little air circulating in the system. As well, cavitation requires areas of very low pressure. So cavitation tends to form where there is extremely high shear in the fluid and this only tends to happen around water pumps. Cavitation makes a sound and is erosive to the surrounding parts, so if this is going on one could see the wear after some time of operation.

The turbulence in and of itself helps cooling flow. Since the coolant at the walls of the passage are hottest, turbulence moves the hot coolant away from the hot wall and keeps the coolant in contact with the wall cooler on average. That means more cooling. Similarly, more wall in contact helps with the heat transfer too.

The downside to turbulence and increased surface area is drag. Depending on the speed and type of pump used, extra drag may result in slower coolant flow which means hotter coolant coming off the block and less cooling for components near the end of the coolant flow circuit.

Like all heat exchanger applications, there are many aspects that are a tradeoff. You almost need to build, instrument, and test to see if they will work. Like most aftermarket modifications this is probably not practical. If you're just adding turbulence in a few critical areas I suspect the net effect is positive.

David

Only a slightly related note: I wonder if it's possible to modify the cooling passages so that each rotor housing is cooled in parallel, rather than in series. You'd have to add ports and stuff but that might help solve the problem of excess rear rotor heat.

the only way i can see to cool in paralell would be to add block offs and external ports to the rotor housings but i think that is going overboard in thinking that the heat exchange is going to make such an aggressive difference which i don't think it will. the tension bolts just mess with the coolant flow paths to make it nearly impossible to do internally.

i'm sure it will work a bit better but we have seen plenty of front rotors blown to know that it isn't simply a rear rotor cooling issue(of course i would lean on the rear rotor detonating before the front if AFRs and timing were perfectly equal though). the most ideal thing would be to have the freshest coolant going across the combustion side of the engine, which is already true anyways.

I haven't had a chance to look at irons since I thought of this, but aren't there coolant freeze plugs on the front iron that could be replaced with a nipple that would lead to the leading plug coolant passages?

My idea is to take a Bosch auxiliary water pump off of a VW (I'm pretty sure I still have one around here) and take coolant from the lower radiator hose and push it through. This would bypass the thermostat with a small amount of cold water, and increase the flow rate through passage.

Have any idea of the flow rate on that pump/

there is actually 2 ports on the front iron, the front freeze plug leads to the trailing coolant passage and the lower block plug leads to the passage just below the leading plug passages. you could block the trailing plug passage inside the iron to keep the water pump coolant from disrupting the add-on pump flow, i really only see this working for the trailing plug which in theory should be effective as it is the hottest part of the motor aside from the exhaust port. the exhaust port cooling isn't as important as the combustion side cooling IMO. it's been documented that the trailing(top side) of the combustion chamber around the trailing plugs is the hottest area and most susceptible to where detonation occurs.

i thought this was something racingbeat does also?

they do, as well as another shop that i can't recall the name of. racing beat doesn't do it quite as aggressively as i did but they do it more towards the intake side of the housing versus just the combustion side.

You may find this article about the dimples in golf balls useful.

I'm not an expert either, but I think it applies here.

http://www.aerospaceweb.org/question...cs/q0215.shtml

I can't find any exact info on the VW pump, but similar Bosch pumps are used on Cobalt and Lightning A/W intercoolers and from what I see on those, it is around 2-5 gpm.

Karack, I had forgotten about the fact it is the trailing side that runs hotter. There would be no need to block off the flow from the main water pump, and in fact, I believe that would be a poor choice, since if the aux pump failed, then there'd be no flow through that region. Instead, you would allow the aux pump to assist in accelerating the flow of coolant through the crucial area. The coolant is also the coldest you could get if you route it from the outlet of the radiator.

Of course, then there is another pressing issue. The main drawback to a centrifugal pump such as the Bosch is that it is awesome at creating significant amounts of flow, but it lacks the ability to flow when it must push/pull against a resistance. The resistance in this case would be the thermostat. Therefore, you would need to bypass the thermostat with a sufficient volume so as not to restrict the auxiliary pump flow.

On an car that is going to be used without a heater core such as mine, this is quite simple. Use the heater core nipple on the rear iron (conveniently located at the coolant passage we need to cool), and route a hose to the water neck.

In this picture, blue is the freeze plug where I propose to pump cold water in, and red is the outlet for this auxiliary circuit. It would the be routed into a nipple on the upper water neck.
Attachment 722867

Any critique or errors I overlooked?

^^ You might want to search for a really long thread in which Barry Bordes partipated on a similar topic. There was a lot of good info in that one about both this weave porting stuff as well as hot spots in the trailing plug area and coolant re-routes.

Why not tap the water pump, weld a bung between the trailing plug and run hose. Kinda like what that 26b has.

gracer7-rx7- Yes theat thread NEEDS to be brought up at this moment. thats were ^^^^ idea came from. I used to have the thread in my fav. on my old laptop but it got broke. i been searching for it with no luck. Has SO much good information and will answer tons of questions. So many good ideas, cooling mods and such

Found it!! So full of OMGoodness information

https://www.rx7club.com/rotary-car-performance-77/why-apex-seals-fail-866513/page9/

Racing Beat charges $100 per housing for this service, which leads me to believe they have some sort of CNC program set up to crank these out. I notice they specify the housings shouldbe used for race engines, which leads me to wonder if they believe there might be some long-term issues with removing the material.

Hmm interesting...Well guess theres only 1 way to find out lol.

i can only assume they noticed some failures due to the raw aluminum not having been treated prior to assembly. the raw aluminum is more susceptible to the chemical reaction of gases being created during the cooling system boiling off on hot spots in the engine or minerals from hard water becoming statically charged and discharging on the surface with least resistance.

i have seen it in plenty of cases where there is heavy electrolysis around the spark plug bosses and exhaust port casting, the areas not affected still had the oxidized protective layer where the pitted areas looked more like the base metal. i will harden the surfaces before i plan on putting the engine back together to fix this. i however don't have plans to bypass the cooling system and add an external pump for these passages like some others have done at this time so i will only be testing the porting aspect of this modification for now. but the idea is better for getting fresh water to those areas.

my first rotary engine build in my personal car(first rotary rebuild ever for me) had the worst case of electrolysis i have ever seen to date and i dealt extensively in figuring out the cause. the water jackets were completely compromised in some areas and i still have the housings that i use for painting fixtures for the irons.

I can go with that theory, adding only that sacrificial anodes are very likely to be needed even on protected coolant jackets and using a good coolant mix.