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 Post subject: Re: RX-7 Rotary Cooling
PostPosted: September 25, 2009, 9:54 pm 
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rx7locost wrote:
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The lessons I took from this are that rotaries are inherently evil and don't belong in a Locost.


Now Chet, that cuts to the bone! Of course I may just change my mind when I'm up and running. From what I have read, about 1/3 of the cooling of a rotary comes from the oil cooler. After seeing the insides of one of these, I fully believe it. The insides of the rotors themselves are cooled with oil that continually flows in and out of the rotor.

You know I kid, but only because I think so many folks think cooling these wankels is no different than cooling a piston engine. After reading Ron's page I remember cringing when reading that someone was going to use a Civic radiator.

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 Post subject: Re: RX-7 Rotary Cooling
PostPosted: September 26, 2009, 8:38 am 
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On most engines, a third of the heat goes to the oil, the water, and the exhaust.

Oil is definately a coolant.

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 Post subject: Re: RX-7 Rotary Cooling
PostPosted: September 26, 2009, 8:55 am 
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chetcpo wrote:
You know I kid, but only because I think so many folks think cooling these wankels is no different than cooling a piston engine. After reading Ron's page I remember cringing when reading that someone was going to use a Civic radiator.

Hey, I resemble that remark! :)

The stock cooling system does not look like all that, so I was thinking that a super-duper Civic rad ought to suffice. But after reading these horror stories from competition, maybe not. I am not planning on using the car for competition, except maybe to try autocross just for fun, but I'd hate to gamble on the wrong equipment.

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 Post subject: Re: RX-7 Rotary Cooling
PostPosted: September 26, 2009, 11:01 am 
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Honestly a wenkel is taboo in most circles. Most people are either intimidated by them or think of them as unreliable and simply put a crap engine. I personaly think that if built and.....this is the most important part..TUNED right, they could be as dependible and reliable as a piston engine. There are actually some guys that use them in experimental aircraft with awesome results. Ill see if I can find the site where I read this but there have even been stories where the engine would loose coolant(donated to the plane from a high mileage car and installed without a rebuild) and the pilot would still have minimal power and was able to land the plane(will find the site and story).

Anyhoo there are numerous factors that can contribute to a wankels demize. Cooling is usually #1. Specially when you turbo an engine or do any performance upgrades. A bad tune is usually #2. Detonation will destroy a wankel in no time flat.

For my build i was considering a 442+4? If I understand correctly that is a longer and wider chassis from the original "book" design? (please corect me if i am wrong)

With that chassis i should have enough space to sidemount 2 custom built radiators and an oil cooler. I do plan on having the rads plumbed in series so cooling should be fairly adequate if executed properly. This probably wont be my, or rather i should say our only build since my wife and i plan on building two locosts. So lessons will deffinitely be learned and new ideas allways formulated.


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 Post subject: Re: RX-7 Rotary Cooling
PostPosted: September 27, 2009, 12:33 am 
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Ron just sold his car but he posted a picture of the front end.

He mounted an oil cooler on top of the nose with a duct that exits the air behind and a radiator bellow it.
here a link to the add, http://www.casc.on.ca/forums/showthread.php?t=17786
you will see on the last picture how it's set-up. That Oil cooler is a thick mother... If you look closely you can see his original radiator in front below.

here a few pics I took a few year back.

Image

Image

Image

Cheers,

Fred


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 Post subject: Re: RX-7 Rotary Cooling
PostPosted: September 27, 2009, 1:22 am 
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Gee and I've had 3 3rd gens and 2 2nd gens with never a failure of any system including the radiator system. Never overheated one no matter how hot it was and how hard I ran it.

I did fry the brakes on the track once, well actually I boiled the brake fluid, but that's the closest to a failure I ever had with an RX7.

I'd own another in a heartbeat and wouldn't be afraid to stuff one in a Locost.

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 Post subject: Re: RX-7 Rotary Cooling
PostPosted: September 28, 2009, 12:30 am 
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I read somewhere that Ron's issue was airflow related, once he found the solution he went back to modified motors and never looked back. He did block some cut outs he had done on the hood.
Image

He did have some side vents.
Image

On issue on the Locost is that the air does not have an issue entering the nose, but getting out is. It can't get out from the bottom in untill it hits the engine as the nosecone prevents it and that first piece of floor that's welded or rivited, not that would be a good solution. It's normally pretty cramped in there, so the hot air need to be given a chance to escape. Loovers are one solution. The outher is having the sides gilled as we did for our cars...
Image

Cheers,

Fred


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 Post subject: Re: RX-7 Rotary Cooling
PostPosted: September 28, 2009, 9:52 am 
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Interesting, I had run across his site before, but this is the first time I see that he was using a +4 nose with a standard width rear. I have been considering something similar.


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 Post subject: Re: RX-7 Rotary Cooling
PostPosted: September 28, 2009, 10:07 am 
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He started with a +4 and then narrowed it again.

That looks like one of Jack McC's catfish noses.

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 Post subject: Re: RX-7 Rotary Cooling
PostPosted: September 28, 2009, 5:17 pm 
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Pete B wrote:
He started with a +4 and then narrowed it again.


Actually if you read closely, he started 4 wider and 4 inches longer (I don't see mention of height, but maybe it was a 442E). He then took 8 inches out of the length and 4 inches out of the rear width, keeping the forward +4 and changing where the angle started from the rear of the Scuttle to the front of the scuttle to make up the difference (but IIRC, my calculations put the revised "break point" at the firewall/footbox rather than the front of the scuttle when doing a +4/0).

http://www.softarc.com/~ron/locost/Oct2002.html


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 Post subject: Re: RX-7 Rotary Cooling
PostPosted: December 6, 2010, 8:59 pm 
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Sorry to re start an old thread, but I am doing a rotary build, and am planning on using 2 motorcycle rads in series (one from an R1 and the other from an RZ500). I am decently confident that this will pose no problems. I am running a stock port 12a, with only minor mods. I have had multiple RX-7's including a heavily tuned 1990 turbo. The biggest cooling problem I have ever had is Exhaust temps are on the extreme side. I believe if most of the exhaust is on the outside of the car this should drastically lower underhood temps.

Oh and I plan on using ducting to pull air out of the engine bay. while side mounting the rads and front mounting the 12a oil cooler.

Does anyone else see problems with my set-up.

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 Post subject: Re: RX-7 Rotary Cooling
PostPosted: December 6, 2010, 9:06 pm 
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carguy123 wrote:
Gee and I've had 3 3rd gens and 2 2nd gens with never a failure of any system including the radiator system. Never overheated one no matter how hot it was and how hard I ran it.

... and using a radiator and oil cooler larger than can fit into a Locost no doubt. As was said, the problem isn't the engine, it's the chassis/nose of a Locost being so small that a proper rotary cooling system is a serious challange. My brother used to race RX-2s and RX-3 and we used seriously huge radiators and oil coolers... Yup, they never overheated, but what's that got to do with a car where there's less than half the needed radiator space? Apples and oranges.

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 Post subject: Re: RX-7 Rotary Cooling
PostPosted: December 7, 2010, 9:23 am 
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As stated before, the crucial issue with the Locost design is getting airflow in and out as much as the size of the rad/cooler units.

I have been advised to use the 1st gen oil cooler as it is a great unit but expensive and hard to find. I am also planning extensive engine bay exhaust ducting as well as a couple electric fans for the oil cooler itself.

Another nationally competitive SCCA autocrosser running a rotary Westfield found the belt driven stock water pump lacking with 2 driver cars on hot days and went with a electric water pump he can let run between heats. autocrossing challenges cooling systems with all the grid/staging idle time involved. Less of an issue for track day and road racer guys.

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 Post subject: Re: RX-7 Rotary Cooling
PostPosted: December 7, 2010, 1:08 pm 
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have you looked at the oil cooler off of a w123 mercedes diesel? eg, behr # W0133-1598233(for an 82 and up), able to keep a 3 liter diesel oil temp under control even at a 300hp tune. you pay for the name if you buy it new but its pretty cheap at your local picknpull and roughly 19" long as i recall. i'll measure a '79 if anyones interested in dimensions, they should be about the same size iirc and i have one in the driveway.

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 Post subject: Re: RX-7 Rotary Cooling
PostPosted: December 7, 2010, 3:50 pm 
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I can add another data point on the rotary cooling. The best I can relate to is cooling at idle. Sitting in the garage trying to get things adjusted with the MegaSquirt, the engine comes up to temp fairly rapidly. In my application, the cooling fan is controlled via the MS. Presently, when I hit 185 degrees, the cooling fan comes on. It is set to turn off at 180. The fans runs a fair amount of the time I'd say about 50-75%. It does keep up, but I am a bit worried about when I actually start running down the street if I will need to do something else.

I am running the Civic radiator with a 14" electric fan (I think) and the 2nd gen oil cooler.

That Mercedes oil cooler looks about the same size as the 2nd gen. The 2nd Gen cooler includes a oil bypass thermostatic valve for faster warmups. Don't know about the Mercedes.

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