All right, planning out a project for a roadrace; will be about 200-230whp NA and will be ducted.

First off, about what is necessary for aftermarket oil coolers? The aftermarket FD stuff seems to be a pair of 19 or 25 row coolers, which looks for the Setrab stuff anyway to be about 11x6 or 11x7.5 inches each, but not sure if that's on the small side for my uses because most are doing street stuff, or on the large side because they're turboed.

Secondly, about how large of a dry sump pump is needed? I know there's not a heck of a lot of choice on pressure sides but that's not the same as no choice and it would be annoying to have to go spending money more than once. And no, given the price of it I'd rather not just get the Mazdaspeed front cover.

Thanks!

 

1. since the FD is turbo, and the turbo adds heat, that the larger coolers would be about what you'd want for a road race car. it would be interesting, in concept to do the BTU calcs, but i guess you only really know the fuel amount, and time...

2. no idea, but i'm reading a 911 book at the moment, and they are dry sump. well its a German car dry sump, so they really just have a smaller oil pan... anyways, those are 2 stage, suction and um, blow? and early on they had the small street one and the race one, but the street ones keep getting bigger until it becomes bigger than the race pump. so possible that too big would be hard to do.

 

Yeah, there's way too many unknowns and fudge factors for calculations for my taste, and frankly I've seen the result of industrial type systems designed by the calculations once or twice. "What do you mean we can't run that test during summer?!" On the other hand, measuring BTUs going out through the coolers afterwards might be fun.

 

actually you could go backwards, and do the BTU calcs for what Mazda used stock, and then just multiply

 

Or I could be lazy and look at the area of the old Mazda factory competition oil cooler now I think of it - that's probably sized reasonably close to "right" for racing conditions with an NA 13B.

 

The stock oil cooler is fine when ducted well or else run a pair of them in sequence.

 

I'm making that power in my 13b and just use the stock cooler with a duct. No oil heat issues even at our hottest races.

 

I never had good oil temps with a single stock FC cooler, even with creative ducting. Stock port, non-turbo engine.

We went to two stock oil coolers plumbed in parallel with proper ducting and have never looked back. Sub 200 deg oil at the filter pedistal no matter what the conditions.

 

I think I can package aftermarket coolers into a Miata a lot easier than one or two of the OEM FC ones, is all.

 

What's your elevation?

 

We race primarily in the midwest so sub 2000ft in every case. Which anything below 2000ft is basically all the same from the perspective of pressure and air density.

We raced road atlanta and MRLS for the nasa championships and story was the same there, sub 200 deg all day long, even in 95deg ambient

 

I have my oil coolers stacked in front of the radiator. You can block the radiator with oil coolers without an issue in the FC as long as that's the only thing in front. No intercoolers, no condenser coil, no other coolers. Reason being if you have lots of oil cooling you take some load of your water cooling needs.

 

My observation from the limited "racing" (auto-x and kart track sprints) in my RX-8 is-

Oil temps really skyrocket with very high rpm engine operation on an NA rotary. So, it is really going to depend on your individual set-up.

I have an auto with 1 oil cooler so I am always spraying that cooler down as soon as I park. If the course has me on or near the rev-limiter for the full 50 seconds or so you wouldn't believe how hot the oil gets in that short time. If the course has me shifting into 2nd and 4-5,000rpm there is very little heat put into the oil.

I think you can find a bar chart from Mazda that shows the increases of energy losses with rpms that includes friction. I think friction is a big part of the oil heat input from high rpm operation.

If you are building an NA rotary that will have close gears and porting that makes its power where a stock engine was rev-limited I would go overkill on the oil cooling.

If you build a rotary with flexible powerband and stock gearing that is lazily buzzing away between 5-7,000rpm oil cooling probably isn't as critical.

My 2 cents.

 

And in contrast.

I never had an issue with my oil temps on my 400rwhp FC with just the stock oil cooler moved up to the front of the bumper opening and oil mods (more pressure/flow and capacity).

I even had an oil temp gauge in that car. I barely got oil temps over 100C even on 1,200+ft elevation change 2.2mile hillclimb in 100F weather.

I went to a different turbo and 26psi boost for more torque and I expected to see a rise in oil temps, but they didn't because now my peak torque was 4-6,500rpm so that is where I drove it.

Oil temps= frictional heat.

 

It's easy to forget about heating vs RPM - overkill it is!

 

An interesting statistic about small block Chevys is that roughly 50% of the oil temp comes from the oil pump itself.

I firmly believe that bigger oil pump is the WRONG answer for high RPM use, as the distance from the inlet to the back of the pump increases as the pump gets larger (wider) and this increases oil heating and the likelihood of the pump cavitating. You need enough pump to make your desired pressure and NO MORE. Any more than that wastes power and heats the oil up since all the extra volume is just being blown out the regulator.

I have no problem making 100psi oil pressure with a 12A oil pump. 25psi at idle, 70psi at 3000rpm, not sure when it hits 100 (hard to see both gauges at the same time ). No need for 100psi at idle, so this is perfectly fine. Never have had an oiling related failure when pressure is maintained. (front O-ring... RX-8 cover is THE FIX for this problem) I also have never noted the high RPM oil pressure dropoff that people note with the large oil pumps, proof that they are cavitating at high pump speeds and mine is not.

 

Well, eliminating oil going into the front cover entirely is, I'd argue, an even more reliable fix for that. But yeah, from working in R&D at a bearing manufacturer, it's amazing how little oil is actually needed to lubricate.