rynberg

I disagree with that statement. Oil performs 25-40% of the engine cooling. You've obviously never tracked the car in 90+F heat with the stock single oil cooler and an oil temp gauge....

KD's concept seems like a lot of work when a lot of people do not have problems with running too hot. I guess I'll have to see more of the "finished product" to lose a little skepticism.

dgeesaman

iTrader: (7)

Nope, I haven't. I have dual oil coolers

But seriously, it's a very subjective issue - oil and water both cool the engine.

Although running a water/oil cooler instead of air/oil cooler seems interesting.

Dave

ptrhahn

iTrader: (9)

I agree, oil cooling is not to be overlooked.

I'm not sure what is to be gained with the dual rad setup really. Bottom line is you have three heat-exchangers that need airflow... the oil cooler(s), the water cooler, and the air cooler. Not sure what you gain by playing the shell game and running two water coolers on the side with a central oil and air cooler, instead of two oil coolers on the side and a central air and water cooler... Also, if your going to route your coolant all over hill and dale, you'll want hard fittings like the oil system, and that means tapping all the water fittings for -AN... expensive.

I think the only significant cooling system innovation to date is the V-mount design because it means that none of the exchangers are sitting behind any of the others...

airborne

The only advantage I see for this setup over the V-mount is that you're removing a lot of hot air from the engine bay. Sure the air going through the oil coolers and IC is gonna get warmed up but not as much as going thru the rad. They do plan on using AN fittings and they are relatively expensive. How much does the V-mount run anyway?

Its hard to tell how much just doing this helped rallimike since he cornered the cooling market all at once

rallimike

iTrader: (1)

"Oil performs 25-40% of the engine cooling"
Not to be argumentative, but I don't think so. Someone smarter and more ambitious than I could compare the volume of water to oil in the engine and multiply it by their ability to absorb/transfer heat, and I suspect the water is carrying most of the load.

rallimike

iTrader: (1)

"KD's concept seems like a lot of work when a lot of people do not have problems with running too hot. "
The issue is not about running too hot; it is about removing the heat from the engine compartment, thereby minimizing heat soak and lowering intake temps.

rallimike

iTrader: (1)

"Also, if your going to route your coolant all over hill and dale, you'll want hard fittings like the oil system, and that means tapping all the water fittings for -AN... expensive."

From what I understand, this is Dave's plan. I tried several configurations: Silicone hose elbows with aluminum pipes, custom aluminum elbows with straight rubber hose...and ended up with S/S flexible hose. It's not that expensive and eliminates a LOT of hose clamps. My setup has a total of 3 hoses, from engine output to engine input.

jsplit

sounds interesting, got pictures by chance of your set up?

rx7tt95

From everything I've read over the years, 2/3 of the cooling is done by the oil system, not the coolant system. It's oil running around inside those rotors, not coolant :-) I can't recall the first place I read that statement. Perhaps someone else can chime in. Too much other stuff spinning in my head at the moment.

Kento

Not to be argumentative , but the volume of either coolant or oil, and their comparative heat absorption/transfer characteristics have nothing to do with which medium is carrying a more critical load. This is not to say that oil temp control is more crucial than coolant temps; it's just that you have to remember that the rotor face area absorbs a lot of combustion heat, and is huge in comparison to a piston engine, with literally no way to transfer that heat other than by oil cooling. Yes, the coolant performs the majority of the engine cooling, but the importance of oil cooling in a rotary shouldn't be overlooked.

Yes, it may have an "easier job", but what you're overlooking is that radiators are much more efficient the greater the temperature difference. This is why a single radiator is often the most desired setup; multiple radiators (oil or coolant) are really only used for packaging (space requirement) reasons.

rynberg

Water is carrying most of the load -- 60-75%. Several long term Mazda racers/engine builders claim that oil is responsible for at least 25% of the cooling. From personal experience, I can tell you that my water temps are noticeably cooler now that I am running dual oil coolers. The rotors and eccentric shaft are only cooled by oil. Oil also cools and lubricates the turbos. IMO, every FD should have came with dual oil coolers and not just the R models.

Well, a FMIC doesn't get heat soaked and it keeps intake temps very low. So does a V-mount for that matter.

Sorry, I just don't see the point of this "upgrade". It looks like a TON of work and expense. Until I see water, oil, and intake temps from someone who regularly tracks the car, I will continue to remain a skeptic.

matty

i think they plan do to just that. I dont know about tracking this project car but i am sure it will be on the dyno for a long time.

airborne

when i talked to dave@KD he mentioned speaking to someone at Griffin about the physics of it all and why a dual rad setup can be very effective but that was like a while ago and i forget. it seems safe to say that oil, air, and water temps all effect each other and are important to a reliable car.

could someone throw out the price of a v-mount? do you have to purchase a new IC and rad or is it a matter of pipes and mounting? i saw the rotary extreme kit for $2850. when i talked to KD the price was no where near that. even with ordering the rads as "one-offs" instead of a group buy.

one observation that raised my eyebrows is when i heard how rallimike's IC was still frosty after a decent drive in cold weather. anyway i'm sure a few people will give it a shot and we'll see what happens.

rallimike

iTrader: (1)

OK. One more time. My water temps are much lower with the dual radiators than they were with my oem radiator. Even though I do not have an oil temp guage, the increase in oil pressure is an indicator of lower oil temps (I am running 2 Setrabs, giving me twice the capacity as stock). That aside, the point to the mod is to remove the heat from under the hood, the benefits of which should be obvious. The result is, using a SMIC mounted 9" from the engine, I get intake temps of 0 to 10C above ambient, which is an improvement of 20 to 30C from what I had before. These are my OBSERVED results, not an opinion.

rynberg

Sounds good, but track experience is far more telling. Do you have a write up on the forum or can you post a full description of everything you've done -- including time and expense?

airborne

just got a response from KDR and it looks like by Nov they might have kits ready to go.

Kento

There's some photos and a little description in this thread:

https://www.rx7club.com/showthread.p...6&page=1&pp=15

It should be noted that rallimike is using (or was using) a CWest front end with enlarged oil cooler openings, although it appears that KD will manufacture setups for the stock front end...

airborne

KD has made it work with the stock front end, and with the stock fan setup. On rallimike's car the fans really don't kick on, thats why KD mentions "This car will have a cooling system so that the cooling fans hardly ever run. "

rx7tt95

Might not be a bad solution for 20B cars to look at if it in fact works as advertised :-) One could theoretically "v" mount the dual radiators with dual oil coolers, making the V in a vertical plane instead of a horizontal plane like the current IC/radiator Vmount setups.

I'd still look up the oil cooling percentage...I know it's substantially higher than 25%.

t-von

iTrader: (8)

Here's something to think about. Don't look at the small holes as being too small. Think about that hole and it's location as being less restrictive. Look at the C5 Vette? I think that car scoups air from underneath the front nose. In a stock Fd there is very little air flow to the engine bay through the mouth(due to the stock rad angle, SMIC set-up, and other crap that blocks flow). I can imagine that a really well designed radiator in the original oil cooler locations would really work. Air would easily pass through the rad and out the back without restriction making it very effective at transfering away heat (even at low speeds). I mean hell.....this is the way radiators are suppose to work right?

Another thing to think about. I was listening to Rob Golden at Sevenstock and he made some very interesting comments. He said just because a rad is thicker doesn't mean that it will cool better. A thicker radiator will usually need more air velocity to pass through the core because it's more dense. Also he claimed regardless of size, ducting was the most important thing in terms of how efficiant your cooling system will be.

t-von

iTrader: (8)

I just wanted to add my opinion of what KD is trying to do.


Since they are planning on putting two radiators in the oil cooler spots, they could easily use one of the older 1st or 2nd gen oil coolers in the front and then mount a IC directly on top of it. This way nothing would block the large opening and both units would appear as one.

Kento

If there was "very little airflow" through the engine bay through the intake nacelle, then the car would simply overheat cruising on the highway. There is sufficient room for airflow, and the undertray provides some negative pressure at its trailing edge to help "draw out" the engine bay air. Have you seen the stock "ducting" for the airflow exiting the oil cooler areas? It leaves a lot to be desired IMHO; it doesn't even extend all the way over the fender well liner and connect with the oil cooler, it just terminates at the top of the liner, which itself is far from being sealed completely.

You get that velocity by proper ducting both entering and exiting the radiator core. As an aerodynamicist friend once said, "You need to make the air want to come in..."

t-von

iTrader: (8)

In a stock Fd, I'm sure you'll agree that the air doesn't exit the radiator as efficiantly as it should(especially when compared to the FC's). With the stock rad being angled so much, the air has to change direction before going through the fins and core. That in itself will slow down its velocity. Then add in the fact that the air now has to travel up and under the SMIC ducting and find it's way around all the plumbing in the engine bay. Overall my point is, once it enters the front nose, it needs to pass through and exit the rad as quickly and as efficiantly as possible. This makes the cooling system more efficiant.

As far as overheating on the highway, at those speeds air more or less is being forced through( because of the pressure build-up in the front). In these conditions the air doesn't have much chance to find all the nooks and crannys to pass through(which is what happens at lower speeds because even air will take the path of least resistance). So no you won't have overheating problems.

To add to these comments. I was on my way back from sevenstock and got stuck in traffic in Phoenix Az. I-10 was shut down for a couple miles and everyone had to deture around. In all my years of owning rx7's not once did I ever see my engine temps rise the way they did in that 20 min time span. I even had the A/C on so the fans would run. As soon as my intake temps reached 200F my engine temp gauge started to move up slowly. I damn near panicked because everyone knows that if the (non linear)stock temp starts to move, things are really really hot.



You are very right, but the stock FD's set-up doesn't really allow for this to take place very efficiantly(especially behind the radiator). There is far too much stuff in the way for the air to pass through smoothly. Thats my point about the air flow issue in the engine bay.

Kento

Well, not to drag this out any more than it needs to, but that's one of the reasons why the FD's stock radiator core is relatively thin. Yet it still gets the job done; once I sealed up the gaps around the radiator, I never had any overheating problems with it, and the actual reason I replaced it was because of the plastic end tank leaking.

Airflow must be "forced through" regardless of whether you're going 30 mph or 70 mph. If anything, the slower airflow at lower speeds allows it a better chance of dealing with passing through all the obstructions behind the radiator; higher velocity airflow will have more of a problem because of the turbulence (and pressure buildup) it will cause. The FD's radiator positioning (and engine bay airflow) is far from ideal, but it's not as bad as some are making it out to be. Cooling systems are designed to work properly at highway speeds (not cruising, but any acceleration situations), because that is usually where the engine is under more of a load and creating the most heat. The only way you can design a cooling system to work "efficiently" at both 30 mph and 70 mph is to make the radiator larger and increase the cooling system capacity, both of which add weight and frontal area, two areas the FD designers couldn't spare.

I've been stuck in traffic for longer than that, and never had an overheating problem. Yes, the coolant temp got high enough that the fans came on, but they kept things well under control.

rynberg

The only time I have almost overheated on the highway (other than when my t-stat went out), was driving up the Grapevine hill on I-5 going into Los Angeles. The ambient temps were 95F+. By the time I reached the top, my water temps were just pushing over 225F, with me babying the car. The rest of the drive, the temps were between 190-210F with the A/C on.

I have talked to other FD owners who've experienced the same thing.

Okay, back to the topic on hand.