When it comes to plumbing the oil system, the simplest and most common method is run the oil coolers in series like Mazda did. Hot oil from the pan exits the oil pump front cover and typically travels to the passenger side oil cooler, then the driver side oil cooler, before returning cool oil back to the block for filtering and to pressurize the engine.
The positives of this layout are simplicity with less oil lines, which means less work, cost, potential leak and failure points. The primary negative of mounting oil coolers in series is increasing the pressure drop, reducing the oil pressure to the engine due to the oil pump having to push oil through two oil coolers in a row (series).
We decided to run the oil coolers in parallel, which reduces the pressure drop of the oiling system, delivering more pressure to the engine, which is crucial for the reliability and longevity of rotaries. This is especially important when making a lot of power or during extended track use. This concept is relatable by imagining blowing through a straw, then blowing through one that is twice as long (series0 vs two shorter straws at the same time (parallel).
Thermal efficiency and cooling are technically better when two oil coolers are run in parallel vs two coolers run in series because heat exchangers are more efficient when there is a greater temperature differential between the oil and ambient air. Two coolers in parallel both receive the hottest oil in the system, allowing ambient air flow to quickly reduce temperature. By comparison, when two oil coolers are in series, the second oil cooler receives oil that is much cooler than the first oil cooler, resulting in the second cooler having a lower temperature differential between the oil and ambient air, and thus, less cooling efficiency. In practice, there does not seem to be a significant cooling difference between running two coolers in series vs parallel.
We used the 145*F Improved Racing Remote Engine Oil Filter Mount with Thermostat to eliminate the factory oil filter location, mount the oil filter under the car for easy access and replacement, to replicate the function of the factory oil cooler thermostats, and filter the oil hot to keep any contaminants slowly collecting and reducing flow in the oil coolers over time, which probably isn’t a major concern.
We used an M18x1.5 to -10AN male adapter fitting on the front cover of our 13B REW engine. We used a 30* fitting on the newly made Earls UltraPro -10AN stainless steel hose to greatly reduce the pressure drop compared to the stock banjo fitting. Our oil line now connects to the Improved Racing Remote Oil Filter Mount with Thermostat.
Running the oil coolers in parallel adds an additional oil line going to each cooler. When fully installed, the new oiling system is pretty neat and there’s plenty of room for the additional lines. The new mounting location of the filter is very nice and makes oil changes significantly cleaner and easier.
When space is tight, the Radium Engineering Low Profile Swivel Fitting is a very well-engineered solution that has the ability to rotate 350-degrees after being tightened down, and can handle extremely high pressure for fuel and oil, up to 400psi. The low profile -10ORB to -10AN male swivel fitting (PN: 20-1000-1010) was used on the oil coolers.
These Radium Swivel Fittings made the routing of our oil lines very clean.
Quick Reference:
Page 1 – Stock FD RX-7 Oil Coolers
Page 2 – Hayden HD Cool 778 Oil Coolers
Page 3 – Oil Cooler Ducting
Page 4 – Improved Racing Remote Engine Oil Filter Mount & Thermostat
Page 5 – How to Make Earl’s Performance Stainless Steel Hose
Page 6 – Oil Plumbing Series vs Parallel & Radium Low Profile Swivel Fittings
Page 7 – Raceonly Billet Remote Oil Filter Pedestal & Front Iron Oiling
Page 8 – Raceonly Billet Oil Filler Neck & Improved Racing Catch Can
Page 9 – Crank Venting from Gutted OMP Port & Turbo Drain Fittings
Page 10 – Raceonly Billet Power Steering Reservoir
11 comments
I don’t think I could park this thing on the street knowing the man hours invested.
Good job. Helluva build.
This has been a great build to follow along. I noticed in the radiator articles you were calling it the BJR radiator. Are there plans for some of these parts to go into production?
I called it the Billy Johnson Racing (BJR) Radiator to give it a name because it was a custom build to my specifications for the FD platform. I’ve sold a few to people who reached out to HQ Engineering and ordered one, but this is a high-end motorsports radiator that’s priced in line with similar 50mm motorsports radiators (>$1,000) that should outperform anything on the market from my research based on its dimensions and efficiency (that fits within stock frame rails). The majority of FD owners are street guys who are use to $400-500 drop-in replacement radiators that are only slightly better than stock. If you need a significant improvement in cooling, you’ll have to spend more than double that wherever you go.
Thank you 🙂 It’s far from over…
Wow, beautifully done!
Out of curiosity why did you go with stainless braided lines over nylon braided? I’ve been choosing nylon braided lines since they’re lighter and easier to work with but I don’t have the experience with A/N lines you do.
I’m a big fan of nylon and use it in many applications, especially for those areas that will not see abrasion or impacts. We chose stainless because it was the only option at the time in the PTFE UltraPro -10AN hose, stainless is generally better protected for mission-critical fluids like oil lines that might see debris impacts, and because this new hose is so flexible and light, there really aren’t any downsides other than maybe a few ounces per foot. This -10AN is very light (37% lighter than traditional rubber w.stainless braid) and is extremely flexible with a 1.772″ minimum bend radius (vs 6.0″ minimum bend radius for the all-rubber Super Stock hose and 4.0″ for the rubber-lined stainless steel braided Auto-Flex hose). The UltraPro and new Ultra Flex 660 Stainless & 650 Kevlar Steel & Pro-Lite 390 Nylon hose are a significant improvement in quality than the impression that you or I might have on thinking of Earls as old-school, old-technology ‘hotrod’ hose vs many high-end motorsports hose brands. I’d bet that once you experience UltraPro & UltraFlex hose first hand, you’ll change your impression on Earl’s, like I did.
Thanks for the info Billy. I’m actually working on an oil cooler and catch can setup for Project EF Civic. I was going to use Earl’s nylon braided line but I will definitely take a look at the UltraFlex lines for the cooler itself. It’s a shame this sort of info isn’t easier to find on their website.
Happy to see that parallel flow oil cooler setup. A bit curious to hear that in prior history, others’ experience with the parallel vs series flow didn’t show dramatic differences in performance. I wonder if that was due to airflow restriction of the factory bumpers. Anyway, the reduction in pressure drop is worth the parallel setup alone. But I expect your setup to do well as you’ve properly accounted for the airflow.
Any particular reason you went with the Radium catch can over the Improved Racing one? Or just personal preference.
Love the update. Love all the blue anodized parts. Love the attention to detail.