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Rules of the Rotary: Mazda RX-8 Tech Tips

Mike Allen
Mazdaspeed Motorsports Development
1421 Reynolds Ave.
Irvine, CA 92614
mazdamotorsports.com
(800) 435-2508

To avoid getting an RX-8 with a bad engine, it helps to know the history of the car. Check lemon law records, title history, and look at the warranty history to see if engines have been replaced. Telltale signs of a weak engine are oil smoke, overheating, and hard starting–especially once the engine is hot.

Before you buy, take it to a dealer to run a compression test. Any rotary engine needs a special compression gauge. The spark plug hole is going to give you the highest pressure of the three chambers, so you need a tool that will show the pressure in each chamber. Dealers have a special tool with digital readout that can do this.

These cars have perfect 50/50 weight distribution. That’s the big advantage of a rotary engine: It’s so compact, you can mount it very far back in the chassis. The rotary will run at high rpm and has good reliability when it’s taken care of.

When you go to a track, watch your oil consumption. Make sure the level stays full. Also keep an eye on your temperature. If you’re running in an area with high ambient temperatures, I recommend upgrading to a bigger radiator.

The metering oil pump delivers a small amount of crankcase oil into the intake to lubricate the apex seals and other components. It’s hard to fool that system in the RX-8 because it’s electronic. You can run the supply line to a separate reservoir if you want to run different oil in the metering system, or you can block off the feed completely and pre-mix oil with your fuel.

We duct the front brakes on our race cars, but I know a lot of guys who don’t. The car has really, really good brakes. If you have a street car that is on track only part-time, I’d just put good pads on it and call it a day.

Mazda made improvements throughout, but 2009 and up are the best years to buy. They improved the oil metering and the fuel-injection system to help reliability.

The 2004-’08 cars had an Aisin six-speed manual transmission, which is fine for street duty but not the best in a race environment. Mazda produced its own unit for 2009-and-up models, and it’s much stronger.

You can swap this transmission into older cars with minimal effort—just make sure it comes with its shifter. Everything bolts in, and they use the same driveshaft. The connectors on the reverse and neutral switches are different.

There’s not a lot of weight to take out unless you’re gutting the interior. The Sport model is probably the better one in terms of weight because you don’t get the sunroof or navigation.

Jim Mederer and Ryusuke Oku
Racing Beat LLC
4789 E. Wesley Drive
Anaheim, CA 92807
racingbeat.com
(714) 779-8677

The Renesis side-exhaust-port engine features a convoluted exhaust passage that really limits power. The most we’ve ever seen in a street-ported engine is 249 flywheel horsepower.

Every bolt-on seems to gain 4 horsepower, and these gains are fairly cumulative. A straight pipe, however, makes only a small improvement. A ram air duct potentially adds power, but there’s no way to quantify it because we test on a dyno.

I spent literally months on the dyno chasing parameters to improve the tune. Turns out the stock timing is just fine, but the mixture is very rich above 7500 rpm, ostensibly to keep the cats cool. I didn’t see clear signs that this made a difference. Our tune corrects the high-rpm mixture and gains about 4 horsepower. We also raise the redline to 9300 and turn on the cooling fans much sooner to help keep engine temps in check.

We’ve tried both supercharging and turbocharging on behalf of Mazda. The results were not particularly impressive. We made something like 275 horsepower with an Eaton supercharger–Mazda’s choice–on a six-port engine. It did improve the midrange noticeably, but the actual power output wasn’t substantial for the complexity involved. With the turbo, we made 300 at about 10 psi.

There are major, major problems with both of these setups. There just isn’t much space to put these things, so it makes working on and maintaining them very difficult. The engine itself is capable of taking a fair amount of abuse from a super or turbo, but the heat issues are very, very extreme.

Cooling the engine is critical, and that’s one of the reasons not to super- or turbocharge. Everything is so tightly packaged that the air simply doesn’t get out of the engine compartment. As a result, the car is sensitive to overheating. It’s always helpful to clear away anything you can that blocks air from getting out.

I did a bunch of studies regarding that to try to improve cooling. The only thing that seemed to work was a 3-inch lip all the way across the underside of the front subframe. That actually has a small beneficial effect. It creates a low-pressure area behind it and pulls air out of the engine bay–but it also drags on the ground on hard cornering and generates a lot of noise, so it’s not something I wanted to be a Racing Beat product.

The stock shocks are very good. The biggest thing you can do for handling is add bigger anti-roll bars. They eliminate all the body roll and make the steering extremely sensitive. Aim the car, and it goes where you point it. Some people put $3000 into coil-overs but then go slower through corners and have an extremely jarring ride. The car doesn’t need really stiff springs. A good-cornering car is actually pleasant to drive.

The shocks for the best handling are Konis, but they will make it more difficult to drive over rough surfaces. They have a lot of damping, which I personally like a lot, but some people find them too firm. They’re also pricier than the Tokicos.

Steve Leonard
V8 Roadsters
156B Highway 75
Blountville, TN 37617
v8roadsters.com
(423) 323-4271

We’re well along in developing an engine swap kit for the RX-8. We’ll have two options: the General Motors LS-series V8 and the LFX V6 from the new Camaro. We’ve put in 18 months of work testing this swap. Watch our website for when the kit becomes available later this year. It will have a similar price to our NC Miata kit.

The V6 retains the character of the RX-8, but with better power and gas mileage. The LFX engine makes 323 horsepower and 278 torque; it’s lively, bulletproof and turns 7800 rpm. The Aisin six-speed transmission shifts great. You can get a complete pull-off for about $4500.

Dave Lemon
Mazdatrix
730 Gundry Ave.
Signal Hill, CA 90755
mazdatrix.com
(562) 426-7960

RX-8s have fantastic handling and brakes. I still daily-drive one. I take it to the track, drive it all day long, take people on track rides in it, and drive it home. I’ve always run that one on 87-octane fuel and have had no problems whatsoever, so that can save you a little on your gas bill. They’re thirsty engines, there’s no changing that.

The port configuration of the Renesis engine does not leave enough metal in the side housings to do much porting before you hit water. If the motor’s apart, just clean up the ports a bit and you will get some gains.

I love ’em–rotaries are all I do. The blue car on our website is the one I bought in 2003. We have a nice chin spoiler but don’t usually run the rear wing. Its engine is a hybrid using RX-7 rotor housings combined with the Renesis side housings and custom manifolds. It makes 436 horsepower at the wheels on 11 pounds of boost. It’s been very reliable in Time Attack.

Tune aftermarket turbos carefully to avoid internal engine damage. To make a turbo or supercharged Renesis last, you must be conservative on boost and never run lean. Pushing 6 to 8 psi will give 240 to 270 horsepower at the wheels.

We’ve had great results from the Tokico D-Spec spring-and-shock package we sell at Mazdatrix. The spring rates are very well chosen, and the range of shock adjustment allows for comfortable street driving all the way up to the stiffest setting, which is just right for full track use.

Change your antifreeze regularly to prevent internal engine corrosion.

An aftermarket exhaust is more for looks and tone than power. We’ve found the most noticeable increase in acceleration by putting in a lightweight aluminum flywheel.

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Comments

View comments on the GRM forums
kevinh333
kevinh333 New Reader
11/14/17 10:33 a.m.

Great information; unless you have a second gen car (09-11) in which case most of the data does not apply, especially regarding springs which do not install from gen 1 to gen 2 with the same results in performance and ride-height.

If on the other-hand all you are looking for is "the look" or "stance", any lowering spring will work but if you want to truly enhance the already superb handling you are out of luck (if you own a second 2nd gen car).

Any recommendations?

fidelity101
fidelity101 UltraDork
11/14/17 10:34 a.m.

These are all great and accurate but you're missing two critical items. The ignition and starter these tend to give off a false sense of a bad engine. They usually just need coils/plugs/wires kind of tune up or a new starter. The 04-08 starters were a little weaker and if it doesn't crank fast enough combined with a weak spark you tended to flood to the engine which then people would assume it was blown. Great way to pick up a cheap rx8 this way. With the 09+ the stater improved with the transmission, more Kw and more teeth on the gear.

If you can't/don't want to take it to a dealer to get a proper compression test you can use a piston tester by holding the shader valve open and watch the pulses. best best is to use your phone to record it so you can avoid unnecessary excessive cranking.

A little clarification on the exhaust, there aren't a lot of gains with a full exhaust but the gain is weight loss, there is a big opportunity there because like mentioned above there is not a lot of places to cut weight out of this vehicle. For instance the stock driveshaft is carbon fiber! I would 100% back up the claim that the engine needs a lightweight flywheel - it really wakes up then.

I daily an S2 rx8 and I love it, I have a "short" commute so I don't mind the economy its all about the smiles per gallon! the suicide doors make it great for brief case storage and ease of access. If you can get a touring without a sunroof it gives you the HIDs and fog lights which are well worth it.

colinshark
colinshark New Reader
11/14/17 7:52 p.m.

I'm surprised this isn't mentioned, but I'm a fan of fuel-premixing on all rotaries. Particularly on the S1 RX-8s, it makes up for the stingy oil injection. I use a "sta-bil" bottle, which lets me measure the dosage pretty easily.

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