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Mazda RX-7 Buying Guide: Powertrain

There are lots of myths around the RX-7's rotary - PH puts them to bed!

By Alisdairsuttie / Monday, October 16, 2017

Let's deal with the big misconception about the RX-7 FD's 13B-REW engine straight off: it is not unreliable. Yes, the rotary motor needs more care, attention and regular maintenance than most other performance motors, but with an attentive owner these units will easily cover more than 100,000 miles without any issues. The reliability only comes into question when the car is neglected, which has been the case when the cars were at the bottom of their depreciation curve.

Many poor examples have now been broken for parts, which helps alleviate the scarcity of some components. There's also a small but strong network of specialists for the RX-7 that can service, repair and rebuild the engines to standard or tuned specifications with excellent reliability.

Needs revs, and using them is no hardship

Needs revs, and using them is no hardship

Mention Mazda rotary engines and the conversation will quickly turn to compression tests to make sure the engine is in good health. This applies to the FD as much as another Wankel-powered car and is the first place to start when looking at a car to buy. There are several specialists who will be able to do this and tell you whether it's worth continuing with the purchase or if you need to budget for an imminent engine rebuild.

A compression test will tell you if the engine's apex and side seals are giving up the ghost. Anything between 7 and 8 bar of pressure is good, while below that is a cause for concern. If the reading is low, a rebuild is on the cards and that's around £3,000 at a specialist. The colour of the engine oil is also important and if it's black you should be wary.

All rotary engines use oil, so quarter of a litre per 1,000 miles is nothing to worry about. However, an engine that needs more than this should start to ring alarm bells and you should also check the engine has been treated to a premium mineral oil from the previous owner and the level checked with near religious devotion - many owners recommend this every petrol fill. A full oil and filter change is best carried out every 3,000 miles.

On the subject of fuel, it's best to stick with a premium 97- or higher brand. As for economy, you can expect around 20mpg when cruising gently on the motorway, but that can drop to as little as 8mpg in town or when pushing the car.

You also need to be aware of flooding the engine when starting, which often occurs when the engine is switched on for very short periods, such as moving it around a forecourt. If this happens, do not keep turning over the motor in the hope it will fire. You need to remove the spark plugs, dry them off and let the excess fuel evaporate from the rotary chamber naturally. It's a pain, but this process will avoid damage to the motor and the cost of a rebuild.

Another tell-tale of an engine that needs work soon is steam from the exhaust on start-up. It points to deteriorating coolant seals, which go brittle with age and heat in the engine bay. The correct coolant is required and needs to be changed once a year to avoid it becoming acidic and weakening the seals in the system. This can be a source of leaks and even more dramatic blows.

The air separator tank can split and allow coolant to leak. For anyone looking to take the RX-7 on track, an upgraded tank and radiator are the way to go.

While inspecting the engine bay, check the original intercooler is in place if the car is meant to be standard. It's positioned in the front right of the bay and should also take a look at the air pump in the left rear of the under-bonnet area to make sure it's present. Many have been removed when they fail and a blanking plate put in its place. This isn't an issue in itself and many tuned engines have the blanking plate, but it can make it difficult to get the engine through an MoT emissions test.

Gearbox tough, but fourth to fifth can be tricky

Gearbox tough, but fourth to fifth can be tricky

The solenoids that operate the turbos can fail because of under-bonnet heat, which results in the turbos coming into play erratically. High temperatures also cause the rubber pipes for the turbos to fail, so budget for replacements. As for the standard twin turbos, they should last the same length of time as the engine before needing a rebuild. When working properly, you should be able to feel a very slight step in power when the second turbo comes in at 4,500rpm.

Tuning is hugely popular with the RX-7 and it responds very well. The first port of call is an Apexi Power FC ECU upgrade for around Β£1,000. It allows more control over the engine management and future-proofs it for further tuning. That usually entails improved induction and a larger single turbocharger, which will cost from around Β£3,500 depending on the make and how much power you want.

A larger bore exhaust is also a common add-on and you can expect to pay around £600 for a cat-back system. With more power, you'll also require higher capacity fuel injectors and they come in at around £95 per injector, plus a more powerful fuel pump for £150.

The RX-7 isn't especially tough on its clutch, so a standard replacement for £350 isn't a wallet-wrecker. However, with larger power outputs, you'll need a stronger clutch and they start at around £450 and rise all the way to £2,500 for ones that can handle up to 1,200hp.

Lastly, we need to mention the five-speed manual gearbox. It's tough, but listen and feel for a poor shift between fourth and fifth gears. It's quite common and most owners just live with and change gear a little more slowly as a result.

PHer's view:
"I love the twin turbos, the kick from them is highly addictive. You can, and should, redline the car as often as possible - Mazda even recommends it to help prevent carbon build-up in the engine."
Jamie Collins

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