– Rotary engines do not have a reputation for being entirely reliable, but Andy Duffin’s three rotor racing FD RX-7 has proven to be exceptionally reliable. We’re here with Richard from Green Brother’s racing in New Zealand to find out what makes this peripheral port 20B tick, and how it remains reliable in the heat of competition. So what is it about your rotary engine builds that you’re doing differently to others who are struggling with reliability? – I don’t think we’re doing anything really different, but we’re using, in this particular engine, all genuine Mazda parts, along with Iannetti ceramic apex seals. – I just wanna talk about the apex seals a little bit there, you’re using ceramic seals whereas the factory naturally aspirated engines use carbon and then there’s steel seals as well, what’s the advantage with using a ceramic seal? – They’re a lot harder, a lot stronger, and they never wear out. – So in terms of long term engine reliability or engine performance they hold up better than a carbon seal? – Yes they do. – Now I also understand though that the ceramic seals are very intolerant of detonation, basically shatter and can destroy an engine? – They’re actually more tolerant than a steel seal, but if you do detonate hard enough, then you’ll do a lot more damage than a broken steel seal. – So it’s reasonable to say that if you’re going to use the ceramic seals, you really need to have your tune absolutely perfect first? – Yes definitely. – Now the engine in Andy’s car is a 20B, it’s peripheral ported, can you just talk to us a little bit about the advantages of peripheral ports over potentially something like a bridge port? – For me a peripheral port takes less time to do than a bridge port. You also get more air flow through the intake. So they have better efficiency than a bridge port, so ultimately you’ll make more power. – So in terms of the air flow, they’re superior to a bridge port, so you are gonna make more power. In terms of the shape of the power and torque curves though, do you find that a peripheral port really favours just making that power right at the high RPM, maybe giving away some mid range power and torque? – Not really, they’re quite similar in power, a bridge port versus a peripheral port. A peripheral port will generally hang on a bit longer up top and make a bit more power. – And what sort of RPM are you revving this 20B to? – This one goes to 10500 RPM. – Now for World Time Attack this year, you’ve gone and added nitrous, well in fact you tested the nitrous system last year, it had a few mixed results. For a start though how much power is the engine making without the nitrous, just naturally aspirated? – Without the nitrous it’s around 500 horsepower at the wheels. – And the nitrous system, this is really essential to be competitive here at World Time Attack in the class Andy’s running in? – Short of turbo charging, yes, nitrous is the only other option. – So that nitrous kit, I wanna talk about how that works, so can you talk us through the system, what size the shot is, and how it’s being introduced into the engine? – It’s about 150-200 horsepower shot, but it’s variable ’cause the stepper motor used to control the nitrous flow and the stepper motor is controlled by the ECU. It increases flow based on speed and RPM. So the faster the car goes, the more nitrous it puts in, and the higher the engine revs, the more nitrous it puts in. – So I think this is one of the areas that’s maybe a little bit misunderstood with nitrous systems, they’re normally or traditionally a really simple system. There’s a solenoid that opens and closes, when the solenoid’s open, the nitrous flows through a jet, and the upshot of that is that depending on the engine RPM, depends on how much time there is available for that nitrous to make its way in through the intake port so essentially you get a higher increase in power and torque at lower RPM where there’s more time available, so you’re controlling that with a stepper motor? – Yes. – So from the driver’s perspective, obviously if you’re introducing quite a large amount of power reasonably suddenly on the throttle position, that can have an effect on the driver’s ability to modulate or control the power, so how are you getting around that? How are you working with Andy to make the car really drivable with the nitrous? – There’s several conditions in the Link ECU that have to be met before the nitrous will be introduced. Of course the big one being speed and RPM. So basically as he rolls into the power, the nitrous comes in gradually, so it’s not a hard hit, so it makes it much more drivable. – And you’re using that speed condition so that in low speed corners where the car already has more power than he can put to the track, the nitrous isn’t being used? Is that how that’s working? – That’s right, so it puts in a little bit of nitrous at the top of second gear, more in third, more in fourth and then all in fifth and sixth. – Now with a nitrous system essentially it’s sort of a chemical supercharging is an easy way to refer to it, you’re adding additional oxygen straight into the intake port of the engine. But of course that needs to be mixed with additional fuel to maintain a safe air fuel ratio. So how is that being controlled? Is this a wet nitrous system where the jet includes fuel and nitrous or are you doing this through the ECU? – The ECU’s controlling the fuel side of it. We’ve got large injectors and the more nitrous goes in, the more fuel is added by the ECU. – Let’s talk about the ECU. We’ve mentioned it a couple of times, what are you running in the car? – It’s a Link Thunder ECU. – And you’re, obviously as we’ve talked about, you’re controlling the nitrous there, what other functions are you using in that G4 Plus Link Thunder ECU to control the engine, stage injection I’m assuming you’re running? – Yeah stage injection. – What size injectors is the engine fitted with? – It has 1000cc primaries and 1600cc secondaries. – In terms of the engine protection as well, that’s another issue with rotary engines, they certainly don’t like to run too hot. Are you using any strategies in the ECU there to help control that and maybe warn the driver or save the engine if something goes outside of the bounds you’re happy with? – Yeah so we’ve got protection set up for low oil pressure, low fuel pressure, high engine oil temperature, high engine coolant temperature, high gearbox temperature, high diff temperature, basically, you name it, it’s there. – So as an engine builder in particular, let’s forget about the diff for a moment, but as an engine builder in particular, the ability to bring in these sort of safety strategies with the ECU helps give you the confidence that the engine is gonna remain reliable? – Yeah definitely. – OK now last year you guys turned up and you had a pretty good run but didn’t quite go 100% your way and we talked last year and you were having a little bit of an issue with the nitrous maybe not behaving exactly how you wanted it to. What’s changed since last year and what did you actually find the issues were? – More experience second year around, and we’ve also gone to a better fuel. So we have higher octane fuel, and just spent more time on the dyno and fine tuning on the track back in New Zealand. – So last year you were running on just a pump fuel? – Yes. – And this year what have you gone to with the higher octane? – We’ve gone from 98 pump gas to an Elf 102 octane. – So how has that additional octane been useful with the introduction of the nitrous? What issues were you having last year that that’s fixed I guess? – It’s limited engine knock and it’s a much more controlled burn. – OK so in terms of that knock, you’re actually using the knock control strategy in the Link ECU I understand? – Yes. – You’re finding that quite effective? ‘Cause I think that’s probably relatively rare in the rotary tuning world, would I be right in saying that? – Yes it works well. – Now when that car comes back in from a lap around the track, from a session around the track, what are you looking for in the data in order to either help, A, improve the car’s performance, or B, ensure that everything is working how you like? What’s the first things you’re looking at? – First and foremost I’m looking at temperatures and pressures and then I’ll look at EGTs, lambda, part throttle tune up, and drivability. – And are you using this in conjunction with feedback from Andy to make changes? – Yes. – Now obviously with a nitrous set up like this, you don’t quite have the flexibility that a turbo charged engine can have in terms of being able to easily increase the boost pressure, but you’re quite happy with the power level you’re at, what were you actually making on the dyno with the nitrous active? – It’s about 670 horsepower at the wheels with the nitrous. – That’s a pretty stout naturally aspirated 20B. Look it’s been interesting to get some insight into that engine and in particular the nitrous system, thanks for your time here, and we wish you guys all the best for the rest of the day in competition. – You’re welcome, thank you. – If you liked that video, make sure you give it a thumbs up and if you’re not already a subscriber, make sure you’re subscribed. We release a new video every week. And if you like free stuff, we’ve got a great deal for you. Click the link in the description to claim your free spot to our next live lesson. You’ll learn about performance engine building and EFI tuning, and you will also have the chance to ask questions, which I’ll be answering live. Remember it’s 100% free so follow the link to claim your spot.