Andy's Sad Rev Head Page!

The RX-7 featured in this article is a series 1, 1978 Japanese import model. Whilst this car came out with only drum brakes on the rear, they can be upgraded and the advantage of using this type of car is that it is exempted from Australian Design Rules. No charcoal canister etc. Saves a lot of stuffing around!

Forget bridge port/ peripheral port etc. Go the turbo!. The two choices available are the series 4 or the series 5 intercooled, injected turbo 13B’s. By far the most popular way to get hold of one of these is from import mobs. Most are over in the Eastern states, although Rotomotion and All State Imports here in Perth can supply these engines. For a good deal, check out the adverts in Fast Fours and Rotaries magazine- a complete S.4 package including coil packs, computer, wiring loom etc was offered at $2000, a bargain by anyone’s standards. Of course, you have to be careful as you can’t drive the car before buying!

The motor in this car is a series 5, bought off Rob Mitchell, and came supplied with the factory computer, coil packs, air flow meter and pressure sensor. Rob didn’t want it any more because it wasn’t fast enough! Hopefully the rather horny 20B sitting under his bonnet now will satisfy his urges (or if that fails maybe a blond haired sixteen year old girl will do!).

Once you get the old motor out and get ready to fit the new one, sit down and plan. Unfortunately, the "oh yeah, no worries, mate, she’ll be in after the weekend" thing won’t work, especially when you look at where the turbo sits on the new motor and where the steering box is in the old car! Where’s that angle grinder? Solution? Simple- just ‘pop’ the turbo forward by a few inches. The way to go about this is give it to a reputable rotary mob like Rotomotion and a blank, signed cheque, or if you are a bit more adventurous, read on. Five things are required: A mig welder, quarter inch or half inch (if you’re brave) steel plate, oxy set, lots of beer and swearing. Oh, and a drill press helps too. Once you have all this in hand, get down to the workshop.

The first thing top do is take off your turbo assembly and exhaust manifold. Both series 4 & 5 manifolds will be similar, except that the series 5 has a twin scroll manifold and turbo to reduce destructive (towards power) exhaust gas interference waves travelling inside the manifold away from the turbo inlet port. Because the manifold is asymmetrical, the first step is to turn it upside down- hey presto! you’ve moved your turbo forward. But not enough. This is where the five essential components come in to play. First off you sit down and have a beer. Or two. Then , the next day, hangover permitting, get brave and take to the quarter inch steel with the oxy set. Cut two rectangles out, slightly larger than the turbo gasket (use it throughout as a template). The aim here is to move the exhaust port(s) forwards by two inches, or around 50 mm. In each plate, cut out an angled hole that moves the ports forward. This is best done with an oxy torch, although can be done using a drill press and die-grinder to tidy it up and angle the edges. The purpose here is to get good flow of the exhaust gases, so the two plates need to sit one on top of the other, the top plate staggered forward, and a nice neat angled hole in the middle. This could be done with half inch steel, but using two pieces of quarter allows for more fine tuning. Once these two are finished, attack the manifold with an angle grinder or die grinder. What you have to do here is take some metal off the forward edge(s) of the exhaust port(s), to aid gas flow. In the case of the series 5, grind the centre port divider below the level of the outlet- otherwise the exhaust gas flow will be restricted from the back rotor, as the effective gap will be much smaller than the forward rotor outlet.

Before you start welding, drill and tap holes in the outermost plate for the studs that hold the turbo on. Typical car designers have put a trap for the unwary in here- the stud pattern is not reversible, so use the turbo gasket here. Firstly, place it over the turbo to find out which way up and out it fits (there is only one way), then transpose it onto your steel plate. Get it wrong and the turbo won’t fit! You can of course spend five hours patiently filing out the holes in the turbo to make it fit, but hey, that’s kindy silly! (Sorry Tyson!). The final step is to measure up and make sure that you’ve moved everything forward enough, then mark it and weld it. It’s best to weld on the plates one at a time, making good strong welds to withstand the rigours of the job. Weld both inside and out, die-grinding the inside to smooth off the joins. So there you have it. You’re either several hundred bucks poorer, or you’ve got through seven slabs of beer, and have a throbbing headache. Who cares, you’ve done the biggest task!

Next up, modify all the oil and water lines to the turbo. Either use rubber fuel/heater lines, or get new metal lines made up. I went for a combination of the two, mainly due to the somewhat restrictive budget! The only other thing to do as far as the turbo modification is concerned is to sort out the air pump and the pipe from turbo to intercooler. I’ll deal with the air pump first, as it’s really easy. Throw it away! Yup, moving the turbo means the air pump bracket won’t fit, so instead of stuffing around making it all fit, chuck it! Sorting out the intercooler pipe is a matter of either making a new one out of pipe (if you have a pipe bender) or turning the old one around so the kink faces the other way. You’ll have to cut off and reattach one of the hose outlets for the blowoff valve, this is where Devcon comes in real handy.

Now that you’ve finished the turbo, it’s time to think about mounting the engine. Don’t even think about it- this is a no smut zone! Anyway, new motor- side mount, old motor front mount. Again there are two ways to do this- get hold of a front mount 12A turbo front cover or weld on a bracket onto the existing cover. I went for the latter. The advantage for series 5 owners to go the latter route is that they get to keep their electronic oil metering pumps- they won’t fit on any other front cover. Rotomotion came to the rescue here and they’ve done a pretty neat job, thanks Brad!

Think you’re finished yet? You’ve gotta be joking! Time to get out the welder and drill press again and move the slots back as far as sensible on the front engine mount. This will help to move the motor forward just that little bit more. Some people have even been known to move the engine mounts forward too- this may be necessary- suck it and see!

Another trap for the unwary is that if you move the turbo forward just a little too far, you’ll get too close to the water pump intake, so either move the turbo back a little or cut the water pump inlet off and Devcon back on at an angle. Don’t worry about strength- Devcon will be as strong as the cast aluminium, which, incidentally, you can’t tig weld as there is usually too much zinc in it(produces nasty, spluttery welds).

The next area to get my attention was the fuel system. Obviously the old pump couldn’t supply the correct flow or pressure for the injection, so the best option is to buy an in line efi pump ($100 from the wreckers/importers) and a couple of efi Holden Commodore metal filters ($15 ea from Coventry’s). Put one filter just before the pump and one just before the engine- this way you’re doubly sure there ain’t going to be any crap in the injectors! Like most other things, this is the cheap way of doing it- some people have been known to put in a feed pump, surge tank and main pump, for around $400, just depends what you want…Of course, replace your crappy old fuel lines with new stuff- varicose fuel lines most definitely are NOT healthy!

The second last area to be dealt with is wiring up the computer. Most people install the Microtech Digi 2 computer, which seems to run the motor quite well, but I much prefer the factory electronics. You have to be brave and have a good understanding of electronics to do this, as most people will not even touch this task! It is, however, made a lot easier by getting yer hands on the official Mazda workshop manual for the series 4 or supplement for series 5. Rob Mitchell had the latter, which he kindly lent to me. Without this the job would be very difficult indeed- there is a section which tells you exactly which computer terminal does what, and a wiring diagram that is logical and matches the information! Amazing! Having studied all the relevant information, go wire up! Most of it is easy- make sure the correct wires go to the coil packs and sort out the power supplies to the computer. Also, one or two sensor leads (for sensors on the S.5 car but not the S.1)may have to be grounded- follow the wiring diagram and work it out… As a word of warning, don’t take the manual literally when it says an input into the computer would be 12V in one condition- it’s a virtual 12V seen at that terminal by your voltmeter, this happens when a semiconductor circuit which switches earth is open circuit… It would be easy to think "hey, the computer needs 12V into it to fool it into thinking this sensor is still hooked up", but it might blow your computer! The only other wiring to be done is the power supply for the injectors and solenoids. These are two black/white and two black/yellow leads on the big unused plug on the harness (normally hooks into dash harness). Chop these off, pair them up and connect to ignition switched, fused 12V.

Another thing- when giving your new engine etc 12V, make up a new circuit, as all up, the injectors, coils etc draw a lot of amps and your old wiring won’t be up to it. Simply get a couple of 30 amp car relays, two power distribution points, and a dual fused link from the battery. These are available from Dick Smith’s, $10 for the distribution blocks and $20 for the fused link. This will provide two circuits, for the injectors/solenoids and computer/coil packs. I guesstimated at 40A for the former and 30A for the latter. For the ignition switched 12V, use one of the old coil feeds, and for the tachometer hook up the tacho lead from the leading coil pack straight into the old tacho lead (single wire with black plug that was on one of the old coils).

One final, supplemental modification to be made if you want is to hook up the new 80A alternator. This required a bit of thought as it’s self regulating, whereas the old one has an external regulator. First step, throw the old regulator away. Before it goes in the bin, chop the plug off- you’ll need it. Then find out on the loom side of the old regulator plug what is what- there is a solid 12V, ignition switched 12V, a pin which lights up the dash warning lights when ignition is on and it is earthed, and three leads that go directly to the old alternator. Choose one lead to the alternator (I chose black/yellow) and keep it. Then unravel the wiring loom from the old engine, all the way to the plug on the engine bay opposite the rear rotor. Chop off all the wires except the water temp sender line, your one alternator lead and the thick battery positive alternator feed(plus oil pressure light wire if you have one). Now look at the back of the alternator. There should be a socket with two pins in it (Mitsubishi alternator). The one on the left is the field(voltage) sensing (for the regulator) and the one on the right the ignition warning light pin. Connect the sensing pin to the thick positive feed arm that comes off the side of the alternator and also bolt the thick wire onto this. Connect the old alternator wire onto the right pin. This will go back to the new relay for the ignition warning light. I used the old hot start assist relay to perform this- any auto relay will do the job, I think! Wire it up as follows: Use the old six pin plug that you chopped off the old regulator. Work out which wire goes where when you plug it into the harness six pin socket- you should have identified on that your steady 12V (not to be used), ignition switched 12V, and the line that when earthed and the ignition is on, lights up the dash lights and voltmeter. The coil side of the relay needs ignition switched 12V and the alternator ignition warning light feed. Careful here- sometimes the relay coils have a diode in them so can only be connected one way round- do it so that the coil is activated when ignition is on and alternator is at rest. Then connect up the switched side- you want to have an earth on one side and the earthing line for the dash lights on the other. You should now have all the lights operating correctly. A last word of warning- the new alternator is 80 Amps, compared to 50-55 Amps from before, so your main fusible link might need beefing up. Other than that, it should all work!

All you have to do now is start the engine and wear a nappy- ‘cos you’ll be sh*ttin yerself the first time you open it up!

Thanks go to Rob Mitchell for selling me the engine, lending me the manuals, helping out generally and providing the odd beer. Tyson Fraser put me on to Rob, sold me his old scoop, and allowed me to peer under his bonnet for long periods of time- it always makes it easier when someone’s done it before you! Cheers John Fleay for the engine hoist and enthusiastic encouragement! Rotomotion did a great job of the ali welding, so credit to them there. Also many thanks to me Father, who helped think through some of the computer wiring stuff and for doing most of the worrying for me! Last but not least thanks to my wonderful girlfriend Naomi, who stood by me while I used her shed and put up with my incessant rantings about rotaries…