20B NA Extend Port First Gen - 295 rwhp

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08-02-2006, 04:01 AM

NA_20B_RX7_

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Join Date: Aug 2006

Posts: 5

G'day,

I bought this car back in 1996 after having owned a heavily modified 2lt Escort for 6 years.

Back then turbo's were still illegal in Queensland and so bridge & peripheral port rotaries were the go. it was normal in the early-mid 90s to see over 60 R100 - First gen RX-7s all bridge or PP'd on a cruise.

I bought the car with the intention of puting a 13b bridge port straight into it. This happened sooner rather than later. The car came with an extend port 13B and after around 2 months it gave in, on pull down the reason being a shonky back yard rebuild.

Maz-Sprint in Brisbane built up a nice 13B bridgey which powered the car for 3 years until I moved overseas.

The car was meant to be driven while I was away, unfortunately is sat, water wasn't drained and I came home a couple of years later to find the alloy rotor housings had corroded. Despite this, the car started first time after a new battery was dropped in. The car ran another 6 months before it was flooded with water.

Maz-Sprint again rebuilt this engine, and after a while I concentrated on something I'd always wanted to do since seeing my first one in '97, a 20B.

The 13B was sold, but not before it went into an Improved Production car and took out the race weekend outright.

Over the years I have been using the 12A Turbo gearbox (which I am still using now behind the 20B) to good success. I also change the diff gears to 4.4s.

I bought a 20B at the beginning at last year and so began the build up. There has been a lot of modifications done and we were pleased to have the car legally blue plated, and as such when I went to rego the car this is the first S3 with a legal 20B.

The car is very different to drive than the 13B Bridgeys, first thing you notice is the torque (and the sound). It pulls effortlessly from standstill in second gear, can even hillstart in 3rd if you like.

Maz-Spint orginally did all the conversion work and built this engine, but due to a contaminent in the oil the engine spun a bearing. Whatever was in the oil peeled the paint off Dyson's workshop floor.

Maz-Sprint had since stopped operating so Dyson Rotary completed the rebuild. At this stage I've almost run the engine in and expect to have it tuned in the next couple of weeks. Craig did a little more porting so it will be interesting to see any improvement over the 230 rwhp the car has made previously.

Everything went together pretty smoothly with the built taking around 4-5 months. One of the biggest headaches was finding a suitable accelerator cable. The one chosen is perfect, even came with the connect to bolt half way along to the manifold.

Since this has been written the 20B has had a new intake fitted with it now making a massive 50 rwhp more just from the intake change. It was dyno'd on a Dyno Dynamics dyno (which read around 15-20% less than a dynojet) and is putting out 295 rwhp

Specs of the car.. (there's a lot more that has gone into the car, but this is what I can think of for now)

Car: Mazda 1983 Series 3 RX-7

Engine: Cosmo 20B, Naturally Aspirated, Extend Port, 2 x 10" Thermos, 3 core radiator, Microtech LTX12.

Driveline: Brass Button Clutch, 12A Gearbox, Modified S3 Tailshaft, S3 Diff with 4.4 gears

Brakes: Stock S3 Ventilated disks all round with Metal King pads

Fuel System: Bosch 044 Main Pump, Pre Pump, 1.5lt Surge Tank, Speed Flow Fittings

Exhaust: Custom extractors 3-2-1, 2 1/2" pipe into a 3" straight through Select-Maz muffler (3" system coming soon)

Wheels & Tyres: 17x7" Wheels with 205/40/17 Tyres

Stereo: Kenwood Head Unit, 2 x 5" & 2 x 4" Pioneer Speakers, Amp, Sony 12" Sub

I'll stop rambling now and post up some pics, videos & sounds

A pic of the engine cleaned, painted and ported ready for assembly