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Special Mens Business R is constantly involved in research and development for new model cars, and as new products and techniques are learnt adapting those changes to our current products to ensure the product range is of the highest possible standard.

As a result of our R&D program it has kept us in touch with many engineers in the automotive field both from original equipment manufacturer's and aftermarket supply companies, swapping idea's discussing certain problems, thus securing us further knowledge from those discussions held.

We use our own in-house Dynopack dynamometer, to constantly check and recheck our products to ensure our company philosophy is maintained.

Dyno chart shows a standard Nissan (Silvia) S15 at 128.2 kw at the wheels after the fitment of a full exhaust and cold air intake system the rear wheel figure jumped to a massive 179.3 kw. just as impressive is the torque which was increased substantially but smoothed right out.



STORY ONE - exhaust system development for Mazda MX5

Our purpose for this development was to discover the most suitable exhaust system for the Mazda MX5 1800cc naturally aspirated engine. We wanted to maintain the original connection points so that we could market individual parts which would replace original parts. Our 2000 model car was used and we made jigs to suit the muffler, intermediate pipe and 2 to 1 collector with catalytic converter combined.

Since the standard header was considered to be a good design we decided to leave this for later and concentrate on the 2 to 1 collector, mid pipe and muffler.

We modified a standard collector, rebent the tubes and welded a 2;1/4" tube to a high flow cat, also another one into a 2;1/2" tube.

Two intermediate tubes were made and also two mufflers 2;1/4" diameter and 2;1/2" diameter. we then arranged with Mike Hicks for a suitable time to test the systems on his car as we had previously arranged.

Mike and his car are ideally suited to our development program as he frequently uses his car both for Mazda Club Track Days and the Supersprint Championship. Mike is experienced and has consistent times, so his feedback would be valuable.

Using our dynapack chassis dynamometer we tested the standard system, the 2;1/4" system and lastly the 2;1/2" system, without any doubt the 2;1/4" system was the best - giving an increase over the entire rev. range with an extra increase in the mid range, maximum increase was about 5 kilowatts at a 6500rpm. This completed the part one of our development. Mike took his car and ran in two events before and during Easter, he gave us a good report - his times were improved and he liked the note from the muffler.

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The next step was to develop the 2 into 1 collector and cat pipe for size, length and joining configuration.

At Mike's convenience we were able to get his car back for a week to press on. The standard 2 into 1 collector is about 1;1/2 dia with a two piece pressed section directly under the double flange incorporating a balance tube, I needed to establish whether this balance tube was important or not, so I made a 2 into 1 collector from 1;1/2" tube without a balance and running into a 2;1/4" tube to a high flow cat, also fabricated the same in 1;5/8"OD and 1;3/4", the lengths before joining is the same as the standard collector. A 2 bolt flange was used directly in front of the cat so that I would only have to use one cat for the entire tests.

Tests were run on the standard collector and the 1;1/2" fabricated one. I was satisfied that the balance tube made no contribution to performance, so I considered it unnecessary to add a balance tube to the other two. At the same time the 1;5/8" and 1;3/4 collectors were tested, results were that the 1;3/4" was clearly superior. The next step was to see if longer tubes would be better.

I fabricated another 1;3/4" collector with 3" longer tubes and compared the two, establishing that the longer one was better. At this stage, the torque curve was showing good improvements in the mid range and increasing. This is encouraging as previous tuning experience on our turbo engine suggested that with tuning this mid range torque can be enhanced significantly.

I then fabricated another 1;3/4" collector, but instead of joining to a 2;1/4" (parallel collector) tube I tapered the joint down to 2" dia and thereafter a gradual taper up to 2;1/4" tube and then into the hi-flow cat.

Our next session was to compare the parallel collector to the diffuser type, results were peak power was only marginally better for the diffuser, but mid range was clearly improved, this lead me to fabricate a cat replacement tube and the next session we tested the parallel collector and the diffuser, both with the cat and without using the cat replacement pipe, results were that the diffuser type was well ahead when used with the cat replacement pipe, so that for track work it would be worth the effort and burnt fingers to remove the cat and replace with a straight tube.

Finally we fitted a stainless steel collector with diffuser and Mike's high flow cat which was on his car from the previous session, we also fitted a later model header from our car.

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Last test good result

Original results from the standard car as we saw it:

76kw at 6500rpm; 530nm at rear wheels 4900rpm

Then with the 2;1/4" system fitted comprising of a 2;1/4" dia muffler, a 2;1/4" mid pipe, a 2 to 1 collector 1;3/4" to 2;1/4" dia with diffuser and hi-flow cat.

84kw at 6500rpm; 580nm at rear wheels 4900rpm

This final test also included a current model header replacing Mike's one. The header contributed about 1 to 1;1/2kw, so the increase on Mike's original car with his header would be 6;1/2 to 7kw or about 8%.

Referring to the Dyno chart, when we used the fan to supply cool air to the engine compartment, an increase of about 2kw was achieved, and from previous experience from our own car, we would expect some good results from a pod filter and cool air.

This will be our next project on Mike's car followed by a programmable computer. With this we will be able to smooth out the dip in the torque curve to get some excellent results. During this time we will also attempt to improve on the standard headers and the computer will be a great help with this.



STORY TWO - upgrade for Mazda MX-5 SE:

Since the release of the SE, we had been keen to investigate the possibilities of an upgrade kit; popular opinion was that the turbo was too small and that it was a lost cause. However we were keen to try and when we had an enquiry from Randy in Melbourne we greeted it with enthusiasm.

Randy's original enquiry was could we bring the SE up to SP performance i.e. 110kw to 125kw at the back wheels within a sensible budget without changing the turbo or the computer. We said that we would give it our best shot.

Randy sent the car up on a transporter for Daniel who picked it up at the depot at Moorebank only 10 minutes away. The car came fitted with a 3" exhaust all the way through to a 3" muffler, and looked quite good. We checked it out and found that our intercooler fitted and needed only modification to the support bar.

We started fabricating a complete set of intercooler piping and jigs to suit, during this time Randy sent up his standard exhaust and we established a base figure of 110km at the rear wheels.


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Our intercooler was fitted with the new pipe work, standard air filter and an air box removed and our cold air system fitted. The standard exhaust was left on and some dyno tests were done to see how we were progressing.

After this the 3" exhaust was tried and dyno tests carried out. Results were quite surprising. The car now produced 158kw at the rear wheels however the turbo was producing 13psi of boost, at this point the computer cuts the fuel.

Rather than replacing the complete exhaust we fitted a restrictor between the two flanges after the cat and reduced it to 2" diameter. This restricted the boost slightly so that the fuel cut at between 6500-7000 rpm, at this point Randy was anxious to get the car back and wanted to drive it at a club track day.

We sent the car back with the advice that we would send him another additional restrictor so that he could fit it further down in the intermediate pipe if needed.

Randy called us the following week and reported that the car was performing well and was judged to be the most drivable car on the day. The fuel cutting out didn't seem to be too much trouble; he also said that the performance was significantly superior to the S.P. cars in attendance at the track.

Several months later Randy contacted us and asked if we could address the fuel cutting problem at the high revs and could we fit a stainless steel exhaust system at the same time.

Once again the car was sent up on a transporter and we decided to try a 2" exhaust system to replace the 3" system. At this point Guy used the intercooler pipes to further develop his jigs and manufactured a small batch of intercooler pipes and had them powder coated, fitting one set of new pipes on the car.

Daniel fabricated a prototype header pipe in 2" diameter with a 2" hi-flow cat. Guy followed up with a jig and a finished article then back to the dyno.

We found the system worked well. It took the max power to 140kw. At the rear wheels boost was up to 9p.s.i.

We thought that if we could get the boost to 10psi there would be maybe another 4 or 5kw to be had.

Next step was to fabricate a 3" header pipe through a 3" cat and reduce down to 2" thereafter to suit the 2" mid pipe and muffler.

This was tried next evening and achieved 10psi of boost lifting total power to 145kw.


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Guy and Daniel took the car around the block and were pleased with the performance - power came on smoothly and drivability was outstanding with an additional surge after 5000rpm, there was no fuel cutting.

Randy called back on Monday to report that his car was returned ok and in time. He was very pleased with the performance. He can now use full revs and feels just as good as before when it had 13psi of boost.



Several tests were done part way through to try to establish the individual results and combinations most beneficial to performance. Even though the air box, the larger intercooler and exhaust system alone and combined with one another did give an increase (the power figure was about 125kw), until the 3 items were combined the 145kw was not achieved.

So it seems for this car the total package is recommended for optimum results.


Technical figures:

Kilowatts: standard car: 110kw

  cold air intake system, intercooler and exhaust combination: 145kw

Torque: standard car: 194nm at 4000rpm

  cold air intake system, intercooler and exhaust combination running 10psi boost: 239nm at 5400rpm












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