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The FTOWA Induction System

May 2004

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Over time, FTOs have had a wide variety of aftermarket induction systems slapped onto them. Simple pod filters on the main pipe, flexible ducting with filters in front of the radiator, filters where spotlights used to be, steel intake chambers, you name it, it's out there on an FTO somewhere.

In more than three and a half years of FTO ownership, I'd not made a single change to that little MIVEC engine, save for a token K&N panel filter in the stock airbox (which had more to do with the cost and availability of the throw-away standard element than any pretentions towards "performance").

But all this was about to change.

Before we go any further, let's take a little ride through the GPX factory induction system.

Let's say a little oxygen molecule foolishly tries to cross the road in front of a MIVEC FTO at full throttle. Our molecule somehow finds itself sucked into the cavity inside that curvaceous front spoiler, and vanishes down a triangular opening that is furiously gulping down air.

Note that the factory intake point is placed in the "dead" spoiler cavity - as opposed to directly in the airflow - so as to draw in as little dust and rain as possible. Minimising induction noise may also be a factor. In factory FTOs, the intake is separated from the radiator by a plastic panel, ensuring the air isn't unduly heated prior to ingestion. Some FTOs seem to be missing this panel (past accident damage, perhaps?), leaving the duct overexposed to hot air when the car is standing still.

Anyway, back to our molecule... which is in for the ride of its life.

Having entered the duct, it makes an immediate 45-degree turn, evades a depression in the duct wall (thanks to an intruding spoiler mounting bracket), makes a series of 45-degree and 90-degree turns, then passes a resonant chamber tee-d into the duct (required to reduce induction noise, at a guess). It then makes a final 90-degree turn, skirts another depression in the duct (this time because of the protruding headlamp assembly) before ending up in the airbox.

At this point, it's about half-way through its trip into the engine.

On passing through the air filter panel, it makes a 70-degree turn, races through a section of flexible duct (to cater for engine movement/vibration), traverses a flattened section of pipe before a final 90-degree handbrake turn into the throttle body.

As far as thrill rides go, that one is up there with the best of 'em. But when you've got only 2 litres engine displacement, no turbocharger and a long, inviting road begging to be taken at speed, there's surely some room for improvement! If we could just straighten out that airflow somewhat, the FTO powerplant might just reward us with a few extra Newton Metres of torque...

That Knocking Sound is Opportunity, Not Detonation

I had been thinking impure thoughts about ripping out the stock induction for some time. Most FTO owners do! But when my old battery finally started to fade, I decided to look closely at turning it into an opportunity to do some serious R&D.

What's the battery got to do with this, I hear you ask? Good question!

The standard battery size and position is the reason for the intake's abrupt 90-degree turn just before the throttle body. The duct then requires another bend further down, which ultimately affects the location of the factory airbox.

Some aftermarket FTO induction systems involve (or require) the total relocation of the battery - usually into the boot. I didn't want to go this far.

However, it was possible to source a significantly smaller Odyssey brand battery. The ES 12V 800 model was only 110mm high, and still packed quite a punch... more than enough for the FTO.

This particular model was available for under $300 from the usual battery outlets. At the time of writing, it was the smallest Odyssey that was warranty-covered for installation in a motor vehicle. Even smaller units were available, but were aimed more at motorcycles, jetskis, etc. Due to its low profile and overall size, it was a bit fiddly to intall on the tray as a DIY job, but perseverance paid off. It was gratifying to have the final result pass motorkhana scrutineering (ie. yank at battery to see if it would fall off).

With this low-profile battery fitted, it freed up the entire engine bay area from throttle body to strut tower. Consequently, it was open season on the factory induction system!

Raw Materials Required

I needed induction pipe, and lots of it. Bent bits, straight bits, funny flexible bits and rubber sleeve bits. As luck would have it, I found that one of Perth's largest truck wreckers was located in the very next suburb!

Having taken a day off work, I spent a glorious morning wading in a trailer of cast-off intake piping, wandering around the 70-odd trucks awaiting dismantling and generally having a good old time measuring and scavenging. My wife is right to worry about me.

The plan was simple...

Reposition the factory FTO airbox so that the inbound air made a smooth, wide-radius bend into the throttle body. This required a 70mm diameter pipe with the correct bends. Many, many bits of truck engine were measured and checked before finding the right stuff.

I came across a Mazda truck fresh from Olympic Dam... complete with caked red Aussie dust on everything! I scored a mass of 70mm ABS plastic ducting for $44.

Back home, I set about building the required bent upper pipe from the various bits of ABS plastic on offer (as well as removing all that lovely dust).

I'd wanted to step neatly down from the wide 95mm airbox exit hole into the 70mm size pipe, but just couldn't work out how to do it. In the end, I settled for a bellmouth intake moulded into the end of the 70mm ducting, inserted into the upper airbox hole and sealed with a thick rubber ring. The remaining bends were assembled with heavy duty industrial silicone adhesive - able to withstand flex, vibration, temperatures of 205 degrees C, etc. etc.

The result was a very neat, factory-look airbox and pipe setup. The airbox would now be positioned North-South in the engine bay.

Initial test-fitting of this assembly looked good. Damn good...

Relocating the Lower Air Piping Assembly

Previously, the incoming air entered the factory box through a hole in the side guard. With the airbox turned by 70-odd degrees, I needed a new pipe assembly.

As I wanted to suck air from the same spoiler cavity as the stock system, it was easy to see that removal of the standard lower piping would enable a new duct to simply duck under the lower radiator support and come back up the other side into the airbox.

I prototyped the new piping using 80mm stormwater drain... 45 and 90 degree bends cost about $7 each, and a metre of straight pipe cost $10. All in all, I used only one metre of pipe and four bends.

With the airbox fixed in place using a simple metal bracket, construction and test-fitting of this pipe was performed over a few hours.

Okay, more than a few. This took a long time to get exactly right! If I'd wanted to suck in air directly under the radiator (ie. through the gaps in the spoiler), it would have made life much easier. However, I stuck to the original Plan, which was to avoid any significant ingestion of rain, bugs, dust and stones by positioning the intakke right up inside the spoiler cavity.

The connection into the bottom of the airbox was fashioned with the aid of my trusty heat gun. The top of the pipe was heated up to fearsome temperatures, and then moulded into a perfect fit through the existing hole. It even clicked in place!

The final pipe position ran down inside the spoiler, under the support strut (where there was previously the resonator box from the stock system) and up between the cooling fan plastic cowl and the metal bodywork.

This stayed neatly out of the way of any cooling fan airflow through the engine bay.

The lower pipe was held in place by an exhaust bracket, and bolted to an existing mounting point. Once bolted on and inserted through the lower airbox hole, the entire assembly was rock-solid.

The system was finished off with a bit of black paint. A small hose attachment was added to the upper duct to mirror the factory ventilation connection.

Dyno Testing Induction System Version 1

The system was installed and immediately tested using the good ol' Home Dyno digital crank angle sensor patch.

Immediately thereafter, the complete stock induction system was refitted and a baseline dyno run was performed.

The results were disappointing. The graph below shows relative torque/power curves from the two runs. The blue lines show the factory intake, and the red lines graph the new system...

There was a very slight increase from 5600rpm to 7100rpm, but nothing that would remotely justify all that effort invested so far. All in all, a big fat zero.

Back to The Old Drawing Board!

The very next day, I revisited my original design for the upper pipe. I had initially wanted to utilise all of the factory system's large airbox exit hole, and just step down to the 70mm pipe to the throttle body. However, at the time, I was unable to fashion a suitable connection. I ended up settling for a 70mm pipe all the way from the airbox.

I had hoped that the straight piping and bellmouth intake would do the trick. However, faced with such a depressingly inconsequential result from the dyno test, it wouldn't hurt to try something different!

It was time to work out how to use the large airbox exit hole in all its 95mm glory.

Out came the grab-bag of Mazda truck goodies, and much creative thought was employed to try and find a good solution. Whatever connection was used, it had to be flexible, tough and able to connect cleanly using the existing airbox position.

I found a flexible rubber boot in my scavenged accessory bag that fitted the bill. It was overlooked in the Version 1 construction plan because I had been unable to stretch either end over the wide airbox exit lip. This time, however, I was not about to be beaten so easily.

With the aid of some useful tools (and my wife) the boot was fitted tightly in place. I then shortened the pipe to the throttle body, fashioned a new bellmouth shape at the start (for better airflow, and also to fit inside the flex shape part of the rubber boot) and voila! Version 2 was ready.

Well, almost ready. After the results of the previous dyno run, I was not about to spend much time and effort with the industrial adhesive - especially as there was a high probability of a "Version 3" attempt in the not-too-distant future! So I resorted to a bit of shameful duct taping as a short term test facilitator. The pipe fit was already snug, but I wanted to ensure it was totally airtight and stable. As long as the engine bay temperatures did not get too high, this would be more than adequate for one more dyno run.

The finished article looked like this...

Dyno Testing Version 2

As before, I ran back-to-back Home Dyno tests using both the complete factory induction and the Version 2 custom design. I was getting very good at installing and removing these things!

I had also given into temptation and cleaned the K&N panel filter. It was filthy. As I was not trying to compare the previous day's runs with a new run, this was not going to compromise any performance comparisons. Both the latest runs were performed using the clean filter, and within two and a half hours of each other.

Here is the result. Again, the blue curve is the factory system. The red curve is the custom system.

Now THAT is more like it.

The new intake setup gives the MIVEC powerplant additional torque from 4500rpm right up to 8000rpm. That large chamber of air between the panel filter and final pipe to throttle body made all the difference in the world. Ladies and gentlemen, we have a result.

No discussion about MIVEC induction modifications would be complete without mentioning the aural feedback issue. At wide open throttle, this induction system does indeed sound more throaty. However, it isn't one of those 150dB screamers like some I could name! It is also indistinguishable from a stock system at part throttle/below 4500rpm. Of course, if you like sounding like a fighter plane on afterburners, you won't like this intake setup at all...


Let's review the main advantages of this system...

  1. It works! Proven gains across a substantial part of the rpm range (from 4500rpm through to redline).
  2. No loss of torque below 4500rpm, so no impact on bottom end drivability.
  3. Throttle response does not seem to have been negatively impacted.
  4. It looks like a factory system (well, once the duct tape is no longer needed!).
  5. This system utilises the standard filter element and airbox.
  6. It draws cool, clean air. Filter will last longer (or need cleaning less frequently).
  7. You won't wake up sleeping babies and old folks five kilometres away.

In short, this system has all the performance you could hope for, but without any of the hassles that would make it hard to live with day to day.

If you would like more information on this setup, please feel free to post any queries on the FTO Drivers Club Forum.

Additional Notes

These tests were performed on an FTO with an unmodified engine (including factory exhaust), on BP 98 octane fuel. Back-to-back tests were performed within a few hours, with the same type and amount of fuel in the tank. Ambient temperatures were noted and corrected for by the Home Dyno software.

I have refrained from putting actual figures on any torque/power graphs, as I haven't recently done a calibration of the Home Dyno setup compared to a real world dyno. At this stage, back-to-back comparisons are the order of the day, as opposed to peak power numbers.

The next step may be to get the upper and lower pipes professionally made, as opposed to the "prototypes" used for these tests. It might also be interesting to continue to experiment with larger pipe diameters between airbox and the pipe leading to the throttle body.

However, for now, I think I'll just go and drive it for a while!

Update - June 2004

I've now reworked the system so that it is a little more robust, and have had the vehicle on a real world dyno. Version 2.5 is now constructed with a steel component between the rubber boot and the ABS plastic intake duct to the throttle body. Painted and clamped, it looks like this...

The dyno run was performed by Hyperdrive Motorsport in Malaga. The operator was happy to discuss any aspect of the process in detail, so - naturally - I asked a lot of questions! They also ran some tests I didn't expect, one of which turned out to be quite relevant to this induction project.

First things first. The FTO produced 146.2 bhp at the wheels, using a Dyno Dynamics chassis dynamometer in 'Shootout' mode. This was a 3rd gear run, so was not cut short by the 180km/h speed limiter.

One of the graphs showed air/fuel ratio. The usual 'dip' (ie. rich mixture) was evident immediately after MIVEC cutover... between 5700 and 6300rpm. With a properly tuned fuel computer, the staff were of the opinion that this torque curve would be freed from that midrange 'hole'. This was apparently common on many Honda VTEC powerplants as well.

It's also worth noting that this dip does not seem to be as severe in my 2nd gear "on-road" Home Dyno runs. Interesting...

Please note that this dyno run was not designed to provide before-and-after results on the modified induction system. If that was the plan, I would have taken the old system along with me, a few tools and a lot more cash! As I'm able to do back-to-back runs using my own test equipment, the real world dynos are simply there to provide hard, calibrated figures for reference.

Along with the air/fuel ratio results and torque curve graphs, there was one test they performed on the car that I hadn't expected. As it turned out, it was the icing on the cake...

The overriding concern when redesigning induction systems is to minimise restrictive airflow, which shows up as a drop in pressure at the the throttle body compared to baseline atmospheric pressure.

Part of the test process was to drop a sensor into the open mouth of the intake pipe behind the spoiler, and 'tee' a second one into the throttle body vacuum hose. The dyno controller could then provide a graph of pressure drop across the entire rpm range.

The staff at Hyperdrive Motorsport commented that the pressure drop across this system was extremely low. They ran off a graph to show this alongside a power curve (see left), and it was never more than 0.16 PSI. Indeed, up to 6000rpm, the pressure drop was barely above 0.8 PSI.

Using a different scale, this works out to be a restriction of between 2.5 and 5 inches of water at the throttle body... clear evidence of efficient air filtering and delivery.

A great result.

If any FTO owners have comparable throttle body pressure graphs for different induction systems, please feel free to email me. It doesn't matter if it's stock, panel filter, pod, etc. The comparisons between them would make for an interesting article...!

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