The Honda Integra TypeR's 1.8 litre twin cam V-TEC engine is a gem, delivering an amazing 78.3kW (or 105hp) per litre at 7900 rpm. And as with many other current high-power engines, making effective modifications to it is difficult - in fact many other owners of Honda Integra TypeR's have previously told me of their woes in trying to find more horsepower through exhaust and intake mods.
Importantly, it's not uncommon for some cars to actually lose power from what appear to be fairly well thought-out changes!
Many owners have experimented with various kinds of intake mods, including pod type airfilters and changing the length of the intake tube prior to the throttle body. Generally speaking, the pod filters gain nothing more than a huge increase in induction noise - which while delicious, can also be intrusive. In terms of power, often the pod filters prove to lose top-end power on the dyno - perhaps the hotter engine bay temps negate any flow improvement (see breakout box). So I don't think that these pods are superior to the OEM set-up, as Honda has already supplied a pod-type filter enclosed in an air-box, which in turn is fed from inside the front guard.
The only modification in this area that may give gains could perhaps be the deletion of the resonant chamber residing in the inner guard, and force-feeding cold air to the stock air-box. But even this I would expect to give only minor improvement.
So what about the exhaust side of things? Aren't all factory exhausts on road vehicles a compromise between noise, emissions and power? Therefore, doesn't there have to be room for improving power to the detriment of the other two? But exactly how should this be done?
The Standard Exhaust
The standard system appears very well designed, using stainless steel 2¼-inch pipe with mandrel bends. There is probably no point in changing this main pipe - but what about the mufflers, cat converter and collectors? The rear muffler is a large resonant chamber, which - from the outside at least - looks to not impose any great restriction, so it was decided to also leave this alone for the moment.
Next up the chain is a straight-through hot-dog style resonator of the same internal diameter as the rest of the pipework - again it was decided to leave it in place. From there forward the exhaust enters the rear of the cat (which looked surprisingly small for the system), and then finally we get to the bottom of the exhaust manifold. The exhaust manifold on the 'R is a 4>2>1 configuration with a design more like a set of extractors than a cast manifold. While it is not a casting, the design still looks mass-produced and certainly doesn't have the pretty appearance of high-end Mugen type stainless systems.
An interesting feature of the system is a small section of tapering pipe between the 2>1 merge and the cat. The tapering section constricts size down to 42mm at its smallest point.
My preferred exhaust technician, Trevor Campbell, was entrusted with looking over the system and offering his expertise as to where gains may be found. Trevor agreed with my first impressions of the worth of the main tube and mufflers, but entertained the idea that the 2>1 collector and cat converter may hold some promise. I mentioned to Trevor that after the 2>1 merge, the internal diameter dropped to 42mm in a smooth taper before entering the cat and that the input and exit of the cat were of the same diameter.
Trevor thought that the exhaust might be designed in this way for two reasons:
Trevor decided to pull the system down from this point forward and to also inspect the headers while he had the system off the car. This revealed that the headers, while appearing crude from the outside, were almost identical to the diameter and length he would have chosen for a custom extractor system. Again it was decided to leave these alone, concentrating just on that 2>1 collector and cat.
Trevor made a custom taper and collector to replace the factory restriction, while still mimicking the concept of having a small lessening in diameter to preserve torque.
We ended up with a pipe that has a 47mm internal diameter at its smallest point. That is only a 5mm increase in diameter over stock, but this represents a 20 per cent increase in cross-sectional area. The ends of the cat converter were also opened up a little to suit. This necessitated the need for a larger flex joint for the front of the cat, with Trevor installing a WRX flex joint he had lying around, which fitted perfectly.
So in all we changed only a 15cm section of the standard exhaust system, with minor cleaning up of the inside of the stock headers also undertaken. The total cost was $300. That's much better than the $2,000 required for some big brand extractors and cat entry - but did the exhaust changes actually work?
To quantify the results, I had taken two baseline performance measurements for the stock car. One comprised a variety of in-gears acceleration times and the other was the dyno measurement of the power available at the front wheels. (Note that the Dyno Dynamics machine that was used has a much greater driveline power loss than a DynoJet dyno.)
From this graph you can see the max power at the front wheels in 3rd gear was approximately 95kW at 114 km/h (which corresponds to 7880 rpm) and tractive effort peaked at 3200N at 92 km/h (6300 rpm).
Another dyno run was performed after the mods were undertaken, but unfortunately this couldn't be done on the same dyno. However, with both being Dyno Dynamics and neither workshop having had anything to do with my mods, I believe them to be reasonably comparable. From this graph you can see the Integra now has a max of 98kW at the wheels in 3rd gear at nearly the same road speed (and so also the same rpm) and that tractive effort rose to 3400N, also at the same rpm. For ease of comparison I have plotted the stock exhausts power curve onto this graph in pencil.
The acceleration times were run on a flat piece of tarmac, with two runs made in opposite directions to negate the affects of any slope. The times (in secs) were as follows:
From this it can be seen that the exhaust changes have done their job - there would appear to be no loss in bottom-end torque - in fact the 4th gear runs improved. To complement this, the top-end has also gained power. On the road the car feels much crisper and definitely feels stronger through the mid range and all the way to the limiter.
Earlier I mentioned compromises - well as expected, there is a trade-off for the modification, but one I am happy to live with. The car is a little noisier in the cabin, but not obnoxiously so. CO figures also did increase slightly to 0.55 percent at idle (1% being the legal limit). While this is a little worse than stock, it is still acceptable.
But for such a small outlay, I am rapt in the improvement!