The Yaris Performance Primer

[eTiMaGo]

There's a lot of information scattered out there on the hot topic of improving the performance of our little cars. So, I will try to summarize everything into this handy thread.

Before we start, please remember that performance does not always mean raw horsepower! Although there are certainly several ways to improve the engine's output, it is wise to play to the car's strengths (low weight and great handling). So, I will explore different options in several "stages", of increasing cost and complexity, as a guideline of sorts.

Also, please always keep in mind the implications of modifying a car. One way or another, you will reduce the lifespan of the car, put more strain on stock components which may fail earlier than normal. So, follow this guide at your own risk.

STAGE 1
Simple, inexpensive mods that will increase the fun factor of your ride.

• Lightened Pulleys - NST has a full range, but you can just start with the crank pulley. These increase the responsiveness of your engine by lowering rotational mass. On the down side, they can make driving smoothly a little more difficult, especially on manual transmissions.
• Good Tires - This is really self-evident, tires are the only contact between your car and the road. Street-rated sport tires are a good compromise for a daily driver which sees occasional racing action. You can also at this point change your wheels, if you're really after performance, you should not go over 16", as bigger wheels are heavier, which will sap a lot of the limited power available.
• Short Shifter - If you have a manual car, this is a must. You'll shift between gears faster, meanign less "dead time" when you are not accelerating. Three options here, NST or TRD which are installed in the engine bay, shortening the lever action on the gearbox, or TWM's which is installed in the cabin, essentially a shortened version of the stock gear stick. it makes for a nice cosmetic improvement too, but may be harder to reach.
• Lowering Springs - Several advantages here, first it makes the car look a lot better, secondly it improves handling somewhat by limiting body roll. Quite a few choices here, Tanabe and TEIN's offerings are quite popular, but there are several others.
• Tie Bars (aka Strut Bars) - The efficiency of the front tie bar is a disputed issue, but it is meant to strengthen your car under heavy cornering, giving more steady, controllabe handling. Rear strut bars are also available, and other underbody stiffening braces if you are feeling adventurous
• Intake and Axle-back Exhaust. On this car, most of the aftermarket intakes and exhausts do not bring a whole lot of power to the table, and if they do, it's mainly at high RPMs. Still, they can dress up an engine bay/rear end of the car, and give a much more sporty sound to the car (which will make it feel faster too ) Many many different brands and models here! We have a few members who have run their cars on a dyno after installing these, aftermarket headers (also known as I-H-E combo), and crank pulleys, it is good for about 10-15HP gain at the wheels.

STAGE 2
More "meaty" mods that will really start to give your car more punch on the track, while remaining affordable.

• Coilover suspension - You could just upgrade your struts to TRD ones, but if you are seriously considering competition with your car, you should go for adjustable coilovers. These will let you lower the car as much as you want, and give you control over the damping force. By altering the balance of this damping between the front and back of the car, you can fine tune the way it will react while turning (oversteer vs. understeer). Other suspension mods can be considered: camber bolts will improve the grip of your tires when in a turn.
• Header and Cat-back exhaust - The stock midpipe of the Yaris is quite restrictive due to the catalyzers and resonator. By replacing those with high-flow versions, and using slightly larger tubing, good gains can be achieved. Micro Image carries Nitto Performance midpipes, or you can get it custom-made. As for a replacement header, DC Sports makes the most promising one. Although Megan Racing offers one too, the DC header has longer runners, which apparently improves mid-range torque. Though, AFAIK, this is yet to be proven by a dyno chart.
• Weight Reduction - Imagine how much easier it is to push around an empty shopping cart compared to a full one. The same applies with cars, lower weight improves your acceleration, braking, and handling. You can reduce weight in two ways: Replacing existing parts with lighter ones (i.e. CF hood and rear hatch), or stripping out unneeded interior trim parts. Bucket seats are also a good option to include here, giving more support to the occupant, and lowering weight. The good thing about weight reduction is you can do as much or as little as you want. You could just remove the spare wheel, tools, and the rear seat bench, or rip out every bit of plastic from the interior.
• Uprated Brake Pads - A bit of an optional upgrade here, since the light weight of the car does not put so much stress on the brakes, but better pads can help against fading during heavy track use. You should also optionally consider at this stage, racing brake fluid and stainless steel hose upgrades for more consistent braking.
• Racing Clutch and Lightweight Flywheel. - An uprated clutch will be stiffer (though the stock clutch is quite mellow to start with), giving you more efficient shifts. A lightened flywheel enhances the effect of the crank pulleys, giving you an engine that will really respond.

STAGE 3
MORE POWER! At the time of writing, there are not a lot of reliable options available to us to increase the output of the engine itself. This is due mainly to an ECU that is notably hard to crack. So, a lot of the following information is still theoretical, or in prototype stages.

• NA Tuning - increasing power without turbos or anything of the sort. This is usually done by using modified camshafts (none available), or higher compression pistons (which are available). ECU remapping is also an advantage, but currently, as mentioned, not fully feasible. There's also a high-flow intake manifold in the works that looks to give a nice increase in power at high revs.
• Nitrous Oxide (also wrongly known as "NOS") - By far the cheapest way to get a boost in power. Due to the design of the fuel system, only a wet shot system would be feasible, but there are concerns over the possibility of the plastic intake manifold cracking under low temperature or in the even of intake blowback. We know of one member here (project y) who is running a Nitrous system, reportedly with no problems.
• Supercharging - Using the engine's rotation to power a blower, which then forces compressed air into the engine, creating more power. Superchargers create a linear increase in power from low RPMs, though the maximum power increase may not be as much as a turbo's. Currently there are two options: Blitz's Roots-type superchager or Power Enterprises' Rotrex-based centrifugal supercharger.
• Turbocharging - A very popular way to increase engine power, by using the force of the exhaust gases to turn a turbine, which in turn forces more air into the engine, thus increasing power. There was a company, ZPI, which has since gone out of business, which offered a kit for the Yaris. Their kit produced a safe, relatively low boost of 7psi, and they claimed a dyno result of nearly 180hp at the wheels. Currently there are several entities, such as our very own Garm Beall working on bolt-on turbo kits, but the main hurdle is once again the engine management.
• Engine Swap - Why bother boosting an economy motor when you could change it for a bespoke sports engine? Several swaps are feasible, I've heard of 2ZZ-GEs, 3S-GE, even seen in a magazine a turbo'ed 4A-GZE in a Yaris! Or you could be blasphemous and put in a Honda engine... or just go crazy and follow the "Project Sideways" philosophy, by changing the car to rear-wheel drive with a longitudinal engine! The main drawback here is the rather limited size of the engine bay, it'll be hard to fit in a bigger engine, and maintenance of that engine may be quite cumbersome. But, in the end, it's probably the only way to create a true mini monster

STAGE 3a
Other stuff not related to the power increasers mentioned above, but which will come in useful at this stage.

• Roll Cage - So that your car doesn't get crushed like a soda can if you get into a bad accident on a track. Can also stiffen the car, improving handling.
• LSD - Limited Slip Differential, this is most useful when racing, as it prevents your wheels from spinning needlessly if they lose traction.
• Uprated suspension components. - I'm not sure if anyone offers these yet, but strengthened suspension arms and polyurethane bushings would help improve handling even more.
• Rear sway bar to stiffen rear suspension.
• Higher performance fluids as an option. Kaaz gear oil made a huge difference in my trans feel, and better brake fluid goes with better pads, IMO.
• A couple of gauges an essential partner with performance mods, I think the most important 2 gauges you can add are water temp and oil pressure. and of course, a TACH for goodness sake.

So there you have it! I cannot possibly claim to know absolutely everything about this car, this post is meant to be a general overview/guideline.