Tuning your car for performance - The basics

I'm going to start this lesson on car performance with a quick basic rundown on some of the terms that will be used and their application.

Imports as they are commonly referred to do not indicate simply cars from overseas manufacturers. In the larger sense, the industry sees them as all sport compact and foreign vehicles. This means that for all intensive purposes, it includes cars such as the Dodge SRT-4 (both neon and caliber platform), Chevrolet cobalt, Saturn Ion, Saturn Sky, Pontiac Solstice, Ford Focus and Fusion, and various other makes and models. In a larger sense, Dodge is now considered an import company since most vehicles are manufactured overseas and foreign hands hold a large chunk of the company these days. On the other hand, Toyota is now seen as an American manufacturer since they have put a huge effort into getting their stateside operations going (and one reason why they are also now allowed to race in Nascar).

Tuning, as most would say, is getting the most available horsepower and torque out of a vehicle for it's intended purpose. Whether this may be drag racing, drifting, scca racing or rallycross, most people do not look into the future and think of things such as reliability, repeatability and dependability. Gathering 4-5 extra wheel horsepower out of a car is nice and all, but doing it at the expense of the motor 45,000 miles earlier isn't very productive for most novices.

Performance, in it's basic sense, is how a vehicle performs over a certain course. This may include items such as elapsed time, top speed, cornering g's, braking and acceleration.

Import tuning and related performance parts and accessories has been a growing trend for the past 15 years, and has really boomed as of late. Though the industry is hurting with giants such as Nopi suspending operations for the 2008 season, the passion that drives these enthusiasts hasn't changed for 50 years. I know what you're thinking, I just said it hasn't changed for 50 years, but that this has only been going on for about 15. Present day import tuners are nothing more then the hot rod builders of the days of old. Sure those guys were the forefathers, they're definitely still around, hell my father is one of them with his 1932 Ford 3 window hi-boy. Fact of the matter is, in their youth, they took cheap, inexpensive, preferably lightest cars they could find and throw as much power into them as they could. Sounds familiar doesn't it? Same thing you're doing. Before it was a Chevy Nova having a 454 big block crammed into it, now it's a Honda Civic taking the B20 block from a C-RV, the b18 cylinder head from an Integra GS-R, and various other models parts. Funny part is both cars are running low 13's to high 12's down the track. We have an advantage, and that's the technology that is available to our newer cars, and using that to pull unheard of power levels out of smaller displacement engines. I for one believe there is a replacement for displacement, and that's boost, juice, and rpm's. Sure the same power adders on a larger motor will still make more power, but with those, the import tuning culture has produced some incredibly amazing cars, and an amazing accessory and performance part line-up tailored to it.

So, now that we have the defined terms for my articles, we can now dive further into them and figure out what really makes these things tick and maximize your car's performance.

Import tuning's most basic fundamental hasn't changed from the good old days. Fuel Pressure. Having control of the fuel pressure on a vehicle is one of the most fundamental keys to any succesful setup on a modified import or sport compact. Stock fuel systems in cars these days are amazing. Direct fuel injection, returnless, ability to calculate injector duty based on various sensors around the motor to reduce emissions, increase driveability, and increase fuel economy. This system is great for stock cars as they can rely on the vehicles engineer to give them a trouble free map that accounts for everything that car goes through stock.... STOCK being the key word.

As you get into more modifications on your performance car, the need to modify the fuel trims increases more. Most piggy-back systems (apex-i AFC, greddy e-manage, HKS V-afr) simply modify either the mass air flow signal or manifold absolute pressure signal (map), and some cars such as the Mazda 3 utilize both. A simple and very effective tool to see where the fuel tables need to be overall is a wide-band o2 sensor. These are far more accurate then conventional narrow-band o2 sensors, and can display your air/fuel ratio across your entire RPM band. My favorites are innovate products, they're simple to use, cost effective, and highly accurate with repeatable results from car to car. These don't do anything to directly give you power, and are simply a tuning device for any vehicle and give you feedback on the performance of the car. Anybody making changes to a vehicles fuel map should have one of these or at least be on a REAL (god damnit I mean real, not a dynojet) Dyno. I'll touch on my hatred for dynojet in an article later, just avoid them.

But back to the fuel pressure. As the most basic and fundamental import tuning point on the vehicle, it is critical to get this correct before any other adjustments are made. Fuel injector flow is based off of a fixed pressure value of a standard viscosity fluid. Some manufacturers rate them differently, but the most common rating for the aftermarket is 43psi, while some vehicle manufacturers rate them much higher. The reason this is important is because the base fuel pressure behind the injector itself will increase it's basic flow rate. A 550cc injector running at 34psi at the rail is putting out far less fuel then a 550cc injector running at 52psi at the rail.

After doing a few pulls with your vehicle, take a look at your overall air/fuel ratio for the duration of your run. If you've reduced the backpressure of your exhaust, opened up your intake air flow, or basically anything to increase the performance and VE (volumetric efficiency) of the motor, the motor will be leaner (Air/fuel ratio is higher then before) then when you started. If there is a noticeable deficiency overall in the ratio, then simple fuel pressure adjustments can fix that. At cruising speeds, the air/fuel should always be 14.7:1, an all-motor car under full load should be about 13.5:1, and a forced induction car under full load should aim for 11.2-11.9:1. The higher the number, the leaner (less fuel) the car is. To raise your numbers to hit the ideal points, decrease fuel pressure, and if you're lean and need to lower the air/fuel ratio, increase fuel pressure.

Depending on your car, you may not see a change, but this is where the twist comes in with all that new fangled technology we deal with compared to our fathers. Modern EFI systems also use LTFT (long term fuel trim) and STFT (short term fuel trim) as values in their table to adjust for changes in the motor. In the beginning they're not much of an issue, but if you don't keep an eye on them as you progress into modifying the vehicle they can severely bite you in the ass down the road and hinder performance.

Most vehicles produced today will let either value increase or decrease by about 25%. Most also are not extremely happy about the change either, and certain side effects such as timing changes, reduced throttle on cars with electronic throttle bodies, and also fuel cuts and limp modes can arrise. This is where that fundamental fuel pressure change really comes into play.

After datalogging your car for a bit with any obd-2 software, you will clearly see where these values are for your tables. Your air/fuel ratio might be spot on for your motor, but if you're trims are already 15%-20% out you're going to be in trouble with a few more performance additions. Make adjustments slowly to fuel pressure, about 1-2psi at a time, and give the car a half hour of driving under normal conditions. Recheck your values and ultimately get them within +/- 5%. This simple change has worked with your computer instead of against it, letting it stay within it's optimal maps and still giving plenty of overhead for changes due to weather, altitude, or anything along those lines. Believe me when I say when it comes to import tuning, understanding this one little concept can save you tons of headaches down the road, and is very important to even the most mildly modified cars.

In my next article on car performance, I plan to touch base on piggy back systems and their effects on MAF and MAP sensors. I'd also love to hear from you on your own adventures with modern sport compacts, problems you've run into and conquered or just simply need help with.

Stay tuned for Tuning your car for performance part 2 - piggy-backs and why they suck.