posted on April 01, 2012 04:00
Ask Sarah: Bargain Basement Mods
By Sarah Forst
My money tree didn't bloom this year and digging through the dumpster outside MotoIQ hasn't been very successful lately, so I know how hard it is to mod a car on a budget. I've seen some interesting ways to be competitive in the import race scene for just pennies. So we’re going back to my roots- the ricer way of modding.
1) One of the first mods most people undertake is an exhaust. The muffler and small diameter stock piping typically restrict the outward flow of exhaust gas from the cylinders. A less restrictive exhaust system can reduce these pumping losses and free up more horsepower. Are you too cheap to buy one of those aftermarket exhausts? Coffee cans do double duty! If you can't at least JB weld them, just e-tape about 5 of them together axle-back (cat-back for more power) and drive it like you stole it. The glossy shine of the can saves you money on a nice fancy tip too!
|Don't worry- no 370Z's were hurt in the making of this experiment!
MotoIQ recently tested this cheap exhaust system. After staying up all night applying aluminum foil trim to Kojima's cup car (if you can't beat them, blind them), not only did the coffee help keep us awake, but the empty cans were bolted up to Project 370Z and dyno tested to see which produced the biggest gain. Folgers was first to rise and shine to the challenge. The strong blend was #1 in our taste test and gave us a burst of energy, but there were no noticeable gains on our butt dyno. Its large 6" diameter may work on some jet-powered turbo car but the decreased exhaust stream velocity didn't help in powering our N/A application, especially at low rpm. Too large a diameter piping and you lose out on the scavenging effect, the vacuum that accelerates the exhaust flow of spent gasses from the combustion chamber and more fuel/air mixture to be sucked into the combustion chamber. The exhaust air also cools down and becomes denser, making it harder for the engine to push it out the tailpipe. Our 2nd butt dyno attempt mimicked gains of 0.2 hp in the top end.
Hills Bros slightly longer and skinnier can is a slightly better choice for the "un-forced induction" 370Z. Low end torque was virtually off the charts. Seriously, we couldn't even measure the number it was so low… At 6000 rpm however, we gained a healthy 0.3 hp over stock, I think... Our last competitor, Yuban, was similar to Hills Bros in size so we weren't surprised to see numbers close to theirs. An added bonus to these cheap exhaust systems- the harmonious whine that would make any Honda equipped with a Flowmaster domestic 40 series jealous. Unfortunately, the coffee cans are only good for one race before they melt.
Don't forget to hollow out your cat to really feel the power. A hollowed cat decreases flow velocity causing flow stagnation and a loss of bottom end power. Not to mention it increases pollution, is illegal, and you won't pass a smog test with one unless you have $250 and a friend at the testing station- don’t ask me how I know these things! But hey, that guy on the ricer forum said it was a good mod, so it must be, right?
2) A 10 degree decrease in the intake air temperature is worth approximately a 1% increase in horsepower because cold air is denser and contains more oxygen atoms per cubic foot. The cooler air allows more fuel (if supplied) to burn. If you wasted all your money at the bar again and now you can't afford that cold air intake you had your eyes on, a trip to Home Depot and $5 for dryer hose is all you need to feel the enormous power gains from the arctic air in front of the wheel well. Your car will race ahead sucking up dirt, water, even fur from the bunny you accidentally slaughtered in front of the You Kill It, We Grill It roadside café. But is your "custom" intake bad for your engine?
|When in a bind, just use whatever leftover hoses and connectors you can find to make your intake.
If you're going "custom," use durable exhaust piping to make an intake. Otherwise, rev the engine a little as you watch that dryer hose condense to the diameter of a straw under all that pressure. Heater hose is as flimsy as a tractor trailer in 70 mph gusts. The hose flexes so much under the sucking pressure that you could draw raw, unfiltered air (and even debris) around where it connects to the filter to the engine's intake system. This could wreak havoc on getting the right air/fuel mixture in your engine. You could run lean, the ECU may detect detonation and pull timing, and bye bye top end power. You may as well remove the floorboards (unless your nitrous system already blew them out for you, AKA Fast and the Furious) and drive like the Flintstones.