So, you just bought a normally (naturally) aspirated (NA, i.e. no turbo) MKIII (86.5-92) Toyota Supra. You want to make that beastgo a bit faster, handle better or maybe just look a little better. This is the place for all the infoon how to make your NA Supra scream, check the FAQs for some answers to frequently asked questions otherwise, read on. There are really only two things that you can (cheaply) do to make your car faster- reduce restriction in the induction (air filter) and reduce restriction in the exhaust (get rid of that muffler!). Here is a list of mods you can do to beef up your NA's performance:
#1 Get Informed
Join SOGI. The Supra Owners Group International (SOGI) is a group of Supra owners worldwide. There are some helpful people on the SOGI email list and tons of good info on the SOGI website.Joining SOGI is free and will introduce you to a group of people that might be able to help you out.
In light of the recent decrease in the useful information to noise ratio on the SOGI list, I would suggest and alternative: Supra Forums.
#2 Get rid of that restrive airbox/filter
Objective - Reduce air intake restriction, raise flow rates.
Solution - get a K&N Filtercharger. It looks sweet, flows freely and it sounds cool too (don't worry, you will get more intake noise using an aftermarket filter). Try to avoid the HKS Super Power Flow. Its name should be changed to Super Dirt Flow. It has poor filtration characteristics and the filter can't be cleaned, it must be replaced. The K&N is the best choice-great filtration, great flow, great economy (1,000,000 mile warranty). More air = more power.
Cost? about $140.
#3 Loosen up that AFM
Objective - Reduce AFM spring tension to increase responsiveness, air flow.
Solution - Dean Marcum's AFM mod. Basically, you will loosen the spring on the AFM's "flapper", allowing it to react more quickly and flow more air. What is the AFM you ask? The Air Flow Meter (AFM) controls the ammount of air entering your engine. This piece of electronics is VITAL. DO NOT mess with it! A new one costs around $200 so be careful! More air = more power.
Cost? nothing, just your time.
#4 Fool your engine into thinking its colder than it really is
Objective - Fool your engine into thinking its is colder than it really is. Cold engines need more fuel and more timing advance.
Solution - Dean Marcum's coolant sensor mod. Basically, you will fool your engine into thinking it is colder than it really is by adding a potentiometer (resistor) to the temp sensor. More fuel, advance = more power.
Cost? about $2 for the potentiometer.
#5 Get rid of that restrictive exhaust
Objective - Reduce exhaust restriction while maintaining back pressure. NOTE: Unlike turbo engines,NA engines need a certain ammount of back pressure to "pull" (scavenge) the exhaust gases out of the combustionchamber. The large "free flowing" exhausts used on turbo vehicles will DECREASE the performance of your NA (within reason, if your NA is putting out more than 350 hp, this doesn't apply to you norshould you be reading this... ;)
Solution - There are many options to do this. The best and most ideal option would be to replace theentire exhaust with 2.5" straight pipe and a free flowing muffler, but this is illegal in most statesand is difficult to have done. If you are having a custom exhaust built, do not exceed 2.5" diameter (unless you have over 350 hp or so) tubing becuase larger tubing will reduce back pressure, reducing the scavenging effect. Cat-back (from behind the catalytic converters) exhausts are always an option, as are free flowing cats. These are the the best options when emmissions are a concern. Ifemmissions are not a concern, "gutting" the cats can be done. NOTE: Tampering with a workingcatalytic convertor is a violation of federal law. "Gutting" the cats consists of destroying the honeycomb metal matrix inside the cat. This can be done by forcing a hammer or other tool into the cat. From my experience, the best solution is to use a 2.5" or so hole saw. I would also recommendputting a piece of tubing in the cat after you have gutted it. The open chamber of the cat causes the exhaust gases to resonate and the results in a very "blatty" sound. This solution combined with a free flowing muffler is a very viable alternative the other discussed methods. Another thing to do would be to replace your exhaust manifold with a header. A header is a tuned exhaust manifold that will help the gases flow out easier. A header will mostlyhelp high end horsepower, and possibly decrease torque. As far as I know, there are really only 2 manufacturers of headers for the MKIII Supra: Pacesetter and Doug Thorley. From what I have heard, the Pacesetter model doesn't fit correctly and need some alterations to get it to fit. I haven't heardanything about the Doug Thorley, they may be out of business.
Cost? depends on the course of action, ranging from nothing (your time) to upward of $400.
#6 Lose that power robbing belt-driven fan
Objective - Reduce load on engine, improve cooling by removal of stock fan/clutch assembly attached to water pump.
Solution - Get a Permacool 14" High Performance electric fan (or equivalent, but make sure it flows more than 2500 CFM).Pull the radiator, install the fan on the radiator, remove the stock fan, reinstall the new radiator/fan assembly, wire it upand you're good to go. No big fan being turned by the crank means the engine can rev more freely, greater airflow by the electric fan means better cooling.
Cost? about $115 for the fan and a temp switch (to turn the fan on when the engine reaches a certain temp).
Now that you have done some simple things to your NA you can enjoy a bit more power and have fun.But by no means should you expect to beat a turbo or a corvette, its just not possible.