TECH TIPS

Here you can find an ever increasing amount of detailed technical information, which can help you with a step by step how to for a procedure, a warning of what NOT to do, and other useful bits of information about Toyota Supras, both found out through my own experience and other sources.

I will endeavour to make sure that all of the following information is true and correct to the best of my knowledge, but I cannot be held responsible for any damage you might cause through incorrectly following guides here, or any other reason.

If you have technical information which would suit this page, please post it in the appropriate area on the forums and it will find its way here once I verify its validity. If you disagree with any information detailed here, please let me know also in the forums, and I will fix it.

Exhaust choice and Overboost

Air Filters and mounting

Wheels and Tyres

MKIV Aftermarket Exhausts and Overboosting Explained - So, you have a MKIV, and you want to put an aftermarket exhaust on it. Sure, you've heard it'll give you more power, faster spool, and a nice, deep, drone of an exhaust tone. The exhaust is an integral part of a car's breathing system, and one of the first modifications recommended for a car's performance. However, with the MKIV Supra, there's a pitfall which you need to beware of.

The way the MKIV Turbo system works, is two identically sized turbochargers, running in sequential fashion, with a single wastegate for *both* turbos. Now, this wouldn't be a problem unless this wastegate wasn't so damned small on the Japanese Specification MKIV Supra. It's ~20mm, and works fine for a stock exhaust. Here's the problem. The stock MKIV exhaust is an extremely restrictive one, and the wastegate on this system relies upon backpressure generated by this restrictive exhaust to help limit the amount of flow through the system. Basically, this means that by replacing the standard exhaust with a big, higher flowing, less restrictive exhaust can cause a problem known as boost creep. The reason boost creep occurs is because the wastegate cannot flow enough air to stop the turbos spooling, once you've replaced the exhaust and removed the airflow restriction.

What can you do to manage this problem? Well, it really depends on how much work you're planning on doing to your Supra. If you're going to be content with minor modifications such as Exhaust, Pod Airfilter, Front mount Intercooler, and raised boost to about 1-1.1 bar (~14.5-16psi), this will end up giving you a Supra which will push out between 350-400rwhp, and run high 12s to mid 13s. If you're happy with this sort of performance, all is well and good, and you can get away with a 3" exhaust (including dumppipe) and this overboosting problem won't occur.

Anything more than 3", as I did with my Supra, and you're going to hit problems. I decided when I bought my car that I wanted it to be very powerful by the time I'd finished with it. Consequently, I decided to put a 4" exhaust on just so that I didn't have to replace it later. Boost creep hits when you're on full boost, pushing hard, and the amount of airflow needed to pass through your now fully opened wastegate is too much to fit through, hence this remaining air flows through the turbos still, continuing to spool them and create more power, more air, and just increasing the overboost effect. However fun this feels when you're overboosting, and watching your boost gauge fly up to 1.5-2.something bar before some intercooler pipe (or your engine) blows up, it's definitely *not* good for the car.

My advice is to figure how much power you really want, and decide on an exhaust to suit. If you decide to go for lots of power, but weren't planning on doing the whole lot at the same time (like I didn't), you can get away with a 4" exhaust, with an added steel gasket in the exhaust somewhere to restrict airflow and cause the little backpressure needed to keep the overboosting in check. I found that for my 4" exhaust, a 2" steel gasket midway down the exhaust did the trick just fine, however each exhaust is different, so you will need to fiddle with this gasket diameter to get it just right...

Obviously once you're ready to go ahead with aftermarket turbos and wastegate, you can get rid of the gasket, as you'll no longer be using the standard, tiny wastegate.

Air Filters and mounting - There's lots of options to choose from when looking at Air filters. The most important things to look at are firstly the width of the "neck" of the filter, and secondly how much air the filter can flow. Depending on the filter materials, this changes, but in general a larger surface area for the incoming air to enter the filter, the better. Personally I use a K&N Pod Air Filter on my Supra. It does the job, and has a 4" neck to allow for plenty of airflow.

Mounting the air filter in a better position can really help cut down the temperature of the intake air, therefore helping with your car's efficiency. If you own a Supra, you'll know exactly how hot it gets in the engine bay, and all that hot air is being channelled straight into your engine through the air filter. Many people choose to relocate their air filter down in their front bar, so that it can pick up some nice cool air as it rushes through the vents of the bar. This is a good idea, and should definitely be considered. However, you REALLY have to be careful with your mounting point here, as if you place the filter too low, or in a point where it can easily pick up sprayed water off your car or other cars, you can do some serious damage to your car if water is blown up through the air filter and straight into the engine. So, by all means move the air filter to a place where it will pick up colder air, but be careful that it's not an area that will pick up unwanted water or a lot of dust/dirt.

Wheels and Tyres - As "Grey Imports", some have found legality issues with their wheel diameter and width with the road authorities. I have personally checked this with Toyota and have documentation confirming the exact stock wheel dimensions for a MKIV Supra Turbo. They are a max stock size of 17" diameter, with 9.5" width. As far as I am aware with the current Australian road laws (as informed by the pits when I put my car over), you may increase the wheel diameter by 1", but the width must not be increased. So legally you can only put 18"x9.5" wheels and tyres on.