|  Home |  Tuning GT4 | 
blauw Source: Dennis Heath.

How to run more boost on the 3S-GTE.

This is long, but it covers a lot of issues concerning running more boost.

Ahhh....boost, probably the most misunderstood performance mod. Here's my opinion, on the stock turbo, anywhere around 12 to 13 psi, even 14 psi, is good, but as soon as you start trying to go any higher, you're gonna be out of the turbo's efficiency range. When that happens you no longer are really producing much more air. What you are doing is producing some extremely hot, very thin air at 16 or 17 psi, and will end up with more than likely less power than at 14 psi, and a very stressed engine, which will more than likely one day, have a piston for dessert.

Another problem is that the higher the boost, the higher the cylinder pressures. So keeping the charge air cool becomes more important, i.e. maybe it's time to look into a new intercooler or water injection etc.

O.K., so you have an upgraded turbo and better means of cooling the charge air, now you can run 16 or 17 psi of boost, and be within the turbo's efficiency range, but as Ivan wisely inquires, what about fuel? Well the stock pump is good to 60 psi of fuel pressure, and the stock fuel pressure is approx. 38 psi, but remember that the stock fuel pressure regulator will add 1 psi of fuel pressure for every 1 psi of boost, so if you run 17 psi of boost you are now at (17 + 38) 55 psi of fuel pressure, close to max pressure, which really isn't good cause as the pressure increases, the volume of fuel the pump can supply drops. Time to buy a pump if you want to run 17 psi.

Right, now you have a higher pressure, higher flowing pump, but can the injectors supply enough fuel? Well the answer to that depends on how much hp you're making. If you refer to Jeffrey's page with the formulas for working out fuel requirements you'll see that the stock 430cc @ 38 psi, will allow about 250hp at an 80% duty cycle, but while it's not good to exceed 80%, you could use a 90% duty cycle (IMO absolute max), and you'd be able to get around 280 hp.

However there's another problem, Toyota designed the car to run 8-10psi of boost, and at 12 psi you get fuel cut. The maps themselves (crucial to reliable safe performance) only go to about 12 psi. So your choices now are, get a reprogrammed ECU, that now has maps to accommodate the increased airflow, but even then 16, maybe 17 psi is the highest you can go. Why? Because the stock MAP sensor is only a 2 bar kind, i.e. it reads from approx. -14.7 psi to +14.7 psi give or take a psi or 2, and the Air Flow Meter is only good for about the air equivalent to 16 psi.

Alright let's assume you've done the basics first like intake, exhaust, colder plugs, better spark plug wires etc., plus your upgraded turbo, better means of charge air cooling, your upgraded pump, and your reprogrammed ECU. Next step, IMO, is to hook up the car to a good high quality lambda meter. High quality lambda meters are very expensive (to the tune of U.S.$1,500.00) and precise, I believe there are places that rent them, but don't rely on a stock O2 sensor for accurate testing. Set your boost to 16 psi, and take it for a test run, and check the mixture. Once you're not running lean anywhere, you'll be safe. If you are, it's time to turn the boost down a bit and recheck.

If you want to carry things further, then it's time for larger injectors, a programmable engine management system that uses a MAP sensor and air temperature sensor for mapping, allowing you to throw your AFM and stock MAP sensor as far as you want, and some dyno time.

G-Force does upgrade the ECU.
Left G-Force ECU, right stock ECU:
g-force 1

close up G-Force
One other thing, definitely move up a few octane in gas.

1990 Toyota Celica GT-Four

 |  Home |  Tuning GT4 |