12H-T power boost

Warning: modifying the settings for your turbo boost and injection pump can cause an adrenalin rush: so I did it!  Touch any of these settings at your own risk.

After enjoying the extra torque of the fat exhaust - see link, I set about increasing the boost and fuel to get more performance.  Some had suggested my 12H-T was a bit of a slug.

First. Boost. 

Ages ago I had installed a simple bleed boost controller purchased from ebay.  Standard boost is 7psi. I have been running at 12.5psi for a year or so. My advisors suggested 16 psi or more. I've settled on 15psi as it is what my gauge measures and also it matches the overboost warning light provided by Toyota. 

(Edit March 2011:  Now running 1.4 Bar = 20.3 psi in conjunction with new turbo)

Second, measurement.

Instal a quality EGT, Exhaust Gas Temperature, Gauge or Pyrometer I could tell what EGT I was running. EGT is affected by load, fuel, boost and is an excellent indicator of the stress on the engine. I back off the throttle when the EGT reach 650°C, my advisors say I could go higher. I'm nervous about pushing it too much.

(Edit March 2011: New turbo has dropped EGT by 100°C across the rev and load range)

Third, more fuel.

The little screw that holds the key to more power.

Required 2x 10mm spanners, and 1 x 3mm allen key.

As shown in the photo, undo the cap cover off fitting marked in yellow paint. The outer most is a cap. the inner nut is a lock nut. Under the cap is a long screw into which fits an Allen Key. Mark your start point, undo the lock nut, unscrew the long fuel screw half a turn, tighten the lock nut and test. Keep doing this until you get the solution you are seeking. Caution needs to be exercised and this adjustment should not be done by the faint hearted or those wanting iron clad guarantees of consequences. If you unwind your fuel screw too much, drive hard and do not watch your EGT, you will destroy your engine with too much heat. 

(Edit March 2011: Fuel screw unwound completely, but left in place to keep the dust out. This means I am running the maximum fuel able to be provided by a standard injection pump. There is a similar cap nut and screw at the back of the governor housing. This adjusts off boost fuel. I turned it in too far and smoked out all the cars behind me until the turbo provided enough air to burn properly - around 1200rpm. It drove fast off the line, but was unsociable, so I have backed it out a bit so there is no smoke off boost)


I unwound the fuel screw in stages to eventually reach three full turns and have been amazed at the power increase. I now get full boost at 1900 rpm where it used to be around 2200rpm. The engine is very keen and willing in the higher rev range and  spins easily to the orange line of 3500 rpm. Acceleration from 80kmh to 110kmh in 4th or 5th gear is brisk and it keeps pulling hard at 110kmh+. Keeping up with petrol sedans is now comfortably easy. 

Downside is the ease of too high EGT. 

Solution, add more air ie increase boost. As a test, I ran without the waste gate actuator connected and found the turbo spun to about 22psi and EGT's did not rise as much as before. Even at full power climbing a hill at 110kmh EGT reduced from 600°C to 500°C in the same circumstances. 

Driving without waste gate connected is just too risky for my liking. The orange warning light is flashing on when I accelerate hard and can become annoying and ignored rather than a valuable tool. Boost is now comfortable at 15psi maximum and EGT only rise to danger  levels when I push hard at 15psi, essentially creating an overfuelling leading to high EGT. Engine blow by increases with increased boost, increasing oil consumption a little. Be careful!!

Fuel consumption has not changed to any noticeable extent. I recently completed 3000km on vege oil with the high power settings and got 12.5l/100km. Running around on diesel instead of vege produces quite sparkling performance for a 2750kg vehicle. 

October 2016

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