Outer Limits 4x4 Board

Just installed a boost gauge this after noon to see what its running as Ive allways suspected it to be suss. Here what I am getting:

Around 1800rpm: 5psi
Around 2400rpm: 7psi
Around 2800rpm: 9psi

Then after 3000rpm it starts to taper back off and fall to 6psi around 3400rpm

Is this normal?? I keep hearing 12psi on others. Does the 3psi make a difference?

Cheers, Alec (97 1HDFT 80 Series)

Hi Alec,

that is pretty close to the factory spec. I thnk peak in standard tune should be around 9-11psi. 3psi can make a difference, but not on its own.

my 1hd-t was boosting to 5psi around 1600rpm, 10psi by 2000rpm and peaking around 2200rpm. Depending on how it was tuned, peak was anything from 13psi factory standard to 18psi. (22psi when it blew)

under acceleration mine would see boost start to taper off around 3500rpm but still 10psi at redline

increased boost alone wont improve performance, it will help lower combustion temps and EGTs as you are getting a leaner air/fuel ratio. (more fuel = more heat) Because the combustion temp is lowered, it gives you opportunity to add more fuel along with the boost, this will then see improved power and torque, but also increase combustion/exhaust temperatures again as adding more fuel increases the heat generated. Increasing the fuel settings also increases the boost generated ie increasing boost, then increasing fuel will see boost increase again. The standard waste gate should be fully open by 14psi (if it gets to that) and limits boost at that.

The increase in heat energy will give more exhaust gas velocity and more drive to the turbo, improving spool up time and throttle response.

More fuel added early when the engine is not under boost increases the exhaust gas energy sooner so boost will come on sooner. Peak power may not increase, but lowering the rpm 9through tuning) at which boost is produced makes the 80 more drive-able, more responsive from idle/stand still. Early boost, increased torque at lower rpm means you wont have to rev out the engine as long between gear changes (not sure exactly how this plays out for the softies with autos) so the engine will labour less, and wont be being wound out for as long. Without flogging it, mine was getting off the mark a lot quicker, shift gears a lot sooner meaning it would be at cruising speed sooner.