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      01-20-2013, 01:54 PM   #43
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Drives: C6 Z06, 09 335i, 10 335xi
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Originally Posted by spool twice View Post
I purposely dialed in my high rpm boost the way I did because I get a 2.4 degree timing drop running boost above 13.4psi @ 6,300rpm when temps drop to 60F running just E85/93 octane only, whereas running the same fuel with temps above 80F, I can run as much as 15psi @6,300rpm with no issue's. Can't wait until it warms up again so I can dial in less tapper.

Then again, I don't know why I just don't keep it set at less tapper and just short-shift right before 6,300rpm, it's easier to set the shift light than hooking up the laptop to change boost values

kkashanchi, you can experiement with boost levels up top if your car is happy with it. My AFR value's are +10 from the default G5 ISO values at 3000 and 4000rpm, and +5 @ 2,500 and 4,500rpm.

I'm still below the efficiency range/ max boost per rpm of these small TD-03 below 5,000rpm. Try it at your own risk though.
Fair enough. You sound like you got a good head on your shoulders for tuning.

Originally Posted by Lifted07Duramax View Post
If that is the case than please forgive this stupid question but why does adding a catless DP raise boost alil bit but it is reducing back pressure by quite a bit?
Adding catless DP alone does not raise boost, in fact it lowers it, but when you get catless downpipes, the tuning options within raise boost.

In fact if you just got downpipes on a stock vehicle you will notice lower wastegate duty cycles and lower boost, however, you would have about the same power, it would just run more efficiently.

The stock tune is based on load. So it does not target higher boost if the efficiency is improved. The intention of this design is to have a car that makes "300 HP" in arizona heat, the mountain of Colorado, or the so called normal weather of NYC. Although in practice they dont actually make the same power, the point is the intention is to target load and use the boost to persuade that power up or down depending on efficiency. If you can increase efficiency either with colder air, higher octane, improved exhaust flow or any other means the stock tune will lower boost because it can make the same power with LESS boost because of the improved efficiency.
Maybe someone else can clear up load targeting vs boost targeting in a simpler way. I probably confused everyone haha.

Also don't confuse exhaust back pressure with engine back pressure in which case the latter has to do with the heads and valve timing for a good portion of that back pressure.

Originally Posted by themyst View Post
Back in our day, we were running Procede rev2's with very little taper. IMO, boost north of 6500 is irrelevant, you could make it 8 psi for safety's sake since we should be shifting well short of that on stock turbos.

Now that my flatline is fixed, I can shift at optimal points... it's a great feeling.
This is true, I rarely drove past 6500 RPM. I remember seeing a good 15.5 PSI at 6000 though with 12 degrees of timing on methanol.

Originally Posted by Enron Exec View Post

Same can be said with full throttle at XXXX rpm in 2nd gear versus full throttle and the same XXXX rpm in 5th gear. The loads on the engine are completely different because of the gears and the speed of the vehicle, so therefore the exhaust pressure to spool the turbo will be very different as well.
Good point.

Much easier to ramp up the boost in 3rd of 4th gear compared to 1st and 2nd.
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Last edited by Jeff@TopGearSolutions; 01-20-2013 at 02:01 PM.