I can build 9 psi boost on transbrake, but if I try to build more boost, it reach 10.5 to 11.5 psi and fall off to 7 to 8 psi. I have played with timing and fuel, but it’s the same.

I’m really lost, hoping someone can give me some advice.

Running 16 psi on dyno and on track is no problem, but then the converter flash at 6000 rpm.

My build is a 4.8 L20 LS engine with ported 799 heads, Compcams 54-428-11 228/230 @.050 and 0.570 lift. Holley Hi-Ram intake with 105mm TB. NRE 71mm twin turbos, compr a/r 0.82, turb a/r 0.84. 46mm Precision wastegates with 1.5 psi spring. I control boost with 50 psi air pressure through 2ea dual port mac valves (dome pressure only).
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Thanks,

Roy

 

ON the TB are you pulling all the way against the converter or are you using a 2-step?

 

I use the the Holley Dominator rev limiter #1, set to 4800 rpm, spark only.

 

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Are you trying to use "boost builder"

You might want to mess with 1D tables . Example :

 

Yes I have used the 1D table, and tried to pull different amount, with same result.
As you can se from my datalog picture, I use Holley boost builder with fixed timing at 10 and 3 degrees (two different runs, dotted lines are from one run).
The boost is building, when pulling timing, but falls off when it reach 11.5 psi.
The engine is not completely up on the two step, which is set to 4800 to 4790, maybe I should have a bigger gap on the two step on and off?

 

Most people use spark high only , no gap .

Have you tried a lower RPM on the 2-step .

 

Seems to be very lazy even trying to get up on the converter . Maybe try full timing until it gets to the two-step , but try a lower RPM like 4000 , 4200 .

To me it looks like the converter is tight or its just not making power down low .

Im not up on LS stuff so Im not sure on what timing it should have trying to get up on the converter , but my SBC likes full timing to make the power down low . Have to try to get to the chip ASAP

 

Case solved!!!
I tried to lower the rpm limit on two step to 4200 rpm, which gave me 5.3 psi after seven sec.
I then tried to rise my limit to 5800 rpm, which gave 14.5 psi steady boost after five sec.
I just have to play with ignition, as it was too high from idle to pull up to two step.
The advanced table didn't kicked in before I got full boost, because rpm activation set to 5700 rpm, but I don't think I need to pull timing.
Thank you all for giving me good inputs to solve this .

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Nice job