does a boost leak/problem hurt startability?

Hauling 140K all of the time, I'd be concerned about the durability of the driveline components...especially putting big power through them.

As to your original question, though, it shouldn't affect startability because generally speaking, you're letting out the clutch at idle when there is no boost being made anyway. The leak will make the biggest difference once the turbo(s) spool up to start producing boost, and pressure escapes through the leak.

Fix the leak and fuel mileage should increase. Power will increase. Startability should remain the same, though.

 

As long as you're on a hard packed surface you'll be able to take off. If you're on softer ground you'll struggle. I have 3.91 rears on 11R24.5's. Mine starts off great in most places. One time I overloaded by a few tonnes in a freshly cultivated field, it took off okay but it really moaned and groaned a bunch, and forget about leaving bull low until I got out of the field.
And I second the motion as startability is dependant upon clutch engagement torque which is usually determined at idle or no more than 800 rpm, so boost is of no effect. But if it's not quite running right low end torque may be effected.
My last truck had a 450 Mercedes with 3.58 and 11R22.5 tires. I new it would have problems with those rears so I put in 4.11 rears at a cost of $5,000 when I started doing super bees. I never had a problem launching that.

 

The replies that have been posted work if you are only talking about the first 2 seconds after you let out the clutch. After that the boost has huge affect. The ECM does not let more fuel in until it sees boost from the sensor.

 

If your CAT's boost system has a waste gate (betting it does), it will only make about 31 or so lbs of boost. That's where CAT has them manually set from the factory.

Also, if you're running it like most by trying to stay near peak torque, you'll never see horsepower anywhere near what your engine specs at. Mine reaches a peak HP of 430 at 2100rpm. Yet I never run above 1500 rpm because peak torque is at 1200rpm. So, (1500/2100)*430=307 HP. And my ScanGuage backs the math. Using those numbers but changing it to 600hp, you'd be getting in the ballpark of 428hp at 1500rpm.

 

I'm not arguing the point. Just curious where you are getting your numbers from. Mechanical gauge, ECM, or elsewhere?