Cam and springs for 04 5.3 w sts 8 psi

[stssilverado]

I need valve springs, but i figured while I'm in there I'll change the cam. Can anyone recommend a cam to give a decent idle and everyday driveability to work with comp 918 springs. The rest of the truck is stock except for sts 8psi and Nelson Tune.

[SportSide 5.3]

Limit exhaust duration on a street driven turbo.

Because of the pressure in the exhaust manifold, turbo motors have a longer 'power stroke' then N/A, SC, & Nitrous cars. These motor's power stroke is from 0 to 90 degrees. Turbo motors continue to push for another 45 degrees of crank rotation. Hard one to follow, but true.

Stock cams work so well with turbos becuase of the lack of overlap & small lobes. Aftermarket cams are setup for N/A & SC's for the most part & open the exhaust inside the power stroke of a turbo motor. Average spot to open the exhaust valve is ~45 degrees BBDC @ .050 lift, which is ~ 70-80 BBDC @ .006 lift (depending on ramp-rate). So, the exhaust lobe on a turbo motor *should* be opened late to avoid bleeding off power. At roughly 60 degrees BBDC is were you can open the exhaust valve. Add this to the lack of overlap on a turbo motor, because exhaust manifold pressure is ALWAYS higher then the incoming intake charge (by 1.5-2 times depending on compressor efficiency) & you can see why large cams don't work so well with these motors.
So, if you're following me, a street turbo motor is limited to ~ 260-270 total duration on the exhaust side. & that's WITH ~40 degrees of overlap @ .006. (nominal stock overlap)

Track turbo motors use more traditional N/A grinds as they stay in the upper RPM band were overlap will actually help the turbo make power. But it KILLS the low-end.

Turbos make full boost by ~3000rpm therefore make tons of torque, so most don't notice that the N/A cam they're using is bleeding off power.

I'm going for the most efficient combo as possible.... This new cam will open the exhaust @ 60.5 degrees BBDC. As opose to 69 BBDC w/the stock cam in there now.[/b]

To make since out of all of that. Depending on how much rpm you are looking to turn, you might use a camshaft like the following

210/208 .56/.54 112 + 0

as to many n-a grinds you will see offered that look like the following:

208/210 .56/.56 112 + 4

That is purely just an example. I'd actually use the first grind on a n-a setup myself.

[stssilverado]

I truly wish I knew what that meant. I am used to someone telling me the best parts to buy and I buy them. Taking them to a pro and having them installed is my only option. I know very little about the internal workings. I just want to go fast. I'm not opposed to throwing $$$ at the truck as long as it hauls ass. I've already bought the turbo set up with a nelson tune. Just looking for the next step. Allen is looking into a cam for me also. It just seems he's been really busy lately.

Thanks!!

[rosscob]

If Allen is on the case you will probably be OK. He did the same for me on my whipple cam. I love it!