I have 2 pulleys that I got with my radix. I was told they are 2.75 & 3.25 but I have no way to tell because they are not marked. They are the lightweight aluminum ones and the 2.75? has the built in nut for mounting/removing and the other does not. My questions is how do I know for sure the size and what boost level can I safely run on a stock 5.3? I see sigs that show people running 10 #'s and I don't see any engine upgrades other than bolt ons such as headers, exhaust, etc...What can I get away with and not blow it up? I'm running the standard 3.4" magnuson pulley and seeing about 6-7 #'s on top.

 

You should be able to run the 3.25, but I wouldn't want to try the 2.75. Did you buy the blower used? Sounds like your blower may have come from a 6.0L motor. The LQ4 guys can run the 2.75 no problem, the LQ9 guys usually run into diminishing returns at 2.8 or so, but you'd definitely be pushing it at 3.0. Perhaps you could run a 2.9. Once you get up there in boost (lower in pulley size) you will need serious tuning. I don't think I'd be trying a really small pulley without an in-person tune, that is no time for mail order....

 

How much boost am I going to see with the 3.25" on the 5.3l?
The 3.7 made between 4 and 5, the 3.4" seems to make 6 so if the pattern continues I should see about 8 #'s? Yes/No? Will my tune require tweaking for this?

 

you should probably run the 3.25 and get a good tune on it, then bag that 2.75 pulley up and send it to me for testing

 

You think the 3.25 would be safe with a stock 5.3? What is the boost limit without a built motor about 10 #'s? P.S PM sent on the pulley.

 

yes, I think the 3.25 would be safe. probably see around 8lbs of boost.
I'm at 7 lbs now with no problems. No gaurantees, of course, but I think you'll be just fine. A tune for that pulley will be in order as well.

 

You're running a 6.0, I imagine your engine can take a little more boost and not blink. I'm sure BlownChevy had answered this question 100 times over the phone at work. This is my daily driver and I live too far from work to be without a ride cause I blew it being dumb.

 

The 3.25" should be safe - if tuned correctly. If your 3.4" pulley tune is aggressive (tuned right on the margin of detonation), you will likely run into KR, and perhaps even detonation with the 3.25". If you think you want to run the 3.25" all the time (which you should be able to do safely), I would schedule an in-person tune on the same day the pulley is installed, but that's just me.

Do you have logging software?

 

I don't have logging software, not even a monitoring tool. There is no one around here that does ls edit custom tuning, the only dyno worth a sh*t is 45 miles away. Plenty of ricer shops though. I have a Westers tune, and from what I hear I should have went with Nelson. The truck runs strong but I figure if 3.25" is safe, why not, but I don't have an in town person to do the tune and TX is 12 hour drive.

 

Yes it would be safe. I am running a 3.2 with no knock. I see 9 psi at WOT and 10psi for the last 500rpm's. Adding methynol injection would also help as a safety item and add a little more power in the process.