Im at 5000 feet and I have a 01 L with stage 2 heads, 12" power stack, ported eaton, it22's, and a 4lb lower pully. I dont even get over 10# of boost on a cool 60' day. Whats going on here? Shouldnt I have 12#'s just from the 4#er? Does the altitude rape me for that much boost?

 

I lost several # of boost when I moved from Texas (320 ft ASL) to Arizona (4900 ft ASL). I was wondering the same thing. Does this mean we can run that much bigger of a pulley without a problem?

 

Thats what I was thinking to. Running like a 8# and a 2.75# to get around 15#'s

 

What mods do you have? What boost were you getting? Then when you moved what boost do you get now?

 

That is a very good question. One thing I can say is that here in Grand Cayman,the highest elevation is about 60 feet above sea level and when I push the go pedal I see 10lbs instantly and then it quickly goes to about 12lbs this is based on the factory boost guage.

 

you will lose a couple #'s with the ported heads plus a couple more with the altitude.

 

Yes, altitude kills boost, and yes you can run a bigger pulley safely at altitude. At 5,000+ feet altitude I saw about 13 # with an Apten ported Eaton, a 2.77" upper and a 5# lower. Now after switching to an 8# lower I see 16#.

 

I saw about 10# while in Texas. With the heat and altitude of Arizona I rarely see 8#. These numbers were recorded on the same gauge. The truck is stock currently due to the confusion of why it wouldn't run right up here. I ran it for a bit with a 4# on it and it ran like crap. It actually ran better without the tune than it did with the tune. I got rid of the tune and pulley and am currently completely stock. It runs great, just feels really slow. There is only 91 octane gas here as well. This place is a disaster for a Lightning.

 

5000 feet would be a about 2.7 PSI drop from sea level

 

So should those of us at this altitude just put a 6# on it and use a tune for a 4# or something along those lines and be safe? A dyno tune would be perfect, but the nearest place to even have someone do a good tune is several thousand feet lower than where I'm at so I feel it would be pointless.

 

Changing your amount of boost won't change your A/F if your tune is put together correctly. Also, at altitude you can (NEED) to run more timing, so a very aggresive tune for sea level is a good street tune at altitude. (At 13# of boost I could run 23 degrees of timing on 91 octane gas. I haven't tried that much yet with 16#.)
So speed up that Eaton a bit, it'll make up for some of the HP loss from the thin air.

 

So rather than update my predator, I could go with the old pulley tune and be safe?

 

I didnt see any one mention that ported heads eat up boost. Something to think about too!

JimIII

 

Good to see you join the post Jim 3. As you know I am in Albuquerque 5000 feet plus.
I run your JDM built longblock with stage 2 cams, ported heads along with your Kooks long-tube headers and your dads tune This combo gives 14 pounds of boost with an Apten ported eaton with stock upper pulley and an 8 pound lower pulley.

 

Does the guy that tunned your L tune many L's at high altitude? If so how do I get ahold of him? The guy that is tunning mine said it would be hard to do a safe tune with anything bigger than a 6# lower and stock upper. Do you use a idler pully setup with the 2.77 and 8#?