2008 Sierra RCSB 2wd:

- 5.3 ( possibly going forged piston/rod)
- 4l80e
- Built 3.42 rear Either Eaton True Trac or a Trac Loc
-currently have a 216/220 .560 on a 114lsa cam in a set of 243's

Anyway, I would like to break the 10's and still have a fun street truck. I jumped in on the Huron group buy but have not selected a turbo yet. the billet 7875 seems to be capable of pumping out around 750whp in similar combos while having awesome spool, but is maxed out and blowing lots of hot air and no head room to turn it up if need be. So then i started looking into the S4xx T4 series.. Specifically the s475 or s480 units, but it seems that with the small 75mm turbine they are maxed out around the small point as the 7875 while costing more and being harder to package. Will the billet 80mm compressor wheel flow that much better then the billet 78 in the smaller 7875? Would the s475 or s480 with the larger t4 turbine options (87, 92) still spool decent?

Thanks

 

The old turbo i ran will be perfect. S475 t4 1.0 ar. Lights off quick and does 800 tire. Got 10.82.

Don't over turbo. Properly size to your needs. Too much turbo = lag and not fun for the street.

 

Sounds like your building something similar to my truck. I run a Billet s480/87 T4 1.10ar. it lights off just fine. i can see 5lbs (5lb springs in the gates currently) by 3200 rpm. I will say though that my truck was an absolute DOG down low with the 80e and 3.42's.

 

Go ahead and use 3.73 or 4.10 gears. They will help get the truck moving from a stop and make it feel better on the road in every day driving. Don't buy into the 'you need taller gears to load the turbo' crap.

 

Sevex: What size tire were you running with the 3.42's? What did you change your gears to?

I am planning on running some race stars, welds or similar 17 up front and 15 out back with a 2/4 or 3/5 drop.

I appears with a 28" tire and assuming 5% converter slip the max speed at 6500rpm would be
3.42- 150mph
3.73- 137mph
4.10- 125mph

Just a hard decision as to what turbo to actually go with... after reading fastjweb's build he had better times with a smaller turbo (s369sxe) then he did with a billet 7675, as the smaller turbo lit off faster and got his short track times better. To be honest this thing might see the track 3 times a year, mostly will be a street toy for Mexico fun which is why i am kind of leaning towards the larger turbine to keep temps and back pressures in check. Im used to stick turbo cars with 2 steps and have never had an auto, so im new to spec'ing out a converter and hoping its tight enough to drive in traffic and loose or high stall enough for the track, foot braking to boost hopefully. I guess if it would make a difference i could always spray a 50shot out of hole.

 

Went ahead and picked up the VSR Billet s480 clone with the 75mm 1.1ar t4 hotside. A forged 6.0 is a good possibilty in the future so i can grow into it with this turbo! plus it should still spool decent and make some good power on the LMG 5.3!

 

I was running 255/65's on the rear (grandpa truck, looks bone stock). I ended up going to a 4.10 gear. I was really really tempted to go to a 4.30 but for the price difference it wasn't worth it.

I have a buddy that uses the s369 on his 6.0 and it was insta spool, truck was way fun on the street. that being said even with the converter issues and horrible gearing I could make 5lbs by 3200 with mine, so I don't think spool is that bad with the larger turbo