I run a 1.30 A/R on-center hot sided T76 on my tow rig (very mild 393). It's an old turbo and crotchety compared to the GTS-series stuff. It's making somewhere around 850 crank hp based on weight and ET. I leave at about 4 psi and see about 18 psi peak. Friend of mine is making about 1200 crank hp on a tangential housing small frame T88 on a 408.

I'm personally not a big fan of a T70 because of the peak efficiency pressure ratio, though I understand that the Holset T70 has a different map than that Garret T70.

I personally think the optimum turbo for a fairly large displacement gas motor with moderate power goals is a .96 A/R GTS or GTSH series 76 because it will move a lot of air at relatively low pressure ratios.

I'm building a front mount kit for the GMT900's and will test the cams out , the gains you got are great are you using a 5.3 with 243 heads or 5.3 heads ?

I would put an S400 on your 408. THis is a great turbo and is only $585. I can't post the link though because Majestic Turbo isn't a sponsor here.

it was a completely stock 5.3 with just valve springs, then the cam swap.

spoiling is greatly effected by one thing on a camshaft. And its easy to play with spooltime and tricks to make it come on later or sooner. But there is a cost to everything of course.

R