67/67 over s475

Lighten

Lighten

GA Diesel Mafia
Joined
Jul 17, 2010
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I have an tater built he351 67/67 over a s475 (96/1.32) on my truck and all i can get out of them is about 65psi at the intake horn. With about 30 coming from the 475. Drive pressure is 80 at WOT. The 351 has one of SDs spring gates on it and i have tried different springs, adjustments, i just cant get the drive to boost ratio any closer. It runs good has a kinda heavy haze at WOT i feel like it has more left in it. Do i need to change the secondary? Will it live at that drive pressure? Its a DD and iam gonna try to get it dyno tuned soon i hope. Thanks
 
I'd tighten the spring gate on the secondary. What is your drive pressure now?
 
ok so your pressure ratios if you are at sea level are

overall 5.5
primary 3
secondary 1.6
secondary boost is 11.8psi

you will have a hard time getting much more than low 30's from that primary on a pretty stock truck. you can crank down the secondary's gate. this will force it to work harder but cause the primary to come on a little later. and you might loose a few psi from the big charger. however if you gain 3-4 psi from the secondary and loose nothing from the primary total boost will go up about 10 psi. drive will go up a bit when you tighten the gate.

the larger wheels on the secondary are allowing air from the engine to flow easier to and from the primary (lowering secondary drive) allowing it to flow better as well as the compressor wheel being able to accept the 75mm's air easier lowering primary boost a scosche.
 
I found with extensive testing that when I raised secondary boost that primary boost fell enough to net almost no psi change as well as when I lowered secondary boost. the primary picked up more work and overall boost stayed the same.

a 1.15 housing on the primary gained me 3psi.

it is my opinion, that once turbos are chosen and installed tuning will move the power around not so much raise or lower it. proper sized turbos are key. I personally don't like that size secondary.
 
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