89FormulaLS2

iTrader: (1)

Okay, I have a chance to get a used STS system at a great price. It'll also save me getting the new Borla exhaust kit I was planning on. (And before you say it - I KNOW the STS is not the "most efficient" when compared to a front mounted turbo. BUT the STS solves several problems for my particular hybrid conversion, and the numbers I've seen are acceptable for my goals.)

THE GOAL: I want to keep my car a daily driver car. I want decent traction off the line. (A little Turbo lag might actually be my friend here). I want "normal" gas mileage under 4000rpms. I want 550rwhp+ of KICK-*** power when I give it full throttle with room for improvement down the road (eventually I want to run 9's on the track, but that'll involve a full roll cage which I am not ready to do to my DD just yet).

THE QUESTION: Am I going to be shooting myself in the foot by going back to stock manifolds on a 402ci engine? (Removing the headers and saving the cost of the Borla makes the expense of the turbo kit more affordable right now, AND justifiable to the wife!)
My thought is that for making 700hp at the flywheel, I can adjust the boost a little higher to compensate for anything I lose on the headers........ am I right on this? Or am I going to run into backpressure issues that will REQUIRE those bigger headers in order to get the air out, and to the turbo?
I need to make a decision in the next 36 hours....... PLEASE HELP!

Here is the complete buildup & specs on my car/engine:
1989 Firebird Formula
Functional Ram-Air hood for 3rd gen Firebirds
4th gen TransAm style spoiler
LS2 402ci stroker engine from SDPC
’98 T56 transmission
McLeod Street Twin clutch
3rd gen LSx custom Hawks stainless 1.75” LT headers & y pipe
4th gen gas tank with custom-fit 4th gen fuel lines
Walbro 255 lph fuel pump
Moser 9" rear, 35 spline axles, Detroit Locker, 4.10 gears
Lower Control Arm relocation brackets
3rd gen "Wonder" bar (Tubular steering Brace)
American Racing Spinaker Wheels, 17x9.5 front, 17x11 rear
Front tires are Sumitimo 275/40zr17
Rear tires are Nitto 315/35r17 drag radials
Subframe connectors
All-new interior carpeting
Plush charcoal seats in mint condition from a 4th gen Camaro
4th gen TransAm center console
LS1 style brake conversion
Drilled & slotted rotors with high-performance brake pads
Customized tubular Hawks k-member for 3rd gen LSx conversions
Spohn tubular A-arms for 3rd gen conversions
3rd gen LSx conversion crossmember for T56 transmission
Spohn Chromoly Adjustable torque arm w/front driveshaft loops
Spohn 3” driveshaft
Adjustable Panhard Bar
Adjustable LCA w/relocation brackets
KYB AGX Gas Strut & shocks
Pro 5.0 Shifter
Twin-mount ATI intercoolers

ENGINE SPECS:
SDPC LS2 402ci stroker (4.000" bore, 4.000" stroke), fully balanced
Callies Forged crank 4340 steel
Manley pro-billet 6.125 rods
Diamond custom dished Forged pistons with valve reliefs
Diamond file fit rings
Clevite rod & main bearings
Durabond cam bearings
LS2 complete timing set
ARP head bolts
Comp Cams lifters
Ported LS6 oil pump
LQ9 Ported and milled (65cc) cylinder heads (300 cfm intake flow @ .600 lift)
9.4:1 Static Compression
Cometic head gaskets
Crane custom Stroker cam, 236/246, .600/.600 lift, 115 lsa
Harland Sharp Roller Rocker Arms
Ferrea Valves
Manley push rods 7.400"
Crane spring kit
Manley valve locks
GM valve seals
LS6 Intake Manifold
Jantzer LS1 Ported and painted throttle body
SLP 85mm MAF
NGK TR55 spark plugs
Custom wiring harness from SpearTech

89FormulaLS2

iTrader: (1)

btw, it's a GT67 turbo

onfire

iTrader: (17)

You'll be fine with the stock manifolds for your goals. Most are running that way now.

Red91vette

iTrader: (3)

Yeah, stock manifolds have gone over 1000 horsepower on engine mount turbo setups. Are they they newer manifolds? I heard that the stock manifolds are better then LT's on a STS setup, or atleast just the same so there is no point in buying LT's or any kind of header for a STS setup. Good luck with your set up, post some pics up along the way!

bboyferal

iTrader: (9)

The problem might be your turbo

bc56f100

iTrader: (2)

Yea my buddy had a set of zo6 manifolds on his 6.0l in his 89 iroc. He is runnin a carb setup on it and nos now so no boost, but he went to the long tubes like you have and didnt pick up a hole lot. Yea it did help out but I dont see it being any kind of problem with the turbo!! The manifolds will spool it just as good as the headers!!

bboyferal

iTrader: (9)

I'm sorry, I didn't read 700 flywheel hp... I don't see a problem.

Red91vette

iTrader: (3)

That 67 still should be too small for that 402. You should get more then 700 flywheel. I'd go to a 76 turbo IMHO. I'd let the turbo guru's chime in though.

DrTurbo

iTrader: (3)

The GT67 will get you 700 crank hp, but the backpressure will not be good.

89FormulaLS2

iTrader: (1)

Well, for right now this is going to be purely a street car. I don't want to go with TOO much power, or all I'll be doing is smokeshows! That's why I figured the 67 might be good for right now, and I can always upgrade later when/if I turn it into more of a strip car. Agree?

89FormulaLS2

iTrader: (1)

Can you elaborate on "not be good" - as in, what else would you suggest? Are you saying I should go with the longtubes to reduce backpressure? Are are you saying a bigger turbo would be better INSTEAD of long tubes?

Please elaborate, I want to learn.