89FormulaLS2

iTrader: (1)

*I posted this in the FI section as well, but thought I'd also post here since it concerns headers*

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

300bhp/ton

Personally I really am none to keen on the STS setup and the street is probably the worst place for it. Power delivery and LAG (spool up time after a stall period) I think are it's biggest issues along with the location of the turbo and the air filter.

But that aside you'll need a decent sized turbo to hit your goals, if its a stock kit you are looking at then I don't think it's really the correct way to go with your setup.

In short the STS kit may be fun, but I doubt it will acheive any of your goals with out the need for additional money and parts upgrades.

As for headers, well on an FI setup it's all about flow as scavenging is not as important due to the intake air entering the combustion chamber at pressures above normal atmospheric pressure. So IMO running any form of tubular exhaust manifold will be better than a stock setup. Shorties and mids will be fine, but if you already have LT's then I'd stick with them. They will help extract the hot exhaust gases better and due to effective CR they will allow more boost with less risk.

BTW - Don't get me wrong, I know people have produced great numbers with the STS setups, but I do feel it is a flawed design (how many production cars use such a setup?) and on the street power delivery has to be one of the most important factors to consider.

89FormulaLS2

iTrader: (1)

btw, it's a GT67 turbo

magius231

iTrader: (8)

the STS should be fine with your goals, and for all its "flawed" design there sure seems to be a lot of 10 and 9 second GTO's running it

keep the headers. The stock manifolds will probably not flow enough to make that kind of power. Consider upgrading your I-pipe to 3", preferably ceramic coated.

Expect to pay good $$$ for the goals you want, no matter what route you take. The STS will save some money in the beginning when your power levels are lower, but no matter what route you take, when you start talking 700hp forget about any sort of "cheap" way to do it. That turbo may not be big enough for you either, might want to check on that.

89FormulaLS2

iTrader: (1)

Yeah, I'm thinking the same about the size of the turbo, but I can afford *this* one for right now. Look through my mods....... I know all about spending money, LOL! Nothing on this car has been cheap! But with big cubes AND FI, I think I should be able to reach my short-term goals pretty easily. (The fuel system might be the next big expense).

Thanks for the input.

WILWAXU

iTrader: (6)

IMO go with the headers and save the STS untill you can afford it.

89FormulaLS2

iTrader: (1)

I guess I didn't explain it very well. The headers are already on the engine. I can afford the STS NOW. But, I know headers do nothing to help the STS on a 346ci LS1 engine, so I am wondering how much of a difference the headers would make on my bigger, 402ci LS2. It simply makes it "easier" to justify the STS if I can take the headers back off and get my money back (which I can).

It has nothing to do with affording the STS now, other than I'm buying a used kit rather than a brand new one.

SO far the general consensus on the various threads is:
1. Probably a good idea to keep the headers on, but certainly not necessary to do so - even with the bigger cubes, they won't make THAT much difference for the STS system
2. I might need a bit bigger turbo than the GT67, but the GT67 will certainly make the power I am looking for for now
3. The cam is probably a bit too big for the turbo also


Nothing is set in stone yet, so feel free to chime in!