[TransAm 474]

Good afternoon, I am thinking of doing a Single turbo on my street 461, and I would like your input. I initially had plans to upgrade the heads to KRE, along with a street Solid Roller and Northwind intake, but I have now changed my mind, and think I can possibly have a street car that is more fun by keeping my ported iron heads, and stick with a solid flat tappet camshaft, along with a single turbo and maybe 8-10 lbs of boost, and maybe cost less.

Here is what I have currently in the vehicle

-1974 Pontiac 400 2-bolt block
-Bottom filled to center freeze plug with Pontiacdudes block fill
-ARP Main Studs
-4.155" Bore
-4.250 Eagle Cast crankshaft
-Eagle 4340 H-Beam 6.700" rods
-Ross Flat Top piston 1.385" Comp. height
-Decked to 10.215" (piston .005" in hole)
-Felpro 1016 .039" Head gaskets
-SD Performance Street hand ported 6X-8 Heads 2.11/1.77 Ferrea valves, heads flow 245@.550 int 182@.550 Exh. and Chamber around 100cc
-Current camshaft is an old custom Ultradyne Solid Flat tappet 288/301 Advertised, 255/267@.050, .540"/ 552" lift with 1.5 Harland Sharps, 106° Intake Centerline, 112° Lobe Separation
-Crower Solid Flat tappet lifters
-Rollmaster billet timing chain
-Romac Aluminum/Steel Damper
-Performer RPM Intake
-Quick Fuel 750 downleg carb
Mallory billet distributor
Mallory Powermaster Coil
Mallory HyFire 685 ignition box w/boost timing retard
-1 3/4 Hedman headers
-Dual 3" Exhaust, Dr Gas Xpipe, Dynomax Ultra Flow mufflers, Pypes 3" tailpipes
-TH400 Transmission, 34 element Sprag
-TCS 2800 stall 11" Torque Converter ordered through Dave at SD Performance for a older RA 4 cammed 455.
-Rear Gear is 3.73
-1978 Trans Am 3800 lbs
-Premium Pump Gas Street Car

Ok, now.... I want to put a Single turbo on this and I obviously want to change a few things to work better with the turbo. The camshaft is one of those things, as I figure the current camshaft probably wouldn't work to great with a turbo, so I have contacted both Mark at Bullet and Butler to see what they recommend for another solid flat tappet camshaft that will work well with the turbo, I'm still awaiting their responses.

The second thing I want to change is the Performer RPM intake to maybe a hurricane or Northwind to work better with boost.

I will also be changing the carb for the Fitech 1200 Power Adder EFI system, and I will initially use it to control Fuel only, and control my ignition system seperate.

The third thing is the Torque Converter, I'm thinking either a PTC, or I will get in touch with Cliff and order one through him, or depending on what the cam specs look like, maybe my current converter may work ok, but I almost bet it would be too loose.

Fourth is a Rear Gear change, maybe change it to a 3.23 or 3.42. Current 3.73 is probably a bit to much for a turbo.

Ok, I think that is most of the changes I would like to make to provide a better combination for the turbo. I have been looking and doing alot of research of two turbo's... I have came down to the BorgWarner Cast S480 with a 96 Turbine and 1.32 AR T6, or the VS Racing 80mm billet with a 96 turbine and 1.32 AR T6. Both are close in the same price range, but obviously the VS Racing is an imported turbo. I'm not an expert on turbochargers, so I'm not sure of the street durability of the VS Racing, and I do know that the factory uses Borgwarner turbos on alot of factory turbocharged vehicles, so they are known to be durable I suppose. The VS Racing turbo is appealing, because it is 100 bucks cheaper and has a billet compressor wheel vs the S480 cast wheel. I'm for whichever turbo would be more durable and work best for my application, because the price difference is not much.

From my research so far, it looks like 2 1/4" crossover pipes would work great for the street. For the downpipe, I would keep it 5" for as far as possible out of the turbine, and then reduce it down to 4" and then somehow split it back into my dual 3" exhaust, I havent given that part much thought as of yet, but there is only so much room to work with. I want it to spool as quick as possible, without any lag issue, since this is a street car.

Due to the 9.1 compression, I only want to run just 8 lbs or so of boost, maybe 10 at the most, on pump gas. Maybe increase it 5 lbs at the track along with 110 octane fuel, but it will be mostly street driven on low boost, and needs to have good drivabilty.

With this combination I also want to keep the RPM relatively low, maybe around 5800 max, and maybe make around 750-800 at the crank with room to grow if I want to crank up the boost a little with race fuel. I'm really not sure what it would be capable of, but I know it would be fun.

Any thoughts , input , tips would be appreciated greatly. Thank You