DIY SBC turbo question
 

Hi guys and girls. This is my first post here on DIY-TURBOCHARGING and I am usually not one to ask questions but I am STUCK on a debate of a single turbo or a twin turbo setup. I have a 1966 Chevrolet C-10 step side with a 355 cubic inch SBC engine (8.5:1CR w/75cc smog heads) with 16,000 miles on my rebuilt and have been dying to turbocharge it and have now come across the money to do so. I have put forth my efforts and will succeed. My truck runs STRONG naturally aspirated but just isn't cutting it. I have to have more wins under my belt this upcoming year than I had in my "2013 Fast-Friday season" :) I have built my own carburetor enclosure already and will be using an off the shelf, brand new and already owned Edelbrock #1406 650CFM with manual secondaries & manual choke on top of a basic Weiand 8000 intake manifold with the EGR ports blocked off. The engine is backed by a TH400 transmission. I have my BOV, WG, oil & water feed, return and routing already figured out.

I would like to keep this truck streetable and capable of being driven to work and back home (30 miles round-trip) and sometimes to deliver auto parts which is my self-employed / part-time job. I would like to make anywhere from 4-6 psi of boost on this engine and under 450-WHP

I have answered some of my own questions writing this so this post ended up being shortened and edited but I would still greatly appreciate input and suggestions as I have questions I just cant type yet as occurrences haven't come to mind.

1. Would you recommend a twin-turbo or a single-turbo setup to keep my drivability and eliminate any turbo-lag so that I have power through-out my already narrow power-band? (Stock sized cam with reduced overlap)

2. What size turbochargers would you recommend or suggest be used for my 4-6 PSI SBC TWIN-TURBO build?

3. What size turbocharger would you recommend or suggest be used on a single-turbo 4-6 PSI SBC SINGLE-TURBO build?

I have read in many places that I would be "over-spinning" "over-spooling" "over-speeding" the turbocharger in a single turbo setup with a larger-displacement engine + large turbo + low boost output combo (4-6psi).

Either one should work great here; I'd probably go with a large single turbo myself to hold costs down. Which turbo to use will depend on the RPM range you want it to run in.

Not if you size the turbo correctly for your application. Putting a turbo meant for a little four banger on there would definitely have that effect, though. I once tried to run a K-car turbo on a slant six - it would spool to 10 psi of boost at 1500 RPM, then run out of breath at 3000. A correctly sized turbo will behave a lot better.

Alright, we're on the same page then. I am leaning towards a single turbo set up myself. I have a 355ci SBC with a stock-sized turbocharger friendly camshaft. I'd like to be able to control boost by amount of throttle as I'd like for it to remain a street truck. I currently have a TH400 Transmission and a 3.08 rear-end and I'm betting my powerband ends somewhere around 5000 RPM's as I don't currently have a tachometer in this truck. I'd like to boost the truck maybe 4-8psi for use on a daily basis. I'd like to feel it coming on :) MAYBE 10 after I get an intercooler since I have cast 30 over pistons, 2 bolt main, 10/10 cast crank. I'm not looking to blow the doors off this truck EVERY DAY. I just need a strengthen my powerplant to motivate me to restore the rest of the truck to have a show/drag truck :) I bought this truck 50/50 with my dad 1.5 years ago for $1200 and haven't had a single problem out of it. We've updated parts (distributor, suspension, Driveshaft) and I'm amazed with the motor a $1200 truck gave me to abuse :) Runs strong. Takes the abuse I give it and I run it WOT quite a bit and I feel it wants to give me more and has much more potential and room to make power. What size turbo would you recommend Matt? I don't run this truck WOT 100% of the time. I have a 6 year old that loves raw power and the TORQUE of an engine that puts them in the seat. This is my fun/daily-truck and it gets my family together at the track on Friday nights :)

I'm thinking a Garret GT4088, or possibly GT3582, would be a good fit.

Thank you for your input and suggestions Matt. Do you think this turbocharger here below is of sufficient/adequate size with it's 2.5" exhaust outlet?

"Would you" turn the exhaust into a 3" exhaust just inches after the turbochargers 4-bolt downpipe flange?

I'd "prefer" an oil & water cooled turbocharger. Do you have anything bad to say about this turbocharger only being oil cooled? I properly cool my engines down after hard and abusive runs.

GT35 GT3582 T3 4 Bolt Exhaust Flange Manifold Circular Anti Surge Turbo Charger | eBay

•Type of Bearing - Journal Bearing
•Type of Wastegate - External Wastegate
•Exhaust (Turbo Manifold) Flange: Standard T3 4 Bolt
•Exhaust (Downpipe) Flange: Universal 4 Bolt Circular
•Intake Inlet / Outlet: 4" / 2.5"
•Compressor: Trim 55 / A/R .70
•Compressor: Inducer 61.36 / Exducer 81.87
•Turbine: Trim 68 / A/R .82
•Turbine: Inducer 67.85 / Exducer 62.5

Looks like a not quite exact copy of a Garret GT3582. It may be a little on the small side, but within range for your power goal (particularly with wanting a lot of mid range punch). I wouldn't tow with it, but if you're not towing, go for it.

My current build is using an oil cooled GT4082. I figure it should be fine if I give it a little time to cool off after use.

I do absolutely no towing with this truck and tend to abuse a turbocharged vehicle only within it's comfort zone & safe limits like I'm driving a vehicle that isn't mine and don't want to pay for it's damages lol. I'm not dead-set on making 500hp or a dragster. I'll be happy with 400-425HP as long as I'm safe with EGT & AFR tuning and have a healthy truck with the power to move itself better than before when needed. I am going to use the XS-POWER single turbo manifolds with crossover to route exhaust to my turbocharger. Do you have any input on this item?

Alright I'm up late again researching and I'm looking for a 4-bolt 2.5" turbo to exhaust flange and I would like to find one with a similar bend to this one -> Honda Acura Stainless T3 T4 Engine Turbo 5 Bolt Flange 2 5" Downpipe Down Pipe | eBay

Of course not the 5-bolt pattern or design just the approximate bend ON A 4-BOLT 2.5". I'd like access to a selection of similarly made parts if anyone has suggestions OR A SOURCE :)

Funny, I just ordered a fuel pressure regulator from the same "Speed Daddy" outfit - I'll see if it's actually any good. It should arrive today. A good source for turbo flanges that I've used is ATPTurbo.com; CX Racing is cheaper but parts are a bit lower quality.

Chinese made turbo headers often have durability issues. I would just start with manifolds if you're on the cheap and don't want to fabricate your own headers.

Time for an update - I ended up purchasing XSPOWER SBC single turbo conversion headers that came in the mail Saturday morning . I am happy with the quality and construction of the product but I know the durability over time of this product is mosts issue. The welds are nice and the flanges are 1/2" thick and straight according to my straight edge. All bolt holes line up perfectly too. Even included all gaskets of good quality and new mounting hardware with METRIC bolt heads and SAE threads. My only complaints would be the design flaw of the cylinder #8 and external wastegate piping (I MIGHT HAVE TO MODIFY THIS), the crossover pipe not having two flanges and the headers not being a complete "ready-to-run kit" not including a 3" SS UnStepped Exhaust clamp which is required. I will post some pics of my build as soon as I get the chance.

EMUSA GT3582 turbocharger will be in November 7th.