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Opinions on twin turbo for the K5

Discussion in 'The Garage' started by Shawn, Oct 20, 2005.

  1. Shawn

    Shawn 1/2 ton status Premium Member Author

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    Well, I'm going back from a BBC to a SBC. And I know I'm not going to be happy with the power at this altitude so I'm thinking about doing something like this:

    [​IMG]

    [​IMG]

    Here's another style of header but I doubt it would clear the accessories:
    [​IMG]

    Would basically be a twin turbo on a 350sbc. No intercooler so there's less piping to be worried about when the K5 is flexed.

    Stand alone EFI like Accel or Holley with MPFI or maybe TPI system with larger injectors but still tuned correctly with stand alone or a chip burn.

    I was thinking single turbo but these headers are fairly cheap and there would be less fabrication needed. Looks like it should clear everything. 3" downpipes look like they should clear.

    Boost would be on the low side so the heat going in the engine wouldn't be too bad.

    I think if I had everything coated, the heat wouldn't be that bad under the hood.

    I've seen some kits go for $3k but I think if I keep this on a budget and do most of the fab work myself, and find some used turbo's, I think $1500 is possible (not including fuel management).

    Here's a dyno from Banks Twin Turbo kit which is WAY overpriced but it gives a good idea what is possible on a SBC with a couple snails...
    [​IMG]

    I'd appreciate everyone's thoughts on this before I make the plunge.
     
  2. jim burke

    jim burke Registered Member

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    How are you going to keep it from detonating with the crappy gas we have in CO? Run some high-dollar high-octane fuel?

    What do you use the truck for?
     
  3. Shawn

    Shawn 1/2 ton status Premium Member Author

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    Well, the 91 octane fuel we have goes along with the alititude. Thats why all turbo'd cars (including my WRX STi) can still run just fine on 91 and I even turned up the wick to 20psi with no detonation problems but it does have a lower CR. I'm only thinking 10lbs of boost on the K5 but I'll be sure to watch for detonation first and start with 4lbs when tuning on the dyno and go up from there. My 02 Trans Am WS6 with a turbo, could safely handle 10lbs of boost and thats with 10:1 compression and 91 octane on stock LS1.
     
  4. outlawtorn

    outlawtorn 1/2 ton status

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    maybe for some mud bogging because it doesnt look like the power kicks till about 3800 lol...
     
  5. ryan22re

    ryan22re 1/2 ton status

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    ive been thinking about a similar set up in my k5, think that two smaller turbos would be great (like a t3 from a 5 speed svo or turbocoupe). can buy turbos all day long for $50 a pop and rebuild kits for around $75. i would just use a set of block huggers flipped over, buy a t3 turbo flange and weld it to the header. run the waste gate thats on the ford t3 (set at 10 psi from the factory). and the ford down pipe from the turbos (looks like it would fit with minimal mods). only prob i see is clearance around the brake booster (switch to hydroboost and a heat shield). make a water to air intercooler that sits on top of the intake an viola! twin turbo sbc.

    ryan
     
  6. Shawn

    Shawn 1/2 ton status Premium Member Author

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    Trust me, the torque comes on pretty low. There isn't much lag with V8's
    [​IMG][​IMG]
    I'd be running the lower boost level (green line).

    Good idea on keeping it cheap and simple!
     
  7. mikey_d05

    mikey_d05 1 ton status GMOTM Winner

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    What is the reason you're going from a big block to small block?
     
  8. 350k5

    350k5 1/2 ton status

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    Yea turbos usualy get their most power later in the curve. That's why people generally look into superchragers for gas...that power is always there. You notice the difference the whole way through the curve.

    It will still put out a hell of a lot more then without one, so it's all good. :bow:
     
  9. gauder

    gauder Banned

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    Could also use a small shot of NO2 to spool the turbos quicker. Not the ideal situation for a rockclimber but to each their own. I would think with the size of your engine compartment, running an intercooler wouldn't be too much of a problem though. Check out www.turbomustangs.com, lots of good info there. There is a section for gm's in the forum area.
     
  10. 6.2Blazer

    6.2Blazer 1/2 ton status

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    Gotta' ask the same question? What are you trying to achieve? Just looking to be different or what.
     
  11. ryan22re

    ryan22re 1/2 ton status

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    the t3 turbos from a tubocoupe/svo spool around 2700 rpm on a 2.3. i would guess that on a resonable 350 they would spool around 2000. at 10 psi you would be looking at about 60-70 % increase in hp. so a mild 250 horse 350 could make 400-450 hp and prob around 475-500 lb-ft of torque.

    another cheap option would be the turbine housing from a t3 and a compressor wheel/housing from a gnx/turbo buick. seen guys build a t4/t3 hybrid for less than $200.

    ryan
     
  12. Shawn

    Shawn 1/2 ton status Premium Member Author

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    I think I can build a turbo SBC for the same cost as a BBC and have more power on hand (at high altitude) and get better milage. Plus, I have yet to see a turbo'd K5 so just being different.
     
  13. jhellwig

    jhellwig 1/2 ton status

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    Yeah well my K5 has a turbo........................................trannie that is. :D




    Why is it that you are going for 2 turbos insted of one?
     
  14. ryan22re

    ryan22re 1/2 ton status

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    i would guess for several reasons:

    1. easier to fabricate exhaust system to turbos.
    2. easier to fabricate exhaust from turbos.
    3. two properly sized small turbos perform better than one big one.
    4. looks cool


    ryan
     
  15. Shawn

    Shawn 1/2 ton status Premium Member Author

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    LOL
    Yeah, pretty much.
    Two smaller turbo's have less lag too.

    Those turbo manifolds are only $200.
    I found some used turbo's for $100 to $150 each
    2 wastegates are about $200
    Tubing and misc stuff, I figure $300
    I'll do my own fab work and make my own sealed box.
    So far, I figure a grand.
     
  16. gauder

    gauder Banned

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    A lot of people use the s-10 shorty conversion headers and flip them upside down.
     
  17. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    I can't believe it.......


    Nobody has thought to ask what he's going to do with the 540 he was building/built??

    Is it too late to call "dibs"? :D



    :usaflag:
     
  18. Shawn

    Shawn 1/2 ton status Premium Member Author

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    Good idea. I wonder if they cost the same as the turbo headers?

    Unfortunately, I had to sell that awhile back due to no job and no money. Really sucked having to sell that. I got a call back from the buyer 3 months later. He was all pissed since the place in Vegas that put the motor together screwed everything up. Luckily for him, his machine shop spotted all the mistakes and was able to fix them but it cost him more $$$. I had to send him some cash out of my own pocket since I guaranteed the engine. :doah: I would of just installed it the way it was and found out the hard way that the engine was doomed from the start. My luck with big blocks is terrible since that would of been engine #6! I just want to drive it! :crazy:

    Pics of what happened to my 496:
    http://www.off-road.com/chevy/tech/454engine/problems/MVC-568S.JPG
    http://www.off-road.com/chevy/tech/454engine/problems/MVC-571S.JPG

    Pic of my 540
    http://www.off-road.com/chevy/rodent/540/sb1.jpg
     
  19. sled_dog

    sled_dog 1 ton status

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    forget the boost and compression issue with detonation, how about intake charge heat? With no intercooler, twin turbos, and the 91 octane, I could forsee detonation especially at slow speeds crawling on a trail. Turbos and Superchargers have a tendency to surge a bit. Personally I don't think they are the ticket for trail vehicles. If you really want some nice power and mileage and even dependability, I'd consider a Gen III motor swap myself. But that is me.

    I'd bet those headers you showed don't last for crap in front of a turbo. The heat build up in manifolds is pretty strong when using a turbo. I truly doubt cheap shorty headers will be happy behind a turbo. I'd say Rams horn manifolds would be good but I think they'd block the spark plugs when flipped over.

    I'd think single turbo setup like the Banks kit and stock Chevy Diesel setups. Namely I'd consider, ramshorn manifold on driver side, pipe down under oil pan, to a custom fabbed heavy duty header on the passenger side with the turbo mounted there. Gives you plenty of room for intake tubing. With some of the nice rubber hose joining stuff aftermarket turbo setups use, I don't think routing intercooler tubing would be bad.
     
  20. zcarczar

    zcarczar 1/2 ton status

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    Why not run a Gen III style SBC with a blower? Yeah turbos would be cool, but you lack the off the line power, and turbo's tend to be peaky. Of course you don't exactly do the same type of wheeling I do. Only problem I can see with going twin turboed is that what if your doing some high speed stuff and let off the throttle for a minute to get around something but instantly need the power again when you get around the obstacle, with a turbo I dont think its going to be there when you need it. Where as if you went with a blower its there as soon as you mash the throttle, but then again you dont do high speed stuff like I do in my blazer and the turbos would probably work great for you, and be the demise of me since they dont respond quick enough. Although the only turbo v-8s ive driven are diesels, I couldnt imagine a gas v-8 acting much different.


    Edit: Why not look into running an air to water intercooler? They work very well and its a simply radiator mounted in the intake, a small pump, a few heater hose lines and a small radiator mounted up front. The Joe Gibbs setup that ive seen installed on a few of the trucks here at work works very well.
     

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