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  1. #1
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    Default Twin turbo 400 SBC

    Hello, I am planning on twin turboing my small block chev, on a budget, I can do alot myself, piping etc. I'm running a 400 small block with new rings, bearings, 020 020 crank 20over flattop pistons, roller rockers and a new isky camshaft (camspecs listed lower) looking at 6psi or less. I have 2x t25 turbos off a s14 Silvia here which I could use. The car is also running a fitech efi unit which has the option for timing control. The heads are smog cast heads which I have had cleaned up. 1.5 ratio roller rockers.

    Camspecs as follows


    Valve Lift Int/Ext. 0.445Valve Lash Hot Int/Ext. 0.000ADV Duration Int/Ext. 2700.050 Duration Int/Ext. 216Lobe Center 108


    Will these turbos be adequate for this application, I dont mind what fuel I have to use I have 98 or 100 octane 500m from my house.

    What sort of power could I expect to see and will it be safe for.my engine.

    Will appreciate any advice tips etc when it comes to twin turbo etc.

    Thanks

  2. #2
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    Cam needs a bigger lobe centre for turbo. What's the comp with the flat tops? You wont want any more than 9.5-1. The turbo guys on here know more than me though.

  3. #3
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    The block has been decked and the heads have also been skimmed. I believe my compression is somewhere around 10:1 . Compression tested after rebuild and cylinder compressions were all around 180. As for the camshaft I may look at changing at some point. Cheers

  4. #4
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    HI
    Turbos need to match the application otherwise they will under perform . Refer the agent for a good match turbo parts to application .
    Cast iron restrictive heads and 10;1 compression is concerning .
    Push the early sbc hard and the centre exhaust ports become very hot . There is a special 400sbc high flow head gasket and also spread port cylinder heads to decentralize the heat .

  5. #5
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    I'm not looking to make crazy boost or massive power. Do you think it would be safe with the cast heads this cam and with the 10:1 comp worth these 2 turbos? I literally have a pair of t25s and manifold to suit sbc will bolt right up. I have the fitech efi unit, with ignition control so I can keep the timing conservative and pull timing when boost comes in.

    Thoughts?
    Cheers

  6. #6
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    Hi
    U need the agent or manufacturer to specify the appropriate turbo scrolls and housing if not its a waste of money. Specialist aftermarket operators may have some idea but be careful they will sell whats on the shelf not necessarily the perfect part . The build has to be designed around compression /cylinder head and cam and engine size . Probably 3-7psi boost maybe.
    .

  7. #7
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    You could get 500, but when the engine is shattered you have zero... If you just want to throw parts together, and you dont really care if it blows up or not I say go...

    Making something out of junk can be fun but carefactor has to be at zero, you did ask about 'safe' so I dont know...

  8. #8
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    I also have a 350 engine that is a fresh build 8.5:1 compression. To my knowledge the cam is standard, smog head. I could use this if it's a better option? Do you think the t25s would be a reasonable option? Or is there a better widely available turbo I could try find cheap? I dont want to destroy the engine, I thought the fitech with spark control will keep things pretty safe?
    Cheers

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    Hi
    Contact the turbo maker for info on turbo match to engine . Incorrect turbo match may result in little or no boost . Worse to much . And/ or over reving the turbo with potential explosive results either the tubo or engine or both .

  10. #10
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    Quote Originally Posted by 72ChevCaprice View Post
    I also have a 350 engine that is a fresh build 8.5:1 compression. To my knowledge the cam is standard, smog head. I could use this if it's a better option? Do you think the t25s would be a reasonable option? Or is there a better widely available turbo I could try find cheap? I dont want to destroy the engine, I thought the fitech with spark control will keep things pretty safe?
    Cheers
    You are limiting your choices with the cheap factor, what is cheap $50, $100, $500? You are better off trying to find a china turbo on ebay like a T4, but those need blow offs and wastegates, so it ruins your budget...

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