[Question] twin turbo system
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twin turbo system

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    Default twin turbo system

    Putting a twin turbo system on BBC and was wondering how to control boost without waste gates. Bought the system used and complete but no waste gates came with it and the guy I bought it from said he did not run waste gates and that was the way it came when he bought the boat. Thanks

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    Senior Member oldschool's Avatar
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    Your right foot. What type of turbo sytem is it?

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    Scahill with twin 310E 10 rajay turbos
    Last edited by pecan301; 02-08-2013 at 01:46 PM.

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    Quote Originally Posted by pecan301 View Post
    Putting a twin turbo system on BBC and was wondering how to control boost without waste gates. Bought the system used and complete but no waste gates came with it and the guy I bought it from said he did not run waste gates and that was the way it came when he bought the boat. Thanks
    If you look in the turbo exhaust housings, where the exhaust enters from the risers,, there should be some kind of hole drilled in the housing that acts as a bypass and limits the boost. At Gale Banks, the bypass holes were usually between 1/4" up to 5/8", with the larger diameter hole being more appropriate for pump gas boost. Most of the early marine turbo systems(Banks, Race Aero, PFM or Scahlill) used the Rajay 301E turbos for 454 cubic inch engines.

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    Senior Member oldschool's Avatar
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    Quote Originally Posted by pecan301 View Post
    Scahill with twin 310E 10 rajay turbos
    Alot of the time the Rayjays had a hole drilled in the housing, this would limit the boost. There should be some threads that talk about this, the seach function is your friend.

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    Quote Originally Posted by obnoxious001 View Post
    If you look in the turbo exhaust housings, where the exhaust enters from the risers,, there should be some kind of hole drilled in the housing that acts as a bypass and limits the boost. At Gale Banks, the bypass holes were usually between 1/4" up to 5/8", with the larger diameter hole being more appropriate for pump gas boost. Most of the early marine turbo systems(Banks, Race Aero, PFM or Scahlill) used the Rajay 301E turbos for 454 cubic inch engines.
    Barry is better than the search function. He should be your go-to guy for questions or anything turbo.

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    Quote Originally Posted by oldschool View Post
    Barry is better than the search function. He should be your go-to guy for questions or anything turbo.
    Thanks,, an old friend stopped by last year, he gave me some original Banks literature. This is a guy I helped with his Banks turbo engine after Jack Rex had left Gale Banks and opened Rex Marine. He had bought a brand new Campbell 20' V drive cruiser, that had an "850 HP" Banks engine, the blueprinted one with Carrillo rods and Arias pistons. He kept saying the boat was a dog and made no power,, and invited me to come up to Lake Nacimiento and check it out. I made a trip up there, he was right,, not making as much power as it should,, so I pulled the exhaust elbows and discovered the housings had the large 5/8" bypass housings,, so it explained the very low boost. We were able to trade for some other housings, and it was a whole new boat!

    One of these days I will get the stuff scanned, turbo kit installations, Banks sales brochure, including price list. I think shop labor was like $18 per hour!

    PS, while I was working for Rex that first year he was open, I rebuilt that same engine after an oil pump drive failure, and the engine is still together and running after 32 years! That was my first turbo engine build.
    Last edited by obnoxious001; 02-08-2013 at 03:45 PM.

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    Default Twin Turbo system

    Thanks to everyone for the reply. This is going on a BBC and would like to to run premium pump gas. If there are no holes is there any diagrams that I can get to show were to drill or do they have to be sent off and drilled. Thanks again for all the help!!!

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    If there are no holes, build a spacer block between the manifold and turbo and add wastegates for much better control. Pictures of what you have would help us all help you. Where are you located? Did you buy this system from TTSpectra?
    Last edited by steveo143; 02-09-2013 at 07:08 AM.
    steveo143 AKA DiMarco 21 II



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    Yes, all the suggestions make sense! Or you can scale the turbine and compressor wheel for your engine spec or limit gear ratio in the boat for other general options. We usually weld up the bypass hole and go!!!!!


    Sent from My Boostpower Marine Efi Beacon.

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    Yes I bought from TTSpectra, and I am in West Texas. I will check for hole and post some pics of what I have later!
    Again Thanks for the info and help. It is going on a 2002 Carrera Jet Boat. I have been in touch with Mr. Scahill and he has also been alot of help.
    Last edited by pecan301; 02-09-2013 at 08:16 AM.

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    That should be a blast to drive!


    Sent from My Boostpower Marine Efi Beacon.

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    Here are some pics of my ongoing project. Always been around boats but this is my first turbo system. I hooked water up and started for the first time this weeked and sounded good at idle, but when I give it gas it floods out. I think I have to much carb for my system #78 jets in primary and #82 jets in secondary. I have a 454 Gen6 BBC HO Marine Power 380 HP, I did replace the cam, lifters, and valve springs. The 3/16" nylon tubing coming out of the metering blocks and going to the intake is a mystery to me maybe someone can explain. I have a Demon 850 Blower carb brand new was wondering if it would work, just have no place to hook up tubing on the metering block.
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    Quote Originally Posted by pecan301 View Post
    Here are some pics of my ongoing project. Always been around boats but this is my first turbo system. I hooked water up and started for the first time this weeked and sounded good at idle, but when I give it gas it floods out. I think I have to much carb for my system #78 jets in primary and #82 jets in secondary. I have a 454 Gen6 BBC HO Marine Power 380 HP, I did replace the cam, lifters, and valve springs. The 3/16" nylon tubing coming out of the metering blocks and going to the intake is a mystery to me maybe someone can explain. I have a Demon 850 Blower carb brand new was wondering if it would work, just have no place to hook up tubing on the metering block.
    Put an o2 in the tail pipe. Those older systems usually puddle in the plenum.


    Sent from My Boostpower Marine Efi Beacon.

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