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  1. #1

    Bypass blower for twin turbo 6v92's

    Does anyone know what's involved if you want to replace non-bypass blowers on old twin dry turbo 6v92s with newer bypass blowers? The bypass blower reduces rotor lobe drag and can increase fuel economy.

    If you use the same ratio on the blower is it a bolt on mod, or will the bypass change the air ratio enough to require other mods such as camshaft timing changes, different gearing, or different turbos/injectors?

    Thanks,

    Mick

  2. Re: Bypass blower for twin turbo 6v92's

    Bolt it on.

    Are you sure you want to do that?

    What are you looking to accomplish?

  3. #3

    Re: Bypass blower for twin turbo 6v92's

    Thanks,

    I'm not sure I want to do it, but it sounds like an improvement due to the fact that the pressure on both sides of the blower becomes more equal, possibly resulting in free HP or better economy (less pumping losses at the upper end of the HP curve?).

  4. #4

    Re: Bypass blower for twin turbo 6v92's

    I had Covington Diesel do the switch on my 6V92's and was told that it would make more HP. I never ran the boat before the change so I can't say if it made a differance. I do know that it is the differance between the 450hp and the 485hp in the 6-71 J&T engines. The Covington rep. told me that HP was made of air not fuel. Good Luck

  5. Re: Bypass blower for twin turbo 6v92's

    Hp is made from fuel PROPERLY burned with air.

    To make more HP, you must first have more air, in order to be able to inject and burn more fuel. If you don't have the air, you make smoke and high EGTs instead of power.

    There is no such thing as "free" HP - or free airflow.

    A bypass blower has both good and bad points. On a TA engine it is less trouble than on a TI (such as the 6-71s) because the aftercooler can cool the charge uniformly and breaks up the hot spots that would otherwise be present from the bypass when its open.

    Be aware that the twin turbo Covington conversions can run 500HP without the bypass. Adding the bypass blower will allow you to go to 535HP, but I'm not sure you want to. You can get significant benefits on the 500s by installing step-up blower gearing, and not doing the bypass.

    Bypass blower conversions are not cheap, as you need to replace the blower with a rebuilt one that has the bypass valve in the end plate.

    I have considered this path myself, but decided for now NOT to undertake it. I really don't like the idea of being beyond 500HP anyway on these engines for HP/displacement reasons. With stepped up blower gearing I can run cleanly at 500HP with reasonable boost and EGTs.

    Be very careful to examine the total cost of this conversion. What are you being quoted for the blower, new injectors (required to step up the power), installation of both and prop work required to actually USE the power you just purchased? Now weigh this against the possibility that you may be turning your engines into 1000-hour MTBF wonders, especially if you are inclined to run "200rpm off WOT" with any sort of regularity.

    If you're going to do this then bridge-reading EGT gauges on EACH BANK that are KNOWN ACCURATE AND WORKING are a MUST - not an option - or you will eventually cook something. So is absolutely ANAL maintenance. The 6V92TAs original cooling systme is marginal in warm water to start with - you're going to be pushing it even harder. You may need some kind of boost cooler to keep the operating temperatures and maintenance hassle reasonable.

    The blower ratio is NOT controlled in the blower. The gear that drives the blower and thus controls the step-up ratio is in the gear housing on the rear of the engine. Changing that gear requires recalibrating the governor's shim settings and there is a limit to how far you can go before you run into stability trouble - this is a worthwhile modification, but only as a reasonable (e.g. 5-10%ish) step.

    When you go far enough to start needing to play with the valve timing then you're beyond where I believe is safe for reasonable engine life.

    Again, I believe that 500HP is pretty much the wall for good service life, and that can be done WITHOUT the expense of a bypass blower setup.
    Last edited by Genesis; 07-30-2005 at 10:09 PM.

  6. #6

    Re: Bypass blower for twin turbo 6v92's

    Good stuff, thanks.

    I was mainly interested in making the engines a little more efficient, and not necessarily putting in bigger injectors. My understanding is the bypass equalizes pressure and reduces drag, with perhaps better economy and more usable HP at the high-end (therefore the notion of free HP).

    Genesis, I'd like to hear more about the step up gear you use, and if there might be any benefit to that with 9215 injectors.

    Cheers.

  7. Re: Bypass blower for twin turbo 6v92's

    Depends.

    Bypass does indeed, but it only opens at high boost, which you may not be able to generate anyway with smaller injectors.

    I have 7045s in mine. What's your HP output? My guess is that if you're set up for 435 you won't see much if any use of the bypass, simply because you can't develop enough boost to open it.

    Step-up gearing actually COSTS you a bit in terms of efficiency (but not much) as it overdrives the blower. I'm willing to pay that to get lower EGTs and fewer turbo problems, but I'm set up at 500HP - which is as far as I believe is safe with those motors.

    You need to know what you've got first - in terms of boost levels, EGTs, etc - without that I can't tell you whether there would be any benefit or not.....

  8. #8

    Re: Bypass blower for twin turbo 6v92's

    Thanks,

    I am set up for 435HP, and have the opportunity to make some modifications, as I'm about to rebuild the motors. I have a '73 45C and am now wondering what an extra 130 HP will do for the boat. I also put on 4" mahogany rails and a Slane flybridge, which increased the weight by 900lbs.

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