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Thread: thoughts needed

  1. #1
    Fuel Injected! mudbuggy's Avatar
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    thoughts needed

    Hi boys,

    I have been thinking and researching my new motor, been bouncing between an ls 6.0 with a turbo or a 400 with a turbo and a tbi top. I pulled parts for an ls motor build and I have gone well over 7 grand just building the bottom half. That's it I think it's time for a decision to roll out with the 400. My question is really technical more then anything else but it's still bouncing between my ears continuously during the day. I have searched for an answer or at least something close to it to satify the bagering that is happening inside my head. So here it is, can a turbo be turned on and off as wanted? If I am running a motor and don't need the boost, just leave it off, but if I'm pulling a heavy load of wood and I'm getting on the highway or driving in stop and go traffic can I turn it on? I'm sure that I can do the tubing, it will be a pita, but doable, what about the programming side of it? Can a tbi unit handle the load? I'm reasonably sure that a stock unit from a 350 would limit the system, but a 454 would be an overkill, or at least be counterproductive of having the turbo switchable. I am thinking of having the turbo off for driving to work and doing errands, but if I have a load to pull, or what to play in traffic, just turn it on. Maybe I'm just overthinking the whole turbo thing and just need to run it all of the time. I really want to have this as my daily driver, and want to be able to pull a reliable 20 mpg all the time, or at least when I'm not playing. So is this just a wild notion or what?
    1989 GMC V1500
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  2. #2
    EFI GearHead ! EagleMark's Avatar
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    There's no way to turn off a Turbo, it is a mechanical process.

    Also no reason to turn off a turbo for any driving if tuned right and yes it can be tuned right for all driving. MPG will be higher with turbo so why turn it off for normal driving?

    If you want somthing simplar you don't need all the time and can turn off go nitrous!

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
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  3. #3
    Super Moderator Six_Shooter's Avatar
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    You need to drive a turbo vehicle, so that you can understand exactly how the turbo works.

    The turbo will only spool when there is a load on the engine. At cruise there will be vacuum in the intake, just like being naturally aspirated. It is only when the throttle position opens enough to put a load on the engine and/or a heavy towing load that there will be positive intake pressure.

    I can drive around all day without making any positive intake pressure, if I wanted to.
    The man who says something is impossible, is usually interrupted by the man doing it.

  4. #4
    Super Moderator Six_Shooter's Avatar
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    Quote Originally Posted by EagleMark View Post
    There's no way to turn off a Turbo, it is a mechanical process.

    Also no reason to turn off a turbo for any driving if tuned right and yes it can be tuned right for all driving. MPG will be higher with turbo so why turn it off for normal driving?

    If you want somthing simplar you don't need all the time and can turn off go nitrous!
    In actuality fuel economy will be slightly reduced with the addition of a turbo to an engine due to the more restrictive exhaust flow, however, when comparing to a natually aspirated engine that makes similar peak power, the turbo engine will generally get much better fuel economy, since actual boost pressure is only seen for a very short time.
    The man who says something is impossible, is usually interrupted by the man doing it.

  5. #5
    Fuel Injected! droptopstng's Avatar
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    yes and I shall add if I may that you can run a 2 step boost controller and turn the boost up at the flip of a switch when you want more power but If I were pulling heavy loads I would go roots blower but for me I always keep a spare nitrous kit laying around lol I love it....
    Wise man once said,better to stay silent and let others assume your and idiot than to open your mouth and prove it........and yes im an idiot lol

  6. #6
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    A turbo does switch off and on automatically depending on load. But if you really wanted to you could find ways to keep it from producing boost. For example, you could use a solenoid operated valve from a 4.3 CPFI intake manifold and a large dump valve to switch turbo output between atmosphere and the intake manifold. Or you could use an external wastegate connected to a pressurized air system with solenoid control to send exhaust around the turbo so it's not producing boost. Both of these methods would probably require some tinkering and would add complexity to the exhaust or intake plumbing.

    I have often found power and economy can both be improved when using a turbo but it's all about setting up the vehicle to use the engine's power more efficiently. Many people think a turbocharged engine must be tuned to 12:1 AFR whenever boost occurs but this isn't correct. Like any engine, you can go as lean is you'd like provided you're not doing damage. Tuning to 14.7:1 under light load is absolutely reasonable and is a great way to keep your economy up during unloaded driving. Combine this tuning with a turbo which produces boost at lower rpm and a numerically lower final drive ratio and you've got the potential for great economy when driving with a light foot. And if you decide to choose a smaller displacement engine and use the turbo to make up the difference in power, well, then you've got the best potential to get excellent mileage as long as you're not playing around too much. Of course you might find it very hard not to play around with a responsive turbo engine but that's not the engine's fault.

    GM has turbo code with very neat features such as desired boost based on throttle position, the ability to sense high or low octane fuel and use extra spark advance and the ability to minimize boost and add fuel if excess detonation is sensed. It's better IMO than many aftermarket add on controllers as it all works within the engine management system and can be adjusted to personal liking.

    The throttle body limits total airflow but the real issue you've got to face is the amount of fuel the injectors can deliver. That's very likely to be your power limit. The highest flow injector that will fit the old, large injector pod is about 90#/hr at stock pressure. People have found the power limit of these injectors to be about 300hp. With more pressure you can get more power but you'll need to find the maximum pressure these injectors can withstand. Now if you get the small injector pod from a big block truck TB or a Holley 534-170 you can use an injector rated for 60#/hr at 10 psi. While this doesn't sound like much, the max pressure this injector can stand is 101 psi so you have the potential for 180 lbs/hr fuel delivery per injector which can support double the power of the old big block injectors. (Shhh... don't tell the guys spending money on ultimate TBI mods!). If you decide to go TBI, a 450 hp version is going to get you thrown out of most forums in disbelief. You'll also want to seal the throttle shafts to prevent fuel/air from seeping out when boost is applied.

    If I were building a turbocharged generation IV engine for economy and fun I'd go right to the 5.3. If you're trying to make power while saving fuel, the trick is to use less displacement rather than more. The 5.3 in NA form makes more power than any stock 400, they're as plentiful as cockroaches in the junkyard and there's just as much demand for one so they're cheap. LS family parts bolt onto or into this engine and they're fairly stout even in stock form. Take a look here: 600hp 5.3

    Good luck.
    Last edited by 1project2many; 02-10-2012 at 12:07 AM.

  7. #7
    Fuel Injected! mudbuggy's Avatar
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    I wasn't planning anything stock on a 400, nice high quality stoker motor with a lot down low. I figure the truck weights max 6000pds and the load might be 5k ( the heaviest). I don't see a reason to spin above 5500 rpm, because my motor now doesn't do anything above that now. I really want to hit the goal of mpg, but I don't want to spend 7k dollars doing it. I like the idea of the older equipment, especially because everyone 'thinks' that the tbi equipment can't make the power, and for the replacement cost of repairs, compared to the ls motors component costs.

    So the thought is that the motor needs to be built with the turbos (2) for full use, can the 7747 (?) computer handle the 11111111111110000000000000 side of the process or is there another computer setup that would be better designed to handle the ones and zeros side of it?
    1989 GMC V1500
    2002 Chevy Trailblazer
    1988 Dodge Ramcharger

  8. #8
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    400 block with stroker crank is going to want a lot of fuel. Aside from that, you'll want a 1227749 computer and the $58 mask from the turbo Sunbird / Syclone or the custom $59 developed by a couple of Syclone guys and found at code59.org. There are also a few changes needed to run this code on a V8 so you'll want to get some help when you're getting ready to fire things up.

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