Twin turbo 455

Discussion in 'High Tech for Old Iron' started by buick46270, Dec 30, 2008.

  1. buick46270

    buick46270 Well-Known Member

    All the mods are in my sig but if you have any questions feel free to ask. Its all a work progress but ill keep updating as i go on.

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  2. buick46270

    buick46270 Well-Known Member

    and a view from the top where you can see where the turbos are in relation to front of the block.

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  3. 70 gsconvt

    70 gsconvt Silver Level contributor

    Three words:

    OH...MY...GOD ! ! ! !

    That is just toooooo awsome.
     
  4. bobc455

    bobc455 Well-Known Member

    Looks like a great time!

    Got a question for you. When manifold pressure increases, fuel drops out of the inlet stream. This is why carbs need an accelerator pump.

    However with a turbo, manifold pressure can increase when there is no throttle movement (i.e. when the turbos spool up). How do you richen the mixture during this event? I know how this is controlled on a computerized FI engine, but I would think that a normal carb would run (very) lean until pressure reaches an even level.

    Thanks,

    -Bob C.
     
  5. buick46270

    buick46270 Well-Known Member

    You can either take a carb you have and convert it to be setup for a blow through application, or buy one from a vendor that's already setup. If wanting to convert your carb or just looking to learn ( turbomustangs.com ) has very detailed info and explinations of everything. I myself just by one already setup for boost ( quick fuel, csu, pro systems, etc. ) and they set it up for your application and its really close, then just have it tuned on the dyno for a few jet changes.
     
  6. buick46270

    buick46270 Well-Known Member

    also on the fuel side of things, you need a boost referenced regulator. It will increase your fuel pressure one pound for every pound of boost your creating, that way when your motor starts getting into boost, your fuel bowls don't get drained empty.
     
  7. bobc455

    bobc455 Well-Known Member

    So a blow-through carb will feed extra fuel when the manifold pressure increases, even though the throttle is not moving? How does it accomplish this?

    (I already have FI so this isn't a concern for me. But FYI in the FI software, there are two enrichment settings- one for throttle position movement like an accelerator pump, and a second setting to provide additional enrichment when the manifold pressure increases - for example due to a turbo spooling up. I just am not sure how this second type of enrichment is provided on a carb.)

    -Bob C.
     
  8. buick46270

    buick46270 Well-Known Member

    when you say " when manifold pressure increases" are you talking about when the motor is seeing boost? My regulator is setup to give my carb 7psi of fuel, when under boost (say 7#s) the reg (built in boost reference port) will feed 1 psi for every # of boost, so at 7#s of boost the regulator will actually be flowing 14psi of fuel to the carb, but because of the air being forced into the carb (and the fuel as well) instead of sucked through, the carb is still actually at 7 psi. If you had a regualar fuel regulator, and had 7 psi going to the carb, the boost (positive pressure) would force all the fuel out of the bowls and would go dry, and really lean fast.

    Also im not sure what they do or change, but the carbs you can buy for blow through have different or special metering blocks.
     
  9. bobc455

    bobc455 Well-Known Member

    No, I mean when the turbo is spooling up.

    If you stomp on the gas, the manifold pressure will go to atmospheric pressure. That quick increase in pressure (from a vacuum) will cause much of the fuel to drop out of suspension and cling to the interior walls of the intake manifold. This is why we need an accelerator pump, to squirt in extra fuel to keep the in-cylinder mixture from going lean when stomp on the pedal.

    The same thing will happen when manifold pressure increases for any reason, including when a turbo spools from 0 PSI to 7 PSI. Fuel will drop out of suspension and cling to the interior walls of the intake manifold. However since the accelerator pump is strictly a mechanically-actuated enrichment, there has to be some other enrichment for when the intake manifold pressure increases for another reason (such as a turbo spooling up). If you don't, your engine will go very lean during spoolup.

    How is this accomplished in a carb?

    -Bob C.
     
  10. Justa350

    Justa350 I'm BACK!

    The basic fuel delivery of a blowtrhough carb is like a regular carb. The atmospheric pressure in the floats is ultimately what shoves the fuel out of the boosters. It does this based on the pressure differential present at the booster. Like Kyle said, the key is the boost referenced fuel system, and having the bowl vents subjected to boost.

    By increasing the pressure of the fuel in the bowls, and the delivery of the bowls, the pressure differential in the booster occurs under boost just like it does in an NA application. Even under boost, the way a venturi is shaped, it will "feel" less pressure below the orifices in the booster than it does at the orifices. The area of lower pressure is ultimately "filled" by the pressurized fuel in the bowl. Once it clears the booster it has nowhere to go but into the next location of lower pressure, which would be the cylinders when the intake valves open. It does this in proportion to the pressure differential, or in other words, as much as is needed for a given airflow situation.

    If somehow a carb was setup where the bowl vents were not subjected to boost pressure, the carb wouldn't work.

    This is a pretty vague and general summary, but hopefully helps visualize why it works.
     
  11. Justa350

    Justa350 I'm BACK!

    Oh one other thing, it is very common to have the air bleeds restricted, or completely eliminated to prevent a lean situation.
     
  12. bobc455

    bobc455 Well-Known Member

    Thanks, but your answer doesn't seem to address my question. Maybe I'm not explaining properly (despite my best efforts).

    Obviously a boost-referenced fuel regulator is necessary and I understand how it works. However running at 7 PSI is a *static* situation, and there is a *transient* situation when the pressure increases from 0 PSI to 7 PSI (during spoolup).

    I assume you understand why an accelerator pump is required, and how it works?

    During the spoolup from 0 to 7 PSI, you need additional enrichment the same way you need enrichment (from the accelerator pump) when you stab the throttle and the manifold pressure jumps from -10 PSI to 0 PSI. In a fuel injection computer, you can program the injectors to add extra fuel whenever it sees a rapid pressure increase (such as during spoolup) but I don't know how a carb will address this situation since the accelerator pump will have no effect.

    -BC
     
  13. BUICKRAT

    BUICKRAT Got any treats?

    Judging by his previous posts and r&d in turboland, I would have to assume he knows what an accelerator pump does and why it is needed. Can we assume you know how a venturi works and what its role is? Sorry to be blunt, but its clear as mud to me. But then again, I grew up in the world of carburetors. Blow thru's are designed to help eliminate the leaning during spool-up.
    The same way a fi engine increases fuel pressure and increases injector pulse width electronically, a carb does it mechanically...bypasses, variable venturis, etc.
     
  14. Justa350

    Justa350 I'm BACK!

    I guess all I meant is you just jet it richer to compensate for the additional air. The boosters will only shoot out as much fuel as needed. It really isn't very complicated, as the boost doesn't just slam on like the sudden opening of the throttle blades requiring an acc pump.
     
  15. GotTattooz

    GotTattooz Well-Known Member

    buick46270 , can you post a list of parts and prices of all parts involved in the twin turbo set up?? I know the kit is like $2400, but with the blow-through carb, regulator, etc, I'd like to know just how expensive this mod is. It looks beautiful. If I have that setup, I wouldn't put a hood on my car. It's just too pretty.

    -Josh
     
  16. PaCemkr86

    PaCemkr86 WFO Racing

    looks mean, cant wait to see more of this build :TU:
     
  17. buick46270

    buick46270 Well-Known Member

    I didn't get the whole kit from JUSTA350, because i am going to put an intercooler setup on it, from the kit all i got was the turbos, waste gates, and manifolds, ill have to get my own blow off valve, carb hat, and piping.

    - I use the extreme velocities carb hat and 1 inch spacer --$250
    -You can get blow of valves from--$50 to $400
    -If you only have an hei ignition system you will need to upgrade to a 6al or better- $200 and up
    -If your doing an intercooler your looking at-- $100 to $400 plus piping
    -Most street builds you can use Aeromotive A1000 fuel pump and boost referenced regulator--about $475
    -On all your fuel lines, and the drain lines for the turbo i would recommend braided stainless hose, and the hose and all the fitting add up fast, i think i spent $150 on fitting + hose

    Im sure i am missing some stuff but i think thats about all you really need, as far as big stuff for the turbo. You can always but the stuff used and cut the costs way down but i just preferd to have everything new.

    As far as the motor goes you can use it on a stock motor and keep boost low, or have a great street/strip car, or upgrade to some bigger turbos if your wanting to use it for all out race. The base turbos which i got are 54mm and they should support about 800hp at the wheels which is more than what anyone is going to be doing with a stock block on here.

    When i finally get all my stuff going and then to the chassis dyno, ill be able to compare the hp difference from the procharger setup to the turbos. The dyno that i go to reads low on the hp side, and the car makes so much torque it just kept blowing the tires off and they lowest rpm they could start to get reading at was 4500rmp so i was already past the peak torque, and the turbos will make more torque.

    The only difference between my procharger setup and the turbo setup will be the compression, procharger had 9.4, and turbos will have 8.7, but they will both be tested at 10#s of boost for comparison, then ill go up from there depending on the numbers, but im hoping for atleast a 30hp gain at the wheels at the same boost level. And all this still in a 4000# car with 93 octane, and i know it will go faster than 6.5 in the 8th, (i have 50shot of nitrous to make sure of it lol)
     
  18. 70 gsconvt

    70 gsconvt Silver Level contributor

    Just to stick my nose in here, is this about a $5,000 setup if you start with a regular performance engine like, say, mine.
     
  19. Justa350

    Justa350 I'm BACK!

    Not including any costs for engine parts desired, I suggest people expect to pay at least another $1000 over the kit price to have it running. It can be done for less. Depending on parts chosen like carbs and fuel delivery it can also be much more. The nice thing though, is that it allows big performance out of a very modest engine build. Even a stock motor set up right with some turbos is going to romp at the track, if you can hook it up! :)
     
  20. buick46270

    buick46270 Well-Known Member

    You could easilly do it for 5k if your engine was already built up like yours. If you get the complete turbo kit its $2400, you will still have $2500 left after shipping for everything else, complete fuel system will be about $500 if your starting from scratch and using braided stainless and -an fittings still leaving you with $2k. You can modify the carb you have or have someone else modify it for blowthrough for fairly cheep (100-200) or buy one built allready (used or new). The carb i had for the procharger was a quick fuel and was $700 brand new, and the one i have now is a pro systems which was $1200, but got it for $700 used and just rebuild by pro systems. You can always find them cheeper and used if you dont want everything brand new like i do, its just a preference.
     

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