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  • 2 Post By techinspector1
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Thread: Turbos and compression
          
   
   

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  1. #1
    RayDav's Avatar
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    Turbos and compression

     



    I am building a 460 for a 55 Ford wagon and setting it up as a tow vehicle. The current state is here.
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    I have only settled on two things for the engine so far; a 4.5 inch crank and a roller cam, probably CompCams K34-422-9.

    I have a 9K#, 84 E350 with a 7.3 diesel from an 84 E350. I added a turbo that was intended for a 7.3 Power Stroke. It is on the frame about at the rear of the transmission. Five pounds of boost made a huge difference in hill climbing and soot reduction. Installing that turbo required nothing more than some plumbing. That engine seemed to be just waiting for a turbo.

    I have a pair of T3/T4 turbos that were supposed to go on that diesel, but I could not find room on the passenger side. I am going to need to make headers. Turbo headers would be easier to build than long tube. The attitude today seems to be, boost everything. So why not?

    I may very well have unknown unknowns, but the primary question I have now is compression ratio. Everything I read seems to say as boost goes up compression ratio must go down. Could 9:1 tolerate any boost at all? How low would it need to go for 10 psi? Does octane make a big difference, I would really like to run it on regular? Would aluminum heads make a difference.

    Ray

  2. #2
    techinspector1's Avatar
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    Here's a Final Compression Ratio Chart from Blower Drive Service. Static compression ratio is down the left side. Boost is across the top. Anything in the gray area will work with premium pump gas, like 9.0:1 with 6 lbs of boost. Anything in the white area will need E85, methanol, ethanol or racing gas.
    Technical Charts

    Although it is expensive, aftercooling (intercooling) will make a considerable difference, allowing more boost without detonation. So will water injection or alcohol injection. I used 70% Isopropanol alcohol from the drug store to good effect to prevent detonation with an Edelbrock water injection system several years ago. Mix a quart of 70% with a half quart of distilled water.

    You can stay on top of this right out to the ragged edge by investing in a lighted 10X spark plug loupe and inspecting your spark plugs regularly.
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    Choose a place where you can make a full-out run 0-100 or so without encountering the law. A drag strip is the perfect place. Make your pedal-to-the-metal pass, then go to neutral and chop the ignition. If your ride has a steering wheel lock, cut the wire that goes to the coil and put an additional switch in the line that will allow you to cut power to the coil and still steer the vehicle. The whole point is that you don't want to do ANY additional driving or idling once you have made your banzai pass. Let the beast coast to a stop and pull the plugs for inspection right there on the spot. Of course, you will want to keep a strong flashlight with you for pulling plugs at night if you have to.

    Detonation will first show up on the insulator of the plug as little black specks, looking like someone sprinkled black pepper on the insulators. This would be engine oil that was squished out from the top piston ring groove when detonation delivered its sledgehammer blows to the crown of the piston. If you let that condition go unchanged, the next thing you will begin seeing on the porcelain is little silver specks. That would be the pistons melting.

    http://www.4secondsflat.com/Spark_plug_reading.html
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    http://www.biblio-moto-books.net/mot...t/sparkplg.htm

    .
    Last edited by techinspector1; 10-09-2016 at 04:40 PM.
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  3. #3
    rspears's Avatar
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    Quote Originally Posted by techinspector1 View Post
    Here's a Final Compression Ratio Chart from Blower Drive Service. Static compression ratio is down the left side. Boost is across the top. Anything in the gray area will work with premium pump gas, like 9.0:1 with 6 lbs of boost. Anything in the white area will need E85, methanol, ethanol or racing gas.
    Technical Charts

    Aftercooling will make a considerable difference, allowing more boost without detonation. So will water injection or alcohol injection. I used 70% Isopropanol alcohol from the drug store to good effect to prevent detonation with a water injection system several years ago with an Edelbrock system. Mix a quart of 70% with a half quart of distilled water.
    Now that is a helpful chart!
    techinspector1 likes this.
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  4. #4
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    normal standard for sea level atmospheric pressure is 14.7 psi------

    so using a rule of thumb----7 psi would aprox add 50% to your compression ratio and 14.7 would double it---------however, since normally the cylibder doesn't start compressing the charge until the intake valve closes your dynamic compression ratio is less than the static numbrs but if boost is added, you are getting pressure into the cylinder more effiently and those figures get disturbingly distorted-------

    I have had several tow vehicles power by 460 and you don't need boost or 4.5 strokers-------advance cam for early 1970 numbers (pre smog ), good dual exhaust system, Holley 850 carb with dist advance changed to 10* meckanical so you can run a quicker curve with around 36 * and tow away-------My old 1970 F250 which I put a Lincoln 460 into has been in many drag racing publications and the Jim Dunn funny car movie--

  5. #5
    RayDav's Avatar
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    Quote Originally Posted by techinspector1 View Post
    Although it is expensive, aftercooling (intercooling) will make a considerable difference,

    So will water injection or alcohol injection. .
    I think I will have room for an air/air inter-cooler. I even have one left over from the diesel.

    I have bought water/alcohol injectors for my two diesels but have not yet installed them; it is tough finding a place to carry water.

    The only experience with adding a turbo I have is with my one diesel 7.3 IDI in a 9K# van. On that one it made a huge difference, and it has never made 10# of boost. I also have a 2001 Power Stroke in an 11.7K# van, and it can make about 15#.

    The vehicle is being set up as a tow vehicle. It will probably never see 5K rpm. The turbos I have supposedly come in early. Can I be expected to notice 5# boost?

  6. #6
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    Raydav, great info from tech, bds chart says you need a final compession ratio of combined boost and traditional compression to be under 12.4 to run on gas, stay under its not worth the worry, water injection works well but I would be more apt to use it when needing performance, if just driving or cruising I would turn the boost down, you still should have plenty o'power without trying to squeeze out every drop.
    Last edited by Matthyj; 10-09-2016 at 08:01 PM.
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  7. #7
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    Tech really helped you out with that chart. A lot of good advice here. I don't have much experience with turbo charging gas engines as I've only done 1 5.3. But I can tell you keep the boost on that IDI 7.3 below 11psi other wise you'll be spending lots of money.
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