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Thread: Increase boost on stock motor

  1. #1
    Join Date
    Jul 2017
    Posts
    1

    Increase boost on stock motor

    Hey all, I'm new to the super coupes and I just bought me a pulley off of spinning wheels. It says it's in between 5-10 percent. I've heard these cars have head gasket problems, I don't know how many miles are on it because the ODO was broke when I bought it at 86k but it had been sitting for years so it may be close. Who knows. Any ways it's been very well taken care of and been kept up on. I've read some threads that say you should open up your exhaust to help with head gasket pressure...? Which doesn't make much sense to me because the biggest strain on the head gaskets would be on the power stroke when both valves are closed and the cylinder is full of pressure....not when the exhaust valve is open... and it's expelling exhaust gasses? Anyways will this smaller pulley blow my head gasket?? Thanks!

  2. #2
    Join Date
    Dec 2007
    Location
    Salem, OR
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    6,340
    I've heard these cars have head gasket problems
    Mostly from being beat on.

    Just changing that pulley at that percentage isn't going to automatically blow the head gaskets...assuming the engine is in decent shape/not already beat to death and you don't make a practice of beating on it. Even a stock motor will suffer if beat on.

    As for changing the pulley, remember it's kind of chicken/egg thing:
    - if you change the pulley first, the boost on the gauge will increase, along with a change in the power band and an increase in power
    - if you opened the exhaust first, you'd see a drop in boost on the gauge, which tho, wouldn't equal a loss of in power to the wheels - just a change in when that power hits in the band, along with an increase in power

    If you do both, the boost will read near normal on the gauge, you'll have a cumulative power increase, and near stock power band - generally.

    I think doing the exhaust is suggested so often because without it, other mods are difficult to get the most out of - it's better done early once you decide to move away from stock. Anything you can do to improve flow thru the engine helps. Exhaust mods range from hi-flow downpipes and cats to a complete system replacement with headers, larger pipes, true duals and different mufflers.

    It's all a slippery slope, tho - once you start making power mods, there's always a reason to do the next so you can make the most out of the last and that path can be a long one.

  3. #3
    Join Date
    Apr 2002
    Location
    Greenville, IN
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    4,253
    I'm convinced that it isn't so much one thing (slight increase in boost in this case) that increases your likelihood of headgasket issues....it's a combination of issues and wear that do....timing, temperature, type of fuel, boost pressure and some other things too.... Ultimately, you're fighting detonation - where your cylinder pressures spike much higher than desirable. Detonation can cause an otherwise "healthly" headgasket to fail (among other things!) If you increase the boost (and heat out of the SC) without changing anything else, you WILL be increasing the possibility of experiencing detonation. How much OD is too much for a car with or without XYZ mod's is a matter of debate I guess.

    I think the exhaust backpressure has generally been cut loose as the headgasket failure scapegoat, but still can play a part in the equation.

    How's that for a non-answer?
    Matt Haub
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  4. #4
    Join Date
    Dec 2002
    Location
    Merrimac, MA
    Posts
    231
    I guess me thinks any increase in flow on the intake side or restriction in flow on the exhaust side results in more pressure on said power stroke. Conservation of mass. Compressible fluids. Yada yada yada. Ultimately the engine is a pump, less restriction = more efficient = more power. Free up the exhaust. Your head gaskets and butt dyno will thank you.
    1989 XR7 5-SPD - 15,700 miles - Garage Queen

  5. #5
    Quote Originally Posted by KMT View Post
    Mostly from being beat on.

    Just changing that pulley at that percentage isn't going to automatically blow the head gaskets...assuming the engine is in decent shape/not already beat to death and you don't make a practice of beating on it. Even a stock motor will suffer if beat on.

    As for changing the pulley, remember it's kind of chicken/egg thing:
    - if you change the pulley first, the boost on the gauge will increase, along with a change in the power band and an increase in power
    - if you opened the exhaust first, you'd see a drop in boost on the gauge, which tho, wouldn't equal a loss of in power to the wheels - just a change in when that power hits in the band, along with an increase in power

    If you do both, the boost will read near normal on the gauge, you'll have a cumulative power increase, and near stock power band - generally.

    I think doing the exhaust is suggested so often because without it, other mods are difficult to get the most out of - it's better done early once you decide to move away from stock. Anything you can do to improve flow thru the engine helps. Exhaust mods range from hi-flow downpipes and cats to a complete system replacement with headers, larger pipes, true duals and different mufflers.

    It's all a slippery slope, tho - once you start making power mods, there's always a reason to do the next so you can make the most out of the last and that path can be a long one.
    I agree, when I got my car the previous owner had already replaced the exaust with straight pipes and flowmaster 40s and I was wondering about the loss of boost until I looked under the car, haha!

  6. #6
    Join Date
    Aug 2004
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    Latitude: 41.909147 Longitude: -72.450263
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    2,022
    Quote Originally Posted by Fordlover87 View Post
    Hey all, I'm new to the super coupes and I just bought me a pulley off of spinning wheels. It says it's in between 5-10 percent. I've heard these cars have head gasket problems, I don't know how many miles are on it because the ODO was broke when I bought it at 86k but it had been sitting for years so it may be close. Who knows. Any ways it's been very well taken care of and been kept up on. I've read some threads that say you should open up your exhaust to help with head gasket pressure...? Which doesn't make much sense to me because the biggest strain on the head gaskets would be on the power stroke when both valves are closed and the cylinder is full of pressure....not when the exhaust valve is open... and it's expelling exhaust gasses? Anyways will this smaller pulley blow my head gasket?? Thanks!
    My personal opinion on OD SC pulley and or Undersized Jack-shaft pulley. Leave it stock otherwise you will damage your head gasket. Run the correct gasoline and oil and don't use a lot of additives. If you have money to make major modification to your engine and get good advise from a builder, then you can do this. Otherwise leave it as is or you will shorten the life of your SC experience.


    Don't crash into a tree just to avoid a skunk!


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