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leak down?

This is a discussion about leak down? within the Turbo Nitrous section, where you will Drag Racers sharing info on Turbo and Nitrous applications; What is a safe % for a leak down on a nitrous motor for a gen 1 with 20 24 ring gap. Thanks guys.

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    Default leak down?

    What is a safe % for a leak down on a nitrous motor for a gen 1 with 20 24 ring gap. Thanks guys.

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    what percentage do you have? you will probably get a better response that the question you asked.
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    how much spray are you running also? if its a big shot then and if you have too much leakage somewhere the nitrous will find it. Nitrous will find the weak link.
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    I have not done the leak down yet. I was just wondering if i needed to pull the motor out if it was bad or not. It is a new motor. And people just hade worried bc they said that is to big of a ring gap. It will have a big hit.

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    Fresh motor...I like 2% and have seen it many times...Probably OK up to 4%
    Just so ya know, I'm not a nitrous guy, just trying to help.
    BTW, ring gap sounds way large to me....I generally see .014"-.016" with a A-O motor, 81 or 83mm bore
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    Depends on your leak down gauge to if your using a harbor freight one it only pressurizes the cylinder with about 10psi it will so more leak then.there is sometimes not enough pressure to help seat rings try using a motion pro they use about 60 psi get a better reading just my 2 cents and I agree that gap seems a little big. Depending.who put it together if the idea was to spray I know some guys go larger just to be sure the heat doesn't close the ring gap. But still seems to much gap to me.
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    JE recommends 0.0045 per inch of bore for NA, 0.0055 per inch of bore for Nitrous. (81mm=.017")4% is more of a ProStock number for me. I wouldn't pull anything apart until I hit 20% on a nitrous motor. Also, check it warmed up. Cold motors can give false readings.
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    Thanks guys

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    Quote Originally Posted by SixShooter View Post
    JE recommends 0.0045 per inch of bore for NA, 0.0055 per inch of bore for Nitrous. (81mm=.017")4% is more of a ProStock number for me. I wouldn't pull anything apart until I hit 20% on a nitrous motor. Also, check it warmed up. Cold motors can give false readings.
    20%? holy $hit. maybe on a car engine, but not a bike. A well built motorcycle engine should have no more than 2-4% leakdown at the most due to how small the displacement is. Anything over 7-8% and I pull them apart and freshen them up. You will see a mph lost if your motor goes from 3% to 8%.
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    Quote Originally Posted by gixxre750 View Post
    20%? holy $hit. maybe on a car engine, but not a bike. A well built motorcycle engine should have no more than 2-4% leakdown at the most due to how small the displacement is. Anything over 7-8% and I pull them apart and freshen them up. You will see a mph lost if your motor goes from 3% to 8%.
    Mine showed 15% across the board earlier in.the season been running same.number.it always.has.like.I said cheap low pressure testers show a higher %always
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    Quote Originally Posted by race2win View Post
    Depends on your leak down gauge to if your using a harbor freight one it only pressurizes the cylinder with about 10psi it will so more leak then.there is sometimes not enough pressure to help seat rings try using a motion pro they use about 60 psi get a better reading just my 2 cents and I agree that gap seems a little big. Depending.who put it together if the idea was to spray I know some guys go larger just to be sure the heat doesn't close the ring gap. But still seems to much gap to me.

    Try this with your HF guage next time and see if there is a better leak down across the board on your motor..


    1. With the spark plug adapter installed in the cylinder but not connected to the gage set.
    2. Connect the gage set to a suitable source of compressed air. Doesn't have to be 100 PSI. Can be any pressure.
    3. Adjust the gage pressure regulator for a reading of 0% leakage on the "Cylinder Leakage" gage.
    4. Quickly connect the spark plug hose adapter to the gage set. This is the only part I do not like. Instead of a valve to do this part, you have to be real quick and attach the quick connect fitting from the spark plug adapter hose to the matching hose from the gage set.
    5. Read the leakage as a percentage on the "Cylinder Leakage" gage.



    Basically how this works is that the pressure regulator attempts to maintain the preset pressure but it can never do so because of the leakage in the cylinder, so the difference in the preset pressure and the cylinder pressure is presented as a percentage. You do not have to have a big compressor that maintains 100 PSI so you can use this tool with a smaller compressor or even a tank of compressed air from the gas station, if you're really quick connecting the hose from the spark plug hole to the gage set.

    So, with the HF leakdown tester, it's not the working pressure that you are interested in. It's the percent leakage shown on the "Cylinder Leakage" gage. The "Cylinder Leakage" gage reading (as a percentage) does the math for you.
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    Quote Originally Posted by STREETDRAG View Post
    Try this with your HF guage next time and see if there is a better leak down across the board on your motor..


    1. With the spark plug adapter installed in the cylinder but not connected to the gage set.
    2. Connect the gage set to a suitable source of compressed air. Doesn't have to be 100 PSI. Can be any pressure.
    3. Adjust the gage pressure regulator for a reading of 0% leakage on the "Cylinder Leakage" gage.
    4. Quickly connect the spark plug hose adapter to the gage set. This is the only part I do not like. Instead of a valve to do this part, you have to be real quick and attach the quick connect fitting from the spark plug adapter hose to the matching hose from the gage set.
    5. Read the leakage as a percentage on the "Cylinder Leakage" gage.



    Basically how this works is that the pressure regulator attempts to maintain the preset pressure but it can never do so because of the leakage in the cylinder, so the difference in the preset pressure and the cylinder pressure is presented as a percentage. You do not have to have a big compressor that maintains 100 PSI so you can use this tool with a smaller compressor or even a tank of compressed air from the gas station, if you're really quick connecting the hose from the spark plug hole to the gage set.

    So, with the HF leakdown tester, it's not the working pressure that you are interested in. It's the percent leakage shown on the "Cylinder Leakage" gage. The "Cylinder Leakage" gage reading (as a percentage) does the math for you.
    I understand what you are saying.

    Check this picture out the gauge on the left tells you how much pressure if being used to set the gauge on the right to 0% precent. The gauge on the left measure air coming in. On these testers (cheapo harbor friegh) it only takes about 8psi to get the gauge ont he right to 0%. So if you are only blowing 8psi into the cylinder its going to leak out much quicker then if you were blowing 60psi(which is amount that motion pro gauge needs to set right gauge to 0%) into the cylinder going to take little longer to leak past rings.

    The only other example I can think of would be having a bucket with a small hole in the bottom of it. with 8psi its going to leak out faster then it can fill up giving a lower reading. Compared to 65psi that will be able to supply the bucket.

    The second biggest thing with doing a leak down test is that all the cylinder read within 1-2% of each other.

    To me if its building great compression like expected and leakdown per cylidner is within 1% of eachother run it!
    just my 2 cents
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    forgot the picture lmao Name:  12711d1159317340-results-my-leak-down-test-a6-leakdown-tester.jpg
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    Quote Originally Posted by race2win View Post
    I understand what you are saying.

    The second biggest thing with doing a leak down test is that all the cylinder read within 1-2% of each other.

    To me if its building great compression like expected and leakdown per cylidner is within 1% of eachother run it!
    just my 2 cents
    I agree
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    well loose is fast
    i can say that you just have to tune for it
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