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 Post subject: Leak down test?
 Post Posted: Fri Jul 22, 2011 5:19 pm 
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I know your supposed to do a leak down with the engine warm but if you do it cold
what would be acceptable %???

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 Post subject: Re: Leak down test?
 Post Posted: Fri Jul 22, 2011 7:51 pm 
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Since it's a "test/retest" thingie I just make sure I do it at somewhere near the same temperature. Oh, and I always do mine at room temp, whatever that happens to be at the time. =;

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 Post subject: Re: Leak down test?
 Post Posted: Fri Jul 22, 2011 10:32 pm 
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Too many variables to give any kind of useful estimate. I've seen engines ~20% on the gauge I use and be perfectly fine. There are different gauges w/different orifice sizes which gives different readings. Type of rings can change the reading.

I don't bother checking leakdown unless there is something wrong I am looking into. If it leaks high and still runs the same what would you do?

Rick


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 Post subject: Re: Leak down test?
 Post Posted: Fri Jul 22, 2011 11:40 pm 
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I think a leakdown is a good tool for comparing cylinders. Usually with mine if the cylinders are all within a couple of % and around 15 I don't worry about it. I usually replace rings and check the valves after so many passes but I leak it down before I tear it down so I know if I need to look for problems.

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 Post subject: Re: Leak down test?
 Post Posted: Sat Jul 23, 2011 1:00 am 
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I've done both cold & warm and noticed a bigger difference cylinder to cylinder cold. Once the motor/rings/walls are warm things seem to even out better.


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 Post subject: Re: Leak down test?
 Post Posted: Sat Jul 23, 2011 1:22 pm 
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I'm afraid to do one. [-X =; It runs great as it is. That would just be something more to want to do something I shouldn't :-

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 Post subject: Re: Leak down test?
 Post Posted: Sat Jul 23, 2011 8:06 pm 
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I have done dyno tests and leakdown tests on the one engine over many years. This engine was a mechanical injection 400 chev with pontiac heads. It had 8 to 12 percent leakdown at the end of every season racing and made 695 hp on the engine dyno in that condition. Freshened up it had under 4 percent leak on every cylinder and made 730 hp on the dyno. It repeated the same results year after year for 7 years of running. Never varied. So thats what leakdown is worth.


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 Post subject: Re: Leak down test?
 Post Posted: Sun Jul 24, 2011 8:38 am 
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shrinker wrote:
I have done dyno tests and leakdown tests on the one engine over many years. This engine was a mechanical injection 400 chev with pontiac heads. It had 8 to 12 percent leakdown at the end of every season racing and made 695 hp on the engine dyno in that condition. Freshened up it had under 4 percent leak on every cylinder and made 730 hp on the dyno. It repeated the same results year after year for 7 years of running. Never varied.
Was that hot when leakdown was checked? In what type of racing was that engine used? That would be a noticeable power loss and more than I would expect for a season of drag racing. I've raced some engines for 5-6 years w/o freshen and still ran the same, but I have no idea what they leaked.

shrinker wrote:
So thats what leakdown is worth.
At least on that engine.

Rick


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 Post subject: Re: Leak down test?
 Post Posted: Sun Jul 24, 2011 8:49 am 
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Leak checks were done cold. It was a drag race engine. The car actually went the same ET with less power due to traction issues with the greater power.


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 Post subject: Re: Leak down test?
 Post Posted: Tue Jul 26, 2011 10:53 am 
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I have done several leak down tests over the years on my motors and I never have been able to learn anything by it. With gas ported pistons I get 8 to 11 percent if the rings are shot or if they are brand new. I was always quicker with new rings even if the leak down was the same though. I blamed that on the new rings having less area touching the bore. Especially the taper faced 2nd rings I used to run before I went to the napiers.

And I always did the leak down with a cold motor.

Denis


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 Post subject: Re: Leak down test?
 Post Posted: Fri Oct 07, 2011 6:34 am 
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I do mine at room temp also.. if i see less that 95 % im tearing into it..
when you race roundy round stock every little bit counts..
on our stock engines we run total seal rings and you will see 100% on the leak down gauge.
when the competition between tow racers is very close you want to stay on top of your engine and drive train..
we usualy go two seasons without needing to freshen up the engine unless something goes bad..

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