Blow by questions for built motors...2.5 ltr
11-29-2002, 10:11 PM
#1
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Blow by questions for built motors...2.5 ltr
What is a normal amount of blow by with a built motor??? Any guesses?? I am getting a little at 12 psi. This may also be when the engine is still not fully warmed up too. I usually wait till the temp needle moves towards the middle of the gauge. Allowing the forged pistons to get nice and round. I am not using oil either. So, I am just curious...
Paul...
Paul...
12-02-2002, 10:42 AM
#3
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What the hell do you want to know? 
All engines have blow-by. There is no such thing as a perfectly sealing ring set.
Is you oil black when you change it? Do you have evidence of gasoline in your oil? How often do you change your oil with the turbo? Have you tried synthetic? How long have you had your turbo on the car? How long does it take before you notice evedence of something funny going on with your oil? Have you done a leakdown test? What were the results of that test?
Are you sure that your problem is blow-by? Maybe you have a leak in your head gasket that seals when everything expands. maybe a valve has a bunch of crust on it and isn't sealing all the way. Maybe your turbo is burning your oil and you need to change it more often. Maybe you should try synthetic because it has higher duribility at elevated temperatures.
Correct blow-by should be 4.54368% of maximum cylinder pressure at maximum boost, tapering to 2.35782% at 90 degrees ATDC, this reference doesn't change with alternate engine parts.
cheeRS,
Greg
All engines have blow-by. There is no such thing as a perfectly sealing ring set.
Is you oil black when you change it? Do you have evidence of gasoline in your oil? How often do you change your oil with the turbo? Have you tried synthetic? How long have you had your turbo on the car? How long does it take before you notice evedence of something funny going on with your oil? Have you done a leakdown test? What were the results of that test?
Are you sure that your problem is blow-by? Maybe you have a leak in your head gasket that seals when everything expands. maybe a valve has a bunch of crust on it and isn't sealing all the way. Maybe your turbo is burning your oil and you need to change it more often. Maybe you should try synthetic because it has higher duribility at elevated temperatures.
Correct blow-by should be 4.54368% of maximum cylinder pressure at maximum boost, tapering to 2.35782% at 90 degrees ATDC, this reference doesn't change with alternate engine parts.
cheeRS,
Greg
12-06-2002, 11:34 PM
#5
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Ya ya ya... funny scoobyrs25. Troll
Seriously, I wanted to know if other people with beefed up internals had more or less blowby. As there are not that many people posting in the forums that run forged pistons and such. It seems that most everyone is still running stock internals.
As for the questions of how tight my engine is? Well I did indeed have a leakdown test performed and it settled out to between 2.5% to 3% accross the board. I had the valves done as well as the valve seats when the engine was broken down. This was due to a large piece of ring landing that got wedged in the valve seat on cylinder #4. So that is not the case here. As for the oil queston, I have yet to run synthetic oil in my new motor. I was waiting to log in a few more miles before I run synthetic. My deck is O-ringed and has a brand new gasket to boot. I am sure it is not a leaky head gasket. As for the smell of gas, I had the smell when the motor was in the first 1k miles. Then again, it was running rich with the TEC 3 Base Map supplied by Shiv. Cylinder wall washing maybe? Oil changes are 2k miles apart at the moment. My concerns are the results of more oil in my catch can latley. I did however turn up the boost to 12-14 psi and that's when I noticed more blowby. I am curious as to how to gauge what is "normal" for blowby on a built engine. Also, as the oil breaks down, I am assuming the oil is more likely to "squeak by" the rings as the oil grows more and more thin over time. Would that be a fair assumption? I guess I will have to see how things go over time. Thanks for the help so far Greg.
Paul...
Seriously, I wanted to know if other people with beefed up internals had more or less blowby. As there are not that many people posting in the forums that run forged pistons and such. It seems that most everyone is still running stock internals.
As for the questions of how tight my engine is? Well I did indeed have a leakdown test performed and it settled out to between 2.5% to 3% accross the board. I had the valves done as well as the valve seats when the engine was broken down. This was due to a large piece of ring landing that got wedged in the valve seat on cylinder #4. So that is not the case here. As for the oil queston, I have yet to run synthetic oil in my new motor. I was waiting to log in a few more miles before I run synthetic. My deck is O-ringed and has a brand new gasket to boot. I am sure it is not a leaky head gasket. As for the smell of gas, I had the smell when the motor was in the first 1k miles. Then again, it was running rich with the TEC 3 Base Map supplied by Shiv. Cylinder wall washing maybe? Oil changes are 2k miles apart at the moment. My concerns are the results of more oil in my catch can latley. I did however turn up the boost to 12-14 psi and that's when I noticed more blowby. I am curious as to how to gauge what is "normal" for blowby on a built engine. Also, as the oil breaks down, I am assuming the oil is more likely to "squeak by" the rings as the oil grows more and more thin over time. Would that be a fair assumption? I guess I will have to see how things go over time. Thanks for the help so far Greg.
Paul...
12-07-2002, 01:10 PM
#6
Dork
Join Date: Nov 2002
Location: SF Bay Area
Posts: 144
Car Info: 2005 STi, 2005 OXT
Hello,
I might have missed something. How do you know you're getting whatever amount of blowby that you're getting - what are you measuring that with / what tipped you off?
Joel, with some experience building subaru motors
I might have missed something. How do you know you're getting whatever amount of blowby that you're getting - what are you measuring that with / what tipped you off?
Joel, with some experience building subaru motors
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