Need help from internals experts, what amount of blowby is normal at idle?
12-19-2003, 07:48 PM
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Need help from internals experts, what amount of blowby is normal at idle? This is a follow up to a post I had over in the FI section (Hoping to get a little more internals insight over here).
I was getting oil in my intake so I finally removed the PCV system and now have all lines (the back of each valve cover + ls6 valley cover nipple) routed to a breather filter. The PCV nipples on the intake and TB have also been blocked off.
Here is the issue:
The breather smokes while the car is at idle. It’s more like steam (it seems to quickly dissipate and is only really visible just as it comes out). I see the same thing if I open the oil filler cap. I can also put my finger over the nipple on the T where the breather normally sits and it will build pressure (a good bit of air comes out when I remove my finger). Another strange thing is that I routed a line into the car and felt the pressure and observed the flow as the car was being driven under different loads and RPMs. It almost seemed like the amount of air coming out would decrease with higher RPMs and load (more at idle). I was unable to observe at WOT (have to have both hands on the wheels for that and I was alone at the time). As another test, I hooked the line back to the intake nipple just to see if it would create a vacuum in the crank case (without a fresh air source). Sure enough, I could hear a loud sucking noise if I removed the dipstick or the oil filler cap.
What does all this mean? Is it normal blowby or do I have excessive blowby and therefore a ring problem? It has probably been doing this for quite some time, but it is just now visible (without the intake pulling a vacuum on the crankcase).
The heads are brand new (is there anyway it could be related to a valve seal). It seems very unlikely to me.
The car seems to run real strong and all the pistons looked great when I recently had the heads off.
BTW, car has a 2002 ls6 block with stock pistons/rings/crank. It has a blower cam + 71cc ls1 heads and an ATI d1 procharger.
I keep hering some blowby is normal. Does anyone have a good way of explaining what "some" is?
I was getting oil in my intake so I finally removed the PCV system and now have all lines (the back of each valve cover + ls6 valley cover nipple) routed to a breather filter. The PCV nipples on the intake and TB have also been blocked off.
Here is the issue:
The breather smokes while the car is at idle. It’s more like steam (it seems to quickly dissipate and is only really visible just as it comes out). I see the same thing if I open the oil filler cap. I can also put my finger over the nipple on the T where the breather normally sits and it will build pressure (a good bit of air comes out when I remove my finger). Another strange thing is that I routed a line into the car and felt the pressure and observed the flow as the car was being driven under different loads and RPMs. It almost seemed like the amount of air coming out would decrease with higher RPMs and load (more at idle). I was unable to observe at WOT (have to have both hands on the wheels for that and I was alone at the time). As another test, I hooked the line back to the intake nipple just to see if it would create a vacuum in the crank case (without a fresh air source). Sure enough, I could hear a loud sucking noise if I removed the dipstick or the oil filler cap.
What does all this mean? Is it normal blowby or do I have excessive blowby and therefore a ring problem? It has probably been doing this for quite some time, but it is just now visible (without the intake pulling a vacuum on the crankcase).
The heads are brand new (is there anyway it could be related to a valve seal). It seems very unlikely to me.
The car seems to run real strong and all the pistons looked great when I recently had the heads off.
BTW, car has a 2002 ls6 block with stock pistons/rings/crank. It has a blower cam + 71cc ls1 heads and an ATI d1 procharger.
I keep hering some blowby is normal. Does anyone have a good way of explaining what "some" is?
12-24-2003, 11:48 AM
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I have a similar issue but my crankcase pressure is so high that it blows out the dipstick. From the research that I have done seems like a leakdown test is your best bet.
