how bad is blowby

[bingisSD]

when i took off my oil cap the other day I realized that I have really really bad blowby (you know, where puffs of air blow out the top of the valve cover). how damaging is blowby to performance! I raced my friend who bought my b16a del sol and we were neck and neck until third gear when he took off on me (and the mid 90's bmw 328i on my other side took off after third gear as well.

basically i know my piston rings are shot out like a hippies teeth, but how much blowby is too much and how is excessive blowby affecting my performance N stuff

[Miataracer]

Just because you have air pushing out of the oil filler when the cap is off does not mean your rings are bad. There is almost always some air coming out of the bottom end of an engine like that. That is why that little return line goes from the valve cover into the intake. It recirculates that air that comes out back through the engine. Have you checked the compression? If you do have low compression that means there could be a problem, especially if it is mostly at a certain cylinder.

[honda_luvr_2000]

well blowby dilutes motor oil. u'r car has a way of getting a good amount of the bad fumes out of the crankcase like Miataracer said, but not quite how he said.
U have a PCV (Positive Crankcase Ventilation) sytem on u'r car. the PCV valve is on the back of the engine and has a vacuum hose running into the intake manifold. thus the PCV valve runs off of manifold vacuum. when the car idles it has high manifold vacuum, and when it's at WOT it has low manifold vacuum. there is a "plunger" in the PCV valve that is pulled up at idle by the high vacuum, and allows only a small amount of the fumes to come out so it doesn't choke the engine. at WOT there is less vacuum, so it drops the plunger more so that more fumes can come out and be burned off. the tube that comes "from" the valve cover "to" the intake tube, is actually coming from the intake tube TO the valve cover, bringing in fresh clean air to positively replace the fumes in the crankcase. unfortunately this system can't completely compensate for BAD blowby as u said u think u have.

as for how excessive blowby would hurt u'r performance, u'll have less compression on the compression stroke, and less pushing force on the power stroke, so u'll actually be losing efficiency twice every cycle of the cylinder. u'll lose power, torque, acceleration, and MPG. more noticeable w/ more blowby.

[Miataracer]

maybe he has a bad pcv valve

[honda_luvr_2000]

so then what does the PCV valve do?

[honda_luvr_2000]

what air does it control?

[honda_luvr_2000]

well since u won't say, i will.
take the tube off when u r running the car and stick a piece of paper over the end of the tube. it will stick. even w/ u'r finger u can feel a slight suction. yeah no air blows out the hole in the intake, because it is being sucked into the engine, but when the hose is hooked up, it will pull a small bit of air. trust me i know how this works. yes a car has low PORTED vacuum at idle and high PORTED vacuum at WOT. but i said MANIFOLD vacuum. u r right that the PCV valve is a check valve and only allows air to travel in one direction. that is to safegaurd against backfires so they don't shoot up the intake port, thru the intake manifold runner, into the intake manifold, out the PCV valve vacuum line, thru the PCV valve, into the crankcase and ignite the fumes down there. it also, due to the applied MANIFOLD vacuum, regulates the air flow into the manifold. ask around, read up, test 4 u'rself. i know this system like that back of my hand. i can explain y the manifold vacuum is high at idle and low at WOT, if u want me to, but i'll leave that to the curious to ask. don't try to tell how sumthin works if u have no idea.

[Miataracer]

there are a few things you fail to mention. if you take the tube off things can both stick to it (if you are actually touching it) or be blown away from it (if you have it a small bit away) YOU go out and take the hose off of the valve cover. feel just a bit away from the hose. feel that pulse?


the whole thing about the check vavle being there to stop a backfire from entering the crank case? lol

and excuse me for missing the fact that you were talking about MANIFOLD vacuum. and no, you don't have to explain it. it is really quite simple. when the throttle blade is closed there is a vacuum inside the actual manifold because the engine is still trying to suck in air but it can't get as much with the throttle blade closed. when the throttle blade opens it can get much more air so vacuum inside the manifold goes down while vacuum in the intake itself (which is what I was talking about) increases.

everyone has misunderstandings, I believe I could link people to several you have been involved with the past day or two. so why don't you back off before you tell me what i understand and what i dont?


EDIT:

btw, what did you prove by editing your posts?

[Miataracer]

the funny thing is, there is a good chance what i said is what is wrong with his car. don't you think honda luvr?

[honda_luvr_2000]

well wut did u hide by editing u'rs???? yeah i noticed it. um yes the preventing backfires IS correct. sorry i hate it when people tell me i'mwrong when i know for a fact i am right. i'll let it go no problem. as for blowby, that's not caused by a bad PCV valve. that's bad rings.

the way to check for bad rings, is to pull out the plugs and check them for oil on the ceramic. either u will see it or smell it easily.
the PCV valve would have nothing to do w/ the problem he thinks he has. if he has blow by

[Miataracer]

he doesn't know that he has blow by. he said he thought he had blow by because he has air coming out of his valve cover when he takes the oil cap off? it sounds to me like the engine is performing ok, but is just breathing too much.

so how do you know it has too much blow by?

a better way to tell if his rings are worn out would be a compression check. unless his plugs are pretty new it is hard to tell much of what is going on inside an engine if you have old ass plugs in there

I edited my post after you edited yours

[honda_luvr_2000]

ok i reread wut he said, and it came acrss differently. i thought he said he had blowby in the tru sense, but it seems like he duzn't know for sure wut is causing the air to come out. so if he has blowby in the tru sense, then it's rings. but if he just has a pressure build up in the valve cover then yes u'r right the PCV valve is stuck shut and the hose to the intake tube is clogged w/ crap. so i guess he needs to be a little more descriptive. sorry man i wasn't tryin to be an ass, i just come across that way sumtimes i guess. my bad

[Miataracer]

don't worry about it. misunderstandings happen

[bingisSD]

well thank both of you for the input, miataracer you are a pretty agressive guy, id like to see you out on the track. anywho- ive had two d15's two d16's, and a b16a so far this year and this d16 most certainly has uneven compression in the cylinders to say the least. i dont plan on keeping the motor for long. previous owner trashed it terribly. my question wasnt so much if my excessive blowby was from my fried rings, but rather is there a general rule of thumb for uneven compressions? and yes i have put in new plugs recently. I do not know where my pcv valve is located. is it bolted onto the back of my intake manifold, the head, or the block itself?
my main inquiry was- if I had a piston whos compression ratio was off by 1 or 2 how bad would it be on my performance and if i keep driving it hard it wont last much longer will it.
i still have a totally screwed up idle that i know isnt from my fuel delivery system, i was thinking that maybe it was from a super shot out piston ring.

but no my blowby wasnt from that because i left the cap off for a signaficant amount of time so it wasnt built up pressure from a clogged pcv. oh yeah and i have a p28 connected to my d16z6, yet i redline at 6k, and my vtec never hits. i know single cam vtec is not as noticeable as my old camm'd b16a, but i am still sure its not working and im not gettin any codes..

[honda_luvr_2000]

the idle, early redline, and lack of VTEC sounds like u might have a bad sensor sumwhere, which can happen w/o throwing codes, but not too often.
the PCV valve is on the back side of the engine itself, on the head. I'm pretty sure the vacuum hose off of it comes up between the #3 and #4 intake manifold runners. so just follow it down to the sensor.
i'd say check the plugs and see how they look since u said they r fairly new. a compression test will tell u if u have a leak, but it will still be one of five things that is leaking. intake valves, exhaust valves, spark plug, head gasket, piston rings.
if one cylinder's C/R is 1 or 2 off, that could have a deadly effect on u'r crank. as the it turns, it receives pulses of thrust from each piston being shot down. if one is being shot down significantly less than the others, it will give the crank more time to slow down before the next stronger piston, and could eventually snap it.

on a side note: i'll take that d16 off u'r hands if u'r lookin to get rid of it soon