Excessive Blowby?

S

smudgie

New Member

Feb 8, 2006

6

0

0

Feb 13, 2006

#1

• Feb 13, 2006

• #1

I have a '71 302 in my 66, It has '78 351W heads, Hi Perf. cam, Edelbrock intake, Holley 650 carb, headers.

I have just had the heads rebuilt. They were used when I first installed them and they needed it bad..

BUT I still have excessive blowby... The engine runs fine, good HP, But has a smokin' problem. Is it likely the rings? if it is there anything that I can do to live with the problem or use as a band aid? I do not want to put the effort and $$ into rebuilding this block..

any help or answers are appreciated..

 

thehueypilot

Active Member

Feb 25, 2004

1,084

0

37

Medina,Tennessee

Feb 13, 2006

#2

• Feb 13, 2006

• #2

It sounds like the rings/cylinders are worn out. You can put "STP" into the oil which will reduce the blowby a little or you can run thicker oil which will do the same thing. I think they still sell "overhaul" in a can which is the same thing as "STP" ..... otherwise you are just wasting money. Save it for a rebuild kit.

 

LUCAFU1

Founding Member

Apr 19, 2001

496

0

16

Tucson

Feb 13, 2006

#3

• Feb 13, 2006

• #3

your not using synthetic are you?

 

S

smudgie

New Member

Feb 8, 2006

6

0

0

Feb 14, 2006

#4

• Feb 14, 2006

• #4

No synthetic oil used.. How heavy an oil would be O.K. Could I go to SAE30 or higher? I don't drive this car during freezing temps but it does get started on mornings when we are in the 40's. I have tried one can of STP without much luck...

How about piping the breather from the valve cover down under the car so it is dissipated better by the fan. Currently it is coming up through the gaps around the hood... Looks bad, Just a little embarassing...

Thanks,

 

72grande

Founding Member

May 27, 2002

676

0

0

Sunny D

Feb 14, 2006

#5

• Feb 14, 2006

• #5

The smoke you're worried about is comming out your valve covers and not the tailpipe? If so you dont really have a problem. Just need to get you PCV system hooked up correctly.

 

302 coupe

Founding Member

Mar 2, 2000

1,952

3

36

Macon, Ga.

Feb 14, 2006

#6

• Feb 14, 2006

• #6

yeah, just get your PCV stuff hooked up right. They will all smoke if you just have breathers that vent to the atmosphere. However, if its enough smoke to puff out around the hood, you may still have a problem.


As a side note, you would have been better off having the 71 302 heads rebuilt. The "78 351W" heads have the same tiny valves and poor flowing ports, but with the added feature of huge combustion chambers that lower your compression ratio. 69-70 351W heads are the only ones worth swapping with their bigger valves and larger intake port and more compression friendly chamber. I hope you didn't spend much on them.

 

S

smudgie

New Member

Feb 8, 2006

6

0

0

Feb 14, 2006

#7

• Feb 14, 2006

• #7

Thanks for the input...

The next question is how to hook up the PCV system correctly?

I have a K&N filter on the drivers side valve cover "spout?"

On the passenger side I have put in a PCV valve that presses into the rubber grommet. Then hooked this up to the large vacuum port on the back of the carb. This reduced vacuum seriously and the engine ran poor but the smoke stopped coming from the drivers side through the filter.

I then tried hooking the PCV valve to the underside of the open element air filter. This caused it to smoke at idle but less so at higher rpms.. or maybe the fan was just blowing it all away.

Thanks for your help and suggestions.

 

wild70stang

New Member

Nov 11, 2005

317

0

0

Feb 15, 2006

#8

• Feb 15, 2006

• #8

Sorry to maybe hijack this, but I know dittally squat about the function of a breather. I know that you can either put a filter on the top of them, or (for stock) you run a hose to the air cleaner. If oil runs out of the breathers why do you want to run a hose to your filter and get oil in it?

 

72grande

Founding Member

May 27, 2002

676

0

0

Sunny D

Feb 15, 2006

#9

• Feb 15, 2006

• #9

smudgie said:

Thanks for the input...

The next question is how to hook up the PCV system correctly?

I have a K&N filter on the drivers side valve cover "spout?"

On the passenger side I have put in a PCV valve that presses into the rubber grommet. Then hooked this up to the large vacuum port on the back of the carb. This reduced vacuum seriously and the engine ran poor but the smoke stopped coming from the drivers side through the filter.

I then tried hooking the PCV valve to the underside of the open element air filter. This caused it to smoke at idle but less so at higher rpms.. or maybe the fan was just blowing it all away.

Thanks for your help and suggestions.

Click to expand...

I dont know about the 302's, but on my 351c its exactly the opposite. The valve is on the drivers side, and the filter on the passenger side. And you may have to adjust your idle circuit a little afterwards.

 

Tim65GT

Active Member

Feb 24, 2004

1,149

2

39

West Texas

Feb 15, 2006

#10

• Feb 15, 2006

• #10

Here is a link to explain the PCV:

http://www.carcarecouncil.org/Engine/crankcase_vent.shtml

The breather to Air filter connection allows the excess blowby to get sucked into the engine and burned.

It's better than having it run down the valve covers and all over.

Here is a basic diagram of how mine is:

 

Attachments

• PCV.webp

  3.7 KB · Views: 231

wild70stang

New Member

Nov 11, 2005

317

0

0

Feb 15, 2006

#11

• Feb 15, 2006

• #11

Thanks
One step closer to understanding proper engine care