Backpressure Causing Problem - Team Camaro Tech
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post #1 of 12 (permalink) Old Sep 29th, 09, 05:46 PM Thread Starter
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Backpressure Causing Problem

Long post, sorry. After doing a lot searching here and other forums, I thought I would throw out my question concerning backpressure and crankcase pressure. Is it possible to have excess crankcase pressure at higher rpm's due to a constrictive exhuast y-pipe? The reason I ask is because I have had the same problem with 2 different motors in the same car and the common denominator is the y-pipe that comes off the shorty headers. The first motor was a built 355 that would blow oil vapor all over the passenger side valve cover, with or without the pcv in place of 2 breathers as well as a small leak from the back of the oil pan and it was not the main seal. I sold that motor to a friend who dropped it into his car and he had neither problem with the motor. I built the 406 that I dropped into it this spring and the exact same problem with oil vapor and small leak at the back of the oil pan with or without a pcv on this engine. Right now I am in the process of putting a breather catch can assembly in to at least capture the oil the accumulates from the breather. There is no motor problem, I am not burning any oil and there is no sign of oil anywere in the combustion chamber, spark plugs, valves etc. compression is good in all cylinders with no pressure loss. I am really thinking it has to do with the y-pipe that is on the car and am saving money for long tube headers from Stainless works with their matching straight y-pipe fro 82-92 camaros. Again, sorry for the long post but I really wonder if I'm going in the right direction with this since the those headers and y-pipe are about $1100.00 and could use others input or ideas. Thoughts??
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post #2 of 12 (permalink) Old Sep 29th, 09, 05:55 PM
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Re: Backpressure Causing Problem

Rig up a 0-15 PSI gauge in the exhaust system, substitute the divertor valve on the air tube would be good, maybe the O2 sensor location is better, someplace before the single pipe from the Y, or drill & tap the Y for a barb fitting, you can always plug it with a brass pipe plug.

Hard line for the first 1-2 feet due to heat, then run the gauge inside the interior. Road test the car. Start at 30 mph to 70 mph WOT, if gauge registers over 3.5 psi, restrictive exhaust. Also, if you run a vacuum gauge from the intake inside, vacuum gauge will not go to zero for the same reason.

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post #3 of 12 (permalink) Old Sep 29th, 09, 06:06 PM Thread Starter
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Re: Backpressure Causing Problem

Thanks for the quick reply, I have never heard of doing what you describe above and I guess really didn't know that the vacumm gauge not going to zero would show the same problem. Question, when you say that the vacumm gauge will not go to zero, at what rpm are we talking about? Like I said, this has been very puzzling to me since both motors had the exact same problem but same exhaust with the exception of the Flowmaster 3" exhaust system I put on this winter while the car was stored.

White and silver 82 Z-28 with a built 406 running a built 700R4 trans with 3000 stall convertor with 3.73 rear gears. Maroon interior with B+M mega shifter Autometer gauges. Custom 17" wheels and tires and C-5 Vette front brakes. Rear discs coming.
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post #4 of 12 (permalink) Old Sep 29th, 09, 06:16 PM
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Re: Backpressure Causing Problem

I think it's a coincidence. You're going to to get some oil slag without a catch can with or without a pcv valve if you drive hard. Maybe you pushed the motor harder than your buddy. I'm running a catch can on my big block and get no oil slag all over.
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post #5 of 12 (permalink) Old Sep 29th, 09, 06:22 PM Thread Starter
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Re: Backpressure Causing Problem

Well it's true that i do like to drive it hard at times since that is what i built for and as for my buddy with my old engine, he drives it harder than I did and more frequently too. His car runs hooker long tubes with dual exhaust, my car has shorty headers with the y-pipe going into the 3" exhaust. My y-pipe makes some serious bends and gets down to at least 2-2 1/4" where it runs by the crossmember and when it bends and turns under the passenger side of the car before heading back towards the center of the car.

White and silver 82 Z-28 with a built 406 running a built 700R4 trans with 3000 stall convertor with 3.73 rear gears. Maroon interior with B+M mega shifter Autometer gauges. Custom 17" wheels and tires and C-5 Vette front brakes. Rear discs coming.
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post #6 of 12 (permalink) Old Sep 29th, 09, 06:25 PM
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Re: Backpressure Causing Problem

How dose your buddy have his Positive Crank Venting...

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post #7 of 12 (permalink) Old Sep 29th, 09, 06:29 PM
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Re: Backpressure Causing Problem

You clearly need a good exhaust system anyway. Your combo needs 2.5 per side. I guess it could cause excess backpressure and a bad ring seal.
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post #8 of 12 (permalink) Old Sep 29th, 09, 06:32 PM Thread Starter
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Re: Backpressure Causing Problem

He has the same type valve covers and baffles with the same setup I have been using, breather on pass cover with a nipple and tube to his air cleaner and a pcv on the drivers side cover. Only difference between him and I is that I get more vapors and oil than he does. I had that motor in my car for about 5 years and put only about 5000 miles on it when I sold it to him and the entire time I had it in my car I had the problem that he doesn't have. He didn't change anything on the motor since I sold it to him carb to pan. He put his own serpentine system on for his alt and power steering but that's pretty much it. He runs that engine to 6800 with no issues.

White and silver 82 Z-28 with a built 406 running a built 700R4 trans with 3000 stall convertor with 3.73 rear gears. Maroon interior with B+M mega shifter Autometer gauges. Custom 17" wheels and tires and C-5 Vette front brakes. Rear discs coming.
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post #9 of 12 (permalink) Old Sep 29th, 09, 06:34 PM Thread Starter
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Re: Backpressure Causing Problem

Quote:
Originally Posted by Vegas69 View Post
You clearly need a good exhaust system anyway. Your combo needs 2.5 per side. I guess it could cause excess backpressure and a bad ring seal.
That's what I a begining to think that the restrictive y-pipe is causing my problem. This 406 is pushing more compression and the Dart heads are bigger breathing and flow so much more. The long tubes I am looking at runs 2.5" back to a huge collector that runs down to the 3" to hook it up to Flowmaster system. Thanks for all the replies and food for thought.

White and silver 82 Z-28 with a built 406 running a built 700R4 trans with 3000 stall convertor with 3.73 rear gears. Maroon interior with B+M mega shifter Autometer gauges. Custom 17" wheels and tires and C-5 Vette front brakes. Rear discs coming.
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post #10 of 12 (permalink) Old Sep 29th, 09, 07:43 PM
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Re: Backpressure Causing Problem

Quote:
Originally Posted by cc82z-28 View Post
question, when you say that the vacumm gauge will not go to zero, at what rpm are we talking about?
wot

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post #11 of 12 (permalink) Old Sep 29th, 09, 08:55 PM
 
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Re: Backpressure Causing Problem

you could also have a plugged cat converter. install the backpressure gauge into the exhaust system as described above and see.
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post #12 of 12 (permalink) Old Sep 30th, 09, 01:25 PM Thread Starter
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Re: Backpressure Causing Problem

Quote:
Originally Posted by WJPE View Post
you could also have a plugged cat converter. install the backpressure gauge into the exhaust system as described above and see.
Not running one. Car is actually old enough to qualify as a historical vehicle here in Ohio. I only put about 600-1000 miles on it during the about 4-5 months of good weather. It's a hot rod for me.

White and silver 82 Z-28 with a built 406 running a built 700R4 trans with 3000 stall convertor with 3.73 rear gears. Maroon interior with B+M mega shifter Autometer gauges. Custom 17" wheels and tires and C-5 Vette front brakes. Rear discs coming.
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