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Old 01-22-2006, 11:02 AM
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671 Blower

Hi, this is deno. I just have one question about my 671. Is it normal to get suction from the breather holes in the valve covers

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Old 01-23-2006, 06:18 PM
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no, usually its the other way around.
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Old 01-24-2006, 04:16 AM
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re:671

What do you think the problem could be? Thanks deno--
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Old 01-24-2006, 07:07 AM
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Is the valve cover hooked up to the carb base? PCV?
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Old 01-24-2006, 04:29 PM
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re:671 blower

No PCV, just breathers on the valve covers. If I take off the breathers and put my hand over the breather hole on the left or right bank, I get a suction. Thanks, deno---
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Old 01-24-2006, 06:33 PM
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Is the suction your getting at idle? Does it run good ? Has it always done it?
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Old 01-25-2006, 04:50 PM
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re: 671 blower

I know it does it at idle, but I didn't try it at high RPM. Every time I change the plugs it runs good , then I re start the engine the next morning, the plugs are fouled out with oil and gas. I installed new intake valve seals also. I think that I should Re ring it, change the heads, and check the cam. What do you think I should do? The heads are 1967 302/ 327 202- 160's with 66cc chambers. I think that 72cc chambers would be good for the engine. What do you think? Thanks deno---
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Old 01-25-2006, 05:11 PM
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If your rings were bad you would have blow-by pressure and poil coming out of the valve covers.

How do you start your car? With a blower you want to hit the gas once, and then start the car. Do not pump the gas or open the throttle while trying to start it.

Make sure your carbs aren't leaking down and flooding the engine.

Is it gas or oil on your plugs? Are you replacing the plugs or just cleaning the old ones?
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Old 01-25-2006, 06:01 PM
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re:671 blowre

I replaced the plugs three times. I start the the engine once , and it's OK. I pump the gas once, then let off then turn the engine over. the engine will misfire the day after it ran good, but smoked when warmed up. Oil smoke, not gas. I have two 850 Demon carbs on it. The idle mixture screws are in 1/2 turn before the stop. Thanks deno---
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Old 01-25-2006, 07:12 PM
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I've heard of n/a engines getting a suction at idle through the breathers, but its caused by a plugged air filter. I would start by doing a compression and leak down test to see whats goin on. Forget the blower is even on there, and make sure the mechanicals are good. Look for 100 to 160psi on the compression and 10-15% on the leak down. Any weird #'s might mean a problem in the cylinder or a wiped out lobe.
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Old 01-25-2006, 07:13 PM
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Sounds like it is time to compression check and/or leakdown the cylinders.

Check valve lash and cut the oil filter open.
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Old 01-25-2006, 08:00 PM
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How does your oil look? How does it smell? I wonder if you didn't wash down the cylinders a few too many times. What size engine?

With a blown engine you need to keep tabs on your oil, it is not hard to get gas in your oil/crankcase, this is not great for bearings or rings.

From the sounds of it a compression check might be the next step. I still don;t understand how you would have vacuum in your valve covers if you had leaky or bad rings. With the blower I would expect more blow by that a N/A engine.
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Old 01-25-2006, 09:02 PM
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I'd be looking for an intake gasket that was pushed out (lifter valley). You'd end up with suction at times when the vaccuum is high (idle and decel). That would pull a lot of oil through the motor and easily foul plugs. It would most likely look like a bad blow by condition when you build boost and push some oil out the breathers.
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Old 01-26-2006, 04:35 PM
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re:671 Blower

I did a compression test, and all cylinders were at 120 to 125. I did a leak-down test, all cylinders averaged 10 pounds loss , starting at 100 pounds of pressure. pressure dropped to 90 pounds of pressure. The oil is new and the oil filter is new. I adjusted all valves to just short of 1/2 turn after 0 lash. I have hydraulic lifters. Also I adjusted them at the bottom of the cam. The engine was built by Big Alls toy box. I called him and he told me that I would get some suction from the breathers. The engine is a 355. No gas in the oil. Thanks deno--
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Old 01-27-2006, 12:24 AM
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I think you have too much carb on the engine too. Two 850's on a 355 is a little much.

Are you using any oil? If not the smoke you see is not from burning oil. I would bet you are way rich and that's where your problem is.

How much boost are you running? The compression and leak down, prove your cylinders are sealing fine.

You need to figure out what is fouling the plugs (gas or oil). I don't see how it can be oil if your cylinders are sealing fine.
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