Exhaust leak?

FFRBob · #1 (**permalink**) 08-12-2007, 02:33 PM

I've got a fluttering noise that's starting to get more noticeable. The 390 FE is newly rebuilt with a hydraulic flat tappet cam. I broke in the cam with crane cams break in lube and 30wt Rotella by running the car for 10 mins at 2000 rpm. I had to stop to let it cool down, then ran it for 5 more minutes, let it cool down and a final 5 minutes all at 2k rpm. The timing is set at 12 degrees initial with 24 total advance. I did an oil change immediately after break in and didn't notice anything unusual in the oil, but I did not cut open the filter.

I now have about 30 miles on the motor and I'm starting to get a fluttering noise from the engine compartment; it doesn't sound like it's coming from the pipes. It's more obvious when the car is warm and it increases with the rpms. Please say this sounds like an exhaust leak and not a flattened lobe

It's definately not a ticking noise and the car doesn't backfire. I do notice a bit of an initial flat spot when I stab the gas to half throttle, but then it takes off like a rocket. I jetted the carb down one size, but I think I need to jet down one more since I'm at 3500 feet elevation and the plugs were pretty black.

Anyway, help me FE gurus. Thanks in advance.

FFR Bob

MaSnaka · #2 (**permalink**) 08-12-2007, 06:59 PM

Is it possible you have a plug thats not firing? I would associate an exhaust leak with a ticking noise and or backfire at deceleration. If it's leaking at the manifold to headers you should see black deposits at the leak. Another thing comes to mind is a valve adjustment after breakin? I'm only throwing stuff out there for you, I'm no guru.

I have a fe390 that was supposedly tuned for 5000 foot elevation where I bought it and it had 66 jets in the primary and 70 in the secondary on a Holley 750. I live much closer to sea level so I had to change them. Hope that helps. Good luck! John

FFRBob · #3 (**permalink**) 08-12-2007, 07:35 PM

I'll check the spark plugs, that's a great idea. I'm running a Holley Street Avenger 670 and it had 66/68 jets in it. The plugs were pretty black so I jetted it down one to 65/67. I may need to go one lower, but I'm more inclined to take it to Westech and have it dyno tuned when I get rid of this fluttering noise. I'm just hoping it's not a flattened lobe.

MaSnaka · #4 (**permalink**) 08-12-2007, 10:23 PM

FFRBob, I'm curious what oil pressure you have? Did you rebuild you motor yourself?
John

FFRBob · #5 (**permalink**) 08-12-2007, 11:09 PM

The oil pressure is around 70 cold and 50 warm at idle. I bought the motor from Tuff Dawg engines on ebay. They have a good reputation.

convincor · #6 (**permalink**) 08-13-2007, 05:47 AM

Hey Bob,
Mine has very similar sound. Won't do it if you rev with no load on it.
Hard acceleration it won't do it. Only seems to be around 2000-2500 rpm under very lite load... Havn't found it yet. Did it with standard adjustible rockers and still the same with Erson rollers.
One thing I did notice is the intake gasket is starting to look like it's going.
Could be split on the bottom of a port and drawing air through a small split??
See toward the end of this thread- Spark plugs: 7 tan, 1 black

FFRBob · #7 (**permalink**) 08-13-2007, 08:32 AM

Thanks, Convincor. I've been following that thread, too. I think I'll call the engine builder and ask which intake gaskets he used. It's time to pull the plugs and see what they say.

convincor · #8 (**permalink**) 09-03-2007, 06:02 AM

Did my intake last week. here's what I found with 1200 miles on Fel-Pro's
http://s101.photobucket.com/albums/m...ake%20gaskets/
Still got the noise, Going to work with it a little today. Going to try backing the timing way down as it almost sounds like it could be detonation...
Someone else I talked to said maybe piston skirt slap from forged pistons but I don't think so. Next would be to drop the pan and check things out..

FFRBob · #9 (**permalink**) 09-03-2007, 08:39 AM

I found a bad spark plug wire. After it was replaced, I've still got the noise. My next step is to find a mechanic to drop it off with. I'm hoping it's a simple valve adjustment.

c6ae · #10 (**permalink**) 09-03-2007, 10:42 AM

24° total advance is not generally considered enough timing for an FE.
36 to 38° total is more common, with even more than that if using a vacuum advance unit.
An old school technique for locating an engine noise (in particular an exhaust leak) is to use a short length of heater hose as a stethoscope and while listening at one end of the hose move it around the engine compartment until you locate the source of the noise.

FFRBob · #11 (**permalink**) 09-03-2007, 01:12 PM

I have 12 degrees initial advance, 24 degrees advance on the distributor for a total of 36 degrees.

FFRBob · #12 (**permalink**) 09-05-2007, 07:46 PM

Well, I called Tuff-Dawg (D&J) Engines. After I explained my issues, he proceeded to ask me about my timing. He got a chuckle out of my initial timing of 12 degrees. That said, he asked me to set the timing using a vacuum gauge. Since my vacuum gauge is at a buddy's house, I bumped the initial up to 16 degrees and the total is now 40, which is a little high and I'll work on that later. Anyhow, the motor sounds completely different now. I can still hear a very slight flutter from the motor when I rev it, but nothing like before. It may be noise coming up the carb, but it's barely audible, so I can live with it until I get a Westech tune. Oh yeah, it's got A LOT more pickup now. Holy smokes, I love big-blocks.



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