Problems arising from restricted exhaust
08-10-2004, 03:01 PM
#1
Problems arising from restricted exhaust
I tagged this on to my last post about thru prop exhaust,but figured I'd ask this one in general too. I currently have an excessive lean condition with my motor 383 SBC (see Max HP thro prop exhast post). I have put in what JET fuel systems considers pretty rich secondary rods (AX) in the carburator (Quadrajet). Under WOT conditions the motor would ping from the lean condition. With the original sec. metering rods (DA) it would ping weither it was at normal full advance (35*) or reduced (31*). The AX rods worked didn't ping at 31 but did at 35. Is it possible my thru prop exhaust is so restrictive that I am having some ehaust reversion like an EGR valve and that is causing my cylinders to not fill up with a nice rich intake charge? The plugs are coloring oddly. The insulator is like new white (lean) and the side electrode has evidence of minor overheating (slight blue tinge) and the exposed metal sides of the sparkplug are dark black (a little to dark in my opinion for a lean condition). Is this characteristic of what I think my problem is?
08-10-2004, 04:11 PM
#2
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Re: Problems arising from restricted exhaust
There is a thread around here about how to read spark plugs. It's very good interesting reading. If the ring at the tip of the plug is black, you probably aren't lean provided you shut down properly. Is this a new engine? Do you have previous experience with it? 35 timing is a lot in a smallblock. Maybe that's where the problem is.
08-10-2004, 06:27 PM
#3
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Re: Problems arising from restricted exhaust
I am having a simular problem with a stock 454 with a quadrojet. It begins to ping under load but it is not hot and the timing is 8 degree's. what I found is that my secondary's are not oppening properly which causes the lean condition I am thinking!
08-10-2004, 09:00 PM
#4
Re: Problems arising from restricted exhaust
Formula.. Yeah I checked the secondaries yesterday. Had a buddy back there watching them and told him to push them open if it did't do it all the way by itselt. I'm going to start experimenting with the removal of the reversion flappers and switching to the bravo slip type exhaust bellows that disconnects when trimmed up. Goin to go put that on now. seeya
