High flow exhaust

[coolram]

I just replaced my muffler with a Dynomax Super Turbo p#17733(not as quiet as "70" Flowmaster but $70.00 cheaper and supposedly flows better in the 1500->2500rpm)and "serviced" my cat(will replace with a high-flow when I have the $$).I definitly recommend doing this along with the TFI upgrade which I've done too.What a difference.All to do now is adjust carb and timing.

I've noticed a lot of posts about pinging after extended freeway driving.Could a overheated cat(from being partially clogged)cause this?I disconnected my vac advance(after trying to adjust it) and she doesn't ping.I'm going to hook it back up and see what happens.Just a thought.

[ April 13, 2002: Message edited by: coolram ]</p>

[Jerk]

hey! :D I would leave off the vac advance and see if it pings FIRST, then try it with it on. Or atleast pull the manifold vac line and plug it and just run strait PORTED vac to the distributor. Manifold vac is only needed for smoother idle at cold startup, once the engine warms, the CTO (Coolant Temperature Overide) switches the vac advance to PORTED Vacuum instead of MANIFOLD Vacuum. MOST ALL POST 79 V8 WAGS AND CHERS HAVE A PINGING PROBLEM at one point in the driving range anyway...they are just setup too lean , check your timing with a gun that you can dial in advance as rpm climbs, I bet its clocking 42* total at around 3000 rpm! that is way too much for any vehicle, let alone one that uses unleaded gas and is carburated to run lean anyway!most race cars dont run more than 36 to 38 degrees total, of course they run higher octane and way richer too. - Matt

[jeepbob]

Vac advance only works at high manifold vac and this is to increase ign timing at low engine loads for better economy. By going to a higher flow exhaust system it is possible to have leaned out the fuel mixture. You may have to go to larger jets in the carb. A lean mixture will cause ping. Also check te operation of the EGR valve, its function is to slow the rate of combustion by introducing exhaust gasses into the mixture, having the carbon monoxide combine with oxygen in the mix to create carbon dioxide. What this does is lower the amount of oxygen available to burn and lower CO emmisions. This is why modern motors run a leaner mixture. There are a couple more things to check, As Matt suggested you may have too much timing in the motor, I would stt by checking the initial timing, it should be no more than 11 to 12 degrees. If the motor seems to need more than this, I would check the timing chain for stretch as this is the first signs of a worn chain. A worn chain will cause a definite lack of power at lower ign timing settings, and when the timing is advanced the power picks up but the rig gets harder to start esp when warm. You will notice the starter being "bucked" by the motor, this seems like the battery is down or the starter is bad but what it really is happening is the mixturing being fired on the upstroke of the piston and actualy stoping or slowing the starter. This is a common problem on AMC motors. This is also the cause of most of the ping that people complain about. There is a retrofit anti ping kit but from what I can see all it does is cover up the symptons.

[Rogue]

just thought you'd like to know jeepbob, egr lowers nox (oxides of nitrogen) emissions, not that it matters just thought you'd like to know

[jeepbob]

OOPs, I knew it was one of them. It is the air injection pump that lowers the CO emmisions.

[ April 14, 2002: Message edited by: jeepbob ]</p>

[coolram]

Thankyou for the suggestions.At least I'm on the right track from what your'e saying.My timing is set at 8 degrees,carb is set at 1 turn,always run premium which may or may not be necessary now and I've tried adjusting the vacuum advance(got it and the EGR hooked to ported source for now bypassing the CTOs MattW I tried disconnecting vac advance and she doesn't ping and seems to run better).I found the brick in the cat had broken up and would clog to the point that I got black smoke(like she was rich)and a very rough idle.Very definite change with the exhaust(noticable throttle difference)Got my exhaust problem solved now I'll play with mixture and timing to see what happens.