THE PORTAL HUB - Pinzgauers, Haflingers, Volvo 303s and more!

ok i have installed a magnaflow exaust there are no chambers more or less stright through muffler yes it is alot louder. i went with it cause it was stainless and thats what tubing i like to use but i find that going down hill i get small backfires like harley's get. i was wandering if i need more back presure in the muffler but if i pull the choke out halfway or more they go away here are some pics if i can figure out how to add them.

So it is the trophy wife of exhaust systems - beautiful, but not functional.

The engine was designed around an expected backpressure. You have decreased the backpressure, which is apparently leaning out the mixture, leading to backfiring. Lean mixtures also burn valves...I don't know enough about it to say how lean the mixture has to be in order to cause damage.

Check out this site:

http://www.uucmotorwerks.com/html_produ ... uemyth.htm

-Evan

712 with standard exhaust, and I backfire when going down hill in 3rd gear (engine braking), stops when I give it some gas. Does this mean I'm burning my valves?

For backfiring to happen, you need fuel and oxygen. Normal rich running uses up all the oxygen in the air/fuel mixture. so what leaves the exhaust port cannot further combust. If you have an exhaust leak, air can make its way into the system giving you again a air/fuel mixture, which can backfire. When coasting or decelaration you would be pulling very rich mixture into the cylinders, so lean conditions at the exhast valve are unlikely.

The valve burning happens because in lean conditions you have unused oxygen going past the valve. The oxygen is very hot and very active, and reacts with the metal of the valve (and probably seat?) on the way past.

Anyway, I'd bet you are looking at an exhaust leak. Hopefully someone with more intimate knowledge will chime in.

-Evan

Paul, regardless of the popping, id recommend mounting the exhaust a bit more stable than just hanging. The flex pipes cannot handle the constant movement

Can't he adjust the carbs to run a little richer to compensate and he'll be gaining horsepower? Thats what I took away from the article link. A new exhaust was always the first performance upgrade when working on aircooled VWs

Performance carburators usually, in my understanding, have numerous jets available to allow you to fine tune the mixture. The Pinz doesn't have a range of jets to choose from.

Of course, someone could drill out the jets to create a richer mixture. This is getting way past my skill level!

I am actually part way through my own homebrew EFI system using motorcycle throttle bodies. For that I want to mesure the exhaust gas oxygen level with a wideband O2 sensor to tune the system. Products like:

http://www.innovatemotorsports.com/products/lm2.php

are very useful for tuning. The wideband sensor I bought actually plugs into a laptop for stand-alone use, or into my MegaSquirt controller for whole engine control.

-Evan

I've removed my Exhaust to play around with some settings. If I were you playing around I'd check the timing.

Erik,

You kinda lost me. What are you implying with the statement about driving around with the exhaust off?

-Evan

The pinz engine is designed to run period. as shown with those of us with EFI nothing will improve it. You can improve the back pressure or allow the engine to breath easier but it's not going to show any gains. I've leaned my pinz to the point were there is no power as long as I could keep it consistent with all four cylinders I really didn't see it burning valves. Now run it rich and you'l see it in the oil. As your washing the washing the rings. My guess is he more than likely had a problem before but it is more apparent now that he can hear what is going on. I've driven twenty to thirty pinzgauers now. two not gas some I have noticed some form of exhaust leak as you have mentioned but most have the timing way off or valves not checked since they were sold by the Swiss. Figure that's twenty years now.

Erik you bring up a valid point and one I have noticed that most people forget..both mechanics...and laypeople...start at the basics!!!! determine wether your timing is spot on...adjust your valves...check for vacuum leaks..these are all contributing factors to backfiring, poor engine performance...drivability issues...ignition issues. Once you have determined that those issues are as per specifications then and only then can you determine wether there is another issue that is causing a problem...and I would dare say that if and only if the magnaflow exhaust is the culprit of this backfiring issue..a simple added baffle added to the system would curtail the backfiring.....just my 2 cents

I beleive T-Lo has been selling a Magnaflow bolt on kit for awhile now? Could be wrong but he has it listed on his website.