Running rich

lyeinyoureye · Post by **lyeinyoureye** » Fri Sep 14, 2007 3:45 pm

After looking at the volumetric eff curve for the 1.6L NA, I can see how bumping up the fueling a bit can help out w/ low/mid rpm torque, but what does all this excess smoke do to top end power? Can too much fuel actually hurt power compared to an engine running a leaner, relatively smoke free mixture? Based on the 1.5L BSFC graph, it seems like extra fuel definitely hurts the efficiency of combustion above half load past a certain point, so can too much fuel start hurting efficiency even more than it helps power, with the end result being a drop in high rpm power with the mixture past some point?

VWCaddy · Post by **VWCaddy** » Fri Sep 14, 2007 9:52 pm

Too much fuel case result in excess soot and that can clog up the internals of the engine and might also cause too high a combustion temperature. That is sort of the upper limit of diesels, fuel wise, or rather you can get the air/fuel ratio down to the stoich. limit (or within a certain percentage of that). Go below that stoich. ratio and you can't burn all the fuel and get soot and what not. That is the reason that propane fumigation/injection works. It is a clean burning fuel and is able to make use of the excess oxygen in the cylinder to burn and produce power without the resultant soot formation.

http://www.leeric.lsu.edu/bgbb/7/ecep/diesel/i/i.htm
http://www.diesel-central.com/News/cackle.htm

A1-2-A3 · Post by **A1-2-A3** » Fri Sep 14, 2007 9:53 pm

Without a turbo I would say yeah, they sure don't gain much at higher rpms even with more fuel. It would need AIR!!

lyeinyoureye · Post by **lyeinyoureye** » Fri Sep 14, 2007 10:51 pm

That sounds like what I've experienced. It feels like I had more power up top once I turned the smoke screw down, just less torque down low, and next to no smoke. I think turbo wouldn't see this since, at least not for a while, since the more power it makes, the more air it gets, up to a point.