Reed,
I approached Doc about what to do for torque and mileage. I am at the 30,000 mile point on the build and it is still going up. I am a slow methodical tuner taking lots of notes each step of the way.
To get more torque out of the engine, you could install the 40" long Hooker 3X2 headers with 12" collectors. Summit Racing sells them. This was a mod that along with the Super Six the Chrysler engineer Pete Hagenbuch urged us to do and said it would gain allot of torque as well as mileage. He was trying to get me to do this on my Swinger however, I am still at the point of fine tuning the 1920 Holley thanks to Juan's help "The Argentina Slant Sixer". Apparently on all my 1920 Holley's the low speed idle bleeds are plugged. I have opened the idle air bleed up which has activated the emulsion circuit which has benefited in some nice mileage gains by jetting richer. I am in the process of documenting results with larger jets, one step at a time. Eventually I want to go with a Weiand four barrel manifold and run a two barrel.
I am running the stock 1980 aluminum one barrel manifold with no porting. It warms up quicker over the cast iron for better mileage. When running headers you could run water heat under it at the stove box. I am still using the stock exhaust manifold, however, it has been ported out quite a bit at each port and at the outlet The exhaust ports on my head have not been overly ported but the intake has been opened up to match the gasket along with the bowl porting. This seems to produce some good power along with the taller lift cam which is also advanced 4 degrees. I am getting a little more torque with another thought Dr. Dodge shared with me on the valve lash. For a little more seat time I am at .012 and .022 which also helps with mileage and power.
Since the SL6 has alot of windage and most folks don't run trays or scrapers, I am trying 0-30W Mobil One with a Wix 1806 stand pipe filter which has also has netted another half mile to the gallon increase in mileage. It starts up immediately, is much quieter, runs cooler, has 50 pounds pressure and will go from 60 to 90 in a heart beat.
One of my mileage problems is that now that the engine has allot more power, it is tempting to drive it harder and have some fun.
I went through 3 rear ends in 5 years, so I custom built a 8.75 rear end with 2.76 posi to slow me down but I can still break the rear end loose at a light like it was still running a 3.23.
