Has anyone determined how any of the plenum or spacer mods affect gas mileage? I also have the same question if you have the mod *and* the TS reflash.

Also pardon me for asking such a question about a horsepower mod.

 

I did notice in the plenum mod review in "Sport Z" magazine that the A/F ratio went up for the Crawford plenum and 1/2" Motordyne spacer but down for the 5/16" spacer.

 

Hey there.

I had my plenum, cats, and grounding kit all installed at the same time. I have not noticed any changes to my gas mileage.

 

So what does this mean? Is this good or bad?

 

The higher the A/F (Air-to-Fuel) ratio, the leaner the mixture, the better the mileage.

Leaner mixtures also run hotter and produce more power.

 

Please why, or how does leaner mixture produce more power? Thanks

According to some graph (don’t remember where I found it) floating on the net:
14.7:1 is ideal
15.4:1 is best fuel economy
12.6:1 is max power

 

Thermodynamically, 14.7:1 will product max power. This is the stoichiometric ideal, with nothing wasted. Running rich reduces the oxygen that is available to facilitate combustion. Running slightly lean increases the available oxygen. With more oxygen in the chamber, combustion runs hotter. The hotter the combustion temperature, the more power that is produced.

There may be some variables I'm not taking into account, but that's a fundamentals point-of-view.

In jet engines, which run a similar thermodynamic cycle to automotive engines, the limiting factor for both power produced and combustion efficiency is the temperture that can be withstood by the metals just after the combustion chamber.

Oh great...now I seem like a nerd!

 

Sorry to correct you hear, but the best Air to fuel ratio to maximize HP is between 12.5:1 to 13.5:1. If you ever go to a dyno shop to get your car tuned, they will adjust the air fuel ratio to around 13:1. I had a Mitsubishi Eclipse before my G, and it would run pig rich after I added some headers. With a piggy back system I bought, I took it to a dyno shop and they tuned the car around 13:1 compared to running 9:1 at WOT!!! Cars are suppose to run 14.7:1 under normal load.

 

The richer than 14.7 AF is used to cool the combusion chamber and to slow the flame burning speed.

Having just enough fuel molecules for the air always fails as the probabilities of 100% combustion cannot be achieved in the short time alloted.........adding more fuel raises the probabilities while increasing the time that it can occur in.

The extra unburned fuel cools everything..........really depends on the cats and in how many seconds you want them to melt.

 

Both of your comments make sense. Thanks! I'll look forward to my dyno tuning.