[albyneau]

Originally Posted by rmay635703

In reality there really aren't any EPA approved conversions unless it came from the factory, morally however why bother?

Not sure what's meant here by "morally", BUT~
I was doing bi-fuel (petro/CNG) conversions thar were not only EPA approved, but government subsidized as well, back i the early-mid 1990's. Aaah, yes~ here we go:
http://www.arb.ca.gov/msprog/aftermk...s93_022607.pdf
As we all (hopefully) know 49-state emissions regulations pale in comparison to CA's anal outlook on things. These retrofit kits were manufactured by Stewart & Stevenson, piggybacked on the factory ECU, and were relatively (experience as a variable) easy to install. I did several dozen myself while employed in a municipal fleet maintenance garage for a medium-sized (100-250k) city. I even still have the programming software installed on my antique lap- (and I use the term loosely- we're talkin Win95 as cutting edge) top. A search outsde EMod will yield results worth studying as well. The closer you are to mountain/cental time zones the more economical this will be~ as it is there that the largest natural gas field in the world resides, and thereby infrastructure. The farther you get from the sweet spot (between the Rockies and the Mississippi river), the more natural gas will cost you.
BTU's for CNG are in the range of 75-80% of petro-gas, but (at the time I was doing these conversions) the cost per gallon equivalent was in the 40-45% range, and kit price plus labor was around $2000. Supply & demand being what it is, I'm certain the price has dropped...
FYI~
STEWART & STEVENSON LLC (SNS) IPO - NASDAQ.com
The CEO's name sounds remarkably similar to the guy that schooled me back then....
Not gonna type my life away here~ but if you have Q's feel free to PM me!

Peace~
Scott