1) 73 has the most restrictive emissions, however California had massive emissions requirements before most of the country so a 71,72 Cali car can be equipped with all kinds of crazy smog pumps and EGR valves and delay spark vacuum servos.
from an emissions standpoint a 71 non-cali car is going to be the least restrictive. in 72 gov standards started to kick in mid production cars had changes to the engine open chamber heads, and reduced engine choice combinations, they started to detune the cars. in 73 things really locked down and the emissions restrictions really started nation wide.
if you want a real non-emissions car then you should focus on 1971 models, closed chamber high compression heads V4 4bbl cars Q codes, R codes, M codes, SC, SCJ cars.
1a) Not all emissions stuff is a bad thing.
* PCVs are a very good thing, you want a car with the PCV working. it produces negative pressure in the crack case and stops or reduces oil leaks, stops varnish build up in the heads and removes water from the engine.
* fuel vapor canisters are a very good thing also, they vent the tank remove water and get rid of fuel smell. your fuel tank won't get rustly and varnish won't clog up the vapor return lines.
* Distributor Vaccum Control Valve (DVCV) is another good thing that switches a motor from ported to full mainfold vacuum when the car overheats it increases RPM and advances timing and helps cool down the engine.(its a last resort measure)
2) The FMX and C6 are the same gearing, the difference is the C6 is much lighter then a FMX. the design on both transmissions is different but the gearing for all 3 gears is the same.
The C4 is a good transmission it was mainly for lower displacement like the 302 motors they claim the C4 is good to 400HP while a C6 is good to 600 HP.
a lot of drag guys use built up C4s and claim they drop a little time compared to a C6. they say the C4 is lighter.
For the most part you see C4s on 302, FMX on 351 2bbl cars and C6 on 351 4bbl cars. the hot ticket would be a 351 mated to a C6.
i have a 1972 2bbl originally with a FMX that was rebuilt to a 4bbl with a C6 trans i have open chambered head. so from a performance standpoint it is not ideal does fine on the street.
Hi there.. it's me, asking so many questions again, but just trying to educate myself as much as possible before I invest into my Mach 1. My "third" car garage will be ready this weekend after it is epoxy sealed.
In any case, I have two more questions:
1- Is there any difference in regards to emissions between 71, 72 and 73. I hate this emissions stuff and vacuum lines running everywhere. Have you guys removed some of it?
2- Auto transmissions: C4, C6, FMX. Should I worry about which one? I have read that FMX's are heavy and with no too many aftermaket parts, but at the same time they are strong. C4 and C6 are light and with more aftermarket parts.
Thank you again for the wealth of information you guys share.
