i'v did alot of searching and reading on the net about propane conversions. i'v
bought most of the parts i need to do the conversion but still have a few
questions. i know the impco 425 will bolt to a holly base plate but witch
one??? should i use a double pumper base plate or vac. secondaries base plate?
?? 650 to 800 cfm or the 800 to 1000 cfm base plate ?? does anybody know
what holes in the base plate to block off if any??? any help would be great
Does your 425 have the 2bbl base plate on it or does it have the 1bbl base
plate? Either way you could put it on a spacer that is universal for the
size. What is the concern you have? If it have any holes you don't need them
unless you are running some sort of smog or PCV setup that you want to keep
and then it's a matter of checking other installations like yours to see
what is required. What engine is it for and what carb were you running
According to the Impco website it's a standard size.
It's a large file so be patient if you download it.
I have converted cars before and have had no trouble. If you are going to
take on such a job then you must be some what used to these sort of
problems. If you have no idea what you are doing then ask many more
questions. I wouldn't want to see you blow yourself up.
i'm sorry guys it's all going on a 78 ford bronco with a 351m engine. it had
a 670 holly truck avenger 4bbl.i'v took off the base plate and i see two
lines with holes in it for vac. i guess.just wanted to know if they should be
filled in or not. i'm a diesel mechanic by trade. just new to propane. thanks
Sorry to take so long to respond to the last post.
If it has holes for your smog controls, even though running on LPG will take
care of most of the pollutants in your exhaust, you will probably need to
keep them hooked up. It sounds like you have some experience working on
engines so check what the holes and subsequent lines run to and are for. It
could be that you could disconnect them and have no issues but if they are
there they are there for a reason.
Having not worked on that particular engine and vehicle combination I can
not tell from experience. The workshop manual should have a detailed
diagram/schematic of the lines and from there you could tell their
importance. If, on the other hand, you have disconnected the other ends of
the lines because the smog gear has been removed it should be self
You might get more information from a Bronco newsgroup. Also try looking at
any Australian website dealing with LPG. We have been using a propane blend
of gas for many years and one can fill up at most service stations across
the country. 351's are a popular engine in Australia so conversions are
plentiful and smog controls are similar.