Mike Beaton suggested a 403 engine might be a good choice for a 12mpg GMC.
I'd given it some thought but it is not really a "stroker" motor, and
therefore a little weak in the torque department. My thoughts run a little
"madder" that just torquing up a 403. I've been thinking about a 400+ Chev
smallblock AKA mouse (which was a fairly common engine in the 1980's - I
believe that it was discontinued around 1988). HOT ROD magazine ran an
article in JUNE 1977 about building a 352 "long rod" with the 400
crankshaft and 7.2" rods (which cause the pistons to sit a TDC a little
longer, thereby making for a more efficient burning engine and thus
producing more power relative to the gas consumed). This was of interest to
me because 1) it is a Chevy smallblock (150 pounds lighter than the 455)
which means that there are numerous after market parts available at a
reasonable cost 2) it produced 435 ft-lbs. of torque at 3500 RPM; 406 at
3000 3) the long-rod design allowed it to run 87 octane gas without
knocking and still maintaining the same torque figures as the 89 or
91octane gas even though the compression was 11:1 4) the engine buildup
(with Air Flow Research heads) cost under $3000US. 5) the Chevy smallblock
will be "supported" for many years to come.
My thinking runs along these lines: an overbored 400 (which makes a 413)
with the long rods, trick flow heads (which will lower the compression)
with the smaller valves (which will lower the torque curve somewhat); RV
grind on the cam; programmable fuel injection and maybe sometime later a
twin turbo setup (if the bottom end would support it). I have no idea how
well the small block would fit in the GMC space (the big block seems to
work just fine). The gas saving over the life of the RV might just justify
this madness financially (although I think even that might be a bit of a
stretch). But then who ever said rebuilding/maintaining a GMC had anything
to do with rational, financially justifiable actions.
I wasn't really going to say anything about the short-block idea before
doing a bit more research but Mike just forced it out of me.
Please critique this before I go out and spent some "real" money.
Vic Marks
Vancouver
75 transmode
I'd given it some thought but it is not really a "stroker" motor, and
therefore a little weak in the torque department. My thoughts run a little
"madder" that just torquing up a 403. I've been thinking about a 400+ Chev
smallblock AKA mouse (which was a fairly common engine in the 1980's - I
believe that it was discontinued around 1988). HOT ROD magazine ran an
article in JUNE 1977 about building a 352 "long rod" with the 400
crankshaft and 7.2" rods (which cause the pistons to sit a TDC a little
longer, thereby making for a more efficient burning engine and thus
producing more power relative to the gas consumed). This was of interest to
me because 1) it is a Chevy smallblock (150 pounds lighter than the 455)
which means that there are numerous after market parts available at a
reasonable cost 2) it produced 435 ft-lbs. of torque at 3500 RPM; 406 at
3000 3) the long-rod design allowed it to run 87 octane gas without
knocking and still maintaining the same torque figures as the 89 or
91octane gas even though the compression was 11:1 4) the engine buildup
(with Air Flow Research heads) cost under $3000US. 5) the Chevy smallblock
will be "supported" for many years to come.
My thinking runs along these lines: an overbored 400 (which makes a 413)
with the long rods, trick flow heads (which will lower the compression)
with the smaller valves (which will lower the torque curve somewhat); RV
grind on the cam; programmable fuel injection and maybe sometime later a
twin turbo setup (if the bottom end would support it). I have no idea how
well the small block would fit in the GMC space (the big block seems to
work just fine). The gas saving over the life of the RV might just justify
this madness financially (although I think even that might be a bit of a
stretch). But then who ever said rebuilding/maintaining a GMC had anything
to do with rational, financially justifiable actions.
I wasn't really going to say anything about the short-block idea before
doing a bit more research but Mike just forced it out of me.
Please critique this before I go out and spent some "real" money.
Vic Marks
Vancouver
75 transmode
