Originally Posted by Texas442

I recall reading that 1970 Rallye 350 4spd got different carb than the automatic. If so, what is the correct number? Thanks in advance.

Originally Posted by rob1960

Good info, that would make sense with Olds going to the "286" stick cam as a mid year change & pairing it with the 442 "253" stick carb. That's the same cam that my '68 400/4spd uses.

Originally Posted by BlackGold

Hold the phone, guys. This issue isn't so simple.

Kurt, that chart in the June, 1970, Service Guild Product Training Manual has too little space to list all of the application info, so I wouldn't trust as the end-all authority on carb usage.

The truth of the matter is that the QV-code 350 used the 7040250 carb, while the QB-code 350 used the 7040253 carb. If you are lucky enough to know whether your Rallye 350 came with a QB or QV engine (say you have the build sheet or original oil filler tube tag), then you have your answer. Otherwise, you'll have to do some work and may never be sure which carb is "correct."

At the beginning of the 1970 model year, all A-bodies with 4-bbl 350 and manual transmission received a QV-code engine (except the W-31, of course). Part way through the model year, Olds introduced the QB-code 4-bbl 350. For the remainer of the year, it was installed in all A-bodies with 4-bbl 350 and manual transmission (except the W-31 again). The QB-code engine first appeared in the 1970 Engine Assembly Manual (the document which defined to the Engine Assembly Plant how each engine was to be built) on November 24, 1969. Of course, that doesn't mean they actually started producing QB-code engines on that date; it could've been months later.

There is anecdotal "evidence" that the QB-code engine was created specifically for the Rallye 350. That may be, but remember that the automatic Rallye 350s still received the QV-code engine, and plenty of plain-old Cutlasses received the QB-code engine; the QB was not exclusive to the Rallye 350.

I'm not an expert on Rallye 350s, but here's the dates I see on the factory literature. The Rallye 350 Wholesale Car Order form is dated November, 1969. The pages in the Assembly Manual covering Rallye 350 special items are dated January 8, 1970. And Dealer Information Bulletin 70-I-14, dated 2-20-70, announced the new Rallye 350 option using the words, "Olds Division will soon release ..." implying it was not yet available at that date.

The implication of all this is that it is likely that all manual-transmission Rallye 350s ever built received a QB-code engine, and thus the 7040253 carb. However, if Rallye 350 production started earlier than the literature implies, and if the QB production started later, then it wouldn't surprise me if there are manual-trans Rallyes out there with QV-code engines. But I am confident that if you have a late-build, manual-trans Rallye 350, it should have a QB-code engine.

So what's the difference between the QV- and QB-code engines? I'll put that in another post.

Originally Posted by BlackGold

Regarding the difference between QV and QB engines:

The 1970 Engine Assembly Manual calls for
identical parts used throughout these two engines
with the following exceptions:

Cylinder Head Assembly:
QV = 405584 (used on all other 350 exc W-31)
QB = 408187 (unique to QB)
Note that these Head assemblies were "loaded,"
including valves, springs, etc. The only
difference between these two was probably
the springs.

Carburetor:
QV = 7040250 (used on all other 4 bbl 350 exc W-31)
QB = 7040253 (unique to QB among 350s, but also
used on TU 455 (manual-trans 442s))

Camshaft:
QV = 400084 (used on all other 350 exc W-31)
QB = 393859 (unique to QB)

Spark Plugs:
QV = R45S
QB = R44S (unique to QB among 350s)


The 1982 Olds Parts Illustrated Catalog
lists only three differences between the
QV and QB carbs:

Primary Jets:
QV (7040250) = 7031970 "70" (.070")
QB (7040253) = 7031969 "69" (.069")

Primary Rods:
QV (7040250) = 7040701 "52C" (.052" tip)
QB (7040253) = 7040699 "48C" (.048" tip)

Secondary Rods:
QV (7040250) = 7033658 "AT" (.0667" tip)
QB (7040253) = 7033655 "AU" (.0527" tip)



Note that the QB carb is jetted significantly
richer on both the primaries and secondaries.

Regarding the cam for the QB-code engine:
The new 393859 cam is nearly identical to
the 400165 (automatic 442) cam in terms of duration and
overlap. They were also ground on the same
blank. The only significant difference is that the
automatic 442 cam is essentially installed 3 degrees
advanced, while the manual 350 cam is installed 4 degrees
retarded. Makes sense! The 442 is cam'ed more for
low-rpm torque; the 350 more for high-rpm.