Go Back  ClassicOldsmobile.com > General > General Discussion
What's the correct carb # for Rallye 350 4spd? >

What's the correct carb # for Rallye 350 4spd?

General Discussion Discuss your Oldsmobile or other car-related topics.

What's the correct carb # for Rallye 350 4spd?

Old February 13th, 2017, 06:07 AM
  #1  
1971 442 conv
Thread Starter
 
Texas442's Avatar
 
Join Date: Jun 2009
Location: Austin, Texas
Posts: 628
What's the correct carb # for Rallye 350 4spd?

I recall reading that 1970 Rallye 350 4spd got different carb than the automatic. If so, what is the correct number? Thanks in advance.
Texas442 is offline  
Old February 13th, 2017, 06:31 AM
  #2  
Registered User
 
rob1960's Avatar
 
Join Date: Mar 2009
Location: Ohio
Posts: 466
As far as I know there were only 2 different carbs listed for 350s in 1970. 7040250 was the regular 350 4bbl carb regardless of trans & the W31,regardless of trans, used the special "255" carb with out the primary metering rods & piston. There is a decent 4bbl carb chart on 442.com that shows all the carb #s & their associated jet & rod sizes from '66-'72
rob1960 is offline  
Old February 13th, 2017, 06:44 AM
  #3  
Registered User
 
GEARMAN69's Avatar
 
Join Date: Jan 2008
Location: TEXAS
Posts: 1,266
Originally Posted by Texas442 View Post
I recall reading that 1970 Rallye 350 4spd got different carb than the automatic. If so, what is the correct number? Thanks in advance.


A 4 spd Rallye would be the mid year change QB 310 rated 350 (286 cam) with a 7040253 Q jet that does still have primary metering rods unlike the W31 carb
GEARMAN69 is offline  
Old February 13th, 2017, 07:09 AM
  #4  
Registered User
 
rob1960's Avatar
 
Join Date: Mar 2009
Location: Ohio
Posts: 466
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.
rob1960 is offline  
Old February 13th, 2017, 07:21 AM
  #5  
Registered User
 
GEARMAN69's Avatar
 
Join Date: Jan 2008
Location: TEXAS
Posts: 1,266
Originally Posted by rob1960 View Post
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.


My 4 spd Rallye was missing the original engine other than one head, intake and balancer and while building the automatic Rallye 350 engine from the parts car I scored a good used 400 4 spd 442 286 cam that was low miles pull out for $20 and paired with NOS Johnson lifters. Oddly the 68 310 auto engine I got with the deal on the rallyes had a 69 442 253 carb on it so I may run that.
GEARMAN69 is offline  
Old February 13th, 2017, 07:22 AM
  #6  
Registered User
 
jensenracing77's Avatar
 
Join Date: Feb 2009
Location: Brazil Indiana
Posts: 9,777
I have heard this for a couple years now but have yet to ever see an original 4 speed car with the 253 on it. Every one I have been around that was known to be original was the 250.
jensenracing77 is offline  
Old February 13th, 2017, 07:49 AM
  #7  
Registered User
 
GEARMAN69's Avatar
 
Join Date: Jan 2008
Location: TEXAS
Posts: 1,266
Not a Rallye but this guys Supreme had one in the Rallye build time


https://classicoldsmobile.com/forums...de-engine.html
GEARMAN69 is offline  
Old February 13th, 2017, 10:36 AM
  #8  
1971 442 conv
Thread Starter
 
Texas442's Avatar
 
Join Date: Jun 2009
Location: Austin, Texas
Posts: 628
Great Great info!!! I also just found this helpful old thread (see link below). So now, I need to find the build date of the car to determine if it got the 250 or 253 carb.

https://classicoldsmobile.com/forums...50-carb-s.html

Originally Posted by BlackGold View Post
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 View Post
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.
Texas442 is offline  
Old February 13th, 2017, 11:44 AM
  #9  
Registered User
 
Join Date: Apr 2011
Location: Nor Cal
Posts: 1,235
70 carb

I have a 7040250 carb for sale. needs a rebuild
$120 shipped
Gerald Nickels is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
jharsh
Body & Paint
2
December 30th, 2016 01:25 PM
wagonmaster
General Discussion
3
June 17th, 2014 08:13 PM
1320dragmonza
Transmission
6
August 2nd, 2013 03:46 AM
11971four4two
Cars For Sale
37
April 29th, 2013 09:30 AM
jensenracing77
Electrical
0
April 26th, 2009 04:46 PM


Thread Tools
Search this Thread
Quick Reply: What's the correct carb # for Rallye 350 4spd?


Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.