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i have ben looking for a 0250 carb for it and was told the other day that it is not the right carb for a 4 speed rallye. where would i find out what is correct for my rallye 350 4 speed. if the 0250 is not correct i have ben wrong for a long time. the rallye 350 just had a regular 350 wether it was a 4 speed or an automatic so i thaught it had the same carb.
i have ben looking for a 0250 carb for it and was told the other day that it is not the right carb for a 4 speed rallye. where would i find out what is correct for my rallye 350 4 speed. if the 0250 is not correct i have ben wrong for a long time. the rallye 350 just had a regular 350 wether it was a 4 speed or an automatic so i thaught it had the same carb.
My automatic Rallye has the original drivetrain and it came with the 7040250 carb on it. I read that the 4 speed car should have 7040253. I've never checked but I will get out there this faternoon to see what it says on the card on my 4speed Rallye (it the rain ever stops !?!)
Your 250 carb is correct (auto and SMT). The 253 is for SMT 442 carbs. Right out of the June '70 Olds Service Bulletin (concurring with other sources, too)
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.
Last edited by BlackGold; Sep 11, 2015 at 02:50 PM.
Reason: Removed incorrect statement about automatic-equipped A-bodies and QV engine.
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:
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.
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:
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.
Excellent detective work! And very objectively reported. It just underlines how important it is to use every available source of information to put things together. Admittedly I've paid a little less attention to small blocks.
Now to augment what you've found, are there examples out there? And corresponding build dates?
Midyear changes have always been the hardest to document.
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 received a QV-code engine (except the W-31, of course). It didn't matter if the car was an automatic or manual, or any other options. Part way through the model year, Olds introduced the QB-code 4-bbl 350. For the remained of the year, it was installed in all A-bodies (4-bbl 350) with 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.
I never said Thanks for this post from a few years back it helps me with my car a lot
Glad to help. I just wish more people with a QB-code Cutlass (whether Rallye 350 or not) would post their build date.
I have an early build car but not the original engine nor paperwork but I believe they all did that's what I am going with. 01C (3rd week of January 1970)
Last edited by GEARMAN69; Sep 11, 2015 at 12:06 PM.
I have the 253 carb and a four speed with a 02D build date the original owner said the only thing he did to the car was replaced one valve spring, other than oil changes second owner said he only did clean up work also so i do beleave it is original to the car . Mine also was after the spoiler mandate was lifted
Just so I am clear on the QB engine - Only manual transmission 1970 A-bodies with the 310-hp engine built late in the model production year had the QB engine. All automatic transmission 1970 A-bodies, no matter of the assembly date, have the QV engine. Is that correct?
I just want to be certain as my brother just purchased an automatic equipped Rallye 350 that has a 1978 Quadrajet on it and he is looking for a correct carburetor.
Just so I am clear on the QB engine - Only manual transmission 1970 A-bodies with the 310-hp engine built late in the model production year had the QB engine. All automatic transmission 1970 A-bodies, no matter of the assembly date, have the QV engine. Is that correct?
I just want to be certain as my brother just purchased an automatic equipped Rallye 350 that has a 1978 Quadrajet on it and he is looking for a correct carburetor.
Automatic Rallye with AC is QP , QN with out AC
You're referring to the 1970 L74 engine, but I think you should be more specific and call it the QB code engine. "L74" by itself doesn't mean much -- it depends on what other options the car has:
L74 = QV (and later QB) code for SM.
L74 = QN code for AT exc AC.
L74 = QP code for AT w/ AC.
The QB code was the one introduced mid-year for manual trans 4-bbl 350 cars. Here's how it differed from the previous QV code engine:
Oh....both the QV & QB versions of the L74 350 4-bbl engine were for manual equipped cars and the QN & QP versions of the L74 350 4bbl engine were for automatic equipped cars.
So my brother's automatic and A/C equipped Rallye should have the 7040250 carburetor with the appropriate jets and metering rods. Now to find that information.
Sounds like that QB engine would be quite a performer. I wonder if they used a QB equipped Rallye 350 when they compared the Rallye performance against standard equipped 383 magnum Road Runner when they were evaluating it. According to the one post, the Rallye was equivalent to the Road Runner in performance tests that were conducted by Oldsmobile engineering.
Oh....both the QV & QB versions of the L74 350 4-bbl engine were for manual equipped cars and the QN & QP versions of the L74 350 4bbl engine were for automatic equipped cars.
So my brother's automatic and A/C equipped Rallye should have the 7040250 carburetor with the appropriate jets and metering rods. Now to find that information.
Yes, your statements are correct. I see now where I made a major mistake in my earlier post when I said:
At the beginning of the 1970 model year, all A-bodies with 4-bbl 350 received a QV-code engine (except the W-31, of course). It didn't matter if the car was an automatic or manual, or any other options.
This is incorrect! The automatic 4-bbl 350s were QN (no A/C) and QP (with A/C). Sorry for the confusion!!!! I'll correct my earlier post.
Want to thank BlackGold for the excellent reference information. I recently purchased a '70 Cutlass S four speed and this will help me determine which engine I have. Exactly the information I needed; thank you.
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:
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.
By the way thanks for this thread. Lots of good info.
I came across this in the super tuning booklet. It seems to indicate that the 7040253 carb should have the AT .067 secondary metering rod, not the AU you quoted. Any idea which is correct. I am trying to build my motor to stock QB engine specs.
By the way thanks for this thread. Lots of good info.
I came across this in the super tuning booklet. It seems to indicate that the 7040253 carb should have the AT .067 secondary metering rod, not the AU you quoted. Any idea which is correct. I am trying to build my motor to stock QB engine specs.
Pat
Did anyone ever find out which is correct? Is the Super Tuning Guide maybe suggesting to use the AT secondary metering rod instead of the AU secondary metering rod? Anyone selling a 7040253 carburetor?
Ok, that clears it up. It sounds like the one from Oldsmobile. I believe it also covers 68 and 69 in different sections. I recall getting one in 1970 from Rich Powers at Oldsmobile. I saw it again from GM Heritage Center.
With all the discussion about carb numbers/applications, I happened to recall that I had a 350 intake that I removed from a 1970 Rallye 350 decades ago... I became a little perplexed when I recently checked the carb number (7028251)... Being principally a 68 application number I believed it may not have been the original carb for the Rallye, and a remanufactured carb was installed somewhere along the line... Doing some further checking, I find this carb was also used on the 68 400 as well as the 68 455 Hurst... I haven't factually substantiated this as yet, but if true, I may have to find myself a 68 Hurst to attach the carb too......
With all the discussion about carb numbers/applications, I happened to recall that I had a 350 intake that I removed from a 1970 Rallye 350 decades ago... I became a little perplexed when I recently checked the carb number (7028251)... Being principally a 68 application number I believed it may not have been the original carb for the Rallye, and a remanufactured carb was installed somewhere along the line... Doing some further checking, I find this carb was also used on the 68 400 as well as the 68 455 Hurst... I haven't factually substantiated this as yet, but if true, I may have to find myself a 68 Hurst to attach the carb too......
If not a Hurst/Olds, then at least a nice '68 442 to go along with the carburetor. lol
Thanks, that's pretty much what I had, except it didn't have the fancy front and back covers. Great basic stuff for anyone wanting performance from a 350 or 455. The suspension tips work also. I used some of the stuff on my '68 Hurst/Olds, a lot more stuff on my '70 W-30 auto.
