airborne1942

I have a 1970 Oldsmobile, Cutlass S, Rallye 350. it has the numbers matching 350, 4 barrel carb, and it has an original factory 4 speed. should this car be a QV engine or a QB? I have a book that says it should be a QV, some people says it should be a QB so I'm confused what should it be?
thanks! Brian

BlackGold

Does your car still have the original engine? If so, does it have the original carb? The QV used the 7040250 Q-jet, which was also used in other applications. The QB used the 7040253 Q-jet, which was unique among the 350s but also used on the TU 455.

What is your car's build date? The QB engine first starts showing up in the engineering drawings in late November, 1969. But it wouldn't surprise me if it took some weeks or even months to be installed on the line. If your Rallye 350 was built really late, it would certainly be a QB.

firefrost gold

I have the 253 . From what I have found with the help of black gold the QB has larger jetting and the cam from the 69 400 . Little hotter than the auto cars

airborne1942

my car does have the matching number engine, the intake and carb has been changed! the build date on the trim tag is 04D, the chassis service manual says the 250 should be correct, and the 253 should be on a 455. I bought a 250 and put on my car, how hard is it to find a 253, and y'all say that should be the correct for my car?

firefrost gold

Take a look at this thread

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

I have the same engine assembly manual he has. ( mines a copy ). It has all the cam numbers , carbs, trans options to what. Got what when being built.

BlackGold

The Chassis Service Manual says lots of things which aren't true. It was published at the beginning of the 1970 production year (in 1969), long before many running changes were made. In it you won't find ANY reference to the QB-code 350.

With a build date of 4th week of April, I consider it extremely likely that your car came with the QB engine. Note in the other thread referenced by "firefrost gold" that I know of a documented (with build sheet) QB-code Cutlass built in mid-April.

GEARMAN69

My Rallye 4 speed car has a Body tag date of 3rd week January 70 , I will never know for sure since I dont have the original engine. I do have a 70 250 carb though off the 1st week 70 tagged auto AC Rallye I parted. But.. I do have a 69 253 carb I may run as well.

The factory rated HP of 310 in 68-70 before QB change to 210/210ish 286/286 .472 cam is very suspicious to me with a tiny 187/200 250/264 cam .400 cam.. Seems like you would need the 210 286 cam to just get to 310 hp considering the poor headflow

firefrost gold

from The 1970 Olds cutlass engine manual the QV had a 7040250 carb it has a cam 400084 250/264 intake 0.400/0.400 exhaust and 36 overlap .


The QB has 7040253 for the carb and 393859 cam that is 286/286 intake and
0.472 /0.472 on the Exhaust 58 overlap . intake is the same on both heads

anthonyP

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.

anthonyP

Which carburetor did you use on your Rallye? Do you still have the 7040250 carburetor?

GEARMAN69

I have the original 7040250 carburetor from my Rallye parts car (auto A/C) and will keep it for now. Only the center section and and top were saved. From the weather exposure the base was too rusted corroded up even after soaking in Acetone ATF mix for a month. I also have 7040250 carburetor original to my newly acquired 310 hp 70 wagon keeping it obviously too. I suspect my 4 speed car came with a 7040253 carburetor but until I have one I will use what I got. I also have a 69 442 4 speed 7029253 carb I may just run it IDK yet.

GEARMAN69

For Automatics the codes are QN or QP depending on AC if anyone needed it.

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:

anthonyP

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.


Thank you for your help.

BlackGold

This is not true! As Gearman69 pointed out, the automatics used the QN and QP engines. I apologize for the mis-information I posted previously in another thread. I have now corrected it.

anthonyP

Thank you Brian for all of the valuable information. I'm always learning something new about all of the Oldsmobile models.

1970greensupreme

Build sheet for my 70 Supreme QB code

anthonyP

Wow, that is one awesome factory ordered Supreme.

Bet this Supreme surprised a lot of 383 Road Runners, 351 Mach 1's, SS-396 Chevelle's, and standard GTO's back in the day.

Wonder why the carburetor box has ** in it, do all build sheets have this same notation for the carburetor?

oldsmobiledave

A Sherwood Green, Black top, 4 speed Supreme with M-21, 3.91 posi & QB code 350. Now that is a nice car. Well played sir.


Would you mind posting a picture please.

anthonyP

Just a thought, was the QB engine installed after January 1st if someone ordered their 350 4-speed with A/C, or was the QV engine used? I do not recall anyone mentioning that their QB equipped Cutlass had air conditioning.

1970greensupreme

It's a shell now in primer, frame hanging above my lift, int in dry basement and body on a rotisserie, LOL