I'm looking to put a 455 in my car but was curious as to how you would tell if the carb is a 750 or 800 cfm? Are there any designations or part #'s which would suggest its either one or the other??

I wanted to use a 800 cfm carb so thats why I'm asking...

 

For a street car, 650 should be big enough

 

I haven't been able to run across part numbers yet.

http://dyeager535.topcities.com/qjetidentify.html

 

I was told that my stock 455 Q-jet was a 780, but I don't how to tell either. Just took some pix of mine. Do these tell anyone anything?



DSC_6720.jpg

 

I might've found a 750 cfm carb and he is saying it is a Boat/Marine carb and the part # on it is 7045282. Is this a good carb?

When I asked if he had an 800 cfm carb this is what he told me..

"they didn't make a pre-smog (nor a marine) olds 800 cfm carb. to get an 800 cfm olds carb you have to get a 1975+ carb (one with all the smog stuff on it)"

Does this sounds right??

 

I always understood that Quadrajets were about 750 cfm. I say 'about' because their variable venturi design means they'll yield the cfm that is on demand variably in relation to throttle and vacuum up to around 750 cfm. I've also been told that, despite Buicks and Cadillacs alleging an 800 cfm version, that was a automotive urban legend and no quadrajet was actually marketed as an 800 cfm. Does anyone have any input on this?

 

If you look down the primary throttle bores there a distinct ridge below the venturi cluster on the bore wall. It's about 1/8 inch thick roughly where it necks down to a smaller bore diameter. That would be a 750cfm. The 800cfm carbs have a much smaller ridge. This video shows exactly what I'm describing.

http://www.youtube.com/watch?v=xuqz5Bs96Tw

 

I knew about the differences in the bore and realize there were two different castings. I was told that despite the difference they'll both only flow around 750 cfm in real world application. Thanks for the video.

 

Great video and very informative!!

The carb I'm looking at has a part #7045282 but the 8 in the id # is throwing me off.. It says its for "Non-GM, possibly Mercruiser Marine"... does anyone know what that means??

 

Not sure what that means either. I know in 1970 Mustang used the Q-jet for a while. Mustang is Ford, Merc is Ford... who knows? From what I found the numbers break down like this:

7045282

704 = Decade produced 1970-75
5 = year produced 1975
2 = Model: Quadrajet (4 bbl) Federal standards
8 = Division: 8= nothing / 5 = Oldsmobile (6 & 7 = Pontiac)
2 = Even numbers - Automatic Transmission
Odd numbers - Manual Transmission

In my 1964-76 parts catalogue this carb doesn't show up. Only the following 4 barrels show up for 1975:
350 V8: 7045183 / 7045250 / 7045246 / 7045483 / 7045550
455 V8: 7045185 / 7045251 / / 7045484 / 7045551

 

I had a 403 Olds and I believe they came with a 800 cfm carb so I was wondering if this q-jet carb would work on an early 455 motor?

 

Yes, however a fairly stock 455 doesn't require more than a 750.
Here is a good site for Q-Jet info..
www.cliffshighperformance.com/

 

On some of the 800s, you have to bend the secondary linkage to get the throttle blades to open fully.

 

Anyone know the CFM on the factory 2bbl carbs? Like on a 72 Cutlass.

 

Around 300cfm I think. 2bbl's are measured differently though so not really sure. Sheesh I'm a lot of help!

 

I was thinking 300-350.

 

The carbs that people think are 800cfm are not. 500" Cadillac carbs,no. 403 carbs,no.Stage 1 Buick,no. If you want a true 800 cfm carb,then you need to go to the mid 1980's,like a Chevy truck or van.Sounds funny,but true. Just flow one.

Yor 455 doesn't need an 800 anyway.Same reason Cadillac 500's didn't get them or need them.They don't spin fast enough to require that amount of cfm.

 

http://www.camaros.net/forums/showthread.php?p=1197693

4th post lists 2bbl cfm. Most 2bbl are measured at 3"Hg while 4bbl are at 1.5"Hg

 

Cool. Thanks for the help.

 

Doug Roe's book states Q-Jet flow ratings by venturi size, not model year, ie: 1-7/32" venturi=800 cfm, 1-3/32"=750 cfm.