Do we over carburetor cars?

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Valiant63

Valiant63

Early A-body Valiants
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I am wanting to buy a carburetor for a 68 318 engine in my 65 Valiant. it has a 4-barrel Holley carb and Edlebrock intake on it currently that came on the engine, but the carb won't work. I am wanting to replace the carb with like a 625cfm Carter carb, but one guy on here was telling me that a 525cfm carb came on 383 engines from the factory and would be plenty of carb. Is he right, and should I go for a smaller carb to get better gas milage? The engine has the heads milled .040 and a better than stock cam in it, don't know specs. It is just a street car.
 
525 cfm was enough for the low rpm C body/truck spec 383. The hp version and above needs more.

Regarding your 318, if you just want to cruise around and get decent mileage then I agree you should use a small carb like the 525 Carter or a 600 Edelbrock.
 
I think as long as you stay around the 600-650 range you will be good. Not a bad idea to study up on tuning carbs and how to read plugs.
 
Thanks for the information so far. So what do you others think about using a 500 or 525 Carter carburetor?
ToolmanMike... Where would you recommend that one read up on tuning the carb and reading spark plugs?
 
It totally depends on the type of carburetor.
 
Valiant63 said:
Thanks for the information so far. So what do you others think about using a 500 or 525 Carter carburetor?
ToolmanMike... Where would you recommend that one read up on tuning the carb and reading spark plugs?
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Google is your friend. I don't see a "how to" article here on FABO but if you try the search function I'm sure you'll fins some info.
 
Thanks Mike. I will check into it.
Rob... I would like to stick with a simple Carter carb or an edelbrock, but will use a Holley if I have to. What Carter carb is good to use?? I really liked the factory 273 4-barrel carb that I had from a 65 or 66 Barracuda.
 
A thermoquad can be the best of both worlds, IF you can find a good one. I will also note, that in MY experience, mopars tend to be pretty tolerant of overcarburetion, compared to sbc
 
replicaracer43 said:
A thermoquad can be the best of both worlds, IF you can find a good one. I will also note, that in MY experience, mopars tend to be pretty tolerant of overcarburetion, compared to sbc
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This. A TQ is a great carb,has small primaries for cruising around and getting decent economy,and mother of god huge secondaries that gulp huge amounts of air. Chrysler felt 800 cfm TQ were fine on theit 318 cop car motors with 360 heads. Reason being the air door over the secondaries is vacuum operated and works on demand from the motor,so it will only ever get as much as it wants.

And it's why rustyratrod is right as usual. Any given motor will respond differently depending on CID,and believe it or not,the type of trans (manual vs auto) has some effect as well.

For an automatic trans car behind a 318,something like a 600 to 650 cfm vacuum secondary eddie or Holley would work great.
 
I have a 770 street avenger Holley on a 318, short block never been apart at 120,***. Runs great, no complaints. Does it need the 770? naw......
 
Keep in mind, the engine "pulls" through the carb. The carb does not "push" or cram air and fuel into the motor.
 
I have a 600 Holley on my mild build 318 and it responds to that very well. Unless you are planning on racing, there is no need to over-carb your car.
 
These are the specs for a CASCAR Race Engine,(owned by NASCAR)...CASCAR is the premier late model professional circuit series in Canada.

371 cu. in, W2 cyl heads, 10.0:1 compression, cam is Mopar p#4529972 .555 / .555, 252 / 252 mech
2.02 / 1.6 valves, mopar #p4529408 intake manifold and a 390 cfm Holley carburetor
it dynoed 521 hp @6400 and 472 ft.lb @ 5100

These engines are restricted to 3.58 stroke and one 390 cfm carburetor....
 
I agree a 340TQ on a 318 based motor will run incredible,hard to beat!
 
Wow...i thought that CASCAR 371 would spark some comments.
I would have thought those numbers with a 390 cfm Holley would be impossible!
 
it sounds similar to restrictor plate racing and it also sounds like you were trying to draw attention to Cascar rather than answer the question about carbureted engines. I didn't see an opinion of yours about carbureted other than CasCar uses a 390 carburetor. I'm still uncertain as to what carb to get. I just want to get a used carb that's relatively reasonable in price and will work well. I'm afraid that in my current state and lack of energy, that I might get a carb that isn't rebuilt and then not want to rebuild it.
 
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no...just an example showing big carbs aren't necessary so yes we probably over carb our street cars.
These of course are very specialized engines.I still can't wrap my head around 520 hp with a little 390 cfm Holley in a small block.
 
soon or later most all carbs will need some love, embrace it and it can be very satisfying and save you a ton of money
 
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