I have a 69 Cutlass with a 455 in it. A prior owner did many modifications many of which I can only guess at. I'm sure it has at least a mild cam in it. It has an Edelbrock Performer intake with a 1406-3007 carb. This is a 600cfm carb w/electric choke. I am curious about what the 3007 means and if this is too small a carb for my motor? From what I read this is mostly recommended for 350ci or a small BB. I assume I am getting better mileage, but am I starving the engine?

thanks,
Steve

 

Considering the smallest Q-Jet is rated at about 750 cfm, the 600 is way too small.

 

Just for reference the standard qjet for Olds 455s was the 750 CFM model, but the later 170 series 800 CFM’s work great as well.

I didn’t remember they made 600 CFM models, but then I’ve always used big blocks.

600 CFM may give you better mileage, so there is a benefit to a smaller carb, unless I miss my guess, generally people here with 455’s are aiming more at power than economy.

 

Absolutely 100% potentially untrue. If it has big enough jets in it it could get worse mileage than a correctly jetted 850. More internet crap.
I wouldn’t do anything less than a 750 for even a mild 455. But whatever you get buy a wideband and jet it right.

 

Cutlassefi is exactly right. That’s why I put “may” in my note above.

Am I wrong though in thinking a smaller carb, correctly jetted, would get better mileage than a correctly jetted large carb?

I ran a 600 CFM Holley for a while in my 455 in the 80’s. The only feature I remember was that my mileage went up and the car got slower. But this was at the very beginning of my tuning experience, so there’s no telling how correct the 600 jetting was, nor how far off the jetting of my comparison 780 CFM 3310 was.

If you just bolt any carb on your engine and don’t tune it, any performance you get out of it is more or less winning the lottery. And about as likely.

His advice is exactly right. Whatever carb you choose, get a wideband oxygen sensor which will tell you in AFR or Lambda what the carb is mixing up for you at idle, cruise, WOT and everywhere in between in real time. Widebands are a tuning bonanza to amateurs like me who like carbs.

Cheers
cf

 

If your just cruising around the 600cfm will work fine. If you want to get some performance, then get a bigger carb.

 

Whats the point in having a 455 if all your doing is cruising around? Why handicap a 455 with a puny carburetor? Might as well have a 2bbl carb and single exhaust.


You can have a 455, excellent power, and decent economy if everything works well together. That means everything needs to be correct for it’s intended use.

 

Matt69olds and oldcutlass are on point. 50 year old 7.5 liter Olds 455’s are never, ever, going to win any kind of mileage economy challenge.

Might as well enjoy low end torque and gobs of power at the cost of using a bit more gas.

I’d go with at least a 750, or an 800 if you want to dial it up a bit for power. But per EFI’s suggestion above, don’t plop it on & hope. Get a wide band & tune it.

cf

 

Handy little tool by Summit
https://www.summitracing.com/newsand...cfm-calculator

 

I don’t go by these calculators, never have. Here’s what I DO believe, vacuum at the end of a Dyno pull. I’ve had mild 455’s with 850’s on them still pull over an inch of vacuum at 5500. That tells me it’s NOT too big.
What these calculators don’t take into consideration is the overall volume of the intake tract. I believe AED has a great write up on their website about this.

 

[His advice is exactly right. Whatever carb you choose, get a wideband oxygen sensor which will tell you in AFR or Lambda what the carb is mixing up for you at idle, cruise, WOT and everywhere in between in real time. Widebands are a tuning bonanza to amateurs like me who like carbs.]

Can you tell me more about the sensor? Is this in the exhaust pipe, where does it sense?

thanks

 

Will it still pull those numbers in the car with all the accessories, mufflers, air filter, and driveline? Maybe a chassis dyno would give a better picture?

 

Phoenix,
I used to work in control systems. I’m no expert, but my work there taught me that outputs from systems, when read critically, can tell you how to tune inputs. Here’s how I apply that logic to my ancient analog cars. In my case two 1966 455-equipped, carbureted Oldsmobiles.

Why Use an O2 (oxygen) Sensor?
An 02 sensor is what every fuel injected car/truck/vehicle uses to determine how much fuel to inject into the incoming airstream. I put them on my carbureted cars since I was never trained as mechanic and never developed an “ear” for tuning.

Reading Exhaust Oxygen and Telling the Computer What to Do
In modern cars, an 02 sensor tells the fuel management system to lean out or enrich the spray from the injectors. If the 02 sensor reads rich (lambda <.99), it tells the fuel management system to spray less fuel to achieve optimal combustion for a given demand (i.e. your foot…). If the sensor reads the exhaust stream as lean (lambda >1.01), it tells the fuel management system to enrich the injected mixture for a given demand — your foot again.

What are they and where do they live
02 (Oxygen) sensors live your exhaust pipe(s) about 6-8” from the exhaust manifolds. They read exhaust oxygen content & translate that into a voltage. That voltage is reported by a gauge as either lambda or translated to air/fuel ratio (AFR). If I have it right, lambda is the most precise reading, but less understood in the U.S., by V8 aficionados. AFR is more popular among the U.S. V8 crowd, but is derived from lambda. When I stuck 02 sensors on my cars, I started with AFR, but eventually went to Lambda since it’s fuel independent.

Air/Fuel Ratio (AFR) vs. Lambda
The short version of the AFR vs. Lambda story, if I have it right, is that AFR goals depend on the ethanol content in our fuel. So when California or my fuel supplier monkey around with the ethanol content of my gas, if I use Lambda, I can adjust relative to 1.00 with whatever they’re doing that month. When I use AFR, I don’t know whether I’m aiming at 14.2 as perfect combustion for E85 gas. or 14.7:1 for actual pure gasoline. At least in my town, they don’t announce the ethanol content of gas. Without lambda, I’m guessing about the goal. So I use Lambda.

Why use and 02 Sensor for a Carburetor?
In carbureted systems, AFR/Lambda tells you whether you need to change jets, rods, or whatever to achieve perfect combustion at idle, cruise, WOT and so on. In my case, I watch how the engine behaves at idle, cruise, & WOT + everywhere in between to get as close as I can to lambda of 1.00 at cruise and idle, and aiming at .90 or so lambda at heavy throttle. I’ve observed that it’s normal to have rich lambda in warm up (.85-.95) and very lean when going down hill with the throttle off and no demand (1.10 -1.15).

Basically the 02 sensor reads the oxygen content of the exhaust stream to measure whether piston combustion on one or two banks of cylinders is complete. If combustion is complete you get lambda of 1.0 or 14.2 or 14.7 AFR depending on which scale you use. Fuel injection systems react to those exhaust inputs with fuel maps. With carburetors you have to react to those exhaust signals by changing rods, springs, jets, etc.

I can confirm that using a wideband oxygen sensor is one of the best tuning investments I’ve ever made. If you’re trained, you can probably hear or feel the right tune, but for those of us without professional training, 02 sensors are great. But it’s only in the last few years that their cost fell below a few hundred bucks putting them in range of hobbyists.

02 Lifespan is not Infinite
Finally, I should mention that these sensors living in a 400F caustic exhaust stream don’t last forever. On modern cars (not Olds 455’s) I have the impression that the 02 sensors last about 70-80,000 miles. One cool feature in fuel injected cars is that when 02 sensors fail, they run the car rich so as not to burn valves. What you need to know as a modern car driver is that when your mileage suddenly starts to suck, one culprit could be the 02 sensor protecting your engine.

Hope this helps you all. What little I know.

Cheers
cf

 

If I’m wrong on the points above, please correct me.

Got no big thing about being wrong.

Would be delighted to learn more.

Chris

 

On a carbureted car, you really don't want to run the AFR that fuel injected cars run. It's too lean. Carbs, not be super precise fuel metering devices, you want a margin of error. Instead of 14.7, you probably want to run it at 13.5 or so, and under more load, 12.8, IIRC. Carbs also don't adjust themselves for altitude, so a bit richer (unless you live at high altitudes), is good for overall driving.

 

I disagree. The only reason you would need an idle that rich would be because of a large camshaft, and that would be for a carb or EFI.
Stoich on Pump gas/E10 is 14.1, not 14.64. And WOT depends on a lot of things, cam, compression, timing etc.
And as you go up in elevation you’ll need less jet, not more. So if you tune at sea level you’ll be on the rich side there anyway.