Timing Chain Inspection and Replacement
- Thread starter Tynan918
- Start date
C.F.M. = Engine Size (C.I.D.), times maximum R.P.M., divided by 3456.
I have a stock 305...what is max rpm for a stock 305 ?
"6000 RPM is THE limit. Otherwise, your stock cast iron bottom end starts to break, your valvetrain will get coil bind and heads probably don't have enough air to breath. It sucks to spin a rod and then hear that permanent knock and miss until you rebuild. Generally, 5500RPM is the redline."
"5500RPM IS THE REDLINE."
305×5500÷3456 = 485
Current Carb : 600cfm
Projected Carb : 500cfm
600-485 = 115
500-485 = 15
By swapping carburetors, I'm closing up a whole 100cfm not even being used...the projected carburetor is more suitable for my engine.
Also, the projected carburetor has annular boosters, rather than standard boosters the current carburetor has. An annular booster externally appears similar to a standard booster but employs an annulus, or channel, to move fuel around the circumference of the inside diameter of the booster. Edelbrock's annular booster uses 12 small, equally spaced holes to introduce fuel into the incoming air. These multiple small holes do a better job of shearing and efficiently vaporizing the fuel as it enters the airstream. Oftentimes, this means less fuel is required, especially at low speeds, to make the same power.
This is an annular booster removed from the carburetor. You can see several of the smaller holes on the inside circumference of the booster. Edelbrock has anodized the annular boosters red to make them easier to identify:
Suitable size and better fuel economy with the projected carburetor...😎👍🏾🎯‼💯
Height and hood clearance ?
I currently have a 1405 Performer Series carburetor and a Performer RPM intake... specs :
Manifold Height - A-4.20", B-5.25"; Carb pad height: 4.27". (Carb recommendations: Edelbrock AVS2 or Performer Series 650-800 cfm.)
Manifold Operating Range - 1500-6500 RPM
Carburetor Height - 3.25
Carburetor CFM - 600 cfm
I'm swapping those out for a AVS2 Series 1901 and a Performer EPS... specs :
Manifold Height - A-3.74", B-4.80"; Carb pad height: 4.27". (Carb recommendations: Edelbrock AVS2 or Performer Series 500-650 cfm.)
Manifold Operating Range - Idle-5500 RPM
Carburetor Body Height - 3.25"
Carburetor CFM - 500 cfm
Current setup height equation and total :
4.27+3.25 = 7.52
Projected setup height equation and total:
4.27+3.25 = 7.52
Same height...no hood clearance issues, no modifications needed...
Pretty sure my decision to swap carbs and intakes is a smart decision for a stock/street engine, given the numbers and math... 🤷🏾♂🎯‼💯
Last edited:
Its your money, spend it how you want, but you're going to notice no real difference.
Why did GM put quadrajets on 305s in our cars? These quadrajets flow north of 700 cfm. The one on my 305 in my SS is a 750 CFM unit. It works fine. A 600 cfm carb on a 305 is not too big, and you'll just be wasting time and money by changing it.
You need to do a bit more research on carburetors, and how they work, before you proceed, In My Opinion. You could change jets on the carb you have and lean it out for far less than a new carb costs.
It's quite funny, actually, as I look at what you're doing and compare it to what I'm doing on my car. I recently finished installing a TKX 5-speed manual, had the rear rebuilt with a posi carrier, replaced the flex fan with a clutched unit, and now I'm looking at replacing my carb, too. I want to take better advantage of the manual trans with mechanical secondaries, so I discussed it with my dad, who's been building engines and cars for 50 years, and he suggested a 650 cfm holley for my 305. Take that as you will, our setups are quite different, and my engine is far more built than yours is, but they're both 305s, so there's not going to be that big of a difference.
Why did GM put quadrajets on 305s in our cars? These quadrajets flow north of 700 cfm. The one on my 305 in my SS is a 750 CFM unit. It works fine. A 600 cfm carb on a 305 is not too big, and you'll just be wasting time and money by changing it.
You need to do a bit more research on carburetors, and how they work, before you proceed, In My Opinion. You could change jets on the carb you have and lean it out for far less than a new carb costs.
It's quite funny, actually, as I look at what you're doing and compare it to what I'm doing on my car. I recently finished installing a TKX 5-speed manual, had the rear rebuilt with a posi carrier, replaced the flex fan with a clutched unit, and now I'm looking at replacing my carb, too. I want to take better advantage of the manual trans with mechanical secondaries, so I discussed it with my dad, who's been building engines and cars for 50 years, and he suggested a 650 cfm holley for my 305. Take that as you will, our setups are quite different, and my engine is far more built than yours is, but they're both 305s, so there's not going to be that big of a difference.
Last edited:
Agreed, save a boat load of cash even if he spent some money and installed an O2 sensor to really learn how to tune a carb. I did just that and really learned a lot about how each tunable component would affect the AFR at different situations.
This. I installed an AFR and Vacuum gauge in my dash. I use those to monitor engine operation and its helped me quite a bit in tuning out issues, too. Possibly the best $200 I've spent on tuning.
Yea my 02 sensors are cut, and no cat converter, a welded straight pipe is in place.
You will still need to tune that carb and probably swap out some of the jets to really maximize the MPG
You don't need a cat to run an Air Fuel Ratio gauge. In fact, you want it installed before the cat, so you get an accurate reading.
The thing about carburetors that you seem to be misunderstanding is that the CFM rating on a carb is the amount of air flow that passes through the carb at a certain amount of vacuum under the throttle blades. The jet, booster, squirter nozzles and air bleeds are what control the fuel flow on a carb. Changing to a smaller CFM carburetor helps with throttle response, drivability and lower rpm fuel distribution because it brings up the air speed lending to better fuel distribution. No carburetor is going to be perfectly tuned for your engine out of the box. If you're too lazy to bother tuning it, the 500cfm will be a closer match to your needs than the 650cfm but when properly tuned you should see little to no difference between the two.
As previously stated, GM used 700-850cfm carbs on stock motors in these cars, hell ford put 1000cfm worth of carbs on a 289, Chrysler put 1400cfm worth of carbs on their stock engines. Carburetors are all about tuning the fuel flow to match the incoming air.
As previously stated, GM used 700-850cfm carbs on stock motors in these cars, hell ford put 1000cfm worth of carbs on a 289, Chrysler put 1400cfm worth of carbs on their stock engines. Carburetors are all about tuning the fuel flow to match the incoming air.
- Status
Similar threads
