Choosing Carburetor for 1970 Road Runner 383

[RoadRunning]

Update - one Holley rep recommended the 650 CFM classic per above, another Holley rep recommended the 770 Street Avenger over the phone. LOL. Leaning towards this threads recommendation of the 750 CFM. Question - I have a single fuel feed currently. Most of these 750 CFM are dual feeds but there are single feeds also. Should I go single fuel feed or dual?

 

[oldbee]

Formula is.. cfm = cubic inches x rpm divided by 3456. Then you need to multiply cfm by volumetric efficiency the get "real" cfm needed. Stock eng/heads is probably 80%. Have fun, it works out lower than you would believe.

 

[Lazerwolf]

Update - one Holley rep recommended the 650 CFM classic per above, another Holley rep recommended the 770 Street Avenger over the phone. LOL. Leaning towards this threads recommendation of the 750 CFM. Question - I have a single fuel feed currently. Most of these 750 CFM are dual feeds but there are single feeds also. Should I go single fuel feed or dual?

Dual feed is fine. Just to clarify, the dual feed (such as the 4150/4160) is not a double pumper, just dual feed. Never had any issues with mine and even found a dual feed line on Ebay with fuel pressure gauge it in. Works fine for me.

 

[RoadRunning]

I think I am going to go with 0-80459SA. It is a single feed 750 Holley classic electric choke and vacuum secondaries. It will keep the setup simple and should get the job done well.

 

[oldbee]

Running- should work pretty good. I ran a 780cfm Holley for quite awhile&loved it. Did you play with cfm formula at all? You can change rpm and get quite a fluctuation in cfm. I.e.- cruise rpm or wot.

 

[moparwacko]

I think I am going to go with 0-80459SA. It is a single feed 750 Holley classic electric choke and vacuum secondaries. It will keep the setup simple and should get the job done well.

Excellent choice for a mild build such as you've described. Basic 4150 design, so you'll have tunability for future if need be. 20-7 adapter ($10)bracket will be needed ---don't "fab" something. I also would suggest an insulator for street use. I'm partial to Holleys on performance engines, having built/rebuilt probably hundreds over decades, but do admire the driveability of an Edelbrock on stock setups. Eddy's can be very successfully tuned for performance use, but you better understand their design. I can't speak to Demons, not enough experience with them other than basic rebuilds, and tuning.
Good luck!

 

[moparwacko]

Excellent choice for a mild build such as you've described. Basic 4150 design, so you'll have tunability for future if need be. 20-7 adapter ($10)bracket will be needed ---don't "fab" something. I also would suggest an insulator for street use. I'm partial to Holleys on performance engines, having built/rebuilt probably hundreds over decades, but do admire the driveability of an Edelbrock on stock setups. Eddy's can be very successfully tuned for performance use, but you better understand their design. I can't speak to Demons, not enough experience with them other than basic rebuilds, and tuning.
Good luck!

 

[moparwacko]

Sorry, brain fart.........
It's a 4160 basic design.......duh
Got a really old 4777 apart on the bench, got 4150 on the brain.
Forgive me

 

[RJRENTON]

To all the contributors......one important issue has been overlooked . ...no one mention the rear gear ratio or compression ratio..... and....cam specs (duration, lift, overlap, degrees advanced or retarded), compression ratio....all effect mixture velocity and subsequently cylinder filling. Carbs with lower cfm's on a 383 engine a moderate cam (similar to the stock hp grind) USUALLY provide acceptable performance with a 3:23:1 gear. 3:55:1 gear will tolerate a little more cam. The more gear (hihher numeric ratio) usually tolerates more carb and cam. Vacuum actuated carbs like Holley 3310 or an Edlebrock carb with velocity actuated secondary (or demand secondary like the oem Carter AVS) work extremely well when jetted for the operating conditions not what your next doors neighbors cousin heard his brother in law said you should do... which is generally wrong...... Use common sense, do your own du diligence . ..which will result in you having a better understanding . PM me if you want...
Cheers,
RJ Renton

 

[440fish]

Ive got a barely used 650 holley w/ Vac secondaries and electric choke. 50 bucks and its yours.

 

[bee71]

My AVS 4966 works really well.

 

[Phillipkj4]

I think I am going to go with 0-80459SA. It is a single feed 750 Holley classic electric choke and vacuum secondaries. It will keep the setup simple and should get the job done well.

How do you like it, I am about to grab this exact one at summit for my 383.

 

[oldbee]

RJ has it right.. Don't go too big & mech.sec. are are a big no-no on the street w/o gearing,headers,hi-stall conv's(on autos). Vac. sec. make everything so much better in driveability. We all like to "talk" high cfm, but on the street it doesn't always work. It's all a synergy with what's on the car.

 

[RoadRunning]

How do you like it, I am about to grab this exact one at summit for my 383.

Just now got my car in shape to drive a bit (had to replace the whole fuel system due to tank corrosion). Still not enough time driving to know how I like the carb yet (750 CFM Holley 0-80459SA).

The hood is still off the car but it seems to have a lot of fume smell to it. We also notice drops of fuel spilling out of the exhaust pipes a bit. Furthermore, when I go down a hill in 2nd gear with my foot completely off the gas, I fear the car is going to die unless I give it some gas. Any tips on how I should tune this beast?

Thanks!

 

[oldbee]

‘Running’, sounds a lot rich to me; look at your plugs first off.

 

[RoadRunning]

I think we found the main issue. We were doing all this with the hood off. When we put the hood on, we realized we had the air grabber hood vacuum lines open the whole time which was causing a vacuum leak when the hood was off. Now that we realized that, turned the switch off, connected the air grabber, the vacuum leak should be gone.

Now, the car starts up great. 1 or 2 pumps of the gas peddle and it fires right up. The idle seems to be good also. However, after the car is warmed up, if we shut it off and then try to start it back up while it is still warm/hot, it will crank but not start unless I pump the gas peddle again. I would expect the car to start up immediately without pumping any more gas to the carburetor. Thoughts?

 

[oldbee]

Yup, kick yourself, lol.

 

[Jcharger]

Concerning starts and a pump or not. I have had both types of behavior (one pump and go on warm) and no pumps and go (on warm). I use an MSD now, and wonder if it is more than just the carb, maybe the ignition. I think I end up training myself for the behavior that works.

 

[Johnpat]

Does the phrase,to much information come
into play here???