How much carb is too much carb

[BSB67]

I did think so. Made me laught though.

 

[WileE]

First, I'd recommend a different dual-plane intake, that manifold does not belong on your stock application. Second, the Holley 3310 is a great carb, a very versatile piece we'd install on many various engines, it's fine if the systems working as designed.

 

[lewtot184]

You might want to verify TDC mark on the dampner. If it's slipped you'll never get the ignition curve correct. 383's aren't very good at producing torque. The intake manifold makes that problem worse.

 

[lewtot184]

Another thought is altitude. If your over 5000ft above sea level a re calibration will be needed. 74 jets should be too fat.

As far as vacuum goes high elevations will noticeably reduce vacuum. I live at around 700ft and the best vacuum I can get at idle with a stock cam, intake/carb, with a good clean burn is 16". If by chance the short block has lower compression pistons (2bbl or worse) along with a single plane intake, and low oxygen percentage, and poor timing curve power will be in the toilet.

 

[4speed68rt]

Probably too rich. Find out what the factory jetting was on the 3310 and go down at least 6 sizes for your altitude. Advance the timing until it's hard to crank then back off a little.
Probably not the best intake manifold for a heavy car either. Perfomer or a stock one would make it more responsive.

 

[Bluefish]

Probably too rich. Find out what the factory jetting was on the 3310 and go down at least 6 sizes for your altitude. Advance the timing until it's hard to crank then back off a little.
Probably not the best intake manifold for a heavy car either. Perfomer or a stock one would make it more responsive.

Wont idle and pops thru carb is a lean indication. Vac leak or poor fuel transition first to check. Make sure timing is correct before you do anything.

 

[RemCharger]

I have a 69 383 with a TM6 and a double pumper flowed to 930, it runs 12.50s.
Guess I'm the wrong guy to ask about carb size lol.
But seriously, the 3310 is the best carb for that application. Congratulations on not running an edelbrock power choker

 

[BSB67]

Congratulations on not running an edelbrock power choker

 

[Geoff 2]

One thing the Torker does not have is......torque. The 383 engine has one of the highest ros/stroke ratios of any American V8 engine. In laymans' terms that means it doesn't generate a strong carb signal at lower rpms. At high rpms, it will shine....
The 780 Holley has 4 barrels, all 1 11/16". The 383 came from the factory with a 625 Carter that had 1 7/16" primaries for great throttle response; & large 1 11/16" secs for HP. And that was with a dual plane intake. The engineers knew what they were doing....
You have a single plane intake that is drawing from two large barrels for initial acceleration, with an engine that has poor signal.

If you want to keep the Torker, get an Edel 600ish AFB or AVS2. There will be a night & day difference everywhere in the rpm range. Or a TQ, but they are getting hard to find.
This sounds like a stock engine. So it would be lucky to have more than 80% VE or rpm higher than 5500 rpm. That requires a carb with around 520 cfm of airflow. Any more airflow is wasted, not used, can be detrimental because oversize throttle bores/venturiis have reduced signal strength. A bigger carb might make more HP, but it would be from better booster design signal strength etc, NOT more airflow.

If you go to a dual plane intake, the above 600 carbs will also work well. I would keep the Holley for a paper weight....or boat anchor.
Below is a test between a 600 Vac Sec Holley & 625 Carter AFB. The AFB made 17 ft/lbs more tq, 17 hp more....& used less fuel doing it.

 

[66 Sat]

What size engine was this fabled Carter vs Holley test carried out on?
Maybe the Carter made more power and torque because it was a 625 vs a 600? Perhaps that paper-weight, boat anchor junk Holley 750 that the OP owns would have made another 17hp more than the Carter?
Or maybe it made more power because it was tested on the Edelbrock dyno and not the Holley dyno...

 

[lewtot184]

Back in 1970 I had a 383 4spd car I beat the snot out of. It had a stock short block and heads, but a dp4b intake, small hydraulic cam, and 1 3/4 headers. I usually ran a 780vs holley with a best et of 13.22. Took the car to the track with a 4618 avs, no other changes, and the car ran exactly 13.22. Neither time was the engine poorly tuned.

 

[451Mopar]

Why I was mentioning tuning the idle/transition circuit is that at low speeds, under around 40 MPH, with a large carb you are mostly running on the transition circuit and really not into the main metering because the throttle blades are just slightly cracked open.
A smaller carb will hurt maximum power output at wide open throttle, but allow running on the main metering circuit much sooner because the throttle will need more opening at the lower speeds.
Racers will use very large carbs, but they normally operating them at idle or wide open throttle, and with a clutch or high stall converter, might never run in the lower 1,000 - 3,000 rpm range.
At high altitude, I found that "street" calibrated carbs tend to be lean in the idle / transition circuit. Race carbs are usually are much richer, so usually they don't need as much changes. When I first started making metering block and air bleed changes, I bought a billet metering block with the screw-in bleeds and restrictions.
After doing a few, I got a pin gauge set to better measure the opening sizes, and a pin drill set to just modify the original metering plate(s) and have the billet plate for tuning other carbs.

 

[Bluefish]

Why I was mentioning tuning the idle/transition circuit is that at low speeds, under around 40 MPH, with a large carb you are mostly running on the transition circuit and really not into the main metering because the throttle blades are just slightly cracked open.
A smaller carb will hurt maximum power output at wide open throttle, but allow running on the main metering circuit much sooner because the throttle will need more opening at the lower speeds.
Racers will use very large carbs, but they normally operating them at idle or wide open throttle, and with a clutch or high stall converter, might never run in the lower 1,000 - 3,000 rpm range.
At high altitude, I found that "street" calibrated carbs tend to be lean in the idle / transition circuit. Race carbs are usually are much richer, so usually they don't need as much changes. When I first started making metering block and air bleed changes, I bought a billet metering block with the screw-in bleeds and restrictions.
After doing a few, I got a pin gauge set to better measure the opening sizes, and a pin drill set to just modify the original metering plate(s) and have the billet plate for tuning other carbs.

I agree. When you start changing high and low speed air bleeds or moving emulsion around and drilling IFR's , you really learn what's going on. I ran a 1150 Dominator 2 circuit on the street on a 511 and it ran flawlessly. Easy starts, long idling times and no hiccups of any kind. If a carb is tuned for what you're doing the size really doesn't matter that much. Smaller carbs are easier to get there for sure, but then you give up some high-speed performance. My 511 does have a 5400 8" vert and a large cam. My Dom was so well dialed that at the track it was just a high-speed bleed change to put the AFR where i wanted it and many don't know this, but a turn of the mixture screw can help at hi speed as well, if you just need a little more. They work all the time. At some point in transition, that IFR turns into an air bleed, but i really don't understand that part of it. I now use twin BLP 700ish 650's and they are even better for street manners than the 1150 was. If the gentleman had a stall vert and a performance cam i see no reason why the 750 would not work perfect. I ran the same 750 vac sec on a 340 ( 4 speed and 4.10 gears) and it ran great, but when i switched it out for a 750 double pump BG it was better. Accelerated much faster with the double pump. Its all about having the right pieces to the puzzle and tuning it correctly. You need to start with a good sound engine with the proper ignition timing with good wires and fresh plugs. Then you start on the carb. Even with the combo the gentleman has, the 3310 should work just fine if its clean and tuned properly.

 

[Geoff 2]

66 Sat,

The engine was a 1972 350 Chev engine. You obviously know NOTHING about Edel history.
Edel did not start making AFB carbs until the mid to late 1980s.
If you had a 1979 Edel catalog, which I have, you would see part #s such as 4301 & many, many more. They are all part #s for Holley carbs...& Holley carb parts.

Yes, Edel was selling Holley carbs, tweaked with milled air horns, altered met blocks looooong before they made & sold AFB/AVS carbs.

 

[66 Sat]

Cool.
When was the test performed though? You said the engine was a 1972 350 Chev.
What was the date of the dyno comparison?

Regardless, you keep posting the same single dyno test from whenever performed by whoever (perhaps with an agenda, perhaps not), and instead of usefully contributing your knowledge to the forum you act almost like a troll, throwing in these blanket statements about Holley carbs that alienate you from many people, instead of acknowledging their advantages but then offering up an alternative.

You know a lot (but not everything). Try to use your knowledge more constructively.

 

[lewtot184]

I wish there was a better system of rating carbs other than cfm. Cfm by itself is lacking in my opinion.

 

[Geoff 2]

66 Sat,
I don't know when the test was done. Obviously after 1972.....
I don't need a lecture from you. Ignore my posts if you don't like them. I get people thanking publicly [ on the forum ] & privately for comments/help I have given.
As far as offering up an 'alternative' to Holley carbs, I am doing that all the time....I mention Carter...alot.

 

[RemCharger]

the same single dyno test from whenever performed by whoever (perhaps with an agenda, perhaps not),

Current information. No agendas. It's the straight dope.

 

[66 Sat]

66 Sat,
I don't know when the test was done. Obviously after 1972.....
I don't need a lecture from you. Ignore my posts if you don't like them. I get people thanking publicly [ on the forum ] & privately for comments/help I have given.
As far as offering up an 'alternative' to Holley carbs, I am doing that all the time....I mention Carter...alot.

So the test could have been done during or after Edelbrock had started negotiations with Carter on a licencing agreement or similar regarding their carburetors and the dyno test could have been a marketing exercise?
I'm only asking because you said I know "NOTHING" about Edelbrock's history (which is mostly true) but at the same time you are using test data which may not be entirely impartial to sway the OP into purchasing a new carburetor when many other experienced people here are saying the 750 Holley he already has is perfectly fine.
I have also publicly (and privately) thanked you in the past for your help. As I said, you do know a lot, but your bedside manner could use a little work. This isn't A Bodies you know, where arguments are mandatory. Here we discuss things...

 

[Geoff 2]

Just put me on ignore. Discussions are the same here as on any other website. Made up of a mixture of people. I will continue to publish that AFB v Holley graph as it mirrors my own experience, & I have no reason to believe it has been doctored or is fake.