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Carb recommendations

67 Coronet Conv

67 Coronet Conv

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Hello, thinking about swapping out my Holley Street Avenger 870cfm, think the carb is a little to big for my motor set up. Car is for cruising but like to take it down the track a couple times a year.

Any recommendations on the carbs below? Car/Motor specs below

AVS2 800CFM
Slayer Quick Fuel 750cfm
Summit series carb 750cfm w/vacuum secondaries

1967 Coronet Convertible
440 30over
Performer RPM Heads
Mopar Intake?
Steel Crank
Harland Sharp Roller Rockers
Mopar purple shaft cam 312/312 adv duration? 0.590in lift
Stock bottom end
727 trans
3:23 rear
Motor was at 9.8:1 comp ratio before heads, thinking closer to 10.5

Thanks

1047C139-9030-47D0-B09F-05C6B6644C75.jpeg
 
1 vote for the Quick Fuel.
 
I don't think the 870 avenger is too big of a carb by any means. A couple of things I would address before the carb swap of which I would probably recommend the 800 AVS2 which is great all around street carb but the camshaft is quite large for a street cruiser and the 3.23 gears looks to be too tall of a gear for your combo. What stall range of a torque convertor are you using because a stock convertor and the camshaft and gears you are running that engine would probably be kind of a pooch on the bottom end until it gets wound up.
 
I just got one of Summit's 600 CFM carbs for a 361 big block and I couldn't be happier. If you're looking to cruise most of the time, I'd go with the Summit carb. Worked just about perfect out of the box and it has new and improved annular discharge nozzles that greatly improve MPG and performance.

The other carbs you posted are probably up there too, performance-wise. Just my $0.02
 
If a six pack at 990 cfm was ok on a stock cam, iron headed 440 I can’t see why an 870 should be too much on your significantly more agressive version. Needs deeper gears (3.91) and a 11” converter at a minimum though.
 
Carb is not to big, not even close. What exactly are you trying to achieve with the carb swap?

How does it run at the track?
 
Stock 440 that came with a Holley was 575 cfm, calculations shoe at 84 percent volumetric efficiency about 650 cfm. If you don’t do all the mods suggested 750 cfm should work.
If you run anything over that that I would run a vacuum secondary carb. if you have steep gears and a converter go for the 870.
once you get your selection on hook up a vacuum gauge, at wide open throttle
If it reads at or above 1 in or above you can use a bigger carb.
 
kramer said:
I don't think the 870 avenger is too big of a carb by any means. A couple of things I would address before the carb swap of which I would probably recommend the 800 AVS2 which is great all around street carb but the camshaft is quite large for a street cruiser and the 3.23 gears looks to be too tall of a gear for your combo. What stall range of a torque convertor are you using because a stock convertor and the camshaft and gears you are running that engine would probably be kind of a pooch on the bottom end until it gets wound up.
Click to expand...

no idea on the torque converter, got the car 1.5 years ago. Any way to tell with out dropping the trans?
 
BSB67 said:
What are trying to achieve with the carb swap?
Click to expand...

for the car to run better and reliable. Had to be towed home a few times. Swapped the ecu thinking that was the problem. But a few people said that the carb was to big. Just want to be able to drive the car with fear of breaking down. Seems that I keep needing to adjust the idle screw, set it and the next time I drive it 2-3 weeks later need to readjust it.
 
I agree with BSB67 and kramer. The carb is NOT too big especially with the modifications you've done....I'm not trying to sound like a dik here but tuning any carb takes time and effort. Getting it right is much more than just tweaking the screws and swapping jets.

I know this isn't what you want to hear...but the glaring mismatch with your combo is the camshaft. With a 106 LSA and approximately 265 degrees @ .050, you will have a very tough time getting good street response out of it with your compression/weight/gearing & stall regardless of the carb. The intake valve closes later which dribbles off additional cylinder pressure and there is a large amount of overlap with that cam which will make tuning down low a hassle.


Of course, none of that is likely the cause of the car quitting on you and needing to be towed. That sounds like a whole other issue; maybe the coil crapping out when it's hot, poor connection somewhere, fuel pump or supply issues...

That is a beautiful ride by the way!
 
67 Coronet Conv said:
for the car to run better and reliable. Had to be towed home a few times. Swapped the ecu thinking that was the problem. But a few people said that the carb was to big. Just want to be able to drive the car with fear of breaking down. Seems that I keep needing to adjust the idle screw, set it and the next time I drive it 2-3 weeks later need to readjust it.
Click to expand...

Its important to be clear.

So you drive along at 60 mph and it dies?
or
You get someplace, and it wont restart?
or
After driving a while as you slow down taking your foot off the the gas coming to a stop, it dies?

And, what was done to get the car to restart it after it was towed home a few times? Was something fixed in the carb? Adjusting the carb frequently is not fixing or even helping anything.

We don't have much info here really. I'll just make some wild guesses on the fuel side:
1) if it dies while just driving along, but starts when its home - vapor lock.
2) If it dies at low speed, or wont start, fouled plugs due to the cam being way too big and it will always foul plugs no matter what carb you have. I cannot imaging a more mis-matched cam for what you got, and what you're trying to do.
3) There is no fixing the poor idling and low speed driving with that cam unless you put 4.30 gears in and a 4200 rpm stall, and let it idle at 1200 rpm.
4) an intake manifold leak making all of the above worse.

It could be electrical as others have mentioned. But if it is electrical and you fix that, it will still run like crap as low speed and foul plugs.
 
My guess is with that very large cam for the street the idle needs to be so far open it’s pulling from the idle transfer slots and fouling the plugs. The best way out of the problem is a milder cam, then everything will match.
 
BSB67 said:
Its important to be clear.

So you drive along at 60 mph and it dies?
or
You get someplace, and it wont restart?
or
After driving a while as you slow down taking your foot off the the gas coming to a stop, it dies?

And, what was done to get the car to restart it after it was towed home a few times? Was something fixed in the carb? Adjusting the carb frequently is not fixing or even helping anything.

We don't have much info here really. I'll just make some wild guesses on the fuel side:
1) if it dies while just driving along, but starts when its home - vapor lock.
2) If it dies at low speed, or wont start, fouled plugs due to the cam being way too big and it will always foul plugs no matter what carb you have. I cannot imaging a more mis-matched cam for what you got, and what you're trying to do.
3) There is no fixing the poor idling and low speed driving with that cam unless you put 4.30 gears in and a 4200 rpm stall, and let it idle at 1200 rpm.
4) an intake manifold leak making all of the above worse.

It could be electrical as others have mentioned. But if it is electrical and you fix that, it will still run like crap as low speed and foul plugs.
Click to expand...

First time no start after about an hour of driving 10 miles. Started fine the next day. Swapped out the MSD Blaster 2, read somewhere the ecu doesn’t like it and put in a flame thrower.

2nd time, does at low speed. Started the next day. Replaced ECU with cheap one from summit.

thinking the plugs may be super fouled, I’ll swap them today and report back. Thanks for the help.

may just deal with the cam for now until I’m ready to pull and rebuild bottom end.

thanks for the help
 
Swapped the plugs, looks pretty fouled. Guessing I should swap these out every 2k miles or so?

thinking of pull the motor on the winter to swap out the cam. For what’s it worth the car is kinda of a dog, I was expecting it to be faster than what it is. Thinking with the cam change hopefully be a little quicker.

Any recommendations on a cam for the set up I’m running?

thanks for everyone’s help/input

image.jpg
 
Did anyone in this thread mention Fouled Plugs

Yep
 
If you are keeping the 3.23 gears and assuming stock convertor and your not chasing horsepower numbers for a street cruiser you might entertain these camshafts
Mild: https://www.summitracing.com/parts/sum-6401
More aggressive: https://www.crower.com/camshafts/mo...50-440-b-compu-pro-hydraulic-cam-282-hdp.html
I would recommend keeping Lobe seperation on camshaft 112 to 114 degrees and not going past 230 degrees on intake duration.
You didn't list intake manifold but I would probably go with a performer RPM dual plane and stay away from the single plane for your application.
I would definately pay alot of attention to what BSB67 says he is pretty sharp on having mild type combo's that perform very well.
 
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