How much is too much dual quad

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How many CFM is too much for a ......383 +.030 over, Edelbrock Performer heads, MSD ignition, headers, auto 727 with 2400 converter and 3.91 gears. Currently has a FAST EFI. It is not my preference, but I would like to try dual quads with an Offenhauser intake. The carbs are two 600 cfm Holley 4160s. Am I wasting my time with this? Ideally I think I would be better off with two 400s, but I would like to use what I have now just to see if the engine will respond to it. However, as you can imagine, removing all the hardware from the efi that is on there now is quite a task if I know that the two 600s won't work and I don't know that. Am I wasting my time, or would it be worth it to slap them on?
 
That's a lot of fuel going in. Two 400's is just about right. (800 cfm)
 
That's a lot of fuel going in. Two 400's is just about right. (800 cfm)
Agreed, is it just a waste of fuel, or a matter of not using a WOT, or would it bogg to engine down. I wouldn't be asking if the engine had not had the heads, headers, digital ignition, cam all added. 650 to 750 would be my choice for a stock hp 383. Knowing 2 quads sharing 1200 cfm is probably only equivalent to a 900-950 single 4 barrel, leaves me with the question. Do I have a chance with two 600's? Can I re-jet them any to make them work? Am I just wasting my time?
 
If you are going to put dual quads on and have the 2 600's, put them on and try them. Here is my list why.
  1. they are vacuum secondary, so on the initial hit it's only 600 cfms. So would a 600 Double Pumper be too much for your motor?? Obviously the answer is no.
  2. the vacuum secondary's will open as the motor calls for it
  3. Only gas forced in the engine is by the accelerator pumps. Carbs are not forced induction. The engine syphons gas and air into the cylinders.
  4. Do you know how much CFM's are placed on top of a stock 340 6 pack?? Hmmm....
 
That's a lot of fuel going in. Two 400's is just about right. (800 cfm)
Are you talking just the accelerator pumps???? It would only be the same as a 600 Double Pumper Holley, which would be too small for his combo. Carbs don't "dump" fuel into a motor, accept for the pumps. And the tuner controls the shots from the pumps. They are not superchargers or blowers or any form of forced induction. The engine "pulls" the air/fuel into it. It will only pull so much air and the tuner controls this and matches the fuel with jetting, power valves, vacuum secondary springs.....
 
If you are going to put dual quads on and have the 2 600's, put them on and try them. Here is my list why.
  1. they are vacuum secondary, so on the initial hit it's only 600 cfms. So would a 600 Double Pumper be too much for your motor?? Obviously the answer is no.
  2. the vacuum secondary's will open as the motor calls for it
  3. Only gas forced in the engine is by the accelerator pumps. Carbs are not forced induction. The engine syphons gas and air into the cylinders.
  4. Do you know how much CFM's are placed on top of a stock 340 6 pack?? Hmmm....
Ya it's all about the "coolness factor" Good thing the 6 pack set ups had vacuum outside carbs. They really couldn't use or didn't need all that cfm.
 
Ya it's all about the "coolness factor" Good thing the 6 pack set ups had vacuum outside carbs. They really couldn't use or didn't need all that cfm.
Get it out of your head that carbs are forced induction. His engine will only pull what it needs. He will tune the accelerator pumps initial shot by the squirter nozzles, pump arm adjustment, and the size of pump (30cc or 50cc). After that, the engine only pulls what is needed for air and he will tune the jetting to match.
 
Yep this sounds about the way everybody sounded when I said I wanted to put them on a warmed up 318...
I had them as I have now, a Carter performance AFB625 on the back that I got free from us scrap metal customer taking it warm off of a Chevy truck and said the choke doesn't work. And a 1406 Edelbrock 600 on the front.
Of course on the 318 it was rich as hell but also I didn't know anyting about how to tune them I just knew it was run way faster LOL and proved so at the drag strip. Now that I've had more experience and some more tools and a 410 I've been able to fine tune to about 14/7 at idle and trying to get at 12/5 wide open throttle. I don't get enough wide open throttle times to be able to turn it well. I've been seeing much richer stuff like 11/3 but I don't think I've been able to hold it down long enough to let it settle out, it may be just spiking...
I say try it you might like it you have the stuff... I used what I had/have. My car runs near perfect with 1225 CFM LOL and I don't believe it really works the way you think it would in Theory.. the nice thing is the engine is going to only at some point take what it can use and there's always plenty to take...:thumbsup:
 
Get it out of your head that carbs are forced induction. His engine will only pull what it needs. He will tune the accelerator pumps initial shot by the squirter nozzles, pump arm adjustment, and the size of pump (30cc or 50cc). After that, the engine only pulls what is needed for air and he will tune the jetting to match.
Oh I understand and I am a lot smarter than you think I am. The op has a Fast fuel injection set up on it now. It almost sounds like he is a young gun looking for a wow factor tunnel ram sticking out of the hood. If he was experienced and knowledgeable he wouldn't have asked "how big is too big" in the first place. Think about that before you talk him into it.
 
100% agree on the coolness Factor!!!
But it was more than the coolness factor.... that is why the 6 pak was rated at more horsepower.

I'll never understand people saying "too much cfm's forces too much into an engine. Especially on vacuum secondaries. That is such a myth and old early 70's talk it's just funny. Cylinders are like syringes. They syphon only so much. Tune to match the air going into the cylinders and let 'er rip! I pulled a 600 off my stock 360 with 2.45's (and at that time no headers) and went to a 770. Guess what? E.T. dropped at the strip.
 
Oh I understand and I am a lot smarter than you think I am. The op has a Fast fuel injection set up on it now. It almost sounds like he is a young gun looking for a wow factor tunnel ram sticking out of the hood. If he was experienced and knowledgeable he wouldn't have asked "how big is too big" in the first place. Think about that before you talk him into it.
I'm not talking anyone into anything. He asked 1 question. "Will the 600's work or be too much and be a waste of time". I answered the question he asked. IF he would have asked what worked best, I'd had given him a different answer.
 
How many CFM is too much for a ......383 +.030 over, Edelbrock Performer heads, MSD ignition, headers, auto 727 with 2400 converter and 3.91 gears. Currently has a FAST EFI. It is not my preference, but I would like to try dual quads with an Offenhauser intake. The carbs are two 600 cfm Holley 4160s. Am I wasting my time with this? Ideally I think I would be better off with two 400s, but I would like to use what I have now just to see if the engine will respond to it. However, as you can imagine, removing all the hardware from the efi that is on there now is quite a task if I know that the two 600s won't work and I don't know that. Am I wasting my time, or would it be worth it to slap them on?

That's a lot of fuel going in. Two 400's is just about right. (800 cfm)

Waste of time

100% agree on the coolness Factor!!!

Never mind ye' all! Sorry I took the time to answer his question, because 1 minute after he posted this thread, he posted the intake and carb combo for sale ...
BWAHAHAHAAA
:rofl::rofl:
 
Also I should say I tell everybody it would be a lot faster if I had one of those computer carburetors I could tune with my cell phone. BUT, I love my dual quads and I would hopefully never have it any other way....
 
Agreed, is it just a waste of fuel, or a matter of not using a WOT, or would it bogg to engine down. I wouldn't be asking if the engine had not had the heads, headers, digital ignition, cam all added. 650 to 750 would be my choice for a stock hp 383. Knowing 2 quads sharing 1200 cfm is probably only equivalent to a 900-950 single 4 barrel, leaves me with the question. Do I have a chance with two 600's? Can I re-jet them any to make them work? Am I just wasting my time?


Those two 600's are WORTHLESS. You can use 2 650's and be way better off.

The number one killer of TR engines is over cramming them. Number two us under carb'ing them.

Get on the phone with a true carb guy, like Thumpr carbs in FB or Mark Whitener or BLP or Braswell and let them fix you up with two good carbs.

The 1850 Holley was garbage when it was drawn up, unless it's some dead stock deal. And then it's useable.
 
My call to Edelbrock was about the biggest joke obtaining information on how to tune these carburetors. When I told the guy adout the two carburetors I had he told me that I couldn't use those. He highly recommended that I buy two new- I think it was 500 cfm's or something because that's what his coworker is running on his dual quads. I told him I'd been running those carbs for years now and I just needed help tuning them and he had nothing...
 
Never mind ye' all! Sorry I took the time to answer his question, because 1 minute after he posted this thread, he posted the intake and carb combo for sale ...
BWAHAHAHAAA
:rofl::rofl:
I want to try them on my car... for sale LOL
Now I realize it's a low rise manifold. If they're not sticking up out of your hood what's the point??...
 
Never mind ye' all! Sorry I took the time to answer his question, because 1 minute after he posted this thread, he posted the intake and carb combo for sale ...
BWAHAHAHAAA
:rofl::rofl:
Smart man. lol he should stick with the EFI or if he likes to tune, a 750 dp and RPM intake would be my choice.
 
Those two 600's are WORTHLESS. You can use 2 650's and be way better off.

The number one killer of TR engines is over cramming them. Number two us under carb'ing them.

Get on the phone with a true carb guy, like Thumpr carbs in FB or Mark Whitener or BLP or Braswell and let them fix you up with two good carbs.

The 1850 Holley was garbage when it was drawn up, unless it's some dead stock deal. And then it's useable.
agree. I am not a 1850 fan.
 
Hey, thanks for the inputs from all of you. Quite helpful and mostly appreciated. The judgement call that “sounds like he is a young gun looking for a WOW factor tunnel ram sticking out of the hood” couldn’t be further off. At 73 and having bought Mopars from my first one in ‘63 and one every year through the 60’s and a Cuda in 70, the Wow factors left me years ago. My WOW now is a Viper and a ‘67 GTX. Yes, I do tune them myself and have been doing so for longer than than most on this site. I do like Holleys and run a 850 DP from PRO on the 440 in the GTX. I am WOWed by it every time I take it out. On the Duster with the EFI, I would run a 700 or 750 DP if I had my choice. However, the Quads do provide a WOW factor, and without cutting a hole in the hood. When the car goes up for sell, that WOW Factor helps sell it. Not having experience with dual quads, I asked the “pros” on this site to find out others experience and recommendations. For those that responded, thank you. Yes, I have put them up for sale, even before I asked the question about trying them, not after. There are other For_Bodies Only sites. Check B body site. To 318WillRun, thanks for the advise. You hit right on what I was after. Whether I keep these quads, or sell them, I will be running dual carbs of some optimum level at the point in time that I remove the EFI. It will be removed. It just does not feel a part of you if you don’t do the adjusting. Continued comments are welcomed and advise on the linkage would be appreciated.
 
Whether I keep these quads, or sell them, I will be running dual carbs of some optimum level at the point in time that I remove the EFI. It will be removed. It just does not feel a part of you if you don’t do the adjusting. Continued comments are welcomed and advise on the linkage would be appreciated.
Thanks for clarifying. I agree, adjusting is part of it. :) Please keep us posted on when you decide and post pictures
 
Hey, thanks for the inputs from all of you. Quite helpful and mostly appreciated. The judgement call that “sounds like he is a young gun looking for a WOW factor tunnel ram sticking out of the hood” couldn’t be further off. At 73 and having bought Mopars from my first one in ‘63 and one every year through the 60’s and a Cuda in 70, the Wow factors left me years ago. My WOW now is a Viper and a ‘67 GTX. Yes, I do tune them myself and have been doing so for longer than than most on this site. I do like Holleys and run a 850 DP from PRO on the 440 in the GTX. I am WOWed by it every time I take it out. On the Duster with the EFI, I would run a 700 or 750 DP if I had my choice. However, the Quads do provide a WOW factor, and without cutting a hole in the hood. When the car goes up for sell, that WOW Factor helps sell it. Not having experience with dual quads, I asked the “pros” on this site to find out others experience and recommendations. For those that responded, thank you. Yes, I have put them up for sale, even before I asked the question about trying them, not after. There are other For_Bodies Only sites. Check B body site. To 318WillRun, thanks for the advise. You hit right on what I was after. Whether I keep these quads, or sell them, I will be running dual carbs of some optimum level at the point in time that I remove the EFI. It will be removed. It just does not feel a part of you if you don’t do the adjusting. Continued comments are welcomed and advise on the linkage would be appreciated.
You said Duster so I'm assuming you're talking about doing this on a duster. I found a hood for 60 bucks to cut a hole in.
 
But it was more than the coolness factor.... that is why the 6 pak was rated at more horsepower.

I'll never understand people saying "too much cfm's forces too much into an engine. Especially on vacuum secondaries. That is such a myth and old early 70's talk it's just funny. Cylinders are like syringes. They syphon only so much. Tune to match the air going into the cylinders and let 'er rip! I pulled a 600 off my stock 360 with 2.45's (and at that time no headers) and went to a 770. Guess what? E.T. dropped at the strip.

Well there IS trial and error, but the idea that a carb "only flows what it needs" can ALSO get you into trouble. The big big problem with oversize carbs is that they don't generate enough AIR VELOCITY to properly operate. This is a situation that does NOT happen with EFI. With a properly tuned / tunable EFI you can put a bucketload of throttle body on the thing and the worst pretty much happens is that throttle pedal "feel" gets "too fast" in other words barely touch the throttle, and "a lot" happens.
 
It depends on a few things. Type of carburetor. Size of carburetor. Style of linkage. Progressive or straight. Two Thermoquads, for instance, although unorthodox, the engine could probably stand two 850s. Since the secondaries on the Thermoquad are regulated by engine vacuum, that means the engine will only use however much of that total 850 CFM each that it needs. Two 850 Holleys would drown it, while two 850 Thermoquads properly tuned would peel up the asphalt. Same with the Carter or Edelbrock AVS style carburetor, since they also have 100% vacuum regulated secondaries, like the Thermoquad. The Rochester Quadrajet is another example of a vacuum regulated secondary carburetor. Also, regarding the linkage, a progressive style linkage will allow the carburetors to come in more controlled a little at a time, instead of all at once like straight linkage. So unless you nail down which carburetor and linkage you plan to use, the answer is pretty all encompassing.
 
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