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Which carb would you choose and why?

 
  #1  
Old 09-03-2013, 01:26 AM
FatherDonald74
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Which carb would you choose and why?

I have a 78 Bronco with a built 400 and C6 combo. The stats are as follows: 351M with 400 crank/pistons and bored to 408 with a custom ground cam, 4V Cleveland heads from a '71 Mustang, Edelbrock Performer Intake, Accel Distributor, MSD Blaster coil, Holley 4150 Double Pumper with off-road needles/seats, 1-ton brake booster, and new 3.73 gears.
All the mods except for the gears were done by the previous owner. He said he had around $5,000 in the engine alone and I'm inclined to believe him judging by it's power. When I got it the previous owner had an early style propane injection assist setup on the truck, I believe it was something like "Fuelmeister". Anyway, I removed the propane system because I don't want to have to worry about finding two fuel sources and now it doesn't run very good without it. I expect it was tuned and timed with the propane factored into the equation. The last few times I ran this truck it was so hard to start, it backfired from the carb and exhaust like crazy, and sounded like a hit and miss engine once it finally started. It took about 5 minutes of warming up even in 65 degree weather before I could even slightly rev it without the carb burping. The timing and carb must be off since removing the propane.
This truck has been sitting in my barn for about 5 years now and hasn't ran in the past 1 1/2 years so before I go and try bringing it back to life I figure I should flush the fuel system and clean the old fuel/gunk from the 4150 Holley. My question is, is the 670cfm 4150 a good carb for the engine setup in my truck or should I put a 4160 Holley(600cfm) on it that I have from my old 460 equipped F350?
I know there are lots of people who say 4V Cleveland heads and Holley Double Pumpers are both items better suited for high revving, lightweight racing applications but I can tell you what, once my engine finally warmed up and stopped sputtering, even with it being out of tune it had so much power it would plant me back in my seat like my Late Model dirt track car from back in the day. It had tons of power just off idle even with 35" M/T's and a C6 with it's 2.46 first gear ratio. It may not have ran perfect but it had some power.
So what I'm getting at here is that I know it will need to be re-timed and the carb re-tuned so it doesn't pop and backfire like a Chevybut what I don't know is, which of the aforementioned carbs is the better choice for my engine considering all the mods that I have listed? Personally I think the 4150 with a rebuild would do the trick but I would like to hear from those who have ran a similar engine setup with either of these carbs to find out which has been more responsive and required less frequent tuning.
I plan on using this truck for hauling the family out in the woods and to the local cruise-in on the weekends. Well, that is what I hope to do with it but it seems like life always gets in the way.
 
  #2  
Old 09-03-2013, 06:36 AM
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This is coming from a Q-jet and Edelbrock fan, but I think that you'd be a little happier with that smaller carb on there. That 4160 is a good piece of equipment, especially if it's somewhat recently re-sealed and doesnt have the throttle shafts ovaling out their bores.

Anyhow...to really get ANY proper tune out of it, regardless of what people say about tuning by ear and all that good stuff, one of your steps should be to install a good air/fuel ratio meter.

Good luck with it, it sounds like a fun combo!
 
  #3  
Old 09-03-2013, 07:56 AM
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Originally Posted by psychlopath View Post
This is coming from a Q-jet and Edelbrock fan, but I think that you'd be a little happier with that smaller carb on there. That 4160 is a good piece of equipment, especially if it's somewhat recently re-sealed and doesnt have the throttle shafts ovaling out their bores.

Anyhow...to really get ANY proper tune out of it, regardless of what people say about tuning by ear and all that good stuff, one of your steps should be to install a good air/fuel ratio meter.

Good luck with it, it sounds like a fun combo!
x2 on the smaller carb(higher air velocity=quicker throttle response) and the A/F gauge.

A good vacuum gauge is also very valuable for dialing in the tune.

I'm a big fan of the Edelbrock carbs too...I'm on my third one and all have performed the same...set it and forget it.

All of mine have come from National Carburetors, a carb rebuilder and all have run right out of the box. http://www.nationalcarburetors.com/
 
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Old 09-03-2013, 02:57 PM
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Generally, the formula for figuring out carburetor size is:

(Engine CI * Max RPM * VE) / 3456

VE is volumetric efficiency. Most stock engines are around 80%. Mild performance 85 - 90%. Highly built and modified, somewhere between 90 and 100%.

What's the max RPM of the engine? 6500?

(400 * 6500 * 0.95) / 3456 = 715cfm

Both of those may actually be a tad small if you want to get the FULL potential out of your engine.

However, as others have said, smaller carbs give you better throttle response. And, ask yourself how often you rev it up to 6500 RPMs.

Granted, sometimes that's all thrown out the window. I run a 600cfm Holley on my 300I6 and it runs great and gets decent gas mileage.
 
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Old 09-03-2013, 04:10 PM
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I already have an air/fuel ratio gauge and a vacuum gauge and many other gauges installed and working properly. Vacuum was good last time it was running but the carb always seemed to be too rich no matter how it was tuned. ?
I never had this truck on the road but the previous owner said it would rev at 6500 all day long. It really doesn't take much gas pedal movement to get this beast screaming past 6000.
I was actually thinking about rebuilding both carbs just for the heck of it, using the 4150 on the Bronco and putting the 4160 on my logging truck(79 F350 4x4). I like having all the power to spare with the built 400 and I really love the sound all those horses make through the dual 40-series Flowmasters, however, I have been thinking about yanking out the engine and selling it to someone who actually needs that much HP. I would like to take the drivetrain from my 78 F250(D60's front/rear and NP435), put those in the Bronco and put a 300 inline 6 under the hood. Most people swap the 6 for a V8 but I want to go the other way. I just love the idea of having the legendary reliability of the 300-6cyl., 1-ton axles, and a low geared NP435. If our country keeps on the same path we're on now, pretty soon nobody will be able to afford keeping all those high-performance parts on there trucks/cars and we'll be looking for the simplest, most reliable drivetrains possible. The 300/NP435 and D60's under a second gen. Bronco would be the epitome of reliability/toughness coupled to the best-looking truck ever made!
 
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Old 09-03-2013, 05:36 PM
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  #7  
Old 09-03-2013, 09:18 PM
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If you have an air/fuel ratio gauge, you should be able to tell if it's running fat or lean in any RPM, and not be guessing by how it seems. Tune to what that tells you and you'll be as good as youre going to get, as far as the carb goes. From there, you can check the tune on things like vacuum and mechanical advance...these make a HUGE difference in how an engine scoots and I very rarely see anyone pay them any attention.

Personally, I think youre going to have a hard time properly metering fuel with the double pumper carb you mentioned, but plenty of people love 'em. Plenty of people think that running pig rich and hard starts are just part of how a carb works, too, for that matter...I've just never been a big fan of anything but vacuum secondaries.

But, all that aside, unless I missread it sounded like you already had both carbs. Why not try both to see which one you like best?
 
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Old 09-04-2013, 05:14 PM
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Originally Posted by TurboBronco View Post
Enjoyed reading your writeup on FSB, awesome work! How's it running? Done a gas mileage test yet? One thing that perked my curiosity is when you said it was at 14hg at 2500 RPM idle. What's it at at normal (600 - 700) idle? Should be around 19 - 20 on a nice tight engine.
 
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Old 09-04-2013, 07:22 PM
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Originally Posted by AbandonedBronco View Post
Enjoyed reading your writeup on FSB, awesome work! How's it running? Done a gas mileage test yet? One thing that perked my curiosity is when you said it was at 14hg at 2500 RPM idle. What's it at at normal (600 - 700) idle? Should be around 19 - 20 on a nice tight engine.
And I enjoyed reading yours as well! (Many times!)

It is running great! Pump the gas pedal to put some gas in the carb, hit the starter, and it's running. The oem fuel pump and the fuel regulator seem to be doing a great job of providing gas to the carb.

I put in a full tank Tuesday morning, so I won't know the mileage until this weekend or early next week. I'm at 3/4 of a tank and 92 miles, so right now, it doesn't look like it has improved...I normally get about 340 miles per tank, which is usually 13 MPG. I am hoping to get 15-16, but I believe the Eddy 500 is set a little rich in cruise and power. I've ordered 2 sets of rods that will lean cruise out some, so I think I am going to have to do some tweaking to get the mpg's up.

I've tweaked the vacuum since that initial break in and in park, at idle, I am getting 21-22 hg. Idle in park is 1000 and in gear, 900. It vibrates the truck below that, but at 900 at a stop light, it is pretty smooth.

I am interested in the Summit carb you and 250 Restorer(?) are looking at. I am anxious to hear how it performs. I believe he has ordered one, so hopefully we will hear something soon.
 
 
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