Okay,

I have read through many threads regarding 'which carb to use,' and have found great things to consider, but I am thinking that what I do and need my truck for is very specific and different than most posts I have read. Seems like most are discussing daily drivers, I am not.

What I have: '74 f350, 2wd, dually, dump bed, 4.56 gears (I think), 4 spd w/granny, efi exhaust, electronic ignition...stock intake/1bbl carb

What I want to do: my stock intake has many broken tabs from POs, so I need to get a new one. I picked up an Offy c, so I figure (and would like) to go to the Offy setup and not get another stock intake.

While I would like decent gas mileage, it is not a huge deal as I put only a few thousand miles a year on the truck - it is a work truck often filled with yards of gravel/dirt and/pulling a trailer/going to the dump. I find myself doing a lot of driving from 1500 - 2500 rpms (in fourth, 55 mph is just under 3000 rpm...which is pretty much the max I push it). So I figure I need more low-end torque than maybe some of the other posters that are looking good gas mileage. Maybe we are looking for the same thing, as I could be wrong?

From reading posts, I thought I had narrowed it down to an Edlebrock 500 (mainly because many posts said it was a very reliable, set it and forget it carb, AbandonedBronco and others...with the only negative being gas mileage), but when I spoke to National Carburetors, they thought I should get a 390 (which of course I have read good and bad about). They said it made even more sense for me to go with the smaller cfm carb because I do most of my driving around the 1500-2000 rpm (I am rarely on the freeway) and need the power down there (going up a hill in 3rd around 35 mph with a load).

So I now must post this and ask, which carb to use?...remember, I just want simple, power, easily adjusted, not have to adjust it often (although I believe I will have to do that every now and then regardless with any carb), and being able to rebuild/get parts too.

I would plan on installing a heating plate under the intake as well.

Thank you in advance for any advice/info.

Gudor

 

My DD needs/wants are similar. If you have a heated intake, and operate at lower RPM's and your power needs are not exorbitant, I would consider a 2 BBl variant of some type. I am getting good results with similar gearing using an older version of Ford's 2 BBl's. I now use a 2100 Auto-lite (50 years old), but the bolt pattern is the same as a newly mfg'd Holley 2300. Do the math with CFM needs, and you may find that you don't need a MUCH bigger carb that what a 2 BBL can offer. Just a different thought as opposed to "bigger-is-better", especially if economy/simplicity is part of the concern. It's all about tuning, and since Holley's, or Weber's Or Carter 2G's are sold new still, rebuilding is not an issue..

My prejudice stems from using a worn out Holley '94 on my first car..(Icouldn't find a resonable Stromberg Core to rebuild) Stromberg's http://www.stromberg-97.com/ are NOW sold new again...talk about retro.

As an additional note: if you do try a Holley 2300 and it doesn't fit your needs, with VERY unsatisfactory results, I'll send you a good used unbroken stock manifold, and a good used carter yf from the 70's for free. (I'm THIS curious how this 2300 Holley works for a 300-6 with an improved manifold).

Good luck

 

If you plug the numbers into a carb calculator a 300 probably only needs ~200cfm at 3,000 rpm.

The 390 is a better fit than a 500 according to the calculators (you'd have to rev it to 7,000 rpm to "need" a 500 cfm carb). It should meter fuel more accurately at low rpm. How much difference does it make in practice? I'd have to try a 390 to tell you.

My truck hasn't lost anything at low rpm with a 500 cfm 4v and Offy C vs. the stock intake/carb and has more power everywhere you could theoretically notice a difference. Now does not run as well as stock when the engine/carb is cold but I attribute that to losing the breather and choke stove from the intake as much as anything else.

Two barrels and four barrels are rated differently, divide the 2v cfm by 1.41 to get the equivalent 4v flow rate. If you're considering a 2v, that is. It may indeed work very well for your application. There are millions of 2v carbs out there to be had on the cheap.

 

Thank you for the replies...

John, it is a nice offer regarding the stock intake. I do have a good 1bbl carb, so I could go back to the original intake if necessary. I failed to mention that part of my desire to go to the offy inake/upgraded carb (not necessarily 4bbl) is because I would like to one day get another truck as a daily driver (once again a ford 300)...and preferably I would have the same setup in both trucks - but that is pretty far out there in the future and I am gathering that maybe the same setup for a 'hauler' and high mpg DD is not appropriate...if someone has an opinion on this, please do share.

Both of you discussed the 'necessity' of me really needing a high cfm carb...I think I need some general educating in carbs...does a high cfm carb only 'matter' at high rpms? If I am at 1500 rpm, and step on it (to go up a hill/etc.), does it not matter how 'big' my carb is? Will I not see a big difference accelerating (in the 1500 to 3000 rpm range) with 1bbl vs a 4bbl carb (assuming both are well tuned)? We have little flat land in Seattle, so I often am driving around 35 mph and hit a hill...and I want to be able to go up a decent upgrade in 3rd, and not in 2nd where I can only go about 20 mph before I am way over 3000 rpms.

I remember reading that our engines will last 'forever' if you keep the rpms low...

Thank you once again.

 

If it were me, I'd go with the holley 390. The smaller bore size is going to help with your low end torque, which is important if that's where you're mostly operating. I didn't have much luck with mpg from one but others have.

Cfm rating is the MAXIMUM amount of air/fuel that can pass through the carb. From there, you find the maximum amount of air that can flow into your engine and pick a carb accordingly.
Since cfm is in cubic feet and your engine is rated in cubic inches, you use the formula: cfm = (engine ci * peak rpm) / 3456.
As such, you can find how much air is flowing into your engine at any given rpm by replacing peak rpm with current rpm. Since that is based on the size of your engine, it remains relatively unchanged based on work load.
If it does deviate from that it'll actually be less, since the lack of air/fuel is where engine vacuum comes from, (if that makes sense.)

So a 200cfm carb and a 700cfm carb will both be flowing the same amount at, say, 1000rpms. The 200 is just going to run out of breath sooner. On the flip side, the 700 may have soggy performance because the fuel metering is designed for a larger engine. That's where carb selection comes in.

 

I just logged on the post a question hoping that baron or bronco would respond. I've got the offy dp and split exhaust bolted up to my straight six. I had originally planned on the edelbrock 500 but finding one local is being difficult.
One said they can't even get one. Another said it's a week away. The 600 are sitting on the shelf ready to go from just about anywhere. What would it hurt if I went the 600 route over the 500???
My truck isn't going to be a work truck. Especially after I get that shiney new wood floor in my stepside. Just a cruizer with my shop logo on it. More or less rolling advertising. I'd like to cruise down the highway at 65-75 without a stuggle. (and it actually did that fairly well with the lousy 1v) Would a 600 be too much carb for my stock 6er?

 

If it was me I'd go with a 2V carb over a 390 cfm 4V.

If you want a new carb a Holley 2300 2V carb ( list #4412 ) is a good carb to run on the Offy C-series( with a 4V to 2V adapter ) .

Otherwise a used Autolite 2100 or Motorcraft 2150 2V carb is also a good & cheap choice. They are cheap to buy and easy to rebuild.


If you want a 4V I'd go with the Edelbrock 500. The Edelbrock is a lot easier to tune on the 300. The Holley 390's are very finicky.

 

Not if it's vacuum secondary. The engine will probably never need or use 600cfm but it's not "too much". It's only going to run on the primaries (less than half the rated flow capability) except at heavy/WO throttle. Lots of people are running 600 cfm carbs with no worries.

A bigger carb may, repeat may, need more tuning than a smaller carb to get it crisp at low speed. Depends on the truck, location, the carb, whatever. I'm partial to Edelbrock carbs just because they're so easy to work on, but if you get a deal on a Holley 600 then slap it on and see how it drives.

 

Another thing to remember with the 300 is that while it is relatively small in overall displacement each cylinder is pulling 50 cubic inches of air on the intake stroke. Equivalent to a 400ci V8. Mine holds 22" of vacuum at idle. There's plenty of vacuum to keep a 500-600 cfm carb happy at low speeds. A well tuned 390 cfm might be marginally better or it might be a lot better but my money would be on marginally. If I ever stumble across one on the cheap I'll let everyone know how it stacks up against the Edelbrock 500.

 

Thanks baron. Would you suggest recurving the distributor. (i've done the dsII swap) or just wait and see how it goes first?

 

each cylinder is pulling 50 cubic inches of air on the intake stroke. Equivalent to a 400ci V8.

...yes, but with 2 less cylinders, it adds up to 25% less air moving than a 400.

But yes, they do work with a 600 cfm carb, I hope.

 

Sounds like I should/will go with an Edlebrock 500 if I go with a 4V - while the 390 might be the 'perfect' size, it sounds like the Edlebrock is much less of a hassle with little difference in performance.

However, maybe I should look at a 2V. From reading, it looks like the 2150 is the same or superior to the 2100 (minus simplicity). If I go with a 2150, would I want the 1.08, 1.21, or 1.33 (I think those are the #s, are there others?)? Also, what about the metering rod adjustment (with acceleration) that some of them have? Is that a different model (IE not 1.08, 1.21, or 1.33) or is that an option for those models? Would that option be useful to me? How would I know a carb has that (if I found a used one?)

So, Edlebrock 500 or 2V?

And thank you once again for the great info.

 

there also is a 1.14 which was common. I actually have some of the later 2150's with the metering rod, but since I usually use a 2100 and preferably a 63 or earlier (they use standard Holley jets), I'm not really sure when they started doing that.

If I may share an opinion, whichever carb you use, your choke choices may influence what kind of tinkering you may need to do especially since winter is coming on. I personally have found a few manual choke versions that might have come in in Ford truck. This makes for a very simple carb. Early 2100's-2150's were HOT-AIR chokes, and then a mix of electric etc.

I actually have a few 1.02's and a 1.01 all pre-64 manual choke. I am now using a 1.02 (C3) and even w/o the choke closing I can start it easily with a couple of pumps of the throttle. I will hook up a cable though in a few weeks. FYI my 1.02 is main jetted w/.049's. and has great torque from 1200 rpms and up...

I would not ever sell any of my manual choke 2100's..These carbs are getting old though so finding a good used core may be challenging.

I also have a 351W powered Bronco that today I just bought NEW 600 Holley for. That gives me 2 spare 600's and a few parts for rebuilding but my curiosity of a 2300 is most pressing since they are NEW..and one thing about a carb, the throttle shaft is always moving, and wearing.. so a carb with a removable throttle plate assembly is not a bad thing since you can rebuild the throttle shaft easier. Many older 2100/2150's which is a sold block bodied carb (which is a plus) could have shaft wear issues..and harder to fix-solve w/o diligence.

Incidentally, I have the same transmission as you in my 86 Bronco. I usually just leave it in 3rd, and anything from just above an idle and up, it will just keep building rpm's..and will lug=very well. I purposefully don't operate at over about 2100 rpm's ever..so my cfm needs are low.

The one thing to look for I think is a carb that will atomize fuel well at as low of an rpm as possible for this engine. Of course my Bronco is NOT a hot rod but is .030 over with a mild cam, efi head, and exhaust and Clifford heated intake. (for your cmparison) I also run NON-ethenol 92 octane.

As far as 1 2150 with a metering rod, I could send you a pic of one if you really need it. otherwise, maybe a visit to say mike's carb parts http://www.carburetor-parts.com/ may show you the differences, he seems to be good with his video's.

I have sometimes bought parts from him since he has single gaskets which allows me to cheaply refresh a 2100. There are only 3 actual gaskets, and an accel pump. http://allcarbs.com/ is good as well although farther away.

this place has good diagrams

http://carbkitsource.com/

good luck happy carb hunting.

 

The 2100's are simpler. The 2150's have the metering rod. So the driveability and MPG's are slightly better with the 2150 over the 2100.

The 1.08, 1.14, 1.21,1.33 are the venturi size. The 1.08's and 1.21's are the most common. If your engine is mostly stock a 1.08 will work fine. If you plan on more mods in the future a 1.21 or 1.33 would be a good choice.

 

Excellent input Fordman. I took so long in my reply that I missed your post.
BTW how can a guy REP someone or is that reserved for paid members?