After reading through a boatload of posts it appears there are essentially three performance intake manifolds for the 300: the Clifford 6=8, the Offenhauser-C, and the Offenhauser-DP.

The -C and the 6=8 manifolds have one huge intake port and the runners are undivided. They supposedly provide better upper-rev performance but do not perform as well as the -DP at lower revs.

The -DP provides better low-rev improvement over the stock log manifold than the other two. It also allows better gas mileage unless the driver gets into the secondaries a lot.

Optimum carb cfm is roughly 400+. Opinion seems mixed whether to hang in the 400-500 cfm range, or for raw speed to use 600-750cfm carbs.

It would seem that for someone who normally drives fairly conservatively, and would like to improve mileage as well as performance, that the -DP coupled with a 400ish cfm four barrel carb, maybe the Chevy 250 lifters, would be good.

So: Is all that accurate?
If it is, what would be a good SIMPLE (like probably needing only basic adjustment) carb to look for? Carbs aren't completely foreign to me, but I really like simple and basic.

 

Whatever Ford used or OEM is pretty simple and it's hard to go wrong with that, because it was designed for that particular application.

Carbs are simple, but they have a whole bunch of those simple - different circuits i.e. idle, transition, acceleration, power, and cruise. People sometimes get these mixed up or are unclear when and how much effect they have under different conditions. It is probably rare that a carburetor is tuned correctly, that's one reason they went away.

 

Hi HoustonDave,
Sounds like you're pretty spot on in your assessment.

One thing to add, the Clifford and the C allow you to use a two barrel carburetor, should you want to go that route.

IF you can keep your foot out of the secondaries (which I can't), a four barrel can usually get better gas mileage than a two barrel.

I found the Holley 390 to be too small. Some like them, but for some reason, I got terrible gas mileage with mine. It was quite a shocker going from 21mph to 12 on the open road. In the gas mileage department, I felt like I'd taken my truck out back and shot it.

I then tried a 600cfm Holley, and even though performance was definitely lacking, I got 15mph in town and 18 on the highway. It just wasn't all that fun to drive.

Next, I tried a Holley 465cfm and was really pleased with it. Finally had my low end torque back! And still good gas mileage. I finally sold it because I simply wanted something more updated (it's archaic even for a Holley and hasn't been updated since the 60s).

Right now, I have a QuickFuel 450cfm and really like it. It seems to be just about the right size all around for the 300. They're also well built and very decently priced:

https://www.summitracing.com/parts/q...RBlhoCFqPw_wcB


That said, from what I've heard (haven't set one up on mine), Edelbrocks are a lot easier to set up and run for a daily driver, if you don't want to fuss with them. They make a 500cfm, which I think is a great size too. Holleys will almost always give better performance and mileage, but that's because you can really fine tune them. Edelbrocks are a bit more slap on and go.

That said, I've had great luck with just throwing a Holley on and having it drive great.

Also, don't rule out an open plenum (Offy C or Clifford style) intake if you run upon one. I had one on my stock 300, and it performed very well. A tiny bit soggy on the low end, but I think that had more to do with the 600cfm carb than anything else.

 

I thought the only thing available without a long wait (or paying Cliffford's high price) was an Offy-C - just bought a DP IN STOCK they say from Summit. Now for the carb....

 

So in a very unscientific way I am thinking in the 450 to max 600cfm range
a) the QuickFuel above is a good option, along with
b) maybe Edelbrock 1403
c) Holley 600cfm 804575A d
d) Summit M2008 (Anyone know anything about this?)
All in my (Meager) price range, hopefully all functional. From what I see I probably don't want to go above 600 cfm (and honestly the only reason for a 600 is that I can also get a rebuilt one stinkin' cheap. Which brings up the subject of rebuilds - I see folks like National Carburetor flogging theirs. My normal take on rebuilds is not positive; have seen too many "clean-'em-up-and-call-it-rebuilt" parts...is that unjustified nowadays?)

 

If you do go with a 600cfm Holley, go with the 1850. I had an 1850 and an 80457. They performed the same, but for some reason, my best with the 1850 was 19mpg but only 16 with the 80457. No idea why.

If you're thinking of a 600, I'd still go with QuickFuel's 600cfm. I personally think QF carbs are better quality than Holleys, they have more features, and cost less.

I believe F-250 restorer tried the Summit M2008. You'll have to pick his brain about it.

 

Leaning more to a 450cfm than a 600 (as I listed above, it's essentially a dead stock 300 and will at most get Chevy rockers) - now we get to the new vs. rebuilding question. The 4548 looks pretty common and was used on a lot of Fords - maybe a used 4548 and rebuild it?

 

My personal opinion on new vs. rebuilt.

With a rebuild, you definitely pay less, but sometimes the headaches that come with it just aren't worth it. I went through around 4 different carbs and all were rebuilt (by me), and finally had had enough and just bought a new one. A worn out carb is more than just gaskets. Worn throttle shafts are a common issue and can be a real pain to deal with. Of course, you just might get lucky and get one in great condition and it won't be an issue.

As much as I loved the Holley 465, it was probably around 30 - 40 years old. The throttle shafts had some wear, and the only way for me to fix them was to ship it off to a carb repair guy to drill them out (couldn't find someone to do it locally) and rebush them, or buy a new one. Holley doesn't sell base plate replacements for it.

I probably wasted 3 - 4 years dinking around trying to get old carbs working right when I really should have just bought a brand new one from the beginning and skipped all the headaches. (Granted, QuickFuel only released their 450cfm last year, but that's a different story).

On the other hand, this is my daily driver, so I need it running really well. For a weekend toy / farm truck, you probably won't know the difference between a rebuilt and new.

 

as usual, good points - rebuilding I can do and have done, but the throttle shafts - good reminder, especially on an old carb. Mine is semi-daily - I usually drive the grocery-getter half the time, the truck when I want to smile. Now, off to price carbs again.... thanks!

 

Update - the Offy manifold arrived Friday from Summit!! Wow, that was fast. Mainly due to financial constraints wound up with the Holley 4 barrel; bought a Holley-rebuild directly from them. We'll see how it all works out. Probably take me a month to get all the new parts in. They shore do look purty, though... my thanks to F250 Restorer and Abandoned Bronco for their input.

 

Sounds good. Which Holley did you go with?

And awesome you were able to get the manifold, I know they continually keep getting back ordered, so it's nice they have some in. I hope Offenhauser realizes that there's a line of people waiting for them and punches some more out.

Keep us posted.

 

Wound up with an 80457, figured I would use it as a test bed and see if I needed to upgrade later. (Holley already notified me they shipped. The difference between the shipping from these companies and Amazon who promises Prime 2-day shipping but doesn't mention that their suppliers take 5 days to get an order out the door, is amazing.)

Edit same day: Reading other posts it appears I will probably hit clearance issues with the linkage... I am thinking a 1/2" or 1" non-metallic spacer below the carb may be a good idea to purchase now along with a Mr. Gasket combo gasket? Any cons to doing so?

5/26 edit - ordered a 1" phenolic spacer to resolve both height and heat issues before they strike. Carb came in (ah, it's lovely) already and Summit's shipment is out for delivery today... their shipping is GREAT.
One interesting point - since I had a little extra time I measured the flange thicknesses on both the EFI exhaust manifolds and the Offy DP - both came within a coupla thousandths of .46". Not sure how I got lucky there!