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View Full Version : 2BBL vs 4BBL carb & manifold


McRoth
11-05-2004, 05:25 AM
Well, I've kinda heard two stories on this & I was hoping you guys could set everything straight. I have a stock 4bbl carb & manifold that I want to put on one of my Waggys but I'm not sure which one it would be better on. Would it be best on my daily driver, mainly highway driving, or on my soon to be off-road jeep? My one friend said that 4bbl carbs use more gas & someone else told me they were about the same unless you really hotrodded them? Then I've heard that the stock 2bbl carb is better offroad for angles & such. I was thinking the extra power from it would be good there?

Thanks!

Ruptured Duck
11-05-2004, 05:59 AM
Well, if I were you, I would stay away from them motocrap carbs and use the edelbrock 650 cfm. I'll tell you what I did, I put the edelbrock four barrell on the stock four barrel manifold using a Trans-Dapt adapter part number TRD-2199 from Summit Racing. I have no complaints, this setup works great. As far as fuel economy, the 2 barrel and the four barrel get about the same mileage. So, my recommondation is to go with the 4bbl manifold and get an edelbrock 650 cfm with electric choke. The stock 4bbl carb is OK. The way they work is when you're cruising down the road and are only using a little bit of the throttle, then the main venturis are open. When you put in the kitchen, then the all four of the venturis are open. In theory, this carb would be a 2bbl mostly and a 4bbl when you need it, and also it may theoretically be more fuel efficient, but I had a stock 4bbl and it got worse gas mileage than the edelbrock I am currently using.

AMX factor
11-05-2004, 06:13 AM
I went Edelbrock Performer intake with Edelbrock 1405 carb. Changed cam to Comp Cams 260H and I get the exact same gas mileage as I did with stock cam and 2 barrel carb except I have a helluva a lot more power. The stock cam is really just too slow from these heavy vehicles.

Jayrodoh
11-05-2004, 08:19 AM
4bbl is good for a all purpose daily driver, keep the 2bbl on your off road truck, better torque. Why do I get this feeling we'll be changing your manifold now someday? You fix that rocker arm yet?

Bob Barry
11-05-2004, 09:54 AM
Having just gone to a Performer 4-bbl, I have to say that there really is no justification for sticking with a 2-bbl. The driveability, power and performance are worlds better, and the 4-bbl can be made to work off-road, yes, even the crappy Edelbrocks.

McRoth
11-05-2004, 10:53 AM
Jared, That's on the agenda for tomorrow morning, along with rebuilding the power steering pump. AutoZone had the kit for $11.99 instead of $16 or so at Advance.
I've kinda been leaning toward putting the 4bbl on my DD. Is there really that much difference??!! I'm just getting used to it working right now with the 2bbl & egr & all working right!! Which is a huge improvement over before. I'll probably rebuild the stock Motorcraft for now until I have the money to invest in an Edelbrock or Holley.

Jayrodoh
11-05-2004, 02:23 PM
The 2bbl's are grat offroad because they flow better at part throttle than a 4 bbl does, because the 4bbl has smaller primaries(on stock carbs, aftermarket's can be different). You rarely open the secondaries on a 4bbl offroad unless you are hill climbing or drag racing through the mud. On the other hand, 4 bbl's are great becuase they give you more power on the road and better fuel economy when cruising.

Bob Barry
11-05-2004, 03:16 PM
Originally posted by Jayrodoh:
The 2bbl's are grat offroad because they flow better at part throttle than a 4 bbl does, because the 4bbl has smaller primaries(on stock carbs, aftermarket's can be different).I don't get what you mean by "flow better"??? I find the part-throttle of my #1400 much better than my 2150 EVER was.

Jayrodoh
11-06-2004, 08:43 AM
Aftermarkets are a different animal, I am refering to the stock carbs. The 2bbl "flow" better because they have larger primaries allowing the necessary air/fuel flow to retain torque at a lower RPM.

tgreese
11-06-2004, 10:11 AM
Jayrodoh, are you sure that's right? I'd say that, if the induction system is properly designed and calibrated, there's no real advantage to a 2V over a 4V except in cost and complexity. The 4V primaries are small to ensure responsiveness and good fuel mixture at low vacuum. If the demand for fuel increases (higher vacuum) the secondaries will open. Low vacuum/large throttle openings are handled by a richening circuit that doesn't depend on the venturi size - the power valve on Holleys and Motorcrafts, and needles (?) on QJs, and probably something functionally similar on the Carter/Edelbrock.

Sorry, not trying to be contrary - just that your explanation doesn't make much intuitive sense to me.

Jayrodoh
11-06-2004, 12:41 PM
I'm just basing it on my experience in the past with stock 2 and 4 bbls. Seems the stock 2 bbl worked better than the stock 4 bbl when it came to slower speeds offroad. I guess I shoulda have stated "In my opinion". There are so many carb/intake options out there its hard to say whats better. I've also read elsewhere in a few places that some people prefer 2 bbl's offroad as opposed to 4bbl's. Again, my opnion again.

3jeepsdeep
11-06-2004, 01:37 PM
Primary venturi's on a 4 BBL are actually a bit smaller / leaner than the 2bbl venturi's in most cases - meaning that IN THEORY one might get better efficiency in lower throttle ranges with a 4 bbl carb. However, we all know that it is SO EASY and SO FUN to put one's foot in the carb when there are secondaries to kick in!!

I converted from 2bbl to 4 bbl on my 258 Cherokee -- no change in fuel econiomy on hwy driving, but a ton more pep and torque when it is needed.

regards
df

coh_2lesson89
11-06-2004, 01:56 PM
3jeepsdeep, how did you go 4bbl on a 258 and what brand and cfm did you use.

3jeepsdeep
11-06-2004, 02:13 PM
COH_

I did a Holley 4 bbl, 390 CFM on an Offenhauser 4bbl manifold, about $600 altogether. Eventaully upgraded ignition & distributer, too for an additional $350. With the Off Manifold, I had some issue making the idler pulley for the serpentine belt work out (changed spacer thickness) and accelerator cable bracket had to be "bent / modified" to avoid contact with brake booster housing. Accelerator cable connection conversion was a PITA! actually found best solution by modifying a Schwinn bicycle hand brake cable (the coated kind - less friction).

Been runnin' for 8 years or so -- doin fine.

might be better options available today?? I know a few guys who have put fuel injection systems on their 258's (CJs) and are very pleased with the results -- pricey, tho.

regards
df
dgfranklin1@tds.net