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V6 buffs - best carb?

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Mike S View Drop Down
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    Posted: 06 Apr. 2014 at 11:07pm
I am planning a modified CJ flatfender. Here is what I have gathered so far:

Buick 225 odd fire engine

Comp Cam 63-235-4 - High Energy™ Hydraulic Flat Tappet Camshaft

Offy dual plane manifold

Sanderson Headers

SM 420 tranny (thinking of going to a Ford T18)

jeep Flywheel is coming. 

Meanwhile, I am trying to figure out the best 4 bbl. carb for off-road (mainly) with this engine. Any ideas?

'47 CJ2A -- #114542
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Post Options Post Options   Thanks (0) Thanks(0)   Quote windyhill Quote  Post ReplyReply Direct Link To This Post Posted: 06 Apr. 2014 at 11:35pm
I run a buick v6  offy intake, comp cam,  I have a holly 390, and its not my favorite. I'd go for the smallest truck avenger they make.  As for the t18 I love it!!  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike S Quote  Post ReplyReply Direct Link To This Post Posted: 06 Apr. 2014 at 11:47pm
What is the problem with the Holley 390? I have heard of some issues but would like to hear yours.
'47 CJ2A -- #114542
Warn FF D41 rear
Lock-Right locker
11" drum brakes
Dual master cylinder
T90C Transmission
16 X 6 Jeep truck wheels
Cooper STT Pro tires
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Post Options Post Options   Thanks (0) Thanks(0)   Quote otto Quote  Post ReplyReply Direct Link To This Post Posted: 07 Apr. 2014 at 12:29am
I tried all the 4 bbl carbs available at the time on a 225 (Carter AFB, Rochester Q-jet, Autolite/Motorcraft 4100, Holley(s)) and none of them matched the driveability of the GM 2 bbl that came on it. The only plus to the extra carburetion was that the engine would pull to 5000 rpm instead of 4500 rpm with the 2 bbl. Not worth it in hindsight in my opinion. I was running the Holley manifold.

My engine had a 260H cam, much port work, Buick 350 pistons and headers similar to yours. Of the 4 bbl's, I think the Q-jet is better at handling angles one would encounter going off road than other carbs. I also think the 2 bbl would be better still.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JeepFever Quote  Post ReplyReply Direct Link To This Post Posted: 07 Apr. 2014 at 1:51am
Originally posted by otto otto wrote:

I tried all the 4 bbl carbs available at the time on a 225 (Carter AFB, Rochester Q-jet, Autolite/Motorcraft 4100, Holley(s)) and none of them matched the driveability of the GM 2 bbl that came on it. The only plus to the extra carburetion was that the engine would pull to 5000 rpm instead of 4500 rpm with the 2 bbl. Not worth it in hindsight in my opinion. I was running the Holley manifold..
 
I have not tried any 4 bbl carbs, but can not imagine any better "driveablilty" than the 2 bbl Rochester.  It will function at fairly extreme angles,  and will idle over almost anything.
 
As otto mentioned,  if running high rpm, wide open throttle, then a 4 bbl would be better,  but for "Jeepin'",  I really like stock carb that came on Jeeps with the 225 V6.
 
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote garage gnome Quote  Post ReplyReply Direct Link To This Post Posted: 07 Apr. 2014 at 2:48am
Holley 470 CFM truck avenger. Best thing I've done to my v6. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Metcalf Quote  Post ReplyReply Direct Link To This Post Posted: 07 Apr. 2014 at 3:47am
The offy dual plane has separated runners and a divided plenum if I remember right? 

The truck avenger carbs are neat but they don't have any high speed air bleeds. This makes them marginal for any higher vacuum highway type driving. The mileage will kinda suck. 

They are rare, but there is a 480cfm version of the motorcraft/autolite 4bbl that would work. With a few mods they could work really well. 

My personal 2bbl preference is the motorcraft/autolite 2bbls. I don't think they can be beat off road expect by fuel injection. I developed a neat little mod that uses a custom top cover gasket and some vent modifications to allow them to work PHENOMENALLY off road. It basically turns the fuel bowl into a baffle box system so fuel basically can't slosh out....

Here is the article I contributed.

http://www.fourwheeler.com/how-to/engine/1308-off-your-carburetor-dirt-tuning-the-motorcraft-2100/

The motorcraft/autolite has some really good things going for it....and some marginal things honestly. The best thing for off road performance is that the jets are centered in the bottom of the fuel bowl. This keeps them covered in fuel much more than the holley position. The power valve is also in the bottom. The fuel float level is a little bit of a pain to adjust. I set the fuel level WET in the bowl using a quarter as a gauge. That seems to be about the perfect compromise. The jets can also be changed without spilling any fuel which is a big big bonus. The main downside to the carb is that the PVCR passages ( basically WOT fuel rate ) can really be adjusted. You can drill the passages larger, but making them smaller is difficult. 

I just got done rebuilding my 225 and decided to stay 2bbl basically because it would cost me upwards of $1000 to build a 'proper' 4bbl carb for the 225 in my opinion. 

If I can find one of the small autolite 4100's I might go that direction some day. You can get the 2100's in close to 500cfm versions though so they really aren't THAT much of a limitation...


42 MB that had a one night stand with a much younger 69 CJ5 and a 50s GM truck.



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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike S Quote  Post ReplyReply Direct Link To This Post Posted: 07 Apr. 2014 at 6:26am
Metcalf -- yes, the Offy has two separate runners for each port and a divided plenum.

The lower runners are for the primaries, the upper for the secondaries. It is supposed to provide good low and midrange torque on a 225. 

'47 CJ2A -- #114542
Warn FF D41 rear
Lock-Right locker
11" drum brakes
Dual master cylinder
T90C Transmission
16 X 6 Jeep truck wheels
Cooper STT Pro tires
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Post Options Post Options   Thanks (0) Thanks(0)   Quote duffer Quote  Post ReplyReply Direct Link To This Post Posted: 07 Apr. 2014 at 3:02pm

That's the same manifold I'm using on my CJ5.  I have a 4150 series Holley 450 cfm carb off a 60's vintage AMC 250 V8.  You can do the same thing I did and install extended bowl vents and the spring loaded needles in those or the 390 cfm version for that matter, and end up with your own truck avenger carb.  Just make sure to use the side pivot bowls.  I'm going to say there is just no way to make the end pivot bowls work well off road if you get into steep, off camber situations-baffles, whistle tubes help, but don't really fix the problems.

The advantage of a small 4bbl over a 2bbl is better part throttle response and potentially better mileage from the smaller primaries-if you can keep your foot out of the secondary's most of the time.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Metcalf Quote  Post ReplyReply Direct Link To This Post Posted: 07 Apr. 2014 at 3:11pm
Yup, your going to have to run a 4bbl with that intake....

For an off the shelf option your best bet for off-road only would probably be the 470cfm Truck Avenger. It is still a little big and will take some tuning most likely. 

Personally I would probably mod a 390cfm holley 4bbl. I think the size is a lot better for the buick v6. The smaller primaries should give really nice throttle response. Add a spring loaded needle and seat system for the front and rear bowl. You can buy the truck avenger crossover vent off ebay. I would install that. Then I would probably add one of these to the primary metering block. 

http://www.jetblocks.com/

Set the fuel bowl levels conservative...ie a little low. 

My other suggestion would be to invest $170 in a wideband 02 system you can install to help tune the carb. It takes all the guess work out of tuning the carb. 

I think the biggest win the motorcraft/autolite design has over the holley is that you can change the jets without spilling a drop of fuel. There are some new metering blocks coming back on the market that would allow you to do this but at a pretty steep cost....I think $100+ for the new block. 


42 MB that had a one night stand with a much younger 69 CJ5 and a 50s GM truck.



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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike S Quote  Post ReplyReply Direct Link To This Post Posted: 07 Apr. 2014 at 4:28pm
Thanks to all for you excellent advice, especially Metcalf and Duffer for the detailed suggestions on Holley mods for off-road.

The people on this BBS are great!
'47 CJ2A -- #114542
Warn FF D41 rear
Lock-Right locker
11" drum brakes
Dual master cylinder
T90C Transmission
16 X 6 Jeep truck wheels
Cooper STT Pro tires
Back to Top
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