The Stovebolt Site Forums The Shop Area Engine Shop 1bbl to 2bbl

glad to see some frugal-ness out there...haha

i just spent 39 dollars on 2 roch. monojets to finish up my offy 3x1.

also good to see some guys crossing over from 67-72chevytrucks.com

let us know how it goes!

.later days.
.sam.

lol Yeah I was glad to find a site dealing specifically with L6. Too many V8's "over there" but I still check in.

Hey man, it's simple. Less is more when you deal with used parts.

Less spending means more toys.
And more bugs to work out.
But that's to be expected in our line of interest, eh?

I'll be updating as soon as the outcome comes out.

250supersix,

There have been numerous posts on this conversion, and I seem to recall the general consensus was, more fuel down the same hole won't give you much more performance.

Fuel distribution with multiple carbs would be the ideal way to go. You haven't got much invested in your experiment, and you are having fun, so take some notes and let us know how it turns out.

Stuart

Stuart,

When deciding to just keep the old 6er (rather then dropping in a v8) I had considered the Offenhauser 2x1bbl manifold. I decided though that I wanted my cash for other things as well and decided to take a less expensive approach (Oh boy, here comes my frugal-ness again :rolleyes: ).

I'm a 17 year old bag boy at Albertsons so money is scarce. That and I still plan on brand new exhaust and a hitch by September. So I'm just trying this out for now. If it doesn't work as well as I had hoped, I might end up rebuilding the darn thing next summer and just going with 3 or 4 barrel.

And you're right, it's not a large invesment as well as learning experience so I look at it with severe enthusiasm

Even if I don't notice major contributions to speed and acceleration, it's still a good fix. My carburetor I have right now was ready to croak a LONG time ago. The floats always stick and it just can't handle my lead foot.

So, at the very least, it should be more reliable.

And as far as notes, I suppose I could record acceleration times and top speed? I already know the MPG is going down :laugh:

This is a conversion with mixed benefits.

Pluses:

The Rochester B is not one of the better carburetors built.
The Rochester 2G is one of the very BEST 2 barrels built.

Minuses:

Testing we have done suggests that to break even from a good??? Rochester B to a 2-barrel, the adaptor needs to be at least 6 inches tall.

A much better way to do the conversion is to change intake manifolds.

Jon.

There are 2 different sizes of mounting on the 2GC carbs.

I ran a 235 in the mid 16s with a one barrel carb off of a 292 in my 53 chevy. I tried the 2b adapter and my ets went up. Try it youl like it.You will need a split manifold and a good cam if your trying to up your hp. I used a McGurk cam, I believe it had a 500 lift, the head was milled 100 thou., with 383 valve springs. The block was bored 60 over and I had a 456:1 rear end. Many Mustangs and Cameros were sorly suprised on the streets of Wichita.

For performance and some fuel economy I have had great success with the Holley/Weber from Tom Langdon's Stovebolt Co. It's a 2 stage 2 bl and Tom sells rebuilt ones for $65 or at least he used to. I have a pair of them on my 261 and it runs very well and still gets 20+ mpg. Forman is right that a cam and exhaust will help but you will be surprised how well those engines respond to simply adding carburetion. I ran a single one of those carbs on a 235 in my '62 Biscayne and it worked very well.

I've spoken with Mr. Langdon on the subject. I originally was going to get the Carter/Weber when I found out that it's original application was for a 1983 Ford 4cyl and not meant for 6ers (Carb too small). I did not go with his Holley because by then I had ordered the adapter, an adapter that does not fit the Holley.

I am looking mostly for response, and I will later add headers. Not looking to rebuild the block insides or head. I also am considering a 700R4..... but that's an entirely different story.

CARBKING:
This adapter is about an inch and some change tall. Why would height matter? Is the taper from 2bbl to 1bbl to extreme for proper fuel flow or something like? I figure that it's all going down the same hole, you're just shoving more down there with a more efficient device.

I tried that very adapter and a Rochester 2bbl once,it really didn't improve the performance and the adapter caused mixture issues at wide open throttle.Of course your results may differ.
What did work well for me,I cut open the original carb opening on the intake,reprofiled it to match the two barrel I was using.My grinding got into the double wall area of the heat riser section,some work with a Mig welder was necessary.I then made an adapter plate from one inch thick phenolic material,bolted it to the modified intake after drilling and tapping some holes.Made up a linkage cross over to utilize the stock gas pedal set up. Wasn't all that difficult to do really.
This set up works very well on a 261 engine,gave more power,better throttle response and actually a few MPG too.I didn't use a Rochester carb,but any two barrel should be ok.

250supersix - as to why the shorter adapter does not work as well, I can only speculate; but my guess would be turbulence.

Take a look at Tony's post right below yours.

When we were doing our testing, comparing a GOOD 1 barrel against the two barrel and adapter, we were unable to obtain the same fuel economy or power unless the adapter was shaped, and at least 6 inches tall. However, comparing the 2 barrel and adapter against a warped Rochester B, the 2 barrel and adapter would be better.

For the "do it yourselfer"; a good way to go is to fabricate a new manifold using aluminum with a plenum to match the two barrel of your choice. This can easily be done by using flat aluminum stock for the piece fitting the head, and various tubes and elbows of electrical conduit (from the electrical supply shop). Lay it out and heliarc weld the unit together. The carburetor flange can be made by acquiring one of the newer aluminum adapters, and cutting it to fit.

Of course, if a four barrel manifold can be found, a Carter 400 CFM AFB (9400s or 9410s) will work extremely well (albeit at more initial cost).

I put over 500,000 miles on a different vendors 6 cylinder (400,000 after installing a Carter 4 barrel). This was a 300 CID engine in an extended wheelbase van. At 70 MPH highway, the van averaged 22 MPG, and I have witnesses to this fact. Power was significantly improved over the original single barrel as well. I used an Offenhauser manifold for this project.

Jon.

Carbking's points are very true,in my opinion,the Rochester B carb is a crude device and any other similar sized one barrel is bound to make a noticable improvement in general improvemnet.
On several of my 235's ,I threw away the Rochesters,and replaced it with a Holley 1900 from the 60's Mopar slant 6's.Not that the Holley one barrel is the best unit,but I have a few layin around.It took a little fiddling with linkage and such,but the end result was better response and fuel mileage.And the engines actually ran smoother at all speeds.
I believe Carbking says a Carter YF pretty much bolts on and offers good results.
The single Holley-Weber works ok,but Langdon himself has said the small primary throttle bore may reduce part throttle power especially on a heavier vehicle.And ya still have the suspect adapter issue.
Anyways,here's a photo of a 2300 Holley two barrel on my homemade adapter on the modified stock manifold,261 engine.Again,I used a Holley cause I have them here,any brand 2 bbl off a small 8 should be just fine.It's a clean installation,I even reworked the stock oil bath aircleaner to fit.This carb is a 300 cfm unit as found on the small IHC V-8's,I didn't change jets,the stock choke cable hooked right up.It's been great for several years,way better performance than the one barrel and more MPG's
Carb swap

250supersix, your idea of shoving more down the same hole is incorrect! The fuel is sucked down from the engine, it doesn't matter how big of carb you put on, only so much is going to go down the small intake hole! The tall height has to do with air flow and resistance. Joe

I tried several different 2G's on my 292. I installed an Offy 4 bbl intake and then an adapter for 2 bbl. Seems like I tried 3 or 4 different ones and never could get any of them to work. Each one had its own problem. No ported vacuum, hard to get timing right, idle issues, mixture never right even setting with vacuum gauge, response fine with steady pedal but bogged otherwise.
I installed a small 4 bbl. I've been driving it ever since and that was over 2 years ago. Either do like Tony did and forget about that adapter or get yourself an Offy 4 bbl intake (got mine used on ebay for $125) and install a small Holley or Carter. It's worth the money.
-David

And putting a 4 BARREL on a small 250 inline 6 would be th same as shoving mroe fuel into the motor? Sure, you now have 4 holes to choose from, but it's all still going to the same place. As far as I'm concerned, the 2bbl is still going on. I've devised a plan to set up ncie linkage using 2 bellcranks and the timing just takes... time. Even if I don't achieve better performance, anything is better then the ancient piece of crap I have right now.

Look, I love these forums, so don't get the wrong idea. I respect all of your opinions and am not typing this with any sort of negativity.

But, stacking a 4bbl on a little inline 6 is just about the most outlandish thing I've heard of! If you completely rebuilt the motor from top to toe and added all performance parts, then maybe she could handle the stress. But mark my words, those of you that cut corners while putting on a 4 barrel will end up with a whole laundry list of troubles.

In closing, I'll atleast end up with a carburetor that doesn't get me stuck on the on-ramp (a prime example of my current issues).

Another thing, too, why would an adapter like this be built if it wouldn't make a lickin' difference?

Because somebody will buy it.

250supersix, The whole idea of a 4 barrel carb is that it is progressive in opening most of the time it operates like a two barrel but at WOT the back barrels open allowing max air/fuel mixture.

A single 4 on an Offy or Clifford is about as outlandish as shorts in the summertime. It's been done for a long time, it's nothing new. You're not putting the 4 on a stock intake. You're putting it on a manifold that it was meant for. And as mentioned a couple posts up, you're secondaries on a 4 bbl are not opening all the time. You can even put tighter springs on 'em.
This setup is one of the easiest things to do for a very slight performance gain with easiest maintenance and driveability. You want more performance and a headache, install a 3x1 Offy. Deep pockets and ultimate performance, get fuel injected and a 12 port head.
Do what you want to do and experiment, it's your stuff. But you've got many years of experience (I don't include myself, still much learning to do) here telling you it's basically a waste of time and money.
If you're happy with the results, great. Would you probably be more happy modifying the stock intake or installing an Offy or Clifford? More than likely.
Or.... just install a different 1 bbl.

all points as far as i can see are correct and legitimate.

so, theres not really any need for hostility.

by putting the 2 bbl on your stock intake, and spending a small amount of money, you're getting rid of the old tired model B. you're also gaining a better carb., along with perhaps more air/fuel flow. that alone should improve things on your end.

i will back Mugsy up, tho, in saying that it a 4 barrel is a very good addition to even a stock engine. it simply gives the engine enough air and fuel to make more power, followed with headers to breath. blah blah blah...everyone knows this.

SO!

i say, go for it. i know exactley what its like to be a kid...erm.."young adult", i guess thats what they call us now, and on a very limited budget. aka, minimum wage, or there abouts. i was fortunate enough to score an offy 3x1 fr about as much as your 2 bbl roch. finding monojets on the other hand...was a pain.

regardless.

bolt it on. and enjoy.

if you don't like it, well, modify it until you do, or find something else.

it really isn't that technical. just the basics of hot rodding, i suppose.

-shrug-

.later days.
.sam.

Hmm, well.... lemme go take a look at the stock intake again.

I dunno, I had another crazy idea in my head but I'm just gonna set that aside for now.

While I still retain my original beliefs, I understand where all fo you are coming from. Really, I do. IT's all going down the same hole. I just can't believe that a small jet of fuel covers that entire hole. It doesn't make sense to me. If fuel flow usually covered that much area, I would nto have the gas mileage that I do currently. Tanks would empty a lot quicker than they do.

That being said, I will continue. And if I'm right, then I'll share with all of you my experiences. And if I'm wrong, well I'll go on being a little son of a gun that I am and try something new. And keep trying.

After all, that's what our hobby entails, fellas. You talk and try and learn from your mistakes and try some more. It's all a BIG trial and error.

It isn't just fuel going down the hole. It would be a ratio of about 16.8 to one of air and fuel respectively in a perfect world. It would be similar to putting an air cleaner with an opening equal to the area of a single throat on a two barrel. It will choke it off the same way. You may gain some benefit, but not the full benifit of purposed designed setup. Learning from other people's mistakes as well as from our own is what distinguishes humans from other animals.

It's not liquid fuel in a tiny stream form. The fuel vaporizes and is dispersed more evenly. That's why the exhaust manifold is mated to the intake and why there's a heat check valve.
As mentioned previously, the 3x1 intake provides the best mixture for an inline. It's just a pain in the arse compared to a single 4.

"You talk and try and learn from your mistakes and try some more. It's all a BIG trial and error."
While this is true, this forum is where one benefits greatly from learning of others mistakes which help to avoid pitfalls (and money pits) and error and all around waste of time B.S.
And time is money (so my wife constantly reminds me). It's good to experiment, yes. But, you also must remember, the great majority of things on these old motors and trucks have already been tried by someone else. Learn from them. Carb adapters, exhaust cutouts and all kinds of crazy hoo-hah gadgets and hoo-hah speed equipment for stovebolts and other inline motors has been around
since the 1930's. I'm not trying to discourage you or tell you not to think outside the box. Just that frugality and spend thrift is often not the wisest choice nor does it actually equate to frugal in the long run. As a cheap-arse, I speak from experience. I often do things the hard way to save a few bucks. Take a look at the headlights on my '65. I wasted countless hours modifying some Ford station wagon buckets to work with the 58-59 Chevy truck bezels because they were $7 for the pair (including working headlights). Not time efficient. Time is money, so says my wife. She's smarter than I.
-David

Well in all honesty, I can't say that I fully trust every word I've seen on some of these threads...

Supersix - your last comment could be quite true.

The best part about the internet is that anyone may post

The worst part about the internet is that anyone may post

Having said that, consider the following:

Carburetors are rated in CFM (cubic feet per minute flow). The major contributing factor is the diameter of the carburetor venturi. The same can be said for the diameter of the bore of the intake manifold. Carburetors are rated at a SPECIFIC vacuum. Again, the same can be said for the intake manifold. If you have a normally aspirated engine; there is a maximum amount of air/fuel mixture that may be drawn through a specific size hole in the manifold; as the engine vacuum and the size of the hole are the controlling factors. Assuming the factory one-barrel carburetor can provide this maximum, no more will be gained REGARDLESS of the size of the carburetor installed. This concept is not true if you install a blower; as you can FORCE more air/fuel through the hole than you can PULL through the hole.

Now consider the adapter:

This is a highly un-technical analogy, but true. Think of two different situations on an interstate highway that cause a tie-up. The first is normal highway construction where signs with arrows educate motorists over a 2 or 3 mile period to form into a single lane. The traffic will merge and by the time the traffic reaches the bottleneck there will be one lane. This will be the maximum amount of traffic that can pass in one lane (at a given speed).

Now consider an accident; and the first trooper on the scene attempts to establish traffic control (at the scene). The traffic will back up in ALL lanes, and then jerkily merge right at the bottleneck. Less trafic will flow through the bottleneck under these conditions.

Your manifold is the bottleneck. With a two barrel carb you have two "lanes" that must merge. Compounding the difficulty is that the velocity of the air/fuel mixture at the throttle of the carburetor is less than at the manifold. As the adapter squeezes the two holes down to one, the velocity must increase, and disrupts the flow of air/fuel. This is the reason for my original comment concerning the length (height) of the adapter, and why it should be "shaped".

Now consider a four barrel:

But not just any four barrel! Put an 1150 Holley dominator on this engine and your earlier comment was right on! Please note that I suggested a specific four barrel - the Carter 9400s or 9410s. Both of these are 400 CFM carburetors that are progressive "demand" secondary carburetors. Many talk about vacuum or manual secondaries erroneously, so I try to avoid these terms. The "demand" secondary will open ONLY if the engine provides sufficent "demand" for the additional CFM. Otherwise, it is a two-barrel. But utilizing a four barrel manifold, you eliminate the bottleneck, and allow the engine to breathe as necessary. The same can be done by utilizing a multicarb manifold but the four barrel is easier. Another carb that may be used (if you like Holleys, I don't) is the Holley 390 CFM, but it will require modifications by someone who likes (or at least understands) Holleys.

As far as doing your own thing:

The "school of hard knocks" is probably the finest teacher available. By all means try your adapter and two barrel. If your original carb was shot (as the Rochester B series often is) you will probably see improvement; as the Rochester 2G series two barrel is MOO one of the finest two barrels ever made. I still find it difficult to believe the same company made both the B and the 2GC.

You may see a noticable improvement. However, the concensus of those of us who have attended "the school of hard knocks" is that the improvement will be less than other methods discussed. These forums are a wonderful place to learn.

And there is no single "perfect" solution. If there were, all carburetors would have been produced by Carter

Jon.

Ok Carb king I understand that.

I get what you're saying. And it's what I expected, obviously you can only fit so much through. I guess what I did not mention were my suspicions on whether or not the Type B was actually using the entire intake bore.

So yes, there is some improvement to be expected from my new 2bbl carburetor, but NOT greatly. I've accepted that. You type a very explanatory essay

As for my previous post on not trusting what people say, that was not meant to personally insult anyone. I am just makign sure I'm learnign from th right people. And who would be a better professor of the carburetor, then the Carb King himself?

Anyway, back to bore size. If I were to slightly largen this hole, both in the intake and the adapter, could I expect to find even more improvement. Just a theoretical question as I don't plan on actually going through that much trouble (I'll run to the 3x1 Offy intake before doing that).

Thanks.

Supersix - I cannot positively answer the question as to whether boring the hole oversize would help; as I do not have a manifold to inspect, and the shape of the plenum would be important. PROBABLY there would be a benefit by increasing the size of the manifold bore and using a larger single barrel carburetor, but it would depend on the plenum shape in the manifold.

As to the adapter, I seriously doubt that any benefit would be realized here. There MIGHT be a measurable (on a dyno, not "seat-of-the-pants") improvement IF you bored the size of the adapter using a taper attachment on a lathe, and reformed the taper of the adapter to the new bore of the manifold. I would doubt very seriously if this could be measured on the "quarter-mile", even in hundredths of a second.

The very best you will get out of the two barrel would be as Tony did, reform the manifold plenem to accept the two barrel without the adapter.

And one other thing I forgot to mention in my previous post: before doing any modification, run some type of "baseline" with your beloved Rochester B. You never know for sure if a modification worked unless you have a measurement. If nothing else, run three acceleration runs over a fixed length of road (when there is no traffic, and don't exceed the speed limit) having a friend time you with a stop watch; and average the three runs. Now you have a baseline.

Jon.

Jon,

Want to time my acceleration but I believe you have to floor it to do that? My truck breaks down if I floor it. How should I swerve around this one?

supersix - if you mean the engine cuts out, you may have ignition problems causing this.

If you mean the truck physically breaks down, I have no answer.

Jon.

"Well in all honesty, I can't say that I fully trust every word I've seen on some of these threads..."

Yep, 'tis true. You've always gotta do your own due diligence and homework as much as possible. Especially if your frugal!! Gather all information that you can and make an informed decision. You've also gotta be around longer than a month to figure out who knows what they're talking about.

Ouch. Good point Mugsy, but as I have no life outside of my truck I'd have to say my long hours spent on this site ought to count as two months

By break down I mean the floats stick in my "beloved old Rochester B" and it essentially floods. On top of which a seal is leaking that I have decided not to replace since that piece of junk will be outta here soon as it is.