The Stovebolt Site Forums The Shop Area Engine Shop Dual Carbs (again)

I've been searching and reading a lot about duals carbs. (It's my son's truck and, as a younger person, he would like to have a little more power.) There is much discussion from 5 to 10 years ago so I was wondering if there is any new thoughts on the subject. I was talking to Mr. Lang (former Stovebolter ) about a Clifford dual intake manifold. It's for a 216 but will it work on a 58-62 235? (I've read that it will and I would not have to use the alignment rings but want to make sure.) If I went this route, I would be going with Fenton headers. Is this a combination that would work? Also, I've read about different carbs that would work. One such carb would be a Carter W-1. Currently, my 216 has a Carter W-1, but it's a 1949 model. (The truck is a 1947 1/2 ton) So I would be buying two carbs as, from what I can gather, 1949 was not a good year for a Carter W-1 and, I'm assuming, hard to find. Daytona Parts has a replacement for the Rochester carb. Replacement Carb (Click on the Chevy Replacement tab. above the picture.) Also, their universal carb looks interesting. I do have a Rochester but have read about the issues with Rochesters. (Mr. Lang, however, ran dual Rochesters without any problems). Would the Carter YF work on a dual setup? Any information greatly appreciated. Thanks.

You have the right number of carbs already. Dual carburetion is the wrong answer to a nonexistent question, especially on a 216. If you have the necessary engineering ability and access to a dynamometer, a TIG welder and a full machine shop, you might consider fabricating a 3-carb setup with very small single barrel carbs, similar to the setup on an Austin-Healey 3000 or an early Jaguar, using vacuum piston type side draft carbs for a motorcycle. I'm in the beginning stages of such a project for a 230 inline 6 cylinder.

BTW, I do have the dyno and the machining and welding capabilities to attempt such a project, plus 50+ years' experience building high performance engines. I'm not entirely sure I'm going to have the ability to do a good job of it.
Jerry

I don't totally understand your question???

You state you have a 1949 216 but would it work on a 58~62 235? Which are you going to use? Different carbs will be desirable for each application.

There is nothing wrong with the 1949 Carter W-1 EXCEPT availability of accelerator pumps.

As to the Daytona carbs: I have not personally seen one, have no experience with them, so just asking you a question. Where are you going to find engineering help to make a determination if you have no engineering specifications? Where, other than mail order from Daytona, are you going to get replacement parts if you get a bad tank of gasoline? Who are you going to get the put in the replacement parts if you CAN order replacement parts from Daytona?

Jon.

Rusty, I gather that you are just trying to get a little bit more performance out of your truck.
Unless you are an expert at calibrating antique carburetors and have the patience of Job (~Jobe) to keep them that way, you may want to reconsider dual carbs.
I have a bit of a gear head streak in me, but I went a different route to get a little more performance (quite a bit actually).
I went with a T-5 transmission. That move alone brought my 235 to life! The extra gears keeps you in the middle of the optimal power curve of the engine on every shift.
No more screaming engine before shifting, only to have to deal with a lugging engine in the next higher gear until your speed eventually increases.
With the T-5, every time you shift gears, you are accelerating down the road like right now, Jack!
I also have a Carter YF2100 carburetor which has no dead spots commonly observed in the Rochester B.
I do not want nor need any more performance in this truck. If I had any more, I would have to worry about trying to stop the truck with the stock brakes.
Carl

I have been running dual carbs and three carbs for a long time, and as stated, they require work, and a ton of tuning. It is not a bolt on and go operation. My 250 does run better with dual W-1's from a '48 Chevrolet, #574's, but I also have a $200 air fuel ratio ( wideband ) gauge and vacuum gauge to help tune them. I built the dual manifold I am running, and have it mounted to a stock exhaust manifold. I did this for the heat, headers do not provide the needed heat to vaporize the fuel.

You probably know already, but aftermarket replacement carburetors are mostly pieces from hundreds of carbs and very few are jetted or configured correctly. If you truly want dual carbs, by cores and rebuild them yourself. Both MUST be identical in every way, right down to the minute adjustments.



Joe

Sorry I wasn't clear on my original post so I'll try again. I currently have a running, 216 in a 1947 Thriftmaster. The engine has a 1949 Carter W-1 carb on it. I have purchased a 1958 - 1962 235 rebuilt long block. I'm slowly getting parts together to complete the engine assemblies. One of the assemblies is the fuel delivery system. My son, being a person of the younger generation, was thinking about making the engine perform better. He's read too much here and elsewhere about the roar of a stronger 235 with dual exhausts. So I offered to do some research on Stovebolt to see if the information/thoughts/opinions have changed since the posts on this topic from 5 to 10 years ago. I've read from "DONT'T DO IT!!" to "I haven't had any issues with putting dual carbs on a Chevy inline 6." I was hoping there are Stovebolters who have done this 'enhancement' recently and was trying to get as much info as possible. I realize carbking is the expert and have read his information, especially about the Carter W-1's and the restoration of said carb.
Question 1: Would the Clifford dual carb intake manifold (for a 216 engine) fit onto a 1958-1962 235 engine?
Question 2: If I bought a Clifford dual carb intake manifold, would the 1949 Carter W-1 work on this manifold (of course with another 1949 Carter W-1)? Would Carter YF's work? Rochesters? (The Carburetor shop states that a carb for a 216 would be workable for a 235.)
Question 3: Would other years of Carter W-1 work, be better or be the same as 1949 Carter W-1?
Question 4: If I get another 1949 Carter W-1 and the accelerator pump goes, for example,where am I going to get one? Are they available in kits?
The Daytona Replacement Chey Inline six carb is designed to replace the Rochester B/BC from 1937 to 1967 and fits 216 up to 261. I would hope that they would have done the engineering. (Jon, what sort of engineering are you talking about? I am trying to understand more about carburetion as I research.) If I needed replacement parts I suppose I would get them from Daytona (If I bought from them). But who do people get to put replacement parts in to their carbs? I know there are carburetor shops like Jon's The Carburetor Shop, but I thought people also put rebuild parts into their own carbs. Carl - The plan is to convert to front disc and upgrade to Bendix in the rear before the engine goes in (winter project). Thanks again for responses. Trying to my homework before I buy anything.

It seems you've got your mind made up, so I'll stop trying to confuse you with facts. There are plenty of enablers here who will be glad to help you spend a boatload of money trying to make a multi-carb engine run almost as well as it did before you started tinkering. Good luck!
Jerry

Correction: It's an Edmonds manifold. Jerry, I haven't made up my mind yet - still researching and trying to digest everyone's ideas, knowledge and opinions.Thanks.

I spent 30-something years dealing with teenagers who thought they knew all about high performance- - - - -after all, they had read at least three issues of Hot Rod Magazine! BTW, some of those same kids now are the owners of very successful independent shops, or are line mechanics, service managers, etc. Yes, some of them build very good race engines!
Jerry

Rusty, the W-1 is an excellent carb choice for running duals. Over the years carter kept making improvements so the later ones are a better choice then the early ones. 1941 - 1946, #483's and #574s are what Jon recommends and is what I am using. They are basically the same as the 1949 you have only with the easier to find accelerator pumps. I would hunt down two of these instead of a second '49 model.
Purchase a manifold with the smallest runners to keep the air speed as high as possible. Clifford would not be my first choice. Use stock jetting and carb settings for the carburetor you choose, not the engine it's going on.

On the exhaust system, use exhaust heat if possible to heat the intake, water heat works, but is slow to come up and doesn't get as hot. Stick with 2" or 1 3/4" pipe into a dual inlet single outlet muffler for a mellower tone, true duals sound bad ( in my opinion ) on a six cylinder.

Joe

Jerry - would you (or someone else) please post a picture of the 216/235/261 cylinder head intake port pattern? I don't have one to post.

Thanks. Jon.

"I built the dual manifold I am running, and have it mounted to a stock exhaust manifold."

Rusty,

If you can get Joe to send you a photo of the manifold he built you will be very impressed. It's really a thing of beauty.

Being a geologist, not a mechanic, I'm not an expert in carburetion or any other aspect of engine theory. However, I can state from personal experience that the Carter W-1 is very basic and easy to work on, From the ones I have used it appears that main jets and metering rods are interchangeable between all W-1 carburetors, making tuning pretty basic. The throttle shaft and accelerator pump/metering rod bell crank shaft bores are usually worn out but putting in bushings eliminates the looseness. A Rochester Quadrajet throttle shaft bushing fits the W-1 throttle shaft nicely.

I'll let others more knowledgeable than I comment on the power potential of increased carburetion. I've found a performance improvement from ducting cool ambient air to the carburetor. There is actually a slight ram effect also from picking up the ambient air at various places around the front or cowl of a vehicle. Joe has extensive experience in drag racing and can probably comment on that.

Please disregard my last post. I found a 1953 Corvette intake on Ebay, with good pictures. When I get the software up on my new computer (the old one died after 8 1/2 years) will post the picture on my website.

The reason I wanted the picture was to augment Jerry's comments with a good picture.

OK, dual carbs CAN be made to work on the 216/235/261 as many have found, but never as well as 3 carbs, and only somewhat better than 1 carb. Jerry, Joe, and others have mentioned the limitation of the cylinder head, so the real benefit of multiple carbs (and no internal engine work) is to improve the volumetric efficiency of the engine through a more equal A/F charge to each cylinder. BUT, the Chevrolet 216/235/261 has THREE intake ports; so with dual carbs one has TWO carbs feeding THREE ports; impossible to get exact equal A/F distribution with this setup.

Joe H. HAS made it work fairly well, but Joe is from a family of racing mechanics. He understands HOW to get power from an engine, AND he has the testing tools to tune the setup. His Dad is famous in the racing community. While I know part of the history of Joe's multiple carbs, it would be interesting to hear the full story of how he ended with the W-1's, and how "easy" it is to just put some carbs on the engine and gain power.

Try to find a picture of either the intake ports or the Corvette intake manifold. Chevrolet used 3 carbs on the Corvette because of the port design. Three carbs feeding three ports, all running simultaneously.

The choice of carbs is obviously up to you; but if there are ANY carbs available which can be placed on the engine and obtain perfect (or as near to perfect as can be had) A/F ratios across the range of vacuum and RPM without MAJOR and I do mean MAJOR modifications and tuning, I haven't found them. I suggest the Carter W-1 BECAUSE: (1) readily available, (2) engineering data readily available, (3) parts (other than the accelerator pump for the 684s) readily available, and (4) all of the preceding are relatively inexpensive. Holley, Stromberg, and Zenith all are also excellent choices, but fall short of the Carter W-1 in all 4 or the criteria in the preceding sentence. Rochester NEVER went after the aftermarket, so fall much further short in these criteria than Holley, Stromberg, and Zenith (notice alphabetic order). If you really WANT to use something else, think of these criteria.

Finally, the transmission change suggested in this thread by 52Carl is an excellent idea. I have not personally seen this modification; however, the very best "bang for the buck" on a automatic transmissioned 1964~1966 GTO is to swap out the 2-speed dogmatic transmission for the 3-speed TH-350. Bolt in swap and will lower ET in the quarter-mile by more than 1 full second! How much money would need to be spend on the engine to accomplish the same result? Have seen this done a few times, always with excellent results.

Jon.

Jon, I'm a little confused- - - -didn't the automatic GTO's run a Turbo 400 3 speed? I'm not aware of the Powerglide ever being mated up to a Pontiac engine. Earlier Pontiacs ran either the 4 speed Controlled Coupling Hydramatic or the POS Roto-Hydramatic, but I'm not aware of either one being used in the GTO. I do agree that three speeds beats two, and four speeds beats either one.
Jerry.

Jerry - yes, BEGINNING in 1967!!! The 1964~1966 used the 2-speeds.

Jon.

Despite the remark, there is no "universal carburetor", in truth what they sell is a compromise of various sizes, circuits and internal components which must be tailored (by you) to suit their individual engine, gear, stall speed, driving style etc. The 216, 235 and 261 need slightly different innards just because of the displacement, as well as port sizes, cam timing, etc.

As said, the mixture distribution is best with either the original manifold, or 3 (almost separate) manifolds, since 2 X 1 frequently favors the center port (#3 & 4 cylinders). This cannot be adjusted out, but requires internal modifications to the manifold internally (dams, popsicle sticks, drain grooves etc.).
It's not a bolt-on, it's an engineering project, and many people are sick of it before obtaining acceptable results.

What about a 2-1 adapter and a 2 bbl.? Yes, the extra air (not gas) will increase power, but the original manifold's distribution doesn't transfer over to a new base very well, and the adapter is very tall.

If this were my engine and I wanted a project, I would try making a manifold similar to the Corvette to mount 3 X 1-1/4" H2 or 1-1/2" H4 SUs.

why not a turbo?

Interesting....I am far from an expert and installed dual carbs on a 235 that ran quite nicely....A pair of the smaller Rochester B's (216) on a water heated Edelbrock intake...Stock main jets, I think they were #52's...I carefully removed the high speed "jets" (power valve) from the holder,measured them with a drill , soldiered then shut and redrilled the hole .003 smaller...I re curved the distributor mechanical advance by brazing the advance slots to about 2/3 it's travel and stretching one spring .....Set the timing to 36 degrees at full advance around 3000 rpm, it was about 10 degrees at idle...Modified the vacuum advance by putting a piece of wire on the slotted arm to limit the advance a bit....I used 89 octane fuel....The engine ran better than stock and got what seemed like slightly better fuel mileage... This was all there was to it....And yes the Rochester B's did seem a little fuel like most do...
If you can search back on this site to the early days of this site you'll see quite a few guys were running dual carbs and reporting the same success without using dynos or any sophisticated tuning. Joe H might remember some of the names... Grant and Cosmo ???..It's no secret the single carb in the center of the log intake has terrible fuel distribution and two carbs is an improvement...

So there you go! About as much information as you can get. I say go for it, you just never know what will happen till you try it. I like the challenge.

If it doesn't work out, you sell off the carbs and manifold to the next guy who wants to try.

Joe

You're right, Joe, it's a lot of information. Lots to think about. Thanks again to everyone for weighing in. Still mulling it over.

Here's mine. Another, carb side. The 'holy grail', 848 head, Corvette intake and Corvette exhaust. Better picture.

Cosmo - thank you for posting that link to the carburetor side of the manifold. I clearly shows the tiny equalization tube, which explains why Chevrolet could use as large carburetors (the 2066s Carter YH) as they did. Basically that manifold is of the IR design, which requires significantly larger carburetors than one with a common plenum design.

If I were doing multiples on a stovebolt six, that is the way I would go, except I would substitute Carter YH's from a Dearborn marine engine (which are merely constructed from verypricium) for the original YH 2066s used by Corvette which are contructed from unobtanium or extremelypricium. Although Panic's comment about S.U.'s is intriguing.

Jon.

Jon, what about the side draft Carter the Nash inline sixes used on some applications?
Jerry

There has been mention in this thread that the 1949 Carter W-1 accelerator pump is hard or impossible to get. Do accelerator pumps fail often or after several years or a few years? I have had a 1949 Carter W-1 on my 216 since I got it. (2007) A previous owner had installed it at some point. I bought a rebuilt one from Chevs of the 40s around 2008. Thanks again for any information that helps me understand the discussion better.

The leather pumps, like were used by Carter, last virtually indefinitely, as you have determined.

We still had pumps as late as 2010, but have now run out, probable that your carb was rebuilt using a leather pump.

As the pump used in the 684s is unique to the 684s, there is insufficient demand to do a major run of the pumps, so we have to make each one by hand.

Jerry - the YH's used by Nash are almost as difficult to find as the original Corvette, while the Dearborn variety is somewhat more common.

Jon.

A down draft 2 or 3 carb manifold also has a large plenum...... SU's are interesting but it's my understanding that they have one fault....There is no separate idle jet or adjustable idle mixture. the idle mixture is set by position of the main jet to the needle....Adjusting for the best idle will affect off idle fuel mixture especially on non OEM applications....

I have heard, not to say that I heard correctly, that the tri-carb set up of the original Corvettes was too much carburetor for normal daily driving. The three carbs proved their worth when demanding performance, but the original Corvettes were not built for speed or handling. Because the tri-carb was too much for daily driving and too temperamental, many owners converted to a standard 235 single carb manifold and mothballed the triple set up. Supposedly, this is why you can occasionally find a Corvette tri-carb rig all by itself as a barn find. Could be completely untrue, but that's what I've been told.

My hunch that more were contributed to the number of barn finds by being purchased as dealer accessories to bolt on to non-Corvette 235's than by being stripped and mothballed, but who knows. On a similar note, the Corvette split manifolds that were sold as dealer accessories supposedly way outnumbered the ones that were actually attached to Corvettes and that's why these can still be found, still rare but more common that the triple rig.

I have heard the same about the original mechanical fuel injection on the Corvette 327's being mothballed in favor or a carburetor due to being temperamental.

Here's a link to the often-discussed Soup the Chev! article from the March, 1954 Hot Rod magazine. It explains progressive modifications that were made to optimize the performance of a 261 back in the day. The two carb and three carb modifications are covered at the very end. By the time they got around to the carb modifications, lots of other things had already been done to the engines, so it is by far not a pure comparison to what would happen by adding them to a stock engine. I found it interesting to note that the three carb design was not friendly on the street, similar to the urban legend that I've heard for years regarding the Corvette tri-carbs that I mentioned above.

http://www.earlycorvettes.com/linda/mcgurkhotrod/mcgurkhotrod001.pdf

Interesting string of posts...thanks to all contributors. As for me, I like my lonely single carburetor...

Matt

http://www.superchevy.com/features/...blue-flame-six-first-engine-illustrated/

What would be normal driving of a 235 Corvette?

2500 RPM
3500 RPM
4500 RPM

Tim, interesting article. It mentions that the Corvette 235's had dual valve springs. That's new to me. How did they install a second spring on each valve?

Matt

Isn't the three carb thing kind of a moot point on an AD truck due to firewall clearance? Or is that just an issue with downdraft carbs?

And a single carb conversion on an original Corvette might be an incorrect myth if an upright carb wouldn't fit under the hood!

Matt - the Carter YH could be tempermental (NOT the fault of the carburetor). Somewhere, and I cannot find it, I did a major article on the YH. When I find it, will post on my website. Until then:

(1) Four distinct and DIFFERENT generations of the YH, and many parts WERE/ARE NOT INTERCHANGEABLE!!!
(2) After the genuine Carter kits for the Corvette dried up in the 1950's, THERE WERE NO KITS WITH THE CORRECT GASKETS UNTIL WE REPRODUCED THEM ABOUT 1980!!!!!
(3) Same thing is true for the Corvette fuel valves. The gaskets and valves in the FLAPS kits were simply WRONG!

Corvette YH carbs with the wrong bowl cover gasket and especially the wrong fuel valve (orifice too large) tended to flood, and spill gas on the engine. NOT the carbs fault that the owner or mechanic used the incorrect parts.

Same reason that the Dearborn carbs can be found; fuel leakage on a boat, FOR ANY REASON, is unacceptable.

The YH's were not too much carb for the Corvette. Back when we still had time to restore carbs, did several sets, always with happy customers.

Jon.

Jon, another performanmce problem with the Corvette sixes had nothing to do with the carbs. The first production models were only available with a Powerglide automatic transmission- - - - -"Two speeds- - - -too low and too high!" By the time they made a manual transmission optional, all that was available was a 3 speed Muncie with a non-synchronized 1st. gear. That still made it difficult, if not impossible to keep the engine in a good RPM range to take advantage of the extra breathing capabilities of the 3-carb setup. Road racers got really good at finding 1st. gear by momentarily locking up the rear wheels with either the parking brake, or just nailing the brake pedal and yanking the shifter into first while the driveshaft wasn't turning. Transmission builders loved that technique- - - -it kept them busy repairing transmissions for people who weren't coordinated enough with the brakes and the shifter!

When the Borg-Warner T-10 4 speed with the synchronized 1st. gear came along in 1957, the 283 V8 was the standard Corvette engine.
Jerry

"using wedge-shaped combustion chambers": the author never saw one, or even read anything on the subject. The chamber is many things, but a wedge isn't one of them. If he mistakes "squish" (which it has) for wedge he should expand his employment opportunities.

WRT SU jetting: yes, in most model H the idle mix is controlled by main jet height, but the remaining range of engine speed, load and vacuum mixture is determined by needle profile, and there are several hundred needles. If you don't have the correct one, or your engine has significant mods, the car maker frequently published alternative needle reccos for rich, lean, high altitude, race etc. Otherwise you do R&D...

WRT dual valve springs - there is a specific part number in Group .303 for "1953-55 Corvette 6 cyl.", but I have no other information.

Hey Rusty after everything I read about dual carbs I went ahead and bought Langdon's set up dual webers on an offenhauser intake hot water heat and his hei distributer and coil. Added fentons through dual cherry bombs sounds great. They have electric chokes as well. As fast as you touch the starter this fires and has never run so good in all the time we've had it. Looks like we're near by if you want to come by and have a look PM or email me. Gerry

The dual valve springs on the Corvette really had me curious. I couldn't for the life of me figure out how two springs could be used on each valve. So I did a little research and thought I'd share.

There are some high performance springs out there that are a spring within a spring. One goes inside the other. The inner spring is coiled in the opposite direction as the outer spring. The inner spring looks to be made of thinner gauge wire than the outer spring, almost as though it is a helper spring.

Anyhow, I guess that's how you'd have two springs per valve on the old six cylinder corvettes with 'normal' heads...one inside the other.

Matt

I ran a round track 350 for several seasons with a roller cam and triple springs. It's just necessary to reduce the diameter of the valve guides enough to get more springs in there. They wear out camshafts in a great big hurry, but they allow very high RPM before the valves start floating.
Jerry

In that pic Cosmo posted of the triple in an AD, are those spacers between the intake and carb's OE? Getting pretty close to the wheel well. On second thought, I found a pic with a closeup of the carb base, and see the spacer is needed for the carb to clear the intake. Hopefully there is more room than it appears for that front carb.

Where another component is added to the original single coil spring, it may be another spring with a shorter assembled height, smaller ID and OD, and thinner wire, with an extra step on the collar's lower surface to locate and pre-load it.
Another common alternative is a counter-wound damper, which is usually a thin, flat spring tightly fit inside the outer spring's coils. It suppresses harmonic vibration in the outer spring by friction as the springs pass each other in opposite directions as they compress.

The Corvette dual springs are:
Outer 3836123
Inner 3836132
Also shows a different collar, but only for the exhaust?