The Stovebolt Site Forums The Shop Area The HiPo Shop Multi-carb intakes and carbs???

Hi everyone, I'm trying to learn more about multi-carb setups for 235's before I hit up some swap meets later this year. I have a '54 235 with a '53 235 head. Eventually I'd like to switch from the stock leaky Rochester to a multi-carb setup. This engine will be for street use in a basicly stock '49 3/4-ton with a 3 speed. I'll also be adding dual exhaust via headers or dual manifolds. I like the looks of a 3 carb setup and believe it would function a little better on a 6 cyl than a two carb setup.

First, is there an easy way to ID intakes for this engine to keep from confusing it with something that won't fit?

Second, if I can find a 3 carb manifold, what carbs would be the best choice from a best-sized-to-the-engine point of view. Would 3 Carter w-1's be too much for a mostly stock, low RPM engine? What about Strombergs? I haven't been able to find any info on how many CFM any of these old carbs flow. If someone has the info or a link to the info please post it.

I'm open to any suggestions.

Thanks for the help, Kevin.

Kevin,

I can't help you out with the technical of a multi carb setup, but I can praise your choice! I am also running a log manifold on my 302 gmc engine. I was told Stromberg 97s flow 150 cfm. Add the 5 I will be running and that is 750 cfm. Over carbed??? Hell yeah! If I can get it running it will have the wow factor.

I believe the calcs for a mildly built 235 would put the flow demands at about 350 cfm. Practically speaking, you might get the best performance out of one of the smaller 4bbl carbs like a 390 cfm holley, but what fun would that be?

Think BIG! It looks cool! Might not be to green, or thrifty, in fact it will probably be down right thirsty.

Good Luck!
John

it has been said that a triple setup is hard to balance. a four barrel could be more fuel efficient with their primary and secondary setup.. i have a dual carb setup on my 54/235 and it is not two frugal gas wise. i have not checked the mileage lately because the engine is being overhauled. do a search on this site it might be enlightening ron

Thanks for the input Ron. I have been trying to do as much reading on this site as time will allow and have found a fair amount of info on the dual carb setups but not much on the three carb setups.

All the old hop up books state that dual carbs are the best set up for a road job. I'm running a 3x1 set up on my old 47 but have blocked off the front and back. The tripple was best used for all out racing and now with all the good old carbs getting so worn out and so very hard to find it's even more difficult to get them running. While they dont look 'old timey' I really like the pair of Holley/Webbers from Langdon's and Tom will help you if you need bigger jets etc. Check with Langdon's and Patricks for manifolds etc.

Thanks JiMerit, where can I find copies of the old hop up books?

How well different manifolds/carbs work often depends on the port design of the cylinder head, and how the manifold ports work in conjunction with the cylinder head.

Multiple carburetors that run in "parallel" operation (all carbs operating all of the time) MUST be balanced.

Multiple carburetors that run in "series" operation (one has a "primary" carb, and one or more "secondary" carbs) require less balance.

Examples of "parallel" set-ups would be either the Corvette 6 cylinder with 3 Carter 1 barrels; or the Hudson Twin H with 2 Carter 1 barrels.

Examples of "series" set-ups would be Chevrolet 348 tripower, or Chevrolet 409 dual quads.

Contrary to popular belief, multiple carburetors are NOT difficult to balance or synchronize. I was doing these things as a 16 year-old with a piece of vacuum hose (quite well, I might add) long before I could afford the simple vacuum synchronizing tool called a "Uni-Syn" (available at most motorcycle shops). One simply must understand how to do the synchronization, and pay a little attention to detail.

Again, the big criteria on which would work the best is dependant on head and manifold design.

Obviously, one should use slightly smaller carburetors on a 3-carb set-up than a 2-carb set-up, all other things being equal.

As to the 4-barrel comment; a properly selected and tuned four-barrel might do slightly better (3~5 percent) on fuel economy than a properly selected and tuned 2 or 3 carb set-up. However the 2-carb set-up should do slightly better on power than the 4 barrel, and the 3-carb set-up (depending on head and manifold design) should do a few percent better on power than the 2-carb set-up.

As always, selection is key. Just as one would not normally place a Holley 1150 Dominator on a 235; one must also select 1 barrel carbs of the proper type, size, AND engine fuel curve for the system to work properly. Simply purchasing 2 or 3 carburetor that bolt onto one's manifold is a poor guarantee of success.

Jon.

Thanks for the help Jon. The head is a stock 1953 235 head on a stock 1954 235cid 125 hp engine. I know little about these engines, the stock parts or the aftermarket parts. The exhaust will be duals, probably Fenton maniflods. The intake is yet to be decided but the Offy intakes seem the most readily available. I've read that you like the W-1's for two carb setups on these engines.

Do you think a 3 carb setup would work well on these engines for street use? If so, what carbs would you suggest for a combo like this?

I do want to keep a vintage type look, but I am more concerned with function.

Thanks again, Kevin.

Kevin S,

I could be wrong on this, but firewall surgery is necessary to get the 3X1 combo to fit on the AD trucks. I had a Offy and three BXVD's, but that was on a '54 car.

Stuart

Thanks Stuart, I did not know that. Does anyone know for sure if the firewall would have to be modified to fit a 3 carb intake? If it does then I can rule those out. Thats something I'm not willing to do. I want to keep the trucks sheet metal all original/stock looking.

Kevin- The 3 Stromberg BXOV-2s with the bowl foreward clears the firewall on my 47 coupe. There are other issues to be aware of like your column shift linkage not clearing the back end of a non stock intake, may have to modify. Also Amazon.com should carry California Bill's Chevrolet & GMC Speed manual.

This Speed manual compares different carb, cam etc. set ups via dyno tests done back in '54, old book but a great read, much basic info still applies today.

Kevin,on a mostly stock engine,3 carb's are overkill if you are looking for the "cool factor"good idea,but do as already suggested.Block off #1 & #3carb's,run the fuel lines and install linkage,but don't use them or you will have a tuning nightmare and lousy milage

Dear Kevin;

Yes; 3 carbs is 'way overkill' for a stock engine!!

Find a 2 carb manifold & run the 2bbl Holly/Weber(s). This will give you two single bbl until you 'flore it', then all 4 work.

It's the best of "both worlds".

Good luck.

With respect to all with whom I am about to disagree - 3 carbs on a stock engine is NOT overkill, DEPENDING ON THE CARBURETORS USED!

When in Japan on an all-expense paid "vacation" courtesy of everyone's favorite uncle, I owned a 37 cubic inch 4-cylinder that came from the factory with 4 carburetors.

The trick with any carburetion system is to do one's homework, and pick a carburetor or carburetors with the correct airflow for the engine.

Three Holley dominators on a 235 is overkill. :p Three Carter 750 CFM comp series AFB's on a 235 is overkill. :p 3 Carter YH tag number 2066s on a 235 is NOT overkill (Chevrolet did it on the 1953, 1954 Corvette).

There are other units that may be used.

The cylinder head and manifold runner configuration is more important than the number of carburetors.

And obviously, as Stuart mentioned, physical clearance is somewhat important also.

Jon.

Carbking (Jon), thanks for the clarification. Are there other carbs you can list that would flow right on some mildly built 6 bangers? Can you give us the flow specs for some of the more common carbs like...

Holley 94
Sromberg 81/ 97
Rochester B
Carter w?
Zenith?

This information is hard to find when you are looking for it... may make a great tech tip!

John

BBSD - the manufacturers (with the exception of Zenith) did not publish CFM ratings for these carburetors.

What one must do is homework. Measure the main venturi of a carburetor which was designed for a specific engine. Look at the fuel requirement curve for that engine, and how applicable it is to your specific needs. The Holley 94, as an example, has main venturi from about 3/4 inch to 1 1/16 inch depending on which Holley 94. The Stromberg 81/97 are special cases of the Stromberg EE-1 which have the same sizes as the Holley 94.

But don't feel you are limited to automotive carbs. Someone made a 4 1-barrel manifold for the 2 liter Pinto engine. We built one for a friend who ran one in one of the outlaw racing leagues. We used 4 Mikuni motorcycle carbs. The engine ran like a scalded dog! (So well that multiple carburetion was banned by that league at the end of the racing year)!!!

But if I were going to build a multi-carbed 235, I would want to look at the runner design in the specific cylinder head (are the ports siamesed, are all ports individual, do the ports come to a common point, etc); then, based on this information, look at what 2, 3, or 6 carb manifolds might be available, and look at their port arrangement. The idea is to have each carburetor flow equally into either 1 (6 carbs), 2 (3 carbs), or 3 (2 carbs) cylinders. One wants to avoid an overlap, where 2 carbs are feeding into the same cylinder (this is why tripower doesn't function as well on a V-8 as either a single 4 or dual 4's).

Once one has decided on a cylinder head/manifold combination one can then pick carbs to feed the number of cylinders desired.

I really like the looks of the Corvette 3 1-barrel unit, but I understand clearance may be an issue in some trucks.

I also might try to do 6 1-barrels, fab the manifold (it is really fairly simple to do so using a piece of 3/4 inch sheet aluminum, various electrical conduit bends, and some flanges off some junk carburetors; and then use maybe 6 small engine carbs (Onan generator, motorcycle, etc.).

In manifold fabrication, it is very important (except for all out racing) to run balance tubes from port to port allowing the pulses to even. Trying to do 1 barrel per individual cylinder without pulse control can be a nightmare.

To synchronize multiples of 3 or more, begin with the center carbs, and syncronize the outers to the center.

I personally use solid linkage (all carbs functioning at all times), as I feel this works the best for a street engine. For a race engine, one can use progressive (idle or pace speed on one carb, and everything when wide open).

Jon.

I will completely agree with Jon (Carb King) on his assessment of use of multicarbs. I have used a log manifold with 5 97's on a 270 GMC engine with a lot of success, it was the fastest car in Southern California as far as street racing goes and in 1951 turned just less than 100 MPH at Santa Ana drags. All 5 were working in parallel, it was somewhat of a gas hog but with fuel around 30 cents per gallon, so what. It was very "streetable" too. I have used a 3 carb manifold on a 235 using 3 Rochesters (I know most guys don't like them) but I have had good success with them and they are very easy to tune. Just my opinion but the WOW factor goes with 3 carbs, it is very impressive when the hood is opened to see them all lined up and ready for action. Good luck whatever you do, the 235 is a great engine and almost bulletproof.

Thanks for the input everyone.

I thought 3-1's would function better than other setups on these straight 6's, if properly sized. Since the intake runners are in pairs each carb would feed 2 cylinders. And the rest of the intake would basicly funtion as balance tubes. But it appears it will hit the firewall and I don't want to modify the firewall. I could fab my own, I work as a machinst at my day job and have all the tools, but I'm not sure how the unequal runner length would effect the tuning of the engine. Any thoughts?

chevman32, thats very cool! What car was the engine in? Do you have any pics? My aunt and uncle live in Santa Ana, I was just out there in April.

Kevin, my computer skill have shown their ugly head again, I will try to finish this up before hitting the send button again. My GMC 270 was in a 1939 Chevy 4 door sedan, a real sleeper. It was stock externally except lowered a bit. I raced everything I could find and was never beat on the street. I lived in Montebello but went out to the Santa Ana Drags a lot. Those were the days...

Here is another idea to ponder. I am having a manifold made to take a pair of triple throated webers/solex/delorttos that six cylinder Porsche use. These are the downdraft ones not the side draft. They should look extremely sexy on a 235 Chevy.

Bob

I'd like to find a list of donor vehicles to look in for carbs with the right stud spacing...

Maybe that's a naive notion though...

I also like the looks of the 3 X 1 vette intake. I had one and ended up selling it for 2 reasons. I would have had to modify my firewall and rebuilding the 3 correct carbs w/ the vette aircleaners was extremely expensive. If I had a lot more money, I would do that.

how come all the hating on 3x1 setups?

imo they look the best. dont know how ima set them up yet but i got a offy 3x1 intake, linkage and 2 rochester RP carbs from a 62 truck currently searching for a third. And from my research there would be no problems with firewall clearance.

once i get my 3rd carb i'll be setting it up and see what problems if any i run into

Cool, let us now how it works out.

coolerthanethan,

I don't think it's a matter of 'hating' 3X1 setups, it's the fact that the 235 engine takes so much more work in order to properly utilize the benefits of this arrangement. Without additional "hot rodding", the three carburetors is too much for the engine. They sure look nice, but it could be like the old adage..."if it don't go, chrome it".

Stuart

I am with you I have a 42 with a 235 from a 57 I put in and a set of 3:55 gears I am going to put on a set 16" rims on it as it has 15's on it now. It has updated ingition too, so no pionts
I am thinking a better intake and carb along with a good dual pipe out the back with a cross over.
However before I stick cash in to it I would like to know what works the best?? ANY and all suggestions?
I want to do this correct one time then drive the heck out of it....HELP ......
Thanks and Semper Fi.
Clay
cburtts@ec.rr.com
NC

here is a long thread you'll enjoy

http://www.stovebolt.com/bboard/cgi-bin//ultimatebb.cgi?ubb=get_topic;f=2;t=009469#000000

owning two solex's on my 63 -356. porsche b,c,d 356 solex P11 are two throat as are 44IDF webers. they may be $2-400.ea now and need rebuilding. some are solid (best) and some are split shafts. all the 356 purists want the solid shafts and they have big pockets, thus more dollars out of your pocket. rebuilding a solid (re-bush) job is $250 + ea
912 used split shaft solex.
http://cgi.ebay.com/ebaymotors/1968...550QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
you may be better off finding webbers and they are a great carb.

and talking old stock motorcycle carbs... a pair of amal 229 /289 for my bikes run $1400-1800 pair on a recent ebay sale w/18 buyers

Kevin - for books go to these sites
www.gregsonline.com www.themotorbookstore.com
for carb tech, custom manifolds, the complete set up for your engine, and or any carb work talk to Charlie at www.vintagespeed.com
very spendy, but the quality is the best money can buy. I have purchased two 2 X 3 SBC set-ups from him. Very pleased with the workmanship and attention to detail. Have not had any 1 BBL work done by there shop, but know they do custom inline manifolds and fuel blocks and specialty carb work. maybe you can ship your rochesters to them and they will rebuild them if you like. I know they deal in Strombergs and Holleys alot. They will ream and install bushings for the throttle shafts, etc. They have tons of carb parts, and even have some models recast so its like a new carb and all new internals. Contact them and see what they say. If enough bolters request Rochester B help he may repop the castings as I bet the GM patents have long ago expired. Worth a shot.