The Stovebolt Site Forums The Shop Area The HiPo Shop Headers and Dual carbs on a 6 cyl

Does anyone have either of these installed on there trucks ? Pictures and carb types ? Part numbers .Looked at Fenton and Offenhouser .Looking for combinations that worked successfully in the past.

Mr Fenton and Mr Offenhauser never spoke to one another. The mounting flanges are different thicknesses, however the use of a grinder or a welder to modify the mount brackets make this possible. Also the intake manifold needs to be ground on the bottom side to get clearance from the exhaust manifold. It sounds bad but really not hard to do. I have the headers on the truck and will soon have the intake on. Choice of carbs,plenty.I have holley/webber from Tom Langdon on now, have tried rochester "B"s couldn't stop leaks, am working on monojet 1 bl carbs. Will see what happens with that. Lots of carb choices, holley, carter yf's among others.

Don't get frustrated, lots of people here to help.

You can also get the Fenton intake manifold. That should avoid the fitment issue.

regards,
Leon

If it is column shift you may also have shift arm clearance problems.

Lots of these setups are out there, but very few of them work as well as an original 1-carb system. Dual carbs are mostly eye candy, unless you're dealing with a highly-modified race-only engine. You'll encounter flat spots, backfires, and generally very twitchy low speed and midrange performance, to get a slight improvement in top-end horsepower. It will take a different camshaft, valve and head work, and probably a modified spark advance curve, plus a matched set of the correct size (small) carbs to make a dual-carb/header system work almost as well as a stock setup. Large dollars and LOTS of hassle!
Jerry

Although I mostly agree with Mr Hotrod, I don't believe head work is necessary to run a dual carb setup. you may clean it up a little bit, but porting, polishing and oversize valves are a wasted effort on these engines for a street machine. True it might help in a race engine, but the head work will reduce the intake velocity at low speeds, reducing torque. You would have to spin the engine faster than 4500 rpm to get the increase in hp from the flow work. If we are talking about a chevy 235/ 261, or gmc 270/302, 5000 rpm should be considered a red line. If we are talking about the later 250/292, these motors can be spun significantly faster and could benefit from the headwork suggested.

As a point of refference I am running 5 2bbls on my 302 gmc. I haven't had the engine running in the vehicle yet, but I have had it running on a stand. It looks and sounds wicked. But yes, the 5 carbs are more for eye candy then they are for performance.

On my 58 235 with Split factory exhaust. 3X2 Barrel Carbs (Langdons small Carter/Webers), 3/4 CAM and no head work. The couple times I took it down the track that motor ran great up to 4700 RPM where it just flattened out. That was backed by a T5 transmission and a 390 rear. That truck was very street-able and sounded great, I ran it open headers at the track and there's just nothing like an open header Six.
Mongo

That's my point exactly about the head work- - - -bigger valves, opened-up ports, polishing, etc. It's the final step to making the dual-carb setup work, or any other enhanced carburetion arrangement. Then, all you've got is a high-speed engine. As long as there's one point of restriction, there's no advantage to doing the rest of the work. The possible exception would be if you install a pair of much smaller carbs than the single one it was originally equipped with, resulting in a slight, but useful increase in the total volume available. It's still only going to be useful at or near full throttle, but it's not likely to create as many headaches in the low speed and midrange areas. There won't be as much loss of venturi velocity that leans it out as the throttle is opened up from idle.
Jerry

http://rides.webshots.com/album/573004888TGzvrt

In an earlier album you will see when it had Rochesters. I have not had the tuning issues mentioned earlier. Pretty much set it and forget it. Now I have Langdon's HEI but have not yet installed it. Currently running Clifford tube headers but they are going away in favor of the Corvette split exhaust manifold that I took off of it earlier. I want the heat provided by the split manifold. I did not have any clearance issues when truck was 3 speed on the column but the tube headers are too close to the larger hydra-matic crossmembers...another reason to go back to the vette exhaust manifold.

Is it possible to run dual carbs without other engine work? Certainly.

Will you get any benefit from the dual carbs (other than looks) without other engine work? Probably not, and you may actually lose performance.

If you do your homework, and do everything (especially the selection of carbs) perfectly; you should see maybe a 5~8 percent gain in horsepower (WOT only), and fuel economy.

If you just "throw on what you have" with no regard to applicability to the engine, you can easily lose up to 20 percent in power, and more in fuel economy.

Now, if at the same time you switch to selected dual carbs; you also do head work, change to a more aggressive camshaft, and a better exhaust you will see some major increase in power without a major loss in fuel economy.

Jon.

30 yrs ago I had a shoebox nova with a 250 6cyl, it ran good with a clifford cam and intake w/450 holly, and a header. Google Clifford Performance, they're in Corona Ca.

Hey there, Greg, thanks for posting that link. I'm putting the same setup on my 250, only with Langdons cast iron headers. Nice to see how you ran all the linkages and fuel lines, plus hearing it in teh videos was a great motivator to get 'er done. Hopefully th esetup I bought from Tom will work well together...

eye candy is right on, and i couldn't agree more!!!! i tried running a offy 2x1 with rochesters, ran like crap, then went to newly refurbished and matched carter w1's ran like garbage. i put the original single rochester and stock intake with duals and it runs better than ever. the only other combo i wanted to try is the clifford intake and a brand new holley 390cfm. only to get away from old carbs which get rebuilt over and over and over.


a stock inline 6 needs exactly the fuel/air that the factory put on it. slapping on duals and more gas isn't going to do anything but give you more headaches. i speak from experience. if you can't live without the multicarb look, buy a 3x1 intake block off the outer carbs and only run the center.

I have ran a clifford 4bbl intake with a 390 holly on a 270 gmc. It did quite well, and woke that 270 up a bit. I do believe the primaries are too big, and the secondaries are too small on that carb. There is no comparison between the 4bbl and the 5 stromberg 97s on my 302 gmc. I have had many vehicles with multi carbs. I have had straight linkages and progressive linkages. Let me say there is nothing like running a multicarb setup with a progressive linkage. When those secondaries open up, the engine howels and the smile can not be knocked off the face with a 2X4.

My advice run a 3X1 intake progressively. And remember ... "The person who says it can't be done should never interupt the person who is doing it!"

I have the offy manifold, and fenton headers on my 216, daily driver. I've put on about 8,000 miles on the set up. I ran it for several thousand with Rochester b's, and then rest has been with Carter W-1s. I have aluminum pistons, and my 216 is over-bored. I was careful in setting them up, and syncing the carbs. I get slightly better mileage, and a little more power. Another 10,000 miles, and it will have paid for itself. It looks cool, sounds cool, and cost money. I probably wouldn't do it again though. But it is cool.

The person who says it can't be done should never interupt the person who is doing it!

A major problem with this set up is finding a usable matched pair of carbs. I like the Stromberg BXOV-2s, hard to find and making 60 year old carbs new again is difficult. I've switched to Langdon's Holley-Webers which are progressive 2 barrels. Only issue with these was needing a bit bigger jets, now with that solved she runs super. These are on my 261 with a cam from Patrick's, Edelbrock manifold, Vette dual exhaust, milled head and powerglide intake valves. It can be frustrating setting the carbs, a buddy of mine that's done dozens of these made it all work.

10-4

Almost 50 years ago, my favorite setup on a 302 GMC was 3 x 2 with progressive linkage. GMC 302 was born with a 2 barrel.. either a 4 bolt Stromberg or a 3 bolt Holley. My choice was the Ford 3 bolt Holley which as actually designed for a 272. I ran off the center one which actually gave me improved throttle response at the low end and just puttering around town. The other two opened quickly a little past half throttle. I think a lot of it is in how you drive them. I never opened the end two up until I had my rpm's up so I would get some velocity through them. If I tried giving it too much throttle at low rpm, I had better have a fire extinguisher handy. I think it is a lot in how you drive. I was 35 years old before I drove an automatic. Today there are a lot of 35 year olds who have never driven a standard.

I have been researching and favoring the GMC 302,Just need to find one that I can afford and runs .Looked at the 3 carb set up also.Also going to use a turbo ,just looking for low boost , nothing more than a strong street engine with good manners .Any other info or pictures you have would be great to add to what Im gathering. I would like to use all parts from the 50's to 60's

If you can find a 3-carb manifold for the 302 with the Ford/Holley 3-bolt bases and a set of 15/16" venturi 2-BBL carbs for the 221 cubic inch 85 HP Ford V-8, you should get good low speed to midrange performance on a single carb, and bring the outboard carbs on quickly at about 2/3 throttle. It will take a little tinkering with the progressive linkage opening rate to avoid flat spots, but that's how it was done 50+ years ago, with those same carbs. Nobody turbocharged gasoline engines in the 50's!
Jerry

In 1951 I had a '39 Chevrolet 4 door sedan that I put a GMC 270 engine in. Howard 5 carb. manifold with 5 97's, home made tube headers, lots of port work, big valves and a Harman Collins cam. This was unbeaten by any flathead Ford in 3 years of street and strip racing, and was a pussy cat to drive, full throttle at less that 3000 RPM caused a bog down, but above 3000 it came on like gang busters. Never say never about any set up, there are some of us that can make them work, and work good. At the Santa Ana drag strip It ran 98 MPH before e.t. clocks were used. With gas at less than $.20 per gallon economy was not a consideration, but it used quite a bit.

I've been beating that drum for years- - - - -and getting ridiculed in the process. Multi-carb systems are for race engines - - - - -not for some sort of eye candy on a bone-stock show machine. At least 90% of the people who hang a couple of carbs on a street-driven stovebolt don't know their butts from third base about what they're doing, and they don't have the engine-building experience to make the thing work anywhere near right. Extra carburetion is an integral part of high-speed modifications that make the engine totally worthless for most street-driving situations. By the time the other mods are done to support the carbs, (cam, valves, ports, open exhaust, etc.), low speed and midrange performance goes away, and you've got a high-rpm-only engine that's twitchy at best at low speed, and might not run at all between idle and wide open. They also use gas by the truckload. Thanks for making my point for me!
Jerry

I think the mistake a lot of people make is in actually doing all the flow work mentioned, or in selecting a cam that is too hot. These engines have a relatively low rpm threshold. This work is usually expensive and puts the powerband in an unusable rpm range. True there are advantages to doing this work for race engines. I believe on a street engine much of this work is wasted effort. As I stated above, these multi carb setups can work without all the other modifications. It just takes some tinkering and understanding, and proper selection of the carbs and linkage. There is no reason you can't have a multi carb setup that has good manors around town and gets absolutely rude when you want it to.

Maybe, somewhere, there's a frog with wings, too, but the overwhelming majority of them are still going to bump their bottoms when they jump. That mythical "do everything" carb system might exist somewhere besides in someone's active imagination, but the vast majority of them are still going to be a huge waste of time and money, and run like crap.
Jerry

About a year ago at a small car show I saw a Chev with 3 carbs. He had it running a few minutes earlier and I recognized the 6cy split manifold sound. I looked at the engine and I asked the guy, who is around my age, "Where's your linkage to the end carbs?'. He told me " I only put it on when I circle a drive in restaurant and think I may be challenged. Otherwise I keep the throttle plates completely closed and the idle jets have been blocked off." I would bet its been a while since he has been challenged to a country road quarter. I kind of don't know what to say either when I hear people, on one hand, want more power with multiple carbs, and then on the other hand are afraid to rev their 6 bangers over 3k. For low end torque, a saying that I heard 50 years ago, long before EFI was even thought of, "There is no replacement for displacement." still holds true. A stock 302 with a stock 2 barrel carb will accomplish a whole lot more than a smaller engine with a bunch of charbs.

Back in the late 1960's, there was a fiberglass T roadster running on the drag strips in the Nashville TN area with a really hot 292 Chevy six in it. This one had a roller cam, three 2-BBL Rochesters, 13:1 compression, and ran on an alcohol/nitro mix. The driver only used the two top gears of a 3-speed transmission, and said that he shifted at 6,500 RPM. The car had a thinwall steel tubing frame, and was extremely light weight. There were very few V-8's that could run with him. Somebody had done a very good job of setting that one up, and the driver really liked to let it rev.
Jerry

Does anyone have either of these installed on there trucks ? Pictures and carb types ? Part numbers .Looked at Fenton and Offenhouser .Looking for combinations that worked successfully in the past.Really not looking for any can't be done opinions.

It was stated best below .

"The person who says it can't be done should never interupt the person who is doing it!"

I know my butt from third base and have the ability .Thank you all very much for your help.Rides welcome to all .

"Do or Do Not---There is No Try"

Webstershotrods,

I assume that you have read the HRM articles about Frank McGurk's dyno tests on a 261 and a 216-1 ( 216-2, 216-3, 216-4, 216-5, 216-6 )? I ran a McGurk dual manifold with two BXOV-2s on a 235 and a 261 that I had in a 1953 Chevy 210, back in the fifties. It ran quite well - better than stock - and even my mother did not complain when she had to drive the car.

I later replaced the McGurk manifold with a Harper with three Stromberg 97s, along with a milled and ported 848 head and an Isky E-2 cam. It ran well, but the idle was a little high (about 800 rpm) and it took some experimentation with the accelerator pumps to get the throttle response as it should be (without stumble, etc.).

In the early sixties I got a 12-port head and used a manifold with five Stromberg 48s, just for racing. I put the whole engine in hibernation in 1962 when I went back to school, got married, etc. I now have the engine in a street rod. .

I'm currently building another 261 to put in an AD pickup. I am looking for another McGurk manifold to use the BXOV-2s that I am collecting. I still have the Harper, and I would like to try it at least once.

Sounds as if you have an interesting project. Best wishes!

Hoyt

At least 90% of the people who hang a couple of carbs on a street-driven stovebolt don't know their butts from third base about what they're doing, and they don't have the engine-building experience to make the thing work anywhere near right

Sad, but true.
If playing with mixture isn't fun for you, this will be nothing but misery. In general, there are no "bolt on" multiple carb setups, they all require knowledge of how both an engine and a carburetor work (2 completely different and very complicated topics).
I'm still learning after doing it for 45 years.

Pictures and carb types ? Part numbers .Looked at Fenton and Offenhouser .Looking for combinations that worked successfully in the past.Really not looking for any can't be done opinions.

It was stated best below .

"The person who says it can't be done should never interupt the person who is doing it!"

I know my butt from third base and have the ability .Thank you all very much for your help.Rides welcome to all .

"Do or Do Not---There is No Try"

You mentioned a 302 gmc. That's what I have with a Howard log manifold and fenton headers. The Howard can be run with 2, 3, or 5 carbs. Stromberg 97s have to be used when running 5. I'm not to good with posting pics, but if you pm me I may be able to send you some. Please note my 302 is not installed in my truck, so road tests are inconclusive. I do have the 302 on a run in stand and might be able to shoot a quick video of the motor running with the 5 97s. The motor is running on 2 primary carbs and 3 secondary or dumper carbs. I still need to make some adjustments, but all in all the motor is running as well, or even better than expectations.

Fifteen years ago I ran a dual quad on a small block chevy 350. Started with a box of carbs and built myself a pair of 500cfm carter afb's. Matched all the venturi's base plates etc. A matched pair so to speak. Tried running them in sync but eventually went progressive using back carb as primary and front kicked in at 1/2 throttle. Ran with a turbo 350 and 3.55 gear.
Played with it along time. Ran decent and fairly consistent. Biggest challenge was fuel pressure and float levels. Pulled it off when I built an aluminum headed 383. It sat on the shelf till I sold it. It was fun while it lasted but I told anyone who wanted to run one that it ran the best when it sat on the shelf. Good for a show car but not practical in the long run.

Here's a link to a youtube video I shot this morning of a cold start of a 302 gmc with 5 deuces. This motor sports a full flow oil conversion, 9.5:1 compression using Venolia pistons, Stovebolt HEI ignition, Howard intake, 5 stromberg 97s, fenton headers, mild cam from Tom Langdon, and absolutely no flow work done to the head.



Do you wish you had one yet? :P

GREAT VIDEO

Here's the video of Rick's (BigSix302) 302 that went in his 52 GMC Suburban. This was the first fire and the break in run for the cam. The next week the motor went in the truck and a week later we drove it down to Hutchinson for the ATHS Show, about 300 miles both ways.

Mongo

I have watched that video a dozen times.

It was great meeting you and rick in Hutch. It was better driving Rick's burb.

I imagine they buy that starting fluid by the case.

That's what chokes are for - the number of carburetors doesn't matter.

Turbo shop just mailed the Turbo today !Slow progress but getting there.