Twin H versus Single Carb

JasonNC

In light of the problem of keeping the twin carbs synchronized, is it more feasible to go to a single carb as opposed to staying with a Twin H setup?  I noticed that a number of guys switched from Twin H to single carburetors, especially when gas prices were high.  

iceblade10

I will be interested in hearing opinions on this.  I have the opposite situation.  My 54 currently has a single carb, but I'd love to set it up with Twin H, for no other reason than the "cool" factor.  However, maybe it's best to leave it be.  It's a very original car, and never had Twin H, so...

Browniepetersen

Jason, I must admit that this comment strikes me as odd.  I would akin it to asking a woman if she needs to wear her makeup when she goes out in public?

However, allow me some comments.  I have owned four stepdown Hudson's. Two had stock or rebuilt engines to stock requirements.  Not real sure of the "CFM's (around 300 give or take) the WA 1's but with the stock engines they ran fine at all speeds.  One engine was a 232 and the other a 262. 

Next let's go to my "salt flats racer" that was my first 308.  I drove it for a while with a single WA 1 and it was fine.  Then came the rebuild.  My attempt at building a 7X engine was successful and I installed Twin H because of the fact that I wanted to obtain top speed on the Bonneville salt flats.  It was a good runner all the way around.  Now I have my 54.  I was driving it for about 500 miles when I spun a rod.  I decided to use as many of the 7x features and use this as a daily driver.  When I installed the rebuilt 308 I was running the stock WA 1 carb.  Problem was, the engine was not stock.  The larger valves and the high performance cam changed everything.  Some of the most knowledgeable Hudson folks told me that I would need around 600 CFM's just to get the air into the engine.  With the stock carb I have performance problems at idle as well as on the top end.  The opening in the intake manifold determines the CFM.  There is no way to get more air into the engine than through this check point.  The only answer is the Twin H.  ETTO, I now have the Twin H.  Also, I am not sure by what you mean about "keeping the twin carbs synchronized?"  I have never had a problem with the Hudson set up--when done properly.  Now, if you want some issues try a tri power or a six pack--that can be an issue.  Also, a single carb will only give you a few extra miles per gallon.

Now, with that said, I will add that this is my opinion based on my experience.  I would be disappointed if someone did not have a different opinion.  By the way, your care looks like one that I had.  "Love the paint combination...."

Ken, thank you for the correction.  My 52-262 would have had the WGD  776S As you mention.

StillOutThere

Been using a Uni-Syn for about 40 years.  It is a MUST HAVE for anyone that has multiple carbs. 

Jay_G

I had no problem with the Twin H setup on my stroked 7x 308.  It ran just fine and I thought the carbs were relatively easy to set up.  Just follow the book and use a Unisyn.  Now if you want a pain in the butt to setup try putting the triple webers on that engine.  There are lots of things they don't tell you when you start that project.  Thankfully Jay at Vintage Coach is dealing with that and I am not.  When it is done it will be cool but there is far more to putting triple webers on than bolting up the manifold.

I will say on the twin H you need two identical carbs.  Do not mix and match, get the same number for both, then take them apart and check the components.  They should be identical, if not you will have plenty of problems.

Per

     Long ago I briefly had a Hornet with twin H.  One of the linkages had a hole which was worn.  This left me unable able to adjust things so the carburetors functioned together, since the throttles were not always opening the same amount:  If I set them so the car idled nicely, then when I pushed a little bit on the gas, one carburetor's throttle would move, but the the other throttle was still at idling position.  This caused un-smooth operation. When I pushed the gas a little more, the first throttle moved more, and the second throttle moved a little bit. Still not good running of the engine.  If I pushed the gas pedal way down, everything was alright, because the minor difference in throttle openings didn't matter when they were open a lot.

So, it is important to make sure the linkage doesn't have this kind of play, and as Jay says, the carburetors should be the same.

                       Per

Ol racer

FYI
Twib H is the all around best Induction System for Hudson Stock & mild performance Stepdown Engines. Twin H provides much better air/fuel distribution to each Cyl with almost equal runner design. They will out perform a dual Edmunds single or 2 bbl manifolds, however in fairness the Edmunds do shine up better.. Additionally, Never had to Uni Sync a Twin H and never seen a noticably difference in MPG..

(A huge 2Bbl would out perform the stock 2 bbl if you would mill off the small restrictive carb base, however marginally because of long runner lengths).. Just my opinion..

Geoff

IMHO, the performance of a stock single carb Hornet is like the  famous Rolls-Royce slogan "adequate".   

JasonNC

Okay.  I've never had a Twin H setup.  There's a car that I'm thinking about buying and it has a Twin H.  I just assumed that Twin H had more cons than pros based on some of the conversations I've had with people that had changed from Twin H to a single carb....

dwardo99

I took the Twin-H off my Hornet and did not notice a difference except the gas mileage improved. Adding an oversized exhaust system made a noticeable difference even with the single carb. OTOH, when I was young I had a 51 with a modified 56 engine that had Twin-H and it absolutely went like stink. By far the best running Hudson I ever had. My gut feeling is that on a completely stock engine it doesn't make enough difference to be worth it except it looks cool, but for modified engines it's a different story. BTW, I asked Smokey Yunick what the cfm of the Twin-H was and he said 400cfm. I don't know if that's true but that was what he said. 

Since I am a motorcycle guy, the way I synced the Twin-H is to remove the balance tube temporarily and install plates with hose barbs over the mounting holes. I then used a multiple vacuum gauge (the one i have has 4 gauges) to get it so each carb was pulling the same vacuum and opening at the same time. When tuning fussy antique British motorcycles this is absolutely critical because there is one carb per cylinder. I'm sure the Twin-H is more tolerant. 

joe53HH

I need some education about carburetor syncing. I was not able to find instructions on the internet for the UNISYN. Will the Edelbrock UNISYN 4025 (Summit Racing) work with most single barrel carburetors including the WA-1? Do you need 1 for each carb when syncing?

Lee ODell

On freeway driving I got 4 MPG less when I changed from 2 barrel carb to Twin-H. (20% drop) Had I know there would be such a drop in gas mileage I would have stayed with 2 barrel. Why did I change. Probably like many others, it looks more impressive and to say it has Twin H. If I were to buy another Hornet I would choose one with 2 barrel for the kind of driving I do. Lee O'Dell

iceblade10

Based on these comments, it seems like it would not be worth the time/hassle/expense of putting on a Twin H system, since I already have a 2 barrel that works fine. My 308 already has a 262 head on it, supposedly for higher compression and more HP, so I guess I should be happy with that... :-)

53jetman

You guys better sharpen up your tune-up procedures, as my 54 w/Twin H will average 20 to 21 mpg at 65 mph on a trip.driving on Interstate Hwy.  Granted, it will fall to around 18 mpg on a road with stop lights and stop signs to contend with on occasion.  This is an all original '54 Hornet with 22,000 miles showing on odometer (which I believe is correct), knowing who I bought the car from..

RL Chilton

Geoff C., N.Z. said:

IMHO, the performance of a stock single carb Hornet is like the  famous Rolls-Royce slogan "adequate".   

Agreed.

Jerry-

That's really good.  I've always been told that a Twin-H set up properly should get at least 16mpg on the Highway and sometimes more, depending.  I'd say 20-21 at 65mph is outstanding.  I would think that most folks don't get those kinds of numbers.  

For the record, I have two cars with Twin-H and have driven 308's w/o the twin carbs.  I wouldn't have my cars any other way.  I'd post pics but . . .

dwardo99

I don't know what it did with the Twin-H except I noticed after going to the single carb that gas stops were fewer. With the single carb, on a road trip it would get about 17mpg verified by GPS but I have a proverbial heavy foot, meaning 75mph cruise. My uncle always asked me if I didn't think I was being kind of hard on it and I always told him that I don't have any use for a collector car that won't keep up with modern traffic. If I ever get another one I'm going to put a modern GM overdrive automatic in it and I think that would make it awesome. 

Glowplug

Gas mileage is a result of too many variables to assign good or bad numbers to anything other than your own vehicle. Many years ago I had the fortunate experience of knowing Bernie Sigfried. Our friendship began with a cold call and lasted several decades. He mentored me on many things Hudson to include building my first Wide Bloc, a 54 308. After much discussion the path to completion included reliability, drive ability and dependence on OEM engineering. I bored the block to 318 cu in with stock components for the remainder. Bernie coached me through all aspects including describing the carburetion. We rebuilt a twin H from a 52 Hornet. The carbs were cleaned and overhauled per Carter specifications and installed/balanced per Hudson mechanical procedures manual. One added aspect was driving instruction. Bernie suggested adding a vacuum guage to the dash. He advised, drive as you want but every time you move out of max vacuum your mileage suffers. I learned a lot from my friend, this is how I got 20-22 mpg with Twin H on road trips.

Per

Jerry,

     What transmission, axle ratio and tires do you have?  Years ago I drove from Portland, Oregon, via Los Angeles and Denver to Boston in a 54 Hornet Special.  It had one carburetor, overdrive, 4.56 axle, and almost bald bias tires.  I drove 50 mph because I didn't want to blow out the tires or strain the car!.  The car had about 48,000 miles on it at the beginning of the trip, and went about 4500 miles on the trip. 

      It got about 18 miles per gallon overall, and about 20 on the flat part of the trip that was at sea level, from Portland to Los Angeles.  I was happy to get that gas mileage, but I wondered if it would have been better if the car's axle ratio had been 4.10.

     I am happy to say that the car is still in the HET club, owned by Ron Doviak in Pennsylvania.

                         Per

dwardo99

I use the same technique with my every day car, which is a Mercury Grandma Marquis. For some inscrutable reason it has a tachometer. It's pretty useless except that you know right away when the torque converter unlocks because the rpm goes way up and you know you're burning gas. That little 4.6 V8 does not have much torque and in a heavy car it will unlock with little provocation so if I drive to keep it locked up my gas mileage is better. The LT1 in my Roadmaster wagon has gobs of torque and stays locked up most of the time. It does just about as well on gas even though it is probably a good 500 pounds heavier and much faster.