updraft vs. downdraft carbs

[JohnLaVoy]

We have the Weber system on a couple of cars and find the system works great much improved over the updraft.

[Jim Brierley]

I agree with simonpie. The main difference is the most-used downdrafts flow more air. The Model A is a big engine and can use much more than the stock carb.

[updraught]

Thanks Jim.

Those hotrod types were getting jolly unruly.

[Railcarmover]

Originally Posted by updraught

Thanks Jim.

Those hotrod types were getting jolly unruly.

[Logan]

I've run the stock carb, webers, stromberg 81, 48, and 97's. And strombergs are by far my favorite. They're easy to tune, jets are easily accessible, and in my opinion have more "oomf" behind them than a Weber. The Weber is a progressive two barrel where as the stromberg uses 2 barrels all the time. I like having my power all the time over the little bit better mpg the Weber will give you. I really like the new 97's being built, I've installed probebly close to 5 on customer cars, 2 on mine, as well as a couple rebuilt strombergs and I've never heard a complaint from customers or myself. I've switched out 5 webers for strombergs and all had posotive reviews once the exchange was done.

[Jim Brierley]

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Logan, interesting! Please don't tell updraught that I am a hot-rodder, an old one!

[CarlG]

I am pretty much with Logan. I went thru 2 Webers before I got the new 97 (at the urging of my engine builder). Have been really happy with the 97.

[George Miller]

A lot of it is about the manifold design. I have good luck with 94,s make my own intake.

[zzlegend]

I go along with George. 94's are what I run on my Flathead and my A motor. Easy to re-jet and tune duals. But hey,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, ,,its like the old saying..............................
"There's an ass for every saddle". Run what you like.

[George Miller]

Originally Posted by zzlegend

I go along with George. 94's are what I run on my Flathead and my A motor. Easy to re-jet and tune duals. But hey,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, ,,its like the old saying..............................
"There's an ass for every saddle". Run what you like.

I totally agree every one should run what works for them.

[Purdy Swoft]

My experience with dual updraft manifolds is that if the runner or tube size is too small, installing larger carbs or carbs with larger venturi area will show no improvement over what dual carbs with model A venturi area would allow . My cast iron Uniflo dual updraft manifold that was made for model B use outperforms my cast iron Trojan intake , Both running model B carbs with larger venturis . I feel that turning a Vortex dual updraft manifold that has smaller model A size runners , up side down and installing larger dual throat carbs would have a similar effect .On the other hand the smaller runners could still dump plenty of raw gas while flooding the engine when used in a down draft manner . Its not all about more or larger carbs . Manifold design plays a bigger part .

[Railcarmover]

Weber ICT's are single venturi carbs,34mm.They match the bolt pattern and runner on the vortex intake.

[txkhog]

Also a down draft would get the carb and intake away from the exhaust header temperature

[Purdy Swoft]

Actually , i'm really not familiar with the different Weber carbs . The ones that I've read about have been used on smaller engines like used in the Vega . The models 81 , 97 , 94 & 48 Stromberg style two throat two barrell carbs would have to use adaptors that would mate with a smaller diameter single throat manifold . It seems to me that a manifold that had larger runners and was designed to be used with the dual throut two barrel carb would give better performance and fit .We are talking about different style and type carbs . no harm meant I also consider manifold size and flow .

[Tom Wesenberg]

Originally Posted by txkhog

Also a down draft would get the carb and intake away from the exhaust header temperature

The problem with a downdraft is when you stop, all the exhaust heat goes up and boils the fuel out of the carb. This wasn't a problem in the 70's when we had good gas, but today's gas boils much too quickly.