I ran a 97 on my last car, but want to keep an updraft carb on my new Model A powered project. I have looked at the dyno tests and it is easy to see the 20% or so HP increase when you switch to a downdraft carb (94, 97, Weber). I have also looked at the dyno tests of the dual updraft manifold that Charlie Yapp sells, and it appears to dyno about the same as a single downdraft. My question is where do you look for a better single updraft carb? My understanding is that the B carb is a little better than the A carbs (Zenith, Tillotson), but the difference looks marginal on the dyno sheets I have seen. I imagine there are some Winfield carbs that would outperform a stock A or B carb, but I have trouble working through all of the different models. What size would be a good choice to run as an updraft on a mild A engine (6:1 head, B cam)? Surely there are some other updraft carbs that are a good match for a Model A? Anybody using anything interesting? Where would you look to learn more about other updraft carbs? To cut to the chase, is there a single updraft setup that will perform as well - or nearly as well - as a single 97? Will Kimble
I'm no updraft expert, but the Chevy and GMC C.O.E. trucks of the '40s and '50s used a Carter updraft that I'm sure had a larger venturi and throttle bore than your A/B carbs do. You'll probably have to either enlarge your stock intake flange, or slot the bolt holes on the carburetor.
The original single intake is the limiting factor. A model A carb, modified to model B specs, is an improvement over an unmodified carb; but will not perform with a dual downdraft. With a "perfect" single updraft intake manifold, and a "perfect" updraft carburetor, you could expect WOT performance within 5 percent of the "perfect" downdraft carburetor. Carter, Stromberg, and Zenith all made excellent updraft carburetors. But a different intake would help. Jon.
Doesn't the B intake have better flow/larger bore? I know that doesn't tell you what carb. but may be useful info. anyhow. I'll be subscribing to this one for sure.
B intake and carb are both larger than A. B carb basic design with numerous small mods was used on farm/industrial engines...Vince's site shows some data for a 26 MM venturi (stock was 22 for B), and to my astonishment I actually found one in one of the B-variant carbs I picked up over the years. The visible area difference is quite impressive. I would assume that since Zenith made the 26, its flow is still within the capacity of the throttle bore. http://idisk.mac.com/forever4/Public/pages/zenithBcarb.htm
Thanks for the great info guys. I am still trying to digest everything as I am not very familiar with the updraft stuff. My jalopy is a long term project but it currently has a borrowed carburetor. I will have to return the carb soon, but would like to keep the chassis up and running. Sounds like from this info that a Zenith B carb is the basic architecture I should pursue? And then evolve it from there? I am aware of the limitations of the updraft compared to the downdraft - especially in regards to the accelerator pump - but if I could get within 10% of a down draft (5-6 HP in a 50-60 HP engine) at WOT then I would be HAPPY! Sounds like that is possible, and that there is more room in the Zeniths than I was aware of. My pea brain tells me that an A manifold bored out for the B carb (as opposed to a B manifold) would be the way for me to go, since the A ports are smaller. Don't know if the dyno would agree... I do know I want the heat from the exhaust manifold. What else do you have to do to hook the B carb to the A choke/throttle if you use an A manifold? Looks like a slightly different fuel line would be necessary - and easy. I think a phone call to Mr. Renner will be in order soon. Will PS: Current shot of the jalopy, it is rough & ready:
There are plenty of updrafts updrafts with normal accel pumps. A&B carbs handle the extra shot through a passive system, something like rear barrels of a Q-jet. There exist lots of substantially bigger updrafts, some of them 2 barrels, from big cars and truck applications. The variety of just Zenith updrafts is astounding. Both Ford and Chevy used updrafts on 6-cylinder cabovers into the 1950's.
Another possibility is the Carter RX-O updraft that was standard equipment on 1929-31 Chevy sixes. I've got one lying around somewhere; if you want, I can dig it out and measure the throttle bore. I do remember that it's got a different bolt pattern than an A/B carb, so you'd have to make an adapter plate.
HEATHEN, How much better are they than the '28 and earlier Chevy carb (I have been told that the Chevy4 carb is just about strong enough to run a decent lawn mower )?
Heathen - while I normally agree with your posts, your memory on this one missed. The Carter RX-0 was used on the Chevy 4. The Chevy 6 used an RJH-08. No disrespect intended. And while I really like most Carter carbs, the brass bowl updraft was certainly not one of their finest; plus parts today are EXPENSIVE. Jon.
Try Dennis Pirano. He bores out the A manifold to B spec's. He also radiuses the runners. Check out his web site at modelaparts.net. Click on the dyno, it has several engine combinations and there power (up drafts included). Off the subject but what paint did you use on your last exhaust manifold?
If you ignore the sales pitch at the end; you may find some of the other information presented in this link helpful: http://www.thecarburetorshop.com/Aftermarketupdraftcarburetors.htm Or maybe don't ignore the sales pitch Jon.
You're right---I tarded out on that one. I guess I should have dug the carb out and read the side of it!
what about side drafts?? i'm thinking Linkerts off harleys and indians?? Problem with them would be they dont have an accelerator pump
They are great if you have a numbers matching Indian or Harley. However the Linkert was based on a Schebler design from 1902! We used to do a good business selling SU sidedrafts from Triumphs to the Harley dudes. Big difference in performance, according to them. Jon.
The key to an increase in power is venturi size. Winfield recommended a B size for the Model A. I ran a C (S-CD) on my flathead for a long time and it ran well, good power and fuel mileage. I am currently running a S-CCD on my Riley.
I am bumping up this old thread after reading the Riley information in the latest SOSS magazine. Apparently Riley recommended (circa 1931) going to larger Zenith carbs and offered a custom manifold for them, I think the part numbers for the carbs were M-155 (1 1/4") M-156 (1 1/2") & M-157 (1 3/4"). In the pictures they look kinda like Model A carbs but the fuel inlet is to the left instead of to the right. I searched a little but couldn't make any sense of these part numbers, I guess it was too long ago and not commonly used. Anybody have one of these Riley intake manifolds? Anybody know what newer equivalents to these Zenith model numbers might be? It seems to me that it should be possible to equal the performance of a single downdraft 2 barrel with the proper updraft Zenith and probably a custom intake manifold. But once you leave the Model A and B carburetors it is very difficult to figure out what is out there. Are there any resources I should check out? Tractor carb rebuilders? Any other updraft carb brainstorms out there? Thanks, Will Kimble
There is an absolute world of both information and variety of updraft carburetors. As I stated in my post in this thread a couple of years ago, the original manifold would be the limiting factor, not the carburetor. Updraft carburetors are readily available for engines as large as 1000 CID; very easy to find stuff for the Ford model A. Jon.
One source that is probably within reach...Ford used an updraft on early 1950's 6 cyl cabovers or delivery trucks, and Chevy had something similar. Both were for 6 cylinders maybe 10-15% bigger than a banger and so might be a nice hotrod size. Get a B manifold! No point in messing with the A thing.
Thanks for the input, guys. We are all on the same page with the manifold - I think you have to go into it planning to build a custom manifold. Bruce, the COE carbs look really interesting - thanks for the tip! Looks like there were two for Fords - both made by Holley - the 859-FS was for the 226ci and the 859-H was for the 254ci. I think this might be an interesting place to start, does anybody have any experience with these carbs? Were these gravity fed in the COEs? The literature I found said that the 859-FS has a 1 1/4" mounting flange, anybody know off hand what stock Model A/B is? Thanks, Will Kimble
Chevrolet COE's used Carter Updrafts, GMC COE's used Zenith updrafts on the 2 ton, 3 ton, & 3 1/2 ton COE's, & Zenith side drafts, on the 5 ton, & Heavier gas burner COE's.
Try: www.carburetion.com in Auburn, WA. They have been a great source of information and also expert help with a set of triple side drafts I have on a Stovebolt. Nombc9
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