Paging Purdy Swoft

[tbirdtbird]

Purdy, I recently stumbled onto your post where you showed the Trojan dual updraft manifold. I was intrigued. As you know there is a repop out there which is quite similar.

A knowledgeable racing enthusiast I know suggested these might load up at lower speeds and be just fine at higher speeds.

Can you comment based on your experience?
I am running a stock motor/stock head/stock cam.
3.78 gearset with a Mitchell
We are doing another build with a Stipe B profile .330 lift cam and a 5.5 head.

We do mostly touring (Texas: a couple hundred miles or more at a time one way) and some parades.

I am deliberately not doing this as a PM since others may be interested in this.
Thanks, Dave

[Purdy Swoft]

Tbird, I'm running B carbs on my Trojan and it has never loaded up at low speed. I run another dual B updraft setup on my speedster and have never had a problem with either. Dual updrafts are really the easy way to go for dual carbs. Both of my manifolds are open plenium. I can disconnect the linkage and run on one carb. I'm running 5.9 heads and Winfield super street 3/4 race cams on both cars. I have run dual B carbs on another engine with a stock 4.22 head and a B cam and it run good and didn't lkoad up at low speed either. Without a higher compression head, the dual B carbs and B cam would run faster on top end but you don't feel the dramatic difference as with the full package. I run 3.78 gears in all of my model A's. There is nothing special about my B carbs, they were just rusty swap meet carbs that I cleaned up and used with the original jets. I get better gas milage with dual B carbs than I do with a single Zenith side bowl carb on my 31 tudor. When the high speed jets kick in on the B carbs my speedster, you can really feel the power surge. The more mods the better the results because every little thing counts. You can run dual updraft carbs with no other mods. With no other mods you will mostly just gain a little top speed but won't get the seat of the pants feel. I only use the choke on the front carb. I run the GAV closed on the rear carb. The choke and GAV operate as normal on the front carb. After a brief warm up I close the front GAV because B carbs should run with the GAV closed after warm up. According to the Piranio dyno tests, Charlie Yapps aluminum dual updraft manifold with dual model A Zenith carbs gives a 10 HP increase , Same as dual 97s and a lot easier to set up. With two good carbs, there should be no problem . The only problem that I have ever had with either of mine was a cracked fuel line on the rear carb on the roadster.

[tbirdtbird]

Kool, very interesting, indeed. Thanks.

I see it is suggested to use Tillotsons with the alum. dual updraft because they are less weight. I know nothing about B carbs. I have a pile of Tillies here that I could put into service. (In fact my regular carb on this car is a Tilly since there is no vapor lock with them. Many many folks in our club use them for this reason. Cast iron Zeniths seem to hold onto the heat and the alum. Tilly seems to give it up.)
Comments on the use of Tillies on this manifold?

"you can really feel the power surge" that would be nice but I won't complain if I don't get that feel....I am just looking for better overall performance....

I have Mike's A-Fordable Oil filter kit on the side cover, will it interfere?

[Purdy Swoft]

I have one of Charlies Vortex dual updraft intake manifolds but haven't tried it yet. I think that the vortex manifold is a copy of the old Cragar intake. I believe that an aluminum-pot metal carb would be best for use on an aluminum intake because of weight and heat transfer. I use to run Tillotson and Marvel carbs on original model A intake manifolds and had good service until they warped at the mounting flange. The B carb will give the best performance because of larger throat size and the high speed jet that cuts in at about 3/4 WOT. The B carb is more complicated than the Tillotson. The Vortex intake has model A size runners and that is the real reason that B carbs didn't show an increase over the model A Zenith carb in the dyno tests. Flow tests conducted bt by Richard Lorenz in the FAST news letter shows that the Tillotson model X actually outflows the model A Zenith one and two carbs but not the Model B Zenith. If the intake runners aren't at least model B size, you won't get full benefit of the larger carb size.

For better overall performance, I feel that a higher compression head should be the first consideration. Better camshaft and larger or more carburetors will add top speed but low and mid range power won't be that noticeable of an improvement.For better results, it all works together, Cam, carburetion and compression. Without higher compression, the engine won't have the power to kick up the RPMs. More carburetion will also benefit from hotter ignition and fine tuning of the distributor such as better dist. cam with more dwell and increased ,matched air gaps .

The side cover oil filter will be in the way of dual updraft carbs like I run.

[tbirdtbird]

Thanks for your expertise.

Where do you get the kind with the larger runner? I see one on the Barn that looks like the Trojan but has no ribs cast into the top surface.

The interference of the oil filter is an issue.

I am gonna get one of Charlie's Vortex jobs anyway and do some experimentation.

Wish I had a foundry! haha. I have several other special projects to sandwich in between regular shop work, but I will play with it at some point. If I make any progress I will post it.

[Purdy Swoft]

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From time to time, cast iron dual updraft manifolds will surface on eBay, Thats where I got my Trojan. I got my Uni Flow large runner dual updraft intake from Steve at Berts.