Okay, okay, I know the topic of flathead multi-carb setups (Holley 94 ONLY, not those other things :>)) has literally been beat to death, BUT, most of what I have read is on flathead V8s, with understandably, very little discussion on the HV-12. Sorry, I'm not good with brevity, so here goes. I'm in the old fart category having just turned 65. I purchased my "Retirement Hot Rod" a few years ago, a 1939 Lincoln Zephyr, with a badly knocking, but running engine (HV-12). The oil pump pickup was clogged solid with paper shop towels, so I don't know if it was an error or sabotage, but none the less it ruined the engine. Slowly, but surely, I've been able to find the parts I need to have a viable engine machined. Finding a qualified machine shop has been a rather difficult task. In fact, I thought I found a good machine shop, but that's a whole different story. After being jerked around for just short of 2 years by a famous race engine shop in Charlotte (The Dortons), I collected my parts and brought them elsewhere. Now my engine is in the hands of a very capable machinist, and I believe I've turned that corner. I can't wait to get it back so I can start building it. (BTW, I would have loved to send it to Mike at H&H out in California, but I'm just not comfortable with not being able to visit the shop personally, and I'm not comfortable shipping my engine clear across the country (I'm in central Florida.). I visited a local machine shop after collecting my engine from the Dortons, and while it seemed like they may have had the capability, the place was a disaster, and I just could not see how they could do quality work in such a pig pen. Next! Anyway, with regard to carbs, I'm going with 2 Holley 94s on an original Edelbrock intake (see Pic). (Those air cleaners will definitely be changed to something less restrictive. The second pic is my choice.) Personally, I have no problem building the fuel toilets (carburetors) myself, as I've been doing that since I was a kid. My Mom would get pissed as I would rebuild them (after cleaning of course) on the kitchen table, but she said, "I'd rather you do that than go out raising hell and drinkin'". LOL! I went to diesel and heavy equipment school up in Northern Michigan (Ferris), and wound up becoming a Ford Factory Field Service Engineer, one of the best jobs I've ever had. I found my niche as an automotive instructor, which I've been doing now for over 30 years. So why would an accomplished automotive instructor be asking for technical advice? Well, I don't care how good anyone is, there's always room for improvement, and something to be learned, and flatheads were long gone when I got into the business in the late 70s. Honestly, this HV-12 is my first foray into the Flathead world, and there are lots of folks out there that have way more experience with them than I do. Albeit, they are sadly dying off, and it's getting very hard to find guys who REALLY know them, but I know you are out there. There are a lot of pretenders out there, just like there are a lot of shops I wouldn't take a moped to for repair, but again that's a whole different discussion. When I studied the L-head design of the Flathead it brought back memories of the Briggs & Stratton lawnmower engines I cut my teeth on as a kid. This is just 12 of them sandwiched together with liquid cooling! So, here's the rub: Is the best way to set up 2 Holley 94s for my HV-12 as a Primary carb in the rear with the secondary carb up front on a PROGRESSIVE linkage, or to keep both carbs operationally close to the same, and run them on a DIRECT ACTING linkage, where they both open and close together? I've heard VERY good arguments for both setups, from very experienced and trusted Flathead guys as follows, but before discussing that more detail is in order. Here are the setups I've been told to use: A progressive setup uses a rear primary carb basically untouched other than having an extended throttle shaft added and tuned properly for main jets, the power valve and accel pump linkage. The secondary carb up front has the idle circuits eliminated, the choke plate eliminated and the shaft holes plugged, it also has an extended throttle shaft added for the linkage, has a power valve plug installed, and has the throttle plates custom fitted so no air leakage occurs at closed throttle. The progressive linkage gets adjusted so the front carb comes in at about 65% throttle of the main, primary carb, and the linkage is adjusted so both hit the WOT stops at the same time. A direct setup has both carbs opening together, and both have idle circuits, and power valves. If it runs too rich, then remove and plug the power valve in the rear carb, of course tuning properly in the process with a Unisyn. With that said, here are the arguments I've heard for both setups: Progressive: Runs with better driveability and low-end torque as air flow velocity is higher with just one carb, and then when the single carb starts running out of steam, the secondary kicks in to provide the additional air and fuel flow for top end. Another added advantage is better fuel economy, and while I'm not real worried about that on this vehicle, it is an added benefit. A bigger concern is ring washdown from too rich a system. The direct setup: Both carbs flow evenly, and because both carbs have fully operational idle circuits, they both evenly contribute, with no airflow restriction before the front carb kicks in, so to speak. The advantage here is that the fuel in the front carb doesn't go stale from sitting. (I have a heavy foot, so I don't think that would be an issue anyway, but...) Of course, if the direct setup is tuned properly, it should eliminate any fuel washdown issues from being too rich, thereby shortening ring life, but the possibility for that issue is there. So, now with all that said, let the games begin. Again, I have two highly respected folks, both on opposite sides of the fence, each telling me one is significantly better than the other. For my use (It's not a race car), I'm leaning toward the progressive setup, unless the overwhelming consensus is that experience dictates otherwise. Take the poll and add comments as you desire. Hopefully this will help many folks in the Flathead brotherhood and finally put the issue to rest. Either way, I'll be reporting on my findings once I get the engine built. I'm planning of futzing with both setups to prove it out one way or the other. Thanks, and let's have some fun. Appreciatively yours, GT
No experience of v12s. But on other stuff my thoughts are always two carbs direct, three carbs progressive. When you look at what manufacturers did on later engines that’s how they set them up. I always think that using only one carb for cruise on a twin setup gives you a significantly different intake length front to back. Not sure whether there’s any science to back that up though. Your problem comes with a direct setup when the carbs are too big and the airflow is stalling at lower rpm so the fuel metering is all over the place.
Have not personally set up a 12 cylinder Lincoln with dual carbs. I have set up dozens (maybe hundreds) of dual carb set-ups on 8 cylinder engines in the last 60 years. With the exception of restoring factory units that original came with too large carburetors and progressive linkage; EVERY set up has been with direct linkage. With direct linkage (and properly sized carbs) : better idle, better driveability at ALL RPM's, measurably better fuel economy, and at least as much, generally more HP at WOT. The key is to size the carbs correctly. EDIT: after re-reading your initial post, those "other things" work better in a multiple carb set up. Jon
I would go with direct linkage. I think the displacement of the V12 is something like 267 or something, a little larger than the 239 Ford V8 and I think the "standard" way to set up the V8 with two carbs would be with direct linkage, with progressive if your running three carbs. So my thinking is, if direct linkage is the way to go with a 239 motor, I think it would be best for the larger 267 motor. Also look at your manifold, if you run progressive linkage the mixture will have a long way to travel to the far end, at least further than the closer end of the manifold, It just looks like it would provide more even fuel/ air it both carbs opened together.
I've enjoyed my flathead V8s for many years using direct linkage on a stock 239" with 2 94s, and a built 286" with 3 97s, resulting in very good performance, driveability, reliability and decent mileage. The biggest issue with straight/direct linkage is making sure the carbs are set up and built the same, taking time to carefully tune air/fuel, and then synchronize throttles.
I have dual 94's on my 8BA flathead and ran direct linkage to start with, I later changed to progressive and think it starts and runs better with the progressive linkage. Mild build, bored .060. 3/4 H&H cam and Offenhauser intake and heads; my linkage is set where the secondary carb opens about 60% throttle and still tends to run a little rich. The Early Ford club has a formula to figure CFM, cubic inches x max rpm divided by 3456= cfm; on your engine I used 267 x 3500 = 934,500 divided by 3456= 270.4 cfm. Holley 94's range from about 150-165 cfm according to Early Ford so that puts you around 300 - 330 cfm so about right on cfm, direct linkage is definitely easier to set up so probably won't be a problem.
My HV-12 is 292 CID + 0.20 OS so IIRC it brings the total displacement to about 296 CID. At that, EA PRO calculates the actual CFM at just under 5Krpm to 323, so two 94s with 1" Venturis is ideal. I've run many different scenarios on Engine ****yzer Pro (EA Pro) and the best all around has come down to the pair of 94s using a Schneider 248F mechanical cam. The peak torque hits at 241 lb/ft @ 2615 rpm, and 175 hp @ 4280 rpm. I'm keeping redline at 4800, as any more than that risks catastrophic damage, so this combination is perfect as the torque curve is great, especially down low, and it remains good all the way through up to the power band. What I'm going to do is run the same setup again, but with just one carb to see how much it improves the low end, as a way of gauging the progressive setup, as we already know what it looks like with both carbs. That hopefully will give me the answer I'm looking for.
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