I have a 52 Ford flathead motor with two Stromberg 97s and am going to use a MSD distributor with vacuum advance. The carbs have no vacuum provisions on them,can I use the port in the Offy intake? Or else do I have any other choices? Thanks
Hello..My understanding is the vacuum needs to come from above the throttle plates..drill a hole in the base "above the throttle plates, tap it for a fitting.. Duane..
I'm not all that familiar with the MSD stuff so take what I'm saying with a grain of salt. But, "if" the MSD needs venturi vacuum then you can't use the port on the intake. Also, the second problem you "may" face is that if in fact you do need venturi vacuum.....running two carbs posses another problem for you as your venturi vacuum is now cut in half because of the dual carbs. All that being said, I have several Strombergs that have vacuum ports in them if you find you need or can use one. Just let me know. Maybe some of the guys that run the MSD ignitions will chime in for you. Or, you can call them I'm sure. Matt
This setup isn't directly comparable to anything flatheads had stock--you are going to need to experiment to see if it likes manifold or ported vac (this rig has nothing to do with the '49-53 vacuum loadamatic! This is in terms of advance a typical 1950's-60's distributor with centrifugal curve covering full throttle use and vac advance adding the needed extra advance at low throttle openings for extra power). It is almost certainly capable of better performance than any stock or common aftermarket flathead distributor available up to now because of the vac setup. History 101: The Mallory pattern distributors Ford used '32-48 had an effective centrifugal curve and a marginal vac brake retard system running manifold appended to that. '49-53 had a very poor full throttle curve running off venturi depression and an effective part throttle setup based on ported vac. Aftermarket distributors have virtually all been either centrifugal only or Mallory type vac brake rigs, wasting power and making heat at part throttle. I would first study the performance at full throttle and map the curve with a timing light with vac disconnected. When that part is known and believed to be a happy combination, then try ported and manifold vac to see which the engine prefers. Manifold vac can be tapped right from probably existing hole for wiper hose. Ported vac could be as easy as yanking one of the tiny plugs on the back of the Stromberg base and jamming a piece of br*** tubing into the hole to take the hose. Ol'Ron is experimenting with this right now, using I think '60's Chevy distributors, very similar to the MSD.
Ron currently recommends something like 4 initial plus 16 centrifugal, curve finishing before 2,000, about what a stock '48 has. To this he is now adding 6 to 7 degrees vac. Probably MSD has instructions and parts for limiting the range of the vac can and for playing with its rate experimentally. Choose manifold or ported based on their rec, then try the other way and see how car reacts.
Hello..Here is a picture of the vacuum outlet (look close) it is above the throttle plates.. Will solve the problem.. ..Matt, is this what your talking about.. Duane..
Some of the Bendix/Stromberg 97's made in Elmira during the early to mid-fifties and sold at places like Western Auto, Pep Boys and Ford dealers had the provision for the vacuum port on the base, and the corresponding plumbing built into the center-section off the right-side venturi. These carbs were made as a direct replacement for the Holleys of that era and needed the vacuum provision for the 8B-A distributors. They usually were unmarked where the 97 appears. I think these are what Matt's referring to. Never tried them in multiples but Ol'Ron seems to think it's do-able using manifold vacuum.
For a MSD or actually anything except a loadamatic, you want only either manifold or ported vac--you do not want the venturi signal tap made for use on stock '49-53 applications. On a normal distributor, that would attempt to add in advance at full throttle above the mechanical curve.
Just use one of the two plugs about 3/4-1" up on rear of the throttle body for a ported tap. Done. Manifold tap is probably already there. Venturi tap is not wanted here.
I think the other guys have the vacuum deal handled, but although a quality part, the new MSD's for flatty's seem to have too much total advance built in to them. I have either had them spun and taken some out ( 2-3 degrees ) or use an adjustable vacuum advance.Either way does make a big difference.
Flatheads normally don't need nearly as much total advance static, cetrifugal, or vac as Chevies, and I think this is basically Chevy hardware... Ron's recommendations (or service bulletin specs for '41-8) should ball park things. Remember you can see total centrifugal and vac advance closely enough for a beginning by rotating the parts and measuring (and doubling, don't forget!!) degrees around rim of distributor. Get advance + static in the ballpark and limit vac to fairly small travel, then ge***running and fine tune from there.
I'm running the MSD "ready to run" dizzy on my 8BA type with manifold vac. the dizzy came with a complete set of springs for the mechanical advance. i didn't do any thing except install it as it came. Runs great on the test stand. when I install it on the car will take it to my buddy Ernie Martin, a great flat head mechanic and everything will be set for best performance. Ted
Max, Yeah, those are the ones I was refering to. I have about 4 unmarked and about 10 with large 97's on the side. I've never used them in multiples and a stock distributor. Don't think it would work well. I keep them around for guys who want to run a stock dist. and a Stromberg. Matt
Hello...OK..Help..I'm going to running a 3x2 with 97s on my 241 Hemi..I have a 318 dizzy that is HEI with vacuum..What do I do..I thought I had the answer with my vacuum outlet base like Matt and Uncle Max discriped..OOPS..where so I get vacuum to operate my distributor.. Thanks Duane.. Getting so close to installing my 241 in my 1935..Excited, blood flowing, wake-up in the middle of the night screaming, heart pounding a mile a minute...Whatever..Been a year..
Most vacuum advance units - modern ones at least (disregarding vacuum brakes & load-a-matics) - require ported vacuum. Manifold vacuum will advance timing at idle & retard it under load - ***-backwards from what you want. Check the MSD vacuum can (or call their tech line) to determine which you've got. I'd be surprised if they used manifold vacuum for theirs. Venturi vacuum & ported vacuum are pretty close to the same thing - obviously bernoulli will vary it somewhat, but the relationship to manifold vacuum is the same - inverse. So if you measured just above the throttle plates & in the venturis, you'd get two different readings, BUT they'd work opposite manifold vacuum - low at idle, high at WOT. You might use this to "adjust" the pull on the vacuum advance unit - if you had the choice between the two. Otherwise, if you only have one or the other (ported or venturi) - use it (if required by your vacuum advance unit).
Actually, ported and manifold vacuum run close to the same except at idle and light throttle settings. I ran some tests with two well-matched vacuum gauges and found the vacuum curves were somewhat similar. Here's the info, not particularly for the flat motors, but here's how it went on an overhead. "Ported (or venturi) and manifold (or full time) vacuum taken from my mildly cammed 462" Buick engine: Ported vacuum indicated by PV. Manifold vacuum indicated by MV. Two fairly well matched vacuum gauges connected. Firing the car from dead cold and on the elec choke, MV reads 18-19" and idle is around 900-1000 rpm. Ported Vacuum (PV) read 12" on startup. Once the engine warmed up, MV reads 19" and PV reads zero at about 500-600 rpm. Cruise at 40 mph with a light throttle setting on a flat road gives you 18.5" - 19" MV and just about the same on PV. Rolling the throttle in about half way shows 8-10" of vacuum on both MV and PV during light acceleration. Once at 60 mph MV read 18 - 18.5" vacuum (keep in mind this is a very light car) and PV read 10". Flooring the throttle at 40 mph or 60 mph brought the MV down to 1" or so and PV to zero. The key thing is, at idle with a fully warm engine, MV reads 18.5 - 19" and PV reads zero. Fwiw - stock or very mild cams idle @ 17-19" vacuum, the closer to 19" means better ring seal etc. A 280 degrees advertised duration cam idles 10-12" vacuum. Idle speed in this case = 600 rpm. You can run the engine up to 1000 rpm with no load and the vacuum reading in a well sealed engine will go to 18-19". If you're running dual carbs keep in mind that air flow will be halved in each carb so you may not pull the venturi vacuum levels you did with one carb. It shouldn't be a problem at idle, but as the rpms come up the vacuum advance will not follow rpms like it did with a single carb. All of which makes me think running a distributor with both centrifugal and vacuum advance on a built - or at the least multi-carb - flathead is a good idea. Since stock flatheads run about 21 degrees advance - measured at the crank - that figure should be easy to reach with an overhead type distributor utilizing limiting devices for the centrifugal advance. Vacuum advance will be a bit of an experiment, but I'd start with 10 degrees additional - again, measured at the crank - and see how it did. Keep in mind the overhead distributors vacuum advance retards timing when manifold vacuum drops. Basics are: centrifugal advance reflects engine rpm. Vacuum advance reflects engine load."
No dispute there, C9. When you step on it though, your MV goes to nothing (watch those vacuum wipers), yet your PV should go up at least until RPM stabilizes & there's no more engine acceleration. Yours didn't always in that experiment, so I'm curious...perhaps placement of the ported vacuum matters more than I originally thought (venturi vacuum or just above throttle plates) & as I think "out loud" here, that makes sense - you won't see much difference simply because the port is above the throttle plate, it needs to sense venturi "demand"... Once the engine reaches the RPM dictated by your right foot, they should always even out...as your test sort of proves. Well, it depends. It's not a static situation either, so it's challenging for me to convey what I understand. If you're connected only to MV for your advance & increased vacuum = increased advance, then yes - as your MV drops, your advance is reduced, effectively retarding timing from it's advance position which may be advantageous. If, on the other hand, you're running PV for your advance, your inital stab on the accelerator should cause a drop in MV & an increase in PV until RPM stabilizes when they become close to the same again. SBF are a good example - they use ported vacuum on the "advance" side of the diaphragm & manifold vacuum on the "retard" side of the two-port advance units. Under load, they react roughly inversely. Here's another way I think of it. If using MV for your advance, you have full vacuum advance at idle, when you step on it, you lose this & your timing can only advance as quickly as your centrifugal advance kicks in, which means a net loss of timing initially (you dumped several degrees instantly when your MV went to zero) which doesn't make sense from an acceleration perspective. The faster you rev, the more timing you want - to a point, of course. OK, I've confused myself. I'm going to go lie down in a dark room.
Hello...WOW..OK, If I'm understanding this "PV" (venturi), vacuum above the throttle plates drops with each additional carb..I'm thinking,"OUCH".if I run vacuum lines for each carb..3x2. into one line to the distributor vacuum, I would lose no vacuum and it would increase or decrease at different RPMs..causing the distributor to advance or retard at the needed time???????????????????????????????????????????????????????? OK..Am I anywhere close to the explainations from C9 or Flat Erine I just need to figure out how to run my three 97s with a vacuum advance distributor on my 241 Baby Hemi...What if I bought a machanical distrubutor?????? Thanks Duane..
Regardless of how screwed up I may be on PV v MV or whatever anyone thinks. You can't "add" up your PV on your 3 carbs - hooking them together won't work - you'll never get a higher signal than your "strongest" signal from one of the carbs (man, that even made my head hurt). I'd go mechanical. Eliminate all this vacuum hoo-hah! Too confusing.
Hey Flat Ernie..I thought that might get you..took me awhile to think about it.. You mean 1+1+1 does mean more...LOL I think your right get a machcanical.. Thanks Duane. ps..I have a vacuum distributor now, can I change it to mahcanical or do I have to buy a new one..
I went through this same thing. I had no luck running a vacuum advance distributor on either type of vacuum with multiple carbs. 2 carbs = half the vacuum at each carb. T them back together, you still don't get the full vacuum of a single carb. I had a lenghty conversation with Jere Jobe, the guru of all things Stromberg, and he verified the above. He made the following reccomendation. I took his advice and had great results: I ran the MSD ready to run (no external box), mechanical advance and had great results. You can mess with the different springs it comes with and really get it to run great. http://www.vintagecarburetiontech.com/Frame-709477-homepagepage709477.html?refresh=1173982468736 Jere is a hell of a nice guy and able to explain things over the telephone in a way that I was able to understand. He's an honest-to-goodness retired rocket scientist and a long time drag racer who ran flatheads. Easily the best at what he does. Good luck.
Here's a piece written in the early 50's by Barney Navarro. Known at the time - and now - as someone who knew what the heck was going on with the flatmotors. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ A**** the mistakes made in hopping up engines, few exceed in number the misapplication of spark advancing principles. The chief source of error is the limited information available on the subject of spark lead. That which is distributed, unfortunately, fails to cover some essential factors and very often is no more than a comment to the effect that fuel charges take a certain amount of time to burn so spark must be advanced enough to compensate for the time lapse. Well informed engineers wish that the problem really was that simple. Most ignition system purchasers overlook every factor except the amount of spark produced. The wrong system can cause plenty of trouble: plug fouling, poor gas mileage (even though the engine has no tendency to misfire), overheating in slow traffic, and other maladies. Basically, engines require some means of advancing spark timing as rpm increases since the pistons, in effect, try to get ahead of the burning speed of fuel charges. Combustion, witch takes a definite length of time, must occur when pistons are at the top dead center before the start of the downward power stroke. If burning finishes too early, energy is wasted because the resultant pressure rise produces a force opposition to rotation. This is readily apparent when starting an engine that has too much spark lead; it will actually kick back against the starter’s efforts. Modern high compression engines, while under full load, audibly indicate spark that is too far advanced by pinging. So the popular method of setting spark timing for maximum horsepower is to set it just below the ping point under full throttle operation. Distributors that employ flyweight governor advance mechanisms use a spark advance curve that conforms to the engine’s requirements under full throttle at any point within the rpm range. At low rpm a lesser spark lead is required so the governor advances a small amount. As speed picks up it advances more and more, always conforming to the full throttle full load requirements. On a drag machine, where full throttle and full load conditions are maintained, the flyweight governor is required. But for ordinary driving, which consists mainly of partial throttle operations with Very light loads, it is not enough. Some other means of compensating for varying loads must be provided. The load compensator is necessary because a light fuel mixture burns more slowly than a heavy charge since the concentration is less and flame takes longer to travel from one fuel particle to the other. If the utmost energy is to be obtained from light charges, their burning should be completed at the same point that the heavy charges finish. So if they take longer, the only way to make them finish at the same point is to start them earlier. Consequently, partial throttle partial load operation requires more spark lead at any given speed than is required at full throttle full load. Load compensation is the most commonly achieved by using intake manifold vacuum to actuate a diaphragm. This diaphragm advances and retards the distributor breaker plate and in some cases the whole distributor case. When the engine is operated with Very light throttle pressure, the manifold vacuum is high, so the diaphragm advances the spark timing to produce the most efficient combustion possible. As the throttle is depressed, the vacuum drops of and the diaphragm produces less advance until it reaches a point of being completely ineffective at wide open throttle. Thus the ideal load compensation is always maintained and results in more power from every drop of fuel. The second most popular method of obtaining load compensation, though further from perfection is that employed in Ford V-8 distributors from 1932 trough 1948. Instead of a diaphragm, there is piston brake actuated by manifold vacuum, The flyweight governor mechanism is equipped with a breaking disk which cancels five degrees of the governor’s advance when pressure is brought to bear on its edge. At this edge a spring-loaded piston is located in a small cylinder. The spring is on the side of the piston opposite the disc so it causes the piston to be pushed against the disc. Vacuum is introduced on the spring side to oppose its action and lift the piston off the disc. In action, the high vacuum produced by operation with small throttle openings lifts the piston of the disk, allows the full action of governor weights to take effect and gives the Ford engine five degrees more spark advance. By depressing the throttle further, the manifold vacuum drops off and the spring again pushes the piston against the disc to retard the spark. The flaw in the operation of this mechanism lies in the fact that it is either "full on or full off" and permits no gradual compensation like the diaphragm. Ford’s latest method of controlling spark advance employees an ingenious system utilizing manifold vacuum and venturi vacuum. With this system the flyweight governor is eliminated and in its place is nothing but a diaphragm. This diaphragm not only advances the spark to conform to rpm changes but is also makes load compensation adjustments. All ́49 through́54 Ford and Mercury carburetors have in addition to the conventional manifold vacuum takeoff, such as is found in the throttle body of most p***enger car carburetors, a connecting venturi vacuum p***age. The manifold vacuum, as usual, is obtained from a small port in the throttle body located slightly above the ****erfly’s closed, position, on the side where the ****erfly swings upward to open. When the throttle is closed at idling, the vacuum port does not receive vacuum because it is on the opposite side of the ****erfly. As the throttle is opened slightly, this port is uncovered and a vacuum is applied to the distributor diaphragm to advance the spark. If the throttle is fully depressed, the manifold vacuum is destroyed and no advance takes place. As speed increases, however, the venturi vacuum increases gradually and advances the spark to conform to the rpm. Letting up on the throttle increases the manifold vacuum (Provided it isn’t let up all the way) and the spark receives load compensation. A balance is always maintained so that the correct amount of spark advance is supplied for all speed and load conditions. The greatest installation errors center around the misunderstanding of the late Ford distributors. A distressingly large number of mechanics are unaware of the difference between manifold vacuum and venturi vacuum. In fact many attempt to operate Ford and Mercury distributors by connecting the vacuum line to the windshield wiper connection on dual intake manifolds. This sometimes results from a desire to use the old Stromberg carburetors, which are not equipped with vacuum takeoff. So the simple solution seems to connecting the distributor vacuum line to the handiest apparent source of vacuum. Such practice is worse than having no spark control at all for when the engines idles the spark advances fully and retards as throttle is depressed. There is no venturi vacuum available to advance the spark as the speed picks up and it remains retarded until the throttle is let up. So if the old style carburetors are preferred, the stock Ford distributors must be discarded on the late models. However, Stromberg has resumed production of the old "97" and is now fitting it with a venturi vacuum takeoff to make its use feasible. Four throat carburetion installations also have had their share of improper distributors. Early articles in certain publications gave the impression that no vacuum control whatsoever could be tolerated. It wasn’t pointed out that the only forbidden type is that of the stock `49 through `54 Ford and Mercury distributor. This caused many to purchase distributors and magnetos that were equipped with flyweight governors only. Such installations get very poor gas mileage, so the car owners blame the four-throat carburetor. Even more irritating, is the tendency for spark plugs to foul. Having no load compensation, the spark is never far enough advanced under partial throttle to fire the fuel mixture chargesat the most opportune time. In effect, the engine is being operated with a lower effective compression ratio because burning is completed as the pistons travel down the cylinder bores. And since the plugs never receive a hot flame, soot collects on them. Furthermore, the condition cannot be remedied by using hotter plugs because they will burn up under full throttle operation of flyweight governor distributor with vacuum-operated load compensation device. In practice, the installation of dual intake manifold on Fords and Mercury’s of the ’49 trough ’54 series should be accompanied by a change in distributors such as prescribed in the preceding paragraph. The addition of two carburetors divides the airflow so only half as much airflows through one carburetor as previously at normal operating speeds. Venturi vacuum is dependent upon the air velocity through the venturi so any reduction in velocity will result in less spark advance. And connecting a line to each venturi vacuum takeoff of a dual set up will not increase the vacuum---such a practice is just a waste of copper tubing. The best advice to keep in mind when purchasing a distributor is not to pinch pennies. An inexpensive unit, if it doesn’t do the job correctly, can prove to be the most costly. The bestway to avoid mistakes is to study the problems involved and learn enough about them so that you can select a distributor that matches your engine requirements.
I think there is some muddling going on here between ported vac and venturi signal vac!! PV and VV... PV is just the suction of engine against carb the isn't all the way open but is open enough to expose that port...it will be hich at low load, like MV, and will drop dead at full throttle likeMV. VV is the pull that lifts gas from the bowl through the mainn jets into the discharges up in the venturi--it is created by the venturi effect and exists only when there is fairly high flow through venturis, enough to put carb into main jets. Zero at idle and low RPM, weak but increasing force as speed goes up, highest at full throttle... It is irrelevant to distributors except for the wretched '49-mid fifties Ford stocker. The weakness of the VV made this thing's full throttle advance very weak, sometimes inop...somewhere between bad and unacceptable for a rod, poor choice on a stocker. VV is only availble to tap on the few Strombergs and many Holleys made to use with that distrib. The VV port MUST be blocked if that tap is going to be used to supply PV to a normal distrib! The port is over 2 holes--the one going down goes to PV, the other goes to the venturi and has only negative effects on any distrib other than the Holley Loadamatic!
This is what I have been saying. Perhaps not as clearly (I tend to ramble on, use a lot of words, but fail to actually communicate). As you can tell from the article, (rather than me requoting huge chunks other than the one paragraph I felt validated what I said) which vacuum source you use depends on which it was designed for. In his first example, Navarro describes a system meant to be used with MV. His second example, describes the early Ford vacuum brake using MV & he explains their deficiencies. The third example is the one I cited above & is how the majority of vacuum advance units function now (well, pre-computers anyway). Did I mention I really like the SBF setup with two vacuum ports on the advance unit?
I don't want to muddy the waters too much with OHV vacuum distributor stuff, but I wonder how it would work out for a flatmotor if we adapted a typical GM type distributor to it? Granted, the mechanical advance curve would be less and initial timing would be less not to mention the vacuum advance would be limited, but if it was a reasonably easy adaptation perhaps that would end a lot of the confusion. Then again, maybe not. Although I've read where running manifold vacuum on an early Hemi distributor resulted in the engine running quite cool at idle and in traffic. Enough so that the owner went back to the original timing setup. I think Bruce has nailed the PV and VV thing pretty well. And that's where the comment that I see and hear from time to time which states that timing keeps increasing - on SBC's and the like - as airflow through the carb increases. My guess is that there are more Old Wives Tales about engine timing out there than on any other subject. Probably due to the many different ways of doing it and methods from other era's being carried forward and attempting to apply them to fairly modern timing systems that work differently.
The Chevy distributor, either the '57-~~~1975 small or the huge HEI have advance mechanisms, both cetrifugal and vac, that are easy to alter and have plenty of aftermarket bits to help. The Chevy distributor is also apparently quite easy to alter dimensionally to fit a '49-53 front cover drive. I think the MSD distributors are pretty much design clones of the early Chevy, with the high advance mech and such, just converted to electronic trigger. The Chevy needs the rapid curve springs from the common aftermarket kits and a few degrees trimmed off of the curve, accomplished in slightly diffeent ways in the two generations. Ron's numbers above are the only data I have seen on real vac advance for a flathead; a non-EGR can with its slot blocked some would do...adjustable stops and cans with tuneable spring pressure are available from Crane and likely others. Flatheads need limited static, then rapid advance to a smaller than Chevy number starting right off idle. Ron's numbers are numbers from '41-48 Ford distrib would be the starting point. As I said above, some aspects of cent and vac advance can be checked on the distrib as you work on it. Rate would have to be checked on the running engine or a distrib machine.
I dunno - seen the oil threads lately? Religion & politics. But I suspect you're right - I cut my teeth on SBF stuff, so that's what I tend to fall back on & it may not always translate well...or even be applicable at all.
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