So I got this readytorun Distro for the flathead yesterday and It looks pretty slick. Came with a 12v coil and since I'm going to convert to 12V... actually the great "Unionvillehaunt" will be doing that for me . The stock distro which has vacum advance now...will be replaced by this thing. so do I keep the vacum advance or do I not use it.. If I do use it what springs should I use? at what RPM should max advance be set at? Anyone running this on their flathead? What setup are you using? Thanks in advance!!
Max advance should arrive pretty early, WELL below 2,ooo, and it should start adancing right off idle. Vac advance will need tinkering (Ron H has some numbers) but is a BIG advantage in power. Engine running on centrifugal is very inefficient at low throttle openings, requiring much more throttle than it should need to get sufficient steam. Essentially, with no vac advance you are running retarded, using gas to heat the exhaust rather than push the piston, at all times you are not at full throttle. In the real world, it is only possible to use full throttle for a few seconds at a time, and part throttle is 90% of everything. Better power, better response, and even improved fuel economy will come from proper vac supplement to the curve. AND...think about the special implications of extra exhaust heat in a flathead!
The advance on those MSD's are already setup to run close on a stock flathead . I would use the installed springs first and try it out. If there are problems afer that you can check for the proper advance at each rpm setting by marking your pulley's circumference into degrees. Bruce Lancaster had a post regarding this setup. Do a search.
I have one of the units on my slightly modified engine, 4 barrel, 400 heads, Potvin Super 3/4 cam, .030 pistons, stock crank. I am using the smallest silver springs and the black stop. I currently have my initial timing set at around 5-6 degrees advance, and the MSD combo will give you another 18 to 20 degrees advance all in by around 1900 -2000 rpm. also, I am running the vacuum advance on mine. A rough, and I do mean rough mpg estimate is around 17+, that's with 3.55 gears and an .86 overdrive, and some heavy right foot driving included. One other thing, my engine actually is running cooler since I have done the performance mods.
That's what I'm pushing here...no vac means retarded timing most of the time, and retarded timing in a flathead is dumping the wasted combustion heat right through the water jackets... By the way, study the Loadamatic specs in your manual for tips on the part throttle advance. That horrible distributor was excellent at part throttle, useless at full, the exact opposite of most hotrod distributors! I've heard that '49-53 Fords with stock distributor could frequently post better quarter mile times at 3/4 throttle, because the advance dropped dead at full throttle/venturi signal vac time...
I have one of these on my 8BA (which is now apart and at the machine shop). I took the vac advance off and just ran the mechanical advance. I was running two Holley 94's with no power valves (tried 3.5's but had a lot of trouble with leaks/sticking open and, when they weren't stuck no apparent difference in performance, so I took 'em out), A fenton manifold. mild cam, .060 over. It was a pretty sick engine with two bad cylinders, high miles, etc, yet still ran pretty well. I didn't seem to notice any lack of power from low end to top end, but then again, given the general condition of the engine, there may not have been enough power available to begin with(!). Here is my question . Since it appears that running both vac and mech advance sems to be important. where do I get the vacuum from??? The Fenton has a port just below the rear carb base. Is this the best place, or does the vacuum have to come from above the carb base?? Thanks, Rich
The port on post-1948 94 types will need to have the venturi branch plugged before use as a ported vac source...otherwise it will add a bit of timing on top of the centrifugal curve at full throttle. Look into the openigng, plug the hole that goes straight into venturi. I've never had a distributor with proper vac advance on a flathead, but have been reading Ron's tests. I've only run the '42-48 vac brake type, along with a stint with the wretched Loadamatic. I suspect ported (above throttle plates) hookup will work best (easy to experiment to be sure) because flatheads generally like only about stock static timing, circa 4 degrees, I think due to very high level of cylinder filling at idle. They do like the curve to start right off idle.
Vacuum and mechanical are used as a balance between all happy mediums. A working vacuum unit can give a super increase in fuel econmy maybe even 2-3 mpg. The object is for mechanical ( controlled by rpm) and vacuum (controlled by engine load) to over lap and aid each other. When rpm is high there is no vacuum ( or very low) and mechanical advance works the engine, when rpm is low engine vacuum is high and vacuum works the engine curve. Adjusted properly they will keep the engine ( especially during light throttle cruise) at the very best timing advance you could ever have. With all this said and done , add the word "BIG CAMSHAFT" and all bets are off as every thing moves either up or down the scale of adjustment.
I hate throwing the word wrong out there, so I'll say is isn't exactly correct. Like Bruce has said and I've heard it from several other people, that Flatheads like their advance to start right off of idle, and to ramp quickly up to max advance, about 20 degrees, by 2000 rpm. Actual numbers may vary... The "out of the box" set up on the MSD unit has a curve that is almost flat up to 1500 rpm only giving 5 degrees of advance, then is increases a little faster up to 18 degrees at 3800 rpm. Those numbers are from the set up papers that come with the unit, they are shipped with the heaviest springs and the blue advance stop installed. So, from what Bruce is saying and what I've heard from others, the "Ready to Run" slogan is a little misleading.
Bubba, I have two of your Chevy units on flatheads. How much advance do I uses or do I set it up right on the mark? Thanks Pete
That curve sounds way slow. Ford's best curve ('41-48) had full advance in by 1200, and I've never heard of anyone recommending anything later than about 1800-2000. In by 3800 sounds like one of those utterly useless '70's GM curves... They don't like much initial (this is an engine that can produce nearly full torque right off idle) but should start cranking up by 5 or 6 hundred RPM. Here's a scribbled version of crab centrifugal curve I found on a card here...this is distributor numbers, so DOUBLE them for conversational purposes: 200R...0--1 degrees 400...61/2--8 600...101/2--12 4 degrees CRANK would be standard Ron H currently is experimenting around 4 degrees static plus 16 (a bit slower rate than Ford) centrifugal, 6--7 vac. Vac rate would be a separate flog...
Back to the top for pete otherwise his nickname will be a farce. I do know Jim welds the advance on his units only to allowing a maximum of 20 degrees. His units are the mechanical advance. Bubba, have you tested the units curve to see if they are reaching 18-20 degrees before 2000 rpm? It would be great to see a chart on your units.
Hamb Board distributor post… <?xml:namespace prefix = o ns = "urn:schemas-microsoft-comfficeffice" /><o></o> You had to get me involved didn’t ya?? I have been reading the post but thought Bruce had it under control. Ok some basic ignition stuff. A gasoline engine almost never needs more spark advance than the factory dialed into the engine. May need to come in sooner or later but very seldom does it need more. Looking at the flathead engines built over the years theFord factory never used over 12 degrees ( distributor ) or 24 degrees engine. A average spec is 12 degrees at 1725 rpm distributor or 24 degrees engine at a actual rpm of 3450. So we can safely assume that the maximum needed for just about any engine regardless of design or modification level! Using the actual Ford service bulletin dated April 15th , 1938 they show a range from the low of 950 rpm=8.5 degrees or 1900rpm=17 degrees engine, to a high (model 40A) of 1500 rpm with 12.5degrees or 3000 rpm at 25 degrees. Our own work on our Salt flats engine on the dyno proved that a slight variation from this setting lost horsepower in every case. So lets use this number as a pretty given baseline. Now if you feel due to mods on the engine you need more or less , adjust the initial static timing level either upward or downward to suit your needs. Example : A initial balancer setting of 4 degrees btdc would give a 24 degree distributor a 28 degrees total advance! Now lets look at the rpm level for total advance. I believe that the changes most make on their engines and gear ratios etc make the 3450 rpm level a bit off where we are going to use the engine. So lets adjust the max level to become 2000 to 2500 for a max reading and also make it curve to that position. I believe that the distributor advance should add advance with each rpm change. Our our chevrolet distributor conversions I take all this into account and tailor each unit to fit the flathead factory specs. ALL Chevrolet V8 engines came from the factory with a 12 degree mechanical advance maximum installed as well ( or 24 engine) and the curve or advance rate was tailored to actual engine, camshaft and gear ratio, transmission etc. This feature is a slot in the advance cam unit and a rubber bushing installed to limit the total advance. Also they used a 7-10 degree vacuum unit to overlap the rise and fall of the mechanical advance as well. Now if we know that the smallblock Chevrolet likes 34-36 degrees of total spark advance you would need to advance the initial static timing at lets say 10 degrees and then add the 24 mechanical at wide open throttle the engine would then have 34 degrees of timing. ( Vacuum don’t apply here as wot usually equals low vacuum) A reduction in throttle opening would cause a drop in rpm ( causing a drop in mechanical advance) and a increase in vacuum ( increase in vacuum advance) maintaining the proper advance level for the engine to perform well driving down the highway. So for the sake of discussion lets all agree that the factory do a really good job of building a engine that’s performs under all driving conditions ( and they do) that’s how it works. Ok ?? <o></o> So lets add in the aftermarket wizards that make aftermarket units and performance parts in general. As many people ( and many do ) live in what I call a Chevrolet world then the most products out there are Chevrolet. So lets assume that many of the aftermarket distributors may share some ideas from the parts that were in fact made up for the Chevrolet with a setting of 36 degrees max advance curve. I presently have two aftermarket ( two different brands) on the distributor bench. Both are brand new expensive aftermarket complete distributors. After running both they both have two very different issues to content with. The one has too much advance ( 38 degree total) and the other has too little advance ( 5 degrees). Both were bought for the flathead engine application. I can only guess that someone ( in a Chevrolet world) felt that 38 degrees would work in a flathead engine. The other ( low advance ) beats me as to why other than I guess it didn’t get the correct adjustment from the factory. The big deal is both are very easily adjusted on a distributor machine and could be done even on the car with a good advance timing lamp, however to expect the regular dude to pull this off in a driveway is not being very realistic!! Hopefully at this point you are beginning to understand the issues with these and even older distributors. The story is a little different with each factory automobile but pretty much the same story , you just need to do things different. Now for our conversion distributors. Using the above thoughts I seen some time ago on the HAMB board where some had made up some machined Chevrolet housings and fitted them to the flathead engine. Using what we knew about the Chevrolets and owning a couple modified flatheads we disassembled a basket full of Chev distributors, machined the shafts and housings and modified the advance bushing area to max out at 12 degrees ( 24 engine). For this I had a brass bushing machined to take the place of the rubber bumper on the cam assembly. I elected not to use the vacuum advance as I feel as most are modified with multiple carbs and modified camshafts making the vacuum unit very un-useable. The advance weights are then tailored by changing sprint tension to provide a linear curve from idle to 2500 rpm. This seems to make a perfect set up for the flathead. <o></o> Always glad to help……
The tale of the two curves...all in way below 2,000 or at 3,000...is tha tale of the Mallory patent vacuum brake. The WOT (wide open throttle) curve listed in the good book I believe assumes tight adjustment of the brake dragging down advance rate. The quick curve is the high vacuum curve, or part throttle, and allows full advance to come in a normal driving range. Modern gas is so far ahead of 1941, most have the brake adjustment near full loose, allowing the quick curve into play at full throttle. Crab/59A curve ends at 3450 by the book at WOT, 1200 with brake released...quite a spread. Tuning practice was to back off brake adjustment til the edge of pinging, allowing the engine as exuberent a curve as it could handle. The load adjustment effectively slowed the curve rather than truly shortening it...and it can be speeded up all the way with many engines on modern gas. Minor brake drag is needed to stabilize the movable plate in advance assembly. The Ford (and early Mallory) distributors used a long centrifugal curve restrained by a brake at full throttle, rather than the later practice of a short curve supplemented by a vac advance. Flatheads still really need a modern vac advance...
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