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You wouldn’t want to set it up for a Pontiac, you would want to get it as close as possible to the original Pierce specs since that is what you are running it in.
The ’29 Pierce is a manual advance setup so I doubt there are any weights in the distributor.
HI Eric, Karl’s verbiage would lead you to believe there is no centrifugal advance in the ‘correct’ distributor. The Pierce distributors had advance fly-weights and springs etc. But Pierce was extremely conservative with spark advance. Mostly I believe because of the terrible gasoline back then.
The ‘correct’ distributor for a ’29 is about an inch or more larger in diameter, and I’d be surprised if the fly-weights could be interchanged.
A lot more performance can be had from the Pierce engines if the spark curve is steeper and max advance is earlier in the rpm range. As Karl stated, max advance is at 2600 rpm, but I think that must be for the Pontiac engine, my Motor’s Manual shows 18* max crankshaft advance at 3100 rpm. 3100 rpm !!
So, if your current distributor has the advance that Karl described, that has 27* advance that is full in at 2600 rpm, I think that is a good curve. You might be able to bring that max advance down to maybe 2200 rpm with slightly weaker fly-weight springs.
Does your engine have a UU-2 or a UUR-2 carburetor? With either one, a one-step larger main jet will also help the performance of the engine. With our ethanol-tainted gasoline, and a low 5:1 compression ratio, the ethanol does not contribute any power to the combustion pressures in the cylinders. 10% ethanol fuel in our low compression engines is like 90% fuel, and 10% inert ‘filler’. Ethanol needs a 14:1 or higher compression ratio to burn well.
When you put your distributor on you sun machine, please post the results.
Greg Long
Just a note…….changing the curve and adding timing can make much more power……IF the engine can take it. I would not recommend it on an old engine or back yard rebuild……….rod failure can occour when hammering on it with lots of timing…….on a new engine with inserts….go for it……….just be careful no to run too lean and melt a piston or burn a valve. Pumping up the engines is a fun pastime…….just keep your eyes open to the possible downsides. Ed
I did take it out Wednesday for a drive got it up to 45! still need to tune it in as i just set it to where it started and ran so i could have new exhaust put on it
I would modify some of these statements a bit. The issue with advanced spark is pretty much dominated by preventing spark knock (detonation, ping, etc). That is a function of octane number. When the Dept of Agriculture began doing nationwide surveys of automobile gasoline characteristics in 1936 the average octane number for summer gasoline was about 80 (approximating what the average would have been between the “motor method” and “research method” as posted on the pumps these days). Current regular is typically 87 octane which means it is significantly more knock resistant than the gasolines used in 1936, and spark timing can be advanced significantly over the entire range compared to factory spec. I generally advance spark about 5 degrees over factory. This will provide slightly more power and better fuel economy, more importantly perhaps it will reduce exhaust gas temperature and reduce the tendency for exhaust valve seat recession. It also reduces the tendency to overheat somewhat.
The somewhat increased pressure in the cylinder should not be any problem for the bearings except possibly if the engine is being lugged at wide open throttle at idle rpm, since at higher speeds the centrifugal force of the piston relieves the downward force of combustion.
You don’t want to advance the timing to the point where you ever hear any knock/ping/detonation, as this is the primary factor in cracking valve seats in side valve-in-block engines.
Ethanol in the fuel is not inert, regardless of compression ratio it will burn and create pressure. For our engines typically running rich – more fuel than air for complete combustion – it will probably increase maximum power slightly not reduce it. This is because it carries an extra oxygen molecule with it. The ideal air fuel ratio for pure ethanol is 9/1 compared to 15/1 for gasoline. Our pre-war engine carburetors are generally quite rich delivering well below 15/1. In addition ethanol cools the mixture more when it atomizes in the carburetor increasing the density of air going into the cylinder. The EPA forced many communities to add ethanol in the winter to improve combustion and reduce carbon monoxide emissions of cold engines running too rich. Paradoxically ethanol has less energy content per pound than gasoline, so fuel economy is a bit less. Ethanol creates other problems of course. Basically with ethanol blends you are pouring more fuel in which can deliver a bit more power at wide open throttle but increases fuel consumption.
Jim
James is 100 percent correct with his fuel analysis. The timing of plus five is fine and safe. You can go twenty more and often not cause knocking……but you will increase the combustion chamber pressure off the top of the chart, overloading the bearings. Using fuel to cool the air charge temp along with the extra oxygen works to an extent, developing more power for significant fuel mileage loss……….having tried it to the extreme, it’s possible to get as little as four miles per gallon doing it. I have experimented with all of this…..timing and fuel back in the late 90’s on my chassis dyno at my business. You can cause damage and issues if your not very familiar with what your doing. We used a five gas analyzer in the exhaust to prevent problems, and tune to maximum performance. The ultimate target area is a small sweet spot of trade offs, and not easily achieved. Most cars have incorrect carburetors and exhaust systems that drastically alter the results. For 99 percent of club members, I recommend stock settings and equipment across the board……..mistakes can cause cracked blocks, melted pistons, burned valve, and pounded out Babbitt bearings. What take the risk? Moderation is best if you can’t build your own engines……experimentation can become very costly without the right tools and equipment. Best, Ed.
I forgot to mention cracked heads and blowen head gaskets……….been there, done that with the testing regiment!
Well, Alcohol will not burn completely with a low compression ratio, to me in our engines that means it’s at least partially inert. Try running on 20-30% ethanol !! If you can get the engine to start, it will run absolutely awful.
Burning ethanol-tainted fuel creates a hotter exhaust because the alcohol has not finished burning. That is one reason that fuel mileage suffers: incomplete combustion due to low compression. Adding ethanol was a way of raising octane; because alcohol is a high octane [read: slow burning] fuel. And with inadequate spark advance, the burning is delayed, and more heat and energy go out the exhaust.
Add in the low energy concentration in ethanol, and there is a measurable loss of fuel mileage. And that is in modern cars, with 8:1 and higher compression ratios. The modern computerized spark allows a much more advanced spark that is infinitely varied by throttle opening, spark knock sensors, and Oxygen sensor input to the engine computer.
Greg.
Fuel discussions can be almost endless. Molecular carbon chain analysis and stoichiometry along with heat content issues, fuel density, blending stocks……it’s enough to give you a headache. Blending stocks have changed over the years, giving way to about five basic type pump gas fuels sold to the public since the 20’s. Very long story short, regular E10 pump gas on paper should be fine for any engine………..according to the science, only problem is, it is not. From post war there are very few major problems, pre war is an entirely different story. Another long story made short……tune for performance, idle, equipment longevity. Running rich is safe, lean is a gamble. As Chris D and my father would say……Happy Motoring,