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I would rather not use the original carburetor, but find a suitable replacement from 70s-80s. Replacement carb should be from a 4 cylinder or 6 cylinder 2.4 - 3L engine. These newer carbs are much advanced compared to those primitive Carters. They do better fuel metering at different engine regimes, and provide better acceleration, better fuel economy, and more engine power. Of course adapters and throttle linkage must be fabricated, but it really worth the trouble.

Old style rope seal is the way to go, and they are often sold on eBay.

Out of curiosity, I would take them apart and look at the membranes. If these are original pumps from 50s, all chances are that rubber membranes deteriorated - too stretched out or torn. A new membrane can be cut out of proper material. Now they make stuff compatible with ethanol. Old membranes were not designed for ethanol.

I would stay away from new repro motor mounts. They are known to delaminate, and you understand the consequences of engine jumping off the front mount. Chrysler invented the process of bonding rubber to steel, which enabled the whole "Floating Power" thing. Quality and reliability of motor mount critically depends on using this process.

Low voltage from generator at low rpm is normal, it is one of disadvantages of generator vs. alternator.

Back to capacitor, I would not use any NOS auto parts capacitor because most of them were paper capacitors, and they go bad with age. Use any modern mylar or polypropylene capacitor, 0.15 uF rated at least 400 V. Proper connectors can be soldered on if necessary.

In fact, it is not so complicated. Put in radiator and water pump with huge overcapacity, and thermostat will take care of all regimes and conditions at which engine may work. Mopar added special cooling arrangement for exhaust ports, a nice feature.

12V makes sense. 12V alternator weights less, yields higher electric power, and, unlike generator, works efficiently at low rpm. It is more reliable and worry-free than generator+external voltage regulator. 12V allows transistorized ignition and electric radiator fan, among other things. Vibrator power supply in antique radio is such a bad thing that it should be replaced with a .modern DC-DC converter. Anyway, one cannot have a functional antique radio without at least some expertise in electronics.

Wow - you invented Aamco Brake Gauge! Aamco Brake Gauge

I remember seeing this chart in some performance manual. It is interesting that for different versions of Mopar flat six, safe shaving limits vary rather widely, from 0.020 to 0.090. One of the considerations could be minimal metal thickness for structural integrity, but then different allowable thicknesses for different engines do not make sense. I believe the real issue is valve clearance. It is especially important if a hot cam is used in an engine with shaved head.

Cast iron head has one clear advantage: its thermal expansion is same as block's, so there is no thermal movement during engine's heating and cooling cycles. Not so with aluminum head, which expands at roughly two times the rate of cast iron. This relative movement of head and block requires special gasket that would allow lateral movement without compromising the seal. Aluminum head is more demanding for surfaces finish. With aluminum head, even a single episode of mild overheating may cause gasket failure. Cast iron head is more forgiving in these respects. Theoretically, a cast iron head may be good for CR as high as 8.5, but practically there is a limit to how much shaving can be done without compromising structural integrity. For CR of 8.5, head must be shaved 0.120", which is hardly possible. Edgy head is one-size-fits-all, as it can be used on 201, 218, and 230 engines. Combustion chambers are 70-80 cc. For a 230 engine the calculated CR is 9.3, and for a 201 engine it is 8.3.

Yes, this is what Earl told me. He said that plugs are same as those for the stock cast iron head. One should be careful though and use torque wrench and anti-seize lubricant to avoid damage to delicate short threads.

I have sent my check to Earl on December 19. The head was ready for pick-up on January 30. If not holidays, I believe production time would be about a month. I am not sure if Earl orders castings in batches. In reply to my first e-mail, he wrote that $400 deposit was needed to pay the foundry. While visiting, I saw several heads, some looking finished, others half-way through. Earl showed me one head with open casting holes; the openings have to be filled by welding. Re old Edmunds, I am not sure one can be found in such pristine condition and at reasonable price. I once saw a used Bohnalite head for my engine, but two plug holes were gouged, and surface was pitted. The seller wanted same money as for Earl's head, and there was no guarantee that there was no warping or a hidden crack. Edmunds may warm somebody's heart, but for me and my money its Edgy. I will make and post a few close-up pictures, as time permits.

Yesterday I paid a visit to Earl to pick up a cylinder head that he made for me. Earl lives in a beautiful town of Santa Rosa, about 50 miles North of San Francisco. The day was sunny and the trip was fun, with lush green landscapes of rain-drenched California. The head is a masterpiece, mirror-polished mating surface, superb casting job, and meticulous machining. The pictures on the web site don't do justice to the beauty of the part. Earl answered all my questions re. installation, and we discussed the casting process used to create a part with a complex internal cavity. He told me that he had produced several hundred heads for Mopar flat six engines, all of them in use, with no problems. Earl himself is a passionate Mopar fan and one of the few top experts. He showed me his Chrysler modded for racing in Bonnevile (~140 mph top speed!) with all custom parts you can imagine - head with OHV intake valves, intake manifold, Langdon headers, cam gear and valve covers, 12V electric. As he confirmed, everything but block and crank is custom. Earl's garage is like a museum. Earl is a very nice guy. I highly recommend him for anybody who is contemplating engine upgrade.

I was also thinking ceramic coating, but am not exactly sure whether it is a good thing or bad. The coating, which has lesser heat conductivity than aluminum, should supposedly increase thermal efficiency by keeping more heat in combustion chamber to do the useful work. But hotter combustion chamber is more prone to detonation. The effect of coating is thus similar to that of increased compression ratio. Aluminum head conducts heat better than cast iron, providing for more even temperatures in combustion chamber and allowing for higher CR. By the same token, a piston without coating is more conductive for heat transfer from piston to cylinder walls, compared to a coated one. "Ceramic coating" of aluminum is technologically very simple: anodizing. The anodizing process creates a very tough layer of aluminum oxide on the surface. The fact that anodized piston crowns are not used by engine manufacturers is telling in regard to the advantages of "ceramic coating".

The first carburettors with sequentially opening throttles appeared in late 50s. Advantages of this design were such that in 70s-80s essentially everything that you can call a gasoline-powered car was equipped with these carbs. There were no drawbacks. No pain in the butt. Simple and efficient. This design solved the previously intractable problem of how to improve high power high speed performance without compromising low speed performance and throttle response.

Twin barrel carbs are of two principally different designs. Early carbs had synchronous throttles. This design was basically two carbs in a single body. One hole fed cylinders 1,2,3 and the other 4,5,6. Later twin barrel carbs have throttles that open sequentially: the second throttle beginning to open only after the first has already fully opened. It is functionally same as adding a second carb, but only when the first begins to restrict engine's air intake. Usually, the second barrel opening starts transition from economy to power regime. Some of the designs even have a switch that turns on a light on dashboard when second barrel is opening, indicating that you are in the non-economical power regime.

I used those too, they were not supposed to run for any extended time, or at higher than idle speed. Mixture screw was to be adjusted to the transition from yellow to blue. Very useful for setting idle mixture. The beauty of AF sensor is that it can precisely measure stoichiometry at various regimes: idle, acceleration, steady driving at various speeds, climbing with full throttle.

Wow - a lot of insightful comments. It looks like the consensus is emerging that 30 mpg is not a trivial task, and may be actually impossible. To the point that it isn't worthwhile to do economy mods, instead driving our cars as they are - this is reasonable. Many folks keep old cars to take them to few shows and joy rides during a year, and, in this case, economy doesn't really matter. But if I want to drive it every day, or go on a journey across the country, 30 vs. 17 mpg is big difference money wise. Now gas is relatively cheap, but where I live, just a few years ago the price of regular topped $5. I am sure high gas prices are inevitable in the future. Even if money was not a consideration, I kind of feel guilty for participating in unnecessary waste of precious natural resources... Also, it is true that if fuel economy is the goal, one should drive a modern economical car. I do exactly that most of the time. But there is no excitement in modern cars. They are boring. The argument is the same as why should one drive a Ferrari if a Hyundai takes you from point A to point B in pretty much the same manner? The comment about engine power matching the car weight is right on the mark. Actually, if power of flat six could be increased to 100+ hp, which is realistic, a '37 Plymouth will get into the same lb/hp league as many modern mid-size cars. Weight doesn't considerably affect economy at steady speed, but is #1 factor of poor mileage in city driving, so reducing weight is yet another avenue for overall fuel savings. Shaving 100 lb or more off total weight might be possible. Things like aluminum head and radiator, alternator, lithium battery with supercapacitor, etc. 100 lb weight reduction is equivalent to 3 hp power gain. Calibrating a carburettor for economy using exhaust gas analyzer is a great idea. It is akin to what I suggested for tuning the lean burn: output from an oxygen sensor. A broadband oxygen sensor, aka air/fuel ratio sensor, hooked to a laptop, should suffice, and, unlike bulky stationary gas analyzer, can be used during actual driving to record and collect real time data. From what I've read, EGR somewhat decreases fuel consumption in addition to lowering combustion temperature. It reduces engine pumping losses by reducing manifold vacuum behind the throttle. It is like a little free turbo that uses the energy of pressurized exhaust gas to fill cylinders. EGR is equivalent to reducing engine displacement at steady speed and partial throttle, when only a fraction of engine power is used. Multi-port injection is no doubt the most efficient, economical, and versatile fuel system. Technically it might be possible to transplant MPI from a modern 6 cylinder engine, but that will also require ECU with all the requisite sensors, which is challenging. I am not sure though that MPI would offer significant mileage improvement. Carburettor design much improved since 30s, and later model carbs were comparable to MPI fuel injection in economy. For example, Nissan's KA24 MPI engine in my truck has the same gas mileage as its carburetted predecessor Z24. ECU-controlled air/fuel ratio in today's cars is primarily to ensure certain amount of unburnt fuel for optimal function of the catalytic converter, rather than maximizing fuel economy. Aerodynamics of late 30s to late 50s cars wasn't so bad as one might think. At least their bodies were designed with aerodynamics in mind. The Airflow strongly influenced that, not only for Chrysler, but for other makes as well. By contrast, even later model pickups are boxy and not aerodynamic. At 55 - 60 mph and higher, poor aerodynamics is the most important contributor to efficiency loss, and any improvement here will have noticeable effect. I can see at least two aero mods for our cars: rear fender skirts and underbody panels to smooth out the bottom. Chopped/lowered body are two more, although I am not a fan of those.

I hated to hijack the thread about dual carbs, so decided to start a new one about fuel economy and how it can be improved. It has been stated by Sharps40 that 30 mpg at 60 mph highway driving is impossible. I have to agree. It is impossible to argue against extensive experience. At the time when there were no EPA mileage ratings, Chrysler advertised that some drivers managed to make 20 mpg in their cars. Realistically, this means an average driver should have been content with 15 mpg. But did anyone try modifications aiming at economy? I searched extensively, but could not find anything. All the mods I could find were about increasing power. We can look at how fuel economy of today's cars has been achieved, and whether some steps in those directions can be taken in our cars. 1. Increase compression. 8.5 - 9 is possible in Mopar engines with 78 gasoline. 2. Decrease engine displacement. This improves economy at the expense of performance. The most fuel-efficient non-hybrid car in the USA, Geo Metro, which is capable of 50 mpg highway, has 1 liter 3 cylinder engine. I own 3 of these cars. They are excellent everyday drivers. If my Plymouth had the same dynamics as Metro, I would be very happy. To compensate for the loss of performance of small engines, their rated power is increased by high rpm, 4 valves per cylinder, and variable valve timing. These power tricks come at drastic loss of economy. There is nothing to be gained here for flat six engines, except understanding that 190 and 201 engines are more economical than 230 ones. 3. Manual transmission. Auto transmission is big waste of engine power. Typically, auto car is 20-25% less fuel efficient than stick shift of the same model. However, manual transmissions are not all the same. The most economical are those that have direct drive, like third gear in a 3-speed Mopar transmission. In third gear, friction losses in such transmission are minimal. Unfortunately, with standard rear end and standard wheels, 60 mph in third gear is not where engine works economically. The simplest solution is overdrive, but friction losses in overdrive should be considered. Higher gearing can be also achieved using 3.9 rear end (which I have in my car) and 235/85R16 rear wheels. This combination gives 15% higher final ratio (for comparison, overdrive gives 30%). Taller gearing should be acceptable if engine power is increased. 4. Leaner burn at sustained highway speed. Flat six engines are intrinsically amenable to leaner burn because they have much more turbulence in combustion chambers than OHV engines. Leaner burn requires stronger spark than pathetic 6V ignition can deliver. This is not a problem. Modern transistorized or capacitor discharge ignition should take care of it. Of course, proper jetting will be necessary, guided by output from an oxygen sensor. 5. Better carburettor. Newer carburettors provide more precise fuel metering than primitive OEM carburettors of 30s - 50s. Substantial savings can also be achieved by fuel cutoff during engine braking, which newer carburettors allow. 6. EGR. Reduces fuel consumption at sustained highway speed. This is an easy add-on. 7. Tuned intake and exhaust. Most modern cars have intake and exhaust resonators that reduce engine pumping losses at engine speeds of steady highway driving. 8. Electric radiator fan. Belt-driven radiator fan without clutch easily robs engine of 2-3 hp at highway speeds. 9. Thinner engine and transmission oil. With tight tolerances in Mopar engines, 0W20 synthetic oil should be OK. Pennzoil Synchromesh is an excellent transmission fluid that is much thinner than regular gear oil. Not much savings here, but everything adds up. 10. Radial tires. These have 20-30% less rolling resistance than OEM bias ply tires. Of course, steering would be more difficult, but I don't think this is insurmountable. Our Nissan truck has no power steering, but my petite 115 lb wife drives it without complaints. 11. Good driving habits. Maintain steady speed, minimize hard braking and acceleration, use pulse-glide where appropriate. There are devices that show instant mileage - they are very helpful in learning how to drive for economy. Unfortunately, they only work with fuel injection. A manifold vacuum gauge on dashboard is acceptable substitute. Economy driving is safe driving. Critiques? Other suggestions?

Mopar numbers are 635545 and 635546 for right and left rear cylinders, respectively, according to my parts catalogs.

Aren't we all dreamers here? My '93 Nissan truck is capable of 30 mpg, with careful driving. '37 Plymouth has same curb weight, but better aerodynamics. With higher compression, better fuel system, and stronger spark, the engine might be capable of sustaining 60 mph, while staying in the economy range.

I will, although I cannot promise quick progress. I have full-time job and many other commitments. As to advantages of multi-carb intake on a flat six engine, I fully agree, but on one condition: these advantages are only realized at wide open throttle and high engine speed, when you are trying to squeeze out maximum power. At partial throttle and low engine speed, a single small-bore carb beats a bigger carb, or multiple carbs, in response and economy. As an everyday driver, I use partial throttle most of the time, and full throttle high rpm only occasionally. Accordingly. I am much more concerned with partial throttle performance. My goal is 30 mpg at steady 60 mph highway driving, not winning races.

Saying that 2x2=4 is not plagiarism of elementary school textbook. I just wanted to point that with twin carb setup, degradation of throttle response, as described in the original post, is to be expected. I am thinking of replacing a Carter carb currently on my 201 engine with the two-barrel Hitachi DFP 384, which was used on Nissan Z24 2.4L engine. The flow of this carb is near perfect match to 201, and fuel metering at various speeds is superior to medival Carter's. As a bonus, it has automatic choke and idle fuel cutoff valve.

Custom aluminum head makes most sense to me of all hot rod parts. It makes sense even if I am not interested in racing, as it allows substantial increase in both power and ecomomy, with no downside. Good for everyday driving. Edgy heads are now $950. One might think expensive, but compared to what? To mass-produced heads of modern engines? Even these may cost $300-600 depending on the engine. Custom head is all hand-made. Earl pays $400 to the foundry, and then there is a lot of precision machining work after that. I think the price is reasonable.