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    Racing the early hemi, by Gene Adams

    Discussion of the 331-354-392 HEMIs. And DeDoto
    Adams Performance
    4778 Fox Dr,  Anderson, CA 96007
    (530) 357-5570

    The following essay is a compilation of Gene’s notes that I posted several years ago at (Harvey Racing Engines) Jim Harvey has graciously consented to allow me to post it here. It’s a little dated, circa 1970-1990, but still pretty relevant. I’ll follow up with updates (also previously posted on, and a discussion/dissection of components, tuning tips, and other items of possible interest.

    Be mindful that this information is primarily directed towards injected fuel drag racing engines. Until the Engine Masters Challenge, Gene had zero – and I mean zero – experience with carbureted gasoline engines.


    Through the years, quite a lot has been written about the early Chrysler Hemi engine. The latest and most comprehensive is the Chrysler Hemi Engine Manual by Ron Ceridono, which I highly recommend. This is a very good book that gets into detail on identifying blocks, heads, and various other parts of the engine. It covers building a 392 hemi for the street, however it does not get into building an all out racing engine.

    This paper will explain what blocks, aftermarket parts, and especially cylinder heads to use for racing. What I have found interesting about early hemi’s is that many people take one look and see a big, complicated engine. In reality, there is very little difference in comparison to any other modern V8, and in my opinion it is probably the simplest and easiest. Please keep in mind that I do not claim to have all the answers, as new information is always coming out. To my knowledge, as strange as it may sound, the early hemi has never been thoroughly tested. The Chrysler Corporation quit producing the early hemi in 1958, and I doubt it ever came close to reaching its full potential. As to building this engine for racing, I will cover both blown and unblown versions. I will not get into aluminum block and head derivatives.


    I’m going to talk about cylinder heads first, as they are the most important part of making horsepower. This is probably the least understood aspect of the early hemi engines. One would naturally think that the last and largest of the early hemi’s, the ‘57-‘58 392, would have the heads with the most potential. This is not true, and the ‘56 354 head is not much better. The ‘54-‘55 331 passenger car and some industrial heads have far mor air flow potential for racing. These heads actually have bigger ports. The reason for this is not completely understood. Rumors and some sources say that the later heads were made smaller for improved low end torque to haul the larger and heavier cars that they were used in. This is the reason the aftermarket manufacturers of aluminum heads copied the 331.

    The stock valve sizes from ‘54 through ‘56 were the same with 1.940″ intakes and 1.750″ exhausts. The 392 has 2.00″ intake and 1.750″ exhaust valves. All the heads in stock form flow about 225 CFM maximum. With all out porting and big intake valves, the ‘54 and ‘55 heads can be make to flow as much as 15% more than the ‘56 – ‘58 heads. In total flow numbers, the ‘56 – ‘58 will flow 305 – 315 CFM, and the ‘54 – ‘55 will flow 360 – 370 CFM. When casually inspecting these heads, the differences are not readily apparent. The intake port at the opening is the same, but on closer inspection, one can see a significant difference next to the valve guide area. The ports in early heads are much taller, at 1.675″ as compared to the later heads which are 1.410″, and start tapering to the smaller size immediately from the port opening. The way the water jackets are cast, the late heads cannot be opened up to the size of the early heads. The 331 heads allow the advantage of a much larger valve, as large as a 2.200″ intake. Keep in mind, these high flow numbers are without brazing, welding, or epoxy. One of the mistakes that was made in the ‘60’s with the hemi’s was installing huge exhaust valves at the expense of the intake size, which caused over scavenging. A popular size was 2.0625″, and in some cases even 2.125″ exhaust valves, which was counterproductive. In some instances when this was done, the exhaust out flowed the intake by a great deal. I was guilty of using a 2.0625″ valve myself, not knowing any better at the time. The ideal valve size is 2.125″ for blown and 2.200″ for unblown intakes and 1.800″ for all exhausts.


    Passenger car heads: In the center of the head under the valve cover is a casting ID number. The second digit indicates the year. For example, #1486833-1 is a 1954-331 head. 1556157-1 is a 1955 -331 head. #1731528-2 is a 1957-392 head. The ‘54 and ‘55 heads all have hard seats and heat risers.

    Industrial heads: All industrial heads have hard seats on the exhaust and usually do not have exhaust heat risers.
    Another difference between the various heads is that the 331 heads have .375″ dowel pins and the later heads have .3125″ dowel pins. When using any of the 331 or 354 heads on a 392, manifold spacers are necessary due to the higher deck height of the 392. These are not necessary with stack injectors.


    Stay away from the ‘51 – ‘53 331 engines. They have a very long bell housing cast onto the back of the block, although it can be cut off and converted to the later bolt pattern. ‘54 through ‘58 engines all had a common bolt pattern, without the long bell housing. ‘51 through ‘55 engines have a 3.8125″ bore X 3.625″ stroke, which gives 331 cubic inches. The ‘56 has a 3.940″ bore X 3.625″ stroke which gives 354 cubic inches. These blocks all have the same deck height at 10.390″ and the same size main and rod journal sizes. The ‘51 through ‘’54 require a different front cover than the later blocks. The ‘57 and ‘58 engines have a 4.00″ bore X 3.900″ stroke which gives 392 cubic inches. All the early Chrysler hemi blocks have the same bore centers at 4.5625″. The 392 cubic inch engines have different lifter bore angles, and require a different camshaft.

    There is also a Windsor engine equipped with polysphere heads, which came in three displacements, 301, 331, and 354 cubic inches. Hemi heads will bolt right on the block, although the 300 cubic inch block had a small 3.625″ bore which would require notching the block for valve clearance when using hemi heads. The 300 cubic inch was available in ‘55, the 331 in ‘56, and the 354 in ‘57 and ‘58.

    When preparing a block, the first thing to do is to measure the bore. An overbore of .060″ is about the limit for unblown, .040″ for blown. Then get it sonic tested for core shift. Remove the factory bypass check valve under the rear main cap, which will be replaced later with an aluminum block off plug. An alternative is to tap the hole to .625″ X 11 , thread down to the shoulder, and install a .625″ set screw. Either way will work nicely.

    If you plan on making serious power, you should consider filling the water jackets with hardblock. Install four bolt main caps on the three center mains, utilizing studs. I also recommend using a steel front main cap. The stock rear main is strong enough.

    Be sure to square the decks, and also cut receiver grooves to match the o-rings in the heads. The next thing to consider is drilling and tapping the block for .5625″ head studs. This is an expensive procedure, but with only ten studs holding the head, it is worth doing.


    All early hemi crankshafts are forged steel. The 331-354 crankshafts are good up to about 700 horsepower, the 392, slightly more. After that, I recommend a billet crankshaft. They can be offset ground to get a longer stroke. The front and rear throws have large holes in them which prevents destroking.

    With a .060″ overbore and a .625″ longer stroke, a 354 will yield 427 cubic inches, and a 392 will yield 468 cubic inches.
    A 392 crankshaft can be installed in a 331 or 354 block by turning down the mains, welding up and narrowing the thrust journal, and then regrinding. The counterweights also need to be turned down .220″ to clear the block. By offset grinding the throws and utilizing big block Chevrolet rod journals, even more stoke is available, up to 4.060″. Incidentally, you can put a very long stroke in an early hemi, as the camshaft is located very high in the block and there is no interference with the rods, as with many other V8’s. I once had an .875″ stroke crank (4.775″) in a 392.


    Flat tappet mechanical and roller cams are available from most camshaft suppliers. The lifter bore is .904″, the same as any late model Chrysler V8.

    Camshaft specifications would be according to application. Lobe centers and duration are pretty standard. Hemi’s do not seem to like a lot of duration on the exhaust side. You can be safe using a single pattern cam with a higher intake rocker arm ratio, and I recommend a 1.7:1 intake and a 1.5:1 exhaust.

    Several roller chain kits and cam gear drives are available. A new belt drive will soon be available.


    For a racing engine, I prefer aluminum rods for strength and light weight. I have the piston manufacturer determine the ring pack they recommend for the application. Then I have them position the pin as close as possible to the oil ring, and let that determine the rod length. I do not consider rod length as important as having the pistons as light as possible.


    For a stock rocker assembly, the early hemi was the best. Using a relatively low lift cam by today’s standards, I was able to rev an unblown hemi over 9000rpm. The only modification was hard chroming the rocker shafts. The stock exhaust rocker arm never was strong enough for a blown engine. With today’s hi-lift cams and the high spring pressures, you will need to use an aftermarket rocker assembly whether blown or unblown.


    The hemi has a good oil system with the main oil galley running down the right hand side of the block, feeding the main and cam bearings. There are oil holes in the #1 and #4 cam journals feeding oil up to the rocker arms. I recommend not blocking these off completely, however your could restrict them slightly.


    There are two options. The first, but not necessarily the best is a set of stack injectors. Two companies are now supplying these units, however they will need some work and should be sent to a head porter to match them to the cylinder heads. The second is a tunnel ram manifold, either cast or sheet metal. One of several blower hats can supply the air, and both work equally well.


    There are several suppliers for blown manifolds, injection systems, and blowers.


    There are two options. A MSD battery powered system or a magneto, which both work nicely. I prefer a magneto.
    The hemi, having an almost centrally located spark plug does not need a lot of ignition lead. With a lot of compression or supercharger, 28-30 degrees is the maximum. When unblown on 90% or more, 50-58 degrees.


    Solid copper head gaskets are a must when making high power. They come in a variety of thicknesses, allowing the compression to be moved around a bit. An o-ring in the head and a receiver groove in the block assures a good seal. If water is needed in the heads, the passages must be plugged or water will migrate into the oil pan. If you put enough sealer on the head gasket and head surfaces to keep the water out of the pan, a crow bar will be needed to get the heads off.


    For unblown engines utilizing racing gasoline or methanol, I recommend 15:1, or as high as 16:1 compression, which is not easy to accomplish. To get that much compression, the combustion chamber needs to be really filled up, requiring a large piston dome. This requires a lot of fitting and checking for piston to head clearance and piston to valve clearance.
    For unblown nitro I do not recommend over 11:1, with 10:1 or 10.5:1 usually being adequate. For blown gasoline, 8.5 – 9:1. For blown methanol, 10 – 11:1. For blown nitro, 6:1.

    Block info

    The decision of which block to utilize will probably be impacted by your intended use, a block or parts or you already have, or what you can find.

    The 301, 331, and 354 share the same dimensions, save for the bore. The 392 has a higher deck height, and larger main journals. A 392 crank can be modified to fit a low deck (301, 331, 354 ) block.

    The low deck blocks come in both Poly and Hemi flavors. Hemi heads will bolt right on to a Poly block (also known as a Windsor). One of the ways to distinguish the difference between a Hemi and a Poly is that the Poly blocks have elongated holes in the decks for the push rods. It is common for the later Poly blocks to have core shift. Most, if not all, have a “W” cast on the side.

    The most bang for the buck, by far, can be had by purchasing a complete ‘54 or ‘55 331. It will have the heads that you will be using (irregardless of the power level and/or fuel utilized), and they are relatively inexpensive.

    I purchased three engines last year (two ‘54 Hemi’s and a ‘55 Poly) from a local wrecking yard, for $1500. They were complete and in the vehicles, so I got everything, except that the Hemi’s were missing the valve covers. There were some extra rocker stands and other parts in the trunks, so that made up for the missing valve covers. One of the engines had been freshly rebuilt and could have been a runner. The other two were stuck, but not broken. I disassembled and cleaned everything up, and ended up with three blocks, three cranks, four Hemi heads, six Hemi rocker arm assemblies and two Poly heads. All were serviceable. There is a good market on eBay for carburetors, air cleaners, exhaust manifolds, spark plug insulators, etc., etc. If I had the inclination to sell that stuff off, I could probably almost recoup my investment.

    Gene has purchased also purchased several engines recently. One was a very nice 331, disassembled but totally complete, with a nice set of aftermarket cast pistons, a new timing chain, and some other nice extras for $500. The point is that there are engines and deals out there if you are paying attention.

    A solid combination can be developed by utilizing a 331 block and heads, with a 392 crank. These cranks are getting expensive, at about $750 for a good one, however, a good one is not needed. I traded a beat up crank (one journal torn up with a spun insert “welded” to it) for a pair of valve covers. I had it thermally cleaned, chemically cleaned, shot peened, magged, straightened, offset ground to BBC (gaining a little stroke), and the rear flange ground. Total cost was $480 (6 hours labor @ $80 per hour). I’m utilizing it in my high gear only nitro engine, which is a 392 block. For another several hundred dollars, it could be modified to fit a low deck block. Required is turning the mains, welding the thrust surface, and turning the o.d. of the counterweights.

    Here are some realistic estimates of power of several combinations utilizing production blocks, cranks, and heads.

    A .060″ over 331 with a crank offset ground to BBC size (3.875″ X 3.675″) yields 347 cubic inches. Injected, this combination would be good for 675-700 horsepower on methanol, 750 horsepower on 50%, or 925 on a high percentage of nitro.

    This same engine with an offset ground 392 crank (3.875″ X 4.050″ ) yields 382 cubic inches and would make about 50 horsepower more across the board. Utilizing a 354 block, with the larger bore, would add about 25 horsepower across the board on either engine.

    A .060″ over 392 with a crank offset ground to BBC size (4.060″ X 4.050″) yields 420 cubic inches. Injected, this combination would be good for 800 horsepower on methanol, 950 horsepower on 50%, or 1100-1150 horsepower on a high percentage of nitro.

    The same engine with a .625″ stroker would produce 850 horsepower on methanol, 980 horsepower on 50%, or 1200-1500 horsepower on a high percentage of nitro.

    The numbers might seem a little funny, especially between methanol and 50%. The methanol engine is a high compression engine and the 50% engine isn’t. The loss of compression amounts to about 100 horsepower, which the nitro engine has to make up for. Also, all the engines will be utilizing the same 331 heads, so the power per cubic inch usually falls off due to diminished cylinder filling.

    These numbers are all with stack injection. A hat on a tunnel ram will absolutely make more power, but it’s difficult to know exactly how much.

    Block preparation is virtually identical for any of the above engines. The lower power versions should live with nothing more than main bolt studs, medium power could utilize a girdle (such as Tom Waters’ deal), and the high power versions should utilize four bolt main caps. For double bulletproof, one of Tom’s girdles could be bolted on top of the four bolt mains. The high power versions should also utilize .5625″ head studs.

    Here’s a list of things that need to be done on a block. Some are required for even a mild rebuild, and some are required only if really leaning on the engine. Truth be known, it probably makes sense to spend the extra money and do it right, do it once, and do it all. For instance, four bolt mains aren’t necessary for low horsepower, and .5625″ studs are only necessary for high horsepower. However if you do it right the first time, even for a very mild 600 horsepower engine, then if (actually, when!) you want to go fast, just add nitro (maybe change pistons), and hang on.

    It’s very important to have confidence in your machinist. We make a 300+ mile round trip to drop off parts, and another trip to retrieve them. Sure, it’s a pain, time consuming, and expensive. But we’ve found a gentleman that we have the upmost confidence in, and it’s worth it. Also, don’t be bashful about dimensionally checking your parts when you pick up them up. He shouldn’t mind. In fact, he should be pleased that you’re interested in having things perfect, and he should be proud that he has machined everything spot on.

    I prefer employing a machinist that charges at shop rate, as opposed to the job. At shop rate, it’s economically viable for him to take his time, be fussy, and do a very good job. I tell him that I’d prefer that he take his time and do it as if it were his own parts. I don’t ask him what it is going to cost, and if I don’t feel he has charged enough, I insist that he accept what I feel is a fair price for my requirement of an extra nice job. This might sound a little unorthodox, but you would probably be pleasantly surprised at the quality of the finished product.

    The cost, including parts (four bolt mains caps on the center three bearings, main studs and cam bearings) will vary. Here are the costs from our most recent machine work: install 4 bolt main caps and line bore $350, parallel deck block $75, bore and hone $150, drill and tap for 9/16 studs $125, install cam bearings $25, cut receiver grooves $50. If a Tom Waters Girdle is substituted for the four bolt main caps, then there is a considerable savings, as the girdle costs less than the main caps, and line boring will not be required. If line boring is required, then it probably makes sense to purchase and mount the four bolt mains.

    Figure the block cost at $200 (complete engine $500, about half for the block, crank, oil pump and pan, and half for the heads, rocker arms, and valve covers). The machine work will vary, depending upon how much work is appropriate for your power requirement, but the total should be well under $1500 including the cost of the block.

    basic preparation for engines of any power level (the first few steps – sonic, clean, mag, cryo – are in sequential order):

    sonic test
    thermally clean, shot peene, hot water power wash
    cryo treat

    check line bore
    run a tap into every threaded hole
    chamfer head bolt holes
    make sure that the rear face of the engine is square with the crank
    receiver grooves for o-rings
    install new cam bearings
    install full flow oil block

    Check the intermediate shaft bushing, and install new one if worn.

    The front motor mount flanges are often chopped off for fitment into a dragster, and there are some other sharp protrusions that can be ground off.

    The inlet and outlet passages in the oil filter pad can be tapped for either ½ npt or AN dash 10.

    additional preparation for engines of moderate power:

    four bolt mains, or a main girdle

    additional preparation for engines of high power:

    .5625″ head studs

    crank info

    There are two crankshaft options, stock or billet. I suspect that a modified stock Chrysler crankshaft will suffice for most folks that are just getting introduced to the early hemi. Chrysler crankshafts are high quality forgings machined to a high standard and have an unusual rolled fillet. This fillet attribute is very effective, but expensive. We utilize Bryant billet crankshafts exclusively when a billet is required in such cases as for A/fuel or Junior/fuel. They are stronger, lighter, and can be obtained in almost unlimited strokes. They’re also quite expensive, at around $3000.

    The 331/354 crankshafts are all interchangeable. There are several part numbers, which have no discernable differences, save for some 354 crankshafts that have slightly larger oil holes. The larger holes flow more oil, but remove metal from a very highly stressed area. The 392 crankshafts are all the same, usually part number 1673755.

    Preparing a stock crank will cost around $400, so with a $75 dollar 331 or 354 crank, the total cost would be under $500. A 392 crank is a little more pricey, at between $500 and $750 for a good one. However, a good one isn’t required in most cases due to the offset grinding that is usually performed when having a crank prepared. You might get lucky and find one that is torn up a little for far less money. Assuming $500 for a crank and $400 for preparation, that puts the cost of a 392 crankshaft at under $1000, which is a third the cost of a billet. (And, some will argue, a third as good.)

    Finding a crankshaft specialist that you have confidence in is very important. As with the blocks, we have a gentleman that is GOOD. He’s also a 300+ mile round trip, but we try to combine our block and crank travel. Unlike the gentleman that does our block work, our crank machinist is taking on new business. I highly recommend Butch Stamos, at Stamos Crankshafts, West Sacramento, CA, (916) 376 9019. He is a VERY fussy machinist, has very nice equipment, charges by the hour, and will have your crank ready on the promised date. He’s a one man show, so when you call, you will be talking to the guy doing the work on your crankshaft.

    Offset grind is almost like a free lunch. The stroke can be increased, an otherwise unuseable crankshafts can be made serviceable, friction is reduced, and inexpensive rods and bearings can be utilized. The BBC @ 2.200″ is the most common journal size. Also viable are both large and small journal SBC, and Honda @1.88″ (utilized on some billet cranks, such as in junior fuelers).

    When offset ground, part of the rolled fillet will remain, and there will be a transition to a large radius fillet. It looks a little funny, but is zero problem.

    For a racing application, Butch performs the following operations: thermal clean, shot peene, chemical clean, mag, straighten, and grind. He grinds the flange, and checks the snout. If it’s out, even in the slightest, he might recommend taking a very light cut. Dampers are usually a little on the tight side, so a tenth or so will not usually have a negative impact.

    Dampers are a must on a nitro engine, and a very good idea on a stock crank on methanol. Summit and Jegs both sell inexpensive, but effective, dampers designed for a 340/360 small block Mopar. A new key slot will have to be broached to gain correct orientation for the hemi TDC pointer.

    The stock flange is not tapped, and needs to be tapped to ½ – 20. The hole is the correct size for tapping, so just run a tap through it. We utilize a fixture, but tapping can be accomplished by hanging the crankshaft off the edge of a mill table.

    A very effective compromise encompassing weight, cost, and power is the utilization of a modified 392 crank in a 331/354 block. The 331/354 block is far less expensive, weighs less, and is a little smaller due to the lower deck. A 392 crank can be modified to fit a 331/354 block by grinding down the journal and counterweight diameters, and the throws can be offset ground for more stroke. Such a combination will displace around 380 cubic inches with a 331 block, and 406 cubic inches with a 354 block.

    DeSoto Engines, Junior Fuel

    Gene raced Junior Fuel for three years, from the fall of 1967 to the end, 1971, when Lions Drag Strip shut down. It took him a while to get it dialed in, after which he was more or less unbeatable. The only race he remembers losing occurred when a throttle link broke. His win/loss ratio, including the slow start, was about 75/25.

    The engine was a 1955 291 block with 1956 341 heads. Mondello ported them, 2.20″ intake and 1.75″ exhaust valves, about 270 cfm intake, 16″ zoomies 1.75″.

    The crank was offset ground .125″ and Dodge rods were utilized. Crank was .010″ on the mains and standard Dodge on the throws. Bore was .030″ over, for a total of 305 cubic inches.

    9000 rpm, 92%, 50 degrees in the mag, 10:1 compression, flat tappet camshaft, 180# on the seat, 450# open, Vertex mag, 10.75 X 15 tires on 8″ rims, Hays double disc clutch, stock rocker arms, adjustable push rods.

    The injectors were 2.4375″ Hilborn Chrysler castings cut down to fit the Desoto.

    The car started out as high gear only, 1170# with a 150# driver, with a 3.90 gear. It went 7.53 @ 202.24. With a 4.30 gear it went 7.40 @ 196.

    It was then switched to a two speed. The change added 100 pounds, and it went 7.14 @ 196 (4.30 gear).

    Jerry Glen drove it at first, and just about the time that Gene was getting it sorted out, Jerry went to top fuel, and Don Enriquez began his career driving for Gene.