Racing the Early HEMI, by Gene Adams
Posted: Sat Apr 12, 2008 9:16 am
The following essay is a compilation of Gene’s notes that I posted several years ago at HRE.com. (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 HRE.com), 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.
RACING THE EARLY HEMI
BY GENE ADAMS
FORWARD
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.
CYLINDER HEADS
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.
HOW TO IDENTIFY THE BEST HEADS FOR RACING
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.
BLOCKS
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.
CRANKSHAFTS
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.
CAMSHAFTS
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.
PISTONS AND RODS
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.
VALVE TRAIN
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.
OILING SYSTEMS
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.
INDUCTION SYSTEMS (UNBLOWN)
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.
INDUCTION SYSTEM (BLOWN)
There are several suppliers for blown manifolds, injection systems, and blowers.
IGNITION SYSTEM
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.
HEAD GASKETS
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.
COMPRESSION RATIO
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.
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.
RACING THE EARLY HEMI
BY GENE ADAMS
FORWARD
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.
CYLINDER HEADS
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.
HOW TO IDENTIFY THE BEST HEADS FOR RACING
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.
BLOCKS
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.
CRANKSHAFTS
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.
CAMSHAFTS
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.
PISTONS AND RODS
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.
VALVE TRAIN
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.
OILING SYSTEMS
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.
INDUCTION SYSTEMS (UNBLOWN)
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.
INDUCTION SYSTEM (BLOWN)
There are several suppliers for blown manifolds, injection systems, and blowers.
IGNITION SYSTEM
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.
HEAD GASKETS
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.
COMPRESSION RATIO
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.