Building a Late Model Hemi Stroker - Engine Builder Magazine

Building a Late Model Hemi Stroker

What is the purpose of stroking a motor? The answer is simple: to obtain more cubic inches. And in today’s economic times, it’s always best to achieve “more” with less – as in less money. The key word to many stroker enthusiasts today is “budget”.

However, the word “budget” has a way of being interpreted differently by different people. The original point of stroking a motor with a bigger crankshaft is to keep the original block in order to keep the expense down.

Enthusiasts have, over the years, found a way to stroke whatever engine they could, and some of the combinations have been downright interesting. As explained in Dave Sutton’s article, it’s amazing what parts are available. These days, late model engines are gaining popularity in stroker builds.

Steve Bowman, owner of S&S Mopars in  Winston-Salem, NC, came to me with a personal request to help him build a stroker for his 1969 Barracuda. Because he and his wife, Sheila, have been drag racing for years, Bowman was interested in an alternative restoration that could be used both as his weekend cruiser and drag machine.

His shop specializes in a full line of restoration services and parts distribution, including various Mopar engine builds from stock to blown alcohol Hemis. So, while the idea of putting a Mopar stroker under his Barracuda’s bonnet wasn’t all that surprising, why would we choose a Late Model Hemi stroker?

When compared to the Chevy-based LS engines and the late model Modular Fords, conventional wisdom is that there’s nothing out there for the Hemi. After doing some research, it did seem as if there are only a few specialty engine shops that have dabbled in the Hemi market. Where can you find aftermarket parts if you’re interested in doing it yourself? In the spirit of discovery, we decided to try to answer the questions many people have asked of us. We wanted to expose the Hemi engine to the aftermarket, find some resources for aftermarket parts, and see what kind of power potential we could pull from our combination.

The Hemi

In 2003, Daimler Chrysler made an awesome move in the automotive industry and reintroduced the Hemi. Originally introduced in 1951, the “double-rocker shaft V8” made a lot more horsepower than the other motors available at the time. Three different families of Hemis were built between 1951 and 1971, from a 241 cid Dodge to the legendary 426 NASCAR motor of the late ’60s. However, during the fuel-saving ’70s, Chrysler shelved the motor.

Luckily, in 2003, the 5.7L Hemi returned in the Dodge Ram pickup. A bigger version – the 6.1L followed in 2005 in several of the other Mopar monsters.

Today, the 6.1L can be hard to find in a rebuildable state – and likely to be quite pricey. The 5.7L is somewhat easier to find. After doing significant research we managed to find several 5.7L Hemi engines available to be purchased across the country.

Keeping in mind that you can purchase blocks, cranks and most of the accessories you’ll need to build a Hemi stroker (including complete crate motors) directly from Mopar, critics might ask why we didn’t just do that. In the spirit of the project, we decided to stick to the aftermarket and try to stick to a budget by rebuilding a 5.7L Hemi. We actually found a used engine online at a Mopar Parts Web site for approximately $500. It was tired and in need of a rebuild, but it was complete.

Here is a quick rundown of our 5.7L Hemi engine. It came with a bore of 3.92? and a stroke of 3.58?, which yields a displacement of 345 cubic inches. It has a block height of 9.25?, cross bolted mains, 6.25? rods, 85 cc combustion chambers, 1.65 ratio rocker arms, plastic intake manifold with a 80 mm throttle body that is electronically driven, 9.6:1 compression, one coil pack per cylinder firing dual plugs, and firing order of 1-8-4-3-6-5-7-2. In factory form this engine made 345 hp @ 5,600 rpm and 375 lb.ft. of torque @ 4,400 rpm.  

It gets its name from the shape of its combustion chambers. Hemispherical chambers allow significant advantages with regard to air flow.

The design and shape of the cylinder head eliminates the valve shrouding found on other designs such as the LS Chevy and Modular Ford. These design advantages right from the start mean we have a potent cylinder head for the build.  

That’s a good thing, because aftermarket Hemi heads have proven to be impossible for us to find. Luckily, the stock heads were serviceable. The stock valve sizes for the 5.7L Hemi are 2.00? intake and 1.55? exhaust. A small amount of porting seems to yield high flow at low lift with very little effort. After replacing the stock valves with 2.02? intake and 1.6? exhaust valves from Ferrea, as well as some porting, you can see the comparisons. See the flow bench data in Chart 1.

Of course, there are companies that offer CNC porting for the Hemi cylinder heads, and that’s certainly an approach you can take, but to keep with the budget build, we opted to do it ourselves.

Since we already had our block to build our stroker, the next step was to add the crankshaft. Callies Crankshafts in Fostoria, OH, offers a 4.050? stroke crank that will fit either the 5.7L and 6.1L block. This turns out to be a pretty slick fit when you do the math. If you put it in a 5.7L, you’ll get a 392 cid motor. If you install in a 6.1L you’ll yield 426 cubic inches. So, by installing the crankshaft in either block you’re able to take on some of the Hemi heritage.

With this 5.7L combination we needed a connecting rod that was 6.125? in length. The stroker crankshaft has a rod journal size the same as a small block Chevy, which is 2.100?. We decided to use a complete rotating assembly. As with many stroker suppliers you can order it with private label parts or nationally recognized brand names. Our package included the Callies crankshaft and small block Chevy rods, with Mahle pistons and rings with Clevite rod bearings balanced and ready for assembly. A set of Federal-Mogul main bearings made sure the rotating assembly kept rotating.

Chrysler does offer its version of a 392 Late Model Hemi, but does so using a 6.1L block. This engine has a bore of 4.055? and a custom stroke of 3.795?. It is offered in two different versions from Mopar – either a 525 hp or a 540 hp version. Both engines have 10.5:1 compression with other changes along the way for the horsepower differences.

So, can we make 540 hp from our stoker Hemi? We obviously won’t have the same bore and stroke, but we’ll still have the same cubic inches.

Remember three things when it comes to engine building: heads, cam and compression. This axiom is true today and will still hold true tomorrow. We will keep our engine at 10.5:1 compression for pump gas reasons. We have ported the cylinder heads and you can see the differences between the stock heads and our ported version.

Because we really wanted to cut down on valvetrain weight without going to titanium, the Ferrea valves we’re using are top of the line small block Chevy valves which are .100? longer and hollow-stemmed. We also upgraded to a set of Ferrea’s beehive valve springs, which replace the beehive spring found in the stock Hemi version.

Engine manufacturers have started using this style of spring in late model engines because they are lighter and as you compress them they become more aggressive. They also take up less space, this means you can run them with many hydraulic roller applications without all the spring hassle and still have a lighter valvetrain weight.

We found there are only a few companies grinding camshafts for the late model Hemi. After doing some math and taking into consideration the head flow numbers with the amount of compression we would be running, I knew the grind that I wanted. The problem was that no one offers it. So, I contacted Trent Goodwin at Comp Cams, who took a look at the numbers and, to my surprise, had a camshaft ground in two days. Comp also supplied the retainers for our beehive springs.

My hat is off to Trent for the hard work in grinding the camshaft and I’m sure that he’ll soon be making numerous grinds for different versions of this stroker build.

Keep in mind that there still aren’t too many parts on the shelves for the late model Hemi, although the market has stepped up to the plate in the past couple of years with increasing frequency.

Although many of the internal components were accounted for, there were still several pieces needed to finish. By looking for a supplier with a long history of service to my performance business I was able to find many of them in one stop. Since we were building a modified engine it was a relief to find that Elgin Industries provides a broad range of products for the late model Hemi. We sourced the oil pump, timing kit, valve guides, and pushrods from Elgin. In a project like this, customer service is key, and theirs has always been awesome.

The Hemi’s oiling system looked pretty good in stock form, but we were concerned about what may be available in the aftermarket. Moroso has been in the oil control business for a long time and they offer some nice pieces for the late model Hemi, including an aluminum pan and pickup tube made for some serious performance applications. The pan can be used for wet sump systems with an 11 quart capacity. Wait – did you just read 11 quarts? Because of the design of the Hemi heads and the amount of oil retained in the top end, this capacity is necessary.

The pan includes additional features such as a bung for an oil level sensor or for possible use as a location for an oil heater. It also features built-in trap doors and baffles for oil control and a location for an oil drain if used in a turbocharged application. We also found a great looking set of Moroso machined aluminum valve covers. They are coated with a “black crinkle” finish with the center of the valve cover left in a machined form, and the look really emphasizes the Hemi heritage in a modern design.

And we required modern sealing techniques to keep it all together. We selected a complete set of Fel-Pro gaskets from Federal-Mogul for our late model Hemi. The set includes everything from the one-piece rubber oil pan set to their ordinary line of seals to a state of the art MLS head gasket. We used Fel-Pro head bolts to replace the stock torque-to-yield bolts used during manufacturing. For the rest of the engine assembly we used ARP studs and bolts.

For our top-end, including the fuel system and the intake, we used replacement Mopar parts because of their availability. However, in keeping with the spirit of the build, we’re working on sourcing aftermarket upgrades to the induction system. We’re still trying to keep to some sort of budget!

Dyno numbers were not complete at press time, but this engine is coming together nicely, proving that even a stroker no one thinks is available can be built using aftermarket parts, on a budget and with great results. Look for the wrap-up to this article in an upcoming issue of Engine Builder.

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