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Breaking Rules With Our 392 Magnum Engine Build

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Our original core engine. Notice the small port heads with exhaust crossovers. Also note the non-adjustable shaft rocker arm system of the early heads.

Our original core engine. Notice the small port heads with exhaust crossovers. Also note the non-adjustable shaft rocker arm system of the early heads.

Breaking Some Rules — that’s what we’ve been doing and promoting with our 392 Magnum engine build.

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And with our plans to raffle the finished product and raise money and awareness for the work being done by the Independence Fund (www.indepencefund.org ) for our disabled veterans, we’re really doing something different, at least for us.

“Dare to be different” was what I challenged when I first promoted the idea of taking the engine that’s under the hood and thinking a little outside the box with an engine build.

The premise being to take a less then popular V8 like our 1977 318 Chrysler, and with parts readily available and often used on the more popular so called “Muscle Car” engines, build a powerful and dependable performance alternative.

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Even though the aftermarket continues to pump out new engine blocks for your typical high demand small and big block Chevrolets and Fords, not everyone will be willing to afford one for their particular project, nor do they need to.

Yes, you can still find rebuildable muscle motors, but a good, say for our case, 340, 383 or 440 complete core motor could set you back a hefty amount, and you haven’t even started your build. With our motor as outlined in previous articles, we’ve cleaned, checked and machined up the block we had. We bored it and clearanced the bottom of the cylinders a little and then used our theoretical funds to purchase a stroker crankshaft and a custom set of pistons. And, we also acquired a good set of aftermarket cylinder heads. The rest will pretty much be similar to what we would have invested in a higher demand factory performance engine we might have gone out and bought to rebuild.

Our new EngineQuest head. You can see the larger intake ports and lack of exhaust crossover. Our CH318B heads come from the factory with the early “LA” style intake bolt pattern.

Our new EngineQuest head. You can see the larger intake ports and lack of exhaust crossover. Our CH318B heads come from the factory with the early “LA” style intake bolt pattern.

The difference here will be the quality of the new high performance internals and the added cubic inches. We’ll have 50 more cubic inches than a 340, and we’ll be slightly bigger but substantially lighter than a 383. With our 4” stroke and the cam and cylinder head combination, we hope to make power and especially more torque, like a 440 cubic inch Chrysler. And again, we’ll be substantially lighter. We’ll also know that the engine will go right back in under the hood of the car it came out of with no effort.

Like I said, we addressed the machining of the block and the parts for our rotating assembly in the previous issues of Engine Builder.

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Those articles are archived on the magazine’s website www.enginebuildermag.com. (Just search 392 Magnum on the home page.)

This month we’ll address the cam and lifter choice, our cylinder heads, valve train and adjustable rocker arm conversion. These items, more than anything else will determine the performance potential of our combination.

Right from the start I promised to use shelf stock items and the manufacturer’s cataloging and tech to choose our parts. And that’s what we have here.

Last time we introduced you to our EngineQuest replacement cylinder heads for the Chrysler 318 and 360 Magnum engines. We threw in a twist by ordering their alternate “B” head that is drilled on the intake side for the earlier “LA” style early small block.

The EngineQuest castings are a very nicely finished piece right out of the box. Here you can see the valve seats before modification.

The EngineQuest castings are a very nicely finished piece right out of the box. Here you can see the valve seats before modification.

The thought being that it would open up our options for intake manifolds. Or, maybe someone started playing with their 318 and had already changed the manifold to an aftermarket aluminum piece that you wish to continue using.

Another option would have been to use the “Magnum” style intake pattern and possibly some late model fuel injection. This did not fit the model for our project or the premise of the series, but could always be an option for your customer.

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The Engine Quest heads are beautiful right out of the box, and are a “power improve” piece designed to not only replace a cracked factory head, but they will also out flow and out perform the originals. But how interesting would it be to write about a set of “bolt-ons”? Plus, with the added cubes and the desire to obtain muscle car type performance, we’ll need to modify and upgrade them a bit. I need to thank the guys over at EngineQuest again for their donation, and mention the many other suppliers who have contributed to our build, this time in the form of camshaft and valve train.

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It’s no news that the camshaft and cylinder heads must work together to maximize performance. Right out of the box our heads flow enough air to support the kind of horsepower I’d like to see us obtain, but they must also accommodate the upgraded valve train. So we started with a Lunati cam and lifter kit and then we’ll work up to the valve springs and adjustable rocker arm components to support our cam choice.

Here is a comparison of valves. The ones on the left are from the early 318 heads, the valves in the center are stock 318-360 Magnum and our Ferrea competition series valves for GM LS motors are on the right. Decreased weight with increased size and flow.

Here is a comparison of valves. The ones on the left are from the early 318 heads, the valves in the center are stock 318-360 Magnum and our Ferrea competition series valves for GM LS motors are on the right. Decreased weight with increased size and flow.

A quick peak in their catalog finds us a description and some cam specs that I thought matched our goals. After a call to the generous folks at Lunati, they confirmed and donated a cam and lifter kit to meet our needs. We’ll use a cam from their Voodoo Hydraulic Flat Tappet Cam Series.

Our cam specs look strong for a 340-360 cubic inch motor, but should be quite streetable with 392 cubic inches. The advertised duration is 276/284 (int/exh), with 234/242 @ .050’ lift. The cam has a lobe separation angle of 110 degrees, with a 106 intake lobe centerline. Here is where you need to be careful when upgrading to the Magnum heads. Early small block Chryslers used a shaft style rocker arm with a 1.5 ratio rocker.

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Our Magnum heads use a stud-mounted rocker with a 1.6 ratio. The book specs on our cam state .513/.533” lift (int/exh). Our motor will have a higher theoretical lift .547/.569” lift (int/exh). Now I use the word theoretical for a reason. Anyone familiar with the pushrod angle in the small block Chrysler knows that some cam lift is lost on it’s way to the rocker arms. But, we’ll use these figures to make sure we have enough valve spring, enough valve to piston clearance, enough retainer to valve guide clearance and spring travel so we don’t coil bind. The added lift will be perfect to expand the RPM range and feed our bigger motor, while keeping it very streetable.

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Moving back to making our heads work with our cam and rocker choices, we needed to modify our heads a little. Before choosing a spring, I had to determine an installed height. Since we planned on using shelf parts, we turned to Comp Cams to get their Adjustable Rocker Arm Conversion Kit for the Magnum cylinder heads. In the pictures you’ll see a very complete kit designed to make this a bolt together proposition. The staff at Comp were very gracious to donate not only their rocker arm and pushrod kit, but also the spring retainers we’ll need to adapt our springs to our valve choice.

We had to hone the valve guides slightly to fit the 8mm LS stems. ,002” clearance was given to both intakes and exhausts stems.

We had to hone the valve guides slightly to fit the 8mm LS stems. ,002” clearance was given to both intakes and exhausts stems.

There are not at this time many choices for valves to fit the Magnum heads. This is where some experience searching the manufacturer’s valve specs and comparing them to the O.E.M. specs will net you some options. Because we would like to work with the Comp rocker kit right out of the box, we chose to keep our valve length as close to stock as possible. Our choices looked something like this: stock replacement valves for a 318-360 Magnum; bore the guides for the tried and true 11/32” stem small block Chevy valves; or GM LS or Gen III type valves. At this point I had more then basic valve dimensions to worry about. Stock valves will work fine for some builds. They are a very modern design. They have a 5/16” stem diameter and the exhaust valves are quite large at 1.625” head diameter. Since we are running a substantial amount of valve lift and plan on an engine that will be able to see at least 6500 RPM, this did not seem prudent. Stock LS valves are close dimensionally, but have too small a head on the exhaust valves. There are however, great choices to be had in aftermarket LS valves.

Many of you know or have been previously introduced to the owners and employees at our machine shop, Grawmondbeck’s High Performance Engines. Joe Degraw and Stacy Redmond, owners and avid performance enthusiasts, have been more than helpful and completely responsible for the progress we’ve made on our project to date. And I can’t thank them enough. We were introduced to the third man in this group, Steve Tosel, when he donated the core 318 for our project. And he’s been very helpful for me negotiating the ins and outs of the small block Chrysler. Somewhere along the line, I got the message that it would probably be a better idea for me to come up with something besides Chevy valves, if I wanted a Mopar guy like Steve to build our cylinder heads. Enough said. By going with a valve designed for an LS motor, I was able to keep the small stem diameter, 8mm, and find some valves that were just a bit larger than our stock diameters, which will also help feed our larger motor.

At this point we cut the valve seats with a multi-cutter to fit our larger valves.

At this point we cut the valve seats with a multi-cutter to fit our larger valves.

Most of you are familiar with Ferrea Racing Valves. They had just what we needed to adapt a larger one-piece performance stainless steel valve to our street performance heads. Their generous donation to our charity motor build really bailed me out and I need to thank them. Dare to be different also means dare to work through limited availability, and in this case a little politics. Plus, we ended up with a great set of valves that will surely increase the performance potential of our heads and gave us access to additional shelf parts we’ll need to assemble this combination. We increased the size of our intake valves from 1.920” to an even 2.00” while our already substantial exhausts went up slightly from 1.625” to 1.650”. I could have gone larger on the intakes, but since we are working with a slightly smaller bore of 3.950” and did not wish to open up for any shrouding in the combustion chamber, we’ll hold the intakes at 2.00”. Minor work was required as you can see in the pictures.

To finish our heads we choose a set of dual valve springs out of the Engine Pro Performance catalog. The people at EPG helped us with parts for both our short block and rotating assembly, and parts for our heads. Another group we must thank for their generous donation to our cause. The springs are perfect for the cam selection and meet the fairly short installed height of the Chrysler heads. We used a set of Comp spring retainers that I previously alluded to that were designed for a GM LS motor and a set of Engine Pro 8mm 7-degree machined valve locks. Look at the specs in the books. The parts are there for many combinations. We’ll also use an EPG steel clad viton valve seal that will fit the stock valve guide.

Here is the spring seat cutter in motion removing some guide boss to make room for the dual Engine Pro valve springs. The valve seal shoulder remains stock.

Here is the spring seat cutter in motion removing some guide boss to make room for the dual Engine Pro valve springs. The valve seal shoulder remains stock.

You’ll see in the pictures that we did need to hone the valve guides slightly to fit our LS valves and we did cut the step out of the guide boss to make room for the dual spring. A great alternative to the dual spring would be a set of conical springs designed for a small block engine, but the decision to use a dual spring came back to my design of a factory style muscle engine and a readily available performance spring for the small block Chrysler engine.

Block machined – Check. Rotating assembly balanced – Check. Cylinder heads flowed, machined and assembled – Check. Next we’ll address assembly and then we’ll be ready to dyno and see how we’ve done before we offer you a chance to be a part of our final goal. Details will soon be available on how you can purchase raffle tickets and donate to the fund that will ultimately be our donation to the Independence Fund, and our goal to raise money for a high tech wheelchair that can change the life of one of our disabled vets.

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Dare to try something different. Dare to think outside the box. Dare to get involved. Dare to break the rules from time to time.

And, dare to stay tuned for more!

 

Here is the mix of Ferrea valves, Engine Pro springs, locks and seals, and the set of Comp Cams retainers we used for our high performance valve train.

Here is the mix of Ferrea valves, Engine Pro springs, locks and seals, and the set of Comp Cams retainers we used for our high performance valve train.

 

 

 

 

 

 

 

 

 

 

The heads look like they were made for the larger valves after Steve came in with an 80 degree Bowl Hog to blend the new oversize intake seat to the port.

The heads look like they were made for the larger valves after Steve came in with an 80 degree Bowl Hog to blend the new oversize intake seat to the port.

 

 

 

 

 

 

 

 

 

 

These are all the parts you will kit in the Comp Cams adjustable valve conversion kit for the Chrysler Magnum heads.

These are all the parts you will kit in the Comp Cams adjustable valve conversion kit for the Chrysler Magnum heads.

 

 

 

 

 

 

 

 

 

 

We CC’d our combustion chambers and found them to be 64cc with our new valves. This should put us right about 9.4:1 compression ratio.

We CC’d our combustion chambers and found them to be 64cc with our new valves. This should put us right about 9.4:1 compression ratio.

 

 

 

 

 

 

 

 

 

 

 

 

 

Comp Cams studs and guide plates installed. These special studs convert the 5/16” bolt-down factory rockers to a 3/8” stud mounted 1.6 ratio roller tip rocker.

Comp Cams studs and guide plates installed. These special studs convert the 5/16” bolt-down factory rockers to a 3/8” stud mounted 1.6 ratio roller tip rocker.

 

 

 

 

 

 

 

 

 

 

Lunati Voodoo series cam kit. Hydraulic Flat Tappet Cam. Hot Street cam, likes 2800 converter, Hi-Rise type dual plane intake with 750cfm carb, headers, 10:1 compression and 3.73 gears. RPM Range: 2200-6400 Likes up to 200HP nitrous.

Lunati Voodoo series cam kit. Hydraulic Flat Tappet Cam. Hot Street cam, likes 2800 converter, Hi-Rise type dual plane intake with 750cfm carb, headers, 10:1 compression and 3.73 gears. RPM Range: 2200-6400 Likes up to 200HP nitrous.

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