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INJECTED DESOTO HEMI FOR THE STREET
I'm in the middle of building a 1957 Desoto 341 hemi and am utilizing parts from other engines when available. Photos and text will be added as the project moves along. Some of the information will be added, removed, or modified and anyone with more info to share can email it to me and I will add it to this site. Everything here could be wrong for all I know, so anyone willing to offer up more technical advice are more than welcome to email me with it and I'll post it. Gene Adamms, Don Enriquez, where are you when I need you?. The turbos are from the single turbo non-intercooled Nissan 300 ZX from the mid 80s. My goal is to build an engine twice the size of the Nissan 300 ZX, with twice the power and 1000 lbs less total weight as compared to the original 300. The Nissan actually weighed as much as my 69 Road Runner. The engine will operate with as much as 15 lbs of boost rather than the 7 lbs used in the 300. The 300 made 222 HP at 7 lbs boost so 500 HP should be no problem. The engine will sit in a 1967 Plymouth Valiant. It is a draw thru system using a pair of Holley 600 CFM carbs. The tranny is a well built 727 with 5-1 kickdown lever, cast iron band, and all HEMI internals. The torque converter is a Hughes 3000 stall. As a starting point the engine was bored .060" oversize which will give a total of 352 cubes. Just slightly larger than the 5.7 Hemi of 348 cubes. The crankshaft was ground .010" under and polished for an extra .00025" clearance. The book calls for a clearance on the rods and crank of .0005"-.0015" which is OK for a low power long haul engine, but for higher performance more clearance is desired. The rods are Eagle chromoly H-beam forgings with 7/16" cap screws meant to go on a big Pontiac engine. The width of the Pontiac engine is the same as the Chevy 327 at .940". The Desoto is .930", so .010" were removed at the machine shop utilizing a precision grinding machine. Don't try it with a mill unles you're sure you can keep the fine surface given by a grinder. The sides of the rods should be as straight and smooth as the crankshaft itself. The rod length is 6.625" which is the same as the Desoto tall blocks. The pistons I'm using are Ross forgings with an approximate compression ratio of 8-1. The piston deck height is .045" whereas the stock pistons with a comression ratio of 9.25-1 had a piston deck height of .012". The pistons were fitted with pins to match the rods and the rods are bronze bushed with 3 oil holes in the small end. Although Ross supplied spirolocks with the pistons, I'm all thumbs and ended up using 15/16" internal snap rings available from McMaster Carr out of Chicago. The rings are standard cast iron as chrome has a tendancy to wear away at the cylinder walls. These old engines are getting hard to find and I'd rather change rings than to have to rebore the engine down the road. The pins are standard size Pontiac. I made casting plugs for the timing cover, intake manifolds, and turbo connector. The lost wax casting method was used as I would take the finished wax cores to the foundry. This was done before Hot Heads came out with there product line. I had intended to sell the timing covers, but the foudry owner has died and Bob Walker can handle that now. Mine takes a new style 318-360 water pump and being aluminum weighs only about 4 lbs. The distributor is an aftermarket HEI unit that has more power than the standard GM units. Hot Heads has the adapter for those. I had to shorten mine to clear the intake log ram pieces. If you have the old dual point distributor, turn it into a paper weight and go with the newer HEI distributor. The cam is an Isky Mega Hydra Turbo 270 cut from a stock core. The lift is .465" and the duration is 270 degrees and is hydralic. The timing pack is a double roller chain set for a 360. The pushrods are 3/8" adjustable from Hot Heads. The lifters are 67 Mopar 383. They're getting hard to find and the price at Auto Zone is now about $30.00 each. Just get a set at Hot Heads. Be careful when going with aftermarket lifters and pushrods. The stock early hemi pushrods use a 1/4" ball end and when using modern lifters, you'll find that the socket in the lifters take a 5/16" ball. When ordering pushrods be sure to get the right ends. Bob will ask for the specifics. The 3/8" rods have adjustable ends and are much lighter than the stockers.
The block wasn't too hard but the heads were a little tougher. The heads flow as well if not better than any of the stock small block Chevy heads, but do have their drawbacks. For one thing the tall block heads have a rather odd balance between the intake and exhaust. This is true of most of the early hemis with the exception of some Dodges. The best rule of thumb is that the exhaust flow 80% of what the intake can flow at the same vacuum. If you notice all the tech talk going on in the hot rod world, you'll notice that a common theme is 2.02" intakes and 1.60 exhausts. On the tall block Desotos it is 1.94" X 1.75" with the exhaust ports being very large. Guys used to grind out the exhaust ports thinking that if the ports were bigger, the exhaust would get out easier making more room for the fresh charge. Actually all that did was cause fresh intake charge to be scavenged out the exhaust. Cam grinders got it figured out and the real trick was to open the intake and let combustion pressure do it's work on the exhaust. The 291 heads have a better ratio of 1.84" X 1.50" and the exhaust ports would work better on the tall block motors on gas. The larger exhaust ports on the latter heads work great with nitro where fuel and oxygen come in as a liquid and then after burning, act like the combustion gases from a much larger engine. To get my heads more balanced I opened up the intake ports to the max even cutting through the pushrod tunnels in a manner used back in the 60s known as "tubing" Afer the throat area was opened up and the pushrod tunnel walls appeared, I went no further. Then thin wall brass tubing was sleaved into the pushrod tunnel with JB Weld. The exhaust ports were cleaned up and the thick valve guide bosses were streamlined.
The valves ended up being 2.02" X 1.73" and here's how I did it. The stock valves have a stem of 3/8". By using Chevy 2.02" intakes with the 11/32" stem, the machine shop was able to install thin wall bronze guides. So much for the intake. The exhaust was a little tougher. I got a set of Pontiac 1.77" high performance units and cut off .040" diameter on the lathe. These valves are hard and will require a carbide cutter. The end result of 1.73" was to give more valve to valve clearance than anything else. Hardened seats were used and they too were for the Pontiac valves. Here's why!. The 440 Mopar seats will fit, but they have a greater thickness around the diameter and by putting them in the port there is a lip on the underside of the seat that will interupt flow. The Pontiac seats have a much thinner wall and when installed will give a nice smooth transition into the throat area. The machine shop guy will have to regrind the valves after the diameter has been reduced to make sure that the seats are concentric. The springs are Crane and are part no. 36308-1. They fit 62-89 Ford 221-351 CI. They also fit the Olds 260-455. The set includes chromoly retainers. (I may go with the new "beehive" style springs on my 330 as they'll rev higher with the same spring pressure.) If using a stock or reground stock core set the initial spring pressure at 100 lbs and after a bit they will settle in to being the recommened 90 lbs seat pressure. Go with the Chevy retainers and you're done. Bob Walker can harden your rocker shafts which is desireable when using high performance springs. Don't go too crazy with the spring pressure on these old cams or you'll ruin it. Ever so often there's a roller on ebay. Get it as it is much better material.
As far as oiling goes, mine has a new pump for a 56 Chrysler 354. It flows nearly as much as the Milodon high performance that guys are adapting to their old hemis. If you can't find one, get the Milodon unit from Hot Heads. Be sure to check the clearances for the sump.
I did make a timing cover to accept the late small block water pump. 2 of the bolts that hold the cover to the block are hidden by the pump.
One thing I'm considering is to go with a reverse flow cooling system to increase the octane ability of the engine. If you look closely at your intake manifold you'll see that there is only one coolant outlet on each side. Coolant flows in through the front of the block through a pair of ports and flows backwards until it exits up through each of the ports. On one side the outlet is close to the front of the block and on the other side of the engine the coolant outlet near the back. The one which is closest to the front I find troubling since the water at the back of the block doesn't get circulated out as fast. It has time to just linger getting hotter and hotter. Can you say ping! ping! ping!? On the next engine I will just use a 318 timing cover. The front of the engine will have a 1/8" aluminum plate covering the entire front of the block. It will block off the upper water ports on purpose. Down below on the front of the block is a set of identicle ports that are normally coverd by the factory timing cover. On the top of the 318 timing cover there will be a pair of holes that will each have a 1" aluminum tube coming out straight up. On each will be a coolant hose that will go above each manifold flange and from those will be a pair of hoses that will go into the heads not only in the original locations, but also into the areas previously ignored. 4 ports now instead of only 2. This coolant will now have come right off the radiator rather than having been heated from the cylinders first. Now for the 2 lower block ports. On the aluminum plate covering the block there will be a pair of small thermostat housings maybe from an import or 2.2 Dodge. From there the coolant hoses can connect together and head upward to the top radiator outlet. Basically the radiator hoses will criss cross each other in front of the block with the hot glycol coming out the bottom of the block and heading up to the top of the radiator and the cool stuff coming out the bottom of the radiator and heading to the top of the engine. Should be worth 1 extra point of compression.
I opted to use the A-727 traany for this one, but in the future may go with a 350 Turbo Chevy unit. Here's why. By using the Chevy system you can use the Chevy HEI distributor which hooks up to the computer and by using the Chevy tranny, you'll have the proper harness hook-up to the computer. Plus you can eliminate that annoying throttle pushrod to the carb. It's all about keeping it simple.
Now one would think that using a 7.5 compression engine would be a waste, especially since the stock rods aren't exactly considered high performance stuff. Here's what you can do on this end. The crankshaft has an odd rod journal size of 2-1/16" diameter and there are no aftermarket rods available. The crankshaft will be offset ground down to 2" Chevy size. The offset will net a 1/16" gain in stroke and with a .060" overbore the cubes will be 305". Can you say "5.0 HEMI"? I knew ya could. Now you run down to your local speed shop and grab a set of 6" small journal Chevy rods, do the math to check for piston pin height and let the guys at Ross make you a set of 10-1 forged slugs. Get some header flanges on Ebay and build yourelf a set of block hugger headers with O2 sensor fitting and you're there dude. In a swinger or Duster this could a very fun machine. A real 5.0 Mustang buster! PS! Since starting this page I've taken off the carb system and gone with Hilborns with electronic injection along with much larger turbos and intercooling. The turbos are T3/T4 hybrids with the compressor inlets at 58 mm diameter. Each are good for about 600 HP. A pair of intercoolers are in front of the firewall and clear the grill after some modification. The original grill looks like crap and gets in the way of the intercoolers, so I got a 69 grill and hood assembly which made things a lot easier. The runners above the Hilborns are 4 inch aluminum with 2-1/2" aluminum tubes running down to the Hilborn tube flanges. A pair of 65 mm throttle bodies are in front of the 4" units and recieve air from the intercoolers. Since the turbos now sit further down and away from the block, the air filters are actually stuck out into the fenders in front of the tires. Holes were cut in the inner wells and dams will now sit in front of the tires to keep out dirt and water. Cold air is a must even with intercooling here in Arizona since summertime temps over asphalt here can run as much as 140 degrees. The injectors are 72 lb units. The injection controls are from Megasquirt. It is the V3 unit. The fuel pump is an Aeromotive and will draw fuel through the new 1/2" fuel pickup available from Mancini. The Chevy style HEI distributor has been replaced with the Joe Hunt mag that has been converted to Pertronics ignition. Had to do this since the HEI unit wouldn't clear the Hilborns. There is a pair of blow off valves just before the throttle bodies. Had to go with 2 since the equalizer is after the throttle bodies. I wanted to get a set of of 4-bolt mains from Pro Gram engineering and added for more depenability, but it turns out that they only do them for the 276-291 motors. The main webs on these motors are quite thin and not quite on center with the bolts on the mains. Therefore the outer bolts are offset slightly to the front or back and are only 3/8" to keep from breaking through the web. Unfortunately my new computer hasen't been able to transfer or edit the existing photos, so a new page may be added later. If you'd like a photo of the newer setup please feel free to email me at crossram5@aol.com. Also at crossram5@msn.com. My name is Bill and I live in Tucson Az.
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