DODGE DART Swinger
Can I Do To My 318?
The mild but spirited 318 combo
318 can be an impressive performer. Start by getting the following books:
Mopar Performance catalog, Mancini Racing catalog and HP Books How to
rebiuld your small block Mopar. So, we'll start with the readily
available 1970-1980 318 as a base. These are about 8.5 to 1 compression
motors with flat top pistons. These pistons have a compression height of
1.740" from pin centerline to piston top. For the economy back yard
performance motor, the factory flat top pistons can be reused. There are
also several inexpensive cast pistons on the market to raise the compression
up to 9 or 9.5 to 1. If upgrading to these pistons, have the block bored
.020" or .030" over at your local machine shop for new oversize
For the heads, you have about 3 routes to go here. The original heads can be reworked. Have them checked real close as cracked heads from the late 1970's are not uncommon, especially from the lean burn motors. The small valves will have to be replaced with larger valves from a 360, 1.60" exhaust and 1.88" intake. Mancini Racing has inexpensive stainless valves in stock which are perfect for this upgrade. Have your machine shop recut the valve seats in your heads for the new valves, be sure to get a high performance valve job which has a 70 degree throat cut(some shops use a 65 degree cut which is o.k.). When you get the heads back from the shop, take a look in the throat below the valve seat. Where the throat cut ends at the casting, smooth out this transition with a dremal tool or drill with port polishing sanding rolls. Not too much but smoothing this helps flow a bunch. The best head choice would be the swirl port 318 head (casting 302) made from about 1985 thru about 1991. The 302 casting has a closed chamber that is heart shaped. This is the pre magnum head. Again, treat it like the above 318 head. The 360 head is another chioce. There are tons of these available from the 1970's and are pretty cheap. Keep the small 1.88" valves as port velocity will be higher than changing to the 2.02". Have a competition valve job done, clean up the throat as above. Now the 360 heads have a much larger combustion chamber volume, averaging around 72 cc vs. the 318's 63-65cc. You will have to get these heads milled a bunch to keep what compression you had. Without milling the heads, you'll end up around 7.8 to 1 compression(absolutely no ping though!). So, how much to mill? For each .0048" milled, you remove 1 cc. Looks like you need 7cc removed which is .034". I suggest going to .040" Now as the heads surface is milled, the ports get closer to each other since they are installed on a V engine. Have the intake surface of the heads milled .0095" for each .010" milled from the head/block surface. This will keep the ports in line. Which ones to use? The #302 swirl port castings are the best choice for a mild 318 buildup if you are having them ported. If you are going the un-ported route, go with the 360 heads but have them milled.
For the intakes, it depends on which heads you use. If you use the 318 heads which have the small ports, you should use a small port intake for a smooth transition. The Edelbrock Performer is the best choice. If you use the 360 heads, there is only three good choices: MP M1 dual plane, Edelbrock RPM and the factory iron 4 bbl. I would suggest the M1 since it produces more torque and mid range.
Well, there are a million cam choices out there. The two I would suggest are the following Mopar Performance cams:
P4452759 .430"/.450" lift, 260/268 duration
P4452761 .450"/.455" lift, 268/272 duration
Both of these cams have a lobe seperation angle(LSA) of 110 and a 108 intake centerline(ICL). The "759" cam was developed to make more torque than the original 340 grind with the same horse power. The "761" cam was developed to make the same torque as the 340 grind but more h.p. Make sure you degree the cam in, very important. The 108 ICL is the installed point the factory suggests. My cam choice would be the "761". It will have a lope idle. Be sure to use a dual chain/gear set and match the valve springs to the cam choice. Either of the above cams can use 340 replacement valve springs or Mopar Performance P4120249.
Again there are tons of choices. The Holley 600 (1850) or 750(3310) vacume secondary is a popular choice. My favorite would be an AVS Carter, they are user friendly. A TQ from a 340 will do well, be sure it is from a 340 or install 340 rear jets(around .126" I think). Carter AFB or Edelbrock Performer carbs are easy to work on, run great and are available new.
Headers are a must. The 318 works well with the economical "fit all" type with 1 5/8" primary tubes. Be sure to use 2 1/4" dual exhaust with high flow mufflers like Walker Super Turbo or Flowmaster Mufflers.
The Mopar electronic ignition is a great system Do not use the lean burn system. Recurv the ignition by installing two light springs in the distributor in place of the factory springs. These springs can be gotten from MP as P4007968. Also use the "orange box", P4120505. Set the ignition at 35 degrees total. Use the MP timing tape on your dampener, disconnect the vacume advance, bring up the rpm to 2,500, set the 35 mark on the dampener to the -0- mark on your timing cover. When finished, be sure to reconnect your vacume advance.
DYNO TESTED 318
The proof is in the dyno testing. This engine really performs well and produces the same power as a high compression 340.
Mid 1980's non roller cam 318, rebuilt with stock crank and rods. Arp rod bolts added when the rods were reconditioned. Crank turned .010"/.010". Flat top cast pistons were used. After the block and heads were milled to true up, a 9.2 to 1 compression was achieved. The heads are the #302 swirl port casting from a 1987 318. The heads have the larger 1.88"/1.60" valves installed, competition valve job and were treated to a full professional porting job. Intake is the Edelbrock Performer. Carb is the Holley #3310 750cfm vacume secondary. Headers are basic fit all 1 5/8" primary tube. Cam is the Mopar Performance P4452761 with .450"/.455"lift , 268/272 duration. timing was set at 35 degrees total for the dyno test.
330 horse power @5750rpm.
How does that sound? The exact motor was also dyno run with 360 heads installed and it produced 290 h.p. @5750 rpm. That shows how port velocity is so important. But...290 h.p. is no slouch for a 318. Most of the same information presented here can be applied to the 273.