We've finally reached a point with our Diplomat police car where we canuse a couple hundred more horsepower. Instead of diving into the innersanctum of the 318 now residing between its framerails, we opted tostick a slightly used 360 we had laying around into the interceptor. The360 is from another project car of ours and features a 10:1 compressionratio, an otherwise stock bottom end, a fairly aggressive hydraulicflat-tappet cam, and a pair of mid-'70s 360 smog castings outfitted with2.02 intake valves. Equipped with an Edelbrock Performer RPM Air Gapintake manifold and a 750-cfm Demon carburetor, this little gem knockedout 418 horses and 443 lb-ft of torque on a conservative (stingy wouldbe a better word, actually) dyno. The engine is stout enough to powerour '68 Barracuda project car into the high 11s at 114 mph. So it'sdefinitely up to the task at hand. But we made a couple of changes tothe 360 to make it more compatible with the girth of the '89 M-Body. Thecam would have to go, as it didn't pull enough vacuum at idle to run thepower accessories, and believe us when we say a 3,800-pound vehicleneeds a lot of braking power to haul down from extra-legal speeds. inits place went a mild Crane hydraulic to boost low-rpm torqueproduction. Also, all of the accessories including the intake with Q-Jetcarb would be swapped over to the new engine, as well as the restrictiveexhaust system. Baring any complications with lean-burn compatibility,the Q-jet would remain. The Dippy would then be chassis dyno tested withthe old system and then retested with the new high-flow system todemonstrate the benefits of a good high-performance exhaust system.
No mincing of words necessary. With the hi-po 360 installed between thefenderwells, the lean-burn system wouldn't run right to save its life.Timing changes just didn't seem to make any difference in the way itran. In fact, the car felt outright flat in the power department. Thedecision was made to address the ignition first. so we called ourbuddies at Glendora Dodge for a Mopar Performance electronic-ignitionsystem that comes complete with an orange ECU, a vacuum-advanceelectronic distributor, and a wiring harness to tie it all together.Next on the chopping block was the carburetor. We were never quite atease with the feed-back Quadrajet perched on the Diplomat's intakemanifold, and it ran poorly enough to give us an excuse to try the800-cfm Competition Thermoquad that's been taking up space in ourgarage. Plus, the TQ just looks right.
Pistons: Federal-Mogul TK hypereutectic pistons
Cam specs: 216/228-degrees duration at .050-inch valve lift,.484/.512-inch lift with Crane 1.6:1 ratio rocker arms (.454/.480 with1.5:1 rocker ratio), 112 -degree LSA
Cylinder heads: Aerohead reconditioned "578" castings with2.02/1.60 valves
Induction: Factory cast-iron spread bore with 800-cfm CarterThermoquad carburetor
Exhaust: Factory exhaust manifolds, 3 catalytic converters,single 2-inch exhaust
Out with the old, in with...
Out with the old, in with the new. The tired, but still potent 318 cameout with nary a whimper to make way for some torque production.
The 360 was procured from...
The 360 was procured from our '68 Barracuda project car and was good fora conservative 418 horsepower and 443 lb-ft of torque. With pump gas andshifting at a leisurely 6,200 rpm, the Barracuda consistently coveredthe quarter-mile in the high 11's at 114 mph and 7.40s at 92 mph onIrwindale Raceway's ultra-sticky eighth-mile.
Our 360 required a cam swap...
Our 360 required a cam swap for the engine to be a viable performer. Theold cam featured 242/252 degrees of duration at .050-inch valvelift,producing a whopping 3.5-inches of vacuum at 850 rpm. This cam andpower brakes would amount to suicide on a power-brake-equipped car. Asuitable replacement was pulled from Crane's Powermax line of hydrauliccams (PN H-272-2) featuring a more suitable 216/228-degrees duration at.050 and .454/.480-inch lift at the valve. The hydraulic lifters alsocame from the Crane parts catalog.
The hardened 5/16-inch heavy-wall...
The hardened 5/16-inch heavy-wall pushrods are also Crane units (PN99756-1). they are stronger than stock and should not deflect.
To bolster the new cam's performance,...
To bolster the new cam's performance, we installed a set of Crane Goldroller rocker arms, shafts, and spacers (Kit PN 69791-1) with a 1.6:1ratio providing the small cam with even more lift to the tune of.484/.512-inch lift over .454/.480-inch lift with 1.5:1 rocker arms.
In order to swap a 360 in...
In order to swap a 360 in the place of a 318, some differences need tobe addressed. The driver-side motor mount on a 360 (and 340) has a widerbracket than the 318, but the bolt hole is in the correct location,necessitating a shim to make up the space differential. We located anold alternator spacer, measured, and cut it to length.
The 318s are internally balanced...
The 318s are internally balanced engines featuring neutral-balancedharmonic balancers and flex plates, but 360s are externally balanced. Weused a B&M SFI-certified flex plate in our Barracuda with great success.Our unit was for a 727, while our Diplomat uses a 904 trans. the 727flexplate (PN 10236) is quite a bit larger than the unit for the 904trans (PN 10239) and cannot be used on a 904-equipped vehicle ,as theflex plate will not clear the smaller ring gear.
We got this high-capacity,...
We got this high-capacity, mechanical fuel pump from Holley (PN12-360-11). we wanted to maintain the basic layout of the car withoutdelving into the fuel system. this mechanical pump is more than adequatefor our potential performance level--rated at 110 gph (gallons perhour).