We've finally reached a point with our Diplomat police car where we can use a couple hundred more horsepower. Instead of diving into the inner sanctum of the 318 now residing between its framerails, we opted to stick a slightly used 360 we had laying around into the interceptor. The 360 is from another project car of ours and features a 10:1 compression ratio, an otherwise stock bottom end, a fairly aggressive hydraulic flat-tappet cam, and a pair of mid-'70s 360 smog castings outfitted with 2.02 intake valves. Equipped with an Edelbrock Performer RPM Air Gap intake manifold and a 750-cfm Demon carburetor, this little gem knocked out 418 horses and 443 lb-ft of torque on a conservative (stingy would be a better word, actually) dyno. The engine is stout enough to power our '68 Barracuda project car into the high 11s at 114 mph. So it's definitely up to the task at hand. But we made a couple of changes to the 360 to make it more compatible with the girth of the '89 M-Body. The cam would have to go, as it didn't pull enough vacuum at idle to run the power accessories, and believe us when we say a 3,800-pound vehicle needs a lot of braking power to haul down from extra-legal speeds. in its place went a mild Crane hydraulic to boost low-rpm torque production. Also, all of the accessories including the intake with Q-Jet carb would be swapped over to the new engine, as well as the restrictive exhaust system. Baring any complications with lean-burn compatibility, the Q-jet would remain. The Dippy would then be chassis dyno tested with the old system and then retested with the new high-flow system to demonstrate the benefits of a good high-performance exhaust system.
Lean-Burn Sucks
No mincing of words necessary. With the hi-po 360 installed between the fenderwells, 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 it ran. In fact, the car felt outright flat in the power department. The decision was made to address the ignition first. so we called our buddies at Glendora Dodge for a Mopar Performance electronic-ignition system that comes complete with an orange ECU, a vacuum-advance electronic distributor, and a wiring harness to tie it all together. Next on the chopping block was the carburetor. We were never quite at ease with the feed-back Quadrajet perched on the Diplomat's intake manifold, and it ran poorly enough to give us an excuse to try the 800-cfm Competition Thermoquad that's been taking up space in our garage. Plus, the TQ just looks right.
The Department of Corrections
In our May installment of Stealth Bomber, we ommitted listing the vendors involved, so here they are.
- Just Suspension
- Fairfield, NJ
- (973) 808-0066
- Koni Shock Absorbers
- Hebron, KY
- (859) 586-4100
- Sleeper Suspension Development
- La Verne, CA
- (909) 392-8886
Engine Specs
Displacement: 365 ci
Compression Ratio: 10:1
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 with 1.5:1 rocker ratio), 112 -degree LSA
Cylinder heads: Aerohead reconditioned "578" castings with 2.02/1.60 valves
Induction: Factory cast-iron spread bore with 800-cfm Carter Thermoquad 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 came out 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 for a conservative 418 horsepower and 443 lb-ft of torque. With pump gas and shifting at a leisurely 6,200 rpm, the Barracuda consistently covered the quarter-mile in the high 11's at 114 mph and 7.40s at 92 mph on Irwindale 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. The old cam featured 242/252 degrees of duration at .050-inch valve lift,producing a whopping 3.5-inches of vacuum at 850 rpm. This cam and power brakes would amount to suicide on a power-brake-equipped car. A suitable replacement was pulled from Crane's Powermax line of hydraulic cams (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 also came from the Crane parts catalog.
The hardened 5/16-inch heavy-wall...
The hardened 5/16-inch heavy-wall pushrods are also Crane units (PN 99756-1). 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 Gold roller rocker arms, shafts, and spacers (Kit PN 69791-1) with a 1.6:1 ratio 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 to be addressed. The driver-side motor mount on a 360 (and 340) has a wider bracket than the 318, but the bolt hole is in the correct location, necessitating a shim to make up the space differential. We located an old alternator spacer, measured, and cut it to length.
The 318s are internally balanced...
The 318s are internally balanced engines featuring neutral-balanced harmonic balancers and flex plates, but 360s are externally balanced. We used 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 727 flexplate (PN 10236) is quite a bit larger than the unit for the 904 trans (PN 10239) and cannot be used on a 904-equipped vehicle ,as the flex plate will not clear the smaller ring gear.
We got this high-capacity,...
We got this high-capacity, mechanical fuel pump from Holley (PN 12-360-11). we wanted to maintain the basic layout of the car without delving into the fuel system. this mechanical pump is more than adequate for our potential performance level-rated at 110 gph (gallons per hour).
Cars used for open-road racing...
Cars used for open-road racing (there's a big group) need to have a windage tray to help control oil and to free up horsepower. Since the 360 did not have one, we opted for a Milodon unit (PN 16250) and the corresponding stud kit (PN 81151). Installation was a snap, and the remainder of the bottom end was buttoned up with a Milodon stock replacement oil pan. Milodon's replacement pan features some baffling to help control oil during hard launches or cornering.
Prior to dropping the bigger...
Prior to dropping the bigger mill into our M-body, we took the opportunity to clean, detail, and paint the engine bay.
The Stealth Bomber is equipped...
The Stealth Bomber is equipped with poorly flowing manifolds dumping into a pair of pre-cats, which feed into a catalytic converter farther down range and then a muffler. Restrictive doesn't begin to describe this exhaust system.
We made the decision to retain...
We made the decision to retain the stock intake. Despite the obvious weight penalty it offers, it is a good unit-much like the 340 intakes of yore. Our cam selection was based on peak horsepower in the 5,100-rpm range, making the stock intake a suitable choice.
Installed and running, it...
Installed and running, it was time to address the lean-burn system and rectify its shortcomings. In other words, it was being 86'd.
An MP electronic-ignition...
An MP electronic-ignition kit (PN P3690426) was procured from Glendora Dodge and came equipped with an orange ECU, a vacuum advance distributor, and a wiring harness. The complete kit is a bargain and simple to install. The "orange box" ECU, as it's affectionately known, is purportedly good through 6,000 rpm, which more than covers our planned rpm range.
Our police cruiser was equipped...
Our police cruiser was equipped from the factory with a Quadrajet. This was not some sort of heresy, as all Mopar squad cars were equipped with Q-jets from 1985 until 1989 when the Thermoquad production ceased. This particular unit is a feedback, computer controlled unit. It was a Pandora's box we were unwilling to open.
The Thermoquad is right at...
The Thermoquad is right at home on a Chrysler product. Much like the Quadrajet, the TQ has small, responsive primaries and manhole-size secondaries offering great part-throttle response and a huge kick-in-the-pants when the secondaries open.
Besides, a Thermoquad just...
Besides, a Thermoquad just looks right on our Dippy.