Rebuilding The 360 Short-Block Engine - Necessary Improvements

It all started one afternoon when I returned home from the office. I was getting ready to back the Valiant into my parking spot when the engine mysteriously stopped running. "That's funny," I thought, until I tried to restart the engine. Then I heard the sound of a freewheeling engine that has no compression. After I pulled the No. 1 spark plug and brought the No. 1 cylinder up to the top of the compression stroke, removal of the distributor cap confirmed my suspicions-timing jumped.

The part that bothered me the most is I was unable to get to the dyno before this happened, and baseline numbers of our seasoned engine are unavailable. Oh well, I guess we'll wing it. The 360 in the Valiant is a '71 model that came with a two-barrel carb, 1.88 and 1.60 intake/exhaust valves, and 8.8:1 compression ratio. Peak horsepower was rated at 255 at 4,400 rpm, and 360 lb-ft of torque at 2,400 rpm-definitely not setting the world on fire with performance.

Assessing The Carnage
After we loaded the car on the trailer and got it to the shop, a decision needed to be made: "Do we fix the engine in the car, or take it out?" When I finally reasoned with myself and came to the realization that the engine is an "interference engine" (meaning if the timing chain "jumps", valves will hit pistons), I decided I'd better just pull it. With the engine finally out and on the engine stand, I removed the intake and heads. As soon as the heads were placed upside down on the workbench, I knew it was bad. Every exhaust valve was bent. Worried, I checked the pistons. The carbon buildup on the pistons had quite possibly saved me from piston damage. Only small marks were visible on the pistons and were easily removed. The next question was, how much compression ratio did I lose by knocking the carbon off of the pistons (yep, it was that thick)? Further parts removal, like the balancer, water pump, and timing chain cover, revealed the stock plastic timing gear was now a smooth wheel.

With the top half of the engine on the workbench, it was time for a game plan. Where do I go from here? Do I just replace the bad pieces and put it back together? Not hardly. I decided it was time to put at least a decent top end on the short-block. After all, the engine didn't use oil, had good compression, and the oil pressure was 45 pounds at idle. Nah, let's rebuild the top, add a few aftermarket pieces, and see what happens.

Planning For Improvements
First of all, we knew we needed to replace the exhaust valves. A quick check on the parts shelf netted the required pieces-no need to buy valves. The camshaft was the original piece with enough miles on it to make anyone wonder how many would be left. So we needed a cam. If we're changing the cam, we would need springs as well. With very little coaxing, we decided on a big stick. What about headwork? If we shave some metal off of the heads, we could bump up the compression a little. If we did a little port work, we could make them flow better. Decision made: Headwork was a must. What about the intake and carb? The intake we had been using was an Edelbrock Performer. While this is a good dual-plane intake for engines making power in the idle-to-5,500-rpm range, we wanted to twist this one a little farther than that. The carb we had was a Holley 4150 model with a 650-cfm flow rating from Holley's HP series. Decision: We needed to change the intake, but the carb could stay. We were planning to twist our 360 up to the 6,000-rpm range. With the stock rods and pistons, we thought that would be close enough to the edge without crossing the line into destruction. With that in mind, we decided on a camshaft from Lunati. Camshaft No. 07402 is a hydraulic flat-tappet piece with a 2,500-6,200 rpm range, a .285/.285 advertised duration, and .235/.235-degrees duration at .050. Lift comes in at a hefty .507/.507-inch, with a 104-degree centerline, and a 108-degree lobe separation. Let's not get into a debate whether it's streetable; that's what we chose. The Lunati we chose is comparable to the MP 509 stick, but has a little less duration at .050, with its .235 as opposed to the MP's .248.

Porting 101
The "J" heads that our 360 has are the same basic heads as the highly sought after "X" heads, with the exception of a 1.88 intake valve instead of a 2.02. Even with its fairly good airflow capabilities for an engine of this nature, a little port work consisting of gasket matching and removing some of the "pinch" at the pushrod location was about all we were going to do. To save a little money, I did the basic porting myself. Then the heads were given to Jerry Wilt at Wilt Engine Services in Lakeland, Florida. We had Jerry shave .020 inch from the deck surface. Any more than that and the possibility of intake alignment becomes an issue. We also needed the new valvesprings installed and the guides machined for new positive locking seals. The reason the guides needed machining was the stock valvesprings are a single spring and the Lunati springs for the new cam are a triple spring. Room needed to be made for the smaller inner diameter of the spring and the positive locking seals as apposed to the stock umbrella-type seals. Also, since we are using "seasoned" valves, a three-angle valve job wouldn't hurt either. We also got new retainers for the springs and then had Jerry assemble the whole mess.

Piecing The Puzzle Together
With all the pieces back at the shop, it was time to put it all back together. We first installed the Lunati cam and degreed it in according to the cam card. Next, we used Fel-Pro head gaskets (PN 1008) with a crush thickness of .039 between the block and the heads. The pistons are around .080 in the hole, and in hindsight, the MP Gaskets (PN P4120094) may have been a better choice. The MP gaskets have a crush thickness of .024-.028. That would have bumped the compression just slightly higher and helped the quench a little. With the heads bolted back on using the stock head bolts, the intake-a Weiand X-CELerator single-plane PN 7545-was gasket matched and installed. The X-CELerator is a good intake for the 1,500-7,000 rpm range, and the square-bore mounting flange meant we wouldn't need an adapter plate to mount the carb.

Was It Worth It?
After the engine was reassembled and put back in the car, it was time for some dyno thrashing. We spent the day at Norris Motorsports in Ocoee, Florida, on Mike's Dynojet chassis dyno. With some simple tuning, we had to settle for 292 hp. There is definitely more horsepower in the engine, and I think our cam choice may have something to do with these numbers. Not that the Lunati cam is the issue. On the contrary, our choice of a 235 duration at .050 is the factor; another time where the advise of the cam manufacturer should have been asked. On the plus side, when we upgrade to a better set of heads, this cam will be more at home. With our J heads sporting a 1.88-inch intake valve, there is definitely a bottleneck hampering the flow. We surmised this by the peak horsepower coming in at around 5,000 rpm. Our first pass gave us baseline numbers of 242.3 hp at 5,000 rpm, and the torque numbers were 284.1 lb-ft at 3,000. With some simple tuning, we increased those numbers to 251 hp at 5,000 rpm and 291 lb-ft of torque at 3,600. That's an increase of 9 hp and 7 lb-ft of torque. Minimal maybe, but when you factor in that the factory rated this engine at 255 hp at the flywheel, we increased the numbers at the rearend to mimic the factory flywheel numbers. If you factor in the parasitic loses through the tranny, the Gear Vendors unit, and the rearend, we did improve our little 360. We wanted to hit the spray while on the dyno, but I forgot to bring the guide that let me know what jets to install for each horsepower shot of nitrous. So, in the interest of not installing the wrong jets and melting down a piston, (or having a loud "ka-boom" come from under the hood), we left the 75hp jets in and gave it the old winder-up-and-try-it blast. This time, the junkyard engine responded with 292 hp at 4,900 rpm, and 367 lb-ft of torque at 3,300. Sure, the numbers may be a little soft, but keep in mind that the bottom-end of this engine is 30+ years old, and a beating is a beating. It handled it nicely. Next, maybe we should try a good set of heads, and let this seasoned veteran breathe a little better. Sounds like a plan to us.

Dyno Run 001
2,500 - 5,500 rpm
Barometric Pressure 30.19 inches
Intake Temperature 86.6 degrees
Jetting: 76/79
No carb spacer
Timing 34-degrees total

Dyno Run 007
3,000 - 5,500 rpm
Barometric Pressure 30.23
Intake Temperature 91.2 degrees
Jetting: 72/72
1-inch tapered four-hole spacer
75hp nitrous
Timing: 34-degrees