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.
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.
With the engine out of the...
With the engine out of the car, we pulled the heads. It was painfullyobvious where our compression was going. All eight exhaust-valves werebent.
We decided to disassemble...
We decided to disassemble the heads at home before giving them to Jerryat Wilt Engine Services for the refurbishing they needed.
Since our engine retains the...
Since our engine retains the stock bottom end, a full-blown port andpolish would definitely be overkill. We simply gasket-matched the portsand removed some of the "pinch" in the pushrod location.
We found eight exhaust valves...
We found eight exhaust valves on the shelf, and since the intake valveswere fine, we reused them. We cleaned them all up with a wire brush, andthen sent them to the shop with the heads.
We checked our valve-to-piston...
We checked our valve-to-piston clearance before making the plunge intoshaving the heads. With plenty of clearance, we had the go-ahead to cut.020 inch off. Cutting more than this means the possibility of intakeport and attaching bolt alignment issues.
We degreed-in the cam per...
We degreed-in the cam per the cam card.
We used Fel-Pro head gaskets...
We used Fel-Pro head gaskets to seal the head to the block. This gasketgives us a .039-inch crush height. In hindsight, a Mopar Performancegasket, (PN P41200094) with a crush thickness of .024-.028, may havebeen a better choice.