I put a 79 360 into my 87 Diplomat some years ago. During the time I had it I did numerous things to the 360. One of them is relevant here. Take a stock 79 2bbl 360, add a 340 cam, mid 80's stock 4bbl intake and an edelbrock 750 carb as the base engine. Added a set of J heads, no noticeable change. Added an Edelbrock Performer intake, no noticeable change. Add a set of stock 87 318 (302 castings) heads, very noticeable difference. Down low I had lots more torque. Up top, no noticeable difference. Top speed was a bit over the 125 mph mark on the cop speedo, which turns out to be right about 4500 rpm, same for all three heads and both intakes. The only thing that affected the top speed was if I swapped in my 600 cfm Edelbrock, top speed dropped but mileage went up a lot.

The Diplomat had an A833, 2.94 rear gears and P255/50-R15 tires. I'll bet you have steeper gears, but bigger tires so YMMV.

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