I really don’t think gears will help you. I have tried all different gears behind the M5R2 from 2.73s to 4.10s, and if you have less than 400hp, 3.27s are where it’s at, and 3.08s are a close second. More gear beyond 3.27s just makes 1st and 2nd gear too short. The 4.10s was actually in a car with a 3.8NA, and even with only 140hp, first gear was too short!
I have those exact same heads on the 393 in my F150, although I did spend a significant amount of time porting them. They pull hard to 6k rpms on a 393, and make peak power on that motor around 52-5400rpms. Those heads have peak flow numbers at .550” lift. If you run a cam with more lift than what the heads can flow, you get reversion in the port which acts like a wall to prevent air getting into the cylinder. If you run a cam with much less lift than where the head makes peak flow, you are leaving free power on the table, so with those heads, between .500-.550 lift is the right spec. Duration and LSA determine the power range for a cam. A tighter LSA will make more power, but in a narrower band, and a wider LSA will make a broader power curve, but less total power. For a naturally aspirated street car, you want a 112-114LSA. Boost cams usually have a wider LSA, 116-120, since more power can be made with more boost, but the wider LSA helps make that power everywhere. High rpm race cars with close ratio transmissions will run a very tight LSA, 106-110, since a few extra peak hp is more important than extra torque at 3000rpms. Now for duration, the higher duration, the higher rpm the power band will be moved. The caveat there is having more duration on the exhaust side can help with scavenging, especially on a car with long-tube headers, and that can help make power everywhere. This is why split pattern cams are pretty much the norm for performance cars. Also the rpm range can be tweaked by advancing or retarding the camshaft, so if you want to move the power band lower, you advance the cam, and if you want to raise it up, you retard it. Camshaft specs is one of the least understood aspects of engine building, and if you ask 10 different experts what cam you should run, you’ll get 10 different answers, and rightly so because the cam is what gives the engine its character, and that is a very subjective thing, so there really can never be one right answer. Personally, I’m of the opinion that in a performance setting, running a slightly larger cam than otherwise required, and advancing it 2-4 degrees will match the hp of the smaller cam, but with more midrange torque, which is what makes the car feel fun on the street, and to me, the sacrifice to fuel mileage and idle quality is worth it. That is why I recommended the higher duration. I definitely wouldn’t go smaller than the one he linked though.
