65 Valiant 273 dual exhaust
OK first, you gotto know, that the 30 to 50hp is a pretty big step for a 273, and it's gonna come at some higher rpm like close to 5000. Below 2000 the power may be negligible, and from 2000 to 3000, the power increase is only gonna be 30 to 40 percent of the increase at peak.
Now;
5000 rpm with 3.23s and 77 inch tire roll-out (24.5" tires), will be ~38mph.
3600 will be about 28mph.
So, you will feel the power (with 3.23s) beginning at 28mph and peaking at 38 mph. then dropping off to the shift-rpm.
Is that what you want?
More likely your car has 2.76 gears, and the powerband with those will be 17% higher or from 33 to 44mph.
If you want the powerband to start at a lower mph, then you will need a higher stall TC.
Here is a power curve from a 5.2 magnum. Ignore the numbers. Just look at the shape of the curve.Notice the power at 1800 versus 2800.
Your current TC might be stalling as high as 1800. On this graph that is 90hp. At 2800 on this graph, that is 160hp, or 78% more. This is a serious increase, and it's still the same stock engine. It will change completely the personality of your engine.
The next performance increase would be rear gears. What those will do is bring the power down to a lower speed. 3.91s for instance, are 21% bigger than 3.23s and will bring 2800 down to 15 mph (instead of 28), and 5000 will be closer to 29(down from 38).
Now is the time to pressure test your exhaust system. Ideally the pressure will not exceed 2psi. By 4psi, she is an ugly restriction, and you need to get after it. After the exhaust is taken care of, now is the time for bolt-ons. But at this point it's kindof an all or nothing deal; 4bbl, cam, and headers, as a set. The cam is the secret to unlocking the power. It does this by making the engine able to breath more air at higher rpm. But if the 2bbl is still on there, that's a problem. The headers will work everywhere in the powerband by amplifying what the cam is doing. But again, with the 2bbl on there, they can't do much for the topend. Headers can however, with the 2800TC, help the midrange. So those three work in concert.If I had to do them one-atta-time; it would be headers,4bbl, then cam.
Happy HotRodding
OK first, you gotto know, that the 30 to 50hp is a pretty big step for a 273, and it's gonna come at some higher rpm like close to 5000. Below 2000 the power may be negligible, and from 2000 to 3000, the power increase is only gonna be 30 to 40 percent of the increase at peak.
Now;
5000 rpm with 3.23s and 77 inch tire roll-out (24.5" tires), will be ~38mph.
3600 will be about 28mph.
So, you will feel the power (with 3.23s) beginning at 28mph and peaking at 38 mph. then dropping off to the shift-rpm.
Is that what you want?
More likely your car has 2.76 gears, and the powerband with those will be 17% higher or from 33 to 44mph.
If you want the powerband to start at a lower mph, then you will need a higher stall TC.
Here is a power curve from a 5.2 magnum. Ignore the numbers. Just look at the shape of the curve.Notice the power at 1800 versus 2800.
Your current TC might be stalling as high as 1800. On this graph that is 90hp. At 2800 on this graph, that is 160hp, or 78% more. This is a serious increase, and it's still the same stock engine. It will change completely the personality of your engine.
The next performance increase would be rear gears. What those will do is bring the power down to a lower speed. 3.91s for instance, are 21% bigger than 3.23s and will bring 2800 down to 15 mph (instead of 28), and 5000 will be closer to 29(down from 38).
Now is the time to pressure test your exhaust system. Ideally the pressure will not exceed 2psi. By 4psi, she is an ugly restriction, and you need to get after it. After the exhaust is taken care of, now is the time for bolt-ons. But at this point it's kindof an all or nothing deal; 4bbl, cam, and headers, as a set. The cam is the secret to unlocking the power. It does this by making the engine able to breath more air at higher rpm. But if the 2bbl is still on there, that's a problem. The headers will work everywhere in the powerband by amplifying what the cam is doing. But again, with the 2bbl on there, they can't do much for the topend. Headers can however, with the 2800TC, help the midrange. So those three work in concert.If I had to do them one-atta-time; it would be headers,4bbl, then cam.
Happy HotRodding
