318 heads on a 360
looks like i just need to find a pair of 360 heads with 2.02 valves and maybe little smaller cam
why?
with 3.55s and an automatic; you will hit 44mph@5000, spinning all the way;
and 60mph at about 4000 in second gear. The 318 heads will be fine to 4000. Just put a small-port intake on it.
How much better will 360 heads be at 4000?
What good will a 68* cam be, that doesn't power peak until maybe 5000 with the 360 heads.
Ok sure, the 360 with 360 heads and a 268 cam will make quite a bit more absolute power.
But what counts is the average power, to the shutdown. Furthermore, to get that top-end power, the 268 cam gives up bottom-end power.
Street Cams are like sliding windows, about 1500 rpm wide. When you slide it up, you leave the bottom behind. The higher up you slide it, the more important the heads become, and the higher the stall-speed needs to be, to get away from the soft bottom end.
The proper way to use a 268 cam, which wants to power-peak at around 5000, is to gear the car to use second gear,to hit about your highest anticipated speed.
If that be 60mph, then you would need 4.56s, for 60=5200, now you have the potential to be quick., Now the 360 heads are a must-have. Now an overdrive transmission is a must have.Now the 2800TC is optional. Now your starter gear is 11.17 waaay killer, and street tires cannot deal with that, so you are driving on the two-barrel in first, unless you just like frying the tires.
But you could do the same thing in first gear with 2.76s and now 60=5300. But your starter gear is now a tad on the low side at 8.11, so the 2800TC is back on the table. And now, you no longer need an overdrive.
But if you work the formula backwards, you find that 60 mph requires a gear of 7.00@5000. The engine doesn't care how you get it. So in 1.45 second gear, you would need 4.83 gears. In 2.45 first gear, she would need 2.86s. So, as you can see, there is no way to satisfy the cam in either gear.
But what about at 4000? At 4000 the required gear to hit 60 is 5.11, so with 1.45 second gear, this requires a rear of, wait for it ........ 3.52.....lol. Badaboom!
Wait, you already got those. And you got the 2800TC. And the 318 heads are easily good to 4000. Soooooo, all you need is a matching intake and a 4000rpm cam.
Will it be as fast to 60mph as the 268 with 360 heads?
Since you can actually harness first gear with the smaller cam, and she hits 60 at the optimum rpm. I would almost bet money, that the smaller cam could be quicker.
But hang on, we're not done yet.
The cam does not hit peak power at a specific rpm, but rather, plateaus over a few hundred rpm. say 400. So if you had a cam that "peaks" at 4000, it will have a peak at say from 3800 to 4200. Furthermore, you can, work the heads to stretch the plateau out say another 200 to 300. So now that 4000rpm cam is actually gonna be able to be shifted at say,4500, which is about the limit of the 318 heads. So then, we could run the same percentage higher gear than 3.55s...... if you wanted to. Or you could run the next smaller cam, or you could extend the 60 mph top speed by the same percentage. Since 4500 is about 12% higher, this would be 67 mph.
Ok soooooo what cam is gonna power-peak in the ballpark?
That would be the 318 2bbl cam. But If you have to buy a cam, Then I would not use the Mopar OEM cam, because it has notoriously long clearance ramps that are designed to outlast the engine,lol. as are most oem cams. including the 360 2bbl cam.
So then, you could up-cam one or two sizes, with a fast-rate-of-lift- design, and not sacrifice bottom end torque. Or you could keep it the same which would pump up your cylinder pressure, making the potential for better fuel economy. Or do some combination.
