Upgrading 73 Challenger with 318.

[Fordication]

So, need some advice. My car presently has a 318 in it. I know the 360 is the more powerful engine with greater ability to increase HP. So I may have to replace my timing chain shortly. I was thinking since I am about to remove a ton of equipment I may go ahead and get a new cam, install a pair of ported and polished 360 heads. I know without new pistons I am not going to get a giant increase in power. What intake and size carb should I go with. What would be a good cam for this upgrade? What is the main differences between a 318 and a 360? Thanks

 

[pschlosser]

How deep do your pockets go? I have this bridge, for sale, in New York...
I think going with the 340 has more (power) upside potential, and a greater industry of parts to choose from, compared to the 360.

 

[HPP]

The 318 is a smaller engine all the way around. Not just in the bore and displacement but also in the heads, in the chambers, in the intake, everywhere.

Not only are you NOT going to get a giant power increase with 360 heads, but using LA 360 heads on a 318 will lead to a power DECREASE due to larger combustion chambers that tend to accompany the 360 head.

The possible exception to this would be using the Engine Quest LA bolt pattern Magnum head that would utilize the smaller Magnum combustion chamber and higher flowing ports that allow it to bolt on to the LA block. Expect to spend about a grand to get this shipped and installed. However, at this point you are another $400-500 away from aluminum heads.

With that, then a duplicate of the 340 4bbl cam would be a good match. You could go maybe a size bigger, but you don't want to go too big and sacrifice cylinder pressure since you aren't changing out pistons to get more squeeze or better quench.

Match it with a RPM Air Gap intake and a 650 carb with headers, and you've got a stout 318. But, its still a 318 popping out 300-325 or so hp.

 

[Xcudame]

You really need to consider changing the pistons (something like KB167STD) to get more compression for the bigger chambered 360 heads. Seriously, with higher compression pistons, 360 heads and a 650 cfm carb, it would perform pretty much like a 340 with the 340 camshaft. Assuming it's a later 318 with low compression pistons, with the 360 heads, you'll be down to like 7.0:1 compression! It will be a dog!

If you don't want to change the pistons, you'd be better off getting a good valve job on the 318 heads, running a 500cfm 2bbl carb and the 340 stock camshaft!

 

[Fordication]

So to get HP out of a 318 without rebuilding it, stay with heads and intake and exhaust and just change out the cam. Add a 500 CFM 2 barrel carb and make due until I can change it out for a built 360 Magnum.

 

[moparleo]

Go with a 360/5.9 crate motor. Ported and polished heads on a street motor is just $$$ spent with little to no benefit.
The engine should be built as a complete unit with parts chosen to compliment each other.
Not a little of this and a little of that.
Buy a tested combination.
Actually, ususally less expensive in the end and everything will be new and a warranty from the company who built it.

If you want more power, there is not much difference going with a stroker if you don't need racing parts upgrade.
No rear disc brakes either. Another waste of money on a street car.

 

[pschlosser]

and there are plenty of performance options for the 318 block. Many have built theirs up, when they had few options of another (larger) engine to drop in. headers, camshaft, ported heads, bigger intake, aluminum manifold, NOS, yada yada.

 

[Xcudame]

Yup, just tweak the 318 a little to get some more performance and save up for that 360 Magnum crate engine!

 

[Fordication]

Yup, just tweak the 318 a little to get some more performance and save up for that 360 Magnum crate engine!

That is the plan.

 

[HPP]

So to get HP out of a 318 without rebuilding it, stay with heads and intake and exhaust and just change out the cam. Add a 500 CFM 2 barrel carb and make due until I can change it out for a built 360 Magnum.

Well, I'd leave the heads on it, swap in a 340 4bbl cam, put on an aluminum 4bbl intake, put tubular headers on it, and then a 500-625 cfm 4bbl.

Summit has the cam kit for under $300, a used LD340 or Stealth or similar dual plane intake is $300 off the web, headers can be found used for $100-300. So for under a grand, you can get another 25-35 horses out of it. That will improve the fun factor while you build something else.