I am not a 318 hater.
I'm gonna tell you how it is, and you decide for yourselves.
On the street,
hi-rpm power means almost nothing because on the way to 60/65 mph,you only pass thru the power-peak once.
But, the vast majority of the time, a streeter is between idle and less than 4000rpm, and usually at Part Throttle.
Cylinder pressure makes heat, and heat is power.
More cylinder volume when the intake valve closes, at a higher pressure, makes more power, and specifically more low-rpm power; and it can be measured and quantified as V/P. Read about V/P here
V/P Index Calculation
Here is my opinion of V/P, on the street;
160 or more is overkill with plenty of tire-frying
140 is a fun number
130 is about the min. for street-fun, barely chirps skinny tires with streeter type gears
120 is way too weak for me
110 is atrocious
100 super lo-performance.
What does it mean?
well,
at 800ft;
the '73 8/1 smoggerteen comes in at about 110V/P
the '69 hi-C, 9.0 rated 318 comes in at about
129VP
the 8/1 318 with a 340 cam, 84VP
the 10.5 340,........... at about 128
the 8.5 340 at ........................ 97
the 8.5 360 4bbl, at about ..... 104
the 8.0 360 2bbl at ............... 122
So that gives you something to think about. As you can see, the 318 has both the lowest and the highest in this ranking.
So what is it that makes this possible?
Answer; this is a two-parter;
1) Effective cylinder size when compression begins, and
2) the Effective Dcr.
The 8/1 318 with a 2bbl cam has a mathematical cylinder volume of 652.27cc
but by the time the intake closes, the Effective stroke is down to 2.86 inches, so... the Effective cylinder volume is down to 562.7cc, and the Scr of 8/1 has dropped to an Effective Dcr of 6.88
Now, hear this; Any engine no matter it's size, that produces the same or similar VPs, will, at the lower rpms (up to about 3000rpm), have similar performance.
>lemmee show you;
69 440Magnum
134VP/ Effective stroke 2.58/ E-volume of 620cc @ 7.38 E-Dcr
69 318 / VP of
132 / Effective stroke of 2.86/ E-volume of.. 563cc @7.74 E-Dcr
69 340 / VP of
128/ Effective stroke 2.52/ E-volume of ..... 529cc @ 8.06 E-Dcr
So as you can see, the Effective numbers are all over the place. Yet the VPs are very similar. Try this; take the volume and divide it by the E-Dcr.
the 440 comes to ........ 84.0,
The early 318 comes to 72.7
and the 340 to ............ 65.7
Notice the similar progressions.
>Now, as a 318 owner, you already know what the bottom end of your engine feels like. Lemmee show you what happens to it with a bigger cam;
'73 318 at 8/1, VP of 110, Ica of 50*
at 54*Ica, VP drops to 104
at 58*Ica, VP drops to 97, 273 sized
at 62*Ica, VP drops to 91
at 66*Ica, VP drops to 84, slanty sized
Each of these Ica's represents about one cam size. Notice how fast the VP plummets.
Next;
lets raise the compression by .4 per step with the 318 2bbl cam (50* Ica),and see what happens;
the '73 8/1 smoggerteen comes in at about 110V/P;
at 8.4 the VP climbs to 118
at 8.8 to 125
at 9.2 to 133 target minimum reached
at 9.6 to 141 fun target reached
at 10.0 to 148
at 10.4 to 156, tire-fryer
You see how FAST the VP climbs?
So now we have seen how the Ica affects the VP in an 8/1 engine, and also how the VP climbs with Scr. Now lets see what happens when we add cubic inches to an 8/1 engine, while
keeping the Ica at 50*
the 273 would start out at......................... 95VP
the '73 8/1 smoggerteen comes in at about 110V/P
the 340 would come in at 118VP
the 360 at...................... 126VP
the 408 at...................... 143VP
Wow! look at how those numbers jump!
And how about elevation?
the '73 8/1 smoggerteen comes in at about 110V/P @ 800ft
By 1600 it has dropped to 107.
By 2400 to 104
by 3200 to 100
by 5000 to 93, back in slanty territory.
But of course no sane 318 owner, when contemplating performance, desires to keep the cam stock. Why? Aye there's the rub. Cuz they all want their engines to have that big cam sound, right.
But as I have shown you, that later-closing intake valve, drives the Dcr right into the basement, and low-rpm performance, right along with it.I mean look at the 318 with the 340 cam above;
the 8/1 318 with a 340 cam, 84VP. 84 is slanty territory! Do you really want your burbling 318 to take off with slanty performance?
So there you go, you decide.
Each one size bigger cam, with NO OTHER changes, will move the top of the powerband up about 200rpm. While also moving the Torque-peak up a similar amount, and the bottom end torque falls away easily half that, because of the loss of cylinder pressure/VP.
Going from a 318 cam of 50* Ica to just two sizes bigger, say 58*Ica, will move the power from about 4200 to 4600. That 400rpm is where the power comes from. Say you had 280 ftlbs at 4200= 224 hp. Now say you moved that 280 up to 4600; the new power would be 245 hp sounds sweet right. But what about the power loss at say 2000 stall? That's gonna hurt. And there is only one way to get it back,namely more pressure/more VP.
Now, you can work around it with a higher stall, and or a bigger rear gear. But those carry other downsides. And they do not address the fact that the low Dcr is affecting the power of your engine all the way from stall to shift rpm. AND by the time you pay somebody to install the TC and gears, you could have fixed the problem by one of the other three ways namely; cylinder pressure, Ica, or cubes.
You decide...............
Now, for Performance,
here are the yardsticks I use;
10 pounds per horsepower/ 1.0hp per cubic inch.
why?
well, cuz these numbers make for a fun car. By the time you get to 12 pounds per cubic inch, at 1.0 hp per cube, maintaining the performance is gonna take gears and stall. Pretty soon the car is no longer a DD and no longer a dual-purpose machine. So it sits in the carport 6 days out of seven, with the gas going stale, and the brake rotors rusting, and the tires rotting. Time goes by and you realize that, you almost never drive it any more. But you got 20/30G stuck in it, which you will never get out of it. Then one day you hit the starter, and three valves are stuck in the guides, and that's that.
So, by my yardstick, a 318 is fine in a race-ready 3180 pound car at 318 horsepower. That will be a lot of fun at 800 ft elevation. The same amount of fun as a 360/360hp in a 3600 pound car. Or a 4400 pound pick-up with a 440/440hp.
I don't hate the 318
It's just hard to find a 3180 race-weight chassis, me in it. and
building a 318/318hp is NOT cheap nor easy.
You decide.
Why does it have to be 318/318 hp?
Cuz if Ima gonna spend all my hard earned cash, I don't want no slouch engine. And I don't want to do it twice or three times anymore.
1.0 hp per cube is a fairly realistic and easy target to attain.The engine is street friendly if a lil hard on gas. After that it starts getting expensive, and
by 1.1 it's getting harder/ pricier, especially with the smaller, small-blocks..
By 1.2 the engine is or has, leaving/left streetability behind.
By 1.3, honestly, give your head a shake, you shouldda started with a bigger engine.
You decide.
I tried to keep my bias out of this as best as I could.
