Max effort cam for low comp 318

closed chamber iron heads; maybe.But 1 full point of compression, with alloys, is not going to get you much more power.
But a fast-ramp,solid-lifter cam with a tighter LSA than that dinosaur that is in there now, that sounds promising.

But I think you have a problem with gearing, I would address first; namely 3000/3500 to 6000 with a normally aspirated 318 is asking a bit much. Without knowing much, I estimate 20% more gear. Jump down to the bottom to read my gearing theory.

If you install a bigger same manufacturer hydro in there,
with no other changes, it's gonna lose pressure at 3000/3500 and be slower down there. IMO, you would need to close up the LSA, to gain back some pressure, and or increase the Scr, to break even. That would strengthen the top end as well. But the powerband would be smaller, So it's a catch-22. I think you need to re-evaluate your gearing, and see if it's possible to pick up some rpm at the slower speeds. I'm kindof leaning towards a close-ratio 5-speed, but I haven't found one yet.
The standard A833 has ratios of 2.66-1.92-1.40-1.00, and
splits of .72-.73-.71.. Which means outshifting second at 5600, gets you 5600x.73=4100 in third.
That 340 cam is way past optimum at 5600, but you kindof have to go there to get some decent pulling power in third. Reving that 340 cam to 6000, is way outside it's best window, I'll guess 1100 rpm over peak, and 700 to 800 past a decent shift-rpm.
So to me, that looks like you need a cam about 3 sizes @.050 bigger to satisfy the top-end....... but that will kill the pulling power at 3000/3500.
It might be more prudent to sacrifice some of that top-end for more midrange. In this case going just two sizes on the .050, and increasing the breathing on the heads to pull a lil longer at the top, and still the other tricks for the bottom. And then,again, re-evaluating the gearing.


Here's what you need to see;
Without regard to the .050 numbers,
you need to see the big picture.
The OEM 340 stick is listed as a 268/276/114cam, in at split overlap, here is the big picture;
268int/114 comp/106power/276exht/44 effective o/lap
Notice that the comp degrees are just 114, that's not very much. From the factory your 318 might have made 140 psi cylinder pressure with the factory cam. but with just 114* , now, it might make 120psi, and that is killing your power especially at the lower rpms.
Ok lets go to a bigger cam ,say the Mopar 284/484/114
284int/106comp/102pwr/284exh/52* E-overlap
So now, the comp is down to 106degrees and cylinder pressure may have dropped to 110psi cranking. This is not good for low-rpm.
So lets put a solid lifter cam in there with about the same .050 as the 284 hydro. I'll GUESS, a 278intake, and with your X-heads lets make it a split pattern and lets tighten it up to 110LSA. I get
278int/112comp/107power/284exh/60*E-overlap.. The climbing 112 comp, may have increased the pressure back up to 115psi, which is closing in on the 120 that you may now have.
Ok so lets shelf the X-heads and install some OOTB iron Magnum replacements of 59cc, versus the 72cc or so you may now have. This will reduce your total chamber volume from ~93cc to 80cc, and your Scr goes from 8.0 to 9.15; and the pressure sky-rockets to 136psi.. Well. How do you like that!
So now, your top-end has increased by virtue of the 10* more intake duration, and your bottom-end has increased by virtue of the increased cylinder pressure. And the 110LSA has tightened up the powerband some. You may now be coming out of the corners at 3800, and powering down the straights at 6600. I'm just guessing. So you may need to change the gearing.... cuz when you shift at 6000 into 4th, the Rs are gonna plummet to 4260
However, those shortie headers are costing you some bottom end, and they are reducing the effectiveness of the now 61* of overlap.
So say 20% more rear gear, might put your engine at 4500 in the slow corners, and 5100 in 4th on the long straight. Waitaminute, 5100? I know that number! That is just over peak power on the 268 Mopar cam....... But now in 4th gear instead of 3rd.
Remember in the beginning I mentioned gearing?
Well, the 268 running at peak power in 4th, is gonna make nearly as much power as the theoretical 278/110 running 400 below peak........ Without the powerloss at low-rpm, that we had to spend so much money on, to get back!

So what if we just plugged in a 268 solid lifter cam, and ran 20% more gear? I get 125psi and
268int/120comp/112power/276exh/56E-overlap/108LSA
So the 20%more gearing will get you 3600/4200 at the slow spots and 4400 in 4th before the power increase due to the greater .050 of the now solid-lifter design.... so maybe 4600/4800.... which is about right on the power peak of this cam.
So 3.15x1.2=3.78s;
I'm just guessing, tho, based on your statement of only rarely getting into 4th, and the rpms you so nicely detailed.

My gearing theory
The difference in the Mopar box from 3rd to 4th is 1/.73=37% more, so, a half gear would be 18%, or 1.18x3.15=3.72s
With NO OTHER changes to the current combo, except gearing, at 3.72s over 3.15s, your rpm in the now average 3250 corners would jump to 3840, plus whatever the increased power would bring. AND
where you are now doing 6000 in third, the 3.72s would get you 5030 in 4th; plus you are now on or close to the power peak of the 268 cam, instead of 1100 rpm down the far side of it, so that is gonna push the rpm up a bit, so let me estimate 5300;
I dearly love figuring, but I gotta work in the morning so
Happy Gear Hunting.