Cam and carb selections
My current altitude is 4800 when I go to my aunt's house in the mountains, her front door step is 10,500. My other aunt in tijeras, New Mexico is 6300. So Denver is probably the loose median.
I have never been in your situation,so I just don't think I can be of any help to you.
Ima thinking you're gonna need to inject it, with computerized timing control.
I can tell you what I would try,
and others can tear it apart
fellas;you won't hurt my feelings.
Firstly, the cylinder pressure difference from 4800 to 10,500 is about 30psi. So in order for the 318 to not be a total slouch at 10,500 with correct jetting, the 30-psi down, pressure number, has to remain as high as possible. IMO at ~140psi, My 318 is already slouchy, but you may think otherwise.
But we have a problem at the other end.
With iron open chamber heads, you are limited to about 155psi for 89 gas, and plus/minus 5 psi either way for 91/87 gas. Closed chambers will allow about 5 psi more.
So if you build for 155@4800ft , you will be down to 125@10,500. If you are just visiting, I guess that could work.
As for me, no, 125 sucks. So I would be doing the closed chamber Alloy head deal, with 180psi@4800 and 150psi @10,500
So, because of the sensitivity of this build, for myself, I would need to make a decision, right now, on iron versus alloy, cuz that will determine where to go from here.
Lets say alloy heads are not in the budget
Lets say closed-chamber are not either, and I have to stick with the iron, open-chamber heads, that I already have. So then, 155psi@4800 is my target, so I can burn 89 gas at WOT, 87 the rest of the time.
Ok then right away I'm throwing away that factory cam, because at 46* ICA I got no hope hitting 155psi with open chambers.
So lets see just how much Scr I can build on the cheap, with just an .020 overbore.
Stock heads are 70/72cc
Cheap pistons are gonna be something like .024 in the hole. flat-tops with NO eyebrows.so say 4.8cc
And I'll have to use the .028 gasket at 6.8cc
That totals 82.6cc; oh lordy,lordy.
My swept volume at 3.93bore and 3.315 stroke is 659cc So the Scr is 8.98 This is a slam it together build with only costs being the boring, and the tall cd pistons.
Ok so how can I get to 155psi from here?
Answer; I cannot
This build might make 145psi@ 46* Ica
I still don't know how yur engine is gonna deal with the fueling issue. If you jet for 10,500 it will be way lean at 4800. If you jet for 4800, it will be way rich at 10,500. If you jet up the middle, you'll still be 3 to 5 jet sizes out at either end.
And the power-circuit is gonna go crazy.
With a carb, and a factory-style distributor, I see more broken rings in your future.
Ok bedtime. I'll figure some more in the AM.
Continuing; I'm throwing away the flat-tops, in favor of some reverse-dome, step-D-cups with Q pads.I'm hitting the search now.
Ok that looks easier said than done........
Lets back up the bus.
Since this won't be cheap anyway, lets swap to a closed chamber head. And to get the Q dialed in, we'll need to run the .028 gaskets... which will allow a piston down-in-the-hole up to ~.020. So now I'm on the hunt for those...
Ok, the KB167s pop up right away with a compression distance of 1.810. Thus being, nominally, .0095 in the hole, and that works! With the .028gasket, that makes the Q,nominally, .0375 and perfect.
So now lets find the right size heads for this. Iron is gonna be cheaper, but alloys allow a far higher pressure before hitting the detonation wall. That means, since I'm thinking detonation IS gonna be a factor, with the lean-running, I'd go alloys..
OOps, dog's gotta go,back soon.....
Ok, so now, here's my thinking;
Since I now have plenty of compression, with a great ring-seal, and a new valve job, that means my engine is also gonna have plenty of "suck". This means I can now choose the right cam, and work the Scr backwards to work with the cam!
And so, I'm gonna choose a cam, not for absolute power, cuz with 3.08s in the back, 5500rpm with 27s comes to 53 mph at the top of first/90mph in second; So I couldn't a flying two hoots about absolute power. No, I'm gonna choose a cam to get me some air at altitude and the climbing rpm, I'm gonna anticipate.So firstly, I have to be able to control exactly when the intake closes. That means no spec at .008 tappet rise, no spec at .006, and above all no such spec at 300, that will just kill my pressure.It also leads to just one type of cam; namely a solid lifter cam.
his is not gonna be a hi=rpm build..... because of the aforementioned 3.08s. At cruising,you're gonna see ~65mph=2500, and to pass; 75 =3200 in Drive/4600 in second. So the engine can be 300 rpm past the power peak at 4600, making the power peak to be 4300, just about what the factory cam does. Hmmmmm, no forget it AJ. But the math tells us that whatever .050 the factory cam has, is the right .050 for this combo. If I got this right, IIRC, the factory cam is a 240/248/111 cam, with an.050 on the intake of around 192*, which peaked at around 4200; perfect.
So, the number of interest is the 192*. Next, At this size there is as good as no overlap, so headers are just a distant option; a free-flowing big-outlet log manifold or shorties will be fine.
Since the alloy heads will not require extra duration on the exhaust, I don't NEED a dual-pattern cam.
Since I am targeting a very narrow powerband, I also do not need a wide LSA.
Ok, those 3.08s are gonna get me ~50mph=3000 in second gear, so that is what I'm gonna target. ... because 55mph in "Drive" is only 2300, and your 318 would need to be a diesel to climb mountains at that rpm. So "drive" is o-u-t.
So now we have the rpm fixed to 3000 +/- a couple of hundred rpm, so lets put our Torque Peak right there. 3000 dictates a cam size of 204 to maybe 208. So now we have a pretty good picture of te cam we want
.Namely; 192 to 208 @.050.. So let's run up the middle at~@200
I'm stuck on a solid lifter so, I'm looking at 39* ramps on this cam, and I'll round that up to 240* after lashing. And I am gonna add some exhaust duration, to get some overlap, and reduce the ridiculous amount of power duration; so 252 exhaust after lashing. Because this can be considered similar to a stationary engine, running between 2800 to 3200 at WOT on the 2bbl, I'll tighten up the LSA to 106*. So that gives me the preliminary numbers, namely 240/252/106+3.. Lets see what I need for compression. The Ica on this cam will be 43*. And the Wallace gives the following;
At 10.6 Scr the pressure at 4800 is predicted to be 180, and at 10,500 predicted to be 150; you see the aforementioned 30psi split? Well that looks GREAT, now what's it gonna take to make that 10.6?
At 3.93bore a 3.315 stroke, the swept comes to 659cc, and for 10.6, that requires a total chamber volume of 68.64cc.
The deck clearance at .0095 is 1.9cc, the .028 gasket is 6.9cc, the dish/eyebrows are listed at 5cc, so so far I have 13.7 and that leaves 68.64 less 13.7=55cc for the heads; let's go find some.
IIRC the smallest I have seen are spec'd at 59cc.
Ok with 59cc heads that brings the total to 59 + 13.7=72.7, and the Scr comes to 10.06 ouch
No biggie, lets back up to see what the pressure now comes to. I get 168/138 meh, not bad, Lets close the intake a lil sooner. At 40 instead of 43, I get 171/141, there you go, that will be dynomite, burning 87E10 full time, as long as the engine stays cool. This new Ica, will require a slightly smaller cam, say 196*.050.
I'm not cool with that, plus I don't think I can find one off the shelf. So I'm gonna stick with the former
240/252/106, and the resulting 10.06scr, and the 168/138 pressures.
So where am I on this build?
I bored the engine, installed KB167s, got some 59cc alloy heads,and a solid-lifter cam kit. ,this combo has 34* overlap, so headers will bring torque exactly when I need it, namely 2800 to 3200. But, running at up to 3200, I won't need a 4bbl, yeah ok, passing will be a bit weak at what was it 4300IIRC, in second. But in the mountains,am I gonna pass? If yes, then a small 4bbl on a SMALL-PORT intake will be just fine.
So it looks like I spent a lotta money here, for probably no more than stock horsepower.
But wait! Let's go back to that cam. Recall it was a 240/252/106+3, solid-lifter cam. It closes the intake at exactly 43*, no messing around. The torque peak is hoped to fall in the zone of 2800 to 3200. The power duration is 125*, compared to the 122* of the stock cam, so I know my mpgs has the potential to be similar to the Stock engine. The compression duration is 137* compared to 132 on the stocker, but she's starting from 10.06Scr instead of the nominal 8.0
The overlap is now 27* compared to 22* of the stocker. This won't mean much with log-manifolds at 2800 to 3200; but in passing gear it will make a nice little surge.
Now all that's left is get some big fat hi-lift lobes. @Wyrmrider?
Ok to re-iterate, this is how I would do it.
Is it the best?
No,because we still have to deal with the fueling issue.
Supercharging is probably the best; it will make all your problems go away. Just put yur engine back together, bolt one on, do a lil tuning; and yur done.