My commutes are 60 miles a day. I am very good at driving in an efficient way so I know my 340 can do better. Thank You!
60 miles a day in a 340 car!
Friend, you need a Smartcar.
Or,
Part-1
pull the top end off that 340, including the cam. and bolt on a 318 top end/cam .
I did that in somewhere in the early to mid 70s. That is still my favorite all time engine, and it was just slapped together with left-over parts. I even left the 2bbl on it!.
I'm kidding;
with today's gas that engine would detonate itself to death. But with alloy heads, I wonder.
When people asked, I popped the hood and showed them my Hi-compression big-bore 318. Man you should have heard that thing.
The 318 cam, is not the bad-guy in that 318 engine.
Rather, the bad-guy is the extremely low cylinder pressure.
Would I build a hi-compression 340 with a 318 cam today?
Well hang on a sec, what would be the End-goal?
For the right goal, you bet your bippy I would.
But I think I would change the cam-specs just a lil.
The big deal for fuel economy, in our old carbureted V8s, is to
1) get the rpm down, yet it have adequate Ignition timing.
2) get rid of uncontrolled cruise rpm activity, in the intake ,
3) re-engineer the combustion chamber
4) make the power-extraction cycle as long as you dare.
5) increase the cylinder pressure
318 cars
got some of that down pat. But the smoggers have lousy chambers and even lousier cylinder pressure. Both of which can be fixed. But at what cost?
Part-2
But hang on, the Hi-compression 340s already had a handle on cylinder pressure. Get rid of that 340 cam, fit an appropriate alloy head by re-adjusting the Quench and Piston to Head clearance, and, Badaboom, yur as good as set.
Yes without headers, you likely will loose Absolute power.
But with careful parts selection including headers, you might get most of it back. But, the bottom end rpm, might go the other way with more torque, just what you need to run a hiway gear.
The biggest deal for fuel economy is to reduce the cruise-rpm. But if that gets the intake full of reversion and/or EGR, you cannot control the AFR, and your economy can actually get worse.
Plus, you know, 2.45 gears suck on take off.
So it would seem that just installing a hi-way gear into a car with a high-overlap cam and headers, is NOT the answer; and I found that out in spades. So, for economy without a huge loss in performance, you gotta co-ordinate your choices.
For sure, getting the Revs down is priority #1.
But if it makes your engine labor, getting up to speed, well that is negative economy. So then, whatever percentage rear gear you take out, you need to put that back in the transmission, just to break even.
Usually, this requires another gear in the trans.
But you can get some of that low-rpm torque back, by increasing the Cylinder pressure. The 340 cam has a not-so-modest Ica of about 64*, going to 58, might get you an increase in pressure of up to say 12psi., which could be good or bad depending on what you start with.
But the 318 cam has an Ica around 48* which in an iron headed early 340, is gonna end up with way too much pressure for pump gas.
Whereas, in my case, I have run up to 195psi, still on 87E10. and that's with a 367 engine. I see no good reason that this cannot be done with a shorter stroke 340.
Thus, worrying about too much pressure is a thing of the past. However we still have two other hurdles, namely: quench and piston to head contact. This is where choosing compatible parts come in, or a lil milling of the pistons. But that's no deal breaker.
Finally, after the finished chamber is known, then you can choose a camshaft, with an Ica that supports all your hard work, yet gives you adequate power for your application. And there are dozens of cams to choose from these days, so success is virtually guaranteed.
Since headers are gonna be needed to pick up the power potential back towards 340 power, a 4bbl is also a requirement, as is a 4bbl. While the 340 pkgs may not be ideal for this application, you already have them, and really, they are not that far off the mark. Thus your cost so far are; the alloy heads, maybe a cam, and whatever it costs to fit your pistons, assuming they are up out of the holes too near to the closed-chamber heads.
Now;
At 60 miles per day, 300 miles a week, 50 weeks a year, say 15000 miles a year, you'll have those heads paid for in less than two years, just in the cost of the fuel. That's what I figured for mine.... altho I was only travelling 50 miles a day plus at least 50>100 more every weekend, and in winter, I put a 318 under the hood. I still paid for those Edelbrocks. in two years..
But you know,
if you're using this car just for commuting, why does it currently have a 6000 rpm cam in it? How often are you over even 5000? How about over 4500?
See, the factory 318 cam powerpeaks at around 4200, and if you spring it right, mine goes over 5000.
Admittedly there is not much power over 4500, but in a 340 with bigger ports and valves, where will the new powerpeak be? But wait, who says we have to run a 318 cam? there are lots of better than that cams, available, that also do not have a ton of overlap. It's just a matter of choosing the right one and installing it where she likes it.
Ok wait
Part-3
If your car has headers and a stock type cam, sporting just 44* of overlap, you can kill that overlap, with log manifolds. That will instantly clean up the intake, now making the 104* power-stroke the bad guy. But you can fix that by retarding the cam. Sure that will chew up pressure, but at steady-state cruising with a nearly closed throttle, we don't care. And besides the early 340s already had a preponderance of pressure. Giving up 8> 12 psi is no big deal for a street-340, which rarely gets past Second gear at WOT, cuz of the speeding issue. So then, IMO, that is a valid and super cheap option. and if you already don't have headers, yur already almost there!
With overlap killed, your fuel-economy will automatically increase. Add a tune and a bunch of cruise-timing , and watch what happens. But hey, why stop there? With the intake cleaned up, and the powerstroke stretched out, now's the time to stick in those hiway gears.
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As for me, I opted for a deep-low manual trans, an add-on overdrive, gears for 65= 2240, and a modest 223/230/110 cam, that was 270/276/53overlap advertised. But I installed it for 108*Powerstroke and a 48 effective overlap, all with just 61* Ica, cuz the engine already had a preponderance of pressure.
I could tell you that this combo once achieved 32 mpg US on a certain day-trip, but if I did, at least two guys here will tell you that's impossible. I'll tell you the same thing I told them, namely; Just cuz you can't do it, does not mean that it cannot be done.
The thing is, with that same cam, and with no other changes except for the removal of gas-mizer-tuned Holly 600, in favor of a 750, this car went 106 in the quarter, at least 6>8 mph faster than any stock 340 ever went. So, Most guys will call that Power with Economy but think about it. Really, at 32mpg, it's really Economy with Power, lol.
I ran that combo for ~4 years until the cam dropped lobes.
