If
your cam turns out to be a 270/280/108, the intake side is about the same as was my Hughes 270/276, but at 108LSA, the exhaust side is better. and with more overlap for absolute power.
This cam, in at 107, the big picture is
270/118/111/280/59* overlap/Ica of 62* .....Mine, when in at 109, was
270/116/111/276/53* overlap/Ica of 64*
Notice that power extraction is the same 111*, and overlap is down 6* on mine With that combination of events, I got fantastic hiway fuel-economy with it.
For comparison,
Here is the 340 cam, in at 108*(+4),
268/116/104/276/44* overlap/ Ica of 64* This cam sucked gas, not because of too much overlap, cuz the manifolds pretty much killed the overlap, but for the lack of Power-Extraction. Compare the above 340 cam, which we know is a gas-hog, to yours
270/118/111/280/59* overlap/Ica of 62* .
The two big deals here are 7* in Power extraction, and 15* in overlap.
As to economy;
The extra 7* is helping your cam, but the 15* overlap is not.
As to power;
the extra 7* are NOT helping whereas the extra 15* overlap is.
IMO, this is a pretty good trade off for most of us.
And finally,
here is a 318 cam, in at 108;
240/132/120/248/20* overlap/Ica of 48*. This is about the smallest cam ever.
Notice the Power extraction is 120*, and overlap is just 20*.. Those two are responsible for the fuel economy of the 318.
In my experience, 120 is excessive and 20* with logs, is dead.
IMO, 112 and up to 40overlap, are still gonna make great economy, even with headers.
In my experience; 111 and 52 Effective can still work, down at 2100, and with headers. I proved it.
In my experience; 105 and 61 overlap are hopeless at making fuel economy no matter what the rpm; I proved it.
IMO; that 59* overlap is gonna mess up the intake and reduce fuel economy, even tho the power extraction is up at 111*.
For Economy with reasonable power, then
somewhere between 53* overlap and 61* is where badchit happens in the intake, and somewhere between 111 to 105 Power extraction, more badchit happens.
IDK which is worse, but I know that cruising at a higher rpm, cleans up the intake of a long- overlap period. and power extraction of more than say 114, IMO is more than a streeter wants, cuz it restricts the other numbers too much.
IMO, the Power-extraction window for a streeter should be like 110* +/-2. and
IMO, a good overlap target might be 54,+/-4
To get them both on the same cam, will likely need a 110LSA or maybe a lil less.
If your engine is short on Scr, and you want to keep your power, yur gonna have to compromise.
The thing to remember is that at cruising speed with a V8, the engine is heavily throttled. So how much Cylinder pressure it is capable of making is not at issue. While cruising, your EFFECTIVE Scr might be down at 4/1. If your engine requires less, then you will close the throttle. If it needs more, then you will open the throttle.
Therefore can a 318 still cruise at 8/1Scr with a modest 135psi.
If you pump your engine up to 185 CCp, but it only requires 80 psi to cruise , then you will need to run the throttles nearly closed, and the extra pressure is good for nothing. Well almost, If you simultaneously reduce the rear gear, then the cruise-rpm goes down, and with it goes the torque. To get it back, at your chosen cruising speed, you need more cylinder pressure, so you are gonna have to open the throttle more.
And that is how you get into trouble, cuz opening and/or closing the throttle changes the fuel-delivery and Cruise-Timing requirements. and there comes a point where the neither carb nor the distributor can keep up. You then need a computer. By experience, I find this point to be about 1800>2100 rpm, depending on the Cam in my 367. I like my Power, so 2100 is already too low for my cam. Apparently the factory thinks that 1980 is about the lowest that they want to run the 318, so it installed 2.45 rear gears. Eventually they even went to 2.20s and 65= ~1800. Drive one of those Diplomats up over the Great Divide, and see how you like that. With the current cam, my 367 runs 65=2240, with 3.55s, in od. The car will run 65=2040 with 3.23s, but the fuel-economy is no better. The slowest I have had opportunity to run it was, don't laugh, was 65=1240, but that was just for a very short time, during the spring changeover from the 318 winter-motor.
I said IF
