These are ~26.1 diameter, so 82" roll-out;
Therefore with 2.76s,............................ 65=2310
That 276/288/114 Summit K6901 is your biggest enemy; go do a compression test.
While the engine is warmed up, measure the lowest rpm at which the vacuum first peaks.
And check your cruise timing at 2310rpm, with the Vcan hooked up.
For an eye-opener;
install a timing tape. Inject #1 cylinder with enough air pressure to push the piston down to the bottom. Then reduce the pressure to about 20psi and bring the piston up on the compression stroke. Reduce the pressure when the piston starts to bounce. Keep doing that until you find the crank-angle, as close as is possible to determine, when the intake valve finally closes.
IMO
2310 is just barely enough rpm to maybe clean up the airflow in the intake.
The biggest issue I see from that cam is the very meager 98* of power extraction, (in at 110, and off the advertised mind you), which leaves plenty of energy still in the exhaust; energy that could have been used to propel the vehicle. You can't do much of anything about that except retard the cam, which brings on another set of problems.so don't do that.
The bigger issue is how to give the engine the ignition timing it craves.
Do this; with the engine warmed up; rev it to 2300 and give it more timing, forget the light, just crank some in. Reduce the speed back to 2300, and more advance. Continue this way until the engine no longer increases in rpm with additional timing. Now read the timing,still at 2300.
I'll bet the number comes in very close to 56 degrees.
Push the D back some and idle her down. Then restore to normal timing.
Now; about that number; whatever you got; cruising at 2300, that is close to what your engine is wanting. What have you been giving it? Rev it up and see. I'll bet less than 45 with a working Vcan. I'll bet less than 28 if not running a Vcan.
This is probably your second biggest problem, the first one being cylinder pressure.
I'm just guessing. Go ahead and prove me wrong.
I mean I assumed you know how to calculate mpgs, and that you have proved yourself right,lol.
Timing and pressure walk hand in hand with rpm to make the big numbers.
When looking for fuel-economy,the 340 does not have enough stroke to waste on long slow acceleration ramps. That 6901 is a small 218/228/114 cam,with ~58* ramps and could be had, from another manufacture, with perhaps as little as 44 degree ramps. The ramp difference, and tightening up the LSA to 110 from 114, could increase your cylinder pressure over 18psi!
Lemmee compare;
your current cam in at 110, should have the following numbers;
276/288/114+4/Ica of 68/112 comp/98 power/o'lap of 54@52effective
This is a 218/228 cam, it wants headers.
Lets shorten the ramps to 44*
and tighten the split to 6*
and tighten the the LSA to 110* in at 107*
but keep the 218*@.050
so; we will end up with a 218/224/110, here we go;
262/268/110+3/Ica of 58/122 comp/113power, o'lap of 45@42 Effective
This is is still a
[email protected]
But now ;
the effective overlap is reduced to 41 from 52, and
power is extended to 113 from 98, and
compression is up to 122 from 112.
You lost only the overlap, which with log manifolds, you were not using anyway!, so I set 'em on fire and trashed 11 of em.
I'm not saying you should run out and get this cam; for all I know the new Ica of 58* could put your engine straight into detonation. That is why I asked for the cylinder pressure readings.
I just have lots of free time to play with.
And I just wanted you to see how the cam lobes can be manipulated to your advantage.
One thing I can guarantee you; if it is possible to increase your power extraction by 15 degrees, while simultaneously increasing your compression by 10 degrees and reducing your overlap 11 degrees, while yet maintaining your
[email protected], phewff there's a mouthful;
as to power, there is no downside to this.
as to low-rpm torque, you will have a good amount of increase.
as to fuel economy,say goodbye to 10 mpgs.
With the new cam, and the higher cylinder pressure, and the fixed timing, your carb will need a new tune , and after you get all that done, you should see mid to hi teens as others have stated.
Now someone might say that the 6901 is a great cam. I'm not saying that it isn't. I'm just suggesting that for your needs,it is not the best fit.
Every time someone speaks of the 6901 the fuel-economy issue seems to come up.