My 360 smokes the 295s at just off idle with 3.55s and a 3.09. Thats a 9.9 starter gear with a 26.6 inch tire. And a 230* cam.And 10.7 true cr. The Dcr is near 9/1
Doing the math my combo is 12/(26.6/2) X 3.55 X 3.09 =9.9; 9.9 X 400ftlbs crank =3959# max theoretical out the axles at 1 ft radius,to the road.
Your combo is 12/(30/2) X 4.3 X 2.45 X 1TC on brake = 8.42; 8.42 x 350ftlbs= 2947# max theoretical out the axles,to the road.Thats a difference of over 1000# theoretical. (guessing at the ftlbs;but the numbers are relative)
But, here it comes; The 360 at 9/1 Dcr and a small 230# cam makes a shxxload of torque right off idle. Your 340 With the extra 12* intake duration, and the less than optimum Dcr, and handicapped by the starter gear and a TC that wont play, is just plain struggling.
But wait Mine breaks traction at less than 2000rpm(pavement).Which is no where near max torque.And your Tc is letting the engine get closer to its torque band.So, your combo has more issues, than just gearing. And more issues than cam timing. And more issues than TC stall. Or timing or valve lash/lifter preload.
Your problem lies at the heart of the build.A mismatch of parts leading to a low Dcr. I am gonna preach this until I die or it becomes accepted.
The short stroke motors lose Dynamic pretty fast with cam selection.The only way to get it back is to bump up the Static cr. Low Dcrs make off-the-line slow engines. Now on the track,a low Dcr can be compensated for easily enough that its mostly a none issue. Up the gears, and up the stall, and you get through it in a heartbeat. But on the street it becomes paramount to have a decent Dcr.
If you want to keep that engine as built, and those 30 inchers,you will need some serious gears, and another one in the trans for cruising,and probably a new TC. That means 4.88s and an A-500.
The only other option is to Re-engineer your Dcr. That usually means giving up the 242* cam and building the static up. Well there is/are other avenues.One, hardly streetable is stall. Plenty of it. The engine needs to flash to where the torque is.The other is tires; little skinny 245/
[email protected] tall. Should be able to light those up. Or maybe 275/50s@ 25.8
I really think you need to reexamine your Dcr.You may find a smaller cam, maybe around 220* will get you an acceptable Dcr. I had a 223*fast-rate a few years ago, in my 360.Dynomite street cam.
Sorry. I thing you mighta got greedy with the cam.
Now, getting back to your low idle vacuum.That cam should idle around 10 to 12 inches, at maybe 800rpm to 900max.I would get a second gauge. If it really is that low, it should be a bear to start.
And if it really is that low, you will have to find and fix the problem. I would be tempted to check the timing with a second light to prove the timing is correct and that all the systems are working. Then I would do a careful search for vacuum leaks. Followed by a compression test, a leakdown test,and determine the degree at which split overlap occurs. Next would be lifter preload. And dead last cam timing.I do the tests in order of ease, time and probability of results.(Split overlap usually occurs within 5 degrees of tdc on exhaust stroke and is a quick and easy cam timing check and doesnt care about lifter preload, so long as the lifter doesnt leak during the test. Test takes a couple of seconds, once access is gained and set-up is complete.)
The very last thing I would do is determine the exact point of intake closing. This number has to be known along with exact TOTAL chamber volume, to determine Dcr.
All the best to you in your search. No malice intended.