My stock stroke mild 360 build ;)
Ok here’s one at idle. The cam is too mild. I don’t like it. I gotta idle down some more, but this is at 1,000 rpm. little pop here and there, ill adjust that. running out of time...or...oil...LOL
Before you start swapping cams, get the PCV hooked up!, and get the thing idling right. You cannot tell much with a high idle. And
Depending on your EFFECTIVE gearing; pushing the powerband up, in a streeter, is rarely a good idea, especially in a heavy vehicle.
Here are some tips;
>For every bigger cam size, (about 7 degrees) from the same manufacturer, and in the same cam style, the powerpeak goes up about 200 rpm, AND, about half that drops off the bottomend, and so, without an increase in cylinder pressure, the bottom end goes weaker and weaker.
So, IMO, I would drive the beast a few weeks and work on the tune, before you condemn the cam.
>The sound you want is a byproduct of crappy cylinder filling at low rpm, due to the late-closing intakes, and partly from the overlap cycle. One thousand rpm is way too high even for the 292/292/108 cam.... which needs a chitload of compression to work right, and drinks gas pretty bad.
>If you get a bog when gassing it in gear, at low-rpm; you will have to tighten up your secondary air door
> to make it idle slow, you will have to retard the IdleTiming to 14* or less; don't be afraid of go there, cuz it will tend to fix your transfer slot exposure. The closer you get to synchronizing the transfers to the mixture screw AFR, with adequate Bypass-Air, the more retarded you will be able to run it, which will slow it down some more. By 600/650 you will be hearing the cam.
But make no mistake; if your Transfer-slot sync is off, the slow-idle will create a tip-in hesitation. This is NOT the timing causing that! That hesitation is 100% a fueling issue.
To compensate for the lack of timing at idle, you will need a 2-stage timing curve. You start with one long-loop advance spring, that allows the soft second spring to barely keep the idle advance from jumping around. I worked my curve to come in fast and hard to 28*@ 2800, and then it slows right down when it hits the end of the long-looper. Then, it takes to about 3400 to bring in the last several degrees. This has worked well for all three of my cams, in my Manual-trans 68 Barracuda. (
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> you will know that you have too much Idle-Timing, by how hard it is to drive it at low rpm.
>The truth is that in neutral, your engine will be most smooth and most happy with a ton of timing. Try it. Just keep giving it timing, a little at a time, until the rpm no longer increases with more timing. Then reduce the idle-timing some 6*, and back the idle-rpm up to say 700, and then start adding timing again, until the rpm plateaus. Now read the balancer. Don't be surprised to see numbers in the high 20s to mid 30s, or more. That is what she wants in neutral, and probably the starting point for cruising on. Cruising 2400 to 2800 in steady state she may want 50 or more degrees!
> but you cannot drive it with that much Idle-Timing; as it is almost a sure thing that it will detonate on acceleration, AND, the power pulses will be way too strong in first gear at lowrpm, AND, it will wreak havoc with your Transfer-slot sync. So put it back to 14* or less at 700rpm.
> I suggest to put 20* into the centrifugal advance, to get you 34* of PowerTiming with 14* of Idle-Timing.This should be pretty detonation safe. Work the tune from there, and after you get the idle/midrange worked out, later you might try a few more degrees of PowerTiming. Try not to get ahead of yourself.
> your open-header tune will be slightly different than after the exhaust system goes on, so keep that in mind.
> if your combo is jumpy on the throttle at low rpm, the easiest/fastest way to get rid of that is to retard the timing, at whatever rpm it is happening at; and the easiest way to do that is to just retard the idle timing
> if your exhaust burns your eyes, your idle is rich, and your engine needs some more Idle-Air bypass. but prove the idle is rich first. I do this by slowly adding air to the PCV circuit. If the engine likes it, it is/was rich. Some guys slowly cover the airhorn with a shoprag; if the rpm goes up, it is/was lean.
> to get bypass air, you can crack the secondaries a bit, but I have never had any success with that. The engine wants that air to have fuel in it so unless you can figure out how to get that secondary bypass air to have fuel in it, I wouldn't bother. Ideally the bypass air wants to come in thru the PCV circuit, so it can mix with the transfer/idle fuel, before zipping down the runners. A second alternative is thru the primary throttle blades. But be forewarned, increasing idle air will increase idle speed, which, if you back off the speed screw, will readjust your transfer sync. So instead, I use Idle-Timing to adjust my idle-Speed, and that takes us back to my recommendation of 14* max IdleTiming.
> Your ideal transfer slot exposure may be a lil taller than wide, just enough to be noticeable.
