I sortof agree with Bewy.
But, if you started at, in at 106 for example, your Ica would have been 64degrees, and your pressure at 900 ft elevation, with an Scr of 10.2 is predicted to be...... wait for it.... 165psi.
With iron heads, that's gonna be a tough tune on 91 gas, even with your tight-Q.
But the Wallace calculator gives us another clue; the VP is up to a whopping 159. Read about VP here;
V/P Index Calculation
This number indicates a very strong bottom end, that about matches my 11/1 367. So I know exactly what that feels like since I run a 10.97 starter gear with my 4-speed versus your 9.58 plus TC.
Now I have about the same sized cam that you have. Mine is 276/286/110 measured at .008 tappet rise,compared to your 274/280(guessing)/110 , but Comps are usually measured at .006 tappet rise. So mine, measured at .006 will be a lil bigger than the quoted numbers. Hang with me;
So far, our engines should idle very similarly, in terms of smoothness, and will want very similar idle-tunes.
First, I gotta tell you a story;
My engine will idle down to 550rpm, and will pull itself at that rpm, (4-speed and 3.55s) on hard level,flat ground. But it requires the timing to be backed off to 5*. Which I do electronically.
I run an RPM AirGap, a 750DP, and fresh cold above hood air.
To do this 550 business, the transfer slots have to be as good as perfect.
She would not do it with the secondaries cracked. It seems the back cylinders went lean, and the engine stalled.
So, I closed the secondaries up tight, but not sticking, and instead, I supplied the required bypass air by drilling holes in the primary throttle blades. That solved that.
My cam is in at 108.... because that splits the overlap nicely to an Effective of 60*.. The rest of my durations are
276/114/105/286/61/ Ica of 66* and Effective overlap of 60
If you put yours in at 109, you will get
274/114/109/280/57/Ica of 66, and Effective overlap of 56*
So then, it should run like mine except a lil tamer.
Ok so now I'll guess as to why your combo was not "smooth".
A) it's a big cam, it never will. Why? For 2 reasons;
1) with an Ica of 66* the piston is on it's way back up to TDC compression more than 1/3 of the way, when the intake finally closes. This means at LOW rpm, the piston will pump some of that just inducted mixture back up into the intake plenum. So, that messes up the intake, reduces the vacuum making it difficult for the carb to meter even close to what the engine wants, and the engine has to run on what's left over.
2) during the overlap cycle, both valves are open. This is as a result of the long intake and exhaust durations. But, it was discovered long ago, that when your cam is designed like this, it puts a nice lil power bulge on you power curve by the working of the headers, at higher rpms, and especially so thru the power peak. Saweet. No headers no so much workee.
However, at low rpm, the headers yank on the intake manifold so hard, that some of that plenum mixture goes right across the piston and out the header pipes. But if you don't have headers, you don't get that pull. With log iron manifolds, instead, the exhaust pressure is higher than what is in the intake, so during that overlap cycle, the exhaust easily moves into the intake, and voila; EGR without the hardware.
Ok so those are the mechanical reasons
Now we'll talk about the tune.
1) the number one reason for rough running is insufficient engine temp
2) the third most likely, is DRY air entering thru the secondaries , causing the back cylinders grief.
3) the second most likely reason, in YOUR combo with proper cam-timing, is probably, too much Idle -Advance.
Here's the story;
Running at idle, your engine will like 25 to 35 flipping degrees of timing. Here's how you can tell how much yours wants; Just pull the timing in while simultaneously keeping the idle speed at say 750 rpm. Just reset the mixture screws as may be required and keep on advancing until the rpm no longer rises. Now read the timing.
Of course you can't drive it like that... for two or three reasons;
1) the transfer slot is pretty much closed, and as soon as you step on the gas, the engine will want to stall.
2) But if you can get her past that, she will probably detonate severely, and
3) if it actually is driveable, the power-pulses will be so strong, your 2800TC will hammer the tires unmercifully. Why is is this? Three reasons, your cranking cylinder pressure is nearly 165psi. But at closed throttle may only be say 90psi. This gets multiplied in a running engine by the expanding gasses to perhaps 8 or more times as much , lets say just 5 times as much. Which is then 450psi. with a 4.02inch bore, this comes to say 5700pounds of force. Depending on where the crank is, this could make up to 950 ftlbs to the crank, for a brief moment at 750 rpm. And of course a V8 fires 4 times per revolution so it's
BAM-BAM-BAM-BAM
Yeah that's pretty rough when you have a clutch. Your 2800 will soften it some.
But there is an easy cure for that ! incredibly easy. Just retard the idle timing so she doesn't make as much torque............
Everybody wants to run big Idle-timing, like a drag-car, but in a streeter. That might work with a 3500 or better stall speed, but IMO, there is NO good reason to try that. Put the timing into the rate of advance instead and or, if you have to, run a 2-stage curve. This is so easy to fix.
The Science says that for optimum power, you need to have max pressure delivered to the crank at between 25 and 28 degrees AFTER TDC. So your job, as a tuner, is to try and make that happen; by starting the fire earlier. At idle, that might take 25 to 35 degrees of advance. At WOT and after 3500, it might only take 30 to 36 degrees to get it done. The slower you spin it, the more advance it will take to get the magic max pressure in the window of 25 to 28 degrees.
But, As I have already shown you, too much idle timing just causes the power pulses to hammer the tires, hammer your kidneys, and I feel so bad for the poor u-joints,lol.
In your streeter,
at WOT, the first time your engine remotely cares about ignition timing is at the stall speed. So with a 2800TC, below that, you can run absolutely any timing your engine wants. The next place she cares is somewhere between 3000 and 3600. Max timing is generally 34 to 36, on nearly any brand internal combustion engine. The more efficient the chamber, the less it will take.
But the zone from 2800 to 3600 is generally the hardest to get right, cuz everybody wants to run on the edge there. But; think about this for a sec, how much power will you lose between 3000 and 3600 rpm, at WOT, by having the timing not right in that zone? I'll tell you this; you will lose more power if the engine goes into detonation, than you can ever get with 3,4, maybe even 6 degrees not enough timing.. Furthermore, we are not talking about big numbers here. At max power, on the dyno, when published by the shop, I iroutinely I see 7 or 8 hp lost with 2degrees not enough timing. How much is that at 3200 say? IDK, but with a stroker, I wouldn't care one bit. Heck, I don't even care with my 367. With an automatic, shifting at 5500 say, on the 2-3 shift, the Rs will fall to about 3800, so why would you hunt for the max-timing edge, at any less than that? On the 1-2 shift, the Rs will fall from 5600 to 3300, but your tires will be spinning, and your engine on the rev-limiter, so again, as soon as you shift, even with just 350 hp your tires will just keep on spinning. So who cares if the timing is even several degrees short of perfect.
So what I'm saying is, as a streeter, and a newbe, forget trying to find the magic numbers. You have a stroker that should make quite a bit more than 400 horsepower, and with the 2800 and 3.91s, should be spinning any street tire to well over the speed limit most anywhere in Canada. So. So , forget trying for the magic numbers.lol. That's my opinion.
Instead, concentrate on the following;
If your car was mine;
1) you got headers right? If yes then I would back the cam up to 109. If no on the headers, you are so screwed.
2) My combo runs at 205*F minimum coolant temp; that's where my combo runs best, so I would make that happen. My cooling system never exceeds 207*F. This makes the tune so much easier when the temp is rock-steady.
3) I run fresh cold above-hood air, rammed straight down into the airhorn. Why? because ambient air runs about a 30 degree maximum swing here in Manitoba. So the tune I put in in spring, runs the same all summer.
4) I would take the carb off, flip it over, set the transfer slots to a lil taller than wide, just enough so I can tell. Then reset the mixture screws to 50% of their working range, about 3/4T on a Holley-type or 2.5 on a Carter-type. I would close those secondaries up tight but not sticking. And then re-install the carb.
5) I love that big yellow square-top Accell coil.
I would; defeat the V-can for now. Then reset the Idle-Timing to no more than 14*, and limit the centrifugal to 20 Degrees more, for a total of 34*. I would put a 2-stage timing curve in it for 28* at 2800stall, and all-in at 3400.
6) Then I would warm it up on the fast-idle cam. Then I would fix the idle speed (cuz it will probably be too slow). The engine will want some IdleBypass air.
What I do is drill one small hole in each primary blade. I put it on the front side between the transfer slot and the idle-discharge port, and about half-way between the front edge and the throttle shaft. Then I chamfer both sides.
Here's how I figure out how big the holes will need to be;
I Tee into the PCV line, which dumps into the correct general area, or is supposed to, namely on the front of the carb and just below the primary blades. I stick any old metal pipe into the tee, that seals, and pinch the exposed end shut. I leave about 3 inches showing, not important. Then I drill TWO holes of 5/64 as starters. Clean it out, install it, fire it up, and check the idle speed. Repeat by 1or2/64 until you get to 650rpm for now, But do not exceed 7/32; I don't think you will need even that much.
Next, I would put it in gear and make sure it doesn't bang into gear, nor stall. and then, I would take it for a ride, and see how she transitions from throttle closed to just barely open, to make sure she doesn't have a tip-in sag; cuz those really suck.
If you have a sag, increase the idle-speed with the speed screw, 50 rpm, so now at 700 in neutral. Try going into gear again, no stall/ and no banging. Then another roadtest. Make sure you are properly looking for a sag, from throttle closed on the speed-screw to ever so slightly off-idle. Don't get confused with pumpshot.
That should do it.
Now measure your holes, and drill the plates accordingly.
Now, re-install the Vcan on the sparkport,rev it up to 2400 rpm and put it on the nearest fast-idle step. Next work the mixture screws for the highest rpm, then richen it up 1/4 turn, both sides the same, then kick it off the fast idle.
7) If you have done everything as detailed;
This is as smooth as it gets, at 14* Idle-timing. If you want smoother, just retard the timing some more, 3degrees atta time. But don't go crazy looking for smooth; a 274/110 is about 2 sizes from a drag-race cam, it will never be very smooth with that cam, or any other brand like it. .
When you retard the timing; the Idle rpm will go down too, so that will require a change in the Bypass air, and a slight re-adjustment of the transfer-slot exposure. .........
8) But if
it seems that the engine is still too rough, Do a LeakDown test, looking for valves not closing.
9) but if that don't get you smooth, try running the engine a lil cooler or a lil hotter.
10) In my combo, I first installed my rings with not enough ring gap. And yes after failing to find the problem anywhere else, I took the engine out and refit the rings.
11) My 367 at 750 idle displays a barely perceptible lope, and while not dead-smooth, If I had not installed and measured that 276/110 cam myself, I would almost swear that it ain't a 276/110 cam,lol.
Ok so as I said;
that is what I would do.
done
