As noted originally, the distributor has 20º in it now. No argument about a too-fast curve, but it is set to 20º. I'll check that curve again, too. I questioned the tach I used at the time, will use another.
The idle timing will come out in the wash, while setting the Transfer-slot exposure. Make the slot slightly taller than wide to start.Figure out how to get there once the carb is bolted back on. What I do is this; after the exposure is set, I back off the curb idle screw until it just lifts off the adjusting block, counting the turns as I go. Then I screw it back in the same number of turns. And write it down. Then I reset all the mixture screws to the factory settings. On old Holleys this is 1/2 turn from lightly seated. IDK about 4-corner Idle. Also on old Holleys, I close the secondaries up tight but not sticking.Do whatever your carb instructions say, But I have tuned a few Mopar 292/108 cam equipped SBMs, without any secondary cracking.
This is your starting point. Make sure you can get back to it any time you want without taking the carb off again, that gets old in a hurry. Make sure the float level is to the factory spec and remains stable at all times, ESPECIALLY at idle!
Make sure the engine temp remains stable. You can't mess with the carb if the engine temp is going up and down, you will tear your hair out looking for the tune.
Ok now, this is your stating point. You may have to adjust the exposure slightly more or slightly less.. later, to fine-tune the transition from idle to just off-idle, to make it smooth and hesitation-free. But just leave it alone now for a bit. Now pull in a little timing and fire it up. Warm it up to normal operating temp, which should be 180 or so, measured with an IR gun right under the Thermostat. Ok now rev it up to 3500rpm and reset the timing to 32/34, with the Vcan not working.Lockit down, and let the idle return to whatever, and recheck the idle timing. Which should be what? 32/34 less 20 in the D =12 to 14 so that should be close enough for now.
Now what's your idle speed? You are targeting 750/800, 850 tops.
If you are not in the ballpark, DO NOT adjust with the primary curb-idle screw! Cuz that will mess up your Transfer port exposure! Don't do that!.
Ok wait, if you only need like 50 rpm, you can crank the screw up to 1/2 turn either way. If that gets you 750 or 800, super. If not we gotta try something else.
Now , up to this point, I have assumed you don't have ANY vacuum leaks, that your PCV is newish, correct for the application, and properly plumbed, and that the crankcase is properly ventilated. The PCV is your main idle-air bypass. Engines with big cams..... like yours, like lotsa idle air. Since you can't mess with the curb-idle screw without upsetting the Transfer-slot exposure, you only have three places to supply the engine the air she wants , namely; the PCV circuit, secondary cracking, and thru the throttle blades.
>>Ok now here's something you probably know. At idle, the engine is getting it's idle fuel from two sources. The transfer slot is supplying the bulk of it, and the mixture screws are the trimmers. You have 4 trimmers.
If you find that they all have to be set to the very rich side...... then the engine is not getting enough fuel from the transfers, or it's getting too much air from somewhere else. If you dump in more transfer fuel then the idle-speed will just go up. If it goes past the target , you will have to hunt for the unauthorized air.
If you find that the trimmers have to be leaned out, then the transfers are too rich.
SO
If the idle-speed is too fast, that would be highly unusual, and points to a vacuum leak, so go hunt for it.
If your idle speed is too slow;
This is the usual problem; then she wants more idle-timing or more idle-air. If you are at 12* idle timing, go ahead and put 2 more in, but resist the urge to crank any more in, cuz that will just make her jumpy in gear, at very low throttle settings. And if you crank more idle-timing in you will have to take an equal amount out of the D. So if you reset the idle timing to 14, remember you now have 14+20=34 power-timing.
So what happened? Did the idle-speed come up into the target zone? If yes, then fiddle with the mixture screws now to get best quality idle. and then we can move on.
But if no, the idle speed is still less than 750, @14* idle-timing.
Then crack the secondaries until you get 750. Now back to twiddling the trimmers, for best idle quality. If the trimmers want to be lean then close the transfers a half turn. If the target idle speed falls below 750 than increase the secondary opening back to 750. Then twiddle the trimmers some more. Sooner or later the back trimmers and the front trimmers are gonna get crossed up. If that happens, close the secondaries a half a turn, and open the primaries the same 1/2 turn. Return all the trimmers to stock and start over, realizing that you can no longer add air at the secondaries. Just aim for the best you can.
In really stubborn cases I just drill tiny holes in the primary throttle valves to get the idle speed I want. Or rather the engine is wanting.
Ok now lets see what happens at throttle tip-in. First, you might have to reset your accelerator pump linkage. So check that out. And check that the engine is up to temp. Then, just open the primaries very slowly a tiny amount. 1000 rpm is lots. Then back to idle. Try it several times. If no hesitation, you are good to go. I think you will be fine.
No we can mess with the D
I'm running a 17" Flex-a-lite aluminum with a 2" deep blade. An 18" would fit better. They do make a 7-blade that is 2-1/2" deep. It is stainless though, NOT aluminum...it's going to be heavy. I am no fan of flexblade fans. And you already know why. Because you already have a backup electric that you have to manually cycle, to push the air thru the rad when the flex fails to keep up.You can't tune the engine with the water temp going up and down. I would get rid of it all and go with what I know works.
My fan has no t-stat. I manually switch it...don't use it often enough to worry about it.
I have a backwards mounted 5" Mopar Bracket style scoop on the car with a hole in the hood even. The pressure well at the cowl puts air INTO the engine up to around 100mph.
Hmmmmmmm,
are you saying that the air under the hood is being forced down and out of the engine bay by this high pressure air? At what speed does this phenomenon begin? Does it interfere with the air pressure differential across the rad which is the only way that the rad can get rid of the heat? Does it interfere with the carb calibration? or is the carb sealed to the pressure box? Have you actually measured the pressure in there?
Having referred to syncing the transfer port, I assume you are of the ported vacuum group and not the manifold vacuum group? Absolutely, I am all for hooking the Vcan to the sparkport,with a manual trans car. Here's why. The spark port is usually deactivated at about 1500rpm. That means between idle speed and 1500 rpm your engine is seeing very limited advance and it is stable advance,not jumping around with Vcan fluctation. So you can drive down there without the car doing the donkey-kick routine. In your combo, 1500 rpm is about 10 mph in first gear.You need the car to be acting grown-up below 10 miles an hour with a manual trans, cuz you will be spending a lotta time down there. Automatic guys get away with it cuz they don't have a clutch, slamming that bucking-horse routine into the chassis, back into your big right foot, and straight back into the carb. But,why does that happen? Well for starters when you punch 20 or 30 degrees into the idle timing, your throttle opening gets really really small. And your low-rpm torque gets really really big cuz you are re-timing your peak cylinder pressure to occur sooner after TDC,so the cylinder pressure in there is about as high as it can be at idle.
So your throttle sorta turns into an on/off switch. When your foot inadvertently moves the throttle even just a tiny amount, the engine jumps into action. That don't work with a manual trans and 4.56s, because even small amounts of torque spikes get amplified by the gears. Say just 3 ftlbs; that would translate to 3x2.66x4.56=36 ftlbs slamming the rear springs and into the chassis. 36 ftlbs is, for a teener, to die-for.
You are of course welcome to try it. I have 185 cranking psi cylinder pressure. At your possible 150 psi, you might not have as huge pressure spikes. But I sure wouldn't try it during this tuning stage. In fact the Vcan should still be disconnected as per stated, a long time ago,lol.
For the former, by 'sync' you are referring to the amount of slot exposed, correct? That's correct.
I would appreciate some expansion on where you want that to be. See above; a little taller than wide, to start with.
You are NOT of the belief that 12º+ will build heat that leads to detonation? 12* at idle has nothing to do with detonation. Even if it did build heat, a proper-working cooling system would get rid of it long before the engine gets to third gear at 3000rpm.
At some point 'more' initial advance is going to heat the engine. OR, you are saying you want 14º and if that builds heat...just get rid of it! Lemmee go find the context... Can't find it,
but idle timing has nothing to do with detonation. Well ok it could if you had a graintruck. Cuz those operators might floor it at idle, and the loaded truck on soft field-earth barely moves.
But if you floor it at idle with 4.56s, the engine should jump to redline in microseconds,lol. And your engine will not again see idle timing until you stop the car or de-clutch. I think this is a non-issue..
Except that I see you are setting power timing by adding the 20 in the D to the idle timing. That is backwards thinking. You must think power-timing first, and fixing the D to get whatever idle-timing the engine is telling you it wants, including getting rid of the low-rpm jumpyness.
And if you have to slow the rate-of-advance to be all-in after 3600 then that is what you do to eliminate detonation.
Elimination of detonation is job #2 right after getting the darn thing to idle.
You can set the idle-timing anywhere you want, until the transfer slot is thoroughly messed up, and it won't even take throttle opening. Try it if you like. I bet it will idle with 36* idle timing, now slow it down to 800 with the curb idle screw. I bet you can't do it. The transfer will be too short and the engine will stall. Even if you max out all the trimmers and somehow get it to idle at 800.... I bet it will stall the instant you open the throttles...... cuz now the transfers have dried up. and they can't get going fast enough to prevent fuel-starvation and probably a stall, a huge hesitation or a backfire thru the carb to set your face on fire.Don't have your face there when you try it,lol
I gave the target of 12 to 14 to help you get started with a minimum of experimentation. You are free to run more, up to 20* even, but if she gets jumpy at 10 mph down to 6, you are gonna get to hating that.
Do not try to run less than 12*, and here's why. Your engine wants the idle pressure spike to occur at about 15* to 20* ATDC. This gives the best transfer of energy to the crank ; all the fuel in the chamber will get burned up as the piston works it's way to the bottom. Your exhaust valve is gonna open at about 79* ATDC, so you only have 101 degrees to get it all burned up. Whatever is not yet burned will continue burning in the headers heating THEM up, and creating a pressure in there. Now, you have 290* to get rid of that exhaust pressure. If you don't two things are gonna happen; 1) the pressure is gonna back up into the intake during the generous 68* overlap cycle, messing up your idle-vacuum, and 2) the pressure inhibits scavenging during the overlap cycle; and maybe the header sucks a slug of fresh charge right across the top of the piston dwelling there, and into the header..... which is still 400 or so degrees, certainly high enough to ignite that little slug, which then burns right in the header before moving on down the pipe. Some of it may still be there the next time the exhaust valve opens.
So how do you prevent this negative work from being done? You gotta get the pressure to peak where it's supposed to. And that starts with setting the idle timing to some number, to allow the fire to get going and the pressure to peak in the zone.
You can tell where that zone is for your combo, just by watching the tach as you pull timing into it. When the rpm peaks, you are there. Well not exactly,cuz the manifold vacuum is also carrying the zone with it. The peak is gonna be up past 20/25 degrees. And unfortunately,your carb won't work properly with that much idle timing. You can also see it as the header temps drop, maybe a 100*
So, again, I offered 12 to 14 as a starter for your combo, to expedite the search. She might like 16, it depends on your cylinder pressure. But not less than 12* because it's hard on the headers, and with a marginal cooling system I suppose the heat may get up into it, thru the exhaust port. If you have TTIs they're tough, I haven't killed mine in over 125,000 miles.Hyup 3 zeros. Because I have the dial-back timing-box, I can run whatever idle-timing I want,+7/-8 degrees. And I do.Even down to 5 or 6 when the situation calls for it. Can't do that with the Vcan plumbed to manifold vacuum..............
Thanks for your help.I really hope it does help,lol.
