360 Idle Quality
- Thread starter Earlie A
- Start date
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VA is hooked up to manifold port on the carb. I'm not worried about too much timing at idle. In park, the timing is 32 initial + 16 VA = 48 total. In gear, I loose most of the VA, thus the vacuum and rpm drop. I bought the B26 vacuum canister to try to keep the VA pulled in when idling in gear. I haven't put it on yet because it is somewhat of a bandaid fix. If I end up advancing the cam, I may be fine with the current B22 canister. I looked at the Pertronix adjustable canisters, but it seems there are quality issues with them, so I stayed away.
My concern with continuing to advance the timing beyond the 32 initial is detonation when the mechanical advance kicks in under load at higher rpm. I have the mechanical advance limited to 16, but that puts total advance at 48. That's what scares me a little.
I have a T in the manifold vacuum line with a vacuum gauge under the dash so I can watch what's happening.
So if I'm 4-5 degrees retarded now, I could try 4 degrees advanced? Just to make sure I understand the terminology - we're talking crankshaft degrees here, correct?
No.. you advance the cam not the crank.. if you advance the crank you would be retarding the cam
Maybe bad wording on my part. When speaking of a cam that is 4 degrees advanced, the 4 degrees is measured in crank degrees, correct? 4 crank degrees = 2 cam degrees. If the 4 degree advance is measured in cam degrees, then the cam would be advanced 8 crank degrees. Which is it?
It's my understanding that all cam specs are in crank degrees except for lobe separation angle, which is in cam degrees.
The other option is that I'm seriously confused, which is not out of the question.
Possibly. I don't have a wideband sensor on it (yet). But, the Edelbrock carb is new, new spark plugs are a little sooty, and I got 5 mpg on the first tank of fuel. I'm thinking a little rich from not being able to idle on the idle circuit. And for the Edelbrock carb, the fuel pressure is set to 5 psi.
Looks like it's either advance the cam or replace the cam. If I'm going through the effort of choosing a new cam, I guess I should pull a head and measure the piston deck clearance. Otherwise I don't really know the CR.
Are there any companies not having trouble with hydraulic flat tappet cams right now?
Are there any companies not having trouble with hydraulic flat tappet cams right now?
It can get confusing. Here's what no one has spelled out for you. When speaking of advancing or retarding a camshaft, Lets say "we're gonna advance the cam 6 degrees". What that means is, we're advancing the CAMSHAFT six degrees at the CRANK. Camshaft degrees, even though we're moving the camshaft, are spoken about in crank degrees. 6 degrees at the crank = 3 degrees at the cam, since the cam turns half crank speed. But, everyone speaks in crank degrees, since that's how an engine's timing is read. Make sense?
Got it, thank you.
So does it seem surprising that I can run 48 degrees of total timing and have no detonation issues? Does low dynamic compression and aluminum heads allow for that much advance?
are you 100% sure your balancer ring hasn't spun?
Can't say 100%. I will check it again this weekend. The one check I did with a piston stop showed the balancer was correctly displaying TDC. But that was a static test. Can the balancer be correct when at rest and incorrect when the engine is running?
no... no way it would magically line up again.. was just a thought is all
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Currently I have about the same sized cam in my 367, she measures 276/286/110 at .008 tappet. It's in at 108, or was some 18 years ago.
She idles down just fine to 550rpm at 5 degrees ignition advanced. AND, weith a 4-speed, pulls herself around the parking lot, with NO toe on the clutch. She will idle down to 500 but then can't pull herself up any incline.
But, I gotta tell, Currently she is at 10.9/180ish psi.
Here's the deal;
in my combo;
at 180 psi, the 367 makes a substantial amount of Idle Power, and so does not require the bandaid of lots of timing. But, she does, at the retarded timing, require a lot of Idle fuel; and in addition, some Idle-air bypass.
Typically I idle mine at 12>14* because;
this allows a good Transfer slot opening without excessive Idle-rpm. The bypass air just leans her out a hair at Idle. IDK the idle-vacuum and I don't care, and neither does my engine. My VA is plumbed to the spark port and does not operate until close to 2000 in Neutral. My mechanical advance does not start until 1000ish and is a 2-stage; going to 28*@2800 (from 14 initial) and then slows to 32/34 at 3400. This lets me burn 87E10 without any detonation, at up to 195 psi, the highest I have tried..
So , that's my combo.
Now for yours;
Your low Scr is killing your combo.
Your late closing Intake is killing it more.
IMO, in compensation, to try and get the Idle-power back up, you have engineered way more timing into her than she needs. This makes the rpm run up way too high, and in compensation, you back off the curb-idle screw. and so it idles. yeah but at 1400 in Neutral! and then pulls against the Convertor at 850 in gear. this is so messed up. Then, to top it off, your VA starts adding more!
If I am right;
STOP!
Listen up;
the first time your engine cares about timing is at StallRpm.
She doesn't care about timing at Idle, as long as; 1) she doesn't sag at tip-in, 2) doesn't bog when you slam her, 3) if she bangs into gear, that's already way too much.
So I'll tell you how I would fix this, and then you can do whatever you want.
1) I would pull the pistons out and pump up the Scr.
2) I would go down at the least, one or two cam sizes for a streeter, and
3) I would install a higher stall convertor.
Ok but I get it, you just want to get the best from what you have. Therefore;
Lets start over.
0) before you start, make sure that all the air that the engine is getting is coming in thru the carb and thru the PCV system and no where else, that the floatlevel is correct for your carb, the airbleeds are open, and that, if you have a metering rod carb, that the needles are staying down.
1) remove the carb, empty it, flip it over, with the choke disengaged, reset the throttle position with the speed screw until the transfer slot is slightly taller than wide, and I mean just perceptably so.
2) reset the mixture screws into the center of their useable adjustment range. with a Holley this is about 1 turn out; with a carter type, try 2.5 turns.
3) DO NOT TOUCH the speed screw after this. You will control the Idle-rpm with timing.
4) defeat the VA
5) make sure the WET fuel level is correct, then bolt the carb back on
6) you can expect the rpm to be quite high after she starts, so loosen the Distributor clamp a hair in preparation for retarding it.
7) put the car in Park and start her up. Retard the timing to achieve a comfortable Idle-rpm, then let her warm up. Leave the timing lite in the tool box.
8 ) after she has warmed up, reach back there and retard the timing until she is running at around 750/800. Never mind what the timing actually is. If you have a Holly, adjust your WET fuel level now.
9) ok , now we are at baseline.
10) retard the timing until she is threatening to stall, and now you can put the timing lite on her. Get the number, write it down. and include the rpm. that will be your minimum timing.
11) advance the timing until you get to about 850 rpm, and read the timing. Write it down. That will be your maximum Idle timing.
12) retard the timing again to get about 750rpm, write it down, this is gonna be my target.
13) Now, rev her up to ~2000 rpm, block the throttle there and twiddle the mixture screws for highest rpm. When you get it, let the rpm back down and richen up the mixture screws a hair. Shut the engine off. See where your screws are. Counting the turns, screw them in, one atta time, until lightly seated, then put them back. If they are not the same, average them out and set them to the average, and write it down. If they are not at or near the center of their range; then put them there and
14) start her back up. Twiddle the screws for best lean idle, the richen them up a hair again. Shut the engine off and again see where they are. If they are set lean, the engine wants less Idle-gas. If the mixture screws were set rich, then the engine wants more idle fuel. Therefore, reset the transfer slot exposure accordingly, say a half a turn on the speed-screw and try again. As soon as the idle is stable, crank the speed back to 750 using Idle-timing.
15) with the Idle now half-azzed stable, lets see how much rpm-drop we get going into gear. You are looking for no more than 150 rpm, so with foot on the brake, eyes on the tach, drop her into gear. 150 or less? good to go. lets continue to 17) but if she bangs hard go to 16)
16) you got a problem; either you got too much idle power, or the convertor is no good or, is no good for your application. With a low compression engine idling at 750 with what should be 12* or less idle-timing, I'm gonna say that too much idle-power is not your problem, lol. But you never know, sooooo retard the timing 4 degrees to a minimum of 10 degrees, and see if the rpm-drop is less than 150. If it is/does, then whatever you set it to is the magic number..... for this part of the tune. Go to 17)
17) Now we get to check for a tip-in sag.
With the engine warmed up and the coolant stabilized somewhere north of 180, reset your accelerator pump linkage where it belongs. make sure the discharge nozzles start spraying as soon as the the throttles move, but that the throttles are able to open all the way without the linkage binding. The Wet fuel-level now, is gonna be real important. So; with the air-cleaner house installed, and the hood down, and the trans in gear/brakes set;
gently slowly, tickle the gas pedal like you were thinking of creeping ahead a lil at a stoplight. Make sure you tickle it and don't just let your stinking tight convertor pull you. No sag? try it like 10times with various inputs. Still no sags? perfect lets move on. But if you get a tip-in sag, that gets to be very annoying, very quickly.
The tip-in sag happens because the low speed circuit is a hair lean on the transition to, fuel from the mixture screws, to fuel from the slots. It could be the mixture screws, or it could be that the transfer slots are a hair short, or the Wet fuel level is too low, or it could even be a lazy pumpshot, which is kindof normal. See where the mixture screws are. If they are lean, just give them a quarter turn rich and test again. But if they are already rich, then crank up the T-slots with the speedscrew, again 1/4 turn and retest. If you can't get rid of it with a couple of tries, it could be that the gas is stale or more likely that the fuel-level in the bowl is low.
18) Ok so please notice, I did not tell you anywhere what to set your timing at. This is because only your engine can tell you that. Only your engine knows, and yur gonna have to coax it out of her. Let me repeat what I said Earlier; The first time your engine cares about timing is at stall-rpm.
19) If I had told you on line 1, just to set your Idle timing to 12* and reset your carb as required, would you have done it? What's your timing after all this?
20) this method has always worked for me, so this is how I do it.
21) I didn't talk about Idle-Air bypass cuz this size of cam may not need any. Whenever I introduce Idle-air, the idle-speed goes up which can mess up a few things.cuz...................... it's the same as opening the throttle but without adding any gas to it. Some cams need it. Most street cams don't.
22), no I don't care what the idle vacuum is, it just is what it is.
Your combo may take 2200 rpm and 50* of timing to peak the gauge Can you run it like that? Not on the street you can't. Well I can show you how for all the good it would do, lol. Use the gauge on your stock 318 that makes highest vacuum just off idle..
23) This is how I do it. After the Idle-timing is set, you still gotta work out your Power-timing, your rate of advance, and your VA.
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Thanks for the detailed response. I'll have to read over this several times to absorb even a portion of it. You are probably right in that the initial advance is now too high. There is a good jolt when I put the car in gear. I'll continue to work on it on the weekends, and may advance or replace the cam.
Ultimately I would love to build a higher CR engine, but that's not going to happen now.
TT5.9mag
Two atmospheres are better than one
You don’t have 48 deg of total. Any number of degrees of timing added with vacuum advance (either manifold or ported) goes away when manifold vacuum drops (IE you’re on the throttle). It is completely reasonable to have as much as 48 or 50 degrees at cruise when vacuum is high. And no you won’t see detonation there.
My initial timing (without VA) is set to 32 degrees. Mechanical advance is limited to 16 degrees and is all in by 3500 rpm (silver springs on a billet Pertronix). Anytime rpm is above 3500 my total timing is 48.
At a 2000 rpm cruise with 15-20 in vacuum, I may as much as 32 initial + 16 VA + 10 mechanical = 58 with no surging or pinging.
I am going to check the TDC mark on the balancer again and make sure it is accurate, but I think it is. I have an MSD ignition, so timing light could be off, but I have checked timing with both an old Craftsman induction light and a new Innova adjustable light. They both read the same.
TT5.9mag
Two atmospheres are better than one
Well then yes I am surprised you’re not in to detonation, at least on tip at low rpm without downshifting. The one thing that might be saving it is how late it’s coming in. My bet is the balancer is not accurate, even though Bewy thinks I don’t get it.
Possibly, but it's still not necessarily a good thing. Detonation can happen and you never hear it, too, so keep that in mind.
A.
I read post 1 again.
I come up with the cam being 6* retarded, not 4*. Idle vac will be very low, performance poor. It would also explain lack of detonation with a lot of timing. It also explains why the engine needs a lot of ign timing, plugs being sooty from low vac/t-slot open too far.
The cam is not that big & with just under 10:1 CR, should work well. Might be time to get another cam, & you do not need a dual pattern cam with headers, it just feeds power out the exh pipes.
I read post 1 again.
I come up with the cam being 6* retarded, not 4*. Idle vac will be very low, performance poor. It would also explain lack of detonation with a lot of timing. It also explains why the engine needs a lot of ign timing, plugs being sooty from low vac/t-slot open too far.
The cam is not that big & with just under 10:1 CR, should work well. Might be time to get another cam, & you do not need a dual pattern cam with headers, it just feeds power out the exh pipes.
The more I'm thinking about this, the more a cam change makes sense. You bring up a good point with the dual pattern cam. Probably not needed with good flowing heads and exhaust.
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