Rock Able
Well-Known Member
Well, it is 7 with the vacuum disconnected. When you add 12-13 degrees to it, I'm good.
360 Tune Up
- Thread starter Rock Able
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Well, it is 7 with the vacuum disconnected. When you add 12-13 degrees to it, I'm good.
With vac advance on manifold vac, initial could have been as much as 22*, which also could have been a problem. If it was only 12- 13 it should not be a problem at all. Depends what happens when in gear.
Here's how that curve compares to the Plymouth timing specs for a '68 340. So it should be ballpark OK.
I agree with Rob. I think it will run better with an initial of 10 plus. (Factory 67 273 was 10* )
Here's how that curve compares to the Plymouth timing specs for a '68 340. So it should be ballpark OK.
I agree with Rob. I think it will run better with an initial of 10 plus. (Factory 67 273 was 10* )
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Oh WOW!
This is good stuff going up and real quick.
Myself and YR gotcha on the carb and R&D & Mattax are nailing down the distributor.
I think you’ll be running smooth as butter real soon.
This is good stuff going up and real quick.
Myself and YR gotcha on the carb and R&D & Mattax are nailing down the distributor.
I think you’ll be running smooth as butter real soon.
Not exactly. What happens to the vacuum when you step on the throttle. it drops, so the advance that you had at idle with a strong vacuum signal is gone as well.
You want at least a STATIC 12-16* at idle before any other timing changing variable. You basically have 7* timing when you step on the throttle. That's no good.
You guys are great! You all lost me with all your graphs and stuff, but the willingness to share your knowledge to help someone out is a cool thing to see.
The graph shows how the distributors advance. This is there “curves.” To the left is idle and to the right is the rpm climbing. The lines show as the rpm climbs, the amount of advance in degrees.You guys are great! You all lost me with all your graphs and stuff, but the willingness to share your knowledge to help someone out is a cool thing to see.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Plot your numbers on a graph with rpm along the bottom, and degrees advance up the left side. Be sure to NOT include the vacuum advance numbers.
IMO your D has too many degrees of centrifugal, and not enough idle. but the 34* at 3300 is about right.
At your cruise rpm of 65=2240, it looks like the current cruise timing is 27+15=42 and that is at least 10* not enough. And that is partly where your lack of fuel economy is. That engine should run on 87 full-time. It just needs a split timing curve, more idle-timing and less at 2500 but a bunch more at cruising, and the Vcan has to drop out as fast as possible;factory cans are adjustable..
What a lotta guys don't realize is that you can't run a automatic timing curve on a manual trans car.......... because there is no convertor slip; the engine is married to whatever gear you are in .
The AX-15 ratios are 3.83-2.33-1.44-1.00-.79od. with 3.55s, the road gears are
13.60-8.27-5.11-3.55-2.80
Here's one problem I see, correct me if I'm wrong;
at 32 mph, you sorta have to be in third gear to cruise at 2010rpm, at 26+15=41* timing, which is not a problem. But when you roll into the throttle, even just the 26* may be too much. never mind the 15 more in the manifold operated Vcan. And most especially if it doesn't drop out fast enough. And so there is your can of marbles. There is no fluid coupling, so the engine is stuck in rattle-mode.
So what do you do? Downshift right? and now the rpm jumps to 3250 and timing is 34@WOT . On a high compression engine this will be fine. But in your Stock long-block with an advertised 8/1 Scr, it may be too much, and so back to sack of hammers rattleing.
And controlling or trying to control detonation by running rich or cold is not the cure for this.
The cure is to fix the timing.
Lets look at 750 rpm in first gear.
Now the timing is 7+15Vcan=22* which is fine at no load..... but the only way to make it idle is to close the throttles too far which promptly dries up the transfers, and introduces a tip-in stumble, and a cold-idle problem. So you gotta not do that.
So forget about trying to make the engine idle on some pre-conceived amount of timing;in your combo, it does not matter one iota what the idle-timing is cuz the only time you will ever drive at 750 rpm is in a parade on account of with your combo 750 rpm is 4.5mph.
So the proper way to start your tune up is to set the Transfer-slot exposure to about square at the very least; then back up the timing to whatever gets you the idle-speed you want. then adjust the mixture screws to best lean idle. Of course the PCV system has to be functioning,the Vcan hooked to ported vacuum, and the metering rods have to be staying down. If you have fudged with them, put the stock ones back in, and the stock MJs as well.
If your cooling system is rock solid, and you are operating mostly at one elevation, then I recommend to run as hot as you dare, unless the pistons lock up when you shut it off.
If you are running fresh cold air, now you are all set to start tuning. The idle parameters have to be established before you start anything else. And once you have chosen a minimum cooling system temperature, your tune will be locked to it, meaning if you start too hot, and have to back up, then only your idle-tune may still be OK.
Ok so, now that the idle-tune is established, you can proceed
more coming; oops lost in cyber space
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Rock Able
Well-Known Member
Ok. You guys have convinced me I need to alter my mechanical advance curve. Are there articles showing how to do that? Looks like I have to lock in about 5-7 degrees of the initial mechanical advance. That will get me to about 12 - 14 degrees initial with my 34 degrees at 3300 remaining unchanged. I may be able to go to 35. When I add the 15 degrees of vacuum advance, that will be about 50 degrees max. Also, I would change to ported vacuum source.
Have I got this right? Once I get this, I can start working on jetting and octane. My PCV system is working, I have a catch can to reduce oil going into the carb, and my metering rods have the lightest spring (yellow), so they are down. I am back to #1 jet/rod/spring setup, for now.
Have I got this right? Once I get this, I can start working on jetting and octane. My PCV system is working, I have a catch can to reduce oil going into the carb, and my metering rods have the lightest spring (yellow), so they are down. I am back to #1 jet/rod/spring setup, for now.
First thing I'd do is check the advance on the other distributor. If its a shorter advance, then swap vacuum cans and be done with it.
Again. 7* BTC on a stock engine isn't out of line with what you would have got from the factory. So what you'll be doing by bringing that up is making it more efficient.
Articles. When you find 'em, many are half sales pitches and regurgitations of the same.
Your goal is to cut the bottom off the curve.
Disassemble the distributor. Hardest part will be removing the snap ring that's under the felt pad. Second hardest part is removing the reluctor. Take a photo or notes before removing it to remind yourself of which slot the roll pin uses.
With the snap ring and reluctor removed, the rest is straightforward. Slightly lift the plate to free the vac can arm.
Here's a cam plate (aka slot plate) in the initial position. Zero advance.
The primary spring's tension holds the weights against the inside of the slots.
Remove the cam plate. If you were me, I'd measure the slots and distance between for baseline reference. Or you can go from the internet alone if you prefer. LOL.
The stamped number represents the advance distributor degrees allowed by the slots.
Your distributor #2 seems to have about 28* in it. (It may be stamped 14)
You're looking to reduce that by 5 or 6* to 22* advance.
My notes show that 22* will require slots 0.410" long. You can find some other folks findings on the net and their similar.
Weld a tack on one or both of the slots. On the inside! carefully file it back to slot length needed.
Reinstall.
(if you see differences in the photos, its because the photos are of several different distributors)
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Rock Able
Well-Known Member
Piece of cake. We are on the same wavelength. Thanks for the photos and advice this helps a lot.
Rock Able
Well-Known Member
Ok. The deed is done. I now have 12 degrees at idle, 34 at 3300 and the vacuum hooked to ported connection. It's supposed to get hot this weekend. I look forward to testing it and seeing how my temperature is and check my mileage. Initial test drive seems good. Throttle response is good, idle is good and cruising speeds are good.
Thanks everybody! I will let you know how it goes.
Thanks everybody! I will let you know how it goes.
Rock Able
Well-Known Member
Well, the engine seems to run just fine. I can't really tell any difference yet. Hopefully, when I test for gas mileage, I will see a difference.
The temperature thing has got me bumfuzzled, however. It is completely opposite of any problem I've ever had in the past and I've had a few. It actually runs cooler idling that at road speed.
This car (41 Plymouth) has a Champion 3 row radiator in it and a Spal 16" electric fan. I don't have room for anything else. Today, as I drove it on the Interstate, I saw the exact same temperatures as I saw when it had no vacuum advance and much richer jetting. At sustained 70 mph, it would creep up to 200. I know that's within an acceptable range but it has a 180 thermostat (2nd one) and when the temp is 80 or less, it more or less stays at 180. The other weird thing is that it cools better and the temperature actually comes down when I get off the interstate and get on a secondary road (195). Even weirder, it cools on down to 185 idling with the AC running after I pull into the driveway. This engine has the 7" pulley on it and I really don't know which water pump.
I really expect ram air to keep it somewhere around 185. Got any ideas? I'm running out of them, as I've experimented with an undertray and air dam. This doesn't seem to make any difference, as far as I can tell. I will remove it and run it again this weekend.
The temperature thing has got me bumfuzzled, however. It is completely opposite of any problem I've ever had in the past and I've had a few. It actually runs cooler idling that at road speed.
This car (41 Plymouth) has a Champion 3 row radiator in it and a Spal 16" electric fan. I don't have room for anything else. Today, as I drove it on the Interstate, I saw the exact same temperatures as I saw when it had no vacuum advance and much richer jetting. At sustained 70 mph, it would creep up to 200. I know that's within an acceptable range but it has a 180 thermostat (2nd one) and when the temp is 80 or less, it more or less stays at 180. The other weird thing is that it cools better and the temperature actually comes down when I get off the interstate and get on a secondary road (195). Even weirder, it cools on down to 185 idling with the AC running after I pull into the driveway. This engine has the 7" pulley on it and I really don't know which water pump.
I really expect ram air to keep it somewhere around 185. Got any ideas? I'm running out of them, as I've experimented with an undertray and air dam. This doesn't seem to make any difference, as far as I can tell. I will remove it and run it again this weekend.
As long as it stops creeping up, that's pretty good IMO.
In general interstate speeds (60 plus) are noticibly more work for the engine than state highways (45-55).
Not quite sure how it works out with your gearing but this extra load shows as increased throttle opening on my car. vacuum is about the same, rpm is higher.
The oil temperature is probably around the same (in the pan). Getting it around 200 is good. Helps get rid of the moisture collected.
My thinking here is that the coolant temperature is related to engine work.
It is possible that the coolant temperature is being effected by air flow, just doesn't seem like it right now.
The more work the more heat, and the heat exchange should be enough to keep the increase in check. Temps won't be right at the thermostat opening unless the radiator is doing hardly any transfer.
In general interstate speeds (60 plus) are noticibly more work for the engine than state highways (45-55).
Not quite sure how it works out with your gearing but this extra load shows as increased throttle opening on my car. vacuum is about the same, rpm is higher.
The oil temperature is probably around the same (in the pan). Getting it around 200 is good. Helps get rid of the moisture collected.
My thinking here is that the coolant temperature is related to engine work.
It is possible that the coolant temperature is being effected by air flow, just doesn't seem like it right now.
The more work the more heat, and the heat exchange should be enough to keep the increase in check. Temps won't be right at the thermostat opening unless the radiator is doing hardly any transfer.
Rock Able
Well-Known Member
But none of my other vehicles does this....and I have 3 SBC's that don't. Ram Air keeps them right at thermostat setting.
I realize there is more work being done and much more heat being generated but the radiator is supposed to be able to handle 6-700 HP, according to Champion. Air flow is the ghost I've been chasing. The under hood temps get pretty high and I'm attributing some of that to headers. I thought about wrapping them and I think that would lower under hood temps but I don't think it will change my coolant temps. It's starting to look like I'm going to have to live with this "as is" and adjust my fan so that it cuts on at about 205. I don't see the point in running it when it's doing nothing to bring the temps down.
I realize there is more work being done and much more heat being generated but the radiator is supposed to be able to handle 6-700 HP, according to Champion. Air flow is the ghost I've been chasing. The under hood temps get pretty high and I'm attributing some of that to headers. I thought about wrapping them and I think that would lower under hood temps but I don't think it will change my coolant temps. It's starting to look like I'm going to have to live with this "as is" and adjust my fan so that it cuts on at about 205. I don't see the point in running it when it's doing nothing to bring the temps down.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
- Joined
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So what is your current timing at 65mph=2240rpm? My math indicates a new rate of advance of .95* per 100 rpm. If it starts at 1000, then I get
(3300less 1000)/100x .95=22* .. to that add the initial of 14 and 15 from the Vcan, assuming it all comes in, for a grand-total of 51, looking good.
But If she had not got that timing, the fire would start late and would not finish burning in the chambers. Instead, it burns in the headers or logs.
In logs this forces the engine to pump the gasses out of the chambers into a hi-pressure zone, costing you both fuel-economy and additional underhood heat.
Underhood heat is underhood air-pressure, and so ram air gets stalled. But worse is that your carb is now becoming a runaway reactor , sucking in ever hotter underhood air.
In headers, the heat builds even faster, but now the exhaust at least has somewhere to go instead of running from one cylinder to the next like happens in the logs. And the overlap period is foiled by the higher pressure in the pipes. This overlap produces a scavenging effect that allows the engine to draw in more air at the same throttle setting, or at the very least get it moving earlier.. Your job is to put just enough fuel in that air and to get it all burned up inside the chamber, before the exhaust valve opens. Thus your headers or logs will run cooler and so will your engine, and this is the road to fuel-economy.
But IMO having 22+14=36* at 2240rpm is still waaaaay too much power-timing, for a low-compression,probably" stock cam,engine.
I also think, there is no good reason to run 14 idle-timing; it just messes up your Transfer-slot sync, and I'm surprised you don't complain about a tip-in hesitation, and terrible, cold-engine-manners.
And again, with this much timing, the throttles are usually too far down the transfers, forcing you to increase the fueling from idle-mixture screws. Of course that just makes the engine run richer than it needs to be, all the time that it ain't at idle.
(3300less 1000)/100x .95=22* .. to that add the initial of 14 and 15 from the Vcan, assuming it all comes in, for a grand-total of 51, looking good.
But If she had not got that timing, the fire would start late and would not finish burning in the chambers. Instead, it burns in the headers or logs.
In logs this forces the engine to pump the gasses out of the chambers into a hi-pressure zone, costing you both fuel-economy and additional underhood heat.
Underhood heat is underhood air-pressure, and so ram air gets stalled. But worse is that your carb is now becoming a runaway reactor , sucking in ever hotter underhood air.
In headers, the heat builds even faster, but now the exhaust at least has somewhere to go instead of running from one cylinder to the next like happens in the logs. And the overlap period is foiled by the higher pressure in the pipes. This overlap produces a scavenging effect that allows the engine to draw in more air at the same throttle setting, or at the very least get it moving earlier.. Your job is to put just enough fuel in that air and to get it all burned up inside the chamber, before the exhaust valve opens. Thus your headers or logs will run cooler and so will your engine, and this is the road to fuel-economy.
But IMO having 22+14=36* at 2240rpm is still waaaaay too much power-timing, for a low-compression,probably" stock cam,engine.
I also think, there is no good reason to run 14 idle-timing; it just messes up your Transfer-slot sync, and I'm surprised you don't complain about a tip-in hesitation, and terrible, cold-engine-manners.
And again, with this much timing, the throttles are usually too far down the transfers, forcing you to increase the fueling from idle-mixture screws. Of course that just makes the engine run richer than it needs to be, all the time that it ain't at idle.
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Wrapping the headers isn’t a bad idea at all. It is a lot of work for a possibility of zero temp effect. But there is a bit of science behind it working.
In the engine compartment, is there much of an escape route for the hot air?
In the engine compartment, is there much of an escape route for the hot air?
MopaR&D
Nerd Member
What kind of vehicles are your SBC's in, are they also swapped into older-style hot rod vehicles? It sounds like you have an airflow problem, got any pics of your radiator and fan setup? I've always run factory thermal clutch-drive fan and shroud and never had temps creep on the freeway going 80 MPH in my '70 Duster. Might be a case where the shroud for your electric fan obstructs free air flow when you're driving at speed. I'm assuming a mechanical fan isn't really an option though with your custom setup?
Rock Able
Well-Known Member
It exhibited the same behavior with zero vacuum advance, same with advance and several different settings. The tune up ain't the problem, IMO. Thanks anyway.
Rock Able
Well-Known Member
Yes, down and out is pretty wide open. Lots of room. I think there is not enough air flowing through the radiator. Maybe the shroud is restricting it.
Rock Able
Well-Known Member
54 Chevy, 57 Chevy and a 48 Buick. I agree with the airflow assessment. Gotta be an electric fan but I'm about ready to try one without the shroud.
Shroud picture please!
Rock Able
Well-Known Member
MopaR&D
Nerd Member
Sounds crazy but this would confirm if the shroud has anything to do with your issue... remove the electric fan and shroud completely and then drive the car on the interstate again. That looks like it could restrict airflow somewhat.
If it turns out the shroud is the problem I would just try mounting the fan directly to the radiator, as close to the core as possible, with no shroud.
If it turns out the shroud is the problem I would just try mounting the fan directly to the radiator, as close to the core as possible, with no shroud.
Rock Able
Well-Known Member
I thought about that. It's a PITA but I may try it. I've got a couple more tests to run before I do that.
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