Yes I was just looking at Lightning Racing Carbs set. That’s mighty nice of you! Thank you. I will PM you when I receive boosters and banjos.
Comments on my 340 plug under mag
- Thread starter 340inabbody
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Scody21
Just send it
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what gas you running in this thing?
TT5.9mag
Two atmospheres are better than one
Says 92 octane in post 1.
Please @340inabbody post your timing map if you can. If I saw that plug I start by pulling 6-8 degrees from 1500-4000 on the map at all loads and tune back to it. There is something weird going on in your chamber (have you verified TDC on the balancer?) and I’d be overly safe to start tuning. Also, that plug shows your fuel ring is much too wide so after you get the timing situation figured out, you could strip some WOT fuel out of it.
Ok here is my timing MAP. This is Kpa vs RPM. Many places are never hit due to vacuum deficiency. The high advance at idle helps to compensate for in and out of gear differences. With this idle setting there is very little like 100 RPM in and out of gear.
Top rows are WOT ie low vacuum. This is where I believe I need to retard.
Lower rows is higher vacuum.
Top rows are WOT ie low vacuum. This is where I believe I need to retard.
Lower rows is higher vacuum.
Phreakish
Well-Known Member
The area circled in red is where you might be in trouble. If you are trying to emulate a distributor w/o vacuum advance then the numbers should be nearly the same top to bottom. The jump from 19 to 31 at 1500 rpm between 57 and 64 kPa is pretty substantial. You may not spend much time in that cell, but if you get close to it in-between the computer will extrapolate a number somewhere between 19 and 31.
If I were you, I'd try changing the timing in the 1500 , 1800, and 2100 rpm columns to be the same at all kPa values from 64 on down.
I found a link to a nifty excel file that can help you calculate a table based on initial and total plus vacuum with a start/end kPa value.
As for actual timing values, I'll let others chime in on that.
I would think it’s a linear interpolation. But not sure. No smoothing that I have any control of.
Thanks great inputs. I suppose I should not have drastic changes in the chart. When I watch the timing in real time it behaves smoothly. But I can certainly reduce the timing and hopefully kill any detonation and go from there.
Phreakish
Well-Known Member
What you are shown on the screen may be smoothed too depending on how the display filter works and what the update frequency is. If occasionally the values hedge to the low end of say 64kPa between 1200 and 1800, you might get a little blip of excessive advance for a few revs even if it isn't going to the full 32-33, it can likely be well above the 16-20 expected.
Ok I smoothed it out and lowered the timing. What do you think about this? I am not trying to emulate a mechanical distributor. I was doing some of this tuning real time while driving trying to improve the engine idle and transitions. This is why there was an abrupt change as it wanted more timing in certain places right off idle. I’ll try this later today and see how it goes. I an waiting for my higher temp thermostat and contemplating using another carb I have that IS vacuum advance. The one I have is mechanical advance and for my automatic may not be optimal given the issues I am seeing.
glhs0426
Well-Known Member
Just for reference, tuned tuned real time in my brother's 360 Trailduster 9.2:1, 1.94/1.60 ported 302 heads manual transmission, 87 octane, 102° 90% humidity, a/c on. We also worked the idle area to keep the engine rpm stable when the a/c compressor kicks on/off. It idles around 42 kpa @ 800
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This is most useful. I haven’t seen anyone’s actual MAP before. Thanks man! Yeah there is mush to be said regarding real time tuning that this thing can do….I mike your hi timing at cruise! That will help with mpg and clean plugs. I haven’t seen anyone’s reverse idle as I add timing when in gear to balance auto/in gear RPM differential.
glhs0426
Well-Known Member
When tuning this it finally came to me what some efi tuners have said about having timing headroom to "catch" a drop in idle speed. Timing at stable idle isn't set for max vacuum because there isn't any more timing available to raise idle speed for load. i.e. when you drop it in gear, the a/c compressor turns on, you turn the power steering against the stop, the electric fans turn on, etc
Does the car ever hit those high timing points ie high vac/higher rpm?
Tip in is where I need to watch for detonation according to the comments here above. I will be looking at tip in next but detonation is hard to hear a light tip in. I also.need to install my O2 sensor.
glhs0426
Well-Known Member
We spent the majority of our 3hrs on tip in and cruise light and medium throttle. Being a standard was almost like cheating. We filled up with CHEAP no name 87, drove with a/c on during a hot August day. With smooth roads and the manual transmission you could feel surge with too much timing. We pulled 2-3° when we felt surge. It's a heavy 4x4 Trailduster so mileage will never be great, but it runs and drives awesome for a 3.55 gear 4x4 with a mild 360.
We changed the spark plugs after tuning to visually check the tune for detonation. With the fresh set of plugs several WOT pulls were made and then visually checked the plugs. It is at least 2 steps rich, but it's safe and he's happy.
I see needing more tools to tune having an automatic, loud exhaust, and a lumpy cam. 3hrs won't get you close.
We changed the spark plugs after tuning to visually check the tune for detonation. With the fresh set of plugs several WOT pulls were made and then visually checked the plugs. It is at least 2 steps rich, but it's safe and he's happy.
I see needing more tools to tune having an automatic, loud exhaust, and a lumpy cam. 3hrs won't get you close.
glhs0426
Well-Known Member
Forgot to answer the question. No, I haven't seen the whole map used in the high vacuum, high RPM section. It will hit those high numbers, but not all of them. I've seen factory 5.9 Magnum EFI Ignition timing 60° in the right high vacuum, high RPM scenario.
That’s why you use an engine dyno. You can sort that out in a matter of an hour or so.
Other than some sort of knock sensor does a dyno have any way of detecting detonation? Or do you just have to check the plugs after a full pull?
There are knock sensors but they are pretty sensitive.
I just look at the plugs. I don’t even consider what the O2 sensor says until I look at the plugs.
If the plug says one thing and the O2 sensor something else, I believe the plug.
glhs0426
Well-Known Member
Do dynos do part throttle tuning? How do they charge for that? I've been led to believe it's X pulls for X dollars.
You can’t do it on a chassis dyno, or any inertia dyno.
You have to be able to load the engine and hold it there.
I charge by the day and it’s a two day charge if I have to develop a timing curve. I might get it done in one day if I do t have to break in a cam, drop in inner springs and break in the pistons.
It’s definitely two days if have to do all that.
And that’s not accounting for oil leaks and other issues that crop up on the dyno.
You have to be able to load the engine and hold it there.
I charge by the day and it’s a two day charge if I have to develop a timing curve. I might get it done in one day if I do t have to break in a cam, drop in inner springs and break in the pistons.
It’s definitely two days if have to do all that.
And that’s not accounting for oil leaks and other issues that crop up on the dyno.
Mattax
Just the facts, ma'am
If you want to compare with a distributor timing, like we did here, the areas outlined in blue are initial and mechanical advance. The area outlined in green is initial, plus mechanical and vacuum advance.
I don't know what sort of compression, heads, pistons and cam are in the engine, 32 at idle would be for extremely poor combustion and low density fill. A factory 340 would want around 12 - 15 degrees at 640 if emissions was not a concern. AFR around 13:1. A leaner mix will want a little more spark lead and probably will have to idle at 700 to 750 minimum.
Compared to factory timing, the WOT advance looks slow. But that's for an iron headed factory 340 and maybe other changes are at play.
Continuing with the distributor equivalent, there should be no vacuum advance below 6.5 "Hg (101 to 79 kPa MAP).
Between 6.5 "Hg and 10.5" Hg may be able to add in more spark lead. If the engine needs enrichment below 10.5"Hg, then it shpouldn't want more spark lead. That's the fundementals discussed in that other thread.
A MP distributor would provide timing something like this.
I don't know what sort of compression, heads, pistons and cam are in the engine, 32 at idle would be for extremely poor combustion and low density fill. A factory 340 would want around 12 - 15 degrees at 640 if emissions was not a concern. AFR around 13:1. A leaner mix will want a little more spark lead and probably will have to idle at 700 to 750 minimum.
Compared to factory timing, the WOT advance looks slow. But that's for an iron headed factory 340 and maybe other changes are at play.
Continuing with the distributor equivalent, there should be no vacuum advance below 6.5 "Hg (101 to 79 kPa MAP).
Between 6.5 "Hg and 10.5" Hg may be able to add in more spark lead. If the engine needs enrichment below 10.5"Hg, then it shpouldn't want more spark lead. That's the fundementals discussed in that other thread.
A MP distributor would provide timing something like this.
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Mattax
Just the facts, ma'am
I don't see why it couldn't be done on a chassis dyno, if it can do things like constant and step loads. Even if the dyno can do it the operators don't always know how. I've seen that twice. I was going ot try to learn but my relationship was mostly through the partner that left.
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