2002Scoob

Your Mileage May Vary?

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(edited)

It's spring-time, basically, and Brunhilde is outa' her car-hole, and running quite well, if I must be honest. 

 

I'd like to get her to my Bavarian wonder-tuner, but it's a 4 hour drive, and I want to dial it in as best as possible. Not only so I can show up and go 'ta-da!' look what I've made since I saw you last!, but also so I'm not emptying my wallet on premium fuel before I get there. 

 

I just wanted to do a little gut-check, and see if anyone had some data points to compare/share, or tuning suggestions to get better mileage. 

 

What kinda Mileage are you seeing in your DCOE cars? Have any tuning/jetting suggestions for getting some efficiency back?

 

On one tank of premium I was able to get 212km and refilled with 32 liters, or 15.5l/100km or around 15mpg

 

Driving was 50%puttering around town at low speeds, with a few punches here and there, maybe 30% back-road spirited driving, and 20%mixed speed roads 100-150kph

 

Weber DCOE 40 32

-130 Mains

-180 Air Correctors

-55 (f8?) idle jets

-40 pump jets

Schrick 292

+2.5 degree cam-timing

9.5:1 Pistons 

 

 

Idles around 12.5-13:1

Usually 11.5-12.5 when in the progression circuit

Midrange is 12.5-13.8

WOT- 13.5-13.8ish

 

I tried throwing in a 125 main/170 air corrector, which netted a little bit leaner light-throttle progression and lower-midrange with AFR's in the 13.5-14 range, but punch the throttle to accelerate aggressively, and things lean out quickly into the high 15-16's, and higher RPM's are in the upper 14's/15's on moderate throttle and I didn't dare punch it because I know it would only go leaner. 170's is the smallest air-corrector I have... but I'm not fully convinced the solution is less air... I think the 125's are just too small. 

 

Thoughts? 

 

Bonus question.... Just how much do you think having a fully decked head (with the thicker head gasket) adds to the compression ratio with a 9.5:1 90mm piston? 

 

 

 

 

Edited by 2002Scoob

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(edited)

'nuther data-point...

 

Last weekend drove back-roads to Strasbourg on a sunday and back, with a full bike on the roof (shitty aero) and hitting all back-roads that are a mix of start-stop, 40-150kph  and ringing her out most of the way. That took pretty much a full-tank, and was about 230k round-trip.

 

Those Bavarian girls sure know how to drink!

Edited by 2002Scoob
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Smaller jets AND smaller air correctors, if you want to raise your AFR at lower flow

and lower it at higher flow.  

 

Now, "revs" and "flow" are NOT the same thing- to have high flow, you have to have high

revs AND the throttle open significantly, as in, over, say, 15%.  A throttle position sensor,

logged with afr and revs, and you can start to see where the mains kick in, and then the 

air correctors start to shape the curve.

 

I know it seems wrong, but when I had to run small chokes like that, I had a selection of 

air correctors down to 120.  I think i usually ran in the 130- 140 range.  And that got

the car pretty flat afr- wise.  

 

For economy, you're trying to get light- throttle cruise as high as you can without misfire, detonation

or overheating.  It's a real dance, but significantly leaner than stoich is certainly fine under light load at 100 kph.

 

Also, you want to tune your timing to light off that lean mixture early, since it burns slowly, but not 

STAY early as your AFR drops for heavier load.

 

Bonus answer:  depends on how thick your head is now. 

And where your valves have been sunk.

129.X is base (right?  That's why I always cc the head)

and every .5mm raises you maybe .4?  Ish?  there are so many

variables, though, especially in your valves, that the only way to know

is to measure.

 

t

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2 hours ago, TobyB said:

For economy, you're trying to get light- throttle cruise as high as you can without misfire, detonation

or overheating.  It's a real dance, but significantly leaner than stoich is certainly fine under light load at 100 kph.

 

You can go 17:1 if you put enough advance on it. Custom timing curves are obviously easier with electronically programmable ignition but tuning dizzys mechanically is the bread and butter of carb shops, if any still exist. 

 

Lots of part-throttle advance is good for lean (economy) mixtures. Carbs can't do lean mixture at low rpm and high throttle opening unless they're just flat-out too lean everywhere. Lean mixture at low rpm and high throttle angle, coupled with overdrive, is how modern cars get good fuel economy. The (more) open throttle reduces pumping losses, and the engine management can lean it out and advance it like crazy. But half-way there is better than not at all. 🙂

 

I don't know why they decided the Tii didn't require vacuum advance. Maybe it advances timing at part throttle via another mechanism. I know enough about kfish to be dangerous.

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Forever coming with good info, @TobyB

 

Going to process it a bit... and think of how best to angle my next and last jetting approach with these 32's. I think I could afford one more small eurocarb order of under 30, or appx 1/2 tank of gas... as I think some better economy will save me at last that headed there, or more.

 

Once I make it to Bavaria, in go 34's, as that's what I'd like him to tune with. 

 

3 hours ago, TobyB said:

Bonus answer:  depends on how thick your head is now. 

And where your valves have been sunk.

129.X is base (right?  That's why I always cc the head)

and every .5mm raises you maybe .4?  Ish?  there are so many

variables, though, especially in your valves, that the only way to know

is to measure.

 

The head is pretty much at minimum, and I think the max allowed machining is .5mm, and I vaguely remember my head basically being there, so 128.5ish?.. but it's got the .3mm thicker gasket in there... so ballpark it's got .2mm less height overall...ish. So by your math it's mayby only up a few tenths then overall. 

 

Never got it CC'd or did any crazy valve-work.  Just hardened seats and exhaust valves are shaved down for more clearance, I forget how much. 

 

Again, great info! Danke :)

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3 minutes ago, Jimmy said:

 

You can go 17:1 if you put enough advance on it. Custom timing curves are obviously easier with electronically programmable ignition but tuning dizzys mechanically is the bread and butter of carb shops, if any still exist. 

 

Lots of part-throttle advance is good for lean (economy) mixtures. Carbs can't do lean mixture at low rpm and high throttle opening unless they're just flat-out too lean everywhere. Lean mixture at low rpm and high throttle angle, coupled with overdrive, is how modern cars get good fuel economy. The (more) open throttle reduces pumping losses, and the engine management can lean it out and advance it like crazy. But half-way there is better than not at all. 🙂

 

I don't know why they decided the Tii didn't require vacuum advance. Maybe it advances timing at part throttle via another mechanism. I know enough about kfish to be dangerous.

 

Well, I've got a 123 dizzy, so that option is there, and I do have it plumbed for vacuum advance and it works, I just haven't gotten it to work well. It was the root cause of a low RPM stumble when pulling away, and was effectively adding too much advance. With winter approaching I took that part of the map out cuz I didn't have the time to figure it out properly. Another thing I'd like the tuner to look into it's usefulness. 

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Are you using manifold or ported vacuum? 

 

If manifold, did you leave the "sawtooth" in the advance curve so it doesn't go max vacuum advance at idle and cut the timing ton as soon as you open the throttle?

 

I also have a 123 but haven't tuned my vacuum advance much yet. It runs so much better than the stock dizzy that I've not made it a huge priority. I've been messing with other stuff. I still need a wideband too.

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Manifold. It's pulling from a T-barb I machined from brass and spliced into the vacuum hose going to the brake-booster, so behind the throttle-plates. 

 

The curve i used was pulled from... I think a map I saw in an thread post from Zinz. I just plopped it in and expected it to work like an ignoramoose. 

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Well, your vacuum curve should resemble a sawtooth or shark fin. 0 at the highest vacuum, then full vacuum at whatever vacuum you make at cruising throttle at cruising speed, tapering off to less as the the vacuum reduces toward more throttle opening.

 

I don't remember my starting numbers, maybe 80-50 or 80-30? The specs I have state the stock vacuum pot on the dizzy moves 6 degrees of distributor rotation which is 12 degrees of advance at the crank. 

 

I set my max vacuum advance to 6 degrees for starters just so I could drive it without pushing anything too much until I really tuned it. I intend to up it to around 55 degrees total advance once/as the carb is sorted.

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dc6f0580b6cc233f1f76e324eb5a4f3d.jpg

That’s what I had for vacuum advance, but my overall timing was more than it shoulda been in the first place... so the added advance was likely adding to the issue.

Currently, it’s far less advanced at the moment, but I’d have to go pull the map from the car to tell you. I’m already up at my apartment with too many stairs and no elevator... so I can give actual curve tomorrow, haha.


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I've been trying to solve the vacuum map puzzle on the 123 Ignition distributor for a while.  My issues is I am running a single Weber 45 DCOE on a Lynx manifold and have no option to pull vacuum reading from above the throttle plate, so I tapped the Lynx manifold to provide manifold vacuum readings.  I took the car out to record some live data with my son in the passenger seat with the iPad.  The readings I was getting weren't exactly consistent (why is the gauge in inHG and the map table in kPA, shouldn't they both be the same).  For example, at idle, the car would read 14 inHg (47.4 kPA), but it also records 14 inHg at 4000 RPM in a 2nd gear pull.  The only variable for turning on additional advance based on vacuum for the 123 Ignition distributor is engine RPM and it is a single on switch, so using the table in 2002Scoob's post, every time the engine is above 1500 RPM and the gauge is between 9 inHg and 25 inHg (30 - 86 kPa), the distributor will add 7 degrees of advance.  Now with my old map, this would be adding advance in conditions that I don't particularly want or need additional advance, (4000 RPM in 2nd gear, 42 degrees + 7 degrees = 49).

 

What I really want is more advance when I am cruising on the freeway (say 2500 RPM in 5th gear at 24 inHg (81.2 kPa).  Right now, I can't figure out how to achieve this with the limits of the 123 ignition application and possibly only having manifold vacuum readings available.  If I wanted to add an additional 10 degrees of advance to the top of my new Ti map for cruising in 5th above 2500 RPM, I would set the vacuum map to start at 2500 RPM and give is a pretty small range say 21 - 24 inHg (71 - 81 kPa).  Unfortunately for me, I see that condition all over the place.

 

4000 RPM, 3rd Gear - 24 inHg

3000 RPM, 4th Gear - 24 inHg

2750 RPM 4th Gear (downhill) - 24 inHg

2500 RPM 5th Gear - 24 inHg (Cruising)

 

So I currently have the vacuum advance map disabled and am running a straight RPM map based on the Ti until I can find a scenario that works for adding advance when appropriate.

 

Mark92131

 

 

 

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45 minutes ago, Mark92131 said:

I've been trying to solve the vacuum map puzzle on the 123 Ignition distributor for a while.  My issues is I am running a single Weber 45 DCOE on a Lynx manifold and have no option to pull vacuum reading from above the throttle plate, so I tapped the Lynx manifold to provide manifold vacuum readings.  I took the car out to record some live data with my son in the passenger seat with the iPad.  The readings I was getting weren't exactly consistent (why is the gauge in inHG and the map table in kPA, shouldn't they both be the same).  For example, at idle, the car would read 14 inHg (47.4 kPA), but it also records 14 inHg at 4000 RPM in a 2nd gear pull.  The only variable for turning on additional advance based on vacuum for the 123 Ignition distributor is engine RPM and it is a single on switch, so using the table in 2002Scoob's post, every time the engine is above 1500 RPM and the gauge is between 9 inHg and 25 inHg (30 - 86 kPa), the distributor will add 7 degrees of advance.  Now with my old map, this would be adding advance in conditions that I don't particularly want or need additional advance, (4000 RPM in 2nd gear, 42 degrees + 7 degrees = 49).

 

What I really want is more advance when I am cruising on the freeway (say 2500 RPM in 5th gear at 24 inHg (81.2 kPa).  Right now, I can't figure out how to achieve this with the limits of the 123 ignition application and possibly only having manifold vacuum readings available.  If I wanted to add an additional 10 degrees of advance to the top of my new Ti map for cruising in 5th above 2500 RPM, I would set the vacuum map to start at 2500 RPM and give is a pretty small range say 21 - 24 inHg (71 - 81 kPa).  Unfortunately for me, I see that condition all over the place.

 

4000 RPM, 3rd Gear - 24 inHg

3000 RPM, 4th Gear - 24 inHg

2750 RPM 4th Gear (downhill) - 24 inHg

2500 RPM 5th Gear - 24 inHg (Cruising)

 

So I currently have the vacuum advance map disabled and am running a straight RPM map based on the Ti until I can find a scenario that works for adding advance when appropriate.

 

Mark92131

 

 

 

 

Interesting problem. I haven't methodically logged vacuum readings yet so I don't really know what's going on with mine. When I got my dizzy it randomly disconnected and (occasionally) reconnected so frequently it was rather annoying to tune, and the dashboard would work for only one second then it would disconnect and stay disconnected. I contacted their US distributor Jim (I forget his last name) who kindly informed me that the system is sensitive to interference and a high-quality USB cable is necessary.

 

So I got a shielded, shunted, ferrite-cored Jesus cable, and that reduced the random disconnects to the point that I can actually use the dashboard at idle, but it still disconnects every 30 seconds or so, then usually reconnects. I know that the particular model of laptop I'm using has a reputation for excessive interference from USB 3, even above and beyond the normally high interference from USB 3. My next plan is to boot my older mac into Windows 7 and kill USB 3 and Windows 10 together.

 

I never imagined a direct USB connection would be more problematic than bluetooth. That's a pretty low bar.

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2 hours ago, Jimmy said:

I never imagined a direct USB connection would be more problematic than bluetooth. That's a pretty low bar.

 

Give it a break - it is directly connected to the single biggest generator of electrical noise on a car 😀. This then provides a direct path into your laptop, it’s a pretty harsh environment.

 

Something like an RS485 serial would be better but USB is more universal and wouldn’t need any further converter (which may also be unreliable) to work with typical consumer spec laptops. Trying a different computer is a good idea. 

 

3 hours ago, Mark92131 said:

4000 RPM, 3rd Gear - 24 inHg

3000 RPM, 4th Gear - 24 inHg

2750 RPM 4th Gear (downhill) - 24 inHg

2500 RPM 5th Gear - 24 inHg (Cruising

 

There is something weird about your figures. In particular the two in 4th gear as you would expect the engine load to be completely different. The problem here is that we are trying to make this work like the ancient technology of a diaphragm that applies a fixed amount of advance by moving the points plate once the friction / resistance of the mechanism has been overcome by the force of the vacuum diaphragm and similarly a mechanism that reacts to weights being thrown outwards at certain engine speeds. We actually need to start thinking of this as a 3 dimensional problem closer to the kind of maps that are used by engine management systems (I say ‘we’ because I am nowhere near doing this myself so this is all theoretical too). 

 

The 123 equipment is not limited to behaviour like weights and diaphragms and if you want to add a cut or a spike in advance at a certain speed or MAP pressure then you can, you are not limited to typical curves. The interaction between the vac advance and mechanical advance is more complex than it appears as the vacuum advance coming off as the vacuum falls effectively slows the mechanical advance which is coming on at the same time as the revs increase at certain engine loads.  If we can figure out the best advance for the engine at all speeds and engine loads and then decouple that info into the two variables of speed / advance and MAP / advance for entry into the tables then it would be perfect. 

 

Any mathemeticians on here?

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8 hours ago, Simeon said:

 

Give it a break - it is directly connected to the single biggest generator of electrical noise on a car 😀. This then provides a direct path into your laptop, it’s a pretty harsh environment.

 

Something like an RS485 serial would be better but USB is more universal and wouldn’t need any further converter (which may also be unreliable) to work with typical consumer spec laptops. Trying a different computer is a good idea. 

 

 

There is something weird about your figures. In particular the two in 4th gear as you would expect the engine load to be completely different. The problem here is that we are trying to make this work like the ancient technology of a diaphragm that applies a fixed amount of advance by moving the points plate once the friction / resistance of the mechanism has been overcome by the force of the vacuum diaphragm and similarly a mechanism that reacts to weights being thrown outwards at certain engine speeds. We actually need to start thinking of this as a 3 dimensional problem closer to the kind of maps that are used by engine management systems (I say ‘we’ because I am nowhere near doing this myself so this is all theoretical too). 

 

The 123 equipment is not limited to behaviour like weights and diaphragms and if you want to add a cut or a spike in advance at a certain speed or MAP pressure then you can, you are not limited to typical curves. The interaction between the vac advance and mechanical advance is more complex than it appears as the vacuum advance coming off as the vacuum falls effectively slows the mechanical advance which is coming on at the same time as the revs increase at certain engine loads.  If we can figure out the best advance for the engine at all speeds and engine loads and then decouple that info into the two variables of speed / advance and MAP / advance for entry into the tables then it would be perfect. 

 

Any mathemeticians on here?

 

Im not a mathematician but I will be engaging in this for myself. I'll be happy to collaborate.

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