In another economy post DI mentioned that the Feather Duster had a vacuum advance dash pot that allowed a total of 50 degrees advance into the timing at cruise. I wondered how well that worked? Are there draw backs? Was the engine 'flat' feeling there, or did it feel like it had enough torque to carry you down the road nicely. Did it die going up hills? Did you endup having to get into the power valve, and pull timing out by reducing the timing with more throttle.

DI, do you still have the stock Feather Duster set up on your car, and how well does it work? I picked up a feather Duster distributor at Carlisle about 8 years ago, and tried it in this car when it was still carbureted. There was a serious miss off idle in it, so I pulled it and sold it to someone else who felt they could deal with the miss issue.

I have been trying to work out a timing map on the Accel ECU which lets you do whatever you want. Any thoughts about, and or experience with this extreme advance curve for cruise economy? If it was so good why did they not do this always? One would think that since they did not do this always, there must be a down side to it, unless you subscribe to the consipiracy theory about Detroit purposely burying high gas mileage technology.

Sam

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This was pretty much normal with all Carbed cars once they learned it would help the fuel on a cruise. My 71 383 Fury Wagon will pull as much as 66* timing right off idle, hech I got the base set at 24. But it is a 8.2:1 engine. Of course it falls back pretty far when you get into the throttle, but I still total out at 42* when WOT & high rpm. This is a pure stock engine, low compression. But if you can get it cruising 75 mph on the highway it will click off 20 plus mpg. I spent some time on the Dizzy.

A lot depends on the weight of the car, the gearing, and how the Carb is setup, and the engine itself. On Idle and cruise you want all the timing the engine can stand and still be smooth & have no starting problems.


Its tunning like this that allowed me to get 22 plus mpg out of a Tunnel Ram with two 600 vacs on a 383 road runner. This engine even had close to a 600 lift cam with a hugh amount of duration with a 3.91 rear gear. You could also turn around and run 10's at the track and chuck down 1/4 tank of gas in one pass & do it on pump fuel.

At the time we didnt know what we had done, but we had a closed chamber head that was shaved a lot. Then we made a set of D shaped pistons out of a set of flat tops & had 0 deck on the pistons with the steel shim head gaskets. We where just lucky, but now we know all about quench and chamber shape. After looking back I see how we did so good, but IMHO we just lucked out because we didnt know about all this stuff at the time. We where just getting all the compression we could out of the flat tops we had and making room for the oversized valves & big cam lift.

I lot of time was spent on the timing curve & fuel mix with the carbs. Although it took me about 3 months of endless tunning it payed off with great results that was beyound what we knew was possible at the time. It use to drive my wife crazy when she would give me a hard time about that old HotRod. I would let her drive to find out it got better mpg than her 250 6 cyl Nova & drove better to boot.


I have said it before, Small steps, trial & erra, and read them plugs. There is no limit, except the limit of your setup. I use to go for 100 mile drives, just for a 1* change in timing, or one step in jet change. I know, with todays gas prices & crazy work hours its hard to spend that kinda time and money on just tunning. But even 10 hours of dyno time with a great tunner cant do the drivability to the level that it can be done with this kinda approach.


Jess

When it comes to timing Ed's mini series on timing is the best , simplest, most comprehensive method I have ever see.

I would search for that post in combination with DIs Hyperpac tuning notes.

Fact is timing is tedious work. I got lucky and tailored a new curve for the Valaint in an afternoon. It was more about good blundering than good science. ( After lots of head and compression work and a manifold/carb change I ended up with a mechnical curve very close to a stock 65 1 barrel setup out of an iron points Prestolite distributor....go figure.

The weight of the car, gears, engine temp and typical driving patterns didn t change....

The cam timing and CR left me with a torque curve similar in shape to a stock curve ......so I guess the mechanical advance stayed the same/close as well.

Of course initial advance was upped and vacuum advance lowered...

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Yeah....Im the one who destroyed this rare, vintage automobile.....

The FD timing curve is very nasty and won't plug into any other car successfully, it's meant to let max timing occur at most off idle to cruise conditions, which doens't do anything but ping and rattle for everybody else...

THE FD timing curve is like this:

Vacc. advance 17 degrees at anything, and 14 in passing gear to almost full throttle...

12 BTDC initial

(So far you're at 29 degrees at all speeds except idle, and 26 when merging in the highway in 3rd gear- 45 mph-55 mph due to the 2.94's and the OD...)

Now... mech advance for it is 3-7 degrees up to 650 rpm (off idle we now have 46 degrees in a school zone...), you get the last 7-11 degrees up to 4600 rpm (it has a 9r governor and the heavy spring won't let it get to 18 degrees...so lets call it about 52-ish for conservative sake)...

In a fair drag race against my dad one day while learning to drive....

I whopped my dad (driving his stock Feather Duster), against my mom's 68 Valiant (225, 3 on the tree, 3.23 rear, with mom in it mouth hanging open)... the Feather was good for mileage, but couldn't get out of it's way if it had to most of the time... along with that timing curve...you had an EGR that dumped open and allowed a fair amount of Exhaust gas into the intake to 1) kick back the NOX, 2) kickback the extra 5-10 degrees of timing we normally don't have during these speeds in performance curves...3) keep the chamber temp down since the timing probably didn't exactly jive too well with the special calibrated Holley 1945 it had to have


-D.Idiot

"But gratefully the thing passed Portland DEQ everytime it went to be checked..."

Thanks DI, but I am not sure I know how to translate that into a timing map in EFI. At high vacuum, what would the timing look like at each RPM, and then at medium vacuum, what would the timing look like at each rpm range, and then at no vacuum, what would the timing look like at each RPM range? That is essentially what the timing map asks. And then finally, if you were going to compromise something, in an effort to improve acceleration, but maximize cruise economy, how would you do it. Anything is possible with the EFI map. Thanks for thinking about this.
Sam

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Since the EFI Hpak long rod project is getting a Holley commander 950 setup, I took my software and tech manual with me to Baghdad and used graph paper to make a spread sheet converting the MAP values against the rpm values, then translated it to approx inches of vacc. to rpm...

I extrapolated 3 maps based on what I knew then:

Drag race map limited out advance to 30 degrees at high rpm...

MP Street 'respring' (which is what you get from a MP distributor with heavier springs for street use)...10 initial, 20 degrees mech adv. then the 20 degrees of vacc. adv. all out by 8" vac.. or so...

Current Hyperpak respring in my duster as a base map....


In this case:

The map at WOT and high rpm, on a NA hi-po build should go for 30 degrees advance. At Decel where vac.. is high and rpm is high but dropping will have that rpm + full vacc. advance (so 50 degrees or so, always program on the conservative side to start).

In middle rpm with moderate vacc. it can vary from 26-44 degrees of advance...


Now when I get the engine assembled and can test this, it'll all change of course, based on cam selection and vehicle weight/load...so ....

just some thoughts,

-D.Idiot

Thanks, We hope you are safe. WE hear some pretty frightening stories about Iraq these days. I will hold you in my thoughts.
Sam

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I got back to the US in late 2005, so I brought my EFI tuning laptop and maps back with me then...thought you knew that Gunpilot, Rob Simmons and I had 'exited' that country a while back (and I'm not going back).

Of course, the way people drive here, safety becomes a subjective issue anyway...


-D.Idiot

Good News. I think I was inactive on this forum while you were gone.
Sam

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