Recurve Duraspark

[redfalken]

Hey fellas!

I'm taking a new Duraspark II that I just bought to Vintage Racing Motors in Redmond to get it recurved on their distributor tester. Here's the curve I'm going for and some specs for my `62. Probably way too much info but I figured it couldn't hurt. Just wanted your opinion on the curve specs. Anything else I should bring up when I talk to them? I'll have the car with me too.

Desired Curve:
• 750 rpm at idle (in gear)
• Ported vacuum advance at idle
• 12º btdc initial timing
• 24º mechanical advance
• 36º total advance all in at 3000 rpm

Engine block: 1968 200ci, specs unknown, likely stock

Cylinder head: 1982 200ci
• Oversized stainless steel valves (1.5" exhaust, 1.75" intake)
• Three-angle valve job (Top Cut: 30°, Valve Seat: 45°, Bottom Cut: 60°).
• Undercut intake valve 30° (not exhaust valves).
• Unshrouded valves
• Combustion chamber polished and equalized volumes
• Milled head .030 (57cc chambers, 8.1:1 CR)

Carburetor: Weber 32/36 DGV 2bbl progressive

Cam: Unknown, likely stock for 200ci w/hydr lifters:
• 252/256 (duration)
• 7 (int open)
• 65 (int close)
• 55 (exh open)
• 21 (exh close)
• 28 (overlap)
• 348 (valve lift)

Ignition control box: MSD 6A

Coil: MSD Blaster2, 45,000V

Exhaust: "Classic Inlines" Headers w/single 2" pipe

Transmission: C4 Automatic

1971 4-lug 8” Rearend (2.79:1): 2,350 rpm @ 50 mph, 2500 rpm @ 55 mph, 2,700 rpm @ 60 mph, 2,900 rpm @ 65 mph, 3,100 rpm @ 70 mph, 3,350 rpm @ 75 mph

Fuel: generally 87 octane regular

[Luva65wagon]

They may want your social security number and date of birth. And possibly your mother's maiden name. You've given them everything else.



Honestly, if they need more than what you've listed (which is way more than I'd know about my motors unless I built them), they're the experts - and they should be asking it of you. The only thing I see missing is what year/model the distributor come from. Did you mention where you got it from and how much it was? Mine came from Pick-n-Pull and may be the cause of my current issues. I may be looking to swap it - maybe.

I still feel very uncomfortable about the work I did on mine considering the information on-line didn't match my experience when I got inside and started tweaking things. So I'll be watching this anxiously to see what you say and what they come up with.

[SmithKid]

Good thing you're taking the car..... They may need to know what kind of key fob you normally use and if the brake pedal pad is new or worn.

[redfalken]

OK...quit razzin' me. I've got such a bad memory, I keep all this stuff in a Word doc anyway so it was just a cut/paste! You'd be surprised what they might want to know. When I took it in for an alignment they wanted to know how much I weighed. I guess they have a ballast system now so they can put weight in the driver's seat and get it more accurate...

I got the DSII from RockAuto. I went for the Autoline brand which is rebuilt in Canada. I think I went for the `81 Fairmont 200. It was $66.28 with shipping and included the cap and rotor (but no adaptor). There was a $3 core charge but Jeff's getting my old one for his upcoming build.

There are (of course) a lot of opinions on the curve characteristics on the Ford Six Forum and TFFN. Mine has always seemed to like 12 BTDC for initial timing and I figured 3,000 rpm was a good point to be all in considering I'm at 2,900 going 65 mph and 3,100 going 70. The mechanical being 24 at the crank seemed pretty middle of the road.

[falcon cobra]

Hey kenny, thats just what they need to know, I use to set dist. on the old sun machine's years ago, my 327 chev was set at about 12 to 14 at idle and was full in by 2600, by changing the springs and adding to the weights or shaving some off to get what you want...I still have access to a dist.machine at transmission kellys,where I worked a few years ago, good luck, and how much do they want for this service??

[Jeff W]

There was a $3 core charge but Jeff's getting my old one for his upcoming build.

$3.00 - I'll have to raid the girl's piggybanks.

[redfalken]

He's going to it for $60. I've got the springs and tried to do it with Jeff's dial back timing light but the MSD was causing some pretty funky readings.

After the timings down I can finally move on to tuning the Weber!

[pbrown]

Kenny,

I would suggest have all the mechanical timing in a bit earlier. Shoot for 2500RPM.

[redfalken]

Thanks Pat. So what's the thought process to figure that out? I've tried reading through threads on other forums to see what others have done but it seems to be all over the place.

[pbrown]

Generally speaking, getting the advance in earlier will improve your throttle response and accelerate quicker. Getting it in too early will cause detention. Getting all of the mechanical advance in as early as possible without causing detonation is the goal. Mine is all in by 2200 RPM. Of course mine was set from the comfort of my sofa with a laptop.

[redfalken]

Picked up the DS II today. Hopefully I can install it tomorrow and go for a spin...weather permitting. I peeked in through the holes on the base plate and noticed he had flipped it to the 13R slot and replaced both springs with the Mr. Gasket kit springs which are lighter. I've heard some say to only swap one of the springs We shall see!

Here are the specs he emailed:

Advance begins at 800 rpm
22 deg of mechanical @ 2300
14 deg of vacuum advance
36 deg of total all in at 2560 rpm

[MacDee]

I did the "replace-only-one-spring" thing to mine, and I have to zing it pretty high, way more than 2500 rpm, I think, to get full advance. (Need to tee off the tach wire from the Street Fire box so I can use my test tach under the hood!) I really think I need install the other Mr. Gasket spring. My throttle response still sucks....

[Luva65wagon]

One thing I'm still a little vague on is how the vacuum advance works - or doesn't - when I converted to the DSII dizzy. I still have the stock carb on this thing and last night when I was debugging my run-time issues, I did watch the timing marks as I accelerated and it's not advancing 20+ degrees much less 30+ degrees. I didn't have RPM to watch, so I'm not sure what I got for that.

I shut it all down last night after only confirming I got the run issue resolved, so I have more investigations to go on this, but you both have vacuum options I don't have, I think. And I know the original distributor was for using the power valve port on the carb.

Any wisdom out there on this issue?

[redfalken]

Is this the Load-o-Matic setup? If so, here's a link to a pretty good write up and I'll cut/paste the text on using this carb with a DS II. Basically, you can plug the spark control valve and run it off manifold vacuum, wherever you can find it.

http://www.classicinlines.com/Loadomatic.asp

Distributor Swaps
The "Load-O-Matic" distributor uses the "Spark Control Valve" (a spring and diaphragm mechanism), to determine the proper amount of vacuum advance, which is commonly a mixture of manifold vacuum (sensing load) and venturi vacuum (sensing rpm). On the other hand, a conventional distributor uses mechanical weights (speed) and manifold vacuum (load), to provide the proper amount of ignition advance for any given situation.

While you can use a Duraspark or DUI distributor with a stock Autolite 1100 carb, both of these distributors utilize a mechanical advance mechanism that was designed to operate with ported or manifold vacuum. As such they will not operate properly using the vacuum port on the stock Autolite 1100 carburetor. To correct this you need to plug the port on the carb, so you don't have a vacuum leak, and run the vacuum line from the Duraspark or DUI distributor to a manifold vacuum source. This can be accomplished using an existing vacuum source on the intake manifold, or the bottom of the carb adaptor. Or you can create a new source by drilling a hole in the intake manifold and installing a vacuum barb. However, you'd need to remove the cylinder head before drilling, to make sure the manifold is free of any debris that could work down into the cylinders and severely damage the motor.

So...what happens if you do try to use the vacuum port on the Autolite 1100 carb? At idle, the "Spark Control Valve" is open, sending manifold vacuum to the distributor. As such, the engine will idle just fine. However the "Spark Control Valve" will not provide the proper vacuum signal under load and/or speed. All engines need more advance when cruising, and less to none at wide open throttle. However since you are now using the carb (venturi vacuum advance) and the distributor (mechanical advance) to compensate for speed, the ignition system will receive to much advance at cruise and wide open throttle. As a result, the engine may chug and jerk from the over-advanced condition at cruise.

[Luva65wagon]

Very interesting. The part that always cornfused me is the thought that vacuum advance actually advanced with acceleration. I'm sure it was a long-ago forgotten thing I learned in auto shop. I always did well in those classes, but I can't remember much from that time to know why. But that's another story for another time.

I have always thought that as engine speed increases, so does the advance, which of course is true with mechanical advance. But since manifold vacuum actual goes down with throttle plate opening, I always assumed (until today) that the reason you hooked the distributor to the carb was that they had a means of increasing vacuum with throttle opening. This is actually true, to a degree, with the old Load-o-matic distributor and carbs. This article, and a related link on vacuum advance, helped cure me of that assumption. Though this is true with this style carb, all distributors with mechanical advance, which the Load-o-matic distributors lacked, required manifold vaccum.

Bottom line is that vacuum advance is NIL off idle and during acceleration. It provides advance in lean-burn conditions, most common at idle and cruise. Lean mixtures need more burn-time (more advance) and rich mixtures require less advance. Mechanical advance is all RPM based and is the advance you have access to when you are accelerating, AKA "getting it on."

So, that being the case, the specs they provided you, Kenny, of:
Advance begins at 800 rpm (I assume all mechanical movement starts here)
22 deg of mechanical @ 2300
14 deg of vacuum advance (I assume they can check this below the 800 RPM)
36 deg of total all in at 2560 rpm
... would seem to imply that you add mechanical advance to the vacuum advance to get this total. Since they can apply vacuum at any point while on the test bench, this doesn't mean you will have 36 degrees of advance at 2560 RPM at wide open throttle (WOT) under load. So under WOT, I think your max advance may be closer to 22 deg. I can't see you getting another 14 deg out of another 260 RPM. So... how did they come up with this total?

On a side note, I stumbled onto a thread yesterday on the TFFN as I was looking around the Internet about what spark plugs people used when doing a DSII swap since I needed a set (this was on my phone - so it wasn't a serious search) and a guy did a bunch of elaborate mods to his 1100 carb to create "ported vacuum," which these guys on CI seriously denounced the use of. The guy on TFFN really thought this was a requirement to do a DSII swap.