School Me On Distributor Performance

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indirect_connection said:
Oh I understand that there are many variables and each engine combination responds differently. I'm not trying to tune to 1/10 of a horsepower. I'm only trying to move closer to a performance curve vs emission curve.

That's why I focused on just a few questions in my actual post. As for the title, I've found that not being a regular poster, unless the title grabs attention, no one bothers to read or respond.
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Look you have an expert on site [ member ] send it to him and be done ok ! PS glad u didn't buy the Chinese junk from Summit or jegs
 
I think the most helpful part of this thread has been the idle timing vs transition slot exposure. I had experimented with manifold vacuum to the V-can on the the 273. It did seem to help throttle response, but after the change, the car did sometimes want to stall when I stopped at a stop sign. I'll now pay close attention to the idle speed screw as I tune.

As far as the distributor machine, what exactly is the benefit for a modified engine? I see how it could be useful blueprinting a distributor to a factory curve, but if every car responds different, whoever was recurving the distributor would have to guess at would work with my car. If they aren't guessing, then that contradicts some advice given here, and that you can get a close curve based on the configuration.

Either way, I consider this a learning experience, and hope to do everything myself. Carburetor and distributor tuning is becoming a dying art. Much different that the usual diagnosis I do with a scan tool. And timing is one of the greatest mysteries as new vehicles have no timing adjustments available, in fact you're lucky if it even lists timing in the data stream.
 
when tuning a performance engine, tune ignition first and then tune your carburetor. 4secondsflat has a website and offers a tuning book that is really easy to read and will teach you what to look for in a print medium. In the old days (1960's) a speed shop would use a distributor machine and set your mechanical advance at about 16 or 17 degrees and use light springs to have it all in around 2000 rpm with an automatic, or 2500 rpm with manual. To be honest it worked pretty well. Your cam is probably going to require a lot of initial advance for it to idle well. I suggest getting the book, it's well worth it.
 
I agree its important to set the timing first. But the way to do it is this:
Get the engine started using a ballpark initial and a bit extra idle speed.
Once its running and warmed up enough, set the timing to the initial using a timing light and tach.
Then adjust the idle speed down so the throttles are revealing between .020 and .040" to the intake. Or at least try to that.
Then see if the idle mix screws can be used effectively.
After that, tuning the initial timing, idle speed, and idle mix screws a little at time until the strongest in gear at reasonably low rpm is obtained.

The 4secondsflat info is not what I would recommend.
What the speed shops did for drag racing with points is still useful for drag racing with points.
If you know a bit about the engine and the use it still can be set up pretty close on a distributor machine, just not the way it would be for points and 1/4 mile.
Member @halifaxhops has the springs etc to change the slopes and set up the advance rpm on a Sun machine.
 
indirect_connection said:
I'm surprised by the cam comments. It has shorter duration than a factory 340 cam. Plus its designed for fuel injection, so its ground on a 112 LSA. I was expecting the idle to be mild.

Voodoo Hydraulic Roller Cam - Chrysler 273-360 (W/ Long Snout) 264/270
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My bad. Somehow I read what you posted as duration at .050
It very well might be OK.
A timing advance curve similar to what used to come on Mopar Performance distributor would be a good starting point.

If you want t o do it all yourself you can use the engine as a distributor machine.
 
Indirect.
That cam is bigger, not shorter [ in duration ] than a factory cam. You need to compare the 050 numbers, not adv duration. Plus, it has a tight-ish 109 LSA. That is good. But in combination, it has considerable overlap. This means careful tuning. The first thing you need to do is get the idle timing correct at idle, & vac adv connected to manifold vacuum will probably be reqd IF you want the best possible idle quality, idle vacuum & engine cooling at idle. See my recent posts about this in the 'How to ...' section.
Once idle timing is set, theeeen you check the transfer slot-to-t/blade position in the carb. Some people, with big-ger cams, drill the blades for extra air to reset the t/blade position. By giving the engine the extra timing at idle it wants, holes may not be needed or maybe smaller, because the extra timing has increased engine efficiency at idle.
 
So I reassembled the distributor today. I went to check the vacuum advance and it would not hold a vacuum. The diaphragm is shot. Any recommendations for a replacement? Parts store or speed shop?
 
indirect_connection said:
So I reassembled the distributor today. I went to check the vacuum advance and it would not hold a vacuum. The diaphragm is shot. Any recommendations for a replacement? Parts store or speed shop?
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I have them if needed. Need to know what the number on the arm is.
 
Actually ordered one last night. I just matched up the distributor number and came up with Standard Motor Products VC155. I looked at Summit, Rock Auto, and AutoZone. Nobody gives any info on how many degrees of advance, or if they're adjustable. Even the Standard Motor Products webpage was worthless.

The canister I took off says 6.5x on the arm.
 
Don't you just hate it when every bit of new information creates more questions than it answers? I didn't realize that the hex on the OUTSIDE indicated adjustability, so I need to order a new pod. I started searching the web for a breakdown in available vacuum advances, since most manufacturers don't. I did find a paper, written by a guy called Lars. Lars is popular in the C3 Corvette forum I'm also a part of, he is apparently a whiz with Quadrajets. Here is his information, unfortunately it only applies to GMs...
https://www.crankshaftcoalition.com/wiki/images/e/e4/Vacuum_Advance_Specs.pdf

So I went to the Summit site, and started reading numbers off the pod arms by blowing up the pictures. I've found two canisters with the most built in advance (9.5), whose arms match the shape of the cannister I currently have.
DODGE Standard Motor Products VC167 Standard Motor Vacuum Advance Canisters | Summit Racing
DODGE Standard Motor Products VC-168 Standard Motor Vacuum Advance Canisters | Summit Racing

Since they are shaped the same, with the same advance, I assume the only difference is the vacuum at which they operate. On has AG6 printed on the housing, the other AG11. Is this referring to the vacuum that it starts adding timing?
 
indirect_connection said:
Don't you just hate it when every bit of new information creates more questions than it answers? I didn't realize that the hex on the OUTSIDE indicated adjustability, so I need to order a new pod. I started searching the web for a breakdown in available vacuum advances, since most manufacturers don't. I did find a paper, written by a guy called Lars. Lars is popular in the C3 Corvette forum I'm also a part of, he is apparently a whiz with Quadrajets. Here is his information, unfortunately it only applies to GMs...
https://www.crankshaftcoalition.com/wiki/images/e/e4/Vacuum_Advance_Specs.pdf

So I went to the Summit site, and started reading numbers off the pod arms by blowing up the pictures. I've found two canisters with the most built in advance (9.5), whose arms match the shape of the cannister I currently have.
DODGE Standard Motor Products VC167 Standard Motor Vacuum Advance Canisters | Summit Racing
DODGE Standard Motor Products VC-168 Standard Motor Vacuum Advance Canisters | Summit Racing

Since they are shaped the same, with the same advance, I assume the only difference is the vacuum at which they operate. On has AG6 printed on the housing, the other AG11. Is this referring to the vacuum that it starts adding timing?
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LOL...summit says neither one of those is adjustable but they are. The difference is the amount of TOTAL advance you get from the can, and the adjustable part is when the advance starts.

It would be nice if summit printed the advance amount in the description but a quick Google search should tell you.

Or, you can PM @halifaxhops. I’m betting he knows those part numbers off the top of his head and what they pull.
 
slantsixdan has listed some of the specs for SMP made units.
ps. g**gle is no longer very helpful in just finding info, esp on older webpages.
 
Long time for an update, but my first test drive resulted in a slipping transmission.

I ended up using one of the Mr. Gasket springs. It doesn't seem to be too loose, it doesn't start increase timing to maybe 2000 rpm? I don't have an underhood tach, so I'm not exactly sure.

The biggest concern I have is that I'm only showing 15 degrees of mechanical advance. I have base timing set at 15 degrees, and it's topping out at 30. I should be getting a few more degrees. My only thoughts are that I put on the wrong timing tape. I'll have to check.
 
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