Timing/mechanical advance conundrum....

[BFM_Cuda]

Want to be clear on details: are you disconnecting the vacuum advance while you do the test drives? Is it pinging with or without vacuum advance in play?

Tune the mechanical timing first to a "no ping" setting, and then add and adjust the vacuum advance to eliminate any pinging.

[kawahonda]

have you checked your balancer timing mark to make sure it is at true top dead center?

This is a really good question. This engine has never been apart aside from the heads. I suppose it could be pretty easy/quick for me to check this. I know there is that horizontal timing line on the balancer. Is a way to check this is to rotate the engine until this line is at the "0" mark , and that would be for piston #1?

[kawahonda]

Want to be clear on details: are you disconnecting the vacuum advance while you do the test drives? Is it pinging with or without vacuum advance in play?

Tune the mechanical timing first to a "no ping" setting, and then add and adjust the vacuum advance to eliminate any pinging.

This isn't a vacuum advance ping. I know what those feel like. My original vacuum advance used to add 20 degrees in timing. Vacuum advance pinging in my experience comes into play during partial throttle, slightly off-cruise operation. Vacuum advance doesn't have anything to do with pedal to the metal high-load pinging, so I know for sure my advance doesn't have anything to do with it. I'm using a 10 degree vacuum advance by the way.

This could be a carburation issue (needing more secondary jetting. I currently have .098 jetting), but I know for sure that my initial timing has never been where my recurver wanted it...by several degrees. I shouldn't be slogging this car down at 13 degrees initial, but that's all I can get away with. I should be at 18 degrees initial. My plan is to get to 18 initial (I know my engine likes it based on vacuum reading), and then play around with the 35, 36, 37, 38 total range. When I'm playing around with that range and get faint pinging, then turn to jetting--likely secondary jetting.

[kawahonda]

Alright. Got her tuned to 18 initial + 16 mechanical = 34 all in. 17" vacuum.

Great low end without any pinging. I had roughly estimated the plate would give me about 18 mechanical, but it turned out it gave me 16.

I'd prefer to maybe dial back my mechanical just a hair to give me some more headroom to increase the total later on. This would agree with Chryco. At 18 initial, you're probably nearing the max of what it should be set at.

1) Determine highest vacuum @ idle with timing. This is good to have for notes and intial timing shouldn't exceed that. For example, I may be pulling highest vacuum at 17 initial, not 18 initial. I may find that 19 initial may be more ideal. Hard to say.

2) Use this information to determine optimal initial setting. At 18 initial + 16 mechanical, it doesn't leave me a lot of headroom to increase total later on after carb tuning. Of course, I can always worry about this when I'm ready to sink teeth more into carb tuning, which is requiring deserted highways and more plugs at this point.

The FBO plate is really cool. I however find that it makes the ignition more noisy. The plate kinda sits a little loose underneath the cam (on the part that isn't smoothered by the cam), so when it's spinning at a gazillion miles per hour, it causes more vibration noise. You can hear it inside of the car...it kinda sounded a little bit like my fan was on low speed. The plate is still a SUPERB tool at the minimum and will allow you to test and nail exactly the clearance you want, then you could remove and braze up to the exact spec you want. That sort of is my plan.

Stock slot: .383 = gives me 22 mechanical

Current: .349 = gives me 16 mechanical.

There is an in-between position on the FBO plat that is .368, which I estimate would give me 20 advance. I'd need something that is right around .360 if I ever wanted to move it to 18 mechanical.

I feel like now is the time to leave timing alone and jump back on the carb-side of things. The low end pulls great, no stumbles, smashing the pedal down is pretty fun. I need to plan on finding some deserted highways and do some WOT plug chops. My secondaries are .098. I do have .100 jets in an AFB carb that I can tear out.

[RUNCHARGER]

Nice: You're not rich so I'd throw in those 100's right now and not make drastic changes to your primaries as they must be awfully close right now.

[73_Cuda_4_Me]

 

I fiddled around for quite a while, and when I finally up-jetted, it made all the difference in the world...

[headejm]

Good thread @kawahonda! Thanks for sharing. I also bought one of those FBO distributor plates but haven't installed it yet. It is on the list for sure. 

[kawahonda]

Good thread @kawahonda! Thanks for sharing. I also bought one of those FBO distributor plates but haven't installed it yet. It is on the list for sure. 

My recommendation before you install is to measure (know) your mechanical advance exactly. Then when you remove the distributor cam, measure your slots. Then use that as the basis for information (every .015 two degrees difference in timing). The slots and their respective numbers probably work fine for many people, but for example I'm using a "12" slot right now and I get 16 mechanical with it. I assume every distributor/engine is different!

I'm curious to know if you get more noise with the plate installed. My performance points make a nice positive ticking noise that sound like music. With the plate, it kinda is this vibrating ticking noise that I can hear inside the car. I'm sure different distributors will response differently as far as the noise levels are concerned!

Awesome plate...I plan to use mine as a tool, rather than leave it in there forever.

[73_Cuda_4_Me]

One other thing to mention here.... With my stock dizzy springs, I was getting 5 degrees of 'wander' in timing at idle between 800-900 rpm... it was just at the threshold of mechanical advance down that low...

When I made my plate, I shortened the slots from the inside, so the springs were a smidge tighter at idle, and it doesn't start advancing until I get to 1200 rpm...

(Time to mention Chryco here for that tip!)

[kawahonda]

Well, I took it out for another spin and that rattle noise from the plate was really getting to me, so I drove it right back home almost as soon as I left.

Now's a good time to weld up the slot and land at 18 mechanical rather than 16, to give me more tuning head room.

To check my math:

Current slot: .380 = 22 mechanical
Slot I tried: .346 = 16 mechanical

Slot I'm considering: .360-.362.

At 18 mechanical, I'll be able to set my initial pretty healthy still (16-18), but now will have a range to give me headroom as a I richen up carb.

[chargerdon]

curious...  you vacuum advance..is it on the Port or Timed side of the carb ?

Me, im running a Mopar distributor limiting plate:  https://www.ebay.com/itm/Mopar-Distributor-Mechanical-Advance-Timing-Limiter/323099910935?hash=item4b3a416317:g:6yAAAOSwQJhUdOgX

My engine 408 stroker runs around 9.6-9.8 static compression.  I keep the static advance at around 16 degrees BTDC and the limiter plate set at 18 for total of 34.    Then to enhance the idle i keep the vacuum advance on the Port side for another 8 degrees at idle (16 static and 8 vacuum) to give me around 24 BTDC at idle...  open the throttle and the vacuum disappears.   I get fairly smooth idle even with the lunati 703 cam enough vacuum to run the power brakes, and great performance with zero pinging on 93 octane pump gas.   

[kawahonda]

Ported side of carb (stock location for AVS). I do all timing measurements with it plugged up.

This same distributor is going into my 408 too! I heard the magnum strokers like a tad bit less total, 34 sounds about right where I'd want to shoot for with my stoker build.

So I'm trying to keep that in mind as well which is another reason that 18 mechanical advance just seems right not only for this 340 which can take more initial but also future proofed to go into the 408 build and still work well. My 408 won't have too big of a cam though (XR274), so it won't need tons of initial to run. Your cam is bigger.

I run 91 octane gas up here. It's just what's mostly available. There's 93 pumps, but I'd rather not plan a trip to go get gas. LOL.

[chargerdon]

Yeah, im lucky here in NC all premium is 93 octance...  im sure the extra two points help a lot. 

[kawahonda]

I'll finish this up tomorrow. It should look pretty original.

[Chryco Psycho]

Cool looks good , I would have welded the inside of the slot tho .