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Yet another timing problem!

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Just to add, there are a bunch of posts here and other forums stating that 42* total is fine. Such as this one

Post in thread 'Setting the timing on a 383'
Setting the timing on a 383
I read your suggested post. Only post #3 mentions "My car runs good at 42". "unkown compression ratio" Lives in Colorado at altitude. Go ahead and run it. All other posts suggest 36-38 which is safe. So he might get away with it. All this means what? It feels ok by the seat of the pants? Was it track tested? Go ahead and run it. I can tell you I've seen enough burned decks from excessive timing. Not to mention main web damage from detonation. Just trying to give some wisdom of building and racing this stuff close to 40 years.
Doug
 
A 383 with domes in a racing situation using race gas will benefit from 40-42* . Even 45 in 1/8 MI.
But, in a street lower performance situation I'd go 38 max especially with pumpgas as Doug suggested.
 
Thanks! Doug, I appreciate your analysis, no need to get all twisted up about it! I already said I’m going to address it, but surely the best way to learn is to ask?
 
Thanks! Doug, I appreciate your analysis, no need to get all twisted up about it! I already said I’m going to address it, but surely the best way to learn is to ask?
Timing is all relative to head design, temp, comp ratio, fuel, atomization, bore size, dome, and rod length. To make the most power the plug should fire to enable peak cylinder pressure around 15 degrees ATDC. I am speaking here of factory iron heads. To start a BB mopar has a lousy plug location. The chamber isn't the best eithier. So it takes a fair amount of timing to get peak pressure at the desired time. The larger the bore or adding dome to the piston requires even earlier timing. There is a flip side. The closer the peak pressure is to TDC the greater the chance of detonation. Detonation doesn't have to occur very long before the onset of damage. A little high air temp, little bad batch of fuel, a little oil in the cylinder and you are in trouble. A bigger bore 400/440 with a dome might need an extra degree or two when compared to a flat top 383. So what it timing worth in ET? Depends. but I'll give you two instances where less was better. #1 Duster street car, 10.5-1 340, cam , headers. Set at the recomended 35 degrees for a iron head small block. Runs 13.15, 13.16. We reduce the timing to 33 it goes 12.88. Next pass 31 degrees, 12.64. Next shot reducing timing slowed it down, 31 was best. #2 my current 64 Belvedere. 4.5" bore, 15-1 w/flat top piston, Indy-1 heads with far better chamber design and plug location. Most run these heads are run up around 37 degrees. We normally run 34. The car has been 8.96. We slow it down to run 9.25 index. Pulling the timing to 27 degrees kills about .10. So not much. If we cant gain mph with more timing, it doesn't get any more. Hope this helps your learnig curve. Trust me back in the day I owned a car that was a piston melter. It took a few sets before I realised that it had about 4 degrees to much timing. I still own it. Hasn't hurt a piston since 1991.
Doug
 
Thanks! So you’re suggesting total mechanical advance at 34? I’m not racing, just cruising (or more accurately, wrenching! One day…). Mainly I don’t want to be throwing gas fumes out the back so bad nobody can breathe near it!

Right now I’m in the middle of swapping out the bent, leaky trans pan, tyen need to rewire the electric fan, then will get back on the timing. I guess I should order the “keys” to accurately set it, and put in one heavier spring to get total timing in by 3000ish rather than 2800
 
Thanks! So you’re suggesting total mechanical advance at 34? I’m not racing, just cruising (or more accurately, wrenching! One day…). Mainly I don’t want to be throwing gas fumes out the back so bad nobody can breathe near it!

Right now I’m in the middle of swapping out the bent, leaky trans pan, tyen need to rewire the electric fan, then will get back on the timing. I guess I should order the “keys” to accurately set it, and put in one heavier spring to get total timing in by 3000ish rather than 2800
Generally 36 is a good safe all around number with stock style heads. It may like 38 but on the street it may not be noticable. What will wake it up is more timing sooner. Somewhere 15-20 intitial depending on cam and comprssion. But that will require limiting the mechanicle advance in the distributor.
Doug
 
Generally 36 is a good safe all around number with stock style heads. It may like 38 but on the street it may not be noticable. What will wake it up is more timing sooner. Somewhere 15-20 intitial depending on cam and comprssion. But that will require limiting the mechanicle advance in the distributor.
Doug
thanks! I ordered the keys and springs, will be delivered in a few days and I’ll report back.
 
Timing is all relative to head design, temp, comp ratio, fuel, atomization, bore size, dome, and rod length. To make the most power the plug should fire to enable peak cylinder pressure around 15 degrees ATDC. I am speaking here of factory iron heads. To start a BB mopar has a lousy plug location. The chamber isn't the best eithier. So it takes a fair amount of timing to get peak pressure at the desired time. The larger the bore or adding dome to the piston requires even earlier timing. There is a flip side. The closer the peak pressure is to TDC the greater the chance of detonation. Detonation doesn't have to occur very long before the onset of damage. A little high air temp, little bad batch of fuel, a little oil in the cylinder and you are in trouble. A bigger bore 400/440 with a dome might need an extra degree or two when compared to a flat top 383. So what it timing worth in ET? Depends. but I'll give you two instances where less was better. #1 Duster street car, 10.5-1 340, cam , headers. Set at the recomended 35 degrees for a iron head small block. Runs 13.15, 13.16. We reduce the timing to 33 it goes 12.88. Next pass 31 degrees, 12.64. Next shot reducing timing slowed it down, 31 was best. #2 my current 64 Belvedere. 4.5" bore, 15-1 w/flat top piston, Indy-1 heads with far better chamber design and plug location. Most run these heads are run up around 37 degrees. We normally run 34. The car has been 8.96. We slow it down to run 9.25 index. Pulling the timing to 27 degrees kills about .10. So not much. If we cant gain mph with more timing, it doesn't get any more. Hope this helps your learnig curve. Trust me back in the day I owned a car that was a piston melter. It took a few sets before I realised that it had about 4 degrees to much timing. I still own it. Hasn't hurt a piston since 1991.
Doug
Taking the time to share your wisdom with fbbo is so much appreciated, thanks Doug!
 
Motor is a 383, believed to be a ‘69, in my ’66 Coronet.

- Jegs distributor, looks like a clone of the MP one with a magnetic pickup and vac advance. Default light blue springs and I haven’t touched the vac advance.
- Unknown “Purple” cam, but probably the MP 268/284 (they seem to have bought everything from Jegs and that’s the only “purple” cam they have)
- MSD 6AL
- Edelbrock TM3 single plane intake
- Edelbrock 600CFM carb

Symptoms:

Car starts and runs, very rich idle, but pulls OK and mixture seems to clean up off idle, no clouds of smoke etc. Static timing looks to be 30-40*. I can’t check with my dial-back light due to spark scatter, but my old timing light shows the timing is stable and advances as expected both mechanical and vacuum (which is disconnected for setting timing of course).

So far I have checked:

- Balancer TDC is correct, checked many times with a stop and a whistle tool
- Reluctor pickup connections are not switched/swapped
- Distributor is 180* out, but plug wires moved to compensate. Rotor/wire #1/reluctor trigger line up as expected
- Carb is rebuilt and thoroughly cleaned, transfer slots set square And idle screws around 1.5 turns out
- Installed a variable idle air bleed to see if that can weaken the idle mixture, it does need a little air and then it idles ok at 800 RPM and revs fine up to 3K, and the idle screws work. I haven’t tested further as I’m worried about the total timing by that point.
- Plugs are pretty black, it’s only really idled and started on choke so I’m not sure that tells me much.

So - what have I missed? I haven’t checked cam timing... Could that cam and the single plane intake just need a lot of advance and/or fuel?

Ideas?
Degree your cam first. Then if the problem persists, change the intake to a dual plane. Single plane is race only. No bottom torque for street use. Runs great wide open. Lastly a carb spacer made spacificly for your carburetor brand, i.e. AVS must have four hole intake for vacume system to work.
 
Nope, vacuum is not dependant on the spacer, open, 4 hole or two hole. The carb base has a passage that connects the left side throttle bores to the rt side t/bores......for vacuum purposes.
 
I think the issue of idle is largely solved. I guess I should have mentioned that I have a 4 hole spacer, but I didn’t notice much of a difference with or without. It should help heat soak though. I also checked the vacuum passages under the carb, and Geoff is absolutely correct, there are no vacuum passages that would require either a split plenum or spacer on this carb.

The TM6 is within 10lb/ft of the Performer at 3000 rpm, which is IMHO within the margin of error, engine wear, gas quality and timing. https://www.motortrend.com/how-to/hrdp-0712-mopar-intake-manifold-comparo/
 
I’m still waiting to get the kit to adjust total timing which is clearly needed of course.
 
Finally back on the car. Sorted out the gas gauge, installed a relay for the electric fan, tidied up some other wiring, swapped the trans pan for a cast one so NO leaks now - progress!

Tried to start her up a couple of weeks back, and it ran on maybe 6. WHAT? Somehow, while sitting for a few weeks, 2 plug wires backed off the plugs and one came out of its end. Just sitting. Anyway, that was strange but an easy fix.

Today, being a bit warmer, I thought I'd pull the distributor and limit the advance. I've never pulled a distributor before - just never had to - so was a bit nervous about messing something up, but reassured myself that it can only go in 2 ways! I also wanted to clock it like the factory setup and, since the previous owner put it in 180 degrees out, flip that too. One step at a time, no problem. Got the dizzy out, put the 14 degree key in and... it was already set that way.

Now I'm a little confused... 18 initial plus 14 mechanical equals 32 degrees, so I need to re check it with a light. This should be good to go! Yes, will check with vac plugged.

Back soon when I have time to do this. Still working on insulating my garage doors and have other cars to work on too.
 
Close this off.. it’s all back together, everything works, even the gas gauge and clock! Although with an aftermarket sender the gauge is wrong. Whatever. And the odometer broke.

Meanwhile, the timing is fine, maybe I could back off a degree of initial but it starts well. The key to running well seems to have been balancing the timing with the idle speed, idle air bleed and idle screws. I intend to replace my janky air bleed setup,with an adjustable PCV when I can get to installing baffles in the valve covers.
 
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