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Six pack bog

Started by fizz, April 21, 2016, 11:51:18 AM

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fizz

Working on tuning. Slight bog when going to WOT from cruising speed. Of course decreases as I move up in pod spring size. Also pick up some pinging at this transition, until I move up to black spring, then no ping, but seems like a little less power @ WOT with black spring. Runs crisp off center carb. I am going to curve the distibuter hopefully this weekend, I need to lessen the amount of total advance as engine likes initial of 22, but pings after 32. Anyway, is this something that can be tuned out by going richer on the outboard carbs? Maybe that will allow me a little more total advance? Pinging is happening at transition to outboard carbs.

b5blue

  First is the idle set on the outboards? If so how did you do that? How old is this 6BBL? (There are tiny cork seals in the outboards idle needles that dry out.) Do you use vacuum advance? If so try using full manifold vacuum. Check bowl floats height and 6BBL like high volume but only 5LBs pressure. (Carter pump, not expensive.) What cam? Tranny?  :scratchchin:

myk

Aren't we supposed to nail down the timing first, then move on to the fuel system?
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b5blue

Yes...where he is at should be okay.  :2thumbs:

fizz

Cam is a hyd roller w/.560 lift/243/251 duration on a 10 compression 500 in engine. Gas is 91 non oxenated w/octane booster(Race Gas) to 93. Floats on outboards are set to just over the bottom of the sight hole, center carb is right at bottom of sight hole. Carbs were just rebuilt at a reputable carb shop. I have the high volume carter fuel pump from Mancini that I see recommended for this setup. Trans is auto w/3500 stall converter.

fizz

I think I might have to deal with a lean issue to allow proper timing at this point. I am also thinking I have to use stronger springs in the distributer to move my max timing up for after the outboards kick in. And no vacumn advance hooked up. But I am a newb at this level of tuning, so appreciate an advise I might get.

b5blue

  I had my 6BBL 20 years so I start with basic initial settings. Just keep in mind the ping and bog may not be related. I couldn't get rid of ping with iron heads without pulling a bunch of timing out.   My stuff was all very close to stock unlike yours. What's your vacuum reading? I would not be afraid to start swapping springs in the outboards, just keep notes. Bog can come from too early or late transition.
Mine liked 12 initial with 10 added vacuum advance with 34 full using one big and one small spring to give a dual rate on the curve. It would pull like a bull but the iron heads gave a bit of ping at the very top of each gear. No bog at all. (If that helps.)
  With 3 carbs the trick is to not change more than one aspect at a time. Pulling timing was a last resort, it robs power big time.
  Mentally I thought of my 6BBL as center and the twins, what you do to one of the twins you do to the other.  :2thumbs:   

fizz

I have aluminum heads, and agree with you about getting some timing back. I'm thinking it is leaning out on the transition to the secondary carbs. I think I will progress on curving the distributer and then drop down one spring on vacumn pods, then maybe try jetting up the ouboards

fizz

Outboard needles set @1/8 turn. Center carb screws were set for high idle vac, which is 12

c00nhunterjoe

I feel like this is a lean problem not a timing problem. That combo should want more total timing then 32.
Block the outboards with a solid gasket and tune the center 1st and set timing before moving on.

b5blue

  The basics are sounding good. You might be a bit tight on outboard idle screws. I set mine off the intake so just the very tip of the needle peeks out and that was very close to 1/2 turn. (But your not dogging it off idle in gear so leave it be.)
 Try the springs and avoid the ping. Another good test situation is to find a hill or overpass to test while going up. Changes show up stronger for your by the seat gauging.  

BSB67

Quote from: fizz on April 21, 2016, 05:40:26 PM
Outboard needles set @1/8 turn.

Are you using that ever so popular write up on how to tune a 6BBL? The one that tells you that gasoline is flammable?

500" NA, Eddy head, pump gas, exhaust manifold with 2 1/2 exhaust with tailpipes
4150 lbs with driver, 3.23 gear, stock converter
11.68 @ 120.2 mph

c00nhunterjoe

Is the 6 pack setup stock other then the swapped springs? If so, i guarantee its fuel delivery as the factory setup was not designed for bigger cams, cubes, and heads. The outboards are not setup to deliver more fuel. Your options are drill the blocks incrementaly, or convert to adjustable metering blocks. I suggest the 2nd option unless you are trying to fool someone into thinking its "stock" the aftermarket blocks will also allow idle adjustments without carb removal. There is way too much to go into on one of these threads.

b5blue

  It will work he's got 12" of vacuum. Guys said 6BBL was no good with 509 cam and I ran 6 years that way with no trouble.  :2thumbs: Quick Fuel metering plates fit inside the outboard fuel bowls if needed. The center carb should be fine as is. I'm trying to recall power valve?  :scratchchin:


fizz

I did start out using that write up, now I am past that initial tuning. I was looking for advise on whether I was chasing a lean condition when the outboards open. I didn't realize the outboards were not jetable, so will get the promax plates. THANKS

c00nhunterjoe

Quote from: b5blue on April 22, 2016, 07:42:54 AM
  It will work he's got 12" of vacuum. Guys said 6BBL was no good with 509 cam and I ran 6 years that way with no trouble.  :2thumbs: Quick Fuel metering plates fit inside the outboard fuel bowls if needed. The center carb should be fine as is. I'm trying to recall power valve?  :scratchchin:

In this case, vacuum isnt the problem. Doesnt matter what time the outboards open when the carbs metered for a stock 440 are flowing that amount of fuel into a 500" modified engine. Adjustable meter blocks will be needed here in my opinion as well as different diaphram springs.

fizz

Sorry if this is a stupid question, but the objective is to richen up the outboard carbs, which I can do with the promax jet plates? They sell a metering block, which is for the center carb. I feel the center carb is pretty close. Then , switch back to the tall yellow secondary springs and recurve distibuter for intial and total timing.

b5blue

Correct, metering plate not block. I'll see if I can find.  :2thumbs: I had 2 but sold them with my 6BBL.


b5blue


fizz

Hey, thanks, got the promax ones coming. I'll report back when I get somewhere with it.

b5blue


BSB67

Quote from: fizz on April 22, 2016, 01:16:30 PM
Hey, thanks, got the promax ones coming. I'll report back when I get somewhere with it.

1) Yes to your original question. IMO, what you are experiencing is a lean transition.  
2) The changes you are planning won't help, in my opinion.  The problem is not the main circuit.
3) The 1/8 turn out, IMO is one of several things that is simply wrong in that silly write-up.

Here is what I suggest that you do to prove, or disprove the lean condition as the source of the ping:

1) Open the outboard carbs idle mixture screws to 1 full turn (this is likely too much, but this is simply a test).  You will probably need to tighten up the center carb idle mixture screws to help compensate.
2) Raise the float levels in the outboard carbs so fuel spills out freely.

Go for a test drive.  You will learn something, and it won't cost a nickel.

500" NA, Eddy head, pump gas, exhaust manifold with 2 1/2 exhaust with tailpipes
4150 lbs with driver, 3.23 gear, stock converter
11.68 @ 120.2 mph

fizz

Thanks BSB, I will try it this weekend