Latest six pack tuning...
#2300900
05/07/17 10:44 PM
05/07/17 10:44 PM
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mickm
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So, the latest. For a re-cap, 540 Hemi with the mopar manifold and stock repo carbs.
I just went from the 66 jets to 64 in the center carb. AF went from ~13.4 to ~14.0 at cruise, ~12.2 to ~12.6 at WOT. I will go one or two more jet sizes as I'm looking for 12.8-13.2 on WOT, mid 14's fine with me on cruise.
Have gone through almost all the springs, there is always a bog when the secondaries kick in. More pronounced in the lower gears. Goes off the scale lean during the bog, but it least it is a short bog.
Secondaries kick in at 11Hg rolling into it slowly. Also, when 1/2 or more throttle before the secondaries, start to kick in, AF is mid 14's. That seems too lean to me for 1/2 throttle. So I'm going to put a 8.5 PV in next. I spent some time driving around with a vacuum gauge connected, and never saw it go below 11Hg until the secondaries kicked in. Also have a 6.5 PV if that is too much.
Idles well, starts immediately. Have a ways to go, but I'm getting there...
Last edited by mickm; 05/08/17 12:09 AM.
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Re: Latest six pack tuning...
[Re: mickm]
#2301283
05/08/17 06:30 PM
05/08/17 06:30 PM
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Joined: Jul 2011
Posts: 956 Chicago
PurpleBeeper
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It sounds like you're getting closer. I'm sure you have a bog...it "feels" like a bog & it happens when the secondaries kick open...and I'm assuming you're seeing it go lean on your A/F gage too, right?
So, if you have the black springs in the outboards (stiffest) and it still bogs, NOW you can start adding some more "squirt". I suggest that you start off by going up 1-step larger on the accelerator pump cam. They usually have a "1-hole" & a "2-hole" which changes the cam profile slightly. Heck, "maybe" changing holes on your stock white cam would do the trick? I can't remember which hole gives more squirt.
A 8.5 power valve is not needed unless you're running 17" vacuum at idle. The rule of thumb I was told was to take your idle vacuum, divide it in half & that is the number you want on your power valve.
If you're running lean just before you open the secondaries, I think you're lean in the "transition circuit" (?) and that's beyond my tuning skill. I "think" that's where you start modifying the carburetor metering plates & air bleeds. You might reach out to Lewtot on that one. He's very sharp on 6-packs.
70 Roadrunner convt. street car
440+6, NOS, 4-spd, SS springs
'96 Mustang GT convt. street car
'04 4.6 SOHC, NOS, auto, lowered
"Officer, that button is for short on-ramps"
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Re: Latest six pack tuning...
[Re: DAYCLONA]
#2301553
05/09/17 02:18 AM
05/09/17 02:18 AM
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Joined: Jul 2006
Posts: 4,179 California
mickm
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Mick is it truly a "bog"?, I know your new to Holleys/6 packs, but Holley 6bbl transition from 2 bbl to 6bbl will have a momentary "delay" in RPM as it dumps open the end carbs and starts to adjust RPM for all that fuel/air, the 6 pack is not like the previous dual quad set up you had where mechanical primary to secondary transition is continuous between both carbs
What's the current PV?...the 8.5 is to high IMO, personally I'd go with the 6.5
Mike Well, I *think* it's a bog! Right when the secondaries kick in, it falls over for a second while the AF meter goes off the scale lean, and then the secondaries kick in, breaks the tires loose in first. It is better in 3rd and 4th. I'm thinking an 8.5 PV as I never saw the vacuum below 11 the entire time I was driving it, and 11 is right when the secondaries kick in, and then the vacuum drops fast. So I'm thinking get the power circuit in as soon as possible, and maybe that will be the extra it needs. Otherwise, it seems like it will have to be accelerator pump related. Current PV is a 4.5.
Last edited by mickm; 05/09/17 02:19 AM.
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Re: Latest six pack tuning...
[Re: mickm]
#2301605
05/09/17 09:14 AM
05/09/17 09:14 AM
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Joined: Jul 2013
Posts: 1,272 Northern Calyfornua
Sxrxrnr
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Fuel mileage will likely suffer greatly with a 8.5 pv. Unless you are downshifting each time you climb a slight grade in top gear, hard to imagine not dropping occasionally below 8.5 inches of vacuum when cruising except on fairly level ground unless perhaps you are pulling excessively high vacuum at idle. Perhaps with the torque of a 540 hemi, who knows?
Nevertheless when you mash the throttle and therefore expect outboards to open, vacuum should fall close to zero, so whether a 4.5 or a 8.5, pv should open instantaneously. Doubt a 8.5 will make outboards open any sooner however.
But can't hurt to try 8.5 except for a little labor.
Point of curiosity, what is vacuum at idle?
Have you mentioned what cam you are running?
Accelerator pump dialed in properly with longest duration spray?
I might disable outboards so as they cannot open at all. Then running only on center carb, do you still get a leanout when you mash it. If so, I would be looking more askance at pump.
Sounds as though center carb is writing a check that outboards can't cash.
Last edited by Sxrxrnr; 05/09/17 09:29 AM.
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Re: Latest six pack tuning...
[Re: Sxrxrnr]
#2301703
05/09/17 12:59 PM
05/09/17 12:59 PM
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mickm
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Fuel mileage will likely suffer greatly with a 8.5 pv. Unless you are downshifting each time you climb a slight grade in top gear, hard to imagine not dropping occasionally below 8.5 inches of vacuum when cruising except on fairly level ground unless perhaps you are pulling excessively high vacuum at idle. Perhaps with the torque of a 540 hemi, who knows?
Nevertheless when you mash the throttle and therefore expect outboards to open, vacuum should fall close to zero, so whether a 4.5 or a 8.5, pv should open instantaneously. Doubt a 8.5 will make outboards open any sooner however.
But can't hurt to try 8.5 except for a little labor.
Point of curiosity, what is vacuum at idle?
Have you mentioned what cam you are running?
Accelerator pump dialed in properly with longest duration spray?
I might disable outboards so as they cannot open at all. Then running only on center carb, do you still get a leanout when you mash it. If so, I would be looking more askance at pump.
Sounds as though center carb is writing a check that outboards can't cash.
One of the reasons I was going to jump to the 8.5 is that I never saw vacuum that low at all. I drove around for a while with a vacuum gauge connected to manifold vacuum. I know the PV won't make the outboards kick in any sooner, just thinking that if the power circuit is coming into play sooner, that may provide enough extra gas to overcome at least most of the bog. Or maybe I should be calling it a stumble? I don't know. Also, as mentioned, when at 1/2+ throttle, before the secondaries kick in, the AF is in the mid 14's. That seems too high for what is essentially a power setting. At least to me... 12Hg at idle. Cam is 248 @ .050, .605/.580 110 CL. I havne't adjusted the pump yet. I could give that a try. I know there is a cam on there with at least two settings, wouldn't hurt to just go to the second setting. I have run it with the outboards disconnected, and it runs fine, will even chirp the tires going into second!
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Re: Latest six pack tuning...
[Re: Sxrxrnr]
#2301775
05/09/17 03:09 PM
05/09/17 03:09 PM
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mickm
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Where is distributor initial and total timing. I would be looking at having more initial and limiting total advance by distributor modification.
This would tend to lessen tendency of closed throttle butterflies to be improperly positioned in transition zone at idle or light cruise(once idle speed screw is set back as more initial timing tends to increase idle speed). May or may not help current complaint but if initial timing not properly advanced, would likely improve overall performance and responsiveness with an added possible improvement in fuel economy.
Are you running vacuum advance,,,,,if so disconnect and plug line and see how outboards then kick in. initial is about 19, total is 32, which is what it wanted on the dyno. So I'm set for timing. I am running VA, so I will give that a try.
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Re: Latest six pack tuning...
[Re: 62maxwgn]
#2301776
05/09/17 03:11 PM
05/09/17 03:11 PM
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Joined: Jul 2006
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mickm
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With that cam if you haven't done anything with end carb jetting unless I missed it,I think you will still be lean at getting to W.O.T. That's exactly what I expected, but it is coming up rich. As long as my AF meter isn't lying to me. Plugs looked good initially, and did look slightly rich. I do need to check them again now that I've made the jet change.
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Re: Latest six pack tuning...
[Re: mickm]
#2301791
05/09/17 03:34 PM
05/09/17 03:34 PM
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Joined: Jul 2011
Posts: 956 Chicago
PurpleBeeper
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Wow... a lot of stuff. On power valves - If your idle vacuum is 12"Hg, then you should be running a 5.5 power valve. I believe you're over-thinking it. The power valve has nothing to do with the outboards opening.
At cruise, you are in the main metering circuits because your cruise vacuum is 11" and 2 x 4.5 = 9, so the power valve is open. To adjust your cruise A/F ratio, change jets. To change your WOT A/F ratio, change the "jets" in the outboard metering plates.
(See 383man's post below. I think I'm wrong here & he's right)
Last edited by PurpleBeeper; 05/10/17 06:23 PM.
70 Roadrunner convt. street car
440+6, NOS, 4-spd, SS springs
'96 Mustang GT convt. street car
'04 4.6 SOHC, NOS, auto, lowered
"Officer, that button is for short on-ramps"
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Re: Latest six pack tuning...
[Re: PurpleBeeper]
#2301892
05/09/17 06:13 PM
05/09/17 06:13 PM
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Joined: Jul 2006
Posts: 4,179 California
mickm
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Wow... a lot of stuff. On power valves - If your idle vacuum is 12"Hg, then you should be running a 5.5 power valve. I believe you're over-thinking it. The power valve has nothing to do with the outboards opening.
At cruise, you are in the main metering circuits because your cruise vacuum is 11" and 2 x 4.5 = 9, so the power valve is open. To adjust your cruise A/F ratio, change jets. To change your WOT A/F ratio, change the "jets" in the outboard metering plates.
At cruise I'm well above 11. 11 is where the secondaries finally kick in, and I'm well past 50% throttle for that. Unless I don't understand it correctly, the rating on the PV is where it *starts* to open. So a 6.5 PV starts to open at 6.5Hg. My impression was not that it snaps open fully and instantly at 6.5, but that the spring pressure will be partially overcome at 6.5, and then still needs lower vacuum to completely open it. But I don't know if that is correct.
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Re: Latest six pack tuning...
[Re: mickm]
#2302212
05/10/17 06:10 AM
05/10/17 06:10 AM
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Joined: Jan 2003
Posts: 27,421 Balt. Md
383man
Too Many Posts
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Wow... a lot of stuff. On power valves - If your idle vacuum is 12"Hg, then you should be running a 5.5 power valve. I believe you're over-thinking it. The power valve has nothing to do with the outboards opening.
At cruise, you are in the main metering circuits because your cruise vacuum is 11" and 2 x 4.5 = 9, so the power valve is open. To adjust your cruise A/F ratio, change jets. To change your WOT A/F ratio, change the "jets" in the outboard metering plates.
At cruise I'm well above 11. 11 is where the secondaries finally kick in, and I'm well past 50% throttle for that. Unless I don't understand it correctly, the rating on the PV is where it *starts* to open. So a 6.5 PV starts to open at 6.5Hg. My impression was not that it snaps open fully and instantly at 6.5, but that the spring pressure will be partially overcome at 6.5, and then still needs lower vacuum to completely open it. But I don't know if that is correct. You are right. A 4.5 P/V starts to open at 4.5 inches of vacum. So if your pulling 11" of vacum at cruise a 4.5 P/V will be closed and wont start to open until your vacum drops to 4.5 when you step on it enough. Also when at cruise many times you can still be on the idle/transfer slot circuit as I know many times when I cruise I am barely on the gas pedal which I am not even on my main circuit at a slow easy cruise on level road. Ron
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Re: Latest six pack tuning...
[Re: 383man]
#2302606
05/10/17 10:47 PM
05/10/17 10:47 PM
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Joined: Feb 2010
Posts: 1,645 Phila. Pa.
Mattax
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Ron's is correct. A few other concepts may be helpful. The idle system works on manifold vacuum. This includes when the throttle is off-idle or on 'transition'. * The manifold vacuum is the pressure difference that drives the fuel. * It also provides the distribution to each cylinder. Higher vacuum = stronger signal, usually better distribution. * The idle system responds somewhat slowly to throttle opening. The accelerator pump helps cover for the slow response. The Power Valve is there to enrich the mixture when the Load gets high near maximum. * With a powerful engine, high gearing and so forth, it may not be at under full load until 3 gear and high speed. (Best to test at track or on dyno.) The Secondaries (or in this case the outboards) are there to allow more airflow when the air velocity is high enough. This produces more power by providing more air and less restriction (higher pressure) as rpms climb. Finally, find the AFRs that work best. Use the numbers as reference points rather than targets. Some engine combos can go leaner than stoich at part throttle. You may find the AFR curves posted on RFS helpful. AFR Characteristics Under Increasing Loads If the text is confusing, look at the graphs and then come back to it. (The thread was edited by one of the admins when some old and new stuff was joined together.)
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Re: Latest six pack tuning...
[Re: Mattax]
#2303126
05/11/17 11:51 PM
05/11/17 11:51 PM
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Joined: Jul 2006
Posts: 4,179 California
mickm
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Ron's is correct. A few other concepts may be helpful. The idle system works on manifold vacuum. This includes when the throttle is off-idle or on 'transition'. * The manifold vacuum is the pressure difference that drives the fuel. * It also provides the distribution to each cylinder. Higher vacuum = stronger signal, usually better distribution. * The idle system responds somewhat slowly to throttle opening. The accelerator pump helps cover for the slow response. The Power Valve is there to enrich the mixture when the Load gets high near maximum. * With a powerful engine, high gearing and so forth, it may not be at under full load until 3 gear and high speed. (Best to test at track or on dyno.) The Secondaries (or in this case the outboards) are there to allow more airflow when the air velocity is high enough. This produces more power by providing more air and less restriction (higher pressure) as rpms climb. Finally, find the AFRs that work best. Use the numbers as reference points rather than targets. Some engine combos can go leaner than stoich at part throttle. You may find the AFR curves posted on RFS helpful. AFR Characteristics Under Increasing Loads If the text is confusing, look at the graphs and then come back to it. (The thread was edited by one of the admins when some old and new stuff was joined together.) Those charts are some really interesting info, some of which was totally opposite of what I expected, namely that you want part throttle acceleration to be lean. I would have laid down money that you want it rich, just like WOT. Can't say I see why that lean is the case, but very, very interesting. I was worried that I was low to mid 14's at part throttle acceleration, which is still richer than stoichiometric, but according to this I'm fine. Hopefully I'll continue to play this weekend. I'm going to go down 2 more jet sizes, which should bring me to ~13 on WOT, and low to mid 14's on cruise. Next I'll take a look at the accelerator pump cam. Then I will try going up in PV's, a 6.5 then an 8.5.
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Re: Latest six pack tuning...
[Re: 4406bbl]
#2304923
05/15/17 03:29 PM
05/15/17 03:29 PM
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Joined: Jul 2011
Posts: 956 Chicago
PurpleBeeper
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With an engine that big you may have to use a 50cc pump and custom grind a pump cam to give most the shot late. The only way to slow the secondaries after the stiffest springs is to make the restriction smaller in the vacuum line that feeds both carbs, use some 3/16 set screws and drill them out starting at about .030, smaller.029 will open later. Changing the power valve dont work too good on a engine that size because the pvcr the holes behind the power valve are too small. This sounds like good advice. I have heard of people adding restrictions inside the secondaries' hoses or at the carb. You could probably do something similar by drilling out some short pieces of threaded rod (if you have a small enough vise/drill press) and just insert them inside the hoses (no carb modification). One of the old Direct Connection books with all the various six pack tuning tips described drilling out the holes behind the power valve. I did that on one of my metering bodies, but replaced it with another (stock holes) when I was chasing my six pack problems.
70 Roadrunner convt. street car
440+6, NOS, 4-spd, SS springs
'96 Mustang GT convt. street car
'04 4.6 SOHC, NOS, auto, lowered
"Officer, that button is for short on-ramps"
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