6BBL tuning with proven results

[BSB67]

How do you have your idle mixture screws adjusted for the outboard carbs?

 

[lewtot184]

Thanks for posting the link. I didn’t read it all in detail, but it looks like the conclusion was no check balls?

Me, Lew (one of the posters in the 2015 thread above), and two other guys Jim and Steve, spent years together doing track testing on our street 440 cars with the Six Pack. Lew, with his very mild 9.2:1 CR, 3.23, 12” converter, exhaust manifold car on BFG tires was running 13.0s at 107-108 mph, if memory serves me right. He was testing several stock-ish cams at the time, including the MP 0.455”. I don’t recall if he was using that cam when he was running the 13.0s, or the Hughes 2330 or Comp, 270 Magnum. Like I said, we did a lot of testing. Jim and Steve at the time were on our heels, low 13s @ 104-105 with small hydraulic cams, full street trim and exhaust. Jim’s car, after a rebuild, was nearly identical to your car with small tube headers, 9.5:CR and 4-speed. He did install the MP 528 solid. It was running 12.70 at 112 mph. These cars ran well despite us all having crappy 60 ft time of 2.0 or slower.

Personally, I’ve been playing with my Six Packs since 1977, on everything from mild 383 to roller cam 500 inch motors, all in street cars. This includes engine dynos, chassis dynos, and a lot passes at the track over several years in my 440 Charger.

Anyways, here are my high level take aways:

1) The original, unaltered Six Pack works pretty well on just about everything without modifications. Minor mods will help a little. The jetting is pretty close for everything from a stock motor to 11 second street cars.

2) The best track performance for outboard carb opening rate is a function of the car and can only be determined at the track. The same motor might need the black spring in one car, but the yellow spring in a different car.

3) For a typical street car, if you slow the carb opening rate in an attempt to eliminate the sag (lean spike) during street WOT, you may have slowed the car down in et and mph track performance, and it can be a lot - 0.3 sec and 3 mph. Again, it is a function of the car.

Regarding outboard springs, note Lew’s comment about his car slowing from using stiffer springs than the yellow spring.

Couple Pics of the guys, back when cameras had stuff called film.

Sorry if I'm hijacking your thread, I guess that this thread made me a bit nostalgic.

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Wow! I wish we were all together again.

I wanted to stay out of this because my thoughts and real time actions won't sway opinion. I did the check ball thing for the first time in 1970 and a couple of times since. I was chasing the familiar problem of the end carbs flopping open. The check balls will delay that. But in my case at a dangerous cost, delayed closing at wide open throttle and if the wrong balls are used carbs stick open at full throttle. I could tell some scary stories about this but I think the best teacher will let folks try this and make up their own minds. I will never use check balls; never!

The real issue is a cold intake with the vacuum carbs. Cast iron is worse than aluminum and when the temps get below 60 degrees cast iron is damn near impossible to deal with. I won't use a completely blocked heat crossover anymore. Trying to manage heat, especially in the summer, is a real challenge. The only real "solution " I've come up with is a butterfly "valve" in the manifold crossover. I can shut the heat off in summer and put some heat in when temps drop. Gasoline needs some heat to vaporize and cold intakes can give big gulps of air without enough atomized fuel creating the problem. I'm thinking somewhere around 100-120 degree intake temps for the track will the end carb transition.

As for springs I've found thru testing on my car that every step heavier than a yellow spring slowed the car about a tenth. I do believe the purples are a pretty good general use spring. I have stood beside my car on a chassis dyno and witnessed the carbs fully open with yellow springs.

My car ran 13.13@106 with stock exhaust, heads, 9.3 compression, 3.23 gear, 225/70x15 ta radials, 272/.455 cam, 4060lbs. I did get the car to run a little better later on but unfortunately I gave up on it way too soon.

 

[BSB67]

My car ran 13.13@106 with stock exhaust, heads, 9.3 compression, 3.23 gear, 225/70x15 ta radials, 272/.455 cam, 4060lbs. I did get the car to run a little better later on but unfortunately I gave up on it way too soon.

Great Times.

I thought you had some 107-108 mph slips, but et was off a little because of crap 60' times, like 2.3 sec. verses the more typical 2.1 sec. I remeber telling myself that with your more typical 60' you'd be in the 12.9s with me.

Although, if you had some tire spin, that can result is slightly higher than normal trap mph.

 

[lewtot184]

Great Times.

I thought you had some 107-108 mph slips, but et was off a little because of crap 60' times, like 2.3 sec. verses the more typical 2.1 sec. I remeber telling myself that with your more typical 60' you'd be in the 12.9s with me.

Although, if you had some tire spin, that can result is slightly higher than normal trap mph.

the car did do 107.92. unfortunately i quit at 2 passes; disgusted. the problem was me. i had the wrong distributor in the car for the track. i normally ran a slow curve at the track but for some dumb reason i had the "feel good" curve distributor in it. i think i could have got the thing to run 108-109 on a good day. ironically we did all this stuff 25yrs ago! i did build another engine to try all this again that is a little closer to what you had in the charger;...still sitting on the engine stand, lol!

what we did back then was probably the most fun i had with the r/t. on another check ball note i had a chance to work on a friend/neighbor's ford 427 thunderbolt clone. it has all the correct high riser engine stuff; really cool. anyhow it didn't drive or run good and i had the chance to do the carbs and ignition. when doing the carbs i noticed the check balls; pretty sure the trash man hauled them off. put new diaphragms in them with purple springs, kept the calibration stock and what a difference! really neat fun car. seems like the fun has gone out of this stuff anymore.

 

[lewtot184]

i checked the kill bleeds on my aftermarket carbs and they are .046". i've messed with kill bleed sizes and have blocked them before but haven't touched these.

 

[Bird 426]

This is all interesting to me. My B body is a Hemi, dual quads, my '69 Dart has a 418 stroker small block, with a Sixpack.
It's a pretty well built street car. It will start nosing over with anything smaller than #66 mains and 6.5 power valve, that's on no alcohol premium. I am up to 69's now on reg 10% alcohol gas. The ends are at 79's (Promax plates) on the alcohol gas. My air/fuel idles on the ends are anywhere from 1/8 turn out to one full turn out, depending where they end up with a vacuum gauge, laser heat gun and finger over the air bleeds to detect a rise or fall. Purple or yellow springs. One of the biggest changes was mufflers. I have sensitive hearing, removed the open Flow Masters and installed Walker Quiet Flows, changed everything, bogs now and has never run again like the absolute monster it was.

 

[Meep-Meep]

This is all interesting to me. My B body is a Hemi, dual quads, my '69 Dart has a 418 stroker small block, with a Sixpack.
It's a pretty well built street car. It will start nosing over with anything smaller than #66 mains and 6.5 power valve, that's on no alcohol premium. I am up to 69's now on reg 10% alcohol gas. The ends are at 79's (Promax plates) on the alcohol gas. My air/fuel idles on the ends are anywhere from 1/8 turn out to one full turn out, depending where they end up with a vacuum gauge, laser heat gun and finger over the air bleeds to detect a rise or fall. Purple or yellow springs. One of the biggest changes was mufflers. I have sensitive hearing, removed the open Flow Masters and installed Walker Quiet Flows, changed everything, bogs now and has never run again like the absolute monster it was.

Seems pretty rich on the mains when you consider the venturi area. I would start from scratch. Disconnect the vacuum to the outboards and get an O2 sensor so you can see what's going on. You should not need anything more than the stock 62 or 63 jets. Also note how strong your car runs on just the 2BBL. It will be better than you think once you dial in the mixture. Shoot for 12.5:1 WOT and around 14:1 idle and cruise. As lean as you can stand it on cruise but it should fatten up as you roll into it. Cruise mixture is adjusted by the IFR and /or air bleeds because you are on the transfer slot. I got the Quick Fuel metering block for the ability to adjust the IFR sizes. Power valve setting half of idle vacuum to start seems to work out well. Outboards will be a different story. Jet until you get 12.5:1 WOT with everything open.

In place of the check balls on my carbs, I may try a completely different approach to delay and slow the opening.

 

[Bird 426]

Forgot, I have dual AFR's, I am in the window at cruise and wot. Engine is really alive on the 2-barrel. I am an old dog, air bleeds somewhat turn my brain to jello, I can't get my arms around all of it in the tuning arena. My plugs on premium were always sooty, but if I went leaner than 66's, you could just feel that it was going the wrong way, maybe something is leaking. Vacuum is about 17, 20 to 22 degrees of initial timing. Haven't had it to the strip yet, but before I changed mufflers, with 255/60/15 drag radials and 3:55 gears, from a roll, pretty nice ride till 3rd gear. Pretty much broke things loose through 2nd, just stepping on it at 2500.
So it runs good, but I would be open to try something. This coming summer, it's winter here now!

 

[lewtot184]

too much fuel will take the starch out of them no matter whether it's jet area or fuel pressure. people tend to use too large of needle and seats and the floats loose control when a lot of fuel is being pushed thru. float/metering plate interference could be happening. i think most people tend to over jet the 6bbl stuff. it's not race stuff.

 

[Meep-Meep]

too much fuel will take the starch out of them no matter whether it's jet area or fuel pressure. people tend to use too large of needle and seats and the floats loose control when a lot of fuel is being pushed thru. float/metering plate interference could be happening. i think most people tend to over jet the 6bbl stuff. it's not race stuff.

HA! Took me a minute to figure out the geyser on the outboards. I'm running QF plates and the brass floats hit. Switched to nitrophyl and no issues. Floats and fuel pressure are the first things to address to control the mixture.

 

[Meep-Meep]

Forgot, I have dual AFR's, I am in the window at cruise and wot. Engine is really alive on the 2-barrel. I am an old dog, air bleeds somewhat turn my brain to jello, I can't get my arms around all of it in the tuning arena. My plugs on premium were always sooty, but if I went leaner than 66's, you could just feel that it was going the wrong way, maybe something is leaking. Vacuum is about 17, 20 to 22 degrees of initial timing. Haven't had it to the strip yet, but before I changed mufflers, with 255/60/15 drag radials and 3:55 gears, from a roll, pretty nice ride till 3rd gear. Pretty much broke things loose through 2nd, just stepping on it at 2500.
So it runs good, but I would be open to try something. This coming summer, it's winter here now!

The point I want to drive home is the main jets are best sorted at WOT. It's a combination of PVCR, main jet and of course fuel pressure and float level, which comes first. Light throttle cruise is predominantly transfer slot, which is your idle feed restriction and idle air bleeds. Using a Quick Fuel metering block provides the ability to change the idle feed jets. It's important to know your mixture at varying throttle positions and engine loads then make corrections based on that.

 

[lewtot184]

i've gotten away from using main jets for power. power is the PVCR, cruise is jets, IAB/IFR low speed. if you only do jets for power then cruise and power both are changed. what if cruise is good but power is lean? i prefer keeping the circuits tuned separately if possible.

 

[Meep-Meep]

i've gotten away from using main jets for power. power is the PVCR, cruise is jets, IAB/IFR low speed. if you only do jets for power then cruise and power both are changed. what if cruise is good but power is lean? i prefer keeping the circuits tuned separately if possible.

Yes for sure. A good street carb is relatively lean on jets and big on PVCR. My point that was not clearly stated is with an OEM 6BBL carb that balance is already taken into account so all you can do is change jets. And likely not need to change them at all. It's the idle and tip in that needs the most attention.

 

[68 HEMI GTS]

I’ve done quite a bit of testing with 6 packs as well. Every car and combo likes something different. I’ve ran them on everything from 14 sec cars to 10 sec cars. I agree with the above as I set mine up for best ET at the track with slicks. If your tuning them on the street to not feel them open, chances are there’s ET left. I’ve also noticed the big cube engines don’t really care all that much about the secondary opening rate with a decent gear and convertor. My 512 wanted them open right now, i ran the lightest springs on that engine before i went to mechanical carbs. It also had shitty distribution at low speeds. Something that typically isn’t an issue. Some intake work straightened that out though and really helped the low speed drivability. Although I was a little cringe worthy initially grinding on the intake.

This convertor is about a .10 slow from the previous convertor I broke. It was also 95 degrees and humid this day, so it’s got more left.