383 intake manifold changes AFR big time

[Zwap]

Update.
Today I manage to get some time in the garage and testdriving.
The temperature went from 44"F (7"C) to 55"F (13"C) since I did my last testdrive.
I didn't change the main jet, still .110 but I turn the AVS another half turn.
I didn't change the nossels, still .040
I didn't cange the timing, still 18"
I DID change the rod to one step richer at the power to primaries. Pimary jet .098 and .063/.047 rod (.062/.052 rod before).
The result is much better, the hesitation is almost gone.
I did notice that when I let the secondaries open evere so slightly and then floor it there is no hesitation, it goes rich direct without a lean spot, but if I floor it from cruise and it result in a kickdown then the lean spot/hesitation is there but not at much as before (outside temperaure, AVS adjustment or the richer rod?).
I also notice that some WOT testing was about afr 12.5-13.5 but some of them was more at 14-14.5 at the same run just a minute after the other between I floor it from cruise at highway.
It pulls real good and I can't notice any detonation but afr over 14 at WOT is a bit lean to me.
Another thing I notice was that if I accelerate from low rpm at the power on the primaries (less than 6 inches of vacuum) the afr get leaner as the rpm rises,

 

[furious70]

When trying to accelerate and stay on the primaries only you may end up creating enough vacuum to put the rods back in the Jets, gotta watch the gauge close to see what's happening.

Having to add fuel when you increase an engine's volumetric efficiency is what you would expect. The new intake should do that - to what extent is really the experiment here.

 

[CBODY67]

Lots of carb mixture curve calibration is done on an engine dyno or chassis dyno, where the load and throttle can be held constant. Which would be different than on-the-road where the vehicle speed can increase with the same throttle setting. As the speed increases, so can the load, hence the issue of the manifold vacuum not remaining constant, but increasing, which can then allow the power pistons to move more toward their "Eco" step from the "Power" step, as mentioned. For on-road testing, might need to modulate the foot brake to prevent the road speed from increasing very much . . . CAREFULLY, on a deserted roadway.

Perhaps, to digest your information, you might download and print the 50+ page Tuning Manual on the Edelbrock AFB. It has (or had, the time I downloaded it, a while back), lots of charts and strategies. In the Rochester carb book, it mentions using a stopwatch over a marked distance as a means of testing mixture changes, using a vacuum gauge, noting the time/distance results for each change.

You mentioned that you changed both the rod and also tightened the air valve spring, on the same test, which worked better. That raises the question of whether the tighter air valve spring (which would delay full opening of the air valve (less initial air) or the improvement came from the richer rod? Just curious.

Thanks for the updates,
CBODY67

 

[3175375]

Lots of carb mixture curve calibration is done on an engine dyno or chassis dyno, where the load and throttle can be held constant. Which would be different than on-the-road where the vehicle speed can increase with the same throttle setting. As the speed increases, so can the load, hence the issue of the manifold vacuum not remaining constant, but increasing, which can then allow the power pistons to move more toward their "Eco" step from the "Power" step, as mentioned. For on-road testing, might need to modulate the foot brake to prevent the road speed from increasing very much . . . CAREFULLY, on a deserted roadway.

Perhaps, to digest your information, you might download and print the 50+ page Tuning Manual on the Edelbrock AFB. It has (or had, the time I downloaded it, a while back), lots of charts and strategies. In the Rochester carb book, it mentions using a stopwatch over a marked distance as a means of testing mixture changes, using a vacuum gauge, noting the time/distance results for each change.

You mentioned that you changed both the rod and also tightened the air valve spring, on the same test, which worked better. That raises the question of whether the tighter air valve spring (which would delay full opening of the air valve (less initial air) or the improvement came from the richer rod? Just curious.

Thanks for the updates,
CBODY67

Very important to change one parameter at a time, if possible. Unless the changes are not interrelated...

 

[Zwap]

One thing I think about is that the Edelbrock carb tuning guide recomend to tune WOT first and then the part-throttle saying:
"The Metering Rods feature used in the Edelbrock carb allows easy calibration of the part-throttle without change to the WOT metering..."
Is that really correct?
Doesn't the mixture of the primaries affecting WOT at all?
Well, in that case I only changes one parameter and that was the AVS adjustment as the powerstage doesn't affect the WOT metering.

I thought WOT used the mixture from fully open primaries PLUS the mixture from fully open secondaries.
The open area of the primary jet .098 minus the rod at power (.047) giving me an area of .058 and from the secondary jet .110 giving me an area of .095, a total open area of .153 (x2) to possibly feed the boosters with fuel but if I read the Edelbrock carb tuning guide the extra .058 (in this case) from the primaries doesn't affect the WOT metering...

 

[furious70]

I would assume they mean you don't need to change Jets to tune part throttle, rather rods and springs, thereby not changing wot.

 

[Zwap]

But if you change rods then you change the mixture in the primaries.

 

[CBODY67]

In reality, it doesn't really matter which you change first, Eco or Pwr. The beauty of the metering rod carb is that you can easily change things rather than taking the carb apart many times (at least on the Carter/Edelbrocks).

The Pwr side of the primaries does contribute to the total afr the carb produces. So, to me, to tune the primary Pwr, you'd need to go "to detent" just before the WOT downshift (on the non-part-throttle downshift TorqueFlites. Secondaries are still closed, as should be the air valve. Manifold vacuum should be low enough that the rods are in the Pwr position. Once that is done, THEN proceed to a full WOT mixture reading and adjust the secondary jets if needed.

In the Rochester Carb book, it does mention using "jet area" to make changes with. Which generates a long number for the jet area. Then minus the metering rod area and use the resultant number to make changes in small percentages. NOT the diameters, but the areas those diameters represent. A much more accurate way of doing things, as they illustrate, but not the way that is "time honored", by observation.

In any event, ONE change at a time and see what it does, then proceed in the desired direction.

In looking at the jets and rods in the Edelbrock jetting kit for the AVS, you'll notice some "gaps" of sorts in the rod selection, seemingly. Same as it was in the old Carter Strip Kits. Which might be where the charts in the Edelbrock Tuning Manual come into play.

In your "on road" tuning, it might be better to have a co-pilot to read the gauges rather than the driver trying to do it.

Take care,
CBODY67

 

[Zwap]

In reality, it doesn't really matter which you change first, Eco or Pwr. The beauty of the metering rod carb is that you can easily change things rather than taking the carb apart many times (at least on the Carter/Edelbrocks).

That I realize, but the Edelbrock carb tuning guide recomend to tune WOT first and then the Eco/Pwr (primaries mixtures).

The Pwr side of the primaries does contribute to the total afr the carb produces...

Agree and I'd always tuned my carbs with that in mind, thats why I think that the Edelbrock carb tuning guide is misleading. I've never start with tuning WOT but now when I've got this "problem" I read about it in all of the Edelbrock instructions: start tuning Idle then WOT then Eco/Pwr

In the Rochester Carb book, it does mention using "jet area" to make changes with. Which generates a long number for the jet area. Then minus the metering rod area and use the resultant number to make changes in small percentages. NOT the diameters, but the areas those diameters represent. A much more accurate way of doing things, as they illustrate, but not the way that is "time honored", by observation.... In looking at the jets and rods in the Edelbrock jetting kit for the AVS, you'll notice some "gaps" of sorts in the rod selection, seemingly. Same as it was in the old Carter Strip Kits. Which might be where the charts in the Edelbrock Tuning Manual come into play...

That's why I use area calculations. If one area of jet minus rod area works good in Eco with, let say .098 jet, but the Pwr with the rods that availble doesn't work, then I can use another jet to get the same area in Eco and with a different rod get the Pwr to get right afr.
Easily done with an Excel calculation, just changing the jet size to get all of the area of Eco and Pwr from all of the rods that are avablie from Edelbrock, then start testing.
Thats the way I do it, finding an cruising (eco) area that works, then finding an Pwr area that works, then finding a jet/rod combination that matches that areas. Then I go for WOT afr settings.
The reason I start this thread is that I was amazed that an intake manifold made that HUGE difference in afr and I'm not yet sure that it isn't a hidden vacuum leak that I cant find, the jetting is as you wrote earlier more like a top performer 440

The temperature went right down to 35F so my "on road" tuning will take a break but I'll be back

 

[CBODY67]

It might be that if you meter WOT first, then with the available jet/rod combinations, the Eco afr might end up a bit richer than 14.7. If you meter Eco first, then the WOT might end up a bit lean. "Rich" might be considered better, provided it's not too rich. But the Rochester book also notes that best power is made with a WOT mixture that is a little bit leaner.

PLUS, you'll spend much more time in the Eco area than the Power area, which might be a reason to worry about that calibration first. If the Power is a bit lean, then one more jet size in the secondary might just do the trick for the desired total aft?

You mention ambient temp being near freezing. This can be an important factor, too. In some of the first efforts to decrease exhaust emissions, the OEM's tightened-up their mixture calibrations via using heat stoves on the exhaust manifold to aim for a 100 degree F air temp in the air cleaner, going into the carb. This allowed for a generally leaner calibration in some cases, plus a better-evaporated a/f mixture going into the intake manifold. But my observation is that the calibrations for the Federal-spec emissions didn't really change until about 1970, although there were some efforts to get the choke "off" sooner, too. Over the years, I developed my own strategy for getting better drivability with a cold engine in the cold times of the year, with a non-heated air cleaner. One of those things that took time to do, but seemed to work good for me.

Take care and keep us posted,
CBODY67

 

[Zwap]

...Over the years, I developed my own strategy for getting better drivability with a cold engine in the cold times of the year, with a non-heated air cleaner. One of those things that took time to do, but seemed to work good for me.

I run with Spectre Cold Air intake Spectre Performance Musclecar Cold Air Intakes 733 thats why I dont do the jettings when it's too cold but please write about how you solve to get better drivability with a cold engine in the cold times that took time to do.

Sorry, the area I present earlier was .0 wrong, for example the .110 jet is .0095 area NOT .095 as I wrote. And so on, add another .0

 

[70bigblockdodge]

You are way overthinking this, primary part throttle the metering rods are pulled down using the fatter section of the rod. WOT no or low vacuum so rods are up in the jets so small section of the rod is filling the jet,along a completely different calibration. No, one will not affect the other.
As mentioned above.
One thing at a time.
Disconnect the secondaries and run it on the primary side, see what it is at.
Both lean or both rich- change the jet size.
One correct and the other lean or rich change the metering rod. Then bring the secondaries in and see WOT

 

[Zwap]

Maybe I'm overthinking this but it isn't the first carb I've calibrated...
I do the afr adjustment at the primaries first and then WOT, just as you explained.
I don't agree that the primaries don't affect WOT mixture as you write: "No, one will not affect the other"

I'll keep finding an cruising (eco) area that works, then finding an Pwr area that works, then finding a jet/rod combination that matches that areas. Then I go for WOT afr settings. Maybe I'm overthinking it but it use to work.

I was amazed that an intake manifold made that HUGE difference in afr and I'm not yet sure that it isn't a hidden vacuum leak that I cant find, the jetting is as you wrote earlier more like a top performer 440

 

[70bigblockdodge]

I don't agree that the primaries don't affect WOT mixture as you write: "No, one will not affect the other

The part throttle cruise and the WOT are 2 differently metered circuits.
AFR is parts of air to parts of fuel, more air needs more fuel to maintain AFR. If you disconnect the secondaries and set up the primaries for WOT and for part throttle cruise then connect the secondaries and jet accordingly for WOT again, leaving the primaries alone, they are done.
Part throttle cruise and WOT are using the same jet and circuitry but the area is greatly reduced by the metering rod, therefore it is separate calibration independent of the other.
Is your manifold vacuum the same as before the intake swap? If not you have a vacuum leak, the different manifold will not change the vacuum characteristics of the engine.

 

[Zwap]

I think we agree but express ourselves differently.

The manifold vacuum is the same with both intake manifolds but maybe a little odd, about 18" at 700 rpm idle in "P" but up to 20-22" at steady 1.500 rpm in "P".

 

[CBODY67]

Not really odd per se. At 1500rpm, the vacuum advance should be adding more advance, which can increase intake manifold vacuum. What is the vacuum with the car in gear, with the brake on? And on a flat road at 1500rpm? Just curious.

CBODY67

 

[Zwap]

Did some vacuum tests today:
In gear with the brake on at idle 6-700 rpm: about the same, 16-17"
Flat road at 1.500 rpm: about 20"
About 24" when letting the throttle off.

Tried without the PCV connected and of course vacuum plug blocked between the tests. No changes in afr, so I keep the PCV connected. (I know that the PCV don't affecting WOT afr as there's about zero vacuum but just to do something).
The engine pulls really good but I still got a slight hesitation when flooring it and a bit lean at WOT.
To morrow I'll test with retard ignition, larger main jet (secondaries), larger nozzles, I know, one change at a time...

 

[Zwap]

This Sunday it was 60F and I'd only change the secondary jets to .113 and now the afr is just what I wanted at WOT, about 12.5-13.5
The hesitation is there but ever so slightly, now I can't see it on the afr meter anymore but I can feel it very very slightly.

The result in changing only the intake manifold on my engine in jetting to get the right afr is the following:

Mopar M1 dual plane:
Primary jet: .089
Rod: .063/.047 (Area: .0031/.0045 with .089 jet)
Secondary jet: .098 (Area: .0062)

Edebrock Performance RPM:
Primary jet: .098
Rod: .063/.047 (Area: .0044/.0058 with .098 jet)
Secondary jet: .113 (Area: .0100)

That's a HUGE difference to me but the engine seems to want that much fuel and it pulls really good.

 

[CBODY67]

Now take it on a 100 mile highway cruise (with a constant speed, if possible) and see where the mpg might be. Steady-state cruise without any "deep throttle events", as much as possible.

Thanks,
CBODY67

 

[Zwap]

Did a 46 mile highway cruise today (30-60 mph) with a couple of stop at crossings, never going to power mode at primary and filled it up before and after, the result: 2.76 gallons.
Giving me 17,7 mpg?
It should be OK don't you think?