Low speed (1500-1800 RPM) driveability issue

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BLSTIC
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Re: Low speed (1500-1800 RPM) driveability issue

Post by BLSTIC »

Belgian1979 wrote: Tue Sep 10, 2019 1:22 pm
LoganD wrote: Tue Sep 10, 2019 9:46 am I've seen carb intakes, both dual plane and single plane, with such bad distribution that one cylinder will be 16:1 and another will be 11:1. I'd weld bungs in each header tube and move the wideband around, you can use the jetting to help mitigate it but you'll never get it great.

Get rid of the 4-hole spacer.
I think this is the cullprit.

I have no solution to offer but my experience.
I have 8 WB's on my engine and I can see the difference. Obviously with EFI you can have the ecu correct for this. Corrections made by the ECU vary up to 30% from rich to lean cyls on the extreme side of things at idle and anything which is low speed driving.
What had me stumped is that even when balancing airflows between cyls, it still had the uneven AFR's (mine is an ITB manifold which makes individually balancing cyls possible)

What those imbalances in AFR do is that the lean ones start to misfire making for bad driveability, rough running,...

I thought that it could have something to do with injector angle but after I see this post it seems that a carb does the same thing...

On other issue could indeed be the cam. Although if intake reversion would be the reason I would suppose it would show up in the airflow differences...
From what I've seen on my sims, crossover headers make more difference to fixing cylinder-cylinder variation in airflow than anything else, especially at low rpm. Your airflow variations are highly likely to be blowdown pulse from one cylinder screwing up overlap and intake airflow on another
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Re: Low speed (1500-1800 RPM) driveability issue

Post by rgalajda »

GRTfast wrote: Tue Sep 10, 2019 8:54 am I posted this on another forum, posting here to cast as large of a net as possible.

What I am about to describe is the only remaining behavior that I don't like with my setup.

My engine (494 HP. 532 ft*lb):

0.030 over iron block 454
Eagle Crank
H beam rods
9.5:1 compression
Brodix BB2+ rectangular port heads
Federal Mogul forged pistons
0.558 lift 235 @ 0.050 duration hydraulic roller, 107 degree lobe seperation (1500-5600 RPM operating range)
RPM airgap with 1 inch phenolic 4 hole spacer
QFT 1050 cfm 4150:
2nd and 4th emulsion holes blocked
IFR moved to bottom, 0.032 in all 4 corners
IAB 0.063 front 0.073 rear
MAB 0.026 all 4 corners
Primary MJ 78's
Sec MJ 98's
Primary PV 8.5
Sec PV plugged
Primary PVRC jets .073
HEI distributor, 18 initial, 39 all in at 3100 RPM, 10 degrees vacuum advance
1 7/8 primary headers into 3.5" collectors into 3 inch glass packs

The car is a 4 speed manual, 3.27 rear end, 2500 lbs without me it it. When I am driving at a constant speed at low rpm (1500-1800) with jetting anything leaner than 13:1 during this condition, the engine seems to have a very light intermitten miss (low level muffled popping sound) and slightly surges. It is minimal, but noticeable and annoying. Cranking compression is 175 psi +/- 3 psi on all cylinders, leakdown less that 2% (engine is healthy).

If I change to 0.035 IFR's the mixture goes into the 12:1 range and the issue is maybe 75% better, but still not completely gone. As you might guess, the spark plugs do not like that rich of a low speed cruising mixture, as it doesn't take long to foul them driving around with that setting.

This engine has always had a bit of a weird fuel distribution issue where number 1 is richest, and number 2 and 8 are leanest when I jet the carb symmetrically from side to side (based on spark plug reading). I've never done a full throttle plug chop, so I can only say with confidence that the distribution issue is present at idle/cruising (normal street driving). I've experimented some with asymmetric low speed jetting a bit, doesn't seem to make much difference.

I suspect that my dual plane intake is the culprit, but I don't want to abandon it if I don't have to, as it makes gobs of torque in the street driving rpm range, and runs great in all other conditions aside from what I have described above.

Questions:
1. I currently have a 1 inch 4 hole phenolic carb spacer, this was needed to solve a fuel boiling issue (Florida summer stop and go traffic is brutally hot). Would an open spacer help to achieve a more even mixture distribution?

2. Is a single plane intake the real solution? If so, what is the best one for a street big block with a cam that signs off at 5600 RPM?

3. Is it normal that the engine needs an overly rich mixture to run smoothly at the very bottom of the cam operating range, or is this rich mixture just a band-aid for the uneven fuel distribution issue?

Any insight/suggestions are welcome and appreciated.

494 HP. 532 ft*lb was the first sign of a bad combination of parts
You can make 500+ HP 550 ft lb with peanut port heads done correctly.
The divider in the intake ended up being a bandaid .
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Re: Low speed (1500-1800 RPM) driveability issue

Post by Tom68 »

rgalajda wrote: Sun Jan 29, 2023 8:13 am
GRTfast wrote: Tue Sep 10, 2019 8:54 am I posted this on another forum, posting here to cast as large of a net as possible.

What I am about to describe is the only remaining behavior that I don't like with my setup.

My engine (494 HP. 532 ft*lb):

0.030 over iron block 454
Eagle Crank
H beam rods
9.5:1 compression
Brodix BB2+ rectangular port heads
Federal Mogul forged pistons
0.558 lift 235 @ 0.050 duration hydraulic roller, 107 degree lobe seperation (1500-5600 RPM operating range)
RPM airgap with 1 inch phenolic 4 hole spacer
QFT 1050 cfm 4150:
2nd and 4th emulsion holes blocked
IFR moved to bottom, 0.032 in all 4 corners
IAB 0.063 front 0.073 rear
MAB 0.026 all 4 corners
Primary MJ 78's
Sec MJ 98's
Primary PV 8.5
Sec PV plugged
Primary PVRC jets .073
HEI distributor, 18 initial, 39 all in at 3100 RPM, 10 degrees vacuum advance
1 7/8 primary headers into 3.5" collectors into 3 inch glass packs

The car is a 4 speed manual, 3.27 rear end, 2500 lbs without me it it. When I am driving at a constant speed at low rpm (1500-1800) with jetting anything leaner than 13:1 during this condition, the engine seems to have a very light intermitten miss (low level muffled popping sound) and slightly surges. It is minimal, but noticeable and annoying. Cranking compression is 175 psi +/- 3 psi on all cylinders, leakdown less that 2% (engine is healthy).

If I change to 0.035 IFR's the mixture goes into the 12:1 range and the issue is maybe 75% better, but still not completely gone. As you might guess, the spark plugs do not like that rich of a low speed cruising mixture, as it doesn't take long to foul them driving around with that setting.

This engine has always had a bit of a weird fuel distribution issue where number 1 is richest, and number 2 and 8 are leanest when I jet the carb symmetrically from side to side (based on spark plug reading). I've never done a full throttle plug chop, so I can only say with confidence that the distribution issue is present at idle/cruising (normal street driving). I've experimented some with asymmetric low speed jetting a bit, doesn't seem to make much difference.

I suspect that my dual plane intake is the culprit, but I don't want to abandon it if I don't have to, as it makes gobs of torque in the street driving rpm range, and runs great in all other conditions aside from what I have described above.

Questions:
1. I currently have a 1 inch 4 hole phenolic carb spacer, this was needed to solve a fuel boiling issue (Florida summer stop and go traffic is brutally hot). Would an open spacer help to achieve a more even mixture distribution?

2. Is a single plane intake the real solution? If so, what is the best one for a street big block with a cam that signs off at 5600 RPM?

3. Is it normal that the engine needs an overly rich mixture to run smoothly at the very bottom of the cam operating range, or is this rich mixture just a band-aid for the uneven fuel distribution issue?

Any insight/suggestions are welcome and appreciated.

494 HP. 532 ft*lb was the first sign of a bad combination of parts
You can make 500+ HP 550 ft lb with peanut port heads done correctly.
The divider in the intake ended up being a bandaid .
The divider cut down the exhaust dilution in the inlet msnifold, that reduced misfires, owner was happy with outcome. How's using a dual plane as a dual plane a bandaid.
But yer bad combination of parts.
Ignorance leads to confidence more often than knowledge does.
Nah, I'm not leaving myself out of the ignorant brigade....at times.
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Re: Low speed (1500-1800 RPM) driveability issue

Post by F-BIRD'88 »

GRTfast wrote: Sat Sep 14, 2019 3:52 pm
Kevin Johnson wrote: Sat Sep 14, 2019 3:48 pm Still running those hotter plugs? :wink:
Sealing up the two plenums from each other was a game changer. The torque in the 2500-4500 range is nasty.
This is why ever oem uses a dual plane 180° intake with fully divided plenum on ever oem V8 carbed engine since the Ford flat head V8.

Open plenum is for high rpm racing where driving is not a priority. "drivability"
Even single plane intakes see a magical low rpm driving improvment if when the plenum is divided, even thou its not 180° design. The split plenum works on V8's at low rpm low speed driving.
Another "game changer" for all carbed engines for low rpm part throttle street driving is a heated plenum.
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Re: Low speed (1500-1800 RPM) driveability issue

Post by Tom68 »

The separarion of at least 180 degrees for smooth running on engines with more than 4 cylinders dates back to a 1909 French patent.

Ford started using it in 1934.

20220607_091755.jpg

34 Ford V8 Dual.jpg
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Ignorance leads to confidence more often than knowledge does.
Nah, I'm not leaving myself out of the ignorant brigade....at times.
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Re: Low speed (1500-1800 RPM) driveability issue

Post by BLSTIC »

I just wish it was that easy to do with sane sized exhaust manifolds on cross-plane v8s.

Maybe hot-V engines have an advantage here, with more reason to need it on the exhaust vs the intake now that efi and plenums are a thing.
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Re: Low speed (1500-1800 RPM) driveability issue

Post by Belgian1979 »

BLSTIC wrote: Sun Jan 29, 2023 5:24 am
Belgian1979 wrote: Tue Sep 10, 2019 1:22 pm
LoganD wrote: Tue Sep 10, 2019 9:46 am I've seen carb intakes, both dual plane and single plane, with such bad distribution that one cylinder will be 16:1 and another will be 11:1. I'd weld bungs in each header tube and move the wideband around, you can use the jetting to help mitigate it but you'll never get it great.

Get rid of the 4-hole spacer.
I think this is the cullprit.

I have no solution to offer but my experience.
I have 8 WB's on my engine and I can see the difference. Obviously with EFI you can have the ecu correct for this. Corrections made by the ECU vary up to 30% from rich to lean cyls on the extreme side of things at idle and anything which is low speed driving.
What had me stumped is that even when balancing airflows between cyls, it still had the uneven AFR's (mine is an ITB manifold which makes individually balancing cyls possible)

What those imbalances in AFR do is that the lean ones start to misfire making for bad driveability, rough running,...

I thought that it could have something to do with injector angle but after I see this post it seems that a carb does the same thing...

On other issue could indeed be the cam. Although if intake reversion would be the reason I would suppose it would show up in the airflow differences...
From what I've seen on my sims, crossover headers make more difference to fixing cylinder-cylinder variation in airflow than anything else, especially at low rpm. Your airflow variations are highly likely to be blowdown pulse from one cylinder screwing up overlap and intake airflow on another
Very plausible, but a crossover header isn't practical on my car.
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Re: Low speed (1500-1800 RPM) driveability issue

Post by rgalajda »

I run a single plane Victor Junior on my 500 hp BBC with a 780 Holley and it drives almost like an electric motor . As a matter of fact I have tried a number of carbs including a quadrajet , a carter carb, and a quick fuel , all of them were fine if set up correctly.
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Re: Low speed (1500-1800 RPM) driveability issue

Post by rgalajda »

I don' now the specs of that 1050 cfm carb but I suspect a Good carb with a smaller venturi would have drove much better below 3,000 rpm with better torque numbers.
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Re: Low speed (1500-1800 RPM) driveability issue

Post by panic »

Your manifold's divider wall is almost gone.
Close it up. Instant vacuum improvement.
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Re: Low speed (1500-1800 RPM) driveability issue

Post by ClassAct »

F-BIRD'88 wrote: Sun Jan 29, 2023 4:25 pm
GRTfast wrote: Sat Sep 14, 2019 3:52 pm
Kevin Johnson wrote: Sat Sep 14, 2019 3:48 pm Still running those hotter plugs? :wink:
Sealing up the two plenums from each other was a game changer. The torque in the 2500-4500 range is nasty.
This is why ever oem uses a dual plane 180° intake with fully divided plenum on ever oem V8 carbed engine since the Ford flat head V8.

Open plenum is for high rpm racing where driving is not a priority. "drivability"
Even single plane intakes see a magical low rpm driving improvment if when the plenum is divided, even thou its not 180° design. The split plenum works on V8's at low rpm low speed driving.
Another "game changer" for all carbed engines for low rpm part throttle street driving is a heated plenum.


Horse and buggy thinking.
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Re: Low speed (1500-1800 RPM) driveability issue

Post by F-BIRD'88 »

Hardly.. More like smart applied physics.
Vapourization of fuel in the intake absorbs heat.
That heat needs to be replaced to match , or soon vapourization suffers.
Thats why a carbwd engine ,when cold started will fire up initially but then soon stall. The available heat gets absorbed ,vapourization STOPS.
Plenum heat aids quick warm up and low speed driving..
Has nothing to do with a horse nor a buggy.
Poor carbed intake manifold vapourization gives poor low speed and idle quality. Intake manifold Plenum heat is a game changer. Always has been.

Ignorant statements don't change that.
Spark plug and mega volt super lightning ignition box companies love this ignorance. $$$$$
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Re: Low speed (1500-1800 RPM) driveability issue

Post by Tom68 »

F-BIRD'88 wrote: Mon Jan 30, 2023 12:18 pm Hardly.. More like smart applied physics.
Vapourization of fuel in the intake absorbs heat.
That heat needs to be replaced to match , or soon vapourization suffers.
Thats why a carbwd engine ,when cold started will fire up initially but then soon stall. The available heat gets absorbed ,vapourization STOPS.
Plenum heat aids quick warm up and low speed driving..
Has nothing to do with a horse nor a buggy.
Poor carbed intake manifold vapourization gives poor low speed and idle quality. Intake manifold Plenum heat is a game changer. Always has been.

Ignorant statements don't change that.
Spark plug and mega volt super lightning ignition box companies love this ignorance. $$$$$
Not to mention Smokey was working on a hot gas engine.
Ignorance leads to confidence more often than knowledge does.
Nah, I'm not leaving myself out of the ignorant brigade....at times.
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Re: Low speed (1500-1800 RPM) driveability issue

Post by ClassAct »

F-BIRD'88 wrote: Mon Jan 30, 2023 12:18 pm Hardly.. More like smart applied physics.
Vapourization of fuel in the intake absorbs heat.
That heat needs to be replaced to match , or soon vapourization suffers.
Thats why a carbwd engine ,when cold started will fire up initially but then soon stall. The available heat gets absorbed ,vapourization STOPS.
Plenum heat aids quick warm up and low speed driving..
Has nothing to do with a horse nor a buggy.
Poor carbed intake manifold vapourization gives poor low speed and idle quality. Intake manifold Plenum heat is a game changer. Always has been.

Ignorant statements don't change that.
Spark plug and mega volt super lightning ignition box companies love this ignorance. $$$$$


Let me say it this way. Why the OE’s do what they do isn’t why I do what I do.

I’ll type it slower for you.

If you can’t make a single plane intake outperform a dual plane intake you need to take up putt-putt golf.

Horse and buggy thinking is what it is. Just because you are living in the stoned age doesn’t mean I made an ignorant statement. It means you are behind in your thinking.
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Re: Low speed (1500-1800 RPM) driveability issue

Post by ClassAct »

Tom68 wrote: Mon Jan 30, 2023 2:27 pm
F-BIRD'88 wrote: Mon Jan 30, 2023 12:18 pm Hardly.. More like smart applied physics.
Vapourization of fuel in the intake absorbs heat.
That heat needs to be replaced to match , or soon vapourization suffers.
Thats why a carbwd engine ,when cold started will fire up initially but then soon stall. The available heat gets absorbed ,vapourization STOPS.
Plenum heat aids quick warm up and low speed driving..
Has nothing to do with a horse nor a buggy.
Poor carbed intake manifold vapourization gives poor low speed and idle quality. Intake manifold Plenum heat is a game changer. Always has been.

Ignorant statements don't change that.
Spark plug and mega volt super lightning ignition box companies love this ignorance. $$$$$
Not to mention Smokey was working on a hot gas engine.

What does that have to do with performance? You want a hot gas engine try LPG. And kill 1/2 your HP so fast your head will spin.
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