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  1. #1
    FEP Power Member richpet's Avatar
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    Default Dual plane manifold modification.

    So, gonna prove that I can be an idiot... Maybe? Maybe not?

    When I built my motor and installed the FiTech, I had read a lot of posts indicating that the FiTech 'liked' an open plenum manifold better. That sometimes the dual plane plenum divider 'caused issues'.

    So I cut out most of that divider when I installed it. My assumption was that each cylinder was pulling through the same hole at the top.

    What I've noticed is some plugs (cylinders) running leaner/richer than others. Oddly, my four corners cylinders were one, the four middle were the other. IIRC the middles looked leaner than the corners.

    Can taking the divider piece out of a dual plane manifold do this?

    Manifold is an Edelbrock 289/302 Performer (yes, I should have gone with at least the RPM or a Stealth probably).

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    Last edited by richpet; 04-29-2022 at 10:44 PM.
    83 5.0 GT. Quicker than it looks! 10:1 (or just over) 306, Motorsport a332 cam, 140A alt, t5 conv, 8.8 w/ 3.27's, Edel rpm, alum rad, very worked e7's, Holley SA carb, etc... SOLD IT!!!!

    Now an 1981 Granada! .040 over 302, Edel E-street heads... Currently building a 347 because, why not?

    "Never underestimate the power of stupid people in large groups"

  2. #2

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    Interesting, I heard all that stuff about tbi and dual plane as well. I would say the surgery could cause your issue. On cfi there were real problems with the stock manifold (pos) and lean cylinders but that was due to the butterflies on the carb biasing the flow away from some cylinders, particularly at WOT. I did a little grinding on my throttle body and fixed that but I suspect with my performer intake the bias wouldn't be as bad as the old truck 2 barrel manifold that came stock. It doesn't sound like you lean cylinders match a specific plane so I bet the missing septum or whatever the call it could be the issue.

    For what it's worth, I have never heard of this problem with cfi and that is fundamentally the same as a sniper or fitech so I wonder how much reality there is to the concern. I wish engine masters would do a test on it.
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    K&N filter in a stock dual snorkel, GT40 heads, Edelbrock 3721 intake, MSD 8456 Dist., MSD 8227 coil
    Comp cams XE254H, hypereutectic pistons
    Hooker Super Comp Shorty Equal Length Headers, catted BBK H-pipe, full custom duals
    Maximum Motorsports caster/camber plates and strut tower brace, 3.73 rear, dura grip (both Yukon)
    Ford Performance Springs, Firehawk A/S 225/55r16 on LMR TRX r390 wheels (street)
    Federal 595 rs-rr 245/40r17 and 255/40r17 on OE cobra r wheels (race)
    AOD rebuilt with a 6 clutch direct drum, Koline steels stacked with 8 clutches, Kevlar band, superior shift kit, new torque converter. --Everything else stock and fully functional.

  3. #3

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    Would the RPM manifold even fit under the hood ?

  4. #4
    FEP Power Member richpet's Avatar
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    Default

    Yes, with a drop base filter housing an RPM would fit.

    My thought was that if all runners pull from a common center it wouldn't be a problem. Hence my doing it.

    But, I assume (oh god, there I go again) that a single plane manifold has runners of differing lengths compared to a dual plane, so that might be the problem?

    The car seems to run well. Power feels great, economy is what I'd expect (17-22 mpg mixed hwy/town). But those plug readings... Perhaps I will pull them and see how they look again. I am running one heat range hotter that what was 'recommended' for the AL heads (RY13C?) with no detonation or anything, probably 13* initial with a vac dizzy with the screw inside the vac housing thing close to the max performance wise. I may throw the 'recommended' plugs (above) in and see if anything changes. But the plug won't change a result cyl to cyl.

    I had the hotter plugs in the corners, cooler on the middle 4, because of the apparent differences in mixtures.
    83 5.0 GT. Quicker than it looks! 10:1 (or just over) 306, Motorsport a332 cam, 140A alt, t5 conv, 8.8 w/ 3.27's, Edel rpm, alum rad, very worked e7's, Holley SA carb, etc... SOLD IT!!!!

    Now an 1981 Granada! .040 over 302, Edel E-street heads... Currently building a 347 because, why not?

    "Never underestimate the power of stupid people in large groups"

  5. #5
    FEP Senior Member gt4494's Avatar
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    Default

    I've read somewhere that a dual plane will work fine as you modified it. I will do some digging to see where I saw it. If I remember correctly there was a discussion on how much of the separator to remove. I think it ended up being trial and error on a dyno but there should be something about what they settled on.
    "If you can't explain it simply, you don't understand it well enough."
    Albert Einstein

    1984 20th Anniversary GT350
    Almost "Stock"

  6. #6
    FEP Senior Member gt4494's Avatar
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    Default

    Here you go. Start at about minute 17 for the details.

    https://www.youtube.com/watch?v=M2u7d8kajVI
    Sorry it took me so long. LOL
    "If you can't explain it simply, you don't understand it well enough."
    Albert Einstein

    1984 20th Anniversary GT350
    Almost "Stock"

  7. #7
    FEP Power Member richpet's Avatar
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    Default

    I will take a look!

    Sent from my Pixel 6 Pro using Tapatalk
    83 5.0 GT. Quicker than it looks! 10:1 (or just over) 306, Motorsport a332 cam, 140A alt, t5 conv, 8.8 w/ 3.27's, Edel rpm, alum rad, very worked e7's, Holley SA carb, etc... SOLD IT!!!!

    Now an 1981 Granada! .040 over 302, Edel E-street heads... Currently building a 347 because, why not?

    "Never underestimate the power of stupid people in large groups"

  8. #8
    FEP Power Member richpet's Avatar
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    It would appear, based on that (and my previous thought pattern) that cutting out that divider did no harm at all.
    Maybe I just won't worry about those plug readings
    It runs good. It makes good power. It gets decent mileage.
    I might try the cooler/recommended plugs. See if I notice a difference.
    Thanks all!

    Sent from my Pixel 6 Pro using Tapatalk
    83 5.0 GT. Quicker than it looks! 10:1 (or just over) 306, Motorsport a332 cam, 140A alt, t5 conv, 8.8 w/ 3.27's, Edel rpm, alum rad, very worked e7's, Holley SA carb, etc... SOLD IT!!!!

    Now an 1981 Granada! .040 over 302, Edel E-street heads... Currently building a 347 because, why not?

    "Never underestimate the power of stupid people in large groups"

  9. #9
    FEP Power Member gmatt's Avatar
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    Default

    Fords have that long runner/short runner thing going on. The 4 corner runners vs the 4 middle runners. I think fuel distribution issues are a fact of life with this set-up. Not to say it isn't tolerable, as long as it doesn't go extreme lean or rich.

  10. #10
    FEP Power Member richpet's Avatar
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    Default

    Right. And it isn't extreme. Just noticeable. Perhaps all my others were that way years past and I just didn't pay this close of attention. Or check them with so few miles on them. I've put under, but near, 5k on it is all.

    Decided just to leave it be. When I get my stroker motor built it will have a different intake manifold anyway.

    Sent from my Pixel 6 Pro using Tapatalk
    Last edited by richpet; 05-03-2022 at 09:58 PM.
    83 5.0 GT. Quicker than it looks! 10:1 (or just over) 306, Motorsport a332 cam, 140A alt, t5 conv, 8.8 w/ 3.27's, Edel rpm, alum rad, very worked e7's, Holley SA carb, etc... SOLD IT!!!!

    Now an 1981 Granada! .040 over 302, Edel E-street heads... Currently building a 347 because, why not?

    "Never underestimate the power of stupid people in large groups"

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