Dual Plane Manifold with Plenum Separated into 4 Sections

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Dual Plane Manifold with Plenum Separated into 4 Sections

Post by Killjoy »

Hi everybody! First time poster here. 🙂

I've read a lot of topics on this forum and really appreciate the technical discussions that take place here. I want to ask a theoretical question. Basically I don't have a brand of V8 engine in mind. It could be Chevy, Ford or Mopar, etc, but it's a small block.

My question is what would be the pros and cons of taking a dual plane intake manifold with a full plenum divider, no cutout, and divide it again with with an insert that makes a + pattern so that you have two cylinders feeding off of one barrel of a four barrel carburetor/throttle body. How well would this work? I'm thinking it would be something between an IR intake manifold setup and a dual plane manifold setup. Baby IR? It would be limited in top end I suppose based on runner volume and carb barrel size. Probably been done before. Just looking for some feedback or examples; maybe I can put this hypothetical question to rest.

Thanks in advance for any responses. 🙂
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Re: Dual Plane Manifold with Plenum Separated into 4 Sections

Post by rp930 »

Interesting idea. Somebody must have done it by now.
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Re: Dual Plane Manifold with Plenum Separated into 4 Sections

Post by BLSTIC »

I don't think you will have a good time. Carb capacity will be cut in half. You'll get stronger pulsing with dead zones between each pulse, so you'll have to apply ITB style tuning to a 4bbl carb. It would be cool to have a 1000cfm double pumper running on a mild 350, but that's about all it would achieve.

You'll also probably run into event separation problems. A typical dual-plane has each side suck every 180 degrees. If you half that, the layout *probably* won't allow 360 degree separation. You'll end up with 180 degree separation on at least one corner of the carb with a 540 degree dead zone, meaning that the second cylinder will run richer than the first. One of the corners will probably be able to get 360 degree separation and that will get different jetting.

If the layout allows for 360 degree separation of the charge you might have some success.
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Re: Dual Plane Manifold with Plenum Separated into 4 Sections

Post by steve cowan »

I have read stories where people have welded dividers in plenum on intake manifolds and they tear apart,making plenum area smaller probably hurt more than help anything.
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Re: Dual Plane Manifold with Plenum Separated into 4 Sections

Post by panic »

1. the individual runner volumes are all over the place
2. the carb linkage must be converted from progressive (primaries first) to simultaneous
3. the primary and secondary barrels must exactly match (none that I know of do this)
4. 1 barrel is much, much less than needed for 2 cylinders

Bad idea
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Re: Dual Plane Manifold with Plenum Separated into 4 Sections

Post by Walter R. Malik »

I have tried this type of thing on a short oval track engine, using a 750 Holley and 1to 1 linkage, where all the bores are the same and also has 4 corner idle.
Great throttle response but, power was down ... the carb needed to be considerably bigger and an 850 wasn't enough.

On the street this might actually be something good.
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Re: Dual Plane Manifold with Plenum Separated into 4 Sections

Post by BLSTIC »

Would a dual quad with no plenum (throttle to each cylinder) be better?

Certainly wouldn't have runner difference or grouping problems.
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Re: Dual Plane Manifold with Plenum Separated into 4 Sections

Post by JC565Ford »

panic wrote: Fri Apr 23, 2021 9:45 am 1. the individual runner volumes are all over the place
2. the carb linkage must be converted from progressive (primaries first) to simultaneous
3. the primary and secondary barrels must exactly match (none that I know of do this)
4. 1 barrel is much, much less than needed for 2 cylinders

Bad idea

I'm going with this post.
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Re: Dual Plane Manifold with Plenum Separated into 4 Sections

Post by F-BIRD'88 »

You'd need double the carb cfm rating..
How about 2x qjet carbs,
You'd have a lot more fun and sucess with a dual carb to single carb adapter that is fully divided length wise like a dual plane plenum. The 2x qjets secondary air doors can be adjusted to dial in the cfm capacity and secondary opening rate. Linkage could be 1-1 or progressive rear(primary carb) Front (secondary carb).. Easy secondary metering rod and hanger swap for power tuning.
Double the potential air flow capacity (that is very adjustable) Double the fuel capacity. Double fuel needle seats.
Small responsive street friendly primaries.
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Re: Dual Plane Manifold with Plenum Separated into 4 Sections

Post by naukkis79 »

Edelbrock did have manifold where primary and secondary barrels had their own plenums - they used divided runners to head. It was interesting idea, wonder how it performed?
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Re: Dual Plane Manifold with Plenum Separated into 4 Sections

Post by BILL-C »

In 1970 the factory Boss 302 mustangs in the TRANS AM series ran an intake manifold where 1 cylinder was connected to one barrel of the carb . Twin 1150 dominators were used. YES two 1150 dominators on a 302 cid engine.
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Re: Dual Plane Manifold with Plenum Separated into 4 Sections

Post by Walter R. Malik »

BILL-C wrote: Sun Apr 25, 2021 9:13 am In 1970 the factory Boss 302 mustangs in the TRANS AM series ran an intake manifold where 1 cylinder was connected to one barrel of the carb . Twin 1150 dominators were used. YES two 1150 dominators on a 302 cid engine.

YEP ... just as if it was like a big motorcycle engine.
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Re: Dual Plane Manifold with Plenum Separated into 4 Sections

Post by Killjoy »

BLSTIC wrote: Thu Apr 22, 2021 9:56 pm I don't think you will have a good time. Carb capacity will be cut in half. You'll get stronger pulsing with dead zones between each pulse, so you'll have to apply ITB style tuning to a 4bbl carb. It would be cool to have a 1000cfm double pumper running on a mild 350, but that's about all it would achieve.

You'll also probably run into event separation problems. A typical dual-plane has each side suck every 180 degrees. If you half that, the layout *probably* won't allow 360 degree separation. You'll end up with 180 degree separation on at least one corner of the carb with a 540 degree dead zone, meaning that the second cylinder will run richer than the first. One of the corners will probably be able to get 360 degree separation and that will get different jetting.

If the layout allows for 360 degree separation of the charge you might have some success.
Thank you BLSTIC! Your comment about the "ITB style tuning" and "event separation problems" made me go back and trace out the timing events for the various v8s. I came across this example on an old Rover V8. Looks like a single plane intake manifold that's divided down the plenum into 4 sections and laid out so that they could mount 4 SU carbs.

Image
Image

They mentioned that the key to getting it to work was the vacuum balance (like you mentioned). Here is the link to the conversation.

https://www.v8forum.co.uk/forum/viewtop ... 5&start=15

On page 3 there is a magazine article that tested it.
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Re: Dual Plane Manifold with Plenum Separated into 4 Sections

Post by Killjoy »

steve cowan wrote: Thu Apr 22, 2021 11:01 pm I have read stories where people have welded dividers in plenum on intake manifolds and they tear apart,making plenum area smaller probably hurt more than help anything.
Hi Steve Cowan, thank you for commenting! Do you have anymore information on why they tore apart? uneven pulsing intensity? Inadequate welding? Just trying to get a clearer picture of what happened.
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Re: Dual Plane Manifold with Plenum Separated into 4 Sections

Post by Killjoy »

panic wrote: Fri Apr 23, 2021 9:45 am 1. the individual runner volumes are all over the place
2. the carb linkage must be converted from progressive (primaries first) to simultaneous
3. the primary and secondary barrels must exactly match (none that I know of do this)
4. 1 barrel is much, much less than needed for 2 cylinders

Bad idea
Thank you, Panic! After going over BLSTIC's comment and tracing the firing order I realized it really didn't matter if it was a single plane manifold. Seeing as how the firing order is all over the place anyway.

As for 1 barrel not being enough for 2 cylinders, would doing a pancake plenum help out? Allowing a little sharing? Larry Widmer mentioned doing something like that in this thread below about individual runner carbs...

viewtopic.php?f=14&t=18063&p=197608#p197608

"48's weren't adequate for some of the old-school engines running lass than 350cid. I used 58mm Webers on the 494 CanAm engine I ran in my street Boss, but I had to use a "pancake" plenum that was 1.25" deep to allow the engine to breathe,
In the mid-eighties, we converted two of the mini-Indy engines to carbureted configuration for an SCCA race. The rules only allowed Webers with extremely small throttle bores. Once again, a shallow plenum connecting all of them saved the day.
If you have the time to machine one (a plenum), you may find it'll work for you too."
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