Dual Plane Manifold with Plenum Separated into 4 Sections

[Killjoy]

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.

Hi Walter R Malik! So, you actually tried it! This is awesome!

Looks like you addressed Panic's concerns that he mentioned in points 1 & 2.

Do you remember if you did any vacuum balancing like they do for ITBs? How much was it down in power? A guestimate? What size engine? Sorry, all of these questions just kinda tumbled out, hope you don't mind...

[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.

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.




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.

Yeah that manifold design looks flawed. Cylinder grouping is way off and as they mentioned in the article, 5/7 would be a pain to tune. But fabricating a "correct" manifold would be harder. Very awkward to group most of the 360 degree pairs.

You could probably do it in a high rise style fabricated manifold though, without too many sharp bends.

[Killjoy]

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

Certainly wouldn't have runner difference or grouping problems.

Hi BLSTIC, I saw some posts like that somewhere. Something about using dominator carbs but even they were too small. Not having the grouping problems would certainly eliminate a problem. I was hoping for something less expensive and tall though. One less 4 barrel carb and linkage issues. Sigh, high hopes. Lol

[steve cowan]

I don't have any testing myself only just what I have read so not much help sorry,there is a YouTube video of jon Kaase putting his index finger in a tunnel ram plenum on the dyno under full noise, he still has all his digits LOL,dividers ripping out not fixed well enough I would say.
I was reading The Similar Topics below - some very good information there.

[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.

Hi Walter R Malik! So, you actually tried it! This is awesome!

Looks like you addressed Panic's concerns that he mentioned in points 1 & 2.

Do you remember if you did any vacuum balancing like they do for ITBs? How much was it down in power? A guestamate? What size engine? Sorry, all of these questions just kinda tumbled out, hope you don't mind...

The engine was a normal 355 with iron 292 turbo heads ... it was around 1983 and the manifold was an Edelbrock C3BX.

I tack welded some divider plates in the plenums so, the front and rear were divided.
There was some, (but very little), sharing front to rear mainly for having a decent idle. The "4 corner" idle fuel Holleys were new back then and making the linkage 1 to 1 was easy.

Power was great to about 6,000 ... then it just stopped pulling.

EDIT: corner exit was around 3,600 RPM on the 9/16 mile asphalt, flat track.
Not there anymore ... Mt Clemens Race Track, Mt. Clemens, Michigan.

[Killjoy]

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.
Big BIG 8v roar when the secondaries kick in.
More power yet smooth and responsive..

Hi F-Bird'88! Is your example using an Edelbrock 2x4 dual plane manifold?

[Walter R. Malik]

Yeah that manifold design looks flawed. Cylinder grouping is way off and as they mentioned in the article, 5/7 would be a pain to tune. But fabricating a "correct" manifold would be harder. Very awkward to group most of the 360 degree pairs.

You could probably do it in a high rise style fabricated manifold though, without too many sharp bends.

Cylinders 5 - 7 would not be an issue here as this is a 2-plane intake manifold. NO sharing ports intake right after one another.

[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.
Big BIG 8v roar when the secondaries kick in.
More power yet smooth and responsive..

Hi F-Bird'88! Is your example using an Edelbrock 2x4 dual plane manifold?

Nope. Its using a 2x4 carb adapter on a single carb intake manifold..

[BLSTIC]

Yeah that manifold design looks flawed. Cylinder grouping is way off and as they mentioned in the article, 5/7 would be a pain to tune. But fabricating a "correct" manifold would be harder. Very awkward to group most of the 360 degree pairs.

You could probably do it in a high rise style fabricated manifold though, without too many sharp bends.

Cylinders 5 - 7 would not be an issue here as this is a 2-plane intake manifold. NO sharing ports intake right after one another.

I was referring to the Rover 4x SU manifold when I said it was flawed. But yes, 5/7 would not be a problem if he started with a dual plane. 180-540 separation would still be a problem though. It's not as extreme but it still involves airflow that hasn't completely stopped before the next intake stroke begins.

[F-BIRD'88]

For this purpose the 2X4 carb adapter would have a divider runing length wise inside.

[1980RS]

I think the S.P.2.P. intakes were something similar to what the OP is talking about. While they worked good power fell off at 4500 on those intakes. Might have worked good on a an old 283 the ports were so small.