All Big Six Clifford Plenum Divider

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Firepower354

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Firepower 354- good afternoon. - What am seeing on the pic of your DP manifold? Is there a mod in there, or am I confused by shadows? I am not being derogatory. I am always interested in mods to this diamond in the rough manifold, just not sure what I am seeing. . Thanks
Not mine. Offy pic, unmachined casting and foundry pieces, to highlight the lighter colored section, intended as the top section of the DP intake. I like the less-direct 3/4 path, and attempted to emulate it in my cartoon. The stuffer/pig/turtle should reduce volume, split the front 3 and rear 3 apart, and "add" runner length to 3/4, hopefully strengthening the signal seen by the carb, and better atomizing the mix.
 

bubba22349

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Firepower 354- good afternoon. - What am seeing on the pic of your DP manifold? Is there a mod in there, or am I confused by shadows? I am not being derogatory. I am always interested in mods to this diamond in the rough manifold, just not sure what I am seeing. . Thanks

Hi Firepower 354 & Frank, all the posts made by old28racer have been about his Clifford intake that he's using and modding, they have almost nothing in common with the design of the Offy Duel Port intakes? If you look at the first post at pictures 4 & 5 you can clearly see that it's one of the old Clifford 6 = 8 intakes these like all Clifford intakes have removable proprietary carb plate adapters made in both 2V or 4V versions unlike both the Offy duel ports or C intakes which are cast in one piece. https://fordsix.com/threads/clifford-plenum-divider.82636/
 

Firepower354

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Hi Firepower 354 & Frank, all the posts made by old28racer have been about his Clifford intake that he's using and modding, they have almost nothing in common with the design of the Offy Duel Port intakes? If you look at the first post at pictures 4 & 5 you can clearly see that it's one of the old Clifford 6 = 8 intakes these like all Clifford intakes have removable proprietary carb plate adapters made in both 2V or 4V versions unlike both the Offy duel ports or C intakes which are cast in one piece. https://fordsix.com/threads/clifford-plenum-divider.82636/

Clearly. We're all on the same page, but may use a different translator...

The Offy pic was just to show what an Offy C, Clifford, et al, would be like, with the stuffer I drew up, or similar, inserted. The upper runners of a DP, but in full-height, would be of benefit to emulate.

The Clifford insistence on sticking to the Rochester/Carter small-base 4bbl pattern, is confounding, and leads to the stack-O-spacedapters Tom has, exacerbating the already oversized plenum. Since there's not an easily found WCFB to 2300/2100 adapter, a piece of flat plate aluminum, phenolic, etc, would make it a 1-piece, ported adapter, allowing carb to be centered as desired. IMIHO
 
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Frank

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Bubba22349- thank you for the correction. I am ignorant of social media and it's protocol. This forum is the first and only s.m. I've ever done. I appreciate being allowed to participate. The subject is the clifford project, and I barged off on the DP. It is important to me that I stay inbounds because I appreciate the level of genuine, hands on, years of knowledge you and many others have and I want to remain a participant in good standing. Thank y'all for letting me participate, and for your patience with a probie.
 

old28racer

Famous Member
For all following my Clifford divider thread please note that I am in full agreement with Firepower 354 that my current plenum volume is still to big & my 4x2 carb adapter for my Holley 2300 & Autolite 2100 1.08 that is 1" tall just ads more volume.

I just want to try the setup on my 300 4.9L inline 6 like I have it and get a new cruise AFR gauge number. After I have done that I will build a 1/2" thick aluminum adapter with carb studs to take the place of the Clifford 4V adapter & the 4x2 carb adapter. Those two adapters are 1 3/4" tall so the total height of the adapters will be reduced by 1 1/4" witch will reduce the overall plenum volume.

I may also at the same time install a pair of pigs/turtles to the bottom of the divider to reduce the plenum volume a bit more.

What is workable total plenum volume for a 300 4.9L that is mildly built cruiser street motor running the 2300 or 2100 2bbl carb? Motor is operated in the 1500-4500 RPM range 95% of the time. I have a few numbers in mind, just want to see what others think? Thanks
 

old28racer

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I have done some figuring on the plenum volume of my existing Clifford Intake with it's 4V & 4x2 adapter in the main plenum directly below the 2bbl carb. The volume works out to 64 cu in. If you take 1/4 of the 300" motor you come out with 75 cu in as a good starting point. As the 64 cu in is real close to the 75 cu in I am going to try the current setup "as is" the first time.

I will be trying both my Autolite 2100 1.08 venturi carb with .047F jets and my Holley 2300 350cfm carb with .059 jets. Will get new cruise AFR numbers with each carb.

FTF on this site said that for a stockish 300 with a 2bbl carb it needs a small plenum for good throttle response & overall smooth operation.

As I am having some medical problems it may be a few months until I have a chance to get the intake installed. Thanks for all the support on this modification.
 

MikeyLawless

Active member
New to this forum, so this is the first time I've read this thread, and I have a little input from my experience years ago, early 1980s) using a plenum divider. Different application, but interesting result none the less.

It was on a 340 small block Dodge drag car, weighed around 3300lbs. Motor had the factory race heads, an Edelbrock single plane "Victor" manifold, and a fairly big cam. Automatic trans with a 4500, 8" converter. Left on the foot brake as trans brakes for Chryslers weren't available. It was a bit soft on the bottom end, even with a high stall converter. I'd read about a Super Stock racer that used a plenum divider to perk up the low end. So, I did that. It was not sealed around the edges, and was about 3/4" off the floor of the manifold. But man o man, did it wake that thing up! Because the signal at the carb had improved so much, it did need re-tuning. I trimmed down the accelerator pump shot, and re-jetted, and after that, it was nearly 4 tenths quicker in the quarter mile.

So, bottom line....it works! And if it works even half as well on old28racer's deal as it did on my Dodge, I'll be doing the same thing!
 

old28racer

Famous Member
FTF - Thanks for the good word, getting better each day but at 76 it is slow going. Stay safe & well, good luck this race season.

MikeyLawless - Welcome aboard. Very interesting information. Ya a plenum divider that feeds 1throttle bore to the 1-2-3 cylinders & the other bore to the 4-5-6 cylinders will sure help my 300 inline 6 along with better carb signal. My divider is not sealed, but it matches the intake side walls & floor very close.
 

Econo4spd

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Supporter 2020
I just installed my 2nd iteration of this in my Offy C.


Summer project list was hijacked and went sideways...
 

old28racer

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Econo4spd -- I just posted a few question over on your plenum divider thread that I hope you can answer. Thanks in advance.
 

Econo4spd

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I'd read about a Super Stock racer that used a plenum divider to perk up the low end. So, I did that. It was not sealed around the edges, and was about 3/4" off the floor of the manifold. But man o man, did it wake that thing up!

So, bottom line....it works! And if it works even half as well on old28racer's deal as it did on my Dodge, I'll be doing the same thing!
Hmmm. Over in my post, FTF ( also a drag racer and retired Ford Engineer) made this comment last fall:

"The divider not going to be an effective isolator if you leave the bottom open. Any hole bigger than about 1/4" diameter is going to bleed vacuum from one side to the other."

I sealed mine up.

Maybe a sealed divider is more important on a street motor. Apparently a WOT drag car can still benefit from having a 3/4" gap at the bottom of the divider. Maybe the Victor had a huge plenum to start with?
Must have been the lowest priced .4 sec your car ever gained!
 

MikeyLawless

Active member
It was the lowest cost 4 tenths. At least at that point.
It does not matter to me what anyone has to say about it not working. Theory is one thing. Practical application is another.

In your deal, the sealed divider will probably work great. Especially since the air speed won't be nearly as high. I still think you're on the right track splitting the manifold up.
 

old28racer

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ML -- The only real difference in Econo4spd Offy C divider & my Clifford 4x2 divider is that on his Offy C divider he has welded the divider to the intake plenum side walls. On my Clifford I have a milled a notch in the floor of the intake that the divider fits in and I have notched & epoxyed the top of the divider to the 2bbl adapter. I fitted the divider very close to the bottom & walls so there is only a few .000 gap in a few places. Also by 2300 Holley carb base holds my divider down & in place.

I really feel that any setup that rotates the adapter 90 degrees so one throttle bore is feeding 1-2-3 & other bore 4-5-6 along with the divider (with space gap or not) will add performance to a 240 or 300 big block 6. Their might be better intake manifolds for the system but I wanted to use what I had on hand.

I am looking forward to Econo4spd test results & my test results later this year.
 

old28racer

Famous Member
Just want to make sure I am on the right track. When figuring total intake plenum volume you get the volume in cubic inches for the intake box area under the carb and add it to the total volume in cubic inches of the intake runners. Is this correct?

Then with a 300 motor you would take 300/2= 150 cubic inches as a base line.
 

MikeyLawless

Active member
To be honest, I was never that scientific about it. I just tried different things on my small block Dodge until I got the best results. I never completely sealed one side from the other. But still, having that plate extend about 3.5" down from the carb base really woke it up. I tried shorter and longer, but eventually settled on the first one I made which was 3/4" off the plenum floor.
Maybe, for something that will operate at part throttle, sealed sides might be better. I don't know. I'm a trail & error kind of tuner. When I get to that point, I'll try different stuff until I get the best result that I need from my own particular combo.
 

old28racer

Famous Member
ML -- well the only reason I am asking is that with my current medical issue I have a lot of time to be on my computer and ask questions. I am a true old school tuner "set it, test it, modify it until I get what I want".
I have not sealed one side from the other but I have fitted my divider, side walls & floor very close. I think this will help the low to mid throttle funtion as this is a stockish 300 street motor.

others -- Still would like an answer to post #36 above.
 

pmuller9

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Just want to make sure I am on the right track. When figuring total intake plenum volume you get the volume in cubic inches for the intake box area under the carb and add it to the total volume in cubic inches of the intake runners. Is this correct?

Then with a 300 motor you would take 300/2= 150 cubic inches as a base line.
No
The plenum volume does not include runner volume.
The runners are tuned separately and the plenum volume is figured separately.
 

MikeyLawless

Active member
ML -- well the only reason I am asking is that with my current medical issue I have a lot of time to be on my computer and ask questions. I am a true old school tuner "set it, test it, modify it until I get what I want".
I have not sealed one side from the other but I have fitted my divider, side walls & floor very close. I think this will help the low to mid throttle funtion as this is a stockish 300 street motor.

others -- Still would like an answer to post #36 above.
In that case, I would recommend to just run it. See what happens.
 
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