Edelbrock Dual Quad Plenum Volume

[Thumperbird]

Hello everyone,
Would like to strike up one more conversation on plenum volume, port matching, torque, HP etc..
My concern is with regard to loss of low end torque due to high plenum volume and what can I do about it?
Of course I want the best of both worlds, torque monster down low and breathes well at higher RPM's as well.
I fear my setup will yield a fair sized torque curve shift up.

As you may recall I am building a 445 stroker using an Edelbrock dual quad air gap dual plane intake with custom offset spacers and Holley BJ/BK carbs.  This will be mated to Edelbrock 60065 heads mildly ported (gasket matched and blended) bowl and combustion side cleaned up with good valve job.  Custom cam from Lykins with ~.57 lift, 10.2 compression target, decent headers and 3.8 rear. with 28" tires.  Heavy car.

Here is a description of the plenum stack-up:
1.  Dual quad air gap manifold, opened up flange mounts to match carb spacers, radiused all runner inlets within plenum and opened up #8 inlet a bit to balance with others, port matched to 1427 gasket on the other end and blended up an inch or so.
2.  2" rise offset spacers, basically 4x4x2" (open) with a 50 degree slope to separate carbs.   
3. 1" 4 hole plastic spacer to get my carbs up a little higher for aesthetics and add some carb signal.

So overall in summary I am adding quite a few cubic inches to the plenum above the runners and have opened up the plenum at the flange, radiused sharp corners on the inlet side and gasket matched on the head side.  Heads ported to match.

What are your guys thoughts on how much impact this will have under 3000 to 3500 RPM's and what can I do about it.  Not interested in removing the stack as described but can I build the floor of the plenum or ?  Tuning options?

What do you guys do to counteract this issue and move the torque curve down for a given combination?

Thanks.

[Dumpling]

Add a centrifical supercharger.
Plenum issues go away.

[Thumperbird]

Yeah I could but just want to play around with a non-typical old fashioned system.

[machoneman]

Well, since nobody else directly took your post up....

Jack Dittmer years ago designed turtles (see link) for 1st gen. SBC single plane intakes to do exactly what you question. They also can/do redirect flow to improve distribution. Now, as to plenum volume, at the dawn of the Pro Stock era, all the big runners carefully hid the plenums they were experimenting with literally every week to find more hp and or torque. The shapes and volume of said plenums were what they hid from fellow racers.

That all said, it appears that getting to an optimum volume does offer benefits. Yet, unless one can dyno or track test various   
volume changes it's a crap shoot. Often, shaped pieces or aluminum or wood (yes wood!) were added the the floor of the plenums to test various ideas on everything from BBC's, destroked 426 Hemis, 351C's and the like. That and designing larger or small plenums bolted on to the lower runners as most at the time used cast aluminum t-ram bases (think: Weiand, Edel-B).

I'll venture that minimizing total volume could show gains but only with lots of experimentation. Some of our noted builders here may have a formula to estimate the ideal or near idea volume you could run. Let's see if they chime in.   

http://www.jegs.com/p/Brodix/Brodix-Turtle-Intake-Manifold-Inserts/3130850/10002/-1

Some more thoughts here on plenum volume yet it's doubtful much can be gained for your situation.

http://www.enginelabs.com/engine-tech/tech-feature-custom-racing-intake-manifolds/

[scott foxwell]

I'll ditto what machoneman says. Plenum volume is a very application specific subject. Lots of R&D has shown certain trends but for the most part, nothing written in stone other than typically, more is better, right up to equal the displacement of the engine. None of it, however, was related to anything like "loss of low end tq". That will have more to do with runner cross section and length, the first being most critical but also, this applies to an equal runner, "common plenum" manifold design, not a dual plane.
Think of plenum volume as a "reservoir" that the engine has to work with when the intake valve opens.
It's also difficult to quantify what you're dealing with in regards to a dual plane intake. There  really isn't a "plenum" in the traditional sense. If you look at the factory Ford dual quad intakes, they are almost a virtual individual runner intake with no plenum the way they're designed. The only real "plenum" that the engine has to work with is at the end of the runner right under the carb.
Your best bet will be trial and error.

[Thumperbird]

Thanks much gentlemen, that is the sort of info. I am looking for and had not read that article before.
I was thinking of adding a couple generic tapped holes in the bottom of the intake plenums prior to engine build so I had a fixing method down the road for what I now know some call a turtle.  Since this is unknown territory, at least for me, I like to have some options going in to this for any low end problems I encounter.  Been contemplating making sure I have some features (tapped holes again) in my custom spacers to be able to add dividers to extend existing manifold dividers up closer to the carbs as well.

Can anyone chime in with work they have done along these lines on a dual plane, dual quad FE?  Or that magical volume I should be thinking about?  I know I still have no wheres near a full engines worth of cubes within the intake prior to all the runners, but probably 3 or 4 cylinders worth.  Hoping the 1" 4 hole spacers help with responsiveness overall I guess.

Thanks.

[Falcon67]

IMHO, much ado about nothing.  The Weiand Xcelerator intakes for the 351C have an optional 1/2" spacer that comes with a divider.  I have run a 2V 351C open chamber 9.5:1 mild setup with the 2V Xcelerator and tried both the divider and fully open plenum, both topped with the typical 4 hole 1" insulating spacer (Moroso 64930).  I did not note any difference in performance between the divided plenum and the open.  I think your offset spacers will disrupt flow more than anything the volume might be doing.  Also note that on a dual plane, only have the intake and carb flow is seen by the engine at any particular time.

[Dumpling]

Plenum size influences carb signal.
Too large a plenum could lead to a turgid airmass under the carbs.

I have a M/T crossram with two large plenums feeding one-half the engine each.

[machoneman]

Doh! I missed the offset spacers required when running dual Holleys on that Edel-B intake. Still wonder why they didn't set the pads for Holleys or offer a 2nd intake to accommodate them.

I agree that bend in the airflow is more important as it will mess up a bit the flow. Nothing to fix though with Holleys!

IMHO, much ado about nothing.  The Weiand Xcelerator intakes for the 351C have an optional 1/2" spacer that comes with a divider.  I have run a 2V 351C open chamber 9.5:1 mild setup with the 2V Xcelerator and tried both the divider and fully open plenum, both topped with the typical 4 hole 1" insulating spacer (Moroso 64930).  I did not note any difference in performance between the divided plenum and the open.  I think your offset spacers will disrupt flow more than anything the volume might be doing.  Also note that on a dual plane, only have the intake and carb flow is seen by the engine at any particular time.

[cammerfe]

Back at the dawn of time---well the late '60s at least---I was involved with one of the first dozen Cobra Jet mustangs. They were all 'dollar' cars (although I don't believe even a dollar actually changed hands). We had a lot of quiet factory support.

One evening, in the Corban shop, Al Buckmaster and Jack Roush dropped in, and brought with them a new intake manifold. It was the first iteration of the Sidewinder; probably cast in the Experimental Foundry close by Gate 4 at the Rouge. It had no markings of any kind. The plenum was entirely open for a couple inches of depth. We were told, "Hold off putting this on, because we are still running tests."

The ultimate result was that we were told that the entirely open plenum was only the way to go for a stick car---we were running Super 'E' Automatic. Therefore, it was necessary to put in a fore-'n'-aft divider. It was also necessary to add material at the bottoms of the runners at the head interfaces for proper gasket support. We got the welding done but the finish work wasn't done right away; the manifold went on a shelf.

Some months later, I built a 427 for my '67 XR7 GT. I finished the Sidewinder and put it on that engine. It worked just fine, although the engine was a bit 'warmer' than it should have been for daily street driving. I had to add a bit of alcohol/water injection to rid myself of 'ping', even while using Sunoco 260.

Street Hemis were easily had for lunch, on occasion.

KS

[TomP]

Offy "Dial-a-Flow" intakes came with turtles to change the plenum.

I am a believer in small plenum and longer runners.

[TorinoBP88]

Much of the character with low end and possible surging will be related to can duration and overlap. Week were Bret on cam timing, but advance in it should help.

Also consider having a set of edelbrock carbs for putt-putt driving... Or just don't done in traffic, thanks no fun anyway.

[Thumperbird]

Thanks everyone, got a few ideas to consider, thinking of adding features for divider in offset spacers, a few tapped holes in plenum for turtles or similar if and when I need to deal with low end response. 

Just finished cleaning up my intake runners and heads, a fair amount of materail came off for gasket match and blend, was able to open up the exhaust ports quite a bit.  Left the bottom of the intake runners alone other than reduce the casting finish but worked over the sides, top and bowls a bit.  Unshrouded the valves and plugs some.  Fun stuff but messy and tired of what must have been 10 hours with a high speed.  Wife thinks I'm a nut job.