Single vs. Dual Intake Manifolds (LONG POST!)

[Guest Anonymous]

Hope you guys don't mind, but I just posted this on the Chevytalk forum and I wanted to get some additional feedback on this...

 

Just finished reading David Vizard's "How to Build Horsepower Pt. 2 : Carbs and Intake Manifolds" a few times... Excellent book, one of his best if you ask me, and I would recommend it to anyone. But this isn't a book critique, I was already thinking about this, and Vizard happened to touch on the subject in his book.

 

Now dual plane manifolds provide a stronger signal to the carb due to having half the plenum volume of a single, and thus give the carb a stronger signal at lower rpms, ensuring better low end torque and throttle response due to more accurate carb metering. A single plane manifold usually superior above 3000rpms due to the runners having a "straighter" path than they would with a dual, with its asymmetrical runner design, ensuring better, more even mixture distribution and flow between the eight cylinders making it superior at high rpms.

 

Now this got me thinking if it were possible to make a manifold that "grabs" both ends of the dyno curve, with the low-end of a dual and the high-end of a single... In his book, Vizard starts with a Weiand Team G, gives the ports a minor clean-up, and proceeds to radius the upper edge of the plenum into the runners, and adds knife-edged foils at the corners of the plenum. Add a 1" spacer to that, and presto! You've got yourself a kickass intake manifold.

 

Now my question is, why not take a manifold like the Team G or Xcellerator, perform the aforementioned modifications, and install a plenum divider (a la Weiand part # 7547) to make it behave more like a dual plane at low rpms while retaining most of the high rpm advantage. Does that sound like a good idea? Wouldn't a manifold like that be superior to a Performer RPM at everywhere except maybe off idle? Exactly how would installing the plenum divider change the manifold's characteristics? From what I understand, it should increase carb booster signal by a lot and recoup most of the throttle response/low-end torque. Now if we were to radius the base of this divider, that should increase flow some more, and decrease fuel puddling, keeping the fuel better atomized. How would it work in conjunction with Vizard's corner foils? Or Should I use one without the other?

 

I know that very few, if any of you have access to a flowbench and/or dyno. But hopefully if we pool our collective brains together we can figure out if any of this makes sense... I've always liked the idea of a divided-plenum single plane and can't see much of a disadvantage to it, provided the carb has enough cfms. And I can see how Vizard's modifications serve to improve flow and mixture distribution, but not how they make up for the low-rpm deficit like he says they would. I'm just curious to see if all these mods can work together to create a manifold with the best of both...

 

I haven't touched upon the topic of carburation yet... Now the intake and carb are a system, and must be selected and tuned together for best results. If we select say a 750-800cfm vacuum secondary carb with a single plane and ~400-430bhp would we not see significant gains in low-end torque if we milled the choke, knife-edged the throttle shaft & plates, and installed high-gain boosters in the primaries? Aren't improvements in booster signal always a good thing? Perhaps someone can better elucidate me on the matter...

 

 

One more thing, what's the difference between all the different booster designs out there? Annular, straight, dog-leg, high-gain... What are the benefits of each?

 

Hope I haven't bored you guys with all of this, and hopefully we'll come up with some good ideas on the matter... Gentlemen, let's rip this one wide open!

[Guest Anonymous]

I'm a silly, silly boy... Here is the link to the the chevytalk discussion for those of you who are interested:

 

http://forums.chevytalk.com/forums/Forum64/HTML/005165.html

[Kevin Shasteen]

Sounds like an adventure; but sometimes an adventure can get expensive!

 

The little odds & ends on carbs are for fine tuning your carb to your specific needs. Any engine sitting next to another engine of like kind quality will not always run identical to its neighbor-even if the exact same parts are used; go figure, but it just works out that way sometimes & that is where fine tuning your fuel system comes into play.

 

As for modifying the intakes; well the intake manfiold mfg's have done just about everything they can to squeaze every bit of power they could from the typical V8. The problem isnt in the intakes, usually, its in the Cyl.Heads. If you're gonna modify cyl.heads or intake manifolds then you'll need an airflow bench...or else how will you know when you made a positive change -vs- a negative change.

 

The 2valve cyl.head V8 is forced to run their push rods so close together that it poses a limitation on the airflow going into the combustion chamber...read Vizard's next book, "How To Modify SBC Cyl.Heads" for an indepth explanation on the heads.

 

If you want the best of both worlds you'll need a DOHC or aftermarket cyl.heads w/4valve's per cylinder; these heads eliminate the typical restriction on incoming airflow and the arrangement of the two intake valves and the neighboring exh.valves allow for gobs of power at low rpm's and at high & HIGHER rpm's.

 

Dont want to discourage you because it sounds like you're excited about fabricating an intake manifold...go for it; there's nothing like first hand "Hands On" experience...but you gotta keep us updated.

 

Kevin,

(Yea,Still an Inliner)