carb plenum intake design



carb plenum intake design

Postby grumpyvette » December 24th, 2010, 1:33 pm

the larger the plenum volume (up to about 1/3- 1/2 of the engines displacement, the better the peak horsepower potential tends to be PROVIDED the runner and plenum design is near optimal. as the plenum volume is reduced the engine tends to become more responsive due to higher port flow speeds to throttle position changes and the mid and low rpm torque tends to improve, up to the point the runners cross sectional area or plenum size or carb venturies feeding them become a restriction to flow
on a dual plane intake design a single primary and secondary venturie in the carburetor feeds four individual intake runners from 1 of two common plenums
open carburetor spacers under a carburetor are designed for and generally used with single plane common plenum intakes to increase plenum volume
dual plane intakes have twin plenums designed to increase low and mid rpm port flow speeds and work best "in MANY CASES" with 4 hole or divided spacers, that maintain the high port flow speeds but allow more room under the carb to reduce the transition of direction as the air flow enters the individual intake runners, in some cases where the engine is very restricted a single open spacer or lowering the plenum divider wall helps improve flow rates on a dual plenum intake but if it proves to be a huge improvement in that application its almost a guarntee that a properly designed single plane intake would do even better




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common dual plain divided dual plenum
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viewtopic.php?f=55&t=4362&p=11826&hilit=volumetric#p11826
this mod effectively doubles the plenum volume, and effectively converts the intake into a semi-single plane design, but the modification tends to reduce low rpm engine torque and engine low and mid rpm responsiveness, because the added plenum volume tends to slow the low rpm port speeds , because the individual cylinders now can pull from a larger common volume of fuel/air mix in that larger plenum area.


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on a single plane intake design a pair of primary and a pair of secondary venturies in the carburetor feeds eight individual intake runners from 1 common plenum
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common single plane common single plenum

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dual carb single common plenum cross ram
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dual carb ,dual plenum single plane intake

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single plenum dual carb tunnel ram intake

CIRCLE TRACK MAG HAD THIS INFO
Carburetor Spacers
You've likely read or heard about an assortment of consequences when a carburetor is raised (or lowered) relative to an intake manifold's plenum floor. More plenum volume helps high rpm, for example. Or maybe, smaller carburetors like more spacer. This isn't to say these analogies are incorrect, but maybe the reasons are a bit obscure.

For example, let's look at it this way. A carburetor is a pressure differential device. It delivers fuel into a region that's designed to be at less than atmospheric pressure. It's a fuel metering "signal" that allows atmospheric pressure to force fuel into the incoming airstream, acting through the carburetor's bowl vents. By elevating a carburetor, all else being equal, it becomes more remote to runner entries and thus can experience a weaker metering signal. The carburetor tends to act "leaner" in the presence of a decreased signal. Aggregate airflow tends to be the same but there's less fuel flow, so fuel enrichment is decreased.

However, as Smokey often said, "there's one more little item." Once discharged from the carburetor, air/fuel charges are required to make a relatively abrupt turn into the manifold's runners. Air, being compressible can navigate this sudden change more easily than fuel. Increasing carburetor height allows air/fuel charges more time to slow down and make the turn more effectively, often reducing the possibility of air and fuel separation. As carburetor size is decreased and no spacer is used, the problem becomes more critical. In fact, carburetors placed too near a plenum floor can be akin to sticking a hose in a bucket with fuel impingement materially upsetting proper air/fuel mixtures.

One key here is to map brake specific fuel consumption (BSFC) data as carburetor height is changed, assuming carburetor sizing remains the same. If a disproportionate amount of fuel is required for best power and BSFC data are trending higher and higher, chances are good mixture quality is being upset and raising the carburetor is a potential solution.

On the other hand, if you discover that a four-hole spacer is beneficial, possible reasons include the fact the fuel metering signals were insufficient (for the calibration or jetting being used) and stronger signals provided by the spacer helped deliver additional fuel. But in virtually any case, power changes from raising or lowering a carburetor affect more areas than plenum volume.

READ THESE LINKS

http://victorylibrary.com/mopar/intake-tech-c.htm#new

viewtopic.php?f=55&t=858&p=1338&hilit=spacer+plenum#p1338

viewtopic.php?f=55&t=1038&p=1932#p1932

viewtopic.php?f=55&t=624&p=11125&hilit=intake+test+result#p11125

viewtopic.php?f=44&t=392

viewtopic.php?f=52&t=322
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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Re: carb plenum intake design

Postby grumpyvette » December 24th, 2010, 2:17 pm

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when you see guys mount a set of dual Holley carbs on a low rise dual plane intake like this, BECAUSE THEY WON,T FIT CORRECTLY MOUNTED END TO END ON SOME DUAL QUAD INTAKES, where all 4 primary venturies feed only four cylinders and the other four cylinders don,t get fed effectively until carbs the secondaries open, you KNOW they don,t have a good understanding of a carbs function , fuel/air distribution or the dual plane plenum design, even with an open spacer plate
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between the carb base and plenum entrance points fuel distributions going to be horribly unbalanced
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one reason some guys swap to EDELBROCK carbs on dual quad low rise intakes

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obviously IF YOU have the HOLLEY CARBS set up so all 8 VENTURIES in BOTH carbs open EQUALLY over a COMMON PLENUM which is frequently done on TUNNEL RAM INTAKES then thats not an issue

READ THIS
viewtopic.php?f=55&t=444&p=10149&hilit=+dual+quads#p10149

viewtopic.php?f=55&t=109

read all the sub linked info

viewtopic.php?f=55&t=109

viewtopic.php?f=55&t=211

viewtopic.php?f=55&t=1639&p=4545&hilit=+power+valve+vacuum#p4545

viewtopic.php?f=55&t=1442&p=5524&hilit=accelerator+pump#p5524

viewtopic.php?f=81&t=1189&p=2447&hilit=+infrared+tuning#p2447

viewtopic.php?f=50&t=383&p=1637&hilit=+infrared+tuning#p1637

viewtopic.php?f=70&t=202&p=5344&hilit=+infrared+tuning#p5344

viewtopic.php?f=55&t=635

viewtopic.php?f=70&t=3438&p=10844&hilit=power+valve+vacuum#p10844
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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Re: carb plenum intake design

Postby grumpyvette » January 22nd, 2011, 11:52 am

dual plane intake designs
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SINGLE PLANE
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DUAL PLANE
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http://store.summitracing.com/parts/edl ... dia/images
extended divider carb spacer
are usually designed to maximize torque in the 1500rpm-5500rpm range and are usually the best choice in that rpm range even on most street/strip cars used for transportation. runners tend to be a bit longer and USUALLY the DUAL plenums,with each side of the typical 4 barrel carb, having only one primary and one secondary venturie feeding only 4 cylinders on a V8 tend to be a bit smaller this tends to keep the port flow rates reasonably high, increasing volumetric efficiency.
in some cases the divider wall between the dual plenums has been machined away rendering the result a type of bastard single plane design.
as a general rule dual plane intakes generally run best on moderate compression combos with cams having less than about a 235-245 duration at .050 lift and under 10:1 cpr, matching their dual street/ strip rpm band.
keep in mind design changes between manufacturers and different intake designs do effect your results, as will displacement, port cross sectional area,head designs , cam timing,compression ratio and exhaust scavenging.

http://www.youtube.com/watch?v=N_ART4SBmdg

http://www.youtube.com/watch?v=lqqtK0lPjrA

watch these two videos

viewtopic.php?f=55&t=444&p=10794&hilit=tunnel#p10794

viewtopic.php?f=55&t=2739&p=7119&hilit=weiand+edelbrock#p7119

viewtopic.php?f=44&t=392&p=5415&hilit=+test+intake#p5415


single plane intakes
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these intakes vary in design a great deal, most are designed with a single common plenum and shorter intake runners,this tends to reduce low rpm cylinder fill efficiency but allow better high rpm flow rates the better designs tend to locate the runner entrance angles between the cylinder head ports and carb plenum in as strait in-line as possible, this by necessity tends to result in un-equal length runners but at rpm ranges above about 4500-7000rpm that lay out tends to increase the available flow volume
these intakes rarely produce better power below about 4500rpm than a comparable quality dual plane but they do tend to make a bit better peak hp PROVIDED the rest of the combos designed to maximize the intakes intended rpm range.
as a general rule single plane intakes generally run best on moderate-high compression combos with cams having more than about a 235-245 duration at .050 lift and over 10:1 cpr, matching their intended strip rpm band.
keep in mind design changes between manufacturers and different intake designs do effect your results, as will displacement, port cross sectional area,head designs , cam timing,compression ratio and exhaust scavenging.

tunnel ram intake designs
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these intakes are designed to maximize the cylinder fill rates, having a direct strait line flow angle from carb venturie to the back of the intake valve, most are dual quad designs ,placing a carb venturie directly over each port entrance, most use a reasonably large common plenum, similar to a single plane but runners are equal length,the intakes tend to be higher and the port angle and runner length tend to be much better, this usually results in limited low rpm torque hood clearance issues but maximum power in the 5500-8500rpm range, PROVIDED the rest of the combos designed to maximize the intakes intended rpm range.
as a general rule tunnel ram intakes generally run best on larger displacement ,high compression combos with cams having more than about a 250-265 duration at .050 lift and over 11:1 cpr, matching their intended strip rpm band.
keep in mind design changes between manufacturers and different intake designs do effect your results, as will displacement, port cross sectional area,head designs , cam timing,compression ratio and exhaust scavenging.


keep in mind that in most cases its a process of MATCHING all the components in your combo like the cam timing,compression ratio,displacement, rear gear ratio, and exhaust scavenging to the engines intended rpm/power range that will dictate the correct intake selection, failure to do so results in much less efficient power production. theres obviously going to be changes in which intake is a best match, required in your choices in matching the engines needs between a 8:1 cpr sbc 283 and a 13.5:1 cpr BBC 632 displacement , and heads that flow 200cfm on a sbc with those flowing well in excess of 400cfm on a BBC


many guys spend 90% of there porting time on intakes matching the ports to the heads and opening the runners up, but a surprising amount of the potential flow improvement on many intakes involves the port work on the runner entrances in the plenum area.
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IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
grumpyvette

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Re: carb plenum intake design

Postby bytor » September 13th, 2013, 6:57 am

These related videos may already be on the forum somewhere but I couldn't find them.

Edelbrock single plane (Victor Jr) vs dual plane (Air-Gap) intake
http://m.youtube.com/watch?v=i2DvnoHWagk&feature=related&desktop_uri=%2Fwatch%3Fv%3Di2DvnoHWagk%26feature%3Drelated

Weiand Air Strike vs. the Edelbrock Air Gap
http://m.youtube.com/watch?v=Bmj48i_v6-8&feature=relmfu
My 383 build photos
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Re: carb plenum intake design

Postby grumpyvette » September 13th, 2013, 7:20 am

viewtopic.php?f=55&t=58

they were but thanks for posting them again as obviously some of the guys reading thru the site missed them
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
grumpyvette

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