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Carb duel

I love my Chevy Chevette!
Posts: 10
Joined: 07/09
Posted: 07/21/09 08:11 AM

Same engine,  same intake,  different carbs of the same cfm ratings... 750 q-jet VS. 750 edelbrock VS. 750 holley...only difference is spacers and carb

examine the fuel consumption,  and hp&tq curves  

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Posts: 891
Joined: 01/08
Posted: 07/21/09 01:21 PM

Power wise the Holley has them all beat.  

Professional Hi-performance engine builder

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I love my Chevy Chevette!
Posts: 10
Joined: 07/09
Posted: 07/21/09 02:50 PM

agreed,  from my standing point,  each has its own advantage,  i'd like to see some heads up dyno #s and fuel consumption to have a good comparison as to where to make the comprimises...

do I take the q-jet on my cruiser/occasional strip for the mpg's or is there going to be that big of a difference in mpg's with the holley,  and how much hp/tq do i sacrifice for the mpg's

alot of questions that this would help clear up,  also alot of people out there trashing q-jets performance having never run one properly tuned,  i wanna see some dyno results  

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I love my Chevy Chevette!
Posts: 11
Joined: 02/09
Posted: 07/31/09 11:52 PM

acctually love to see this comparison done myself .  i personally think a properly tuned q/jet is a top notch carb . maybe not as much power but better drivability and better fuel economy.. come on guys do this comparison pleaSE!
                                                            REGARDS PHTWGN  
there is no substitute for cubic inches

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I have an SS396 tatoo
Posts: 358
Joined: 12/07
Posted: 08/01/09 07:59 AM

i was just curious... the 3310 holleys first application was a 57 lincoln 430...

they got the design right...    and the power enrichment system and wide open throttle power is just right... as is part throttle ...  i only have a problem my self with idle and transition fuel mixtures..   being a carb that could be put on almost any size of motor.. they work great..  with just basic jet changes..

has anybody ever looked at the ford version of the holley 4 bbl.. the 4180????

it does not have idle mixture adjustments in the metering blocks... they are in the base plate and only affect idle mixture..   the idle transition ports are not effected...

motors run on the transition ports until the airflow across the venturi's is fast enough to pull fuel up and over..    the idle circuit and transition circuits really effect fuel mileage...   just think of circle track racing..  ever notice the flames from the exhaust when they are backing off coming into a corner...  i would think that circle track fuel economy could be improved with base plate idle mixture screws... and changing the metering plate idle circuit screws to a fine pitch screw... so one could fine tune the transition port fuel mixture also.. right now its limited by restrictors...  how many races have been lost by running out of fuel half a lap from the finish line...   this might even get a lap or more of fuel over a race..

my thoughts on the quadra jet...   i agree that they are great carbs... well tuned.. they get great mileage...  there are some secrets .... on the primary metering rod holder...  most people don't know that there are lean adjustments for it...  and that it really really affects power output...

on most later 70s qjets there is a brass double D headed screw in the main body infront of the primary metering rod holder..   THAT is not to be adjusted when the carb is taken apart...  but of course everybody takes it out for cleaning..

if one looks carefully.  they will see a plug in the top cover in front of the air cleaner gasket.  it can be knocked out when the carb is apart...   replacements always come in rebuilding kits...   adjusting this screw with a tool you made a quarter turn at a time... starting with it screwed down... will get you the best mileage.. and then power..   i usually try to set the throttle to 2500 rpms...  then adjust it till i get the fastest engine speed ... with the throttle locked at 2500 when you started...

why is this so critical...   the primarys on quadrajets are much smaller... so the carb gets air across the venturi's sooner ... the primary needles are the metering on the primary booster venturis...    if the setting is too low... the primary will be too lean...  if the setting is too high.. it will be too rich...   this one setting can really wake up a quadrajet..    i have run into several of these double D screws.. that someone carefully sawed a slot into ... crosswise... so a flat screw driver can adjust it...

earlier quadra jets also have this adjustment..  but it is behind a plug in the base plate... between the idle mixture screws...   this early adjustment lifts a little lever that stick up on the base plate..  and stops the extended tip of the metering rod hanger...

afv/avs carbs also have been known for off idle flat spots that are almost impossible to get rid off..   there are idle feed restrictions behind the idle air bleeds in the booster hangers that need to be cleaned... and sometimes redrilled...

do post if you have ideas on the above...

i have been planning on tearing down a quadrajet.. and taking some pictures..  the last one i forgot my camera... but used my cell phone camera.. it was hot and sunny.. and i got too close... the photos were slightly out of focus...

and a tip...    well a tip drill.. most hardware stores and welding supplies have a tip drill for cleaning the welding tips.. a little handle with a bunch of tiny drills inside. a chuck on one end... this is such a great tool for verifying that tiny tiny passages are open...

while i am on a quadra jet binge...

people who swap a 350 or larger for a 305 with the feed back carb and run into terrible problems...  the feed back quadrajet primary metering rods cannot make up for the change in displacement..    so thinner primary needles are needed...  350 carbs can be bolted right on.   but there is one more larger motor that most people don't think about..    the 81 full size cad 6.0/368 in california came with feed back carbs...   so the jetting in that carb could be swapped into a 305 carb for a 350 /355 installation.....  

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I have an SS396 tatoo
Posts: 325
Joined: 07/09
Posted: 08/03/09 09:05 PM

i too would like to see the results of this test but not only dyno results, on the same engine in the same car at the same track on the same day results...i don't ask for much do i?  
68scott385 68scott385 68scott385

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I have an SS396 tatoo
Posts: 442
Joined: 10/08
Posted: 08/04/09 06:40 AM

Excellent throwdown on the carb info there waynep!!! (I learned a lot) actually there was a dyno test in one of the mags chp or super chevy I cant remember which. They used a holley, demon, and Qjet. All of them were 750 CFM. they were built for the engine in which they were tested on. But the best part was all of them were within 15 hp of each other the number was over 500HP the qjet made the most low end torque and the holley  made the highest end number I will try to find the article so I can back this up for sure. It did prove that the Qjets can be built for any application.  

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I love my Chevy Chevette!
Posts: 2
Joined: 10/09
Posted: 11/21/09 06:25 PM

I read an article years ago, on a pretty radical 350 Chevy build. The only thing I remember about the build is they used a 3310 750 Holley carb. When jetting the carb on the dyno, a bigger jet made better horsepower, and torque suffered. Then a smaller jet was tried, torque improved and horsepower suffered. What this tells me is the fuel curve in the carb was wrong for this combination. The carb was rich in the lower RPM range and perfect up higher. When a smaller jet was used the mixture was perfect down low and lean in the upper RPM range. Holley Denominators have air bleed jets so this can be tuned. The more radical you build any engine the better you have to be on tuning your carb. I am now building an engine and have decided to use an Edelbrock carb. It seems that the Edelbrock's system of jets, metering rods, changeable metering rod springs would be a more flexible carb to tune. I wish one of these magazines would build an engine and flog an Edelbrock carb. Who knows, it may come up short 15 ponies, but it may pick up 20 ft-lbs. If I may borrow someone else's words: HORSEPOWER SELLS ENGINES...TORQUE WINS RACES!  

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I love my Chevy Chevette!
Posts: 12
Joined: 01/10
Posted: 01/08/10 12:51 AM

im thinkin for performance holley all the way but for everyday driving edelbrock or q jet  
*if you aint first, you must drive a ford*

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I love my Chevy Chevette!
Posts: 10
Joined: 08/09
Posted: 01/08/10 04:52 PM

Laugh Hi people,
Out here in Oz we the average enthusiasts are
led to believe that holleys and
Barry grant carbs are virtually the same.
I have a B/G speed demon and no problems so far
in 2 years..What % of parts interchangeability
is there. I ask here because I cannot get straight
answers else where. Any replies gladly appreciated.
  All the best...Skyeking... Laugh  

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I love my Chevy Chevette!
Posts: 1
Joined: 04/10
Posted: 04/11/10 09:12 AM

I had a dual line 750 Carter AFB that I took the choke horn off and took out all the casting lines , ran 11.88 in a 406ci. 71 Vega. I never could tune a Holley .
 Going to build the 73 next .  
1996 Chevy Blazer
1990 GMC Avaburb
1973 Vega Notchback

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