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1972 Lemans Stock 350- carb upgrade?

  
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1972 Lemans Stock 350- carb upgrade?

 
kwm219 kwm219
New User | Posts: 4 | Joined: 05/13
Posted: 06/16/14
01:15 PM

I know there are a lot of Carb threads on here, have read most of them and got some great info, but haven't seen a direct answer to my question yet, so hopefully i didn't miss it
I have a 72 Lemans, Stock 350 2 barrel carb and am looking to upgrade.  I purchased an Edlebrock Performer Pontiac Spreadbore 4 barrel intake and wondering what the perfect 4 barrel carb matchup is for it.
Looking for as close to bolt on, no mods, as i can get and taking advantage of the spreadbore with a matching spreadbore carb, automatic choke ect.
are there any mods that i will need to make with this change?
thats for the info guys, long time professional body guy trying to teach myself the motor aspect  

bigD bigD
User | Posts: 142 | Joined: 05/14
Posted: 06/17/14
11:08 AM

We're sorta like Democrats and Republicans. We disagree a lot. Of course, you need a Q-jet. But I much prefer an early model, such as a '68-'70 Pontiac. Or a '68 -'72 Buick. The reason is because the later years began having more and more smog restrictions. Also, beginning about 1971 the Pontiac Q-jets had a huge smokestack vent which requires a hole in the air cleaner base to clear it. According to the Q-jet expert Cliff Ruggles, the later models must have some of the small passages drilled out by hand correctly, in order for them to provide any kind of decent performance.

The early models don't need all this drilling to perform well. My wife and I both rebuilt these early models and won lots of races with 'em.

Here's a couple of links to sites where you can buy good quality Q-jets. I'm sure there are many others.

http://www.everyday-performance.com/quadrajet_carburetors.htm#!/~/product/category=578011&id=33759629

http://www.smicarburetor.com/products/sfID1/28/sfID2/9/sfID3/100/productID/840

Lc9p  

shyrgfuh3 shyrgfuh3
Enthusiast | Posts: 475 | Joined: 11/13
Posted: 06/17/14
11:54 AM

hi;

well there is no real advantage to a spread bore. you can possibly get a square bore on it especially if is an eddy manifold.

i would use an annular boot venturi carb but you will need to mess with the linkage a ***

bolt on is the stock q jet. they work decent when PROPERLY tuned which no mere mortal man can do therefore if it has hesitation or burbles on acceleration you might be sending it off to cliff ruggles for tuning.  

kwm219 kwm219
New User | Posts: 4 | Joined: 05/13
Posted: 06/17/14
04:54 PM

Thanks for the input guys, it is greatly appreciated

One last quick question, what sizes would you stay around?  ballpark of 650cfm for a stock motor?  

thanks again  

shyrgfuh3 shyrgfuh3
Enthusiast | Posts: 475 | Joined: 11/13
Posted: 06/17/14
05:20 PM

Icon Quotekwm219:
Thanks for the input guys, it is greatly appreciated

One last quick question, what sizes would you stay around?  ballpark of 650cfm for a stock motor?  

thanks again


YES, A NICE 650 HOLLEY OR BETTER YET, A 670 "LOW RIDER" ANNULAR BOOSTER HOLLEY. YOU CAN INSTALL THE OPTIONAL LIGHT WHITE SECONDARY SPRING. IF THE SECONDARIES OPEN TOO SOON, TRY A SLIGHTLY HEAVIER ONE. THERE ARE 5 OPTIONS IN THE SPRING KIT.

IF YOU WANT MECHANICAL SECONDARIES, BUY A 650 ANNULAR QUICK FUEL CARB.  

tuffnuff tuffnuff
Moderator | Posts: 2567 | Joined: 12/09
Posted: 06/18/14
09:34 AM

Q-Jets only came in 750 and 800 CFM configuration.

Smile  
When The Flag Drops.,.

tuffnuff

The Bull ***t Stops.,.
tuffnuff

P. Engineer, Engine Builder

bigD bigD
User | Posts: 142 | Joined: 05/14
Posted: 06/18/14
11:41 PM

Icon Quotekwm219:
Thanks for the input guys, it is greatly appreciated

One last quick question, what sizes would you stay around?  ballpark of 650cfm for a stock motor?  

thanks again


A GOOD Q-jet has several advantages over square bore carbs. The main advantage is that until you go to WOT they run on the small primaries. It's easy to get a good smooth low rpm idle, and they will get better mileage, according to the VAST majority of tests done thru the years.

Another major advantage is the large secondaries, which will supply all the air/fuel mixture your engine needs, at the proper rate. There are race cars running in the low 10's and some in the 9 sec zone using a Q-jet. The sec air flap opening rate can be adjusted by changing the spring tension and is kept smooth and gradual by the vac pulloff provided for that purpose.

You don't need to worry about a 750 or 800 cfm Q-jet being too big for your 350. The little 301 had an 800 ! The Q-jet only gives the motor what it can use. The primary jets are changeable. The sec jets are fixed, with the fuel being metered by using sec metering rods, with different size tips, being raised and lowered in the jets by the sec air flap. For a richer mixture, use rods with smaller tips. To go leaner, use rods with larger tips. This is a basic description. Once you become familiar with the Q-jet, they are not that complicated. Hey, if I can learn to do it, most any decent gearhead can learn.

But, there are lots of guys, especially Chevy guys, who will throw a perfectly good Q-jet in the trash and buy a Holley double pumper. They say all Q-jets are junk, and the DP is the only way to go. I ran across lots of these guys. And TJ and I have beat LOTS of these guys at the track with our old Q-jet equipped Pontiacs !!!  Laugh  And we rebuilt all of them ourselves. So, I'm not guessing here. I've been there, done it, and won, with homebuilt Q-jets !   Smile

Here's a pic of the type of plastic vac pulloff that was on the early Q-jets we raced and ran on our street cars. These must be in good working order and have a good vac supply to function properly. They are essential to the proper function of a Q-jet when going from running on the primaries only, to WOT.

Bpw2  

shyrgfuh3 shyrgfuh3
Enthusiast | Posts: 475 | Joined: 11/13
Posted: 06/19/14
12:07 PM

hello kwm;


"A GOOD Q-jet has several advantages over square bore carbs. The main advantage is that until you go to WOT they run on the small primaries."

all carbs run on the front primaries until the throttle or engine vacuum reaches a certain level.



It's easy to get a good smooth low rpm idle..."

its "easy" to get a smooth idle out of most any carb providing it is close to the size needed for a particular engine.



"and they will get better mileage..."

1. at steady throttle with equal afr's a q jet will deliver around the same mpg as a std holley.

2. when properly jetted, at steady throttle, an annular booster carb will deliver better mpg than a non annular one.



"according to the VAST majority of tests done thru the years."

please post even just one link to one of these "VAST majority" of tests. i 'll post one too which shows the 200 year old holley 331o design carb getting BETTER mpog than two different q jets.

Carburetor   Peak BSFC   Carburetor   Avg. BSFC
Holley 3310C 0.432 Holley 3310C 0.447
Swap Meet 3310 0.446 Holley 3310 Reman. 0.461
Edelbrock 0.450 Swap Meet 3310 0.464
Quick Fuel Slayer 0.478 Edelbrock 0.467
Summit 0.493 Q-jet 0.489
Holley 3310 Reman. 0.493 Quick Fuel Slayer 0.489
Q-jet 0.519 Summit 0.527



"Another major advantage is the large secondaries, which will supply all the air/fuel mixture your engine needs, at the proper rate."

Large secondaries have no more benefit to supplying all the air/fuel mixture your engines than a carb with 40/60 or 50/50 venturis. cfm is cfm its quite simple. a q jet that flows a true 750 cfm will flow no more air than ANY other carb on the planet that flows a trued 750 cfm etc..



"The sec air flap opening rate can be adjusted by changing the spring tension and is kept smooth and gradual by the vac pulloff provided for that purpose."

the secondary opening time is adjustable in one way or another on ALL 4v carbs. holley, quick fuel and demon etc., do it with different rate springs on their vacuum secondary carbs and with different rods on their mechanical secondary carbs.



"There are race cars running in the low 10's and some in the 9 sec zone using a Q-jet."

there are cats running in the 7's with holleys or other non q jet carbs.



"But, there are lots of guys, especially Chevy guys, who will throw a perfectly good Q-jet in the trash and buy a Holley double pumper."

that's because they want to run in the 7's instead of in the 8's.  

shyrgfuh3 shyrgfuh3
Enthusiast | Posts: 475 | Joined: 11/13
Posted: 06/19/14
07:22 PM

Hello kwm;


"According to the Q-jet expert Cliff Ruggles, the later models must have some of the small passages drilled out by hand correctly, in order for them to provide any kind of decent performance.

I much prefer an early model, such as a '68-'70 Pontiac. Or a '68 -'72 Buick."



Q Jet expert Cliff Ruggles ACTUALLY said the 76 and LATER [newer] carbs are SUPERIOR to ALL previous designs.

From Cliff Ruggles:

"The later carburetors made in and after 1976 with the later style APT feature are actually superior to all previous designs in every area.

They are just a tad lean as they were produced under tighter emission standards than the older models.  If you plan on using one of them outside of it's original application (obviously), get one of our books and use the rebuilding chapter for complete/correct rebuilding, and the high performance chapter to recalibrate it exactly for the application. We sell complete/correct rebuild/tuning kits for the later units.


BTW, I use a 1977 Pontiac carburetor (part number 17057274) on my 455 engine that powers my 1973 Ventura."  

bigD bigD
User | Posts: 142 | Joined: 05/14
Posted: 06/20/14
12:46 AM

Anyone who does not like Q-jet carbs or Rhoads lifters should not use them.  Smile

http://www.hotrodders.com/forum/holley-vs-quadrajet-178113.html

http://www.78ta.com/HTAF/index.php?topic=4797.25;wap2

http://www.camaros.net/forums/archive/index.php/t-212062.html

http://www.chevelles.com/forums/archive/index.php/t-343488.html

http://www.vetteprojects.com/kstyer/quadrajet.htm

http://psp.aquacomp.net/topic.asp?TOPIC_ID=4801

http://bosshosshelp.com/Menu%20Items/quadrajet/MikeQuadrajet/quadrajet.htm

http://www.carcraft.com/howto/57178/

http://www.everyday-performance.com/quadrajet_carburetors.htm

http://www.smicarburetor.com/products/sfID1/28/sfID2/9/sfID3/100  

bigD bigD
User | Posts: 142 | Joined: 05/14
Posted: 06/20/14
05:01 AM

Icon Quoteshyrgfuh3:
Hello kwm;


"According to the Q-jet expert Cliff Ruggles, the later models must have some of the small passages drilled out by hand correctly, in order for them to provide any kind of decent performance.

I much prefer an early model, such as a '68-'70 Pontiac. Or a '68 -'72 Buick."



Q Jet expert Cliff Ruggles ACTUALLY said the 76 and LATER [newer] carbs are SUPERIOR to ALL previous designs.

From Cliff Ruggles:

"The later carburetors made in and after 1976 with the later style APT feature are actually superior to all previous designs in every area.

They are just a tad lean as they were produced under tighter emission standards than the older models.  If you plan on using one of them outside of it's original application (obviously), get one of our books and use the rebuilding chapter for complete/correct rebuilding, and the high performance chapter to recalibrate it exactly for the application. We sell complete/correct rebuild/tuning kits for the later units.


BTW, I use a 1977 Pontiac carburetor (part number 17057274) on my 455 engine that powers my 1973 Ventura."


Yes, I have a copy of Cliffs book and HAVE read it. He describes in great detail, with pics, the passages that MUST be enlarged by hand with very small drill bits and a pin vise. If you don't have the skill of a surgeon, it's very easy to ruin your carb, or not get the passage large enuff. Also you MUST get the idle bypass air exactly right. These later model carbs had more fed emission restrictions on them, so the factories had to make a lot of compromises to meet these regulations. Thus, the smaller passages and leaner tuning.

The earlier carbs, like the '68-'70's I mentioned were built before all these fed regs became law. Therefore they do not have all the same restrictions as the later carbs. We raced these older carbs and never drilled out anything ! They ran just fine down into the high 11 sec zone. A 1970 B/SA Bird ran real low 10's with an older 750 Q-jet, and won at least one National event that I know of.  Smile

http://www.highperformancepontiac.com/features/hppp_1301_1970_pontiac_firebird/ram_air_iv.html

http://www.knfilters.com/News/print.aspx?id=3432  

tuffnuff tuffnuff
Moderator | Posts: 2567 | Joined: 12/09
Posted: 06/20/14
10:27 AM

Icon Quotekwm219:
I know there are a lot of Carb threads on here, have read most of them and got some great info, but haven't seen a direct answer to my question yet, so hopefully i didn't miss it
I have a 72 Lemans, Stock 350 2 barrel carb and am looking to upgrade.  I purchased an Edlebrock Performer Pontiac Spreadbore 4 barrel intake and wondering what the perfect 4 barrel carb matchup is for it.
Looking for as close to bolt on, no mods, as i can get and taking advantage of the spreadbore with a matching spreadbore carb, automatic choke ect.
are there any mods that i will need to make with this change?
thats for the info guys, long time professional body guy trying to teach myself the motor aspect


OK guys.,. this is what the poster indicated.
1)He has a spread bore intake.,. that is a given
2)What is the perfect match up.,. any spread bore carb, be it Q-Jet, Holley or Carter Thermo Quad.
3)Close to bolt on, .,. so no mods an adapter from spread to square bore is not an option.,. besides that, I have never had much luck with adapting any mismatch.
4)Let's stay focused and not lead him astray with alternative solutions.,. the same rules would apply if he had a square bore manifold and someone tried to sway him into an adapter combo.,. why bother with band-aid solutions.
5)I have messed with carbs of every description including the old Holley 3 barrel.,. they can all be made to work well, when set up properly.

Smile  
When The Flag Drops.,.

tuffnuff

The Bull ***t Stops.,.
tuffnuff

P. Engineer, Engine Builder

76Skylark 76Skylark
New User | Posts: 1 | Joined: 06/14
Posted: 06/20/14
12:02 PM

I have done Most of the Stupid combo's of carbs and manifold Adapters,and for your engine you have the right manifold and your Question is what is the right carb... now its more about your pockets and what you want to spend, I am a huge Q-jet Fan and I can build them so they are attractive to me,they are plentiful and cheap to repair. the Holley Spreadbore is My All time Fav. call Bill Tichnor at Holly His Department is Online sales and rebuilt carbs the prices can't be beat. Tuff can work Magic with a thermo-Quad And he could tell you more but they are not likely to be found on a Pontiac.  so how are your abilites, the Q-jet is first choice as all factory hook ups are right there then the holly and use a small CFM carb till you need more.  

shyrgfuh3 shyrgfuh3
Enthusiast | Posts: 475 | Joined: 11/13
Posted: 06/20/14
02:55 PM

hello;


BOLT ON CARB

Well here’s the deal. What no one is telling you is that if you use a pre 73 Q Jet carb, you will NOT have a choke because the eddy intake does not have a provision for it.

We all agree that the Q Jet will “bolt on” easier, however, it is not hard to connect a throttle linkage to a Holley either and you will have a choke if you use a Holley or quick fuel style carb. The Holleys also come in spread bore.



FIT ON INTAKE

The Holley square bore carb will fit the newer eddy spread bore intakes with NO adapter, just like I said they would. Eddelbrock also says they will right there in their description.



BOLT ON PERFORMANCE AND TUNING

Holley – A Holley square bore will perform close to perfect if not perfect right out of the box. I do not know about the Holley spread bore.

Q Jet – A Q Jet most likely will NOT perform as well right out of the box even if it’s a new eddy carb. I have seen many tuning related performance probs with the new Eddy’s.



TUNING

Q Jet – As I mentioned in a previous post, IF the Q Jet does NOT perform perfectly as a delivered, you need to be a rocket scientist to tune one. Since you are concerned about having a carb that is easy to bolt on, my guess is that you are not a carb expert. Also as I mentioned, you can send it to Cliff Ruggles along with your engine specs and he will make it happy for a price. I would NOT let ANYONE else EVER touch a Q Jet unless I knew they were an expert on them.

Holley – Everyone here that knows the first thing about carbs will tell you that a Holley square bore is infinitely easier to tune especially for a beginner than a Q Jet is.

They come with a 6.5 power valve which is used on 95% of the stock thru moderate performance engine builds and the accelerator pump cams are set close enough for 955 of the builds so ALL you have to do is worry about 4 tiny jets. A 5th grader could tune a Holley. A blind person could take one apart and reassemble one.

 

CHOKE

In 72 and earlier, the Q Jets used a choke that was installed in the manifold. These carbs can NOT be converted to a different style choke. If you do NOT have the provision in your manifold for the choke, you can still use theses carbs and that manifold, but there will be no choke of ANY kind.

In 73 or later they have a hot air choke that can be converted to electric, however, around 73 or soon after, they added a channel across the front of the venturis on the base of the carb. This channel sticks out beyond the mounting surface of an Eddy or stock post 1972 or so intake and cause a big vacuum leak.

You need to verify on any post 1970 carb whether it has this channel or not.


CARB SIZE

The carbs with 1.093 venturis are 750 cfm. The ones with 1.218 are 750 and began in at least some Pontiac carbs in 1973. These carbs may also have just 1 ring around the boosters.


All the carbs below use the same linkage and choke and will work with proper tuning but verify venturi size on the 73 and later carbs or ones with single ring boosters.


1968 thru 1970

7040262 auto trans, 350, 400 and 428
7040263 man trans, 350, 400 and 428
7040264 auto trans, 350, 400 and 428
7040267 man trans, 350, 400 and 428
7040268 auto trans, 350, 400 and 428
7040269 man trans, 350, 400 and 428


1971

7041262 auto trans, 400 and 455
7041263 auto trans, 400 and 455
7041264 auto trans, 400 and 455
7041267 auto trans, 400 and 455
7041268 auto trans, 400 and 455


1972

7042263 man trans, 400
7042264 auto trans, 400


1973

7043263 man trans, hot air choke
7043264 auto trans hot air choke


1974

7044262 auto trans, 350, 400 and 455
7044264 auto trans, 350, 400 and 455
7044267 man trans, 350, 400 and 455
7044268 auto trans, 350, 400 and 455
7044269 man trans, 350, 400 and 455



WHERE TO BUY Q JETS

frankspontiacparts.com

custombuiltcarbs.com

ebay.com  

tuffnuff tuffnuff
Moderator | Posts: 2567 | Joined: 12/09
Posted: 06/20/14
07:10 PM

Icon Quote76Skylark:
I have done Most of the Stupid combo's of carbs and manifold Adapters,and for your engine you have the right manifold and your Question is what is the right carb... now its more about your pockets and what you want to spend, I am a huge Q-jet Fan and I can build them so they are attractive to me,they are plentiful and cheap to repair. the Holley Spreadbore is My All time Fav. call Bill Tichnor at Holly His Department is Online sales and rebuilt carbs the prices can't be beat. Tuff can work Magic with a thermo-Quad And he could tell you more but they are not likely to be found on a Pontiac.  so how are your abilites, the Q-jet is first choice as all factory hook ups are right there then the holly and use a small CFM carb till you need more.

Hey Skylark, good to see you here and welcome aboard.,. Guess I'm just lucky when it comes messing with carbs, but then I have pretty much worked/played with many,,, many carbs of various brands.
Shy, I'm not a rocket scientist and I have no difficulty ripping any carb apart.,. however, you are right, a Holley is the easiest to work on for a beginner.

Smile  
When The Flag Drops.,.

tuffnuff

The Bull ***t Stops.,.
tuffnuff

P. Engineer, Engine Builder

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