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Old 10-12-2010, 07:46 PM
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What Carbs On Your 350?

Ive seen lots of opinions on the best way to carb a 350.but its not that easy.the 350 is a very diverse little motor.from mudding to towing,to drifting and dragging.a lot effects the way we carburate.gears,cam,stall,intake,power band range.a lot of times u read people arguing there difference in opinion.well the difference is welcome here,more for me to study.ive seen all kind of things on top a 350.from 390cfm to 1050cfm. and there owners defend it.I'd like to know what u have and what works for u.what brand do u like,why?I have a 86 iroc-z.1992 L98 block .030 over,zero decked sealed power flat top hyper.pistons,felpro 1010 head gaskets,39 quench,LT4 Hot Cam,218in 228ex @ .50 525in 525ex lift,112 lobe.lunati roller lifters,lunati 7.29 pushrods,procomp 190cc heads i nad them assembled and ported at machine shop.1.6 stainless steel full roller rockers,air gap rpm intake,hooker shorty headers,full hooker exhaust,billit summit dizzy,with accel super coil,edelbrock #1711 130gph mechanical fuel pump.700r4 with shift kit.i think the rest is stock.i dont know the gears,but i know some of u guys know formulas so the car reads 2000rpm @ 60mph,fourth gear is .70,tires are 255-50-16.i have a 750 holly,750 Q-jet,650dp holly,and iv had a 750 eddy on it.i must say the carb fomula has hold true for me.i also have a summit 600cfm that i put 50cc accelerator pump in.im ok at basic carb tuning.my 600 is instant off idle and pulls hard though the range.yhe 650 dp feels a tad shronger 4000+ but the low end trade of aint worth it.my 600 will brake the rear loose at 50-55mph.it feels the best on my motor.i play with my car a lot.light to light,and any time i pull up to a mustang.my speedo only reads 145mph but its still pulling strong. i lke 600cfm and holly on mine

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Old 10-12-2010, 08:37 PM
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Carb I perfer: Rochester Quadrajet.
Why I perfer it: Small primaries make for excellant fuel injection like sensitivity throttle response, great low end torque and fuel economy.
Massive secondary`s provide all the flow that`s needed for wide open throttle blasts. Secondary`s opened up sing a distinctive tune.
Easy to adjust, easy to rebuild, easy to modify.
Float you set once and forget it.
A bit harder to tune but worth it.

What I don`t like about Quadrajets: Small float bowl, so you gotta get creative. Automatic chokes that just about never work right no matter how perfect you set them. Leaky fuel wells you gotta Peen with a hammer to make them stop leaking.

Why I don`t like Holleys: very cheaply made with next to no quality control.
Got tired of having to fix them right out of the box. The Holley Spread, made as a Quadrajet replacement is a complete piece of junk. I could go on but the post would become a book.

Why I don`t like Edelbrocks: Rear entry fuel line, I don`t like running alot of fuel line over a hot intake, it looks bulky and just gets in the way. Praying you get it right trim down metal tang to adjust secondary opening rate. (still shaking my head on what genius came up with that idea)

Why I Don`t like Demon carbs: I had to take it off countless times and fix what the factory did wrong. Road Demon Jr I had was next to impossible to adjust the front float. Had to clean out all the passages due to them having metal shavings in them from the CNC operations. Had to sand down the base plate due to the secondary butterflies making contact with them causing them to freeze closed. Down leg boosters are completely worthless and made for lazy throttle response on the primary side.

So there it is. Each carb has pro`s and cons. However, I found the Quadrajet had the best throttle response and overall best performance. So I work around there short comings.
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Old 10-12-2010, 08:48 PM
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Quote:
Originally Posted by DoubleVision
Carb I perfer: Rochester Quadrajet.
Why I perfer it: Small primaries make for excellant fuel injection like sensitivity throttle response, great low end torque and fuel economy.
Massive secondary`s provide all the flow that`s needed for wide open throttle blasts. Secondary`s opened up sing a distinctive tune.
Easy to adjust, easy to rebuild, easy to modify.
Float you set once and forget it.
A bit harder to tune but worth it.

What I don`t like about Quadrajets: Small float bowl, so you gotta get creative. Automatic chokes that just about never work right no matter how perfect you set them. Leaky fuel wells you gotta Peen with a hammer to make them stop leaking.

Why I don`t like Holleys: very cheaply made with next to no quality control.
Got tired of having to fix them right out of the box. The Holley Spread, made as a Quadrajet replacement is a complete piece of junk. I could go on but the post would become a book.

Why I don`t like Edelbrocks: Rear entry fuel line, I don`t like running alot of fuel line over a hot intake, it looks bulky and just gets in the way. Praying you get it right trim down metal tang to adjust secondary opening rate. (still shaking my head on what genius came up with that idea)

Why I Don`t like Demon carbs: I had to take it off countless times and fix what the factory did wrong. Road Demon Jr I had was next to impossible to adjust the front float. Had to clean out all the passages due to them having metal shavings in them from the CNC operations. Had to sand down the base plate due to the secondary butterflies making contact with them causing them to freeze closed. Down leg boosters are completely worthless and made for lazy throttle response on the primary side.

So there it is. Each carb has pro`s and cons. However, I found the Quadrajet had the best throttle response and overall best performance. So I work around there short comings.
a lot of people like Q-jets,and feel if thats what came on GM why change it. i just couldnt get mine dialed in just right.i bet its me not the carb
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Old 10-12-2010, 10:28 PM
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Love The rochester Quadra-Jet

Just rebuilt one from a BBC 454 and put it on my 350 pontiac and fire try fired up and has run great ever since. Only thing i dont like is trying to find the right Bimetal spring for the choke.
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Old 10-12-2010, 10:37 PM
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Quote:
Originally Posted by AndersonRacing44
Love The rochester Quadra-Jet

Just rebuilt one from a BBC 454 and put it on my 350 pontiac and fire try fired up and has run great ever since. Only thing i dont like is trying to find the right Bimetal spring for the choke.
how is your throttle response?how healthy is your 350?to run good on a 454 and go to 350 with out tuning takes a pretty healthy 350 right?
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Old 10-12-2010, 11:19 PM
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Q-Jet on a stock motor

i bought a new Holley 670CFM Street Avenger for my 350, i love it, worked great right out of the box.
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Old 10-12-2010, 11:25 PM
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Quote:
Originally Posted by FastOrange
Q-Jet on a stock motor

i bought a new Holley 670CFM Street Avenger for my 350, i love it, worked great right out of the box.
its funny u have that carb.ive been thinking of buying one.what have u done to your 350? how much of that 670cfm are u using? im using all of my 600cfm,i may be even slightly under carbed.but my car shifts at 5800rpm if i stomp it,so i realy dont know.i doubt im using much more at that rpm

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Old 10-12-2010, 11:35 PM
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Quote:
Originally Posted by 355ci
its funny u have that carb.ive been thinking of buying one.what have u done to your 350? how much of that 670cfm are u using?
My 350 is 9.5:1, Mutha Thumpr Cam (Which i am REALLY impressed with), Vortec 906's, Comp Valve springs, comp pushrods, scorpion 1.5:1 full roller rockers, Edelbrock RPM intake, and a MSD HEI distributor.

Not sure what you meaning by how much CFM im using, but i have never felt like i need more, and ive had my foot into it many times.

Should mention that im using a 50CC accelerator pump (made a huge difference, way more throttle response, but the 30CC was doing it job just fine!) and a yellow secondary spring.

I used to have a Speed Demon 650CFM, NEVER will use a Demon product again, had better luck with a Holley spread bore that was sitting on the shelf for 20+ years
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Old 10-12-2010, 11:47 PM
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Not sure what you meaning by how much CFM im using, but i have never felt like i need more, and ive had my foot into it many times. i mean i take whats in the motor to get volumetric effeciency,and your shift rpm.and i put it in the calculator
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Old 10-13-2010, 12:01 AM
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my car shifts at 5800. i would guess my red line is like 6200-6500rmp but i never see that. at 5800rpm and 90% volumetric effeciency the calculator says 536cfm 595cfm @ 100%.I will get a 670cfm when i get gears,and 2400-2800 stall. yes the 50cc pump made a big difference in my 600cfm
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Old 10-13-2010, 12:15 AM
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The Quadrajet is a "Air Dam" carb, meaning it feeds what the engine demands.
However, if you notice, all carbs do this, they are fuel metering devices and that`s what they do. Some are just more precise than others. However, if you get into CFM formula`s you`ll notice the CFM on the formula is far lower than what`s already on the car. Like in some cases a hot 350 only needs 585 cfm. But if it`s ran with a carb that small upper RPM performance suffers. So I wouldn`t be worried about formula`s as what they say and what the engine runs best with is a world apart. Quadrajets are rated at 750 and 800 CFM. However, if the engine never demands it, it won`t give it. Another thing to consider is GM had horsepower restraints to go by, so they would limit the throttle opening on the secondary`s to 70 and 80% but it`s easy to mod it to 100%. I played with a Holley street avenger on a friends car. It replaced a older Holley 650. According to his 1/8th mile drag strip slips, it ran the same time and mph it always did. When I drove the car it didn`t feel any different to me either. It was somewhat easier to work on.
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Old 10-13-2010, 12:19 AM
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Quote:
Originally Posted by 355ci
how is your throttle response?how healthy is your 350?to run good on a 454 and go to 350 with out tuning takes a pretty healthy 350 right?
Actually my 350 isnt anything special...yet. its a 1972 so the compression is around 7.8-8:1 all ive done was change the 2bbl for the 4bbl stock manifold and add that 454 Q-jet. Ive put 1-5/8 headers on it, removed the points distributor for an HEI and changed the Turbo 350 auto for a M-22 4-speed.

but yea it runs like a dream, and i just finished all of the choke mechanism and its all working pefectly.
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Old 10-13-2010, 12:24 AM
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DoubleVison.that makes sense to me.for now i dont really see the higher rpms.my larger carbs arent as instant as my 600cfm.what size avenger was it. my 650 dp does pull harder 4000+ but the low end sucks
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Old 10-13-2010, 12:31 AM
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Quote:
Originally Posted by AndersonRacing44
Actually my 350 isnt anything special...yet. its a 1972 so the compression is around 7.8-8:1 all ive done was change the 2bbl for the 4bbl stock manifold and add that 454 Q-jet. Ive put 1-5/8 headers on it, removed the points distributor for an HEI and changed the Turbo 350 auto for a M-22 4-speed.

but yea it runs like a dream, and i just finished all of the choke mechanism and its all working pefectly.
what size is it?750-800cfm?hows the low end idle-3000rpm,mine has hesitations and flat spots.
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Old 10-13-2010, 03:31 AM
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Quote:
Originally Posted by 355ci
i play with my car a lot.light to light,and any time i pull up to a mustang.my speedo only reads 145mph but its still pulling strong. i lke 600cfm and holly on mine
You need to run a 2 bbl. The streets will be safer for everyone!
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