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Old 03-14-2012, 11:07 PM
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1968 impala engine questions 307sbc

hello, new to the forum. hope to get as much help as possible as i am "new" to engine work/modification.

i have a 1968 chevrolet impala custom coupe. all factory engine. 307sbc, 2 barrell carb, 2 speed powerglide-automatic. ram horn exhaust manifold. stock distributor.


PLANS FOR UPGRADE:
-2 barrel carb to a 4 barrel quadrajet
-switch out old distrib for HEI distrib with coil on the distrib cap.
-switch stock exhaust manifolds for headers.
-eventually switch tranny from power glide to 350turbo or 700r4 (but this is not important right now)



MAIN QUESTIONS-
i have purchased a Refurbed Quadrajet 4 barrel carb as well as a original quadrajet intake Cast Number: 340261

first off. will this set up even work?

questions:
-ive seen some people say the Q-Jet is 750CFM..is this too much for my factory 307?
-will this new q-jet intake effect my "Oil Filler Neck" on the front of the block? (in example: will i need to remove the oil filler neck to install or will the q-jet intake not effect the oil filler neck?)

i have no clue what actually connects this carb to the intake as far as hoses and what not...my uncle is helping me and he does not know anything about q-jets so he made this diagram for me to show people to see what info i can find...



detailed answers would be greatly appreciated. thanks in advance. happy motoring

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Old 03-15-2012, 12:32 AM
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First off, a Quadrajet has two models which are 750 and 800 cfm. However, these carbs came on V6 engines all the way up to 500 cubic inch monsters.
The Quadrajet is a "Air Dam" carb, meaning it only flows what the engine demands in air flow, so it doesn't over carberate or under carberate.
However, there are some other areas about your 307 that you need to know about. The 307 has a very poor reputation, and why was for two reasons, the cams that came in these engines were bad about going flat and taking the rest of the engine out with it. The other reason is due to GM never made a performance version of this engine. The 307 was a economy motor, created by combining the bore of the discontinued 283 of 3.875 and the stroke of the 327 which is 3.250. It never recieved a 4 barrel from the factory.
What I suggest if you really want to put some fire in your 307 is first off, swap in the summit racing 1102 camshaft. Next add a double roller timing set. Then add a set of 416 casting heads off a 305. Then add your Q-jet, headers, and other mods. With those list of mods you would see about a 75 horsepower increase. plus better fuel economy. Now, lets see if I can help with the numbers you have on the intake.
Number 1 is the distributor.
Number 2 is a manifold vacuum port often used for the modulator valve on automatic transmissions.
Number 3 is the rear intake bolt hole
Number 4 is the kick down cable bracket for auto trans
Number 5 will need to be elbowed, the straight out fuel feed Q-jets were used on Buicks and caddys. Chevrolet always used passenger side fuel entrance Q-jets.
Number 6 is the heater hose port.
Number 7 is a blocked heat riser passage port.
Number 8 is the EGR passage which will need to be blocked off.
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Old 03-15-2012, 01:06 AM
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thanks for the timely response...

i have never rebuilt a motor...switching the cam and heads and timing set...is this something i can do myself or would be better taking to a pro? i am very attentive to details and prefer doing something myself not only to save money but to learn for myself...

any idea about the OIL FILLER NECK on my current block...with it be effected by the new intake in any way? thanks, feel free to respond with as much information as possible


happy motoring
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Old 03-15-2012, 01:34 AM
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Yeah you can do this yourself. On a SBC it's really a breeze. Even if You didn't want to swap cams I would at least get a timing chain on it. The valve covers you have to replace the stockers are where you'll add oil once you install them. In factory form, the 307 was not meant to be a performer, it was the base budget engine, the low man on the totem pole so to speak. GM installed large chamber small valve smog heads on it which gave it a wheezing 8:1 compression ratio. Many also came with nylon geared timing chains which would get brittle and fall off into the oil pan which would get sucked up in the oil pump screen and cause a catastrophic loss of oil pressure whic resulted in the engine locking up. They also came with a really small Rochester 2 barrel carb and the intake had really small runners designed for high velocity at low RPM to at least get the heavy car out of the hole and moving. Another area where your car is lacking in performance is the powerglide trans. It's real high first gear makes it even harder for the engine to get the car moving out of the hole. Switching to a TH350 would be of great improvement. However, just staying in line with the suggestions I made to the engine first. Once you get your sea legs under you then you can step up and tackle bigger things, believing in yourself is half the battle.

Last edited by DoubleVision; 03-15-2012 at 01:40 AM.
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Old 03-15-2012, 07:24 AM
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Quadrajet Connections

It's been awhile since I've logged into my account, but I'm the UNCLE in question. Neither Ryan or I (Uncle Tim) know anything about what hooks up, and where, on this Quadrajet intake & 4 barrel carburetor, that Ryan wants to install. My advice on install an Edelbrock intake & carb fell on def ears, and now Q-Jet parts have been purchased and must be installed.

ANY information on what must be hooked up, and where, would be helpful. Photos would really help. Visuals can always be helpful!

Ryan, at this point, is not really interested in swapping out cams and timing chains. He's not looking for any marked horsepower gains, so much as just wanting to install the new (old) Q-Jet intake & 4 bbl carburetor, to replace the current 2 bbl carburetor on the 307 engine. Sure, in a perfect world, he'd pull the motor, have it totally rebuilt and install a new cam and all the other goodies. Maybe some day, but not today.

Is there anyone who can see any problems with just swapping out the factory 2 bbl and intake, with the Q-Jet 4 bbl and Q-Jet intake. I guess that's the real question here, other than exactly how to run all the plumbing needed to complete the installation.

Thanks for the INFO on changing out the timing chain. Doing that one thing might help save this engine from future catastrophic damages. That, we could do.

Thank you guys for any help or advice. ~ Uncle Tim

Last edited by littlerocktim; 03-15-2012 at 07:31 AM. Reason: To include new information
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Old 03-15-2012, 07:37 AM
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Uncle Tim;

Thank you for taking the time to help a young guy learn a SKILL and get his hands dirty. These are important things that too many kids seem to be willing to do without.

I won't add much here other than you should at LEAST inspect the timing set. If it has the plastic timing gears, you can also assume the camshaft is probably OEM as well. As previously mentioned, GM had a bad run of cam cores for these, they were soft and would go flat, which usually takes out the valvetrain. Additionally, if the timing set is too worn, you will have serious trouble getting it to keep time, not to mention eating plastic parts is not good for the engines health.

The lesson here is: if the valvetrain expires it will cost much more to replace the damaged parts than the cam lifters and timing set; not to mention having to probably pull the engine again.

With the stock 416 heads off of an early 305, this motor will wake up, although it won't be too much to handle. They're usually a couple hundred bucks refurbished.
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Old 03-17-2012, 07:37 PM
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IMHO: It cost me more the upgrade a 307 then picking up a 350 for less. I know, because I went on that route. Penny wise, Pound foolish. Old Ben F. was right.

Last edited by lg1969; 03-17-2012 at 07:44 PM.
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Old 03-19-2012, 03:57 PM
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anyone have a picture of an Installed Q JET i can use as a reference picture?

thanks
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Old 03-19-2012, 05:03 PM
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If those are your intended valve covers in blue, you need to change one from PVC fitting to an air intake breather to replace air removed by the other PVC. Air out, air in.
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Old 03-19-2012, 06:07 PM
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thanks for the heads up, i actually installed the breather cap already. not sure where i can purchase a PCV PLUG....the Driver side will have Oil Fill cap with a PCV going to the carb. the passenger side willl have the PCV Plugged, with a breather cap...is that right?

i installed the Driver side Valve Cover already. i have to remove the AC compressor to install the Passenger side...


Passenger side:



i will need help once i install the QUadrajet and Intake onto the block, figuring out where all the vaccumes and hoses go. been tryin to get as much info on my carb as possible...i already know that it is an Oldsmobile carb...hope this will not be a problem installing. here are all the numbers i could find all randomly located on my carb...

456200
17054937
2465
3114

a picture of one of these installed would be greatly appreciated

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Old 03-19-2012, 06:57 PM
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right now we are focusing mainly on the carb. i think i will need to get a different Fuel inlet, possibly 90 degrees?...

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Old 03-19-2012, 08:03 PM
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I guess I will peep what people are saying in this thread because I have the same setup in my 307 nova. I'm just found a pair of 305 heads up bmore 4 $50. Already have the dual plane intake and a quadrajet just like this one. The only thing I need help on is the cam. What other brand would b okay beside the summit series. I want the vicious soundin idle. And a nice rpm range 4 tht torque in this joint. Good luck with your build. If yu was in the DMV area. Id tell you 2 see me on the streets or at the track. Got the powerglide 2 but found a 700r4 up bmore 2 4 175. Look on craigslist 4 those heads n negotiate with ppl.
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Old 03-19-2012, 08:30 PM
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any pictures of your carb set up? did you have to install a 90 degree on the front fuel inlet?

not really lookin for "racing" setup. just "enhancing" the 307. all original matching numbers. never been rebuilt as far as i know. runs like a top though, if my pockets were deep enough i would love to go through the whole motor but mainly looking to upgrade from 2 barrel to 4, HEI, double roller timing chain, headers...

im 24 years old and taking most of this on myself to save money and learn in the process..
any pics you can post of your quad set up would be great, thanks boss
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Old 03-19-2012, 08:37 PM
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I mean wholetime y'all further along into the build than I am. I'm just stockpiling the parts until I'm ready 4 erything. Mostly gettin this cam and heads then ill get on the move.
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Old 03-19-2012, 08:55 PM
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ah ok...dont know much about cams to base an opinion or recommendation..fella up there said summit series 1102...not much help sorry man
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