quadrajet on a 250 inline advice

[RichardJ]

You should not be afraid to try the Q-jet. The Pontiac OHC Sprint six that they mentioned had 250 cu in in '68-'69, but the Sprint engine in '66-'67 had only 230 cu in and used the Q-jet. In '66 the OHC Sprint engine was used in the LeMans and then the Firebird in '67.
The secondary air valve will only open as far as needed for the amount of air the engine needs at any rpm.
As 68OrangeSunshine pointed out, the Holley isn't going to ba any easier to setup than the Q-jet. Carburetors are not Plug-N-Play.

There is one thing that bothers me about the Holley 390. It's the smallest 4 bbl they make and they've been making it for fourty years and yet they want $380 for it. At least that's Summit's price. They have several larger carbs for $100 less.

[sixtyeightchevykid]

i dont need a bigger carb though.. i have found there are quite a few people running a holley 390 with a 250.. i think it will be the best bet in the long run... and i never really liked the look of edelbrock carbs.

[jhngardner367]

In 1974,I bought a '73 Olds Omega.It was my first NEW car.It came with a 250cid engine,3 on-the tree,and a 9" clutch.
I got one of the 4bbl intakes and ran a STOCK 450 cfm Qjet,with no problems.
I installed a Dual-point dist.,a 10.5" clutch(Cutlass),and a MrGasket floor shifter.
I upped the timing, by 2deg,and put a better exhaust on it(i.e.,glasspack).
I got 26mpg,if I kept the secondaries closed,but if I "got on it",it would break loose the tires,when I hit 2nd gear,and it outran several v-8's.
SO,YES,YOU CAN PUT ONE ON AN INLINE 6 !!!
By the way,if you use an electric choke,you don't have to worry about the choke cable,just run a wire from ignition switch to the choke coil.
If it seems to push too much fuel,drop 2 sizes on the primary jets AND needles.
HAVE FUN!!!

[sixtyeightchevykid]

jhngardner367 where did you find a 450 qjet?


im still looking for some advice on new carbs, i have been on summit and i think narrowed it down to 3 carbs but still dont know....

http://www.summitracing.com/parts/EDL-1801/
http://www.summitracing.com/parts/HLY-0-8007/
http://www.summitracing.com/parts/EDL-1403/

['68OrangeSunshine]

Originally Posted by RichardJ

You should not be afraid to try the Q-jet. The Pontiac OHC Sprint six that they mentioned had 250 cu in in '68-'69, but the Sprint engine in '66-'67 had only 230 cu in and used the Q-jet. In '66 the OHC Sprint engine was used in the LeMans and then the Firebird in '67.
The secondary air valve will only open as far as needed for the amount of air the engine needs at any rpm.
As 68OrangeSunshine pointed out, the Holley isn't going to ba any easier to setup than the Q-jet. Carburetors are not Plug-N-Play.

There is one thing that bothers me about the Holley 390. It's the smallest 4 bbl they make and they've been making it for fourty years and yet they want $380 for it. At least that's Summit's price. They have several larger carbs for $100 less.

When I bought my 4160-8007, 390 Holley, it cost about $87 new, retail. (1978).

[sixtyeightchevykid]

'68OrangeSunshine the holley 390 is no longer that cheap, its close to 380.

does anyone have any more input on which carb to get?

[dh81k30]

Originally Posted by sixtyeightchevykid

'68OrangeSunshine the holley 390 is no longer that cheap, its close to 380.

does anyone have any more input on which carb to get?

Just a little more fuel on the fire, so to speak.

In 1985 and 1986, Chevy installed Quadrajets on 4.3 v6 engines in C10s. You might consider trying to find one of those carbs from where someone has pulled a 4.3 v6 to install a v8. It would probably be calibrated to be more nearly usable on your 250 (4.3 liters is 262 cubic inches).

Just a thought.

[shawno72]

Ok so we got a thread with no pics so let's see some pics of the setup that is being discussed. I love the 4bbl on a straight six look.

[sixtyeightchevykid]

shawno72 i would love to have pics of the set up on my truck but the reason i started this thread was to find out what to do to have a 4 barrel on my 6.
the plan is to get a carb to put on the offy intake and do some clean up on the engine and for now just bolt up the offy intake with the stock exhaust and later down the road get and install langdons cast headers. but first i need to get input and advice on which carb to get and how im going to bolt it to the manifold so that the primarys are "inline"(for lack of a better way to explain) with the engine.

[beautimus]

the primaries(front 2 barrels) are to be pointed away from the engine. so that the carb is sideways instead of inline with the motor. the straight six tends to run slightly rich on the 2 center cylinders and a tad leaner on the ends due to the unequal lengths of the intake runners. if you put the carb in line with the engine(primaries to the front) the rear most cyl. (number six) will be too lean and burn the piston easily. i hope i am saying this correctly. pain pills are definatley starting to work.
good luck , tony

[jhngardner367]

It came from a junker,and the counterman said it was a 450.I had no reason to doubt him.I remember it was all mechanical linkage,and clean,and I didn't have a problem with too much/too little fuel. I know it was definitely a q-jet,though. I think it was from late '60s ? 4m,maybe?

[DLOE65]

I'd say stick with a Holley 390. They are current, parts are Available if needed and Langdon Stovebolt and Clifford performance both recommend that carb and they are the two big names in straight six performance.
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[DLOE65]

Had this discussion on another thread..

Originally Posted by Vernski
If the manifold is an open plentium the carb can sit in any direction if it's closed or separated then it has to sit one way only to work right...Vernski
DLOE, as Vernski said, it is accepted that facing forwards is fine, especially with a carb spacer, and since you're already rigged up, I would not change it. Tom Lowe on inliners recommends putting the primaries away from the engine to keep the runner length to mid cylinders as long as possible- but the difference made is not much.
Posted via Mobile Device

[geezer#99]

Originally Posted by jhngardner367

It came from a junker,and the counterman said it was a 450.I had no reason to doubt him.I remember it was all mechanical linkage,and clean,and I didn't have a problem with too much/too little fuel. I know it was definitely a q-jet,though. I think it was from late '60s ? 4m,maybe?

Probably looked just like this. Not quadrajet but a look-a-like made by Holley that was 450 cfm. The holley 4360.
http://fs.bookpawnshop.com/4/450-cfm...-fuel-economy/

['68OrangeSunshine]

Originally Posted by sixtyeightchevykid

'68OrangeSunshine the holley 390 is no longer that cheap, its close to 380.

does anyone have any more input on which carb to get?

Yeah, I know prices have gone up since 1978. (Actually it was closer to $83, I found some old notes on the first build.) I ran my 4160-R8007 for 25 years. After a 292 rebuild in 2005, The Holley was suspected of having a warped base and it was time to replace it. When I saw the '05 price on the 390: ~$285, I decided there was more bang for the buck with an Edelbrock 500 CFM 1404, for ~$200.
[I would have preferred it to be a real Carter Performance Series AFB, but essentially, they're the same thing, and Carter's out of the Carb business.]

[sixtyeightchevykid]

DLOE65 what do you mean about the holley... "They are current" ?

'68OrangeSunshine so the reason you went with the edlebrock was price?
if the holley was the same price as the edlebrock would you have gotten the holley?

['68OrangeSunshine]

Originally Posted by sixtyeightchevykid

DLOE65 what do you mean about the holley... "They are current" ?

'68OrangeSunshine so the reason you went with the edlebrock was price?
if the holley was the same price as the edlebrock would you have gotten the holley?

I always had problems working on Holleys myself. I always screwed them up. I usually had a pal who could work on my Holley, if not for beer and burgers, then minor cash.
In 1993, I bought a '67 K/10 Suburban with a 454 and a Carter AFB 9635 [625 CFM] on it. Later, in 1995, I got a '71 GMC Jimmy with 350 and in 1999 put a Carter 9625 [600 CFM] on that engine, since I found I liked the AFB design and it was for me, idiot-proof.
At the time we finished the '68 C/10 L6 292 rebuild, in 2005, my Holley guy was going thru a painful divorce and not available, so economics notwithstanding, I went for the AFB design, albeit an Edelbrock.

But I can't play guitar either. If you're a Holley guy, and have the extra bucks, the R8007 is a good carb, especially with the 50cc accelerator pump.

[sixtyeightchevykid]

so holleys are just more difficult to tune by someone that is not a professional? and the edlebrocks are pretty much anyone can tune it?

['68OrangeSunshine]

That's my take on the subject. I'm sure the flamers are waiting in the wings to get me. Holley has a sizable fan base.
If you're a perfectionist and can spend the time fine tuning a Holley, you will get maximum performance.
If you think your time is too important to be messing with carburetors all the time and just want a unit you can set and forget and get reasonable performance, then the Carter [and by extension Edelbrock] is the ticket.
By the way, I still have my old R8007, 390 CFM Holley. I'm saving it for a ragtop '72 K/5 with a .060-over [301 CI] 292 L6, SM465/Rockwell T221 project. I need to get another Offenhauser intake and maybe Tom Langdon's late series L6 version of the old cast iron Fenton headers. [Fentons were made for the previous generation of GM L6s -- 235, 261 CI.]

[sixtyeightchevykid]

i have decided to go electric choke, and i want vacuum secondaries. but i was looking at the edlebrocks and it says the secondaries are air valve what does that mean?
and what is the difference between the performer and thunder series?

[RichardJ]

The Performer is a cheap copy of the old Carter AFB used on many cars in the '60s. The Thunder AVS is a cheap copy of the Carter AVS used mostly by Mopar in the late '60s, early '70s.
Both carbs (AFB & AVS) have a mechanical secondary throttle valve with an air flow controlled valve above the throttle valve.

This magazine article explains the difference between the counter-weighted Carter AFB (Edelbrock performer) secondary air vailve and the adjustable spring loaded Carter AVS (Edelbrock Thunder AVS) secondary air valve.

"In the AVS, the most notable departure from the AFB design was in the actuation of the secondary. The AFB carb was conventional in the secondary circuit in that it used a conventional booster venturi configuration to deliver the secondary fuel flow. The secondary throttle plates were mechanically operated. In order to provide for a smooth transition into the secondary circuit (without the benefit of a secondary accelerator pump circuit), a counterweighted velocity valve was installed above the throttle plates. The velocity valve acted as an auxiliary to the throttling system, delaying the airflow through the secondaries until engine demand overcame the counterweight and allowed the valve to open. The delay in airflow slowed the progression into the secondary circuit, allowing the airflow through the secondary booster venturi to start drawing fuel.

The goal was to provide enough of a delay in air flow to prevent a lean bog as secondary airflow is suddenly initiated by mashing open the throttle. The system worked, but it had two flaws. First, the positioning of the velocity valve is above the throttle plate and below the discharge nozzles. Besides delaying airflow, this offers little help in initiating fuel flow through the booster. Second, the system was not readily adjustable to vary the opening rate.

In contrast, the AVS carb--designated for its Air Valve Secondary--was quite a departure from convention at the time of its introduction. The counterweighted velocity valve of the AFB was scrapped, and a spring-loaded air door was fitted at the top of the carb. Positioned above the fuel-discharge point, the air valve created a depression, or low-pressure area at the fuel-discharge point. This dramatically increased the reaction rate of the secondary fuel circuit. The function of the AVS's air valve in drawing fuel flow was advantageous compared to the old AFB system's function of simply delaying airflow. The system was so effective that a conventional booster venturi wasn't needed, and AVS carbs were fitted with fuel spray bars, which complemented the air valve perfectly. To cap things off, the spring-loaded air door was easily adjustable for opening rate by simply loosening a lock screw and winding the spring tension on the valve's shaft."

I don't understand why you haven't stuck that Qjet on there already and given it a try.

[jhngardner367]

NO.oldgeezer,it was definitely a qjet.It was marked on it.I do remember that it had a manual choke,and,I think it was mechanical secondaries. This was in '75,and I'm 60 yrs old,now,so the fine points get blurry(LOL) ,but it was definitely a qjet.

['68OrangeSunshine]

I don't know if the Edelbrock "Performer " is a cheap copy of the Carter AFB. From what I've heard, the carbs are still made in the same plant, just the labels [and price tags] have changed.
The Edelbrock "Thunderor" AVS differs from the original Carter AVS by having the same 2-step metering rods as the AFB. Original Carters had 3-step metering ["step-up"] rods, with the mid-range being for power settings like towing, or something. Three step rods required a special "cup"-style jet in the primary stage. Neither 3-step parts are available anymore. I acquired an old AVS that was once on top of a Mopar 440. It had no venturies in the secondary rank, just 1" long 'sprayers.' I thought about rebuilding it as a Thunder 18-something, but, I currently don't need a big block carb, so that project is on hold.
Edelbrock's Thunder AVS has secondary venturies.

[sixtyeightchevykid]

RichardJ, thank you for the explanation, but i still have no idea..

the qjets i have are 750cfm which are going to be too big for my 250.

[sixtyeightchevykid]

ok here are some that ui have narrowed it down to.. thoughts on them and why/?
http://www.summitracing.com/parts/EDL-18014/
http://www.summitracing.com/parts/EDL-1801/
http://www.summitracing.com/parts/HLY-0-8007/
http://www.summitracing.com/parts/HLY-0-80570/
http://www.summitracing.com/parts/EDL-1403/
http://www.summitracing.com/parts/SUM-M08600VS/