quadrajet rplaced with a edelbrock 600

[Alwyn678]

should I keep the quadrajet...it is the original #'s matching carb..Is it worth keeping the rest of the car is #'s matching...

www.rogerscorvette.com/free/yelton.htm

 

[Yoda]

Sure... The original carb will take up a lot less space than some of the stupid stuff I have stored Besides this would be a good time to learn about the quad.. with a carb kit

BudD

 

[Hib Halverson]

An even better idea is to put that Quadrajet back on your engine.

The QJ is a far better carburetor than is the Edelbrock--which is nothing more than updatge of the Carter AFB, the basic design of which predated the QJ by a several years.

The Quadrajet is capible of better performance, better driveability and better fuel mileage than the Edelbrock.

Now, if the reason the Edelbrock was installed was to swap a poorly performing QJ for a street high-performance carb, your best choice is to modifiy and/or properly calibrate the Quadrajet. Do that, and it will outperfrom the Edelbrock AFB.

 

[redmist]

I almost there myself Hib. I must have taken apart my 1407 at least 50 times in the last month, changing jets, rods nozzles, springs etc. I can get WOT, idle, power and cruise modes set but the transition from cruise to light throttle acceleration and off the line sucks.
Any ideas? If your response is get rid of the edelbrock should I go Holley?
355 SBC, 10 to 1, 6 inch rods, 70cc aluminum heads, Flat top pistons, dual plane intake. Running 20 degrees initial, 38 total advance.
I'm running the following cam:
Duration at .006 Lift: Intake 308° Exhaust 318° Centerlines
Duration at .050 Lift: Intake 234° Exhaust 244° Lobe Separation: 112°
Lift at cam: Intake .325 Exhaust .340 Intake Centerline: 107°
Lift at valve: Intake .488 Exhaust .510
Timing at .050 lift: Open Close
Intake 10° BTDC 44° ABDC
Exhaust 59° BBDC 5° ATDC

 

[Alwyn678]

I do not think the q-jet is all that great..

I have much better acceleration with the edelbrock 600 and my mileage went up 7 mpg form 13 to 20.........I feel it is a much better carb

 

[Hib Halverson]

My guess is the reason the Edelbrock 600 ran better is that the Quadrajet that was there before may have needed calibration for better performance or it might have needed repair.

With Vette Magazine's Big-Block from Hell project, there was a short time when we had dual Edelbrocks on the car with a full progressive linkage, ie: cruising on a single carb. I had worse problems with that carb than listed here. I could get the WOT to run great but part throttle and transistion baffled me. I tried different rods, jets, float levels...even changed boosters and altered air bleeds--all the time while using a O2S-driven AFR meter to tune--but I could never get a consistent fuel curve cruising at light throttle. Additionally, I had terrible problems with fuel slosh. Under high lateral acceleration and braking the damn thing would go way rich and even flood the engine to stall at low rpm. No float level change could solve it..

I learned later the AFB design has a float chamber that lacks in fuel control. In fact, that is one reason GM stopped using AFBs at the end of the 64 model year. It's also one reason why road racers of that era, running SCCA's old production clases, had constant problems with AFBs exiting turns and under braking.

As to what's a better choice? Well, for engines, other than all out racing engines, requiring 750 cfm or less, the Quadrajet with proper calibration is the best choice--certainly better than the AFB and in many cases better than a Holley. Admittedly, the problem with the Quadrajet is complexity (compared to the Holley or the AFB) in tuning and adjusting.

Back, before the Big Block from Hell was a project car for Vette Magazine, it had a near-stock 454/365. Mods were a Melling 396S cam, low restriction exhaust, a recurved distributor and a properly modified and calibrated Quadrajet. The car had great throttle response (typcial of QJs) and ran hard. It was built by the late Brad Urban (who later started a business called the "Carb Shop" and specialized in QJ performance mods) The car ran 13.7s at 109 with a 3.36 gear and street tires.

Remember, the AFB was on Corvettes for only three model years. The Quadrajet was on them for 16 years. There's got to be a reason GM deep-sixed the AFB so soon. Also, there's got to be a reason even Edelbrock sells a version of the Quadrajet design.

Now, this is not to say that the Edelbrock/AFB can't be made to work in some situations. Where the carb seems to have trouble are in cases were there is high lateral acceleration or braking forces. Also, cases where the engine has a high-lift, short-duration roller cam and very high vacuum signals are present at part throttle can also be outside the AFB's performance evelope. If those two situations are not an issue with a particular engine set-up, then the Edelbrock is an acceptable carburetor once its properly calibrated.

What I'd do is take that Edelbrock 600 back and try and exchange it for Edelbrock's Quadrajet clone.

As for the above engine configuration, unless it's operated mainly at high altitude, I think it's really iffy on compression and a maybe too agressive on spark curve. You probably can live with 10:1 and the aluminum heads, but you'd better make damn sure that engine cools well and has cold air induction. With your spark, I'd recurve to 34 total with 10-12 initial then I'd add vacuum advance of about 8-10 deg. You wanna watch how aggressive the curve gets in the mid-range. I'd make sure I was running a fairly cold spark plug, too. Also, your WOT air/fuel ratio will need to be spot-on and maybe a teensy-weensy bit rich as a detonation hedge. Whatever you do, you do not want the engine running lean--even at part throttle--with that advance curve.

Be careful if you run the car hard with the spark curve you have, now. In warm weather, she'll may be detonating no matter what kind of pump gas you find. In fact, when you run the car hard, you'll be smart to add some 100-oct. unleaded race gas to the tank such that your overall octane is about 94. On your cam: who makes it? Is it installed straight up? Is it a roller or a flat-tappet grind? Mechanial lifter or hyd?

 

[redmist]

Thanks for the response Hib. I'm glad to know even the experts can't make these things work during transitions.
I have a knock sensor installed with a dash read out. At maximum sensitivity (on the sensor) I only get a medium knock indication at 6000-6500 RPM foot to the floor, otherwise zippo.
I also decked the block to 9" which may be why (good quench) it doesn't rattle.
I also have a AFR monitor installed. Running around 14.5 to 1 at cruise and 13 at WOT. Engine temp never goes above 190 and I do have cold air hitting the carb but not ram air.
You are correct about fuel slosh as well. Engine stumbles when winging it around 90 degree corners.
The cam is an Edelbrock as well, installed strainght up, roller rockers, flat hydraulic.
As a last ditch effort I yanked the choke assembly including the choke rods(blocked the holes), cleaned up and polished the primary and secondary venturies and changed the accelerator nozzles to 23s. It's much better but still has off the line stumble and light acceleration hesitation as well.
I get about 13.5 hg vacum at 950 rpm idle.
I give up
Why are quadrajets so had to calabrate? After going through my edelbrock fiasco and reading Vizard's and Emanual's books on carbs I feel like build a nuclear reactor at this point.

 

[Alwyn678]

ARE U Guys.......Talking about the 600 edelbrock

Guys ...............Maybe I got a good one But I love my Carb and I Can't see changing............

 

[Hib Halverson]

Thanks for the response Hib.

You're welcome. Glad to be of service.

I'm glad to know even the experts can't make these things work during transitions.

(giggle)
Expert? Who, me? I put my pants on one leg at a time just like everyone else here. I have to learn and screw up (somtimes too often) before I learn anything.
That said, after my experience (it was months of work) I'd never use an Edelbrock AFB on any engine ever again. Today, if I was to use an Edelbrock carb, it'd be the Quadrajet clone they make.

I have a knock sensor installed with a dash read out. At maximum sensitivity (on the sensor) I only get a medium knock indication at 6000-6500 RPM foot to the floor, otherwise zippo.

You gotta watch knock sensors on modified engines with big cams. They often sense normal engine noise (such as exhaust noise from headers and valve train noise from big cams) as detonation and either give a false indication or they sense actual detonation mixed with normal engine noise and which the user sometimes discounts or misunderstands. We had a knock sensor with an dash-mounted indicator on Vette's Big-Block from Hell. We eventually deactiveated the system because it constantly indicating false knock above 5500 rpm when the engine made so much mechanical noise.

I also have a AFR monitor installed. Running around 14.5 to 1 at cruise and 13 at WOT.

Again, a case of advanced technolgy sometimes not working as well as we expect. Virtually all aftermarket, oxygen-sensor driven AFR monitors use narrow-band O2Ses which are only accurate in a narrow band of readings where AFR is near stochiometric. On either the lean or rich side, they tend to be inaccurate such that I use them as "clues" to AFR but rely on other methods to determine exact AFR or benchmark its WOT calibration. That said, a 13:1 reading is a clue that your engine may be lean at WOT. I'd do some other testing, like on the chassis dyno or the race track to see if you've got WOT AFR right. Typically, it ends up 12.5-12.0:1.

It's much better but still has off the line stumble and light acceleration hesitation as well.
I get about 13.5 hg vacum at 950 rpm idle.

Hmm. 13.5 inhg ain't much. What's the engine's spark curve and does the Edelbrock cam have some advance machined into it or is it truly indexed at zero? Also, is this car an automatic or a stick and what axle ratio does it have?

I give up
Why are quadrajets so had to calabrate?

I say that because they are more difficult to modify and adjust than a Holley or an Edelbrock/AFB

 

[redmist]

Again Hib thanks for this great info. Even though I had that knock sensor on full sensitivity I still was worried I was hurting the engine.

To answer your questions there is no advance built into the cam based on a re-read of the materials that came with it and a quick check with the less than helpful edelbrock tech line.
The car is a manual with a 3.70 rear and M-21 tranny.

I've got bids on e-bay on a 800 quadrajet and a 780 Holley. If I can pick them up cheap I'll try a three way test, do a free-lance article and sell it to Hot Rod

One last question. Is a an exhaust gas pyrometer of any value in tuning?

Thanks.

 

[Alwyn678]

Hib...Your comments give me a headache

Could u be a bit more......logical

 

[69MyWay]

Car Craft

Great article in this months Car Craft. They take a stock Q-Jet and rework it from scratch. Turns out that it gets better fuel economy and performance than the other aftermarket substitutes of like CFM. They also give a good explanation of why standard formulas don't work very well to determine CFM needs. The Q-Jet is the one carb that has the highest flexibility for STREET use.

Bottom line, if you are racing and running WOT all the time, get a Demon, Holley, etc. etc. Otherwise, a properly tuned Q-Jet can not be beat.

Good reading. It supports what Hib is saying.

 

[Wayne robson]

Take a look at this expensive Qjet on ebay.

Sure... The original carb will take up a lot less space than some of the stupid stuff I have stored Besides this would be a good time to learn about the quad.. with a carb kit

BudD

Hi Bud D and Alwyn678, hope you dont mind me breaking into your site
but i dont know how to ad an attachment, would you mind doing this for me others may interested in seeing this, it is a Qjet that just sold on ebay
item number330140414788, look at the price it sold for, regards wayne.

 

[Vettehead Mikey]

You're digging up a post that's six years old.

What do you want to know about that eBay carb?

http://cgi.ebay.ca/ws/eBayISAPI.dll?ViewItem&item=330140414788&ru=http%3A%2F%2Fsearch.ebay.ca%3A80%2Fsearch%2Fsearch.dll%3Ffrom%3DR40%26_trksid%3Dm37%26satitle%3D330140414788%26category0%3D%26fvi%3D1

Other than 2 people that have more money than brains and the 'need' to have a correctly numbered carb, it's worth $25 as a trade in core just like the ten million Qjets in the world.

 

[Wayne robson]

pricy carb

You're digging up a post that's six years old.

What do you want to know about that eBay carb?

http://cgi.ebay.ca/ws/eBayISAPI.dll...sid=m37&satitle=330140414788&category0=&fvi=1

Other than 2 people that have more money than brains and the 'need' to have a correctly numbered carb, it's worth $25 as a trade in core just like the ten million Qjets in the world.

Hi Mikey, sorry i did that, not very good on the computer still leaning, and know was just surpriced, at what people will pay for some items, approx i month ago, a 1939 41 chev,dash compass, sold for over $5000, more than 30 bid. regards wayne.

 

[RedChev]

Quadrajet

Alwyn, In any case if you don't use it keep it. Some day if you don't go back to it somebody will pay alot of money for that carb. And I would use it. I think the best street carb and in many cases racing carb is the Quad. It is unbelievably adjustable. examples being, primary jet, then rods , power piston needles, and springs, accelerator rate changes and cup size, secondary jets, then needles, and rate of openning and secondary cam curveature changes. It takes patience to dial in a carb, especially on a modified engine. Another characteristic is that you can make almost any engine run real sweet on those small primary barrels, but when you dump in the secondaries, just the sound turns you on, and you can make the secondaries dump as much go juice as you want. Then the transition can be adjusted with all those variables i just mentioned. One precaution: don't warp the main body or the top air horn. That comes from too much soaking and over tightening.
RedChev.