63mako

http://www.gtoforum.com/f50/400-dyno...80/#post304184

Torqued Off

And now we can see my dilemna. Lots of Forum members that I have observed that seem to be pretty knowledgeable AND with experience......and there is no consensus. Quadrajet or Holley.....?? Thanks for you comments....I guess I will flip a coin. What does seem obvious, is that an Edelbrock AVS carb, or any other carbs, are not in the running.

Shark Racer

Here is what I see as facts:
1. Holleys are way easier to learn how to tune and rebuild.
2. If you have a good QuadraJet, you'll be at least a few hundred dollars ahead of the game rebuilding what you have and tuning it.
3. A new Holley will likely run better than a Q-Jet that needs a rebuild.
4. Performance between two comparable carbs (IE, both 750s in good tune) will be about the same.

If you're relying on a mechanic to take care of your carb, he better know Q-Jets. When I did my first Q-Jet work, a friend of a friend helped me and I barely was able to drive my car home. I had a shop work on that, and it was at best, marginally better. I then had a shop that specializes in carburetors and they got the car driving really well.

Then I learned how to work on Q-Jets, and my car drives GREAT.

I probably spent close to 10 hours learning how they work the first time. I can build a well running Q-Jet in a few hours and have built a few.

If you aren't willing to take the time investment or don't have a mechanic who knows them well, go Holley and never look back.

But like Mako said, a new out of the box Holley will require work to get running well too. There's a ton of info and parts to help you out too.

commander_47

you guys crack me up

You and shark make my point magnificently. Couldn't say it better myself.

Where do you get the idea that a Holley won't work on an L48 or a 400hp 383? And yet, somehow a Q junk will? That is just plain incorrect. Holleys were burning up the tracks long before the junk came along. They were stock on all the big motor vettes of the 60's and early 70's.

Those cars, btw, are the collector cars. Not the later q smogs.

Q junk came along with the smog era as a one size fits all. And for 165 hp on a 75 it plods along just fine. Funny, todays KIA comes with 190 hp 4 cylinder. Sheesh.

It cracks me up when your argument for the Q junk degenerates into calling us all ignorant morons for not wanting to fiddle and faddle with a carb that never performs well at the drags or circle track.

I build all my own cars and know the Q inside and out. Won't have one, won't work on one, don't recommend them, and anyone who does is probably a masochist.

Now someone will jump in and claim that their Q equipped car is the fastest thing that ever rolled. Simply go to any track this year and look at what is under the hood. Not Q junk.

The carb is obsolete, not made anymore, and a relic that didn't work back in the day, and still doesn't.

If you like it and want to torture yourself, have at it, but don't try and convince us that this carb is the panacea to all your woes. It isn't. It is the beginning of your woes.

63mako

I run Rochesters and pulled 527 HP. Took 3 of them though.

johnt365

I have a 350 also and have run both a Holley 600 and a qjet.

Holley
Pros - Looks cooler. Fun adjustable accelerator pump shot and cams. Adjustable vacuum secondary spring kit. Easy swap out jets and power valves. Easy to find parts. Lots of fun to tinker with.

Cons - Hard to tune off idle and cruise A/F ratio. Probably have to run new fuel lines.

Quadrajet
Pros- Best Feature - If you have an APT model carb, the off idle and cruise A/F is able to be perfectly dialed in. Fuel doesn't spill when you change jets. Nice grocery getting primaries and awesome power secondaries.

Cons - Fuel can evaporate below the accelerator pump inlet making the starter spin a couple times to start after she sits. Doesn't look as cool. No t-shirts or stickers for a Qjet.

I like both carbs but I am running a Quadrajet now. I have an Air/Fuel gauge and have the following ratios tuned. The leaner cruise numbers are very easy to attain with the APT screw.

WOT- 13.2
Cruise-14.7
Overdrive Cruise-15

If I was committed to the RPM manifold I would look at QuickFuel. It seems like they offer more bang for the buck with features than Holley does.

Cheers,
John

63mako

The Holley that works correctly on your L48 won't work correctly on your 450 HP 383. That would require a carb change, no way around it. With a Quadrajet that swap only requires tuning.

63mako

Like I said in the PM a couple days ago, if you already have the intake installed and don't want to swap it out buy a 670 Street Avenger with electric choke. Easy to tune, parts are cheap and readily available.

Torqued Off

Thanks Mako, I think that is what I am going to do.

leadfoot4

Enough already!!


You've made your point, YOU don't care for Q-Jets......



Having said that, "back in the day", one of my neighbors was a "line technician" at Rochester Products, the place where they made the Q-jets. He could dial in a Q-Jet such that it would outperform a Holley, without a doubt. He gave me a lot of training on Q-Jets, and I set up several of them, however, the ugly face of time has set in, and in all honesty, I have touched one in close to 20 years, so my personal experience is marginal, at best.

The main roadblock to a Q-Jet, these days, is lack of parts availability.

commander_47

That is simply not true. You are totally incorrect here.

It all depends on a number of factors including your engine build, style of driving, and a slew of other things.

Most guys over carb their engines. I am guilty of this myself. It simply comes down to the macho in us.

My 383 ran great with the 600 cfm Holley. Not a single problem. None, but I HAD to HAVE the 670 Street Avenger. Go figure.

There is no way I'll ever drive the car to the level the SA will deliver.

But it's nice to know I could if I wanted to

Most Holleys simply require rejetting. It is pretty easy for most backyard mechanics to do this. Simply take the primaries off idle for a few minutes and then pull a plug.

If it is white and hot, it's lean, if its wet, it's rich. Should be a gray color. Go up or down two or three sizes on your primaries. Try it again. Under the vast amount of circumstances, this will work.

Then make your secondaries 3 to 4 sizes bigger than the primaries. This is a pretty good baseline for your normal hot rodder.

Another technique, since Holleys come already pretty much dialed in, is the old hot rodder technique for mid modified engines. Simply put the secondary jets in the primaries, and replace the secondaries with 3-4 sizes bigger.

That's all there is to it in the vast majority of examples.

As for carb size, there are many formulas on line to figure the correct size. This is a great site that will tell you how much CFM your carb will ever need.

Remember, unless you are full blown racing, the max RPM will almost never go above 5000-6000
http://www.gtsparkplugs.com/CarbCFMCalc.html

63mako

GM used Quadrajet carbs from 1965 to 1990. Over 100 million were used by GM over a 25 year span. They have smaller primaries for fuel economy and better emissions and large secondaries for performance. The secondary side of the Qjet opens according to the airflow requirements of the engine, the same basic carburetor size can be used on a large range of engine sizes. The basic 750 cfm QJet casting was used from 231 CID to the 500 CID Cadillac engine, the big secondary air valves open only as the engine breathes. For example, on a mild 350 Chevy the air valve will never open all the way - because the motor can't use more than 600 cfm or so. GM used 99.99 Quadrajets for every 1 Holley 4 bbl used as original equipment. The last Holley that was original equipment was on a 1970 and were only used by GM for a couple years. A properly sized, properly tuned Holley is a great street strip carburetor. A properly tuned Quadrajet is a great street strip carburetor. If you have a Holley 600 on a hot 383 and never push the car enough to need a bigger carb a Quadrajet is MUCH better suited for your use.

commander_47

I dont agree, and the facts dont bear you out.

Performance data for the q does not justify your claim.

Where are those millions of q junks?

Salvage yards are full of them. Yet, why arent guys flocking to rebuild and use them?

Because they suck thats why.

A normally aspirated engine will only draw as much as it needs. A q junk, under normal conditions is designed to starve the motor and run lean.

If you monkey with it to make it breathe better you defeat the purpose.

To reiterate, the early performance cars, the collectible ones, used holley. GM decided they could make more money with a proprietary carb. And this was the smog era, hence the onw size fits all q junk.

7t9l82

I've run every kind of carb from stromberg 97's to the quick fuel i have now the quick fuel blows them all away. i know a bit about the quadra jet But i know guys who build and tune them for stock and super stock eliminator cars, and they don't have a lot good to say about them.
the dyno results are wonderful for tuning but tell you nothing about real world performance. you take a quadrajet off a car and put a double pumper holley type carb tuned properly and go look at your 60' times.take it out on the street and nail it from a stop light and you Will feel the difference.
and back when we had an idiot peanut farmer running the country and we had gas lines down the block i put a quadra jet ( very well set up) that i put on my 70 LT-1 corvette and guess what it was soggy as hell and the gas mileage dropped , a little but some. i went right back to the double pumper i was running.
if you love quadra jets, go for it but expect to have to scavenge for usable cores and obscure part. my car has a Quick Fuel 750 H.R and thats what i will keep.

Shark Racer

There are very few engines, from the 60s and 70s that can approach the limits of a 500 CFM carburetor, let alone a Q-Jet.

With a Q-Jet, you can command a leaner mixture when appropriate and have the same or better throttle response, plus the same peak power as a Holley.

Frankly, mindsets like yours are the reasons they don't exist in greater numbers. These are far more complex to work on than a Holley and no one will disagree with you on that. Complexity does not take away their advantages though.

They also run pig rich at high RPM to protect warranties - just like modern GM ECMs, and those off-the-shelf Holleys.

And when I'm looking at a 9 second car, I'd be very surprised to find a Q-Jet under there too. Once you start building much past 500 HP, the amount of cash you dump into a QuadraJet to make it support the power level is frankly not worth it. Much beyond about 850 CFM and you're doing really custom stuff - where you'd be much better served to buy a Holley. You'd be out far more cash ahead at that point.

Once you get to the 4 digit CFM requirements you've pretty much only got one choice.

But just because John Force isn't running a QuadraJet doesn't mean it's a bad carb. If I based all of my buying decisions on what I saw at the drag strip, well, my car would be undriveable and I have no idea where I'd put the parachute.

The Chevrolets did. Check your history re: BOPs and you'll find tons of Q-Jets.

leadfoot4

If I remember correctly, FORD even used a Q-jet for a couple of years, on their 429 Torinos.

commander_47

You are sadly, no, make that pathetically, wrong on your history and your facts.

There are no advantages.

Significant negative features of the Quadrajet were:
1.Its leaky fuel bowl. As in nearly all carburetors, the Quadrajet's bowl had pressed-in plugs used to seal holes left after drilling fuel passages during the manufacturing of the carburetor. These plugs in the Q-jet sometimes (especially when rough-handled during a rebuilding) leaked fuel causing; (a) a cold engine being hard to start, (b) erratic idling, (c) poor fuel mileage, and (d) excessive emissions. Many Quadrajets have their fuel bowl plugs sealed with epoxy when rebuilt to prevent leaks.[2]
2.The very small float bowl/fuel chamber can result in fuel starvation in extreme high-performance situations, but can always be traced to a fuel delivery problem to the carburetor, such as a weak fuel pump or a worn/rounded camshaft eccentric that drives the fuel pump lever.
3.The fuel inlet/fuel filter housing threads tend to be very fragile.[3] When care is not taken to align the insert, it is possible for the fuel inlet to cross-thread and to strip when tightened in the main housing. There are several "fixes" available in the aftermarket: New, oversized, self-tapping fuel filter inserts; new fuel filter inserts that seal with O-rings; and Heli-Coil re-threading kits. In nearly all cases, the carburetor will require dis-assembly and internal cleaning of the aluminum thread residue, especially up to and including the needle and seat, (needle valve), to prevent flooding.
4.Almost all Quadrajets today have some amount of warpage of the castings,[4] although less pronounced in the so-called "mod Quad" versions after 1974 which were a bit heavier and better designed to resist warping. The root cause of this warpage is over-tightening the front two carburetor mounting bolts, often in combination with a base gasket that lacks hard nylon inserts for the bolt holes.
5.Over much use, the steel primary throttle shaft will tend to wear the aluminum casting material in the throttle body. This results in a minor air leak and in extreme cases, can cause the primary throttle blades to not close properly. This results in poor idle quality. The aftermarket has responded; several vendors are supplying repair kits for the carburetor body, generally in the form of teflon bushings.


The "soggy" take off of the Quadrajet is often referred to by Q junk proponents as "smooth" acceleration. It cannot compare to the launch of any other decent carb. And soggy is slow and plodding. Not something I expect from a Corvette.

And racers only used Q junk until they could afford a Holley.

As for the folks that keep saying q junks are great for racing? How about this:

Holley Performance Products is an automotive performance company based in Bowling Green, Kentucky. Holley, when based in Michigan, was one of the major producers of carburetors, being supplied as standard equipment on many Detroit-built automobiles.

Later they manufactured carburetors for V8 street and racing applications such as the Holley "double pumper". Holley-style carburetors have powered every NASCAR Sprint Cup team and every NHRA Pro–Stock champion for four decades, these series clinging to the carburetor long after the car manufacturers had switched to fuel-injection.


The above kind of puts the kibosh on any claim that the Q junk is "racing" carb.

And how about this from Lane Automotive?

While the Holley may be the best carburetor for all out drag and circle track racing, a well prepared Q-Jet can certainly give it a run for the money.

Well known Competition Eliminator drag racer/engine builder, and recent author, John Lingenfelter, was one of the first to turn the Q-Jet into a record-setter on his Super Stock Chevys in the early '70's. Knowledgeable Q-Jet racers know that there are not necessarily any tricks to perform, but rather cures for ailments, according to Lingenfelter.


And to the above? Why bother? It's too finicky, it's prone to warpage and leaking. It enjoyed some limited success in the early 70's on the drag strip. Only after the grand pooh bah high priest of the Q Lingenfelter worked some magic. Even Lingenfelter junked it.

After 75, the q was totally finished as a viable means of providing an A/F mixture.

And even when the racers switched to injection.....guess what?

Standard equipment on modern race cars[edit]

In 2011 NASCAR decides to switch from carburetors to fuel injection systems for the 2012 Sprint Cup racing season. Holley's billet aluminum throttle bodies were selected in conjunction with a McLaren Electronic Systems and Freescale Semiconductor.[24]

2012 Holley Hi-Ram intake manifold becomes standard equipment on GM COPO Camaros equipped with the LS7 aluminum block.[25]

2012 Holley's Earl brand transmission coolers become standard equipment on GM COPO Camaros.[25]

2013 Holley HP EFI engine control unit (ECU) became standard equipment used on all of Chevrolet Performance's COPO Camaro factory-built race cars.[25

Shark Racer

Nothing in this post refutes anything in the post of mine that you quoted.

I'd give you an A for effort, but you forgot to cite references. Here they are:

http://en.wikipedia.org/wiki/Quadrajethttp://en.wikipedia.org/wiki/Holley_Performance_Products

cooper9811

Here is practical experience from a regular guy - I have run both in a few configurations:
Moderate 383 (AFR 195 heads, XR270HR cam) with a rejetted Q-Jet (Basically stock aside from jetting changes).
Same 383 with a Holley 750 DP (out of the box)
406 (about 450 TQ) with same Q-Jet

The 383 let me compare the 2 apples to apples - my observations:
- The Qjet was somewhat more efficient at cruise and had great (almost instant) throttle response. Off the line was very crisp, and accelerated quickly if I went to WOT from a cruise. Jet changes were more involved than a holley but not hard.
Once dialed in, never had to touch it.

- The Holley was very easy to set up, but seemed to be jetted rich; Definitely used more gas at cruise. Also had good acceleration off the line. Setup was easy. Seemed to have to check the fuel mixture screws occasionally - could have been me but seemed sensitive to temp changes.

Both performed very well. I would use either with no concerns.

If the OP has not been chased off, my recommendation would be to go the less costly route - cheaper to buy a spread bore intake than a new carb. You can find suitable intakes for cheap on craigslist.

My preference for 2 reasons is the QJet. Why?
- Once set up, requires less maintenance
- More efficient at cruise (Maybe the Holley could be set up to do this, not sure)

Like I said, just a regular guy's experience and point of view - Not based on what "others say" - just based on what I have observed in simple terms.

The13Bats

I like this thread some great info but ad hominem attacks do not help
Not wanting to high jack the op's original post I am going to go start a new thread as I want to see where it goes and be sure I get what I need/want...because until this thread I was going to run a pro built Q-jet....hope to see you there.

https://www.corvetteforum.com/forums...o-go-with.html