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  • 400 Dyno Data (with Holley & Q-Jet Comparison)
  • 400 Dyno Data (with Holley & Q-Jet Comparison)
  • 400 Dyno Data (with Holley & Q-Jet Comparison)
  • 400 Dyno Data (with Holley & Q-Jet Comparison)

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  1. #1
    Member lars's Avatar
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    Default 400 Dyno Data (with Holley & Q-Jet Comparison)

    In a reply I did in the Topic Post “Rochester Q-Jet Setup”
    (http://www.corvetteactioncenter.com/...qj-set-up.html)
    tracksnblades1 had some doubts about the Q-Jet’s abilities compared to Holley-based designs:
    Quote Originally Posted by tracksnblades1 View Post
    There has been a multitude of articles, writings and the sort published about these carbs. Ranging from excellent to BS. In closing I offer no defense on my comment of the Holleys perfromance. There are those still that believe these carbs are superior to FI also. Any carb can be modified to achieve almost ideal fuel curves and atomization that allows vaporization only to occur in the compression cylce. I have not read mister Lars Papers as refered to. I will. I will monitor his dyno tests as available. If convinced I may concur and reject the findings of the greats like Smokey, Barry Grant, NASCAR and the factory big three engineers who chose the Holley on their max efforts. AGE QUOD AGIS Do what you do, Well. Only the Best
    I just finished up another dyno test of a mildly-built 400, and the results follow…

    The engine was a stock-block 400 with stock factory cast iron heads. I got compression ratio up to 10.08:1 with flat-top pistons and the stock deck height. The bottom-end was kept stock with some good rod bolts, and the heads were given a good 3-angle valve job. The restrictive EGR intake was scrapped and an Edelbrock “Performer” intake was used to keep overall engine height near-stock so that there would be no hood interference problems. The owner wanted a very mild cam to maintain engine vacuum and power brakes, so a mild hydraulic roller was used. No other trick parts – the engine was pretty much a modest compression 400 with a mild roller in it.

    The real purpose of the dyno run was to get good numbers for the owner and to get a good tune on the engine, but we also wanted to get a back-to-back comparison of a well-tuned Q-Jet to a properly set up Holley of similar size. Those results came in as expected…

    For the first “out-of-the-box” dyno pull, the Q-Jet was used (17056263). This carb is factory jetted at 70/42/DB, which is awfully lean. I re-jetted the carb to 76/42/DB with a 3/8” float level and .640 secondary rod height. Other carb tuning and parameters were set up exactly as outlined in my Q-Jet Tuning Paper under the “Quickie Performance Setup” section.

    After getting the timing optimized (the inefficient chambers in the iron heads took 41 degrees total timing for best power and torque without detonation – an increase from my initial setting of 37). We were using 91-octane pump gas with 10% ethanol – right out of the gas station down the street. Total timing was coming in before 2000 rpm – a very quick curve.

    The 4 initial pulls we did on the engine showed a “dip” in the torque curve (with resulting “sag” in the power curve) between 3500 and 4000. This is right where the Q-Jet secondary airvalve is starting to open up, and the air/fuel numbers were showing a lean condition right at the tip-in of the secondaries. The stock “DB” secondary rods in the carb have the “short” power tips, which delay fuel enrichment. We installed a pair of Edelbrock “CL” rods which have about the same diameter (just a small tad richer), but they have the “long” power tips. Richening up the secondary tip-in point really flattened out the torque curve and made the power curve a near straight-line shot towards the top.

    Once this had been sorted out and the Q-Jet was correctly tuned, I wanted to do the final run just to prove one of my pet-peeve points: Q-Jets are garbage, and any Holley will outperform a Q-Jet… blah, blah, blah… As I state in all my seminars and papers, a properly tuned Q-Jet will perform almost identical to a properly tuned Holley, except that the Q-Jet tends to produce better torque and throttle response in the low and mid range in a street driven vehicle than the Holley. Now that we had our Q-Jet pretty well dialed in, it was time for a switch to the Holley.

    The Holley I selected was a 3310-1, which is a 750 vacuum secondary with the secondary metering block (not the cheap plate). The carb was set up and tuned to spec with 72 primary jets, 80 secondary, and the “tall yellow” secondary spring was selected to assure that the secondaries would actually open. Choke system was removed to give it all the airflow advantage it could get. Float levels, shooters, and all tuning parameters were all set up correctly and verified and “blessed” by noted NASCAR engine builder Steve Yacki (who was also our dyno operator this day). The Holley was given 2 pulls on the dyno, and we verified that the air/fuel ratio on the Holley was virtually identical to the Q-Jet: The A/F numbers matched exactly at many data points, and were never different by more than 0.5:1 at any time through the entire rpm range – the 2 carbs were metering air and fuel at exactly the same ratio, so there was no “fudging” any numbers on these pulls.

    The Q-Jet bettered the Holley by 15 ft/lbs of torque on the bottom end, and pulled more than 20 ft/lbs at many data points, with a 10 to 20 horsepower gain over the Holley at many points through the range. The Holley produced a couple of peak numbers at limited points, but not enough to give it any advantage over the Q-Jet. The mass airflow numbers through the Holley were also lower than the airflow numbers through the Q-Jet at high rpm, and this can be seen by the drop-off in the Holley performance at the top of the curve. We even did one Holley run with me forcing the secondaries fully open for the top of the rpm range, but this killed all the top-end numbers completely: The carb liked the “tall yellow” spring.

    The numbers between the two carbs are fairly close, but if these 2 engines had been installed in 2 identical street cars, the Q-Jet car would have come across the finish line ahead of the Holley car by a significant margin.

    This is not to say that either carb is “better.” But the fact is, that if you set these carbs up correctly, and know how to tune them, they can be made to run very well. There is no point in replacing a badly-tuned Q-Jet with a badly-tuned Holley or vice versa. A well-tuned Holley will run better than a badly-tuned Q-Jet, and this is what is usually the case in the “Holley is better than that crap Q-Jet” argument. If you have a good Q-Jet and know how to set it up, run it on your street car. If you don’t have a carb, or don’t know how to tune a Q-Jet, a Holley will run fine, but you better be able to tune it, too. Black lines are Q-Jet, green lines are Holley:






    Lars
    Lars in Denver

  2. #2
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    Great writeup Lars!

    People overhere in Holland (at meetings etc etc) always ask me why I'm still running the Q-jet. It may not be 100% perfect now but I'm on the right path and will get there! I have the believe that it will run perfectly altho it seems to be a difficult carb to fully understand but that just takes time and knowledge / experience. Glad to see you backing up the idea I have

    Groeten Peter

  3. #3
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    Would not a Holley 800CFM carb be an Apples to Apples comparison...?

    Is not a 17056263 QJet an 800CFM model...?

    So with reference to your dyno run, what has been proven..?

    A tuned 800CFM carb can produce 10-20hp/tq than an out of the box Holley 750cfm vacuum model...?

    What a Juror/Jurist you are....
    Last edited by tracksnblades1; 11-18-19 at 05:34 PM.

  4. #4
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    For a street high-performance application below 450-hp, a properly modified and jetted 800-cfm Quadrajet would be my choice rather than a Holley of similar air flow capacity. It would the performance would be comparable at WOT and the drivability would be better because of the tiny primaries.

    The Quadrajet, which was the last four-barrel carburetor, clean-sheet-of-paper design by a major car company, from a street performance perspective, was one of the best carburetors ever.

    As for the engine package discussed above, the intake manifold choice is going to kill any high-rpm power, so the engine configuration should be focused on mid-range torque.
    Hib Halverson

  5. #5
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    Hib,

    I'm basically agreeing with you on most points as well as the blanket statement that "same CFM carbs with near identical atomization characteristics will produce similar results".

    But as your choice and preference states "a properly modified and jetted 800CFM Quadrajet". Without definition, One may read and infer, understandably, you weren't satisfied with the original factory QJet's calibration/performance in hp apps from stock to 450hp.

    As for your pick, the 800CFM QJet. The 800 and the 827(830) the holy grail were my favorite QJets too. Some of the 800's actually flowed closer to 835 while some 827's flowed 850 stock. 827cfm Qjets thinking back (missing only the primary Venturi ring) were only available during 1970 or 1971. Back in the 80's when properly modified/adjusted these would flow 1000cfm. Later year modifications could go a little higher. For those sanctioned events.

    While I understand your clean sheet analogy, I believe it was however a derivative of the canceled DOVE diaphragm carburetor.

    As for the above engine package..

    ....well...as a blind juror....reading it as a jurist....

    The Total ignition lead 41* tells the story. for the "Rest of the Story" Probably .020 below deck with a FelPro as well.

    A well prepared 800CFM Qjet will flow considerably more than 800CFM..

    A recent out of the box Holley 750CFM 3310-1 flowed 749CFM. Removing the choke valve +1-2 CFM more. With modifications the Holley can flow considerably more . Missing in the op, the actual flow of each carb. A unique sampling technique....? Tampering..?

    Edelbrock used to offer the Performer intake in speadbore or square variants. Interesting to know how the Holley was mounted..? Adapter for the Qjet or Holley? Two intakes?

    A hydraulic roller cam (no specs)...leaving one to wonder whether the Holley had the optimum booster/tuning out of the box...

    And Hypothetically the QJet car wins by a considerable margin.....and the crowd goes wild....��

    I've read here, Holley carburetor usage in the big three manufacturers were merely marketing promotions, with obscure ancillaries to the OP understanding of such as shared by his connections.

    i believe in 65, if an aging memory serves, the Mark lV 396 chevelle could be purchased with the brand new QJET. Or one could opt for a 425 Hp option equiped with a factory spec'd 780 Holley. Some research may indicate the factory Holley sported Annular primary boosters/straight leg secondary boosters.

    While on the subject of Performance Marketing Promotions and Holley annular primary boosters, May I query..
    ..
    Did the Holley Performance Marketing Promotional Strategies extend to the big three Manufacturers Heavy Duty Commercial Truck engine divisions...

    Did not Chevy/GMC/Ford/International extensively use a large number of Holley 4 barrel carbs on truck engines up to and over 500cu in.

    Its interesting to note, with the selection of carbs available.
    Most Manufacturers chose Holley's for their commercial/agricultural heavy duty truck gasoline engines.

    As I remember most of those engines were low speed, low compression, slow timing, governed, heated dual plane intakes, small port/valve heads w/air compressor/hydraulic, pto ,etc, etc/ accessories driven.

    Additionally interesting GM/Ford, that I'm sure, chose the Holley 4 barrel with annular primary boosters and straight leg boosters for the secondary for most if not all big block tall deck applications.

    I've read here by someone that Holley can't provide the responsiveness, etc, etc, etc..., of the QJET's small primary..
    Conversely GM chose the Holley for their big/block trucks with synchronized and all their unsynchronized transmission offerings.

    One, reading posts here, may become confused why Heavy Truck Manufacturers chose Holley over the QJET.

    After all, don't heavy trucks, with those unsynchronized transmissions, dual disc clutches, hauling, dumping, spreading, backing, pulling need a carburetor that produces big torque @ very low RPMs, big power at higher rpm's, smooth tractable transitions from idle to WO. We've all seen those big trucks spit a drive shaft out like a tooth pick when there's a hiccup or bog/burst of power in those lower gears.....

    Have I missed something.....a promotional seminar .....
    Last edited by tracksnblades1; 11-21-19 at 12:05 AM. Reason: Siri*

  6. #6
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    OMG that is a freakin' long post.
    (sigh)

    Quote Originally Posted by tracksnblades1 View Post
    Hib-

    I'm basically agreeing with you on most points as well as the blanket statement that "same CFM carbs with near identical atomization characteristics will produce similar results".

    But as your choice and preference states "a properly modified and jetted 800CFM Quadrajet". Without definition, One may read and infer, understandably, you weren't satisfied with the original factory QJet's calibration/performance in hp apps from stock to 450hp.

    As for your pick, the 800CFM QJet. The 800 and the 827(830) the holy grail were my favorite QJets too. Some of the 800's actually flowed closer to 835 while some 827's flowed 850 stock. 827cfm Qjets thinking back (missing only the primary Venturi ring) were only available during 1970 or 1971. Back in the 80's when properly modified/adjusted these would flow 1000cfm. Later year modifications could go a little higher. For those sanctioned events

    While I understand your clean sheet analogy, I believe it was however a derivative of the canceled DOVE diaphragm carburetor.
    I suspect you may have more knowlege about the history of the 4 than I do. I was unware there was an 827 cfm version nor have I ever heard of a "DOVE diaphragm carb".


    As for the above engine package...
    well...as a blind juror....reading it as a jurist....

    The Total ignition lead 41* tells the story. for the "Rest of the Story" Probably .020 below deck with a FelPro as well.

    A well prepared 800CFM Qjet will flow considerably more than 800CFM..
    I agree.

    A recent out of the box Holley 750CFM 3310-1 flowed 749CFM. Removing the choke valve +1-2 CFM more. With modifications the Holley can flow considerably more . Missing in the op, the actual flow of each carb. A unique sampling technique....? Tampering..?

    Edelbrock used to offer the Performer intake in speadbore or square variants. Interesting to know how the Holley was mounted..? Adapter for the Qjet or Holley? Two intakes?

    A hydraulic roller cam (no specs)...leaving one to wonder whether the Holley had the optimum booster/tuning out of the box...

    And Hypothetically the QJet car wins by a considerable margin.....and the crowd goes wild....��

    I've read here, Holley carburetor usage in the big three manufacturers were merely marketing promotions, with obscure ancillaries to the OP understanding of such as shared by his connections.
    In some cases that could be true but in the case of GM, specifically Corvettes and Camaros with dual-feed Holleys, the reason was the Holleys with center-hung floats, didn't have the problems with "fuel slosh" during high-lateral acceleration maneuvers. Also, Holley dual-feeds dispensed with the small supply of fuel its float bowl.

    i believe in 65, if an aging memory serves, the Mark lV 396 chevelle could be purchased with the brand new QJET. Or one could opt for a 425 Hp option equiped with a factory spec'd 780 Holley. Some research may indicate the factory Holley sported Annular primary boosters/straight leg secondary boosters.
    The 65 Chevelle w. Z16 had the L78, 424-hp 396 and it used a Holley. As for "annular boosters", I'm pretty sure they did not exist in 1965.


    While on the subject of Performance Marketing Promotions and Holley annular primary boosters, May I query.
    ..
    Did the Holley Performance Marketing Promotional Strategies extend to the big three Manufacturers Heavy Duty Commercial Truck engine divisions...

    Did not Chevy/GMC/Ford/International extensively use a large number of Holley 4 barrel carbs on truck engines up to and over 500cu in.
    Back in the day, the manufactuers who build gasoline-fueled HD truck engines, use Holley and other carburetors but those Holleys only shared a few very basic design features of Holley's carbs for light vehicle, high-performance applications. Also, some of those Holley HD commercial products were 2-barrels.

    When it built HD gasoline engines with carbs GM had no engines larger the 427 ci. I can't speak for the other engine makers such as Ford, International, Hall-Scott and etc.

    Its interesting to note, with the selection of carbs available.
    Most Manufacturers chose Holley's for their commercial/agricultural heavy duty truck gasoline engines.

    As I remember most of those engines were low speed, low compression, slow timing, governed, heated dual plane intakes, small port/valve heads w/air compressor/hydraulic, pto ,etc, etc/ accessories driven.

    Additionally interesting GM/Ford, that I'm sure, chose the Holley 4 barrel with annular primary boosters and straight leg boosters for the secondary for most if not all big block tall deck applications.
    I don't think annular boosters existed back when carburetated tall deck BBCs were offered in HD trucks.

    I've read here by someone that Holley can't provide the responsiveness, etc, etc, etc..., of the QJET's small primary..
    True

    Conversely GM chose the Holley for their big/block trucks with synchronized and all their unsynchronized transmission offerings.
    I'm missed your point, there.


    One, reading posts here, may become confused why Heavy Truck Manufacturers chose Holley over the QJET.

    After all, don't heavy trucks, with those unsynchronized transmissions, dual disc clutches, hauling, dumping, spreading, backing, pulling need a carburetor that produces big torque @ very low RPMs, big power at higher rpm's, smooth tractable transitions from idle to WO. We've all seen those big trucks spit a drive shaft out like a tooth pick when there's a hiccup or bog/burst of power in those lower gears.....

    Have I missed something.....a promotional seminar .....
    [/FONT]
    Last edited by Hib Halverson; 11-28-19 at 12:41 PM.
    Hib Halverson

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