Why can a marine carburetor not be used on a street application?

Discussion in 'Small Block Tech' started by Curmudgeon, Jun 16, 2013.

  1. Curmudgeon

    Curmudgeon Well-Known Member

    It took be a while but knew I had read Kenne Bell specifically recommended the Holley 850 for the 350:

    At last - an aluminum intake manifold for the 350. Kenne-Bell calibrated 800 cfm Carter is the best carburetor for stock or Stage 1 TA manifold. Stock carb is 750 cfm, so don't waste money on a 600, 625, 650, 660, 725 or 750 carb. The little 350 likes the larger 800 Carter [ also good would be an 800cfm QJ from a 455, bob k ]. The 850 Holley also works but the TA manifold is designed for a spread bore type carburetor in the 730-850 cfm range. The Kenne-Bell KB46002 Air Cleaner is designed to fit the Carter 9800 carburetor while clearing the stock Skylark/GS hood. The KB46002 is so efficient it will not decrease performance or horsepower. In other words, the 350 will run as well with the Kenne-Bell Air Cleaner as it does with no air cleaner at all."

    He does not mention if he was running vacuum or mechanical secondaries. Here I need some schooling. I thought it was simple until I started reading the interweb. So what is the difference between the two, advantages, and disadvantages?
  2. jay3000

    jay3000 RIP 1-16-21

  3. Curmudgeon

    Curmudgeon Well-Known Member

  4. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    The Carter 9800 was a Thermoquad, a spread bore carburetor similar to a Quadrajet, with an adjustable secondary air valve, so it is closer in operation to a vacuum secondary type carburetor. I'm sure someone will correct me if I am wrong, but Double Pumper carburetors like looser converters and higher numerical gearing. They make great track carburetors, but for mostly street operation, you will get better fuel economy out of a vacuum secondary type carburetor. It depends on what your priorities are.
  5. Curmudgeon

    Curmudgeon Well-Known Member

    I prefer performance over mileage. I would like to take it to the track, more of a curiosity, but I do drive it like it is on the track (when it safe and free of Johnny Law).
    Would I be correct in my thinking here: vacuum secondaries are going to be controlled by the vacuum of the engine:Dou:; while with mechanical secondaries are controled by my throttle response, In other words, I may want them opened at times vacuum secondaries would have kept them closed?
  6. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    The double pumper carburetors are mechanical secondary carburetors. The secondaries open anytime you push the throttle open enough to mechanically open them. If you think that Q-jet carburetor are the only carburetors that bog, try flooring a DP carb with a tight converter in high gear without a downshift. On the other hand, if you have right converter and gearing, and the engine is in the proper gear, look out.

    Vacuum secondary Holleys use an adjustable secondary opening controlled by a spring and diaphragm. The tuning kits contain a spring assortment so you can tailor the secondary opening rate.
  7. urbancowboy0307

    urbancowboy0307 Silver Level contributor

    I think Joe Oldham gave a good description of Mech secondaries in Muscle Car confidential, I forget which car he's driving but mentions cruising around town was terrible with the mechs as if you let off the gas real quick to stop you were thrown forward as the engine slowed down when the secondaries closed (come to think I think he was driving some 6-pack powered MOPAR, so maybe that was it)

    Could always throw a 2bbl on there, no secondaries to worry about :Brow: :pp
  8. jay3000

    jay3000 RIP 1-16-21

    When you step on the gas the secondaries open as the engine vacuum falls to 0. Not immediately, so as not to cause a BOG condition. BUT, if the engine WERE trying to draw enough air, they would open pretty much immediately.. They open as the engine needs air.

    With an 850 DP you may end up with a situation that you can't go WOT from idle, or even from a foot brake, because there is not enough air draw (velocity) at low RPM for the engine to pull enough air through the huge holes in the carb to atomize the fuel.. You can make up for that somewhat with a giant secondary squirt of fuel (probably).

    Do what you want. We'll look for you to post "this thing falls on its' face every time I stomp it from a stop"
  9. Curmudgeon

    Curmudgeon Well-Known Member

    That's good stuff. I think I am starting to catch on. I can see how mechanicals could be a ton of fun. It might not be too much fun if wanted a friend wanted to drive it. So that will never be a problem. Just to be clear to any readers I have not said anything negative about Q jets (I have been neutral). Oh, I forgot, I did trip the wire on appearance of the Q jet. But that is purely an ipsative visual purgative.
  10. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    As far as I am concerned Q-jets are irrelevant to this thread. I like a good Q-jet, but I acknowledge they are a lot more trouble to work on, and get right. I still like the way they feel on the street, but that's just my opinion.

    You want a mechanical secondary carburetor, just get an 850 DP. Holleys are very easy to work on. BTW, what is your combination again?

    WV-MADMAN Well-Known Member

    This is a tuff one to grasp, but...

    The Thermoquad/Quadrajet style carbs are so different in design from a Holley that CFM ratings are useless to compare them with.

    Youll find 750/800cfm Q-jets on everything from big-blocks to V6s:puzzled:

    The reason is because when a Q-jet is tuned to an engine, it only feeds that engine as much air/fuel as it needs.

    So an 800cfm Q-jet on a 4.3 V6 will only be feeding the engine 500ish cfm.

    But a Holley 850-DP feeds 850cfm period, and as soon as you punch the gas, if your engine needs it or not.

    And, running too much carb can hurt power by lowering velocity and fuel atomization:Smarty:

    You probably only need a 670/700cfm Holley to do the same work as an 800cfm Q-jet.

    Basically, you have to feed your engine as much CFM as it needs, and any more than that is a waste of time.
  12. Curmudgeon

    Curmudgeon Well-Known Member

    This I did not know. If this is true, and I have no reason to doubt you, it makes even harder to compare carbs. Particularly, if one did not know it. Thanks for this pearl of wisdom!

    ---------- Post added at 06:36 AM ---------- Previous post was at 06:13 AM ----------


    I have a set of ported heads to be put on (one head completed and the other just the intake runners left. I have TA 290-94H cam w/TA grooved cam bearings waiting to be installed. That leaves torque converter (2800ish) and gears (3:4ish) to purchase That is the Reader's Digest version. I am keeping track of completed work in my Garage page......

    My son does most of the work. He built the custom four link. My legs flat out suck! If it was not for morphine and oxycodone I would not even be able to do the easy work. I decided to port the heads myself. That was about about 4 or 5 months ago. I am almost done!

    ---------- Post added at 06:53 AM ---------- Previous post was at 06:36 AM ----------


    WV-MADMAN Well-Known Member

    If you really have your heart set on a Holley 850-DP carb, go for it...

    But remember, that's a whole lotta carb even for a built 455.

    This is closer to what you need from the what Ive read about your engine...


    But either way good luck with it, and V8Buick has your back:cool:
  14. Curmudgeon

    Curmudgeon Well-Known Member

    I know I must seem like a stubborn old fart but some how I need to reconcile what most of you are saying the Holley 850 cfm is way too big with what Kenne Bell recommends: 730 cfm to 850 cfm. He specifically recommends either the Carter 800 or Holley 850. One of you mentioned Bell was building a drag car. That is true but he also made it clear in his opening paragraph it was also a street car. Or as he said "street/bracket." His write-up, while being self published, is detailed and comprehensive. As far as I can tell Bell makes no mention of whether he used mechanical or vacuum secondaries. So what is an old fart to do?
  15. Gary Farmer

    Gary Farmer "The Paradigm Shifter"

    As I said before, you're trying to force your opinion and it is you who is upset when someone disagrees. Someone casually mentions Quadrajet and you explode into a tirade (re-read the first page if you've forgotten already what you said). I don't really care why you'd have so many junk Quadrajets in your possession, I just tossed that in as a bonus.

    To clarify my statements earlier that were apparently either disregarded or overlooked due to the zeal in trying to browbeat holleys over everyone's head, there is a place in the market for both square bore and spread bore carbs.

    My only real point of contention was your insistence on square bores getting better mileage than spread bores, that and you started this whole thing with an insult to someone about not knowing how a carb works, where you clearly do.

    Quadrajets are more efficient and get better mileage when compared to a Holley, when they are both operating optimally. That's my point. It's easier more often than not to simply buy a carb and slap it on rather than fool with the Q-jet. But to claim that Holley gets better mileage only reveals the fact that it was replacing a poorly functioning Quadrajet.

    The only way the Holley can come close to comparing in economy is to cripple its performance factor on the primaries. This is less detrimental when you have a spread bore, since most of the performance is coming from the secondaries instead of being divided up more evenly.

    The only one spreading misinformation here is you buddy. I'm happy for you that your failed attempts at properly tuning your Quadrajets resulted in your giving up in frustration and going with a Holly, but don't give the ole Q-jet a bad rap just because you can't grasp it.

    BTW, you're spot on with the Q-jets being used on everything from v6's to big blocks. That's the beauty of the Q-jet. It is highly versatile in addition to being efficient. GM used it for all those years for a reason.


    WV-MADMAN Well-Known Member

    First, I aint your buddy.

    And second, Me and Sean get along just fine and even when we disagree we respect each other.

    I asked Sean a question and if he found it offensive that wasn't my intent.

    Now go tune your Q-bogs and from now on ignore my posts as I will ignore yours.
  17. Gary Farmer

    Gary Farmer "The Paradigm Shifter"

    Show me on the doll where the mean Q-jet touched you.
  18. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Here's the bottom line, the 850 DP will probably give you your best track times and trap speed. You may have to play with it to get it just right. The Street Avenger that Madman linked will be a lot snappier driving on the street, and once you tune the secondary opening rate, you will love it, but, you may give up some peak HP. I don't think you will be able to tell the difference between the 2 carburetors on the street, but I think you would see it on a timeslip. That's assuming you could hook it, and everything else was right. Bigger is not always better. I personally enjoy driving my car on the street, and the Street Avenger is a better carburetor for that. If there was no way for me to use the Q-jets I have, I would put a SA on my engine, it would have to be the bigger one though. http://www.summitracing.com/parts/hly-0-80870/overview/
  19. sailbrd

    sailbrd Well-Known Member

    Here are some facts. The q-jet is the most versatile carb ever made. You cannot buy a new one anymore. They were never ment to be a race carb. They have a vacuum secondary. They are not cool looking. If you want a good one get in line at Cliff Ruggles shop.

    Holley carbs are the best race carbs ever made. With the right setup there is nothing like the hit of some type of HP Holley. NO racer will chose a vacuum carb of any kind over mechanical carb. Holley carbs look cool (I like QuickFuel because they have red metering blocks) Chokes are for sissies :laugh: You can get 210,001 different kind of new Holley carbs. Just off the top of my head you have: Holley, AED, Biggs, QuickFuel, ProSystems, CSU, The Carb Shop, Baker and? All good shops that can help you out.

    No matter what you buy you will need to tune it since you are no longer stock. Trying to get parts for a Q-jet is hard (ask John Osborne) You can buy Holley parts at the local Quicki Mart.

    On the 350's Sean is a damn good source of info.

    If I was you I would go with a mechanical secondary, annular booster 750 or 850. The 750 will be easier to tune. You can go to the above sources and have a carb set up for you and have a lot less tuning. You will still need to change the IFR's, don't know why but no one seems to get those right. Forget the choke.

    Check out Mark Burton's site on how to tune a carb.

    Good luck.
  20. Curmudgeon

    Curmudgeon Well-Known Member

    Larry would a 750 still be too big? The link you posted for Summit, at first I thought you were recommending for me. Thought I was going have to pick up my jaw from the floor.

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