Carb/Distributor Swap?

Discussion in 'General Automotive Tech' started by TheSafariKidd, Aug 3, 2019.

  1. joe_padavano

    joe_padavano Well-Known Member

    Joined:
    Feb 9, 2010
    Messages:
    786
    Likes Received:
    134
    Trophy Points:
    117
    Wagon Garage:
    5
    Location:
    Northern VA
    The secondaries are not computer controlled. They work exactly the same as the secondaries on any Qjet, so again the seller was clueless. There are two adjustments on the secondary air valves on any Qjet - the tension in the air valve wrap spring and the setting on the dashpot that limits secondary opening rate. The factory specs on these take into account the limited airflow needs of the 307. I would not suggest messing with them until you are SURE that the carb is adjusted per the factory specs. There are about a bazillion possible causes for poor running of the CCC system that controls the carb and distributor. A crack in any one of the eight miles of vacuum hoses on the engine will confuse the computer. A mis-connected hose will do the same.

    This is a very stupid computer (it's late 1970s technology) and there are far more failure modes that WON'T set a code than those that will. Here's just one example from my experience. The A.I.R. pump is used to blow fresh air into the exhaust ports when the system is in open loop mode (before the O2 sensor heats up). After that point, there is a diverter valve that switches the air to the converter to keep it from melting. On one of my cars, this diverter valve was stuck open, causing air to flow to the ports at all times. The O2 sensor saw this unneeded air as a severe lean condition and ran the carb full rich, which was exactly the wrong thing to do. Fixing the diverter valve solved the full rich problem.

    As for towing, the carb is the least of your problems. The 200-4R trans is the weak link.
     
  2. TheSafariKidd

    TheSafariKidd Member

    Joined:
    Aug 1, 2019
    Messages:
    27
    Likes Received:
    3
    Trophy Points:
    9
    Location:
    South East Iowa
    Wow, you really know your way around these dinosaurs, thanks!
    I will probaly just leave it alone because i have decided to look for a 350, 403 or 455 to warm up a bit and install next spring.
    Thanks Again :)
     
  3. Poison_Ivy

    Poison_Ivy Dogzilla Fan

    Joined:
    May 20, 2017
    Messages:
    11,046
    Likes Received:
    3,313
    Trophy Points:
    706
    Wagon Garage:
    1
    Location:
    Feeding effigy ice cream to Dogzilla
    I've only experienced these issues the other way around to which the thermostat doesen't shut properly anymore, causing the engine to run too cold. Which is a result of normal metalurgical deterioration
    That alone proves my point. This isn't a question asking if the chicken arrived first or the egg. If the Quadrajet had initially been designed for smaller displacement applications, it would have been built accordingly in miniature or at least the venturi would have been cast accordingly smaller in bore. In that case, it wouldn't have been necessary to tweak an otherwise untweaked carburetor for such applications. I'm sure that Rochester and Carter wouldn't have had any objections to putting a physically smaller Quadrajet into production. That doesen't seem like something GM's executives would have taken into consideration, being that their a corporation motivated by profits, though.
    The only other alternative would have been to build only the miniature version and then mount them in pairs as dual quads on larger applications (It would have made intersting advertisement and sales prognosis). In such a case, you'd have to depend on mechanics who could and would calibrate them properly during maintenance, not to mention the complexity of having that many more parts to install upon line assembly
     
    Last edited: Aug 16, 2019
  4. cammerjeff

    cammerjeff Longroofs Rule!

    Joined:
    Aug 30, 2008
    Messages:
    4,020
    Likes Received:
    568
    Trophy Points:
    287
    Location:
    Belleville, MI
    If it does not rise much above 220F I would consider it normal, for emissions purposes starting in the late 1970's they started running the engines hotter. If it never gets above 225F I would not worry about it.

    I have learned to never change a thermostat anymore unless there is an actual issue with it. Around 10 years ago I changed all the hoses & coolant on one of my older cars, swapped out the thermostat for a new one just because I had always done that. The car started overheating almost immediately, returned the "new" thermostat 3 times with the same results. Dug the old one out of the trash, cleaned it up and reinstalled it. Problem solved. Last precautionary T-stat change I ever did.

    If your T-stat was acting up you would see the temp spike up to 250-260, then plunge back down I would say you had a sticking T-stat. It sounds like you have a 190-195 T-stat installed and it is working normally.
     
  5. cammerjeff

    cammerjeff Longroofs Rule!

    Joined:
    Aug 30, 2008
    Messages:
    4,020
    Likes Received:
    568
    Trophy Points:
    287
    Location:
    Belleville, MI
    The other things you can look at are proper fan shrouding, placement of the fan inside the shroud, and does your car have any baffling to force the air thru the radiator, not letting it go around it. Also a lower spoiler placed just below the radiator can help air flow by creating a low pressure area behind the radiator. Just other things to consider.
    I used to put V8's in the Pontiac versions of Vega's, so I became pretty good at making them cool.
     
  6. joe_padavano

    joe_padavano Well-Known Member

    Joined:
    Feb 9, 2010
    Messages:
    786
    Likes Received:
    134
    Trophy Points:
    117
    Wagon Garage:
    5
    Location:
    Northern VA
    Really? If the Qjet was never intended for smaller displacement motors, why is it that nearly from the beginning of production, it was factory installed on 327 Chevy motors and 330 Olds motors? That 327 doesn't flow a whole lot more than the 307 Olds.

    You really need to spend some time educating yourself about the Qjet and carb sizing in general. The small primaries and triple venturi of the the Qjet allows very precise atomization at small throttle openings and low airflow rates. The air valves on the secondaries match total airflow to the engine's mass airflow needs. Less sophisticated carbs like the Holley can't meter as precisely over a wide range, thus they require a spectrum of carb sizes to match engine needs.
     
    Poison_Ivy likes this.
  7. Poison_Ivy

    Poison_Ivy Dogzilla Fan

    Joined:
    May 20, 2017
    Messages:
    11,046
    Likes Received:
    3,313
    Trophy Points:
    706
    Wagon Garage:
    1
    Location:
    Feeding effigy ice cream to Dogzilla
    Most people didn't know that the Quadrajet was actually more economical than the standard two-barrel,during normal driving, since the smaller primary bores caused the air/fuel mixture to be atomized more completely
    Nevertheless, they ended up as the missing link for in-between engines like the Z/28's 302. In which case, it seems that the Quadrajet was deemed not good enough, being the exception to the faith:

    https://www.hotrod.com/articles/0706phr-1967-chevy-camaro-z28-history/

     
  8. joe_padavano

    joe_padavano Well-Known Member

    Joined:
    Feb 9, 2010
    Messages:
    786
    Likes Received:
    134
    Trophy Points:
    117
    Wagon Garage:
    5
    Location:
    Northern VA
    Seriously? Don't confuse a setup optimized for the race track for one you want to drive on the street. Drag racers use Powerglides for the track because the trans has less internal friction and less weight, and for the very narrowly-defined performance requirements of the drag strip, a single upshift when matched with the correct rear axle ratio, tire diameter, and engine performance is the quickest way down the quarter mile. Does that make it the best trans for street use? Not even close. Same thing with the Holley. It's a great carb for an engine that is primarily operated at wide open throttle, since it is only slightly more sophisticated than a calibrated fuel leak. The simplicity of the Holley makes it a favorite of people who lack the skills or patience to properly tune a Qjet.
     
    Poison_Ivy likes this.
  9. Poison_Ivy

    Poison_Ivy Dogzilla Fan

    Joined:
    May 20, 2017
    Messages:
    11,046
    Likes Received:
    3,313
    Trophy Points:
    706
    Wagon Garage:
    1
    Location:
    Feeding effigy ice cream to Dogzilla
    Well, I guess my highschool classmates who swapped their Quadrajets for Holleys have flunked their I.Q. tests decades before I get to reveal their scores to them. Thanks for the ammunition I could use against them for the next reunion. Only one of them is likely to be still in good enough shape for making his taking a swing at me count, anyway. I'll just have to end up using his wife as a human shield, if he even married
     
  10. joe_padavano

    joe_padavano Well-Known Member

    Joined:
    Feb 9, 2010
    Messages:
    786
    Likes Received:
    134
    Trophy Points:
    117
    Wagon Garage:
    5
    Location:
    Northern VA
    Lots of uninformed people do stuff to their cars because car magazines tell them to. These people apparently don't understand that the car magazines exist to promote the products sold by their advertisers. That's how they make a profit. Holley is a big advertiser. Rochester, not so much. I prefer to make my own informed decisions.

    By the way, did these classmates actually run back-to-back tests to determine if their mods actually helped, or did they rely solely on their "butt dynos"? Hey, if I just spent a couple of hundred bucks on a new carb, I certainly wouldn't say that it made the car slower...
     
    Poison_Ivy likes this.
  11. OldFox

    OldFox Curmudgeon

    Joined:
    Feb 20, 2013
    Messages:
    1,025
    Likes Received:
    176
    Trophy Points:
    135
    Location:
    West Tn
  12. Poison_Ivy

    Poison_Ivy Dogzilla Fan

    Joined:
    May 20, 2017
    Messages:
    11,046
    Likes Received:
    3,313
    Trophy Points:
    706
    Wagon Garage:
    1
    Location:
    Feeding effigy ice cream to Dogzilla
    [​IMG]

    Cross ramming has also its advantages, being that like headers, the goal to achieve peak efficiency lies with equal-length tubing. Traditionally, it was likely undesireable by most automakers, because of hood clearance difficulties and linkage complexities. The one pictured above, although a good performer for its time, would have been even less restrictive, if used with side draught carburetion instead. Since nobody has ever manufactured a four-barreled side-draught carburetor, Chrysler had to live with a horsepower-robbing sharp 90° bend on their version, until the came out with a "Cross Ram" which, like the Hemi eventually evolving into a "Hemi", so that it would fit into intermediate body applications, the original crossram design also was compromised

    [​IMG]

    There are also versions of the latter which are available for GMs. The following is supposedly a Mickey Thompson issue specifically cast for Pontiacs:


    http://www.pontiacparadise.com/parts-id/engine-parts/spc-intake-manifolds.php

    [​IMG]

    I think, they were doing it, because of peer pressure, Joe. Sorta' like grow-ups setting the example for them by playing "Keeping up with the Joneses" between neighbors. The talk mainly surrounded Double-Pumpers and headers. Back then, young people still had sufficient expendable income for such nonsense
     
    Last edited: Aug 19, 2019
  13. Silvertwinkiehobo

    Silvertwinkiehobo "Nothing is foolproof as fools are ingenious."

    Joined:
    Apr 21, 2014
    Messages:
    10,593
    Likes Received:
    1,734
    Trophy Points:
    560
    Location:
    Everett, WA
    Speaking of cross-rams:

    IMG_20190814_180311.jpg IMG_20190814_180249.jpg

    And I talked with the owner; it's on the original 413 Max Wedge. His other car, a '65 Belvedere he just acquired, he said it has a 426 Max Wedge with the cross-ram and is pretty much original.
     
  14. Poison_Ivy

    Poison_Ivy Dogzilla Fan

    Joined:
    May 20, 2017
    Messages:
    11,046
    Likes Received:
    3,313
    Trophy Points:
    706
    Wagon Garage:
    1
    Location:
    Feeding effigy ice cream to Dogzilla
    That looks like a practical header set-up. Which should keep the steering gear cooler than if it were to use traditional header plumbing
     
  15. joe_padavano

    joe_padavano Well-Known Member

    Joined:
    Feb 9, 2010
    Messages:
    786
    Likes Received:
    134
    Trophy Points:
    117
    Wagon Garage:
    5
    Location:
    Northern VA
    I have no idea how cross ram intakes apply to a thread about an Olds 307 motor, but at least here's an Oldsmobile cross ram intake. Oh, look - it uses Qjets.

    [​IMG] [​IMG]
     

Share This Page