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cam installation question

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by 72blazer4x4, May 28, 2001.

  1. 72blazer4x4

    72blazer4x4 Registered Member

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    do i have to pull the engine or can i keep it in to put a new cam in?

    jeremy
     
  2. 2quicK5

    2quicK5 Registered Member

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    You do not need to pull the engine. Just remove the distributor, intake manifold, valve covers, rocker arms, pushrods, lifters, radiator, fan shroud, fan, water pump, balancer, fuel pump, timing chain cover, and timing chain. It's really pretty easy if you know what you are doing.

    John

    1972 K5 Blazer: 400 ci, 4 sp, 3" lift, 35" Tires

    2000 Trans Am, A4
    11.97@114 mph
     
  3. 72blazer4x4

    72blazer4x4 Registered Member

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    i would have to do all that stuff to take the engine out and change the cam right? i was planning on taking the heads off and putting new gaskets there and getting a new water pump so its still pretty easy right?

    jeremy<P ID="edit"><FONT SIZE=-1>Edited by 72blazer4x4 on 05/28/01 09:26 PM (server time).</FONT></P>
     
  4. 2quicK5

    2quicK5 Registered Member

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    You can also pull the heads off and change head gaskets with the engine in the truck. Why are you pulling the heads? You can install new valvesprings with the heads on the engine by using an air compressor tapped into the spark plug hole to keep the valves up when you take the locks and retainers off to replace valve springs and valve stem seals.

    John

    1972 K5 Blazer: 400 ci, 4 sp, 3" lift, 35" Tires

    2000 Trans Am, A4
    11.97@114 mph
     
  5. 72blazer4x4

    72blazer4x4 Registered Member

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    im not sure, i wanna get new heads if i can afford them, and i want a new cam, but the new cam is for sure.

    jeremy
     
  6. Steve_Chin

    Steve_Chin 1/2 ton status

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    To pull the timing cover on a Chevy small-block, you need to drop the oil pan (unless you have a Comp Cams 2-piece timing cover). If you don't drop the pan, there is a pretty good chance of getting a leak around the front of the pan when you reinstalle the timing cover. Bad design on Chevy's part.

    You do not have to pull the engine to do a cam swap, though. Just pull the radiator and shroud, water pump, distributor, intake manifold, valve covers (rocker arms, pushrods, and lifters too), oil pan, harmonic damper, and timing cover.

    Oh: If you're going to a cam with bigger lift than stock, you must check coil bind height and reteiner to guide celarance or you could end up lunching your valve train. Springs can be changed with the heads on the engine, provided the seats already are machined to the proper diameter and depth in the existing heads. I don't like using compressed air to do this swap, because it relies too much on ring seal, the seal of the air fitting, and it can be dangerous if the seal on the air fitting lets go. I like the rope trick better (push a length of 1/4" rope through the spark plug hole, rotate the crank until the piston stops, then release the keepers).
     
  7. travis

    travis 1/2 ton status

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    Also keep in mind that when you up the compression via new cam and/or heads you increase the chance of blowing out the lower end (ie rings) unless you are dealing with well maintained, low mileage engine. A new kit from Summit won't set you back too much. Hopefully you won't need much machine shop work as in my case. I ended up writing the guys a check for $900 just for machine work and assembly back to a short block. I'm not wanting to rain on your parade, just letting you know what might happen. If you are wanting mild performance I would start witht the cam, intake, and carb. You should be able to get a set-up for about $500. Installation is pretty easy.

    Just my $.02
    Travis
     
  8. Steve_Chin

    Steve_Chin 1/2 ton status

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    Travis is right about new (or freshly-rebuilt) heads on top of a well-used block. I've gotten away with it in the past because my engines have always been well-maintained and properly warmed up, but if you have a high mileage engine and don't know about its history, swapping heads may force the bottom end to start getting a lot of blow-by because the valves are sealing better than the rings.

    FWIW, I don't see a need to replace the carburetor if you have a Quadrajet. Just overhaul it and jet it accordingly to your camming and other engine parameters.
     
  9. 72blazer4x4

    72blazer4x4 Registered Member

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    yeah i wanna keep my quadrajet and just get it rebuilt. the only carb i would buy is and edelbrock q-jet anyway.

    jeremy
     
  10. 2quicK5

    2quicK5 Registered Member

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    You diehard Q-jet folks crack me up. IMO, the Q-jet is without a doubt the sorriest aborted atemp at a four barrel carbeurator that I have ever had the the displeasure to own. It is however one of the best two bbl carbs around if you block off what are supposed to be secondaries. :-)

    John

    1972 K5 Blazer: 400 ci, 4 sp, 3" lift, 35" Tires

    2000 Trans Am, A4
    11.97@114 mph
     
  11. Steve_Chin

    Steve_Chin 1/2 ton status

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    I'm not a total die-hard on the Quadrajet, but it gets a bad rap from people who haven't the knowledge to work on them. The same can be said for the Holley (or Carter, or Mikuni, or Weber, or any other carburetor): They get a bad rap from people who haven't got the knowledge to work on them. 204 MPH isn't too bad with an emissions-legal car running a Quadrajet.
     
  12. 2quicK5

    2quicK5 Registered Member

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    Steve, I sure hope that you are not implying that I lack the knowledge to work on a Q-jet and make it run. I have been building engines and racing cars for 20 years now and I have used many, many Q-jets, Holleys, and Carter AFBs.

    For racing, the Q-jet CAN be MADE to run with much effort. For a street performance carb though, IMO it is a lousy choice. It requires constant attention and adjustment, and I'm sure that you will agree that the secondaries are the poorest design of any domestic 4 bbl carb. On the street, the secondaries either open too quickly and bog the car or open too slowly which is bad for neck snapping acceleration. It also has very poor fuel/air mixture distribution on the secondaries. The secondaries are too large not to have a separate accelerator pump for quick opening, both primaries and secondaries feed from a common small float bowl with one float, the secondaries do not have a true 3D venturi in the carb body (just a very crude 2D one formed when the sheetmetal flapper valve opens), the secondaries do not have fuel discharge booster venturis to promote mixing (just a large pipe that dumps in fuel), not to mention that it leaks fuel from almost everywhere (main body primary jet plugs, fuel filter nut etc.). I could go on forever, but these are the main design flaws that IMO make it a substandard carb for street performance. Yes the Q-jet can make the HP for racing, but IMO it lacks the flexibility required for a good street performance carb.

    Holley addressed all of these problems with their model 6210 Q-jet replacement spreadbore carbs released in the early '70s. If you want to retain the stock crappy spreadbore intake then do yourself a favor and get a Holley 6210 (or the newer design 4011 spreadbore series) with mech. secondaries or an Edelbrock Performer AFB clone with an adapter plate.

    John

    1972 K5 Blazer: 400 ci, 4 sp, 3" lift, 35" Tires

    2000 Trans Am, A4
    11.97@114 mph
     
  13. Steve_Chin

    Steve_Chin 1/2 ton status

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    John, I was not insinuating that, but there are a lot of misonceptions about the Quadrajet (and other misconceptions about other carburetors) that seem to be prevailant. The secondary system in the WQuadrajet is not nearly so bad as you make it out to be, and the Quadrajet is arguably a very good carburetor for a mild street type engine. As an all-out race carburetor, the mismatch of airflow from the primaries to secondaries makes it a bad choice. In most Quadrajet moddels, there is a pullover that serves as a vacuum-assisted accelerator pump which functions as the air valve opens. I have also never personally run into a Quadrajet (or any other carburetor that I have made the conscious decision to run on one of my engines) that has required constant readjustment. If the carburetor requires constant readjustment, there is something wrong in the basic setup, no matter what carburetor it is (even the lousy Weber 32/36 DGV/DGAV carburetor doesn't need constant readjustment although it is plagued with stories that it won't hold an adjustment, and the Mikuni PHH series is one of the most stable carburetors I've ever had the pleasure to work with on an engine with multiple carburetors). As you have said, there is no true "venturi" in the secondary throat of the Quadrajet, but the air valve operates much in the same way that the air doors and wing inside of a Predator carburetor function (and, like a "venturi," they all function off of the Bernoulli principle).

    One thing that never gets enough attention in any hot-rodding forum to which I have been (whether it's print, BBS, or clubs) is emissions requirements. There are very few GM performance cars that did not come with a Quadrajet after 1966. In order to maintain emissions compliance, the carburetor must either be an OEM carburetor (the Quadrajet) or have a CARB EO stating that it is legal. Most of the aftermarket carburetors have no such EO because the 50000 mile testing on each model is prohibitively expensive. This leaves many of us "stuck" with the Quadrajet (although it really isn't nearly as bad a carburetor as some would make it out to be).

    FWIW, I've been involves with a number of different carburetors over the last couple of decades myself. These include Webers (down-draught and side-draught), Dellortos, Predators, Mikunis, Carters (both the AFB and Thermo-Quad), Holleys, and the Quadrajet.
     
  14. 2quicK5

    2quicK5 Registered Member

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    Steve,

    I realize that since your GM experience seems to have been mostly Pontiac muscle cars and you live in CA, you have been forced to make the most of the Q-jet for better or worse. However, there are many people on this board that don't live in CA and don't have to worry about emissions requirements on their old vehicles. Although Buick, Olds, and Pontiac Perf. engines after '66 used the Q-jet, all of Chevy's solid lifter hi-perf engines used the Holley 4150 series carb. Most of my experience has been with Chevy performance engines and I prefer the Holley or Carter AFB style carb because I believe it to have a superior secondary design. The Q-jets secondary size is way out of proportion to the primaries for it to be a very good performance carb IMO. The only advantage of the Q-jet that I know of over other 4 bbls is emissions. This is because the primaries are much smaller than other 4bbl carbs, or any 2 bbl carbs, and since emissions testing is not conducted at WOT. If emissions testing was conducted at WOT, the Q-jet would fail miserably IMO.

    John

    1972 K5 Blazer: 400 ci, 4 sp, 4" springs, 35" Tires

    2000 Trans Am, A4
    11.97@114 mph
     

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