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| Offy. 4 bbl. questions https://www.slantsix.org/forum/viewtopic.php?t=14510 |
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| Author: | speedo1 [ Mon Sep 26, 2005 2:45 pm ] |
| Post subject: | Offy. 4 bbl. questions |
I just picked up my mint running/looking 68 225/904 w/ 80k miles. My buddy gave me an Offy. 4 bbl. manifold. Motor is stock ( for now), but, I want to run a 4 bbl. Holley 390 sound right? Also, to run dual exhaust, should I run a Dutra rear with the midified front so as to keep the heat riser, or, does the Offy. not account for this. By the looks of the underside of the manifold, there is some sort of rectangular flange. Lastly, what about linkage? Thanks for all help! |
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| Author: | Rust collector [ Mon Sep 26, 2005 3:29 pm ] |
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Usually, you run the dutra casting in front, and the modified original in rear. From pics, the offy does use the heatriser thingy. |
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| Author: | speedo1 [ Mon Sep 26, 2005 3:50 pm ] |
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O.k., thanks, My dyslexia is showing, LOL. |
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| Author: | Rust collector [ Mon Sep 26, 2005 5:07 pm ] |
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| Author: | Dennis Weaver [ Mon Sep 26, 2005 5:48 pm ] |
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Might I suggest a Carter (Edelbrock) in place of the sucky 390 holley fuel drip   Also, you're probably gonna want to do at least a cam swap if you want to take advantage of the CFM potential. D/W |
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| Author: | Avenger2040 [ Mon Sep 26, 2005 8:28 pm ] |
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What you people think about a Rochester Quadrajet? |
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| Author: | mcnoople [ Tue Sep 27, 2005 5:53 am ] |
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q-jets on a chrysler only if its a dippy |
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| Author: | james longhurst [ Tue Sep 27, 2005 6:07 am ] |
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Quote: Might I suggest a Carter (Edelbrock) in place of the sucky 390 holley fuel drip
dennis- may i add an  to that?-james |
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| Author: | FrankRaso [ Wed Sep 28, 2005 6:42 pm ] |
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What is a "dippy"? 
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| Author: | 62savoywagon [ Wed Sep 28, 2005 6:56 pm ] |
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Dodge Diplomat |
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| Author: | gearhead [ Wed Sep 28, 2005 7:52 pm ] |
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The Q-jet is one of the best and most adjustable carbs ever produced period!!! I think it is an excellent candidate for the slant. It is very easy to limit the secondary airvalve opening to limit the cfm, and with readily available metering rods for the secondaries...jetting for performance is a cinch. The primaries feature a triple boost ring venturi which atomizes fuel better than virtually any other carb and all but extremely high pressure fuel injection. I have been building carbs for most of my life and have tried almost everything at one time or other...and I keep coming back to the Q-jet. On my Pontiac I get 14mpg at 3500 rpm on the highway and 13 around town, and thats with almost 600hp on tap. The primaries on the Q-jet are much smaller than the Carter/Edelbrock and will provide outstanding throttle response on a small engine like a slant. All this being said...two caveats...the low airflow due to small cubic inch will mean that it is best to find a core carb from a small cubic inch chebby (265-327") or you might need to learn a little about idle circuits and how to modify them...course this is true of all carbs...and...because the Q-jet is so adjustable, it means more chance to screw it up if you haven't got a clue... Also, another positive is that figuring out jetting for the Q-jet is much easier than other carbs, especially for fuel economy. Since all the metering rods have the same diameter power tip, and only change in the cruise step diameter...once you have your power tuned, you can keep leaning the primary until good economy without affecting acceleration...unlike Holleys or Edelbrock/Carter or other makes... Most people don't understand tuning Holleys for economy anyway and it involves drilling holes to allow the power valve more enrichment so you can lean the "as provided" to rich main metering circuit...and then you are still stuck with a 50yr old venturi design with low boost and atomization qualities. But I know most of you think of them as junk since people who actually know carbs understand quickly all carbs because they are all based on the same principles, and just different engineers choose alternate methods of accomplishing the same thing. The Q-jet survived as long as it did, and was then made electronic...not because GM was cheap, but because why screw with a good thing. As with all things, including the venerable design of the slant, there are issues from manufacturing and other choices based on compromises, and it helps to understand what they are before embarking on a swap. I have written extensively on Qjet modification and function...and if anyone is interested, I can provide at least some links to my writings on the Performance Years Pontiac forum for further reading and education. But please don't malign what you don't understand...just choose not do use one if you don't like...for those interested I am willing to help. Here is a couple of pictures as examples of the descriptive writings I have done explaining Q-jet features and functions.  I will answer specific questions about the Qjet on the Slant Sizx board, but will only provide links for other information. I have spent hundreds of hours researching, photographing, and writing about Q-jets and won't invent the wheel a second time.  One of my plans all along was to find a four barrel intake and install a Qjet on my slant...but although I have found all sorts of cool other stuff, I am always a day late and dollar short for a four barrel manifold. If someone has a spare, I would trade a well built Qjet for it...or a distributor rebuild and curve job...of course, not till I get back to Oregon and who knows when thats going to be... Karl aka Gearhead 
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| Author: | Avenger2040 [ Wed Sep 28, 2005 8:35 pm ] |
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Hey gearhead!! I want to put a QJet in my Slant (´cause I got a QJet here looking at me), can you share some of your knowledge with me to tune it well? |
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| Author: | gearhead [ Thu Sep 29, 2005 2:39 am ] |
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Yes, but start your own thread specifically about that topic so I don't hi-jack this gentlemans thread any worse than I already have. If you do that...then over the next few days I will search my old writings and post links as well as describe what I think would be issues relating to placing one on a slant. The picture above of the qjet on a slant came from a site where the guy offers a linkage and conversion kit to do what he has done. Karl |
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