I love my quadrajet. If there is a way to make it better, I'm all for it. * An old "atomization" issue was raised by HotRodRivi and has never beer resolved.... http://www.v8buick.com/showthread.php?302756-Qjet-atomization * JW says: Quadrajet is a "wasteful dump at WOT," does not atomize well, "requires 11.0-11.8 AF mixture for best power..... http://www.v8buick.com/showthread.php?256899-3-dyno-videos-and-a-quiz&highlight=3+dyno+videos My questions are: * Can we improve the bsfc "brake specific fuel consumption" by scratches or dimples on the back of the air flap? * Can we improve the bsfc and power by using a 76 degree maximum opening that Super Duty Pontiacs determined years ago? * Are the WOT "lean out" issues with the secondary caused by both lack of atomization and excessive flap opening? I think a dyno can help answer these questions. More: About the flap angle..(never 90 degrees)... http://www.google.com/url?sa=t&rct=...580XC3MiTGAeBRmmA&sig2=qbynUwarkiQhl-4p2X8-2g Atomization; Photos...2nd and 3rd. here... http://customers.skymesh.net.au/hiy_po/quadrajet/index_air_horn_mod.html The cuts on top of the flap (2nd photo) help atomize fuel from the secondary POE. Gives it more double pumper Holley effect.
They really don't need any help. Folks get all caught up in the Internet rumor mill and theory and worry WAY too much about these things. I've done more dyno, street and strip testing that most, with nearly every type of or attempt at a "high performance" carb out there. NONE of them will outrun my q-jet dyno or at the track. Some run just about as well, others come up short no matter how you tune them. The q-jet has survived the test of time and proven themselves to be a great street carburetor, second to none in efficiency, and even better they can double as a race carburetor as well. The big key to using one is understanding how to set the up, and how to keep them full on hard runs.......Cliff
Actually the lack of a true secondary venturi system makes the Q-jet much less fussy on tuning. I consider this an advantage, not a drawback, although my choice of language in that previous post certainly did not get that point across. I would doubt that the addition of a true secondary venturi would do anything to enhance power in a given engine, it would simply make the carb more efficient at WOT, due to better atomization of the fuel. But who is checking mileage at WOT.. nascar maybe, but they are all FI now. JW
I don't think anyone is worried about WOT mill age. Atomization can be good to a point but becomes a negative the closer to the valve you get. Too much atomization your mix will change its state of vaporization the higher the temp. Everything ties in with it, timing, compression,engine temp , outside temp, heads, . Much atomization happens at the instant the valve opens. So I figure you don't want a fire hose at the secondaries. The best thing I have found is how deep you tap in the sec nozzles, I have no dyno so my mods are not approved by others here. So I would ask anyone with a dyno if they have tried shortening the nozzles to just past , even with or before the divider. I like to drill the air bleeds to air ate the mix some , others don't. That is mainly for easing the secondaries open, as the throttle goes wide open you move on to the main circuit. Remove the plugs under the well and even out the passage, radious it smooth, ware the fuel enters the carb before it gets to the seat needs some work, and use a seat with Windows , that's just the beginning, a lot can be done with airflow through all the clumpy casting on the primary side, 1000 cfm is easily obtained and the carb has no prob feeding it.
Anson, there is nothing at all "wrong" with testing without a dyno or drag strip to confirm the results, but without one it's difficult if not IMPOSSIBLE to make direct comparisons, especially when you get close to the ideal result. The problem with "seat of the pants" assessments is that the butt-meter is highly flawed. It will evaluate a change in performance or noticeable transition as a positive or improvement, when actually a much smoother transition will show improved power and performance. Case in point, when testing single plane intakes they ALWAYS feel much stronger on the street or any "seat of the pants" testing. This simply happens as the tires usually slip some and the engine revs quickly into the good power (upper mid-range/top end) where those intakes shine. We will "feel" not only the noticeable transition, but the "rush" of power into the rpm range where those intake really start to shine. Do the same test at the track on back to back runs and the smooth/boring power curve of the dual plane intake will show quicker short times and improved ET more times than not. With that in mind, here we are grinding away and polishing up the q-jet for improved atomization and fuel delivery, then installing the carb and blasting down a city street or back road trying to "feel" the difference. When the actually differences are often measured in hundreths of a second, or even thousanths, it's simply NOT possible to really tell in most cases if we are making improvements, or just aluminum dust on the work bench? Anyhow, as it relates to this topic, we've back to back to back tested q-jets scores of times on the dyno, and even if the BSFC and fuel curves aren't quite as "clean" as some fancy Holley or Holley clone, we've made as much of and often more power trying to do the same thing. My dyno guy HATES to see me coming, and for decades now has tried to outrun these ugly q-jets without success.....FWIW......Cliff
Thanks for the input guys. I used a punch on the backside of a junk flap last week and put several staggered rows of punchmarks right where the fuel blasts out from the tube. It felt really rough to my fingers. Just wonder if it would improve bsaf and / or power on a dyno.
Thanks for the input Cliff, i agree on the smooth approach, just watch footage of Greg Gessler on the quarter mile. I realized that long ago when setting the secdary open rate, set it to ware the tires don't break loose got you there quicker. Have u done any testing with the secondary nozzles , because you say u go to the dyno, but never answer me specifically, or is it top secret info. Have you tried the turbo nozzles? I think they divert some fuel before the divider to try to aim fuel towards front cylinders. Also the other things I mentioned above. As far as messin with the flaps that's butterfly flaps, I think that scratching , dimpling , grovein, would if anything do nuthing.
We've done plenty of testing with nozzles, length, and angle. The cross-drilled ones are horrible, and only used on carbs where they severely limited the opening angle of the top flap. When it comes to "transition", if you feel it, the air door and choke pull-off opening rate and/or spring tension are not dialed in yet. You'd be surprised at how many folks tune and tune on a "tired" secondary flap spring and don't install a new one, or they don't have the pull-off link adjusted correct, or the release time ideal for the application. Then we see all sorts of other issues from folks complaining of stumble/hesitation/bog going quickly onto the secondaries that aren't even carb related, like using spacer without a divider in it, drop base air cleaner putting the lid too close to the carb, or simply insufficient primary pump shot (especially on foot-brake launches). Venting is the last thing folks never address when they have issues. If you have a fast car that hooks and leaves hard, the fuel is trying to spew out every hole in the airhorn and dumping over into the secondaries. Folks tune and tune trying to correct that problem when it isn't a tuning problem at all. Here is what you should see on a hard run for transition: https://www.youtube.com/watch?v=6zVdoLR-VzM Nothing but smooth/steady power from start to finish......Cliff
I have a cross drilled pair and can't tell a difference . Something interesting I have secondary rods stamped , DR across and DX vertical . They have a double taper ware rest on seat. I have AX too but only one taper at seat. Ever seen DX DR RODS?
Nearly as I can remember DX were used in the Pontiac 301 Turbo carburetors. They are very small on the tips, around .030" and the tips are really long. I use metering rods in my own carbs custom machined from the same cores, so the tip length, taper, and included angle is the same for each pair. This is the ONLY way to effectively tune at the track or on the dyno and make predictable changes run to run....IMHO. You mentioned not seeing any difference with nozzle modifications. Not surprised unless you are looking at a dyno sheet noting A/F and BSFC, or comparing back to back time slips at the track. You also have to have a car that hooks and DEADLY consistent at the track to make accurate comparisons. Here is an example, two runs made back to back 23 minutes apart on a "test and tune" night: R/T: .505 .514 60': 1.6230 1.6289 ET: 7.3169 7.3188 MPH: 94.35 94.36 Once you post two runs like those above, then you can make single change and see how it effect the car at every point on the next time slip.......Cliff
Well I'm far from that ever happening. Track wise. I do plan on dyno when ready. Should I chassis dyno or engine dyno or both? I was able to get ahold of Pontiac rochesters yrs back , I tend to think these are the best rochesters for the Buick . As long as you don't use the one with only a single Venturi/booster in the primaries. The only result that I can say that is bonefied scientific is the fact that I could cruise in overdrive at 100mph, and get up to 100 mph with just the primary side of carb. And the time taken to get there.
I have zero experience with chassis dyno's so no answer for your there. An engine dyno is a static test, so helps us cut to the chase for timing/fuel adjustments, but the drag strip is the best place to tune, as there is a LOT more going on there......Cliff
Are you Cliff R . The author of that Rochester book I bought at Barns and Nobles? It says the author is Cliff R. It must be gratifying or somethin when people state things that seem worded exactly the way you wrote it, well I bought your book if that's you, I also have Haynes Rochester book, Rochester carburetor by Doug Roe, Carburstors & intake manifolds by David Vizard, each book has one or two things that the others don't. I out of curiosity put a Chevy truck 800 cfm stove choke the one that looks like the electric, the one rite before the 4MV, on my car and it actually started frosting up, all around the main body, this is in California . That pretty much ended that expiratment.
My major point was about atomization at the backside of a dimpled secondary flap. 1. Roughened or dimpled surfaces can improve atomization and fuel suspension. 2. Fuel particle size is directly related to flame speed in the combustion chamber. 3. Smaller particle size (well atomized) results in increased flame speed. 4. Increased flame speed requires less spark advance, (ignition timing). 5. Less spark advance is less "negative horsepower". (any spark occurance before TDC is negative horsepower) 6. So, improved atomization = improved flame speed = less spark advance = less negetive hp,.... which = more horsepower.
Too many factors go into that one , The Vizard had a good piece on that subject in his port and flo book, did not get good results on v8 engine s . But did on his 4 cylinder race car. and I think dimpling up at the flaps is only slowing down fuel entry, and now I have to quote Cliff " you will need a dyno or track testing to confirm any minuscule gain or loss " Fondling your flaps isn't going to gain you anything , except the Flaps may enjoy the attention
Read this article..........Labled as "Must read" from Circle Track...... http://www.hotrod.com/articles/ctrp-1002-improving-fuel-atomization/ Dimples or cross hatches on the flap would have no effect on the fuel flow. I have heard of cross hatching for years and showed a Qjet flap photo of it in post #1. I don't know if there is any dyno and bsfc info to TEST this qjet application however. The fuel flows through the air and sprays the flap. The rough surface helps atomize the wet fuel.
Interesting article why is everything underlined? Anyway that's stuff I've read in Vizzards books, the new Chevy heads incorporate a fuel shear / dam in the intake port area. The throttle blades of the Rochester carbs are already cross hatched . The question is ware to add dimples, lips ,depends on the intake , heads. I wonder the effect of backcuting intake valves 30deg. It increases low lift flow, but does it decrease shearing of wet fuel
