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#1
08-14-2006, 08:57 PM
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Is it possible?
I just reolaced an Eddy Torker with a Team G,on my hot 440. Now it misses at chevy eating throttle. I checked to see if there was a vacuum leak,but no. I put the same 3310 750 Holley on it(in the process of rebuilding my 850 DP 4779) and I am wondering,if it is possible that the volume from the Team G's runners, is making the 750 starve for fuel(I don't know how to say it). Is the carb too small? Could that do it?
Shaun 
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#2
08-14-2006, 09:14 PM
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A 750 is too small on a stock 440, much less a built one. The stock carb on the 440 was an 850 cfm Thermoquad from '70's on up after all. Best carb to use too. I'd put a Tq on it for sure. Your way too lean if you have a high speed miss. You'll never get it right with the 750 either even if you jet up. It's jsut too small a carb.
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#4
08-14-2006, 10:06 PM
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Like he said, read the plugs, and jet it up a bit. Every manifold gives different vacuum signals to the carb that can give radically different mixtures from the same carb. When you read the plugs be partciular to look for a couple cylinders leaner than the others, it there are some, you may need to stagger jet or do a bit of manifold work. The 750 should be fine, unless it is a very hot engine.
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#5
08-14-2006, 10:23 PM
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750 should be good for 6500R's, I think.
A thermoquad on a team G.........I just realized how funny that is, a TeamG, and adaptor, a vacuum secondary plastic carburator, that also happens to be spreadbore............... Can we all say, holy funky fuel distribution batman?!?!?!?!?
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#6
08-14-2006, 10:28 PM
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750 holley is a little small but to say is can't be tuned out is rediculous.
440's came with 750 avs's in the 60's and somehow they ran well despite not having a TQ. I'd say the problem is more in that the larger manifold has decreased your velocity too much. A larger carb may make it worse. In addition to plug reading, Try a 4 hole spacer under the carb. It may be you've ogne the wrong way with your combo. What cam, gears, weight etc.....?
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#7
08-14-2006, 10:28 PM
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re
It seems strange to me. It is too small for the engine-probably fine for a stocker,but it's far from stock. But it shouldn't act like that,regardless. My guess is I bumped a wire(a loose one-don't know how that could be,but...),or moving the carb loosened up a piece of dirt and it is now in my metering block(it misses on both the primaries and on them together and idles and revs fine-only under a load does it miss). That makes me think it's electrical,or fuel.
The 750 has 78 jets in it now,with a 50 cc pump and a .045 shooter. The plugs show a little lean,but they did with the Torker mani too and still pulled 12.30 at a test n tune(with a spinning start) . It's a 65 D-100 too. Why the miss now? It's something else. Now just to find it. Thanks for the input. Shaun
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#8
08-14-2006, 10:34 PM
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I think it's time for a carb cleaning. Shaun
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#9
08-14-2006, 10:36 PM
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You know, dave may be on to something, higher velocity sometimes requires more fuel, and visa-versa............But your plugs say lean, huh?
If it misses under load, regardless of the throttle setting, I may look into the coil wires, distributer cap..........hell, it's all right there in the front to get knocked around. I take it you have no vacuum advance, right? How's your timing? Oh, and i would love to see pics of your D100! I bet 72challenger and cageman would too, we love sweptlines!
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#10
08-14-2006, 10:46 PM
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It's all new. The dist,coil,ecu-everything. I may be loose somewhere though. I do have the vacuum advance and it seemed to work fine with the combo.It's at 6* initial and 34 at 2000 r's. The cam is installed at 108*,per Comp's tech guy(supposed to be at 106*) and like I said,it ran like a raped ape on Saturday. I just swapped the mani for Team G. I may have to go back to the Torker,but I really doubt that is it. I really appreciate all your input.  Shaun I'll post some pics soon.
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#12
08-15-2006, 12:51 AM
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#13
08-15-2006, 01:04 AM
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If I wasn't so sick of arguing, I would post some "simple math" that would prove you wrong, that 750 isn't to small. Why bother?
(BTW, the TQ has mechanical butterfly's and a velocity opened door caused by the vacuum created under it, the secondary's do not feed fuel untill the vacuum door is opened, so therefore, it is a vacuum secondary carb) Something else I just thought of, you said you tipped your coil over? try and start it a while later, and see if maybe you disturbed the filling in there, and it is causing some kind of problem?
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#14
08-15-2006, 01:13 AM
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There is no air flow through the secondarys till that air door opens. It's opened by the pressure differential between the atmosphere, and the motor. Another name for that pressure differential would be vacuum A big solid cam like that will need a carb with an accelerator pump on the secondary. A 750 is not so much too small that it could cause a running problem. It may limit peak hp. As for the 65 d100..... 12.3's in a pick up is pretty quick if you ask me.  I think the bigger manifold may have been a step backwards. Playing with combinations of 4 hole and open spacers may have yeilded better results than the manifold change. my .02
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#15
08-15-2006, 01:20 AM
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#17
08-15-2006, 01:35 AM
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A 3310 holley works great in a 440 up to about 5500, after that you get a power increase with a bigger carb, this has been tested in a dyno. The difference above that isn't that big, and for most aplications the 750 cfm may work better overall. The thermoquad in 440's came out in '72. I donät care wether it's rated at 1500 cfm, it's a vacuum secondary carb, and just like all the other vacuum secondary models, gives the engine only the amount of air it's capable of using. The flow speed must be so big, that it creates a signal for the carb booster to give fuel. Before the thermoquad, in the "muscle car era of the powerful engines", the 440 four barrels came equipped with either about 600 cfm holley or carter AVS vacuum secondary carbs. It's funny, that suddenly in '72 when the CR and cams came down, 850 cfm was needed to produce less
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#18
08-15-2006, 01:40 AM
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How is that the 440's that made less than 300 hp needed an 850, while the 375 hp models didn't? 
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#19
08-15-2006, 04:57 AM
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A simple question; wonder what opens the spring or counterweight loaded air door above the secondary throttels in Carters? Wonder what opens the secondary throttles in a vacuum secondary holley? A hint; it's the same thing!
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#20
08-15-2006, 05:13 AM
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Shaun,I had a combo very close to yours and mine liked the jets at 85 or 86 square.The torker manifold was only about two hundredths faster than the team g manifold;and the cast iron manifold was the same as the torker.This was with 906 heads that were done at 5800 to 6000 rpm.And its not vacuum that opens the door its air speed thru the carb!
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#21
08-15-2006, 05:44 AM
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#22
08-15-2006, 11:43 AM
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#23
08-15-2006, 02:55 PM
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The spring in the secondary of the holley opposes the opening of the doors, just like it does in a TQ. Stiffer spring, later opening. Air flow opens the secondary on both carbs. The problem is in the terminology. They are both air demand secondary carburators. They work in very similiar fashions. Not understanding that, doesn't make it untrue. .
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#24
08-15-2006, 04:18 PM
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The afb type carbs work off of air flow thru the carb.The holley carbs work off of vaccum but it is not manifold vaccum that does it.If you take the pod off a 3310 you will find that there is a drilled passage going into the pri. side and another going into the sec. These passages join together before the pod.One passage is a kill bleed (the sec. passage)AS the speed of air thru the carb increases the vacuum over comes the kill bleed and the sec. open up.You can make the sec. open up faster by making the kill bleed smaller,but you have to use a big 50cc pump with a big shooter.
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#25
08-15-2006, 04:29 PM
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#27
08-15-2006, 05:25 PM
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That is what I said, I think, the hole you talk of is the venturi, and that is how you get vacuum to control things. In a Holley vacuum secondary the actually have a venturi in the primary bore to sense primary airflow and generate a vacuum signal to open the secondaries, a very good setup as it makes it easy to setup to hold primary airlflow as the secondaries open. As near as I know, as I am not a thermoquad expert by any stretch, the thermoquad opens based on the pressure drop across the primaries (inlet vs manifold) which puts a slight vacuum on the bottom of the air door to open it. The door opening gets bigger as the drop in the primaries (and now secondaries) increases as air volume increases. I guess it would be fair to say the are shooting for a constant vacuum differential carb in a thermoquad, while Holley is shooting for constant velocity in the primaries carb. The choke pulloff is somehow also controlling the air door, but I haven't ever seen an explanation of how it does it, that made sense.
One thing that would be very interesting to see (for me at least) is how much air these 850 cfm thermoquads are actually pulling at full rpm and load on real engines. I wonder a lot about their wide range capability because of the extreme size of the secondaries. To get them to come in quick enough, once they see airflow, they would have to have very low flow reacting boosters, which tend to go way out of mixture range when the flow rates get high. I would guess they could be OK at the low end and get you to 700 cfm without a lot of trouble, but by 850, who knows. Most of the engines we are talking about are probably not pulling any more than 700-725 cfm anyway (small blocks less than that), so it is not really an issue most of the time, I would think. I would think anyone with an engine hot enough to need a real 850 cfm is going to be using something square bore, to get better distribution, anyway. Don't take this as dissing thermoquads, some folks have had very good success with them. I think their biggest benefit is that they are somewhat self sizing, which eliminates all the trial and error (and arguing) about how big a carb do you really need. One of the major problems with folks using Holleys is that they use the wrong size and/or style. The small primaries also give you a good shot at economy, if that is what you are looking for. Anybody got any flow numbers of what their thermoquad engine actually had for airflow on the dyno?
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#28
08-15-2006, 06:16 PM
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The hole I am talking about is not the venturi it is the bleeds that lead to the vaccum pot.The pipe is the carb.
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#29
08-15-2006, 07:03 PM
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C'mon Demonsizzler, step up! YOu got the knowledge. The TQ could also be described as a Variable venturi carb when it comes time to explain the big half, The air doors open according to air flow, not vacuum. That butterfly air door is by no means air tight. As the door opens (when allowed by the vacuum pot) by air velocity it creates a variable venturi across the back portion of the carb, that causes a vacuum (venturi produced) to pull fuel out of the fuel distribution bar, the stronger the air flow, the closer the venturi comes to the fuel bar, the stronger the signal, the more fuel. You can adjust this by bending a tang on the butterfly itself. They use double boosters on the primary side to give a great low speed signal to the fuel circuit. As the vacuum decreases to the enrichment rods due to less manifold vacuum (watch it as you try and start it, the rod tree will bob up and down) , the springs raise the rods to show more jet, and you get more fuel. The vacuum pot keeps the air door closed until the manifold vacuum relaxes the vacuum pot and allows the air doors to open. This reduces the bog that would happen if they just were able to snap open on a throttle blip. Look at one and itll make a little more sense.
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#30
08-15-2006, 07:12 PM
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We got our holes mixed up. The one I was talking about was the theoretical hole in the in the pipe you were talking about. You are absolutely correct on how the Holleys work. You can do a lot of things with the opening by changing the passage sides or adding accumulation. Basically, in a Holley, the spring determines at what primary airflow the secondaries open, and the bleed determines how fast they open once you get to that primary airflow. The previous is at full throttle, they will open slower at less than full throttle because you will have some intake vacuum that will reduce the flow in the bleedoff passage.
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