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  #61 (permalink)  
Old 02-16-2006, 10:22 AM
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Quote:
Originally Posted by rifraf

What do you consider a Q-jet to be?

My q-jets have manual operated secondaries with an air valve. The air valve is not operated by vacuum but by the actual airflow going through the secondaries. Most people don't realize that the Q-jet also has a secondary accelerator circuit, a double pumper of sorts. I modified one of them to have a 1:1 ratio that makes the secondaries open at the same rate as the primaries. Throttle response is awesome, to say the least.

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  #62 (permalink)  
Old 10-26-2006, 02:41 PM
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Carb too big?

I'm listening to you guys, and I'm reminded of when Mike Norris and I were killing our selves in top fuel in the early '70's. We were running a cast iron '92 with the typical 6/71, and an old set of hilborn four port " Laguna lean outs" on top. We would come into stage having to wing the engine 'cuz it was so fat it didn't want to stay lit, and burning the tops of the pistons on the long end. Carbs are alot like injectors in that they work great in a very narrow RPM range, and only adequately any other time.
I did read an article some years back that said "within reason, a too large carb is better than a too small one in that it will only flow as many CFM's as the engine needs at any given time."
However, it only stands to reason that it all hinges around getting close to the correct CFM's for any given engine. The 600 is probably reccomended simply because that's about as small a four barrel as your'e gonna find, and it won't overwhelm the little engine in everyday use.
Did I just stick my foot in my mouth!?!
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  #63 (permalink)  
Old 10-26-2006, 10:37 PM
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Good points Mike. Engines are just a big set of compromises. No engine is good at everything - to get the ultimate top end you give up the bottom end and vice versa. The "smaller is better" mantra applies to 99.99999% of the engines out there 'cause they are mostly run on the street from stop light to stop light. Vac secondaries are a really good compromise 'cause they give you the bottom end you can live with but also give you a lot of the top end that is fun.

And I am honored that an old fueler like you has joined our little chat room here.
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  #64 (permalink)  
Old 10-26-2006, 11:59 PM
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Hey Mike, I'm from Texas too and a couple of years older. We probably rubbed some rubber on the same asphalt. Why don't you come by http://www.nationaltbucketalliance.com/bb/. We share the same kind of roadsters and have a big chapter in Texas with lots of guys to help out. You can probably get a antique tag for that track roadster pretty easy without having to pass emissions.
On the smaller carb is usually better, the reason is that a little engine doesn't suck enough air at low speed to maintain enough velocity in a big carb to drag fuel from the idle circuits. You compound that with a big cam with low vacuum and you have an engine that won't idle at all under 1,000 -1,200 RPM. I have that problem somewhat on my T-Bucket. I have a 60 over 402 Big Block Chevy with a tunnel ram and 2 500 CFM Edelbrocks. (check out my photos) The engine idles around 950 RPM with the throttle blades against the venturis and minimal idle air on one carb. There is enough air leakage in the new carbs that I have to richen the mixture to keep it from melting the headers off. Anyway, on the street, smaller is easier to tune, has better throttle response and is more economical. The only reason we would want bigger is if our buddy is smokin us on the track.

Quote:
Originally Posted by Mike Britton
I'm listening to you guys, and I'm reminded of when Mike Norris and I were killing our selves in top fuel in the early '70's. We were running a cast iron '92 with the typical 6/71, and an old set of hilborn four port " Laguna lean outs" on top. We would come into stage having to wing the engine 'cuz it was so fat it didn't want to stay lit, and burning the tops of the pistons on the long end. Carbs are alot like injectors in that they work great in a very narrow RPM range, and only adequately any other time.
I did read an article some years back that said "within reason, a too large carb is better than a too small one in that it will only flow as many CFM's as the engine needs at any given time."
However, it only stands to reason that it all hinges around getting close to the correct CFM's for any given engine. The 600 is probably reccomended simply because that's about as small a four barrel as your'e gonna find, and it won't overwhelm the little engine in everyday use.
Did I just stick my foot in my mouth!?!
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  #65 (permalink)  
Old 10-28-2006, 07:42 PM
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Hey big guy, how's yer front end??

I looked at your pics. How well does that four leaf front spring work with the big motor?
I have the same front end on my '29, only I plan to change hangers to move the spring above the axle. I'm changing mostly for looks, but also to get just a bit more height. I have 114" wheelbase to work in, so I don't have to shove the 454 out over the front crossmember like I would if I had a stock A frame.
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  #66 (permalink)  
Old 10-28-2006, 11:50 PM
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My front end on the T-Bucket works perfect. I think the original model A spring was above the axel. I had one in '63 and it had a "spring over" axel that had been dropped 6 inches. The stock spring worked fine with a full race flathead, iron bell housing and iron case 39 Ford trans, which is probably nearly as heavy as the Big Block Chevy and modern aluminum case transmission.
Speedway and some of the axel/spring manufacturers might be able to tell you the capacity of the spring. If it is like mine, it can flex a long way before the car bottoms out. With mine, the engine sits far enough back that the weight distribution is about 50/50 so the total is around 950 pounds on the front spring. I think the original Model A Coupe probably weighed around 2800 pounds so we're not getting even close to the stock spring capacity, if that is what you have.
Where in Texas are you?

Quote:
Originally Posted by Mike Britton
I looked at your pics. How well does that four leaf front spring work with the big motor?
I have the same front end on my '29, only I plan to change hangers to move the spring above the axle. I'm changing mostly for looks, but also to get just a bit more height. I have 114" wheelbase to work in, so I don't have to shove the 454 out over the front crossmember like I would if I had a stock A frame.
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  #67 (permalink)  
Old 10-29-2006, 05:20 AM
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Thanks for the carb formula

I will also look at the Holley add ons. Thank you.
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  #68 (permalink)  
Old 10-29-2006, 08:53 AM
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I love Q Jets. They are the best street carb by far. Not hard to maintain/repair once you know the common problems. The Q Jet by design is a very economical carb with small primaries that besides being stingey on gas, are very responsive at low speed. The secondaries and and dual accelerators make it be an awesome performance carb. If you can find them and afford them, the latest models were also pretty good on emissions.

Quote:
Originally Posted by onovakind67
My q-jets have manual operated secondaries with an air valve. The air valve is not operated by vacuum but by the actual airflow going through the secondaries. Most people don't realize that the Q-jet also has a secondary accelerator circuit, a double pumper of sorts. I modified one of them to have a 1:1 ratio that makes the secondaries open at the same rate as the primaries. Throttle response is awesome, to say the least.
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  #69 (permalink)  
Old 10-29-2006, 09:55 AM
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Yeah, everybody I talked to at Goodguys with heavy engines said they were having no problems with their front ends.
I 'm going to try to get the big motor as far back in the frame as I can to take advantage of that long wheelbase. It means I probably won't be able to run a set of laker style headers, but that's ok, as I have some cast iron truck headers that will probably make for a quieter exhaust note, and give some sanity to the car.
I live about 20 minutes North of Dallas in a little town called Highland Village.
It's cool here, every street you go down has some sort of project covered up on the driveway, and there are at least three buckets that I know of prowling around in the neighborhood.
While I'm on the suject of buckets, I just did the Ft.Worth swap meet. A handfull of buckets for sale there, and I'm biginning to see more ingenuity in design that other open wheeled rods. Lots of times, with an A, or deuce, everybody follows the leader, but buckets show more original thinking in suspension design and frame layout than others.


Quote:
Originally Posted by Choctaw Bob
My front end on the T-Bucket works perfect. I think the original model A spring was above the axel. I had one in '63 and it had a "spring over" axel that had been dropped 6 inches. The stock spring worked fine with a full race flathead, iron bell housing and iron case 39 Ford trans, which is probably nearly as heavy as the Big Block Chevy and modern aluminum case transmission.
Speedway and some of the axel/spring manufacturers might be able to tell you the capacity of the spring. If it is like mine, it can flex a long way before the car bottoms out. With mine, the engine sits far enough back that the weight distribution is about 50/50 so the total is around 950 pounds on the front spring. I think the original Model A Coupe probably weighed around 2800 pounds so we're not getting even close to the stock spring capacity, if that is what you have.
Where in Texas are you?
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