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  #46 (permalink)  
Old 07-30-2004, 02:31 PM
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What the heck. I have replaced just about everything else. Why not the plugs too? I don't have a particular preference for plugs, but now that I have the HEI distributor, is there a plug manufacturer that is more desirable to use? Normally I would use a Champion or Bosch plug. Are the platinum going to deliver a hotter spark? This is a whole new topic and I really don't want to get into a big discussion on it now. I just want to get my buggy back on the road running smoothly. I know it will do it if I can get the combination right.

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  #47 (permalink)  
Old 07-30-2004, 05:18 PM
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Well,everyone has a different plug that they think is the best,there are an equal amount of advertisements out there,most hype,for me,I haven't had the best luck with champs,I like the ac delco or autolites,also ngk,I use the cheap ones and replace em more often,beware of cheap sockets,as its easy to get a light crack from a side load,I don't like to use the rubber insert,Im just careful to go in strait while tightening em,and take your time making the gap uniform among them all,good luck,hopefully thats it,I know it can get frustrating,but it sounds like your just about there. Something you may want to try before you dig in is fire it up when its dark and look for spark leaks,I have had new wires and new plugs be bad from the get go.
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  #48 (permalink)  
Old 07-31-2004, 07:40 AM
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A spark generated by a fixed voltage traveling through 0.045 inches of gap will generate the same temperature regardless of the type of spark plug as long as the spark plug does not have some sort of built in resistance to electricity.

If you want a, "hotter" spark, then you need to increase the voltage and the gap.

I used to have a Toyota with an ignition system that could spark over one foot. If there was room in the engine for a 1" spark plug gap, I'm sure it wouldn't have a problem running with a 1" gap.

But, there are additional problems to having such an aggressive ignition system. With that car I've gone through several distributor caps that developed internal carbon traces to the wrong plugs, and several wires that would spark straight through the insulation. So beefing up your ignition system isn't such a great idea. My Toyota came that way stock, and shocked the hell out of me quite a few times.

There are, "hotter plugs" but that's not a brand issue. Rather it's a design issue and all the manufacturers make hotter and cooler running plugs. These plugs have a longer distance from the spark point to the threads for the heat to transfer away from the tip. So this longer distance produces less cooling and thus a hotter tip. This hotter tip can burn crap off the tip and keep a very rich engine running a lot better than cooler rated plug.

If your plug tip get's too hot, metal will start melting from the tip. So too hot is not good either.

I guess someone might try and make a plug using a metal that melts at a higher temperature, so it can handle hotter conditions before it starts to melt away.

Platinum melts at 1675C and iron melts at 1535C, so I guess a platinum plug with a higher temperature rating will last just as long as a iron plug with a lower rating but stay cleaner, so platinum plugs make sense, but how much platinum really is there in a platinum plug? I mean, doesn't platinum cost more than gold? I really doubt that those platinum plugs have pure platinum tips. And also that metal tab that hangs out over the tip? Is that platinum too? It definitely doesn't get hot like the tip, as it's connected directly to the threads part which in turn is connected directly to the block. It doesn't help to have a hot tip with a dirty tab with carbon deposits all over it because it's not hot enough to burn off the crap.

Wait, carbon has a melting point that's 3500C, and it's cheap too. And doesn't carbon conduct electricity? Why don't they make carbon tipped plugs?

Tungsten melts at 3149C

It's because of these unexplained issues that I just buy the cheapest plugs they have every time. And I've never had a problem with my plugs until they've melted away, and I barely ever change them. I had a set of cheap plugs last over 50,000 miles in my Toyota with the super ignition system.

If you read this thread: http://www.hotrodders.com/t43805.html you'll become an expert on different peoples opinions about spark plugs, but you'll learn nothing about the actual plugs themselves. Most problems with plugs are problems with the engine not running right that causes the problems with the plugs. Once your engine runs right, your plugs won't have problems. The other problems with plugs are plugs that are physically broken or the wrong gap.

But hey, they're cheap and could be broken on the inside where you can't see.

Last edited by Terje; 07-31-2004 at 09:12 AM.
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  #49 (permalink)  
Old 07-31-2004, 05:19 PM
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I have posted this before and I will post it again but in a simpler version.It takes a certain amount of air to make 1 horsepower.The only reason we dont run atremendous carb that offers no restriction to incomeing air whatsoever is that you need a small amount of restriction thru the carb to help the carb move fuel into the engine.
My formulas are based on carbs rated at 1/5" of pressure drop which is most 4 barel carbs.2 barrels are rated at a 3" drop and these formulas dont apply.
For a very mild daily driver street engine with an automatic trans and a dual plane intake with full plenum divider multiply the anticipated flywheel horsepower by 1.7 and you will have the correct carb size you need to peovide a 1" pressure drop at the engines peak air conumption level.For a fairly hot street engine with a sinlge plane intake manifold but with only enough stall speed in the covertor to make it drivable,but not the true optimum stall you will need to multiply the peak power by 1.5 to get the best combination since the hot street motor willproduce less signal to the carb and therfore need a way to crutch up the low sped driveablity issues.With a maximum race engine with the optimum induction design you ned to go back to the 1.7 ratio.Good luck.
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  #50 (permalink)  
Old 07-31-2004, 11:17 PM
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Super Streeter,

I suggest you read this article.

http://www.chevyhiperformance.com/te...ose/index.html

Pay extra close attention to page 4, "We were hoping to see even more power with the 950. It definitely produced a low-speed stumble, and we thought about tweaking the idle-air bleeds but refrained since we had come this far without touching any of the other carburetors ." A pretty lame cop out if you ask me.

You should also go re-read the posts in this thread. It appears that jpd37 is making great progress and that soon his carb will be tuned for his engine and his performance will be great.
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  #51 (permalink)  
Old 07-31-2004, 11:25 PM
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Carter AFB's, Edelbrock's

Revious post by ohio dan stated; The AFB/Edelbrock carbs have vacuum operated secondaries. The motor has to flow enough air threw the front bores to max them out before the back half even opens.


Ohio Dan, The Edelbrocks and Carter AFB's are mechanical secondary carbs. There is an air flow valve above the secondarys that opens on air flow demand as the secondaries open mechanicaly acts like as a variable ventury for the secondaries. I have an Edelbrock 600cfm with a wiend single plane manifold on a '65 Mustang with a 302, mild cam, decent heads and headers, it idles fine, does not stumble and runs pretty strong for a 302. I do not believe a 600 is to small for a small block if setup and jetted right. Several years ago I used to run a Carter AFB 625 on a chevy 283 with out any problems after a rejet and metering rod and jet change. It idled and ran great, with a stock small block manifold and headers with a stock cam.

Last edited by gcrmcc; 08-01-2004 at 07:47 AM.
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  #52 (permalink)  
Old 08-01-2004, 09:13 AM
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There is an air flow valve above the secondaries that opens on air flow demand as the secondaries open mechanicaly
The throttle blades technically open mechanically. However, there will be no fuel flow threw the secondary booster venturi until the motor is able to flow the air needed to open the air valve. For the air valves to open, a pressure differential has to be realized. A lower pressure under the valve, and higher on top will overcome the counter weight and allow the valve to open. Without a vacuum under the air valve, the secondaries would never introduce more fuel. On, what I consider a "Mechanical Secondary" the secondary booster sees air flow immediately after the throttle is opened to the full position. That's all controlled by how far you push on the gas peddle. Vacuum or velocity would have no bearing on when it opens. Dan
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  #53 (permalink)  
Old 08-02-2004, 10:37 PM
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AFB and edelbrock

The AFB's and Edelbrocks are mechanical secondaries and the air flow valve is described on the Edelbrock web sites as "A mechanical secondary air velocity valve in Performer Series carbs senses air-flow according to demand and automatically regulates a smooth transition from part throttle to wide-open throttle." This I wrote in my previous post and decided to check thier web site to double check my self. The secondaries do not rely on vaccum from primaries to open the secondary air valve.
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  #54 (permalink)  
Old 08-02-2004, 11:23 PM
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Hmm,Ive always veiwed an on demand secondary carb as a vacuum secondary,you don't call the distributer advance port a above venturi siphon port do you? It may be set up differant than a holley,but it still opens on demand only,you still gotta move enough air to make it open em up,just like a Q jet,just how I see it.
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Old 08-02-2004, 11:39 PM
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The secondary throttle plates are opened mechanically on the AFB's and Edels, The Holley's that have vacuum secondaries have a vaccum diaphram chamber that opens the secondaries, as it is slower opening than mechanicals they don't need the air flow valve. As for vaccum ports for the distributor, I call them manifold vaccum and venturi vaccum.
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  #56 (permalink)  
Old 08-03-2004, 06:51 AM
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You mean only the lower plates of the secondaries,but the secondaries still don't open(flow air) until they can be accepted by the demands of the motor,right? So to me the secondaries are not open to breath at the demand of your foot like a manual Holley would be. They need vacuum,vacuum operated secondaries. By opening the lower secondary plates you only create an opportunity for the secondaries to open up for flow completely.

What do you consider a Q-jet to be?
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  #57 (permalink)  
Old 08-03-2004, 07:33 AM
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Q-jet is a vacuum secondary carb. Vacuum secondaries are the best of all worlds - only as much venturi open as needed for optimal responsiveness but plenty of flow area @ max load. Can be tuned for superior performance at all speeds and loads. Key word there is 'tuned'. They get bad raps from people who don't tune them properly.
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Old 08-17-2004, 10:47 AM
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I want to thank everyone that has contributed to this post.

My motor is finally running smoothly with good steady power on acceleration and at cruise speeds up and down the dial. My settings, after cleaning and rebuilding the Edelbrock 1405 (600 cfm) Performer consist of replacing the metering rods by one stage leaner and using the orange metering rod springs.

My rich living days are over and the motor is much happier now. It starts right away and once it has warmed up for about a minute (manual choke) it settles down to a decent idle. I think I need to work on the cold start settings a little more, but the improvement compared to before in remarkable. I'm no longer embarrassed to sit at a light and have to coax the car to stay running.

Thanks to all of you, especially Terje, for your patience and encouragement. All the additional discussion on related topics has also been very educational for a rookie just beginning to learn the basics to tuning a normally carberated motor. I am truely in your debts. Maybe some day I can return the favor.
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  #59 (permalink)  
Old 08-17-2004, 06:51 PM
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Quote:
Originally posted by Terje
My Toyota came that way stock, and shocked the hell out of me quite a few times.
I just read through all this and had to laugh at that. I was trying to track down a bad wire by pulling them one at a time (motor running) and got to experience firsthand what you're talking about. I was amazed how far the spark would jump.
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  #60 (permalink)  
Old 02-16-2006, 09:40 AM
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Q-Jet

The Q-Jet has a small screw and spring that sets tension on the top set of butterflies on the secondary side. You can adjust this to allow the air to flow at a lower or higher RPM. Watch this though because you can really kill your gas mileage by having these open early.

This is a great carb for performance when you take the time to learn to adjust it. When I was in my 20s I had a garage. It got to where most of my business was rebuilding carburators. I learned to tweek the quadrajet because in the earily 70s, the manufacturers first attempt at controlling emissions was to lean out the carbs until they would barely run. I maintained a fleet of Federal Agent cars. They were continually getting outrun by people in older muscle cars. The 396 Impala and 440 Dodge cop cars really woke up with some adjustment on the metering rods and jets and secondaries.
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