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  #41 (permalink)  
Old 09-20-2022, 06:36 PM
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Patrick your not going to believe this,I did the rag test and they opened fully however I also removed the zip tie on drivers side and put a bread tie on the diaphragm rod before the test. I removed the rag and they did open fully on the second run. My zip tie was to wide, so anyone doing this test use a skinny zip tie. All and all the power wasn’t much different. I think I will have a dyno and tune session and maybe better sidepipes. Lastly a double pumper but I hope not. It was noted that Holley recommends DP for our cars, would it also benefit from a larger nozzle on vac sec? Thank you all for your help
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  #42 (permalink)  
Old 09-20-2022, 07:10 PM
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That was a successful test. I know in our local club we have a set of shorties that we test with and scare neighbors with (they are not really side pipes at all more like two foot long side pipes). If your side pipes were extra restrictive, and since your engine is really just a big air pump, that could account for the reduced venturi air flow that you are seeing and the corresponding lack of power and inability to open the secondaries. So, I agree it's either the carb (which could still be just malfunctioning despite the fact that we got the secondaries to open with the rag test) or it's restrictive pipes. I think it's going to be one or the other so I would first try swapping out whichever part was the easiest for you to swap out. If the dyno guy could pop on some temporary straight pipes out of the primaries that would be lovely. If not, swapping on a mechanical secondary carb would be the next test. Let me ask you, is your Cobra loud enough? I know that's a subjective question but does it ever set off car alarms when you go by them parked on the street?
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  #43 (permalink)  
Old 09-21-2022, 06:51 AM
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Maybe I wasn’t very clear but it was the wide zip tie being to tight and preventing sec from fully opening, with that off and a bread tie on they do fully open. My pipes are not overly loud in fact when I built it EM asked me if I wanted loud or louder I chose loud so I imagine they are more restrictive. What do you think of a larger Squirter? Before I try a DP.
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  #44 (permalink)  
Old 09-21-2022, 06:53 AM
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Default Truly grate thread

Learning so much from this thread.

Greatly appreciate All the insights and expertise shared here.

Congrats on the Success of an informative test!
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  #45 (permalink)  
Old 09-21-2022, 07:43 AM
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Originally Posted by cobragene View Post
Maybe I wasn’t very clear but it was the wide zip tie being to tight and preventing sec from fully opening, with that off and a bread tie on they do fully open. My pipes are not overly loud in fact when I built it EM asked me if I wanted loud or louder I chose loud so I imagine they are more restrictive. What do you think of a larger Squirter? Before I try a DP.
Of course the squirter only squirts that one initial squirt when you hit the pedal and the little arm pushes the pump. After you've taken off, and that initial squirt has made in through to the cylinders, that's it for the accelerator pump. BUT, I encourage you to monkey around with the carb. Change the squirter, change the color of the cam, change which screw hole you use on the cam, none of that can really hurt anything and the more you do the more comfortable you get at doing it. The next easiest switch out will be to test a different carb, since it appears you're getting all you can out of the one you've got. But if you click my car's audio track here:

Click Here for My Car's Sound

Does your engine sound kind of like that, or would you say it's much quieter?
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  #46 (permalink)  
Old 09-21-2022, 07:49 AM
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From the Holley website:
“For high performance engines a carburetor with mechanical secondaries has an inherent advantage over a carburetor with a “controlled” secondary system (air valve or vacuum diaphragm). This is possible because a controlled secondary carburetor, until it reaches wide open throttle, will not have as great a pressure drop below the throttle plates as would a mechani- cal secondary unit. The greater the pressure drop below the throttle plates the more dense will be the fuel/air charge to the engine and, hence, the more output.”

Swap out the carb and be done with it.
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  #47 (permalink)  
Old 09-21-2022, 07:53 AM
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Swap out the carb and be done with it.
Noooo, half the fun of owning these cars is working on these cars. If you fix the problem immediately then you deprive yourself of continued satisfaction.
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  #48 (permalink)  
Old 09-23-2022, 01:20 PM
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Default Simply amazing......

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Originally Posted by patrickt View Post
Does your engine sound kind of like that, or would you say it's much quieter?
Sounds absolutely fantastic!!

Something truly missing from today's "flashlight" cars.
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  #49 (permalink)  
Old 09-23-2022, 06:52 PM
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I would say yours might be a tad louder, you have louder pops
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  #50 (permalink)  
Old 09-23-2022, 06:58 PM
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I would say yours might be a tad louder, you have louder pipes
OK, good to know. My side pipes have a just bit more baffling than the standard ones from Stainless Specialties (now long out of business of course) but not a whole lot. The standard ones are noticeably louder.
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  #51 (permalink)  
Old 10-05-2022, 06:16 PM
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Update I purchased a cheap bore scope and the pipe going through the muffler is about 1.25”. I think I better get either 2.5 or 3” classic chamber pipes. I don’t want it ear shattering so should I consider 2.5 with packing or longer ones without? Can anyone recommend a shop I could send my collectors to and have them assembled? Patrick you have been a huge help and great teacher, thanks to the others input also.
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Old 10-06-2022, 11:05 AM
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I replaced mine with 3” internal baffles. Sounds like a top fuel dragster. Go with the 2 1/2” pipes if you don’t want to go deaf.
Still won’t solve your low on power problem.
That’s the carb.
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  #53 (permalink)  
Old 10-06-2022, 06:14 PM
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Originally Posted by cobragene View Post
Update I purchased a cheap bore scope and the pipe going through the muffler is about 1.25”. I think I better get either 2.5 or 3” classic chamber pipes. I don’t want it ear shattering so should I consider 2.5 with packing or longer ones without? Can anyone recommend a shop I could send my collectors to and have them assembled? Patrick you have been a huge help and great teacher, thanks to the others input also.
I have the 3" Classic Chambered mufflers. They are quite loud. With my iphone/db app lying in my lap, idle is 94 db. 45 mph in 4th gear is 103 db. I began using ear plugs after the Classics were installed.
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  #54 (permalink)  
Old 10-06-2022, 06:36 PM
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Mine are 95 dB at idle a foot away from the pipes. I really don't consider them too loud. These are the "quiet type" pipes from Stainless Specialties made about 17 years ago. They are quieter than a Harley, kind of as loud as maybe a big truck going slow up a hill if I'm ever so gentle on the throttle going down the street.

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  #55 (permalink)  
Old 08-03-2023, 07:22 AM
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Update tried a DP because I came across a free one and I just had to rebuild it, barely a noticeable improvement, so I went back to the vac sec. I have a front and rear Sidepipe baffles I drilled an 1.5” hole in the rear one and it made a very noticeable in seat of the pants power, the secondary’s are now opening 100% which before they were only about 80% open with the lightest spring, sound did increase a little but I think I am going to drill the front baffle also but I can only get an 1.25” hole saw up there. My pipes are 23 years old and ceramic is starting to rust so I am looking at a set of Gasn pipes, anyone have any input about those pipes?
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Old 08-03-2023, 07:28 AM
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Quote:
Originally Posted by cobragene View Post
Update tried a DP ...
Very good. It's always nice to read the eventual followup that finds the problem. You know, you could always fashion easily removable plugs to go in those holes you drilled and just pull them out for a spirited drive and leave them in for slow quiet cruising. I haven't actually seen exhaust cut outs since the 70's but they did work.
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Old 08-03-2023, 07:54 AM
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Default Which Reminds Me...

I had my engine dyno'ed with the side pipes attached. My side pipes were specially crafted by Stainless Specialties to add just a little extra baffling but still provide a satisfying exhaust note and rumble. But, those side pipes rob you of a good 75 horsepower and I wanted a true number from the engine. You can play lots of games with a dyno, but putting side pipes on the engine when you test it is the big crippler. At my local club though we have a set of shorties you can borrow and bolt on if you're doing something serious. You have to wear hearing protection though when you do.
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  #58 (permalink)  
Old 08-14-2023, 06:11 AM
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I actually prefer the vacuum secondary on my cobra and mine easily blows the tires off at will, it's just the vacuum secondary (mine is an 800 AVS style) is more predictable going into a corner in terms of laying down the power. a mechanical secondary can hit like a small nitrous shot going around a corner and can (and often will) unload the tires right at the time of maximum lateral g's....not ideal.

A well-tuned Vacuum secondary is great in a light car, if you think about what happens when the tires break loose you are reducing the load on the motor which also reduces the draw on the carb venturi.

I've been drag racing for 45 years I know holley double pumpers backwards and forwards, but I still prefer a Vac secondary on a street driven Cobra. A lot of people don't even realize the secondary shot in drag racing is more for helping launch the car under high-traction high-load conditions when the primary shot is already used up, once you're at WOT and the butterflies are open the motor just wants booster flow...the pump shots are already out of it. My drag car has 5300 stall and I leave off two step at 3600 rpm....so my rear pump shot works more like most people's front shot.

I suspect on your FE 428 you may want to look at your ignition curve either not having enough initial or not a fast enough curve below 2800-3200. after you optimize that you can start optimizing the carb jetting, pump cam and shooter and rear diapragm. I prefer a thumbwheel rather than changing springs and always optimize the primary barrels/shooter, pump cam before moving on to the secondary.
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Last edited by Streetwize; 08-14-2023 at 08:24 AM..
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  #59 (permalink)  
Old 08-14-2023, 07:25 AM
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I actually prefer the vacuum secondary on my cobra and mine easily ...
I have a theory that anyone who doesn't agree with your post has never had a truly optimized vac secondary carb on their street car, Cobra or otherwise, and just knows not of what you speak.
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Old 08-14-2023, 08:27 AM
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Thanks Patrickt, for the kind words.

BTW your's is one of the most beautiful Cobras I've ever seen! That color, the attention to detail and the stance look truly amazing.
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