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  #1 (permalink)  
Old 09-05-2022, 08:26 AM
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Default Low on power?

I can blast off in second gear hold the brake lightly and only burn about 30’ then grabs and goes, I hear some can just jab it in 3rd and break them loose, I am lucky to jab it in 1st and break loose if it’s cooler out. FE 428 10:1 780 Holley vac sec open 3/4-7/8 with the lightest spring ,tall oval air cleaner, RPM performer, edelbrock heads, 36 total timing, hyd. Cam .539 280 ,at .050 230 lobe sep 110. 350 gears 29” x12” MT S/R tire, WR toploader. Runs great I just feel I am leaving some on the table, may try to get some Dyno and tune time. The tubes in side pipes are rather small, I guess that would be a good and cheap place to start? Any feed back would be much appreciated.
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Old 09-05-2022, 08:32 AM
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Swap out the vacuum secondary carb for a double pumper and you’ll break em free.
The vacuum secondary carb is better for drive ability as the secondaries open as vacuum dictates. Mechanical secondary carbs just open up and dump power. Not as controllable.
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Old 09-05-2022, 08:37 AM
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PS. Nothing has changed in the 5K miles and 22 years since l built it. Compression is 180-190
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Old 09-05-2022, 09:10 AM
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The Everett-Morrison I used to have ran a 410 ci Windsor engine and it would break the tires loose in 3rd gear from about 3,000 RPM by just pressing the throttle smoothly to the floor. It was designed for maximum mid-range torque rather than peak horsepower. . . My current car, a Cheetah, has a 427 c.i., small block Chevy that will also roast the tires in the first three gears.

My opinion is that your engine is not optimally tuned for the type of driving you want to do. Rather than throw parts at it, I suggest you find a reputable dyno tuner who can both optimize your carburetor and timing, and suggest what other components might be limiting performance (e.g., carb, intake, exhaust, etc.). That will give you the best bang for your buck in the long term IF you can find the right dyno guy.
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Old 09-05-2022, 09:59 AM
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Quote:
Originally Posted by cobragene View Post
I can blast off in second gear hold the brake lightly and only burn about 30’ then grabs and goes, I hear some can just jab it in 3rd and break them loose, I am lucky to jab it in 1st and break loose if it’s cooler out. FE 428 10:1 780 Holley vac sec open 3/4-7/8 with the lightest spring ,tall oval air cleaner, RPM performer, edelbrock heads, 36 total timing, hyd. Cam .539 280 ,at .050 230 lobe sep 110. 350 gears 29” x12” MT S/R tire, WR toploader. Runs great I just feel I am leaving some on the table, may try to get some Dyno and tune time. The tubes in side pipes are rather small, I guess that would be a good and cheap place to start? Any feed back would be much appreciated.
Remove 780cfm Holley Vac Sec carb
Replace with 650CFM Holley double pumper-04777C
Try it fresh out of the box, do not adjust carb, do not adjust timing just yet.

In addition, maybe check tire pressure in rear tires, want to burn out more, add additional pressure


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Old 09-05-2022, 02:12 PM
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As others say replace your vacuum carb for a mechanical one. Quick Fuel 750 is highly adjustable. Biggest improvement I got was changing the pump cam to a red one. Gives great instant response.
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Old 09-05-2022, 05:00 PM
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Those third gear tire spins can be a disaster. My cars rear end kicks out to the right in s snap..
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Old 09-05-2022, 06:23 PM
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Originally Posted by scootter View Post
Those third gear tire spins can be a disaster. My cars rear end kicks out to the right in s snap..
Have you checked your rear upper shock mounts?


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Old 09-05-2022, 11:39 PM
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A lot also depends on your tires.

With the Avon cr6zz, flooring it at the top of 2nd and 3rd gear is now a possibility (roush 427r).

With the indy 500 tires the car came with, I'm pretty sure you could spin in 4th..
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Old 09-06-2022, 09:12 AM
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Spinning the tires is fun, and looks cool, but it's really a bad thing. It demonstrates lack of traction and control. If you mash the pedal and it hooks up and goes like stink, that's what it's supposed to do.

There's no such thing as too much power. Only not enough control.
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Old 09-07-2022, 07:44 PM
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Spinning the tires is fun, and looks cool, but it's really a bad thing. It demonstrates lack of traction and control. If you mash the pedal and it hooks up and goes like stink, that's what it's supposed to do.

There's no such thing as too much power. Only not enough control.
You’re missing the point, I don’t necessarily need to spin the tires but not being able to like others leads me to believe I may be low on power.
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Old 09-08-2022, 05:09 AM
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You’re missing the point, I don’t necessarily need to spin the tires but not being able to like others leads me to believe I may be low on power.
You may very well be mistaken.

In addition, most people want to eliminate wheelspin, so perhaps your cars previous owner set up his driveline and suspension properly to eliminate the wheelspin. Why take the wheel backwards from round to square other than to stroke your ego or show off to your friends?

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Old 09-08-2022, 08:47 AM
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As we seem to be wandering off topic a bit, I'll add two things. First, when power and traction get high enough, something in the driveline has got to give. For a street car I prefer the weak point to be the tires. I'd much rather have to back off the throttle to keep the tires from breaking loose than to twist an axle. . . Second, I find it hard to believe that anyone who buys a Cobra doesn't have an ego with regard to engine power and performance, even if they never actually make use of all of it. For example, peak horsepower makes a difference in performance only at wide open throttle when approaching the car's maximum speed. Before that it is torque that defines performance. Yet many Cobra owners who will never approach maximum speed have paid an extra $20K for an engine with a big dyno peak HP number just so they can talk about it with friends and strangers. . . Is that a wise use of money? Probably not, but it is very much the way most of us on this forum think. Cobras are immensely impractical cars so it is completely sensible that those who own them want impractical amounts of engine power.

Mark Donohue said, "If you can leave two black stripes from the exit of one corner to the braking zone of the next, you have enough horsepower." I doubt his quote would have been remembered if he had said, " .. you don't have enough traction."
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Old 09-08-2022, 09:33 AM
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Quote:
Originally Posted by cobragene View Post
FE 428 10:1 780 Holley vac sec open 3/4-7/8 with the lightest spring ,tall oval air cleaner, RPM performer, edelbrock heads, 36 total timing, hyd. Cam .539 280 ,at .050 230 lobe sep 110. 350 gears 29” x12” MT S/R tire, WR toploader. Runs great I just feel I am leaving some on the table, may try to get some Dyno and tune time. The tubes in side pipes are rather small, I guess that would be a good and cheap place to start? Any feed back would be much appreciated.
I'm running a similar mill, but slightly heavier on cubes and cam. I replaced my original Yokohama tires with MT S/Ts. If I stab the throttle more than an inch or two the tires break loose. If I give it WOT it literally scares the crap out of me, even after 16 years. I think the same ought to apply to your car as well, so I think something is not right. Now, that doesn't mean you have something big wrong, like a broken connecting rod, rather it means something small is not set right, because you say the car runs great. I think the solution is something really simple and easy and if I was standing over your car on a Saturday afternoon I bet I could find it pretty easily. With that in mind, the first thing I would check is that your progressive throttle linkage is opening all the way. Have someone get in the car while you stare at the linkage, have them push the throttle to floor and see how far the throttle linkage opens, then do it by hand and see if you can open the linkage farther by hand than they could by foot.

Last edited by patrickt; 09-08-2022 at 09:37 AM..
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Old 09-08-2022, 05:21 PM
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If I wanted to do a burnout, in a parking lot with no obstacles I'd raise my rear air pressure from 18psi to maybe 28?

I pay for my own tires.
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Old 09-08-2022, 07:20 PM
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Quote:
Originally Posted by mrmustang View Post
Have you checked your rear upper shock mounts?


Bill S.
Yes. I modified the rear shock mounts years ago and run the 335 PS2 Michelins. 514 has a lot of torque.
Sorry for getting off topic. I run a Bigs 950 CFM Stage 2 on my 514.
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Old 09-09-2022, 06:59 AM
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Good point Patrick and that was the case which I corrected about 6 months ago, it was opening 80-85% but not much improvement. I even wired the vac sec closed and not a great deal different, the most I can get them to open is about 85% with the lightest spring. It feels more like a potent small block.
Incoming I don’t really want to do burnouts, I am just using that as a gauge if you will, I run 25 psi.

Last edited by cobragene; 09-09-2022 at 07:02 AM..
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Old 09-09-2022, 08:23 AM
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Good point Patrick and that was the case which I corrected about 6 months ago, it was opening 80-85% but not much improvement. I even wired the vac sec closed and not a great deal different, the most I can get them to open is about 85% with the lightest spring. It feels more like a potent small block.
Just so that I'm clear, and forgetting about your secondaries for the moment, you're positive that your primary butterfly valve is opening 100% when the pedal is pushed all the way to the floor. That's 1/2 of our primary goal, which is to ensure that both the primaries and the secondaries are opening 100% under peak load. With a vacuum secondary carb, the secondaries can not function at their best unless the primaries are opening properly. If you are absolutely sure that the primary side is opening 100% (and the only way you can tell is to remove the air cleaner and look down the top of the primary side of the carb while somebody steps on the gas pedal) then we'll move on to the secondaries. If you can't get the primaries and secondaries to open 100% fully when you're flooring it while going up a hill then there is no point looking elsewhere for the problem until you remedy that one.
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Old 09-09-2022, 09:22 AM
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I did check again yesterday, looking at the butterfly’s they are opening fully. Would my old air filter element which is shorter create more vac to open secondary’s more? I want to try that but it’s off the road for a few more days. Thank you for your help
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Old 09-09-2022, 09:35 AM
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I did check again yesterday, looking at the butterfly’s they are opening fully. Would my old air filter element which is shorter create more vac to open secondary’s more? I want to try that but it’s off the road for a few more days. Thank you for your help
Yes, restricting the air flow to the carb will actually make the secondaries open sooner. That's why you often read threads on other forums where guys buy expensive free-flowing air cleaners and then complain that it made their car run slower (because the secondaries are no longer opening). Of course, for best performance you want as much free flow as possible and then tune your vacuum secondaries to open properly based on the new venturi vacuum values. One simple and easy test is to wire your throttle in the wide open position and then reach over to the vacuum secondary and with your finger push the plunger up in to the housing and see if the linkage feels reasonably smooth. If you were able to put your fingers down to cover the holes that lead from the venturis to the vacuum secondary canister you could then let the plunger loose and it should stay put. But doing that requires three hands. If the the plunger did not stay put that would indicate a leak in your diaphragm or maybe the little cork gasket.
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