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  #1 (permalink)  
Old 10-07-2008, 06:55 PM
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Talking What's your Cobra's top speed?

I've been looking into options for diff and gearbox (T56) ratios and came across this gear ratio calculator. So I entered 6500rpm, 4.11 diff, 0.50 trans gear and 275/50/17... nearly 252mph!!

http://www.corral.net/tech/gearcalc.html

It left me wondering, is it likely that anybody has really driven a Cobra at 200mph (ala Shelby's Super Snake)? Without major downforce assistance of course.

What top speeds were you guys getting at the Nats over the weekend?
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Old 10-07-2008, 07:05 PM
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I've got 3.91:1 gears in mine and they feel nice. I reckon any shorter than that and it will be wheelspin city. It's pretty lively with 3.91.

6th gear is really just a economy overdrive in the T56. You are better off looking at your speeds in the lower gears.

I reckon the ideal in a T56 equipped Cobra for street and track would be 3.73 or 3.91

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Old 10-07-2008, 07:20 PM
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You're right Mike but the question remains... just how fast can a house brick fly?

I have the option of swapping my Skyline 4.11 centre with 3.89 diff + axles from a 200SX.

Also Mal Wood offers custom gear sets... check out the available ratios under "Cobra's".

http://www.malwoodauto.com.au/

I get confused at this point... which of those options would make my 0-100kph drive ratio longer using the 4.11 diff?
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Old 10-07-2008, 07:20 PM
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I dont think there would be enough room in the drivers compartment for a set of nuts big enough to do 200MPH in one of these cars, I read somewhere that 165MPH was pretty much it but then that was with the old suspension.
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Old 10-07-2008, 08:12 PM
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Sambo, check ya email .... sending you an excellent gear calculator.
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Old 10-07-2008, 08:27 PM
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Thanks Les, got it.
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Old 10-07-2008, 08:32 PM
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Sambo You can even play with custom gear sets with that calculator as it doesn't rely on a data base of production transmissions.

Remember tho, it's in MPH not KPH
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Old 10-07-2008, 09:05 PM
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Yeah I saw that. I'll convert it to kph when I get a chance.
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Old 10-07-2008, 09:15 PM
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Yep, I'm gonna do mine too.... just not got around to it.

My gearing is that shown on Calc 5.

My thoughts are these:

For strictly a road car with a mild cam .... 3.31 or similar
For a road car with a mid size cam which will see some track work ... 3.50 or similar
For a Track car with large cam which will see some road work ... 3.70 or similar

That's using the Tremec T56 or TKO 600
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Last edited by Rebel1; 10-07-2008 at 09:22 PM..
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Old 10-07-2008, 09:43 PM
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Les, are you suggesting the bigger the cam, the higher the peak torque delivery?
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Old 10-07-2008, 10:13 PM
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Quote:
Originally Posted by sambo View Post
Les, are you suggesting the bigger the cam, the higher the peak torque delivery?
Nooo, not at all, but I am referring to where the peak torque occurs in the power/rev band.

On the track you spend most of your time in 2nd and third gears at higher RPM.

Not so on the street.
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Old 10-07-2008, 10:17 PM
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With modern transmissions (overdrive) I reckon you might as well go around 4 to 1. I have a 3.91 to 1 and revs are still quite low on the freeway thanks to overdrive. Unless you want to break the land speed record I cant see the point in installing tall gears (like 2.92 or 3 to 1) with a modern transmission.
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Old 10-07-2008, 10:51 PM
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Quote:
Originally Posted by cameron02 View Post
With modern transmissions (overdrive) I reckon you might as well go around 4 to 1. I have a 3.91 to 1 and revs are still quite low on the freeway thanks to overdrive. Unless you want to break the land speed record I cant see the point in installing tall gears (like 2.92 or 3 to 1) with a modern transmission.
That depends I feel on what first gear ratio you have. If for instance you had a TKO500, earlier 3550, or T5 with a 3.27 first you could/would only use it for pulling stumps. It would be way too short and cause so much wheel spin one wouldn't use it. It would be faster and as effective to start in second.

Even a 2.66 first T56 with a 3.91 rear will give you tyre frying take off so may be more effective with a 3.7 rear. I tend to feel the more torquey engines would be better off the 3.5 or 3.7.

At the other end of the rev range it would be cam dependent. ie a T56 with a .74 fifth and 3.91 rear will be pulling 2100rpm at 100KPH.. In 6th at the same (legal) speed it would be at 1420rpm so even with a mild cam it (6th) may well not be truly usable until you got well into the 130KPH mark at 2150rpm.

All very personal tho.
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Last edited by Rebel1; 10-07-2008 at 11:23 PM..
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Old 10-07-2008, 10:57 PM
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Quote:
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Nooo, not at all, but I am referring to where the peak torque occurs in the power/rev band.
That's what I meant.
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Old 10-07-2008, 11:05 PM
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I think Sambo that this question can be answered by any of the 6ltrs LS$ ( because Sambo has a 6Ltr) owners who were at the nationals.

What rear end do they have, what gear box, what tyres, and how did they perform of the track.

If they then also commented on the same car as a road car we would all have something real to compare rather than theory.

Who had 6Ltrs of glorious chev/holden power at the Nationals?.
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Old 10-07-2008, 11:19 PM
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How long is a piece of string,
It's not how fast you want to go ,it's how long do you want to spend in the lockup
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Old 10-07-2008, 11:32 PM
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Hey Sambo

when you're done maybe you can rustle up a few Vics and we can head over to Lake Gairdner (SA) and clear the pipes

http://www.dlra.org.au/
(dry lake racers Australia - I think Deb/Doug were considering going to speedweek this year until cancelled)

Just on the whole rear ratio thing - If I had a T-56 and overdrive then I'd be going for pretty high(numerically) diff ratios, you'll have more punch in the lower gears when you need it and still have the ability to cruise up the Hume to Winton

LoBelly
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Old 10-07-2008, 11:37 PM
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Quote:
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How long is a piece of string,
It's not how fast you want to go ,it's how long do you want to spend in the lockup
And that's why I suspect the early to mid three gears are good for the street. It's not about top speed. It's about a balance of performance,noise, comfort, and fuel consumption.

All of the Cobras I've driven have had the mentioned transmissions and rear ends ranging between 3.3 and 3.9 with engines in the 350 - 400rwhp mark.

It is very noticeable to me that those road cars using 3.3 or 3.5 are more pleasurable to drive on the street. You don't have to rev the snot out of them. You don't draw attention to yourself just taking off from a set of lights. Yet the same cars will fry the tyres at will.

Keep in mind also, that wheelspin is not necessarily fast, traction has always been a problem with these cars.

Track work however is a whole different story.
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Last edited by Rebel1; 10-08-2008 at 04:02 PM..
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Old 10-07-2008, 11:45 PM
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I know top speed is not what it's all about but we still haven't got any top speeds from the weekend!

I've heard that Cobras start to lift off the ground at about 230kph. Either that or your face begins to contort from all the turbulence? Like that old Bond movie when the villains put him in the gravitron.

Last edited by sambo; 10-07-2008 at 11:47 PM..
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Old 10-07-2008, 11:56 PM
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I believe that based on the laptop data from our car and confuring with Gary Walthers car we were doing approx 223kph at the flag.

SpookyPT
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