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Kirkham Motorsports

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  • 2 Post By Morris
  • 1 Post By saki302
  • 1 Post By t walgamuth
  • 4 Post By spdbrake
  • 2 Post By Tom Wells
  • 1 Post By saki302

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  #1 (permalink)  
Old 06-24-2022, 04:37 PM
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Default Scary Handling

Was hoping to lean on the wisdom of fellow Back Draft RT4 owners here. About a month ago I purchased a beautiful RT4B with the Roush 427 motor and Tremac transmission. The car is stunning to look at and rocket ship fast, but the handling does not feel like it would be good for track days. For reference sake I am a very experienced SCCA road racer so I do notice exactly what the car is doing when I push it in the turns.

My main gripe is that the rear suspension feels like it needs more rebound dampening and probably more spring rate. However I understand that the shocks are non-adjustable for rebound dampening. Also the steering rack is too slow for track work.

Are there any solutions to this for the RT4? When I called Back Draft they told me there are no other shocks or steering racks available for the car.

Thanks
Gary

Last edited by Kartracer; 06-28-2022 at 04:39 PM..
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Old 06-24-2022, 05:05 PM
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Welcome to the Cobra world.

They're all like that.

First, the car has way more horsepower and torque that can be mechanically transferred from the power train to the road surface. Typically the tires are the weak link. Cold tires on cold pavement make the situation even worse.

Second, the short wheel base magnifies over-steer and under-steer events (wheels breaking loose) by an order of magnitude.

It's the nature of the beast.

You may improve it but you won't eliminate it.

Having a small block car by the nature of the lower hp does make it less deadly and more streetable.
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Old 06-24-2022, 05:26 PM
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Are they all like this, meaning all manufactures? For instance would a Superformance be an improvement or basically the same thing?

It honestly seems like the pogoing is so solvable as well as the slow steering rack. Just needs more rebound dampening at the rear to slow the pogo down, steering rack that is more like 2 turns lock to lock instead of 3 1/2. Sadly it doesn’t seem like these fixes are available.
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Old 06-24-2022, 05:59 PM
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As they say “Speed Cost.....How Fast do you want to go”....

Every car is different and only the pro’s change thing to get the chassis to do what you want it to do.

Many folks just think building the car is all you do......not at all.....you have to then test and change much like a race car.....the mfg’s are not interested in sorting out a chassis.....

And the original cobra’s were terrible susp3nsion set ups....start with your bump steer on the front as well as the rear.....
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Last edited by Morris; 06-24-2022 at 06:04 PM..
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Old 06-24-2022, 10:53 PM
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The Cobra Valley upgrades on the superformance cars take away all the bad tendencies.

Stock, on my first drive home I took a left up my hill, and gave it a *little* gas- I almost had brown underpants..
Decade old tires did not help.

With the new suspension and better tires on the track, the only thing you have to watch for is trail braking oversteer and lift throttle oversteer- though the second is nearly nonexistent with the suspension upgrades.

-Dave
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Old 06-25-2022, 05:52 AM
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The 2.5 turn lock to lock rack is available from Speedway motors. If your cobra is like mine it has a T bird rack in it. Mine is power.
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Last edited by t walgamuth; 06-27-2022 at 08:01 AM..
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Old 06-25-2022, 08:44 AM
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Get a corvette.
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Old 06-25-2022, 09:02 AM
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The t bird rack is a direct bolt in from flaming river.
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Old 06-25-2022, 02:27 PM
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Quote:
Originally Posted by t walgamuth View Post
The t bird rack is a direct bolt in from flaming river.
This was the only t-bird rack I could find there. Do you have any more info?

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Old 06-25-2022, 03:04 PM
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There are several threads on this subject in the Backdraft forums on this site. Folks have removed the manual MR2 rack and used a power Z3 rack with success.

The search function is your friend. I never need to ask questions as there is so much info on every subject here, which is great.

Even google searches using BDR cobra steering, or Backdraft cobra steering for example finds results faster on this site than the internal search engine.
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Old 06-26-2022, 04:07 AM
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Kart,

A suggestion from left field: your rear shocks may be a little too short.

Left field means I have a Jag rear, not BMW.

Having said that, my symptom was the same: in hard cornering the carís rear would skip sideways - kinda like the pogo-ing you referred to.

I substituted shocks that were about 1Ē longer and that problem went away.

Shot in the dark,

Tom
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Old 06-27-2022, 10:24 PM
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The standard problem with stock superformance cars is too much rear and not enough front sway bar. Worth checking into also.
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Old 06-28-2022, 01:15 AM
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Quote:
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Kart,

A suggestion from left field: your rear shocks may be a little too short.

Left field means I have a Jag rear, not BMW.

Having said that, my symptom was the same: in hard cornering the carís rear would skip sideways - kinda like the pogo-ing you referred to.

I substituted shocks that were about 1Ē longer and that problem went away.

Shot in the dark,

Tom


So, not enough droop/rebound travel?
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Old 06-28-2022, 04:51 AM
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Quote:
Originally Posted by saki302 View Post
The standard problem with stock superformance cars is too much rear and not enough front sway bar. Worth checking into also.
What he said ^^^

In these light, short wheelbase cars with IRS, it's a common mistake to over stiffen the rear suspension with sway bars and stiffer springs that are really speced for cars weighing hundreds of pounds more. After experimenting with the Jag rear in my Unique, I went with lighter springs and no rear sway bar at all which gave me the optimum balance between ride and handling for spirited street driving on very twisty (and often bumpy) roads. The original setup used stock Jaguar springs installed by the previous owner and they were ridiculously stiff. With the lighter springs and no rear bar - yes, there was a tiny amount of body roll but it wasn't significant and with the rear suspension allowed to travel freely, the ride was supple and comfortable. The rear end would plant far better when getting on it early out of a tight turn and the previous tendency to skip out on hard exits when the surface was a bit uneven was completely gone. Those who track their cars will need the extra stiffness in the rear, but for me - the ride and handling were spot-on. Cobras don't have to live up to the rep of being uncomfortable and ill-handling. Check out some road tests of street 427 Roadsters and in some of them you'll find the testers pleasantly surprised by how nicely the cars rode and handled.
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Old 06-28-2022, 06:26 AM
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I took off the rear bar on mine looking for more rear grip. It works fine without it and if coming off a corner hard it will lift the inside front wheel.
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Old 06-28-2022, 06:35 AM
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Quote:
Originally Posted by bobcowan View Post
This was the only t-bird rack I could find there. Do you have any more info?

https://www.speedwaymotors.com/New-T...aign=CSEGOOGLE

Mine looks like this. Two large bolts holding it in. IIRC there are numerous options available. I believe mine has an aluminum barrel instead of steel. I would recommend calling them before ordering.

I also suggest buying a new rack over a rebuilt. I have the same rack in my 39 Studebaker Coupe Express which has a fat man front suspension and mustang 2 style suspension. It has an annoying inch of play.

In the Cobra I am running with a chevy ps unit, the Studey has a mb pump which came on the mb engine.
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Last edited by t walgamuth; 06-28-2022 at 06:42 AM..
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