IRS Chassis flex?

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fastbacker
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IRS Chassis flex?

Post by fastbacker » Wed Feb 25, 2009 2:12 am

I'm wondering where and how much the type I irs chassis flexes under hard cornering with, say wide tires and a stiff suspension. My guess would be the rear torsion tube in relation to the pan/body and also the front beam in relation to the pan/body. Not sure how much though.

The reason I'm trying to figure this out is to possibly weld in some reinforcement bars to stiffen up my "in the works" 69 street bug. The car's at my friends fab shop undergoing a major transformation. The front end is done and we're getting ready to move onto the rear suspension. Then the engine and tranny. The parts list (all of which I have) are:

-3" narrowed beam
-CB dropped spindles modified by Lanner to accept 944 turbo calipers
-944 turbo narrow arms, t-bars spring plates and brakes
-901 5speed w/ lsd converted using all of [email protected] parts
-914 2.4L converted with DTM - 195hp
-964 wheels (6&8X16)

helowrench
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Post by helowrench » Wed Feb 25, 2009 10:49 am

I have been keeping my eyes open for a list of the stiffening sheetmetal used for the 'vert chassis. these parts would go a long way to achieving the goal you seek. If you find any info please share with us.
Also look into a "kafer brace" as it ties in the engine mount horns, and the shock mounts to allow them to stiffen up each other. (this can be done with generic rod ends from Grainger/Tractor Supply with hand fabbing, I would also make an attach to the boby sheetmetal over the trans or so)

Rob

kdf
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Post by kdf » Wed Feb 25, 2009 4:49 pm

The rear suspension mounts are important, but there isn't much you can do to bring more camber stiffness. You can of course change to urethane bushings (or in extreme case metallic bushings). I would prioritize stiffness in this order: Camber and toe stiffness, damper mount stiffness and as last torsional stiffness.

With the power you'll have, you will want to stiffen the engine mounts.

I know you mentioned that you've already done the front, but stiffening the front beam is important so I wanted to mention it. You can move the beam just by standing on it in stock form.
Changing the rubber to urethane between the steering shaft and the steering box also makes a small difference.

The devil is in the detail. The stock bug isn't made stiff because it wasn't meant to be a sporty car.

fastbacker
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Post by fastbacker » Thu Feb 26, 2009 1:24 am

kdf wrote:I would prioritize stiffness in this order: Camber and toe stiffness, damper mount stiffness and as last torsional stiffness.


I know you mentioned that you've already done the front, but stiffening the front beam is important so I wanted to mention it.
I'm sure it's not easy to explain but I'll ask anyways, how?

Thanks for the informed input!

volkdent
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Post by volkdent » Thu Feb 26, 2009 1:53 am

These may be helpful tied into the beam stiffeners...

http://www.eyeball-engineering.net/Floo ... fners.html

Jason

helowrench
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Post by helowrench » Thu Feb 26, 2009 11:17 am

thanks volkdent, I knew I forgot something.

There is also a stiffener that connects the lower bar of the front beam to the two bolts that are at the front of that floorpan stiffener.

I am unable to find pics of them right now, but I remember that they looked easy enough to make.

rob

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681tonburb
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Post by 681tonburb » Sat Feb 28, 2009 8:15 pm

I was thinking of this to before I started my rebuild so I just had a tube frame built for my car. I would think its going to be alot stiffer then the VW pan was.

Image

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bugninva
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Post by bugninva » Sat Feb 28, 2009 8:18 pm

very nice.... :wink:

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681tonburb
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Post by 681tonburb » Sat Feb 28, 2009 8:51 pm

Thanks I need to get some updated pics now that it has a floor and the welds are cleaned up. It will also have the 944 aluminum arms and Brembo brakes on it soon.

fastbacker
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Post by fastbacker » Sun Mar 01, 2009 1:03 pm

I'm curious if you could weld the stock tunnel on that pan to retain the vin.

helowrench
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Post by helowrench » Sun Mar 01, 2009 2:21 pm

add the rear mount points, and then you can just bolt the ENTIRE 924/944/968 rear torsion tube housing and supension right in.

BTW did you make drawings for that beautiful frame, if so, how much do you want for a copy?

Rob

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FJCamper
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Chassis Flex

Post by FJCamper » Sun Mar 01, 2009 6:56 pm

Image

Yes, the Type 1 chassis flexes, and it's worst place is right where you see the yellow highlight.

The only genuine fix I know of for it is a rollbar system that ties the rear shock supports to the main hoop and then to the chassis near or beside the seats.

Our current bar connects to the body in the rear cargo area, which of course helps the chassis somewhat, and the chassis floor just ahead and beside the seats. We tie the front contacts together crossways under the car with a heafy piece of aluminum U-channel mountd open side down.

It makes a nice front jack support bar.

FJC

fastbacker
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Post by fastbacker » Mon Mar 02, 2009 2:50 am

So are you saying a six point rollbar with the front bars (door bars) coming off the main hoop and and going down diagonally to the heater channels just in front of the seats?

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681tonburb
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Post by 681tonburb » Mon Mar 02, 2009 3:38 am

I’m sure you could just weld the tunnel over the frame so that the vin plate is there. We don’t have to worry about that here no one is going to check it.
I thought of using the 944 torsion tub and bolting it on but the 944 track with is to wide. The 944 is 68 and the bug is 60.
I didn’t build the mane part of the frame I had it built so that it could be done in a jig I was worried if I did it my self I wouldn’t get it straight. I was delivered to me like you see it in the pic and then I added the rear suspension and floors. Originally I was going to add a mustang front suspension on it but I ended up needing to save some cash so I decided to use a VW front end now.

helowrench
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Post by helowrench » Mon Mar 02, 2009 9:49 am

Type 3 is also a bolt on affair.

swingaxle torsion assembly has the engine frame horns on it, while the IRS does not have the engine mount horns. track width should be the same as well.

Rob

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