30mm or 27mm torsion bars?

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Bareass
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30mm or 27mm torsion bars?

Post by Bareass » Wed Jun 12, 2013 12:58 pm

Hey all
I'm looking to rebuild my suspention. I have Koni yellows with Shenkle SS Rear Springs, and stock torsion bars and sway bars, on my 84 GTV6.

i was thinking of taking the front sway bar from my Milano Verde parts car, and looking at springs.

the car will be run on the street with track days fairly often.

would 30mm TBs be too sticff for the street?
would 27mm TBs be too soft for the track?
Is there something else i should look into?

Thanks all
Bareass
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Re: 30mm or 27mm torsion bars?

Post by fedezyl » Wed Jun 12, 2013 7:26 pm

I have 27mm bars with koni yellows in my giulietta, it's great for the street and the occasional trackday, add a thicker roll bar and you are set for the track too.

30mm are too stiff I think.
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Re: 30mm or 27mm torsion bars?

Post by Duk » Wed Jun 12, 2013 9:29 pm

How about 28-29mm bars?

For the short bars:
22.8mm TB has a WR of 93lb/in.
25.4mm TB has a WR of 143lb/in.
27.3mm TB has a WR of 191lb/in.
28.7mm TB has a WR of 233lb/in.
30.0mm TB has a WR of 279lb/in.
32.0mm TB has a WR of 360lb/in.
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Re: 30mm or 27mm torsion bars?

Post by Bareass » Thu Jun 13, 2013 3:54 am

i haven't seen 28 or 29mm bars.
I've only seen 27, 30, and 33.
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Re: 30mm or 27mm torsion bars?

Post by Duk » Thu Jun 13, 2013 5:12 pm

Pace Engineering and I believe Beninca, here in Australia can provide them.

Either that or you buy some 30mm bars and have them machined down.
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Re: 30mm or 27mm torsion bars?

Post by Mats » Fri Jun 14, 2013 12:23 am

30mm bars on a super light 75TS is a nice street setup with the right shocks, Koni is not the right shocks for a 75/Milano. Not ever. They do nothing.

IMO it's very difficult to go too stiff up front with torsion bars, get the largest you can and adjust rear spring rate to suit. But you must get some other shocks!
Mats Strandberg
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Re: 30mm or 27mm torsion bars?

Post by Duk » Fri Jun 14, 2013 1:13 am

Mats wrote:30mm bars on a super light 75TS is a nice street setup with the right shocks, Koni is not the right shocks for a 75/Milano. Not ever. They do nothing.

IMO it's very difficult to go too stiff up front with torsion bars, get the largest you can and adjust rear spring rate to suit. But you must get some other shocks!
Too large and you wreck the chassis!
The fact is, these things have a feeble chassis. Too much spring (too fat a torsion bar) results in too much chassis flexing! The end results are cracks and general loosening of the spot welds.
Get the right TB matched with the right dampers and match those with the right rear springs with the right dampers!

Learn the importance of natural frequencies and go from there. :wall:
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Re: 30mm or 27mm torsion bars?

Post by Bareass » Fri Jun 14, 2013 4:42 am

i don't know if this makes a difference, but i have an 84 gtv6 with the longer TBs, not a 75
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Re: 30mm or 27mm torsion bars?

Post by kevin » Fri Jun 14, 2013 3:25 pm

28mm bars work well but for pure track solid 33mm are perfect but then roll cage is a given and will stiffen chassis along with extra welds which also stop chassis tearing underneath . Just put an RS kit on and stay on generally smooth roads .
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Re: 30mm or 27mm torsion bars?

Post by 75evo » Fri Jun 14, 2013 10:15 pm

30mm torsion bars are ok. Beninca sells the torsion bars, and re-valved konis as a package. Excellent package. RS kit is also excellent, tested them on a friends 24v milano.
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Re: 30mm or 27mm torsion bars?

Post by Mats » Sat Jun 15, 2013 11:43 am

Duk wrote:
Mats wrote:30mm bars on a super light 75TS is a nice street setup with the right shocks, Koni is not the right shocks for a 75/Milano. Not ever. They do nothing.

IMO it's very difficult to go too stiff up front with torsion bars, get the largest you can and adjust rear spring rate to suit. But you must get some other shocks!
Too large and you wreck the chassis!
The fact is, these things have a feeble chassis. Too much spring (too fat a torsion bar) results in too much chassis flexing! The end results are cracks and general loosening of the spot welds.
Get the right TB matched with the right dampers and match those with the right rear springs with the right dampers!

Learn the importance of natural frequencies and go from there. :wall:
Have you seen this or is it old wives tales?
We've all heard it but I have never seen it, I have seen a broken torsion bar mount in the cross-member but that was on a track car that had been driven hard on the track with 30mm bars for ten years and it was rusty in the area in question. Never ever seen a cracked alfetta chassis.
Mats Strandberg
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-onemanracing.com-
-Strandberg.photography-

GTV 2000 -77 - Died in the fire.
155 V6 Sport -96 - Sold!
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Re: 30mm or 27mm torsion bars?

Post by Duk » Sat Jun 15, 2013 4:58 pm

Mats wrote:Have you seen this or is it old wives tales?
We've all heard it but I have never seen it, I have seen a broken torsion bar mount in the cross-member but that was on a track car that had been driven hard on the track with 30mm bars for ten years and it was rusty in the area in question. Never ever seen a cracked alfetta chassis.
1 of the guys, Sheldon, on 1 of the Australian Alfa forums showed pictures of cracks in the chassis of his 90. http://www.alfaclubvic.org.au/forum/ind ... 7#msg48547

He was using 32mm bars and some 6 to 12 months before he showed his pictures, I had asked about what TB's people were using in their road going cars.
http://www.alfaclubvic.org.au/forum/ind ... 1#msg30561
Sheldon McIntosh wrote: I'm running 32mm TBs on the track car, combined with yellow Konis (which haven't been revalved to suit yet), which I thought would be hellishly stiff on the road. It's actually bloody fantastic on the road, and I will be doing it to all future V6s I own. Cuts down any hint of wallow on freeways, and over expansion joints and such the car is just so flat and composed. It's definitely not too harsh over bumps (except for very, very sharp ones), and overall I would say the ride is more pleasant than with standard TBs.

My girlfriend even managed to fall asleep on the last EMR I did in the car, so the ride can't be too bad. Although as I'm doing my engine swap at the moment I did discover a couple of cracks in the headers.....Carbon Monoxide doesn't make you sleepy does it?
A 32mm TB has a WR of 360lb/in and the car still manages to have a great ride quality??? :?
Only because the chassis is doing more twisting than the torsion bars were. :shock:
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Re: 30mm or 27mm torsion bars?

Post by kevin » Sat Jun 15, 2013 11:09 pm

My chassis on race car started to pull apart where the torsion bar mounts joined the floor . I had original Auto delta rolled spline 28mm torsion bars WITH RS font coil overs . But our roads to the track used to be horrendous as I even lost my exhaust on the old road to Swatkops . Once the roll cage was properly welded in and a few touch up welds underneath it was perfect for its last four years . ( oh an they fixed that road)
There were a lot of gtv3.0 that came with 28mm bars here but if you could find a good quality 30mm then that would be best for your situation . GregSef calculated I would need a 33mm to replicate my current coil over set up which is 180kg up front . But that was full track set up . Can't tell you what it is in lb as in work with SI units .
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Re: 30mm or 27mm torsion bars?

Post by Mats » Sun Jun 16, 2013 1:36 am

Strange, the cracks would originate from where the stress concentration is high, this seems to be in the area where the castor-rod mount blends into the general engine bay surface?
What kind of bushing does he use? A stiff poly bushing in there would introduce twisting loads not present in the original design.

Smooth Koni shocks? Guess he has them on the loose setting... :lol:
Mats Strandberg
-Scuderia Rosso- Now burned to the ground...
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GTV 2000 -77 - Died in the fire.
155 V6 Sport -96 - Sold!
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