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29mm or 31mm tb's

I have a couple sets of tb's for my 84 narrow body turbo. I haven't weighed it yet, but after the mods I plan on doing I would expect something in the 2650#-2700# range.

Should I go with 31mm tb's or 29mm? I currently have both with ER polybronze bushings to be installed when I install the tb's. The car will be used for mostly street here in TX hill country and some DE's at some point when it's back on the road. I also have a set of coil over's but I understand there is some additional work that needs to be done there with regard to some gussets at the shock mounts in the rear? I was planning on running either 22mm or 23 up front. Custom valve shocks would follow.

How harsh are the 31's?

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84 911 Carrera w/ 930 t/p,efi'd,dizzy free,HFS turbo[/COLOR], 78 930 RoW no option sunroof coupe, 64 Corvette roadster, 71 911T, 73 911E, 67 Bronco survivor. 71 FJ40, 2001 Boxster
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Old 05-31-2013, 07:55 PM
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I just moved from 26 to 29 and did notice a significant increase in stiffness but I also went from stock front bars to 21mm. Not uncomfortable necessarily, but certainly harsher. On the other hand, it has improved squat significantly.
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Old 06-01-2013, 05:57 AM
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After few trials of different sizes, I run 22 & 29 with excellent results: firm, predictable and no rubbing. 31s are a little too stiff for the street IMO.
Old 06-03-2013, 06:43 AM
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tb

Quote:
Originally Posted by Miguel Antonett View Post
After few trials of different sizes, I run 22 & 29 with excellent results: firm, predictable and no rubbing. 31s are a little too stiff for the street IMO.
Thanks for the comments. I am leaning to either 22/29 or 22/31 all custom valve shocks.
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84 911 Carrera w/ 930 t/p,efi'd,dizzy free,HFS turbo[/COLOR], 78 930 RoW no option sunroof coupe, 64 Corvette roadster, 71 911T, 73 911E, 67 Bronco survivor. 71 FJ40, 2001 Boxster
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Old 06-03-2013, 09:03 AM
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BTW, I missed mentioning that I also have adjust Konis installed, and that made significant difference/improvement.
Old 06-03-2013, 09:50 AM
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I was wondering.
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84 911 Carrera w/ 930 t/p,efi'd,dizzy free,HFS turbo[/COLOR], 78 930 RoW no option sunroof coupe, 64 Corvette roadster, 71 911T, 73 911E, 67 Bronco survivor. 71 FJ40, 2001 Boxster
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Old 06-03-2013, 09:51 AM
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I have 22/29 mm torsion bars. Feels great on the street, but the rear is too soft for the track. Specifically, 22/29 is not balanced compared to a stock 930.

Stock 930 18.8 / 26

so 22 / 29 is 87% stiffer in the front and 55% stiffer in the rear

I am going to switch to 31s in the rear (keeping the 22s in the front) or go for 23/33

IMHO, I think the following are good setups:

21/29 56% stiffer front 55% stiffer rear
22/31 87% stiffer front 102% stiffer rear
23/33 124% stiffer front 160% stiffer rear

These rates are for 930s, for which people tend to want stiffer rears, however the logic might apply to narrow body turbo 911s too.
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Old 06-03-2013, 02:23 PM
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Quote:
Originally Posted by Yargk View Post
I have 22/29 mm torsion bars. Feels great on the street, but the rear is too soft for the track. Specifically, 22/29 is not balanced compared to a stock 930.

Stock 930 18.8 / 26

so 22 / 29 is 87% stiffer in the front and 55% stiffer in the rear

I am going to switch to 31s in the rear (keeping the 22s in the front) or go for 23/33

IMHO, I think the following are good setups:

21/29 56% stiffer front 55% stiffer rear
22/31 87% stiffer front 102% stiffer rear
23/33 124% stiffer front 160% stiffer rear

These rates are for 930s, for which people tend to want stiffer rears, however the logic might apply to narrow body turbo 911s too.
I agree the balance is critical or you will induce more understeer or oversteer than you would like.
I have 22/31 hollow bars in my street/track 930 and the ride is well controlled on track but not really too harsh on the street either. Could it be more hardcore for track yeah, but I do well enough by driving to track days with it while other faster cars get trailered to events. The ride on the street is not much more stiff than the stock bars were. The squat and dive are still present slighlty now, but not to the point I am rubbing tires. And my car is lowered to slightly less than euro ride height but not as low as some track only cars.
One added benefit I noticed was I wasnt detroying cv joint boots after track events because the suspension wasn't going thru such extreme ranges of travel as with the stock springs.

fred
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Old 06-04-2013, 09:22 AM
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I run 21/30's in my narrow (SC) bodied turbo. I don't know how much difference 930 versus 911 suspension pickups make. Must make some.

Rear was nowhere near enough to control squat with a 3DLZ, but seems fine with a K27/HF, as the power builds over 2000 instead of coming in with a bang over 3000...

The 21's are supple enough that the front stays stuck over ripples or on uneven road, instead of bouncing or skating over them. If I only ever drove on perfectly smooth asphalt, I'd probably put 22's in.

Oh, I daily-drive the car and have over 30,000 miles on this setup. It's firm, but I don't consider it harsh - probably should mention I run 225/45/17 & 255/40/17.

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Last edited by spuggy; 06-04-2013 at 07:22 PM.. Reason: Realised 17" wheels and low profile tires aren't a given...
Old 06-04-2013, 05:57 PM
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