I was just poking around their website and ran across this:
http://www.umiperformance.com/catalo...roducts_id=326

I've been looking for something stiffer than the typical 25mm solid rear bar but not as stiff as a typical drag bar. I was wondering:
- it lists it as now adjustable, showing 2 link holes, are they further forward or back than stock (forward would make it less stiff, back would make it stiffer
- has anyone played with moving the housing bushings inward to soften the bar?

1.25" should be about 31.75mm, I've been looking for something that will act like roughly a 27-29mm bar (assuming stock geometry), I'm wondering if u used the forward hole and moved the bushings in some you could get the equivalent out of this one?

 

no one has any thoughts? Not even UMI?

 

Hey 83. Sorry for the delay.

The holes on the drag bar lengthen the arm by 1" over stock.

I measured the torsional effective length at 34-1/2 inches for both bars (drag and 22mm). The arm length is 9" on both with the forward hole on the drag bar being 10".

The rate at the bar end was 241 lbs per inch deflection on the 22mm and 1005 lbs per inch deflection on the drag bar. Moving to the 10" arm reduced the rate to 814 lbs.

I use this calculator as a quick method for comparing bars. Standard disclaimer applies as this calculator is only a tool for quick comparisons and doesn't take into account all that happens to affect bar rate (material, arm deflection assumed as zero, etc).

http://www.circletrack.com/car_racin...tor/index.html

It's generally accepted that moving the bushings inward/outward produces a negligible change as you're still having to twist the same 34-1/2 inches of torsion bar.

ramey

 

Thanks Ramey. Good info, but pretty much confirms that what I wanted to do probably won't work, though i'm not sure that I agree that the bushing location is negligible, I think that a lot of autoxers have found that an inch or 2 can make enough difference that you can fell it on the course, I used to fine tune my 83 using bushing location and swapping rubber vs poly bushings on the back (usually wanted to make them softer).

That spreadsheet you linked to is pretty useful. now I'm thinking about grabbing the biggest street type rear bar that I can find, cutting part of the arm part off of it and welding on some flat pieces to work with heims like you use and make it adjustable from 7-10". I'm betting a 25mm bar with the attachment point at 7-7.5" would be stiff enough to work as a reasonably effective drag bar but still be easily adjusted to something that would be quite usable for street and autox use.

Do you guys sell your drag bar hardware separate from the bar (links, brackets, hardware)?

 

Fwiw hellwig and hotchkis make adjustable rear bars for the 3rd and 4th gen that are a bit more suitable for thing other than drag racing. Around 22m iirc. The hotchkis ones are hollow, the helwig ones are solid.

Just another option to look into.

 

Hey, good morning.

We do indeed sell the parts separately. Hit me at ramey@umiperformance.com for pricing.

It would be interesting to do some testing and see how much of a difference bushing location makes but at the moment, I just treat that variable as negligible. As an example, the spreadsheet considers the arms as "infinitely" stiff when in actuality the arm bends in addition to the torsional component of the center of the bar. So, a long arm bar loses more than a short arm bar. That's part of the fun of this hobby - tuning and seeing how things work.

ramey