Mono vs Twin Tube Design... And Preferred Spring Rate?
 

Basic rundown:
'87 TII w/400+whp w/no accessories with only carpet, seats, and a radio
Will see most of its time on the street with aggressive driving through the mountains
Will see track use (Road Atlanta being the most as its just a few minutes away) periodically

My question to both the die hard, track only car and the street/track warriors such as myself... What is your preferred spring rate for your car and why? Preference on the subject of mono tube or twin tube design?

I am new to the fine tuning of suspension game so excuse my ignorance. After researching for days on what type of setup I should be getting for my car, it seems mono tube is the general rule of thumb of awesomeness. But why? I was planning on picking up a set of the Tein Flex's only to find that the mono tube design is only offered for the FD whereas a twin tube design is the only offer for the FC.

Also in comparison to many other options, the Tein Flex's look to be a considerable amount softer than the competition (6kF/5kR). For my intentions with the car, it seems a 7kF/6kR would be damn near perfect.

Anyway, thanks for your time. If you could, please respond with what "category" your car would fall under and your preferences to keep it cleaned up and easy to read for anyone else that may have concerns with this.

-Tyler

Stripped Track only car:
Struts: AWR racing E-Prod Bilsteins
550 lbs/inch spring front
Shocks: AWR Remote reservoir Blsiteins
400 lbs/inch springs rear
Suspension techniques sway bars front and rear, both in stiff setting.
Splitter + rear wing

Car is 2305 lbs wet. 400 rwhp on Yokohama slicks. Beats up on Corvettes and Porsche GT3's regularly

-Trent

Just curious, would you happen to have a picture of your car? I feel that there's not enough pictures floating around of the track only 7's.

Are the AWR bilstiens adjustable?

By twin tube do you mean the ancient style where there is no barrier between the gas and the oil? Or a modern damper that has an external reservoir?

Sorry. I'm referring to the older style in modern dampers. IE: a 'tube inside of a tube'... Not an external reservoir setup as those are just out my budget.

Gotcha. Well they both have advantages and disadvantages. I was surprised to see that the Tein Flex and Super Drift are both twin tube design.

Twin tube advantage: longer available stroke in a given package length
Disadvantage: Oil isn't isolated from the gas, so foaming can be an issue, narrower piston gives less room to engineer the valves.

My own setup is a 1990 T2 with the Tein Super Drifts, an RB front swaybar and no rear bar. I picked the SD based on spring rates (no drifting for me), the Flex had very similar spring rates to my old K2RD setup that used KYB AGX struts and I wanted something stiffer. Interestingly, the Flex has stiffer struts than the Super Drift, even though the drifts have stiffer springs. Tein will custom valve things if you know what to ask for though. I've attached the shock dynos they sent me, which are made with the dampers set to full stiff.

The engine was built to go to high HP levels as I progressed but I ended up never needing more power (I used it for HPDE, and more power just means you use up the consumables quicker) so I ran it on low boost on the stock turbo and IC, ~213HP at only 8PSI. The handling was pretty neutral with this setup. The car is still around (and is going up for sale as soon as I find where I put the title!) but has been retired from track duty as I purchased a proper race car so I could start racing instead of doing DE. (The FC doesn't have a class it would fit into)

On the chart, rebound is on the top and bump on the bottom, left is front, right is rear.

Edit: Depending on how old you are, the Super Drift is too stiff for street driving, especially if you plan to drive it a lot. It puts a smile on your face when you hit a curvy road, as long as it isn't bumpy.

Thanks for your insight, Gene. Definitely some good info to chew on.
Also if it is of any interest, I am planning on running 275 up front and 315 out back with 400ish whp.

And as far as age, I'm pretty young according to the birth certificate... But the handicap tag and back surgeries makes me as old as they come! With primary street use, it seems like the rate with the Flex's is the way to go while still being 'sporty' and responsive.

I have JIC FLT-TARs on my FC which have monotube dampers (inverted monotube up front) with 7kg/6kg springs. and I would have to say the spring rates are pretty good for the street as long as the roads are too bumpy. I would definitely take my rear sway bar off though with those rates, the car got much more stable after I did.

overall I'm fairly pleased with them. but would go a different way if I were to do it again. (probably AWR strut housings with bilsteins or koni race shocks.)

kinda
 

AWR's are height adjustable; but you'd have to have the tubes re-valved to accommodate the new spring rate.

http://www.rxracing.com/wp-content/u.../Indy20082.jpg

http://www.rxracing.com/

Is someone driving that car?

we tried a bunch of different spring rates on the FC, and we found that the drivers liked it better with 8/6 or 8/5, but laptimes don't drop much if at all running something like the 350/225 setup.

the big difference is that 350/225 rides like stock. so if you would like a softer sprung car, its doable and it won't hurt your laptimes measurably

as far as shocks go, most of the locals skip the JDM/CDM stuff and go right to something good like koni

#27 pics
 

The car has come a ways since that pic above. Latest stuff is on my blog at www.rxracing.com

The bilsteins are non adjustable. One less thing to mess with at the track, which keeps me happy.

I had the K2RD kit with those rates before I went to the super drifts, I'd hardly call it riding like stock :) I'm from NYC where the streets are an unholy mess though. Once you get to the highway it's fine.

well now, paul ko's wife (of k2rd) and i have matching FC's. they are both blue 87 gxl's with ABS, built 1 month apart even.

mine is low mileage and 100% stock, theirs is higher mileage, and its stock except we took the 350/225/agx combo off the race car and put it on this one.

as an aside after 2 seasons of racing, and 3-4 of trackdays, the agx's were still good, which was a pleasant surprise.

anyways, they do ride differently, but the differences are weird. on a smooth road the 350/225 is a little, jiggly it doesn't compress the spring much. on medium and bigger bumps they are more equal, the factory suspension can be a little floaty too.

i looked at the spring rates vs travel once, and it made sense as to why the rides are like they are. the factory used a soft spring that is compressed quite a bit stock. its something like a 100lbs spring compressed 4-5"

so the amount of force it takes to compress the next inch between the stock spring and the 350 spring, is actually fairly similar, but the second inch, the stock spring takes like half of stock, as the compression puts them on different curves

this isnt a super serious post, but we do actually have a good condition stock suspension car floating around