how to keep it straight @ 150+ mph

[MakotoS13]

okay so i'm lookin for high speed stability. the S13 isn't long or wide enough. these are problems. we can add a few inches to the width of the car but the wheelbase is pretty tricky to jack with.

i'm hoping that positive caster will make the car significantly more stable at speed, have any of you guys tinkered with this much? i'm gonna have to get some more parts from SPL

mods:

KTS coilovers
SPL RUCA
SPL tie rod ends/Z32 inners
energy suspensions poly bushings all throughout

also, i've discussed this with a few S13 owners and my suspension is so stiff that sometimes on certain bridges it "bounces" or "bucks" due to the wavelike design that the segments of the bridge form. at the dang speed limit its like i'm in a saturn5 rocket. i dont think there is much we can do about this short of getting better spring setups (silkroad/whatever).

i figure that once i get more caster, wider wheels/tires, and the weight of the V8 up front it should correct a lot of these issues or at least help.

discuss.

[Drunk Bastard]

why, exactly do you want to go 150? i dunno if you're car will do it.....EDIT:just re-read and saw the v8 part (COOL!!!!)

anyways, if you wanna go 150 get a bike...but then again i remember that you were hatin on the guy who crashed his bike goin like 160...so....what are you gonna do?

:wtf:

[sr240mike]

I've gotten the 240 up to about 140+. All I had was a slight shudder due to possibly out of balance tires.

[spdfreek0o]

I think that the V8 will make your car unbalanced. Maybe softer spring rates or get a coilover that has helper springs, or a taller sidewall on your tire. Or just deal with the "bounces" and "bucks"

[s13driver]

a functional rear wing/spoiler might help in stability

[Var]

More caster...9º would do nicely

Toe in for the alignment. Creates stability at high speed

WIDE TIRES..at least 245's. If you can do stagger, go 245/275

Aero Kit...not just for jDM TyTe drifters

Functional Wing

And obviously make sure your suspension arms and everything are in good shape..which i know you do anyways.

Probably having a wider track would help too..but i'm not sure. So low offset wheels . Dont use spacers at those speeds.

[Var]

As far as gearing..what are you gonna do? You should run the 300zx TT diff. i think it's got a 3:90 gear ratio. Also run 18 inch rim/tires. Your v-8 *probably* wont have a very high redline...so think about that. I forgot the link to the top speed calculator.


edit: here it is

http://www.mysportscar.com/tools/topspeed.htm

and according to this (http://www.hardcore50.com/technical_articles/GearRatios.htm) website, you probably be using the T5 with the .78 5th gear ratio.

This means IF your car revs to 6500 rpm with the stock final drive of 4.08 with 275-40-18 tires, your top speed will be 162mph

[MakotoS13]

S15 diff with S15 ring / pinion. 3.5 i believe.

[redsuns3838]

i have NAMS tension rods and silkroad coilovers on my S14 but from what i felt when i had the tension rods installed, steering was a lot more confortable, and seemed easier to control. and you probly need new tension rods anyways if they are still stock so..id spring for sum if i were u.

[Mike Wazowski]

S15 diff with S15 ring / pinion. 3.5 i believe.
3.692 :wavey:

[chlatboy]

150mph...man thats some scary shit. Just make sure your brakes dont fukk up.

[MakotoS13]

thinking of goin with a rotora kit someday. muey expensivo but fuggin dynomite, i reckon.

[Maeda]

Lower offset wheels will widen the track.

Take off the coilovers. Dampening for drifting coilovers is no good for highspeed running, and neither is the springrate. SOFT suspension is key.

Caster would be good.

Wider tires on sort-of wide wheels, so you can run some sidewall.

[chlatboy]

4 piston aint good enough?

[MakotoS13]

Lower offset wheels will widen the track.

Take off the coilovers. Dampening for drifting coilovers is no good for highspeed running, and neither is the springrate. SOFT suspension is key.

Caster would be good.

Wider tires on sort-of wide wheels, so you can run some sidewall.

but i loooooooove my KTS's dude. is there any way to get a softer springrate in em? i think they're 8/6.


edit: wtf was i thinking?

[Var]

Doug. first number indicates front spring rate, and the second number..the rear spring rate

I still dont know if a rear stiff setup for a 240, although i've been promoting one for the past year. someone should try it. The KTS have 8/6 rates.

[Flybert]

Lower offset wheels will widen the track.

Take off the coilovers. Dampening for drifting coilovers is no good for highspeed running, and neither is the springrate. SOFT suspension is key.

Caster would be good.

Wider tires on sort-of wide wheels, so you can run some sidewall.

What he said.

Plus some canards for the front bumper and a large wing out back. O, and some nice front and rear underbody panels to get less turbulant airflow.

[JDMs13]

oh.......and dont forget your full coverage insurance at those speeds! :wavey:

[lilredstiffy]

i would suggest holding the steering wheel straight

[Rich_S14]

Not as important as caster, but make sure the camber isn't very negative. If you're going to be making a lot of downforce, your camber will be more negative at high speeds.

[thx247]

eh, I'd just focus on aero at this point. 150mph aint no joke, and aero will make a big difference at that speed. Fixing the front bushings and tie rods is important if you have the stock stuff up front still. Its old and busted by now and doesn't work very well at 60mph never mind twice that. Keep air out from under the car for now, you can do that pretty cheaply with some plastic or sheet metal.

[kandyflip445]

mods:

KTS coilovers
SPL RUCA
SPL tie rod ends/Z32 inners
energy suspensions poly bushings all throughout




Fixing the front bushings and tie rods is important if you have the stock stuff up front still. Its old and busted by now and doesn't work very well at 60mph never mind twice that.

:wiggle:

You think chassis bracing would help at that speed? To lessen the flex and inconsistancies of the alignment settings?

Just trying to throw it out there.

[RBS14]

actually, I would keep the kts coils with the springrates they have. You will want front and rear wings that dramatically increase your car's weight at speed. Ideally like double. So with your S13 weighing 5000lbs at 150mph, you will need 8/6 springrates. The 8/6 will then feel like 4/3, which is what you want, in terms of "soft" suspension. Almost all race cars are set up this way. That's why it looks like they are soooo bouncy at low speeds, because their springrates have to be stiff enough at speed. A wider track will help with stability, but if you have the proper downforce, it will be negligable. I think an S13 could be a fine Wangan style car, the chassis dimensions are great.

[Jeff240sx]

Wings and track. Suspension bits aren't necessary.. most people with adjustable suspension don't use them for what they're made for. Most cars built for speed all have the same generalized shape. Look at a corvette, or McLaren SLR, or most other cars. A massive, raked hood for front end downforce, and a raised rear end, which makes the whole car act like a rake, and gives downforce overall. Followed by underbody/rear diffusers, and usually (however, not in the case of the 'vette) a spoiler.
Now, I've done 135 in my 240sx. It handles decently.. but not like a car designed for speed. Matt and Scott had 170mph runs in Trogdor, the 544whp sr20det s13. My corvette I've had at 160.. and everything is smooth, stiff, and responsive.

Where will you be driving 150mph at, anyway? That makes a giant difference in what you need to build towards. Racetracks are cheaper/easier to build for.. highways you need extra insurance for stuff like pavement changes, ect.
-Jeff

[Dousan_PG]

cool john told me what your doing dood
i like it alot haha

yeah but you DEFINATELY gotta dump the coilovers!!!

good luck, sounds like fun!! haha...

[thx247]

:wiggle:

You think chassis bracing would help at that speed? To lessen the flex and inconsistancies of the alignment settings?

Just trying to throw it out there.


lol, i just reread his post. I thought he was thinking about getting those things.

[sdtouge]

if someone else wrote this you would flame them.

[$D$]

^yeah he would, lol. you need a front splitter that is strong, and a wing.do you have sway bars? also a cage, or a deathwish. ive hit 7000rpm in 5th gear on a near stock 240 and it is pretty scary, i dont think your suspension is too stiff either.

[CHARLIE2020]

I think if my 91 SE-R could do 150mph+ and have no stability problems a S13 240SX shouldn;t have none either ofcourse with some nice suspension etc etc but nothing radical.

[Rich_S14]

I've been in a nearly stock 300ZX at 160 mph, and it didn't seem very unstable. The Z only had boost up (15psi), eibach pro springs with stock damper, mufflers, and 350Z Touring model 18x8 wheels.

[Pacman]

S15 diff with S15 ring / pinion. 3.5 i believe.

3.5=Z31 Turbo diff. It'll bolt up from my understanding.

[tastyratz]

lol yea man look at the hell I took on my underbody diffuser thread I made lol. you start this and nobody bitches. if I say I wanna go that fast people will tell me to stop using the internet or something lol. def agree with the underbody diffuser idea :-P the functional wing and aero ideas, etc. aero is key, and 8/6 isnt a bad rate for that speed. alot of people were talking about caster alot... how does caster affect the high speed stability?