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Thread: Cuda's Cars, v2.0

  1. #151
    Senior Member
    Join Date
    Jan 2014
    Yeah, I figured.

    Pretty much yields one possibility: Live with it.

  2. #152
    Quick post-SanDiego brain dump.

    Went full soft on shocks for Friday TnT. Car felt fun to drive, fairly neutral on TnT course. Maybe a bit too much rotation on throttle above 4k RPM. Played with stiffening front bump. No real improvement in corner exit on power. In fact it got slightly worse as the tires got heat in them. T ran after, and thought the car was too loose on throttle. We disconnected the rear bar. I rode for a run. It felt quite stable but not pushy. So we left it for Saturday competition. Meanwhile a few other shock adjustments were made. Oddly, adding more front rebound relative to rear rebound made the car loose in transitions -- the opposite effect compared to other cars I have run.

    On Saturday, car was very loose on throttle. A big difference compared to the practice course - and usually the difference is more subtle. Even with the stock rear bar disconnected the car was happy to over-rotate on part throttle. Front bar is full stiff. We played with adding more front bump again to try to fix it, and we lowered rear tire pressures further. Down to 30psi.

    The car seems to roll side to side and feels a bit lazy and soft in the lateral transition. I'm told from observers there is still no perceptible dive or squat. Adding rebound all around seems to sharpen the initial steering response, though you can still feel the weight and slight sluggishness in transitions.

    Saturday night we lowered the rear ride height 3 turns on the KW perches. Not knowing what this would do to toe. I asked J-Rho and he said it would lose toe-in. So possibly a net wash in balance. The car was mostly the same I felt, with maybe a slight improvement in power-down, and it had more resistance to turning in well in the off-camber corners. This latter effect could have been due to course design. For our last runs we went down a bit more in rear tire pressure, in spite of our pyrometer readings, and it seemed to help on the last run. Oddly both days I felt my last run was better, but the times didn't show it. The Dunlop Z2s didn't seem to be getting too hot. They were no more than warm. 120 degrees tops. Teddie was sure her final run Sunday was her best but again, the clock disagreed.

    Anyway, I talked to a few people who said that their cars were looser on Sunday than on Saturday. So perhaps lowering the rear ride height helped more than I think - if we hadn't, it's possible the car would have been crazy loose Sunday.

    The good news is it's not hard to get the front end to work well. The not so good news is it's proving difficult to get that much grip from the rear of the car. We'll keep trying. For El Toro I've hooked up the rear sway bar again, anticipating a more understeery surface, and I've also thrown a complete monkeywrench into the works by throwing Hankooks on the car. We'll see what happens. Driving around town the diff chatter has a different feel between the two tires. Strange. Anyway, I haven't checked rear toe since lowering the back of the car mainly because I don't want to spend another $80 fixing it just yet.

    Oh, and the catch cans need to be drained after 3 runs. If they aren't, the car burns oil through the exhaust on the 4th run. This is rather tiresome. Can we make a better solution legal in ST?

    It's late. Got to drive to El Toro in the morning. I'll have more pictures up when I get back. Here's a quick one for now, and in-car video of (nearly...) all of my runs in San Diego.

    I think the few times I turned into a corner and turned out again were mainly due to my habit of having a very quick turn-in. Exacerbated by my time in the E36, and made no better by the light steering in the Z32. It's a quick ratio so you don't really need an armful of steering on turn in. Got to refine that from my side, but also make the car less hyper-responsive to it if I can.

  3. #153
    Senior Member
    Join Date
    Jan 2014
    I meant to mention the other day your tribulations with the catch can scenario have proven to be really helpful to me. Since I put the Fiero on the good suspension and sticky tires, I've been noticing a fair amount of oil burning that I thought was happening at high RPM or maybe during throttle overrun at high RPM. I assumed that having put a pile of time and money into the handling that was the cue for the engine to develop a problem. It'd only make sense...

    Turns out it's happening on higher G right turns at high RPM, eg big freeway on & off ramps. Never happens when turning left, only right. It probably would have taken a LONG time for me to diagnose the actual problem if I hadn't been so familiar with yours. So, thanks!

  4. #154
    No problem! Glad my hack build could help in some way.

    Warning: Long autox report and bench racing to follow.

    A few further SD Tour thoughts.

    This is the new alignment system at my local place, with these devices that clamp on to the outside of the tires. I was kind of wondering how accurate that would be (depends more on the operator than the tolerances of the equipment?) compared to the traditional setup. This new thing also can't properly measure toe in inches since it doesn't know the wheel diameter. (I know, I'm crazy for always thinking of toe in inches rather than the more absolute measurement of degrees!).

    So, how close was my weight guess of 3100lbs?

    Ignore the corner weights - I hear SCCA scales are never leveled. Anyway, with that much fuel I'm sure the car is under 3100lbs normally. I figure 3075 or so on 1/8th of a tank (I wanted to test this at El Toro but the scales were never open when I wanted to weigh). This is a little bit lighter than I expected. I now think a build with a high priority on weight savings (custom light and loud exhaust, aluminum shocks, early no-airbag hardtop, etc) could get to 2,950. Not that I'll go there. I may get to low 3000s if I really feel like throwing more money at the car.

    Here are some action shots showing the car working (Teddie driving):

    Seems to be enough body roll, without being excessive. San Diego, IMO, has decent grip even though cars feel slidey, loose, and sluggish to respond there.

    Squat and dive, on the other hand, doesn't seem to exist much. The car should still be under hard braking here:

    Rear sidewall flex...

    This angle makes it look as though the rear wheel is slightly toed-out with zero or positive camber. I don't believe either of those would be the case, although toe out is possible, I suppose, after we lowered the rear.

  5. #155
    El Toro ProSolo debrief, then!


    In the week between San Diego and El Toro I reconnected the rear sway bar, changed the transmission fluid to MT90, and bolted on a set of 2011 build date Hankooks RS3s that had barely been used. Local knowledge says this particular tire has an affinity for El Toro's surface, and they came with my WedsSports, so why not. [And yeah I'm running them on the Rotas... long story]

    The trans drain plug had plenty of metal on it, embedded in a layer of dark grey goop. I wonder if the fluid in this car has ever been changed. In spite of this, it shifts fantastically. Better than the 98k-mile transmission in my 1991. The only hint that anything could be sub-optimal is a whine in 2nd gear. It sure sounds like that whine is coming from the rear end, not the trans, but it only does it in 2nd gear... funny.

    So surprise surprise, there was a practice course at El Toro this time. Since the car was still so new, and I hadn't run it on RS3s before, I thought it would be a good idea to get a basic idea for tire pressures and balance. The TnT was on a section of runway that was sandpaper concrete. Super high grip. I could feel the car sort of bind up and release (and repeat) on the initial phase of corner exit. I'm thinking this has to do with the diff being fairly tight. Aside from that, the car felt better than ever, having no real trouble getting power down while straight or otherwise. Braking performance seemed a bit less on the Hankooks. Slaloms felt as good as one could expect from a car this heavy. I was one of the few STX cars in the 39s that I know of, but half a second behind Clint's ITR. I settled on pressures pretty similar to what I ran on Dunlop Z2s.

    The area of El Toro we used for the Pro is very good asphalt that behaves much like concrete.

    I started with shock settings close to what I used in San Diego, just with the rear bar connected since El Toro tends to promote understeer in comparison with San Diego. In the Saturday AM session, the Z seemed a little loose, and I felt like I had the opportunity to gain a decent chunk of time with a solid run each side so I disconnected the rear bar. And also went down 2 clicks on front compression in an attempt to make sure the car didn't push too much entry to mid corner.

    It felt slightly better, though clearly it wasn't a large difference and I still had to wheel it. It felt slightly softer in the back, transitioning that little bit slower.

    I wanted to keep looking for more time in the setup. I looked at video Saturday night to make a decision whether to re-attach the rear bar for Sunday (since I didn't improve as much Saturday PM as I thought I would), or to try something else instead. In the end I decided to soften the front shocks both in bump and rebound. Bump in an attempt to further reduce the mild push at times, and rebound in a (futile) attempt to help the car launch a little better. It actually launched worse on Sunday morning. But more than that, I felt like the car had become too soft in lateral. I think I may have gone the wrong way in setup. I made it easier to drive, but probably no faster. Theoretically softening the car would add grip but it ended up that the weight of the car could be felt more.

    After sitting 3rd on grid for Sat PM runs, and 2nd on grid for Sun AM runs, I was disappointed to finish competition runs in 4th, later to become 5th when Yanase took his runs (congrats if you're reading this!). I think I drove the car well and pretty much got the most out of it. I did see in data I went nearly 3 tenths faster in the second half of my final Challenge run (second side so the tires had warmed up a bit). That was an all or nothing run scaring all the cones to try to beat Tom Berry after being behind on the first side. It wasn't enough. Anyway, there's not a lot more to be done to the car other than fine tuning what's there and maybe taking another 2.2% off the overall weight. From a bench racing perspective, there's good and bad to be seen. The Z32 is still teasing me just enough to make me want to continue with it.

    Good: Despite finishing 5th, the bottom end of the trophies, I was only .235 from the win. STX was crazy.
    Bad: Max threw down a dirty run in his STR BRZ that was .5 faster than what he stood on. So I'm not quite as close as it looks initially.
    Good: There may be a bit more time in the car if I can figure out how to make the rear end work better.
    Bad: I was giving away 3 tenths to 60ft (perhaps 4-5 tenths to 200ft where the first turn was?) on each side to Max's BRZ. If I could have made the car launch properly, I would have been there at the top. Most of my 60ft times were 2.5 or low 2.6. I think I had one or two high 2.4s. And either lots of wheelspin or lots of wheel hop, or both. Really tricky car to launch. I know Hankooks don't launch well, but I wasn't the only RWD car on them either...

    The challenge I see is that acceleration is no better than the typical cars in class, and I don't get any more tire for my extra 300-500lbs of weight. The more transitions on course, and the more slippery the surface, the less competitive the car is. A series of 50-70mph sweepers on concrete would be the perfect autox course for this car. We're not likely to see anything like that at SCCA events.

    At the moment I'm thinking the next steps look something like this:

    - Softer rear springs (460lbs down to 400?) combined with a stiffer rear bar. I want more squat on acceleration, without softening the car too much in lateral for transitions. The rates for the stock rear bar and Stillen rear bar are unknown... This could be a "try it and see" situation. Perhaps raising the rear ride height back to initial spec would be useful here too. Don't want too much understeer to creep in. Do want stability, but willingness to rotate and change direction are important too.

    - Take some locking out of the diff. Easiest way to try is synthetic fluid, and if that's' not enough maybe add some friction modifier. If that fails, I can try to reverse another set of plates but it'd be a major hassle to remove the diff and LSD again. It's not so easy.

    One potential downside to this two-pronged change is a stiffer rear bar unloading the inside rear more, making it easier for the diff to spin up the inside tire if it isn't tight enough. I don't know where the margin is with the diff. I definitely don't want to turn it into a $1500 open diff when I could have just run the VLSD for that! Last year my maroon Z felt more free (not loose, mind you) on corner entry and mid corner. Like you could really carry good speed into a turn with little to no drama. The blue Z doesn't feel like that, and I think the diff is the main reason why. I get the impression, without any real data to back it up, that I have to slow the blue Z more in the first half of a corner to get it to turn.

    Sometimes on course the steering would get temporarily heavy, I think when turning back the other way quickly, as in the 2-cone "hard slalom" thing near the end of the courses. Would this be a rack issue or a pump issue most likely? I have a persistent slow leak from the pump (not the hose), and often the first time I turn the wheel after having been stopped for several minutes (engine off or on) it's heavy, and then gets light again after 5-10 seconds.

    I should probably check where my rear toe is at some point too.

    I think for this car to be truly competitive it would need more wheel/tire, or more power, or less weight (on the order of 2-300lbs). The only one of those that's even possible in the current ruleset is more power. I imagine if one were to build an engine to the letter of the rules, spend more time trying other parts and dyno tuning, and running 100 octane, one might gain some more power. Wild guess 10-20 rwhp.

    Of course, one would have to figure out how to get that power to the ground for it to be most useful.

    El Toro is the best!

    In-car shenanigans!

    The car is still teasing me just enough to make me want to keep trying things... That might change if I ever back-to-back it with a GT86.

  6. #156
    Senior Member
    Join Date
    Jan 2014
    The binding up definitely sounds like you have too much deceleration torque applied. I don't know much about adjustable diffs and how to modify that, but that is what it currently sounds like. I would start there before trying to band-aid the issue elsewhere. If might also help with the power down problem you are having. I'd recommend only changing one thing at a time.

    I am personally of the mindset to run stiff springs and soft/no bar to allow complete independent action of the suspension.

    the heavy steering action might be from fluid cavitation on switchbacks. I'd eliminate the leak before I would chase anything else out.

  7. #157
    The binding feeling I describe is on corner exit, when I get back to throttle at lower RPM (higher RPM the car would have enough juice to overcome the outside rear tire and powerslide). There may be too much decel locking as you say, but it's less than the accel locking (it's a 1.5-way diff). I'm speculating the diff is overall still too tight despite being set to "60%" locking by KAAZ USA as opposed to the 100% they typically ship with.

    In the past I have preferred not to use stiff bars at both ends, too. On this car I'm considering it. The suspension seems to have a lot of resistance to fore/aft pitch movement, proportional to lateral roll. And it's a street car so I don't want to go too crazy on spring rates.

    Eliminating the PS leak means buying a $550 pump... don't wanna.

    My catch can drains also leak oil, considerably. Not cool. Even after I've drained the cans. Go figure.

  8. #158
    Senior Member
    Join Date
    Jan 2014

    Personally I'd try a 50% lock-up or something lower before I mess with the suspension too much more. And because it is less expensive .

    A search on shows a 1991 Power steering pump in Hollister CA for 50$. 831-637-5795

    A few are actually in Fresno, CA in "Fresno Foreign Wrecking". Off of a 1990. 559-485-3666

    Where are your catch cans leaking at?
    Last edited by Godson; April 17th, 2014 at 06:05 AM.

  9. #159
    A pump off a junkyard car is a risk if contaminants get inside. If the pump was easier to change, maybe... kind of a tough one I think.

    I don't have the tools to rebuild/change the LSD, honestly. Needs two people and air tools. My friend who helped me the first time went way above and beyond with the car so I don't want to ask him again especially so soon. I'm thinking synthetic diff fluid (Redline 75w90), possibly with a bit of friction modifier added, might accomplish a similar goal as deactivating another set of clutch plates. Kaaz says synthetic oils increase wear on the plates. I just don't know. I not only want to reduce locking under accel and decel, but preload as well. Not sure if a more slippery fluid would accomplish that too.

    The catch cans have hose extensions running down to the bottom of the car where brass drains reside. The drains are leaking.

  10. #160
    Senior Member
    Join Date
    Jan 2014
    Seems the first step by step I found is a 6-8hr job if you rebuild it yourself. Hmm...

    Remans are in the 70-200 range.

    The Synthetic will cause slippage from the friction modifiers depending on the oil. I'd ask Kaaz about that one. I am sure there is a tech guy that could give you some pointers.

    About the drains, do you have a link or photo of what you used?

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