| Author | Message | ||
| Philip Airey (Pma1010)
Junior Member Username: Pma1010 Post Number: 76 Registered: 7-2002 |
Anyone know the size of the rear 328 bar? | ||
| Gordon Hollingsworth (Gordonh)
New member Username: Gordonh Post Number: 8 Registered: 5-2002 |
Philip, I can't remember the wheel/tire combination on the 328, but if you are using the same combination why not use the 328 rear ARB? It is available, as are all the mounting bushings. | ||
| Terry Springer (Tspringer)
Member Username: Tspringer Post Number: 363 Registered: 4-2002 |
I gotta really agree with Rex. Your problems are all tire related, ignore everything I said before. I should have asked about tires, but assumed you were running a DOT track tire... The G-Force tires are good, but the Hoosiers are IMHO much better. No other single modification you can do will have as large an impact as going from street to track tires. The absolute very best "street" tire available pretty much sucks compared to even a mediocre track tire. I tracked a '95 Porsche 993 for a while. Road Atlanta is my home track, when I got a set of 17" Kinesis wheels with Hoosiers, it dropped 4.5 seconds a lap off my average times. Massive improvement.... Get a second set of wheels and some serious track tires, then play with pressures a bit. I bet you will be happy. | ||
| Rexrcr (Rexrcr)
New member Username: Rexrcr Post Number: 41 Registered: 11-2002 |
Ps. It's difficult to compare ARB's on different cars by simplifying to diameter only. It's the whole system that's ultimately important: Bar diameter, length of the arms, width of the effective torsional portion, the geometry of where the bar links to the suspension, the characteristics of the entire suspension (springs, roll centers, wheelbase, etc.) | ||
| Rexrcr (Rexrcr)
New member Username: Rexrcr Post Number: 40 Registered: 11-2002 |
I think you're trying to set up your car with mismatched tire construction/compound and old technology tires at that. You've adjusted the roll-couple distribution off factory settings and gone the wrong way, more push. I've found the AVS too soft with no grip advantage for their apparent low durometer (wear fast, spongy non-responsive). The best bang for buck is investing in new tires, otherwise you'll spend time trying to learn how to set your car up on poor tires, then what? They wear out, you install a matched set of hi-perf new tires, and your set-up is off again. BFG G-Force KD's seem to be the ultimate in compromise ultra-high performance street tires available today. Or if you really want fun at the track, go with Hoosier DOT legal race rubber on your original wheels. If you've never driven an R compound tire before, you're in for a treat. Even though you street drive and in that situation your tires are fine, plenty safe, I suggest you start with a better foundation, then tweak the rest of the hardware. My company can fabricate an adjustable bar for you, email some photos and dimensions for a quote. | ||
| Philip Airey (Pma1010)
Junior Member Username: Pma1010 Post Number: 72 Registered: 7-2002 |
Rex I have tracked the car at Gingerman, Road America and Blackhawk and expect to continue this pattern of use plus Putnam Park to come next year (averaging about an event a month where conditions and commitments permit!). So a mix of short, tight and longer, quicker tracks. Road mileage is a couple of thousand a year. Alignment is stock but as I am in the process of doing all the front bushings (sway/rack/control arm) I'll need to get an alignment done. My thought is to keep the stock settings. On tires, I am running A008Ps on the rear (AVS's on the front - long story) and have played with varying pressures within a 35 - 40 psi range. Typically running the rears 2 - 3 lbs higher than the fronts. Clearly changing the F/R aspect ratios has dialed in even more understeer. Given the car was set up for understeer anyway on the original 14 inch Campags (205/70) and the later cars have a fatter rear anti roll bar for the 16 inch/stepped aspect ratio FR, I think it makes sense to me to go to a thicker bar. This was confirmed by a friend's experience. The best outcome may be an adjustable bar but I don't know who makes one. My guess is it is a $500 - 600 fabrication Philip I'd ideally like adjustable shocks, but can't justify the investment. | ||
| Rexrcr (Rexrcr)
New member Username: Rexrcr Post Number: 36 Registered: 11-2002 |
Phillip, What are your alignment settings, different from stock? How do you use the car? 99% street and 1% track driving, 50/50? Easiest tuning (no cost but time) is definitely the tire pressure adjustment drill. What pressures do you run, what tracks, what tires. The tires influence the greatest amount, then the spring/damper/alignment package, then anti-roll bars, of course baseline suspension geometry is important, but I assume you're only interested in what can be changed (relatively) easily. I agree that in general, a wider rear tire is a wise choice given the weight bias, though believe it or not, Ferrari tunes the chassis for understeer and the wider rear exacerbates the situation. Keep a log and do the pressure adjustments first. If you desire total control over the dynamic behavior, invest in shock/spring package that is adjustable, email me for details. I've set up many Ferrari owners seeking that ultimate compromise street/track package. | ||
| Philip Airey (Pma1010)
Junior Member Username: Pma1010 Post Number: 69 Registered: 7-2002 |
Mitch I was advised to go unequal F/R (like the later cars & 328s). 328 owner advised on a fatter sway bar. I've played with tire pressures quite a bit but it is very sensitive -- too little to get more grip and it is squeeling like crazy. My guess is you'd have to go something like 40F, 35R which sounds, "interesting". Terry I looked at heim joints at the front but wasn't prepared to make the investment. An adjustable rear bar would be great. My guess is the 911 can be provoked into OS without the bar. The 308 chassis set up is biased to understeer Philip | ||
| Terry Springer (Tspringer)
Member Username: Tspringer Post Number: 362 Registered: 4-2002 |
Hmmmmmmmmm I also have a '77 GTB though mine is all bone stock. I may do some suspension mods if I decide to keep the car in the spring (may sell and try to get an early 12cyl car). I have never tracked the car, because I also own a '69 Porsche 911S with a 2.7RS engine and track suspension and I dont see any way to ever make the 308 as fast as the 911. Its a weight thing, the 911 is only 2000lb. I would however love to hear about how the cars are to drive on the track when setup well! Anyhow, it would seem to me that spring rates could be as big an issue as the bars. I would think a rear bar at least as stiff as the front would be required, preferably with adjustable drop links so you can tune it. I would opt for a front bar that was also adjustable. Im clearly dont know about these cars specifically, but 18mm and 15mm sound very small as bars go. My 911 runs a 22mm front bar and the rear is stock 15mm with deliberatly old bushings. Lots of guys who race the early lightweight 911's dont run a rear bar at all. The large front bar with adjustable heim jointed links allows tons of tuning ability. Ive found on the 911 at least, that between the front bar, camber and toe settings, corner weighting and tire pressures, the cars can be tuned as much as is necessary. Do you want to remove some rear grip to try and balance the car, or perhaps add more front grip? If its possible, I would try the add more front grip. Is there room to run 235 or 245 front tires? Can you decrease the front spring rates while leaving the bars static? Have you played with camber and toe settings? Is there a good way in these cars to tie the front shock towers together and strengthen the front end? Wouldnt more power be nice so you could just balance the car on the throttle? ;) Ahhhhhhhhh more power is ALWAYS nice but usually not so easy  | ||
| Mitch Alsup (Mitch_alsup)
Member Username: Mitch_alsup Post Number: 268 Registered: 4-2002 |
Another option is to adjust the air pressure in the tires to achieve neutral balance again. Why did you not put equal sized tires on F/R? | ||
| Philip Airey (Pma1010)
Junior Member Username: Pma1010 Post Number: 68 Registered: 7-2002 |
Curious if anyone has upgraded the sizing of their anti roll bars and whether they'd share the results. My 77 GTB was originally supplied with a small (15 mm?) rear bar (front is 18mm, like the later cars). I complete track events in the summer and have upgraded to 16 inch rims and 245/45 rear tires and 225/50 fronts, versus the 205/70x14 all round stock. Net, net, I've put more understeer into the car. To help combat this, I am looking for advice on sizing for upgrading the rear bar. A friend (2.46 at Road America in his 328) advised a larger rear bar - he upgraded his and shed 4 secs from his lap times. Unfortunately he's off on the West coast and the car is in the Mid West so we can't measure it. Anyone have a recommendation? Philip |