Dan Baldwin

Perusing the 'stang forums, found multi SoloII champion who has used the T2R in the past, but then they started failing on him. Now he's apparently back to clutch-type (Auburn or Eaton). Wavetrac doesn't make sense to me. Seems like a mild locker/torsen combination. For there to be any differential action, the 4x convex/concave interacting faces have to be worked apart, presumably against a spring preload. But after 1/8 of a turn, the convex feature is being indexed against the next concave feature, with the preload *adding* to slip. Seems like it would act like T2/TrueTrac with a 4x/rev anti-slip/pro-slip action superimposed. Anyway, at $1200 it's not a contender... Starting to lean towards the TrueTrac. Unfortunately they insist on non-synth gear oil, and I'm not adding a cooler. Really hate the idea of a ton of breakaway/preload on a clutch-type though. Hell, I might just run the "standard" Ford Racing TractionLok as used on the factory '03/'04 SVTCobras for less preload (presumably) and remove the rear bar if required for rear thrust grip.

Thnks, Jon! Doh... Really want to avoid ridiculous preload. LOVED the clutch R200 in the Z. No probs holding 250hp on Hoosiers, picking up the inside front exiting corners, with next to no breakaway torque (bought with ~23 lb-ft, 18 lb-ft last time I'd checked it). Supposedly the TrueTrac is between T2 and T2R in terms of torque bias. Seeing a range of 2.5-3.5 for it. Good enough, maybe? Is the Yukon a direct enough copy of the Eaton Posi to also have at least a smidge of additional lockup under load? Still on the fence... What about Auburn cone-type?

Long time no post! Z is gone, but I need a new LSD for the current ride: ~530hp LS2 FD RX-7 The T2R that was been in it is worn out Apparently it's not unheard of. Looking at options for a new limited slip carrier, got it down to: Eaton Posi (clutch-type) Yukon Duragrip (supposedly an Eaton posi clone for less $$$) Eaton Detroit TrueTrac (helical gear type similar to T2). Definitely like the rebuildability aspect of the clutch-type units after a helical wore out on me. But apparently these clutch types don't employ ramps like the old R200 clutch LSDs which increase clamping with applied torque. However, Eaton literature implies that it *does*: "When torque input increases the clamping load on the clutch packs increases." I guess that the clutches do see a smidge more clamping due to the force from the pinion gears trying to push the side gears apart, but it couldnt' amount to anything like as much with the Salisbury/Nismo ramp style. Anyway, need something that will give good torque bias ratio and still be very streetable, while able to tolerate hard track usage on Hoosiers, and occasional drag strip or Texas Mile runs. I think I'd be OK with any of the three options listed above, but looking to tap into the vast knowledge reserves of HybridZ before deciding.

FTR, I was running 35degrees (i.e., full) advance back when I was running the stock N42 head (with ~.010" shave) with stock cam, stock SU carbs, stock everything, at 10.25:1 CR, on pump gas, no problemo. Stock N42 with flat-tops should be 9.8:1. I dunno, maybe a 3.1 with N42 and KA24E pistons is somehow less detonation-prone than the same head with L28 flat-tops... PA, actually, SP rules don't allow a different number of cylinders! Kinda arbitrary if you ask me... I went 0.8 seconds SLOWER in the monster RX-7 in October than my best time there in the Z Power steering issues. I.e., I didn't have any. VERY high effort and ZERO feel, I couldn't throw the car around with any confidence at all. Situation now rectified, as of today

If you run it hard while it's detonating away, bad things... But you wouldn't do that I hope. If you get detonation/pinging, back the ignition timing off and you should be OK. If there's any chance at all you'll be tweaking this motor (cam, triples, headwork, etc.), I'd go with the flat-tops. If you just want a no-worries stock build, with less potential for building n/a power, go with the dished. That would probably let you run 87 octane, too.

Dropped in to see what's shaking and plopped myself right into the same P vs. N "discussion" that's been ongoing for eons now! I drove the Z down to Atlanta last week, to be shipped from there to its new owner, fellow HybridZ-er Bob_H. So, end of an era for me, but it's going to a very good home. The Z was partial trade for his (now my) '94 RX7 with 500+ LS2 V8 horsepowers. Wheee!

I wouldn't bother with dished pistons... FWIW, I ran my 3.1 with a stock N42 at 10.25:1 CR for years with a stock cam, at 35deg advance. Currently at ~11.5:1 with the N42, with a 310deg/.550" cam and some headwork (minor bowl reshaping), running pump gas with no problems. Last dyno runs it made the same power from 34deg to 38deg total advance. That said, I am aware of at least one stock N42/flat-top build where ignition timing had to be backed down to 26deg, so ymmv... Me? I'd go with the N42/flat-tops, particularly if future mods are planned (cam, porting, etc).

There isn't any gyroscopic precession because the braking torque is on the same axis that the wheel is spinning on. No, you won't. For one thing, "momentum" is mass multiplied by velocity. When you hit the brakes, "momentum" will decrease as speed decreases. It won't INcrease. It may seem like where you locate the caliper will affect how the wheel is loaded/unloaded, but in reality it doesn't matter where the caliper is clocked, the load on the tire will be the same for a given level of deceleration. If you locate the caliper such that when you hit the brakes, the caliper is pulling DOWN on the rotor, it might seem like you should get more load on that tire, but if you do a free body diagram of the individual wheels/tires and for the car, you'll see that this isn't so. The caliper may be pushing DOWN on the rotor, but the rotor's pushing UP on the caliper with exactly the same force. Net effect on "downforce" at the tire contact patch is zero. The additional load on the front tires under 1-g of braking, for a 2500 lb. car with a 20" high center of gravity and 92" wheelbase is going to be 2500 lb. * 20"/92" = 543 lb. Which is the amount that the rears will be UNloaded. Regardless of where any of the brake calipers is clocked. It's a kind of sickness...

The unsprung part of the car is indeed *part of the car*! Having them clocked at 6:00 does lower the c.g. Optimal placement would be a bit off the 6:00 position (aft of 6:00 for the fronts, forward of 6:00 for the rears) in the interests of minimizing polar moment. For my perfectly optimized car, I have the front left caliper at 4:30, front right at 7:30, left rear at 6:45, right rear at 5:15.

The key word being "look". Many have been able to run decent compression ratios with the N-heads, and it's easier to get higher c.r.'s with the N-heads (less shaving, no need to shim cam towers). Again, here's my N42-head 3.1's history: 3.1 liter, stock N42 head (shaved ~.010 from previous rebuild), stock N42 cam, unshaved KA24E pistons, 2mm gasket, 240Z carbs. 10.25:1 CR, timing had to be knocked down to 10* initial/35* total advance to eliminate ping (I had stupidly and wrongly been running +15* initial/+43* total) 290*/.490" Schneider cam, 2" Jag carbs 10.25:1 CR, timing bumped back up to 18* initial/43* total (again, a mistake) with no ping, 180rwhp 310*/.550" Sunbelt cam, Sunbelt porting and minor bowl work, 3x2 45mm carbs, thinner head gasket 10.8:1 CR, 217rwhp at 43* total advance, 235rwhp at 34* - 38* total advance (lesson learned, it's *stupid* to just run as much initial advance as you can while avoiding pinging) Rebuild w/ eyebrowed 89.5mm KA pistons, 11.3:1 CR, 255rwhp at 35* total advance Recent rebuild of middle 1/3, shaved head, 11.6:1 CR, not dyno'd, still running 35* advance on pump gas

yes

It's not the kind of thing that's going to be "resolved" via discussion on this forum. JMort's link gives some insight: http://forums.hybrid...846#entry914846 Here's another link I came across last night (which references the author of the above link): http://cgsuspension.com/ackerman.htm From which: My takeaways: 1) What you set toe for and whether you want pro- or anti-ackerman is going to be driven by how the tires you're on respond at the load levels they're subjected to (rough estimate, a decently set-up 240Z should be loading the outside tires to on the order of 1000 lb. and the insides at on the order of 250 lb.) 2) The unloaded inside tires' grip is a weaker function of slip angle than the loaded outside tires. So the effect of toe-out or pro-ackerman is more to do with additional DRAG at the inside tire giving a yawing torque in the "right" direction, helping to rotate the car on corner entry. Of course this additional drag is slowing you down on corner exit, but then you're unwinding the steering anyway. In this regard I would definitely prefer more ackerman to more static toe-in. 3) It would be good to know if the data accounts for the inside tire having adverse camber... Seems to me that ackerman is only really going to have an effect in very low-speed corners. The amount of toe-out you get for smaller steering angles (~6degrees or less) is going to be in the tenths of a degree, even with fairly full ackerman or even "over-ackerman". Toe-out with steering angle isn't linear, and at zero steering angle the change in toe-out with steering angle is zero. It "ramps up" with increasing steering angle. For reference, cornering at 1-g around a 100' radius equates to 39mph, a very low-speed corner for a road course. In that situation, assuming 5 degree slip angles for the outside tires, "full Ackerman" would give you 5.26 degrees slip at the inside tire. 0.22 degrees of the difference is from ackerman steering (.04deg difference in trajectory angles of front tires). It turns out that the aforementioned BMW M3's relatively extreme amount of ackerman is a smidge less than "full" ackerman. So for this *quite* low speed steady-state cornering situation, the difference between the extremes of parallel steer (Corvette, 240z), and full ackerman (greater than the high-end-of-ackerman outlier BMW's), is .22 degrees, or 3/32" of toe-out. So, I guess if that saves 3/32" of static toe-out for the same amount of turn-in responsiveness in very low-speed corners, I'm all for it. In particular, if the turn-in at medium to high-speed corners is good, and greater responsiveness is desired for very low-speed corners, more ackerman would be the preferred way to do it in the interests of keeping static toe-out minimized and keeping the same stability for medium-speed and faster corners. BUT, if the tire grip vs. slip-angle vs. load curves look more like the "anti-ackerman" case shown above, parallel-steer might be "better" overall. Long/short, I no longer think it's necessarily a waste of time/effort if the handling is good at higher speeds but turn-in responsiveness sucks at low speeds. But I wouldn't go by feel alone. Whew...

I glanced over it. I understand the concept of more ackerman generally helping with turn in on lower-speed corners. I can appreciate that for a given amount of turn-in respones, more ackerman would reduce the amount of static toe-out. At road courses, for higher-speed corners, whether ackerman helps or not will depend on how the tire lateral grip vs. slip angle curve and how it varies with load. If at lower loads the tire develops maximum grip at a lower slip angle, I want anti-ackerman. If at lower loads the tire develops maximum grip at a higher slip angle, I want pro-ackerman (generally speaking, of course it depends on the curves). In any case, the stopwatch is the ultimate arbiter of what works and what doesn't. But if you were able to do back-to-back testing of stock ackerman (apparently parallel steer) vs. 100% ackerman vs. M3-level over-ackerman, you'd still have to optimize each individual setup in order to draw conclusions. This isn't terribly likely to happen... I have to say I still haven't seen anything that indicates to me that optimizing ackerman is going to gain much if anything in terms of speed at the track. Maybe for autoX...

The problem is that you don't have a basis to say what direction is the "right" direction. You *FELT* the change it made? For one thing, it is possible to *feel* a change that doesn't exist (placebo effect). For another, what *feels* better isn't always faster. I would think you might want to maximize lateral grip for smaller-diameter lower-speed corners as well! You are *assuming* that it has a significant negative effect. The engineers who are responsible for the Corvette's steering geometry might beg to differ... OK, I just did the geometry, and for a 30ft radius corner (that's pretty tight!), assuming zero toe at the rears, outside tires at 5deg slip angle (assuming for a moment that that is optimal for the loaded tires), and with zero ackerman (parallel steer) and zero static front toe-in, I'm only seeing 3.5degrees of slip angle at the inside front. That would be less than optimal even assuming the chart that suggests anti-ackerman. 11.6 degree steering angle, btw, or 206 degrees at the steering wheel. So, I will concede that *some* ackerman *should* be better for maximum lateral grip. FWIW, with 100% Ackerman, I get 5.9 degrees of slip angle at the inside front for the same cornering conditions, which would be close to "optimal" going by the chart on the previous page of this thread that suggests pro-ackerman. (fwiw, 12.75 degrees steering angle average at the road wheels, 227deg at the steering wheel) The tire you are running will determine what is the theoretical optimum amount of ackerman, but it looks to me like it will generally be between zero and 100% Ackerman. But *STILL*, I don't think the Corvette guys necessarily screwed up TOO too bad going with parallel steer. I still doubt that there is going to be all that much in it one way or the other. The M3 would have inside tire slip angle of about 8 degrees for the above cornering case (30' turn radius, outside tires at 5deg slip), which would be significantly GREATER than "optimal" for the more pro-ackerman case of grip vs. slip angle vs. load. I also don't think that the M3 guys necessarily screwed up too too bad by having what appears to be entirely TOO MUCH ackerman. Again, it appears to me that there's not much in it, particularly for our cars.

Look at Figure 1 in your link which shows lateral force vs. slip angle for different normal force or load on a tire. This would argue for anti-ackerman. Now look at the plot of lateral force vs. slip angle for different tire loads you posted previously in this thread. That one argues for pro-ackerman. Who ya gonna trust?! I think you're knocking yourself out for very very little, EVEN IF you did testing to figure out what the grip vs. slip angle vs. load relationships are for the exact tire you're going to be using under the exact conditions and range of loads you'll be using them under. Without knowing what those relationships are for your specific tire and load range (and additionally what the *actual* range of steering angles is for your those tires under the conditions you're trying to optimize for), there's no way for you to know what to aim for.