JMortensen

Someone made their own strut top, and that explains the camber too. The Bilstein strut insert is not the source of the camber. What you have there is actually pretty good. Looks like the PO wanted more neg camber and did what he needed to do to get it. It's a lot like Tom Holt's rear strut setup: http://sth2.com/Z-car/shocks.htm

My own experience with an E31 which has better quench than the N head but not as good as the P head and had all the rough edges in the combustion chamber smoothed out and chambers cc'd, etc was that while running about 11:1 compression with a .490/280 cam, I needed 95 or 96 octane to prevent pinging, which I had to mix race gas and pump gas to get. I did have to drive it once on 91 pump gas and had to run 0 degrees advance at idle, and was worried about burning up the exhaust valve the whole time I was on the road. My previous build was a dished piston with that E31 and the same cam. It probably had about 8.5:1 compression, ran on 87, and despite all the warnings you see for cams saying "only for high compression motors" it worked just fine. Definitely had more bottom end with the flat top pistons, but I could drive it daily with triples, the cam, a heavier pp, and 2.5" exhaust with no problems at all, and it made a LOT more power from the mid range on than the smaller cam I had used before. I think a more important thing to look at is how much power you're going to get out of that extra point or two of compression. I think if you try to find some specs for that you might find that you're not getting a whole lot for the extra effort, so if it's not a full on race motor, then why bother to run the compression right on the edge where you need to worry about detonating it to death? And if it is, you might as well use the N head, because it will probably require a bunch of chamber reshaping to get the compression up to 13 or 14 to one anyway, and the smaller chamber is probably the better one to start with.

There is an engineering rule of thumb about how far to extend the rod end out that says you should have 1.5x the diameter of the shaft in the threads. That means you can move the rod ends out 5/16" IIRC. You can measure it up and figure it out yourself. Since you have rod ends on both sides, that should mean that you can make the arms 5/8" longer without violating that principle.

Sweet and Appleton are the two others that I'm familiar with. Supposedly Woodward's stuff is a lot better, but it is definitely a lot more expensive.

I was talking to a guy who has a Woodward rack on a BMW, and I'm pretty convinced I'm going that way. Reason? I don't want to literally tear the stock rack apart. I'm going to be putting a lot of strain on the rack due to the crazy tire size and scrub. He was telling me that the Woodward rack is a lot beefier than any stock rack he's seen and that the loads that it can put up with are pretty tremendous.

Yep. That was a semantics issue for sure. I don't have anything more really that I haven't already said. I did find the site below which has a bunch of stuff supporting what I have said, and also has some interesting views on anti-Ackerman and definitely supports using both in different situations. Unfortunately it quotes Carroll Smith before he retracts his view supporting anti-Ackermann and quotes Staniforth in what must have been an earlier version of Competition Car Suspension where he is not yet totally convinced about the benefits of Ackerman. According to the page AA is more useful than I gave it credit for, but if you look, the places where they suggest it to be used are in very high speed cars, NASCAR and Australian V8 Supercars, etc. and very fast corners, which are both places where you want stability and don't want the drag that might be associated with a lot of Ackerman or toe out. You might note that there are some tire traction graphs there that curve the opposite way from the one you posted, suggesting for the tire tested Ackerman would be helpful even by your standards because the inside would need a higher slip angle to achieve maximum grip. After reading the page I wish I had those RCE magazines from 2001. Looks like Erik Zapletal took the time to prove the "LF brake on the roundy round car" theory, which in and of itself might be enough to justify using Ackerman in a Z which IME has a pretty strong tendency towards understeering. http://www.smithees-racetech.com.au/ackerman.html Here is the meaty part: I also found this little video, but I think it would be better if they started with no slip angle graphs, and then turned the wheels, added the graphs, added the Ackerman, changed the graphs, etc. As it is, I don't think it shows much of anything, but it does seem to suggest that the Ackerman relationship still exists after slip starts, because the lines still point to the instant center after the slip is accounted for, and they still wouldn't if you made the same movement with the parallel steer. It's more of a "what could have been", but I thought you might like to see it. http://www.racecartuner.com/03/207.html

Depending on how those inner tubes are positioned you can effectively change the length of the control arm too, that might be a factor. I recall setting my control arm jig at 15" from the inside pivot to the outside pivot. You could check yours and see where you're at. You'd want the middle of the hollow tube to the rod end on the outside. I think stock is 14.5". I made mine .5" longer to avoid these issues. One thing you DON'T want to do is unscrew the rod ends a lot to make the arm longer. That is a bad idea. But you can rotate those sleeves, although you will then be adjusting roll center, sometimes you gotta do what you gotta do.

Looks like Tom hasn't been around in a couple months. He had a custom CV axle made shorter as I recall. I know it was discussed on the forum here. Jay Hitchcock did the same thing and he made his too short and had to redo them longer. There's a thread his modified 280ZXT CVs here: http://forums.hybridz.org/index.php/topic/61716-half-shaft-update/

FIA rules don't require a diagonal. If you wanted to build that cage to be SCCA legal, you would have to build it slightly differently. Change the diagonal, and there might be some other small changes to door bars and such that would be needed. Not a big deal. Bolting in a diagonal is not going to pass tech.

I really feel like we're getting somewhere here, so I'm back to drive the point home. The slip angle can be different on each side of the car because the steering angles can change relative to each other on each side of the car. If you're looking at the slip angle of the car as a whole, you're right but that's a pretty simplistic way of viewing slip angle. Why not look at the tires individually? The loaded side dominates, and determines the path of the car as a whole. Call it 0 toe, because where it points is where the car goes. I don't mean that literally, but even when you're sliding, it's the loaded tire and the amount of steering input that is going to determine the path of the car. If you come at it with this realization that the outside tire is at 0 toe, you can see how the inner wheel can be toed in or out independently using a static toe setting, bumpsteer, Ackerman, or all 3. The inside tire is the "victim" of the outside tire, kind of like being dragged behind the truck on the landing gear, but it is going to do its own thing and its individual slip angle will be a result of the loads, its toe in relation to the inside tire, and the direction the car is traveling (dragging it at). I think this gets us back to the static vision of toe that you seem to have. The inside tire can have toe in or toe out relative to the outside tire, and the effect could be a higher or lower slip angle. The slip angles have to be able to be independent. If they aren't then your idea of running toe in to change the slip angle of the inner tire doesn't make any sense, right?

OK, I think I really nailed it this time. Read carefully and I think you'll get the picture. The ideal slip angle will give more lateral force, what you've suggested won't because the lateral force is reduced, and what is there comes at the expense of the tires fighting each other. Each wheel has it's own slip angle as shown in 2.33, and a tire's slip angle is relative to the path of its own travel, not the other tire. As I said, in the other graph which has vertical loads more like what a Z would see, the optimal slip angle comes at 2 degrees less for the less loaded tire. So if you ran parallel steer and .412" toe in (this would give you 2 degrees of toe in on a 225/50/15 wheel), then you would have your theoretical maximum grip when the outside tire hit its perfect slip angle according to your theory. Nobody runs that. Why not? Now if you could steer (and even better camber) each tire independently, then it would be possible to do what you want to do and get the maximum out of each tire around every corner. But since the radius of every turn is different, the toe requirement on the inside tire relative to the outside is going to be different on every turn. The outside tire determines the path of travel for the most part as stated before due to its taking the weight transfer. The inside, in order to hit this perfect amount of grip, would then have to somehow sense the radius of the turn and the slip angle of the inside tire, and then point 2 degrees less on ITS OWN path, not relative to the outside tire, to maximize traction. If it were possible, you might even be able to turn the inside tire first to get the Ackerman effect on corner entry, and then bleed off the toe out until you got to the optimal angle. That would be seriously cool. Unfortunately this is currently un-possible. One last example of why it is not going to happen, then I'll call it quits and let you guys figure it out for yourselves. Staniforth has a graph on p70 of turn radius and degree of toe change in order to maintain perfect Ackerman steering. A turn of 40 foot radius has a toe difference of 1 degree for the tires to run the appropriate paths around the turn with no scrubbing. A turn with a 15 ft radius has a 6.5 degree difference if the wheels just follow the curve with no scrubbing. So let's say you want to set toe to optimize lateral acceleration on both tires for both corners. On the large radius turn, if you run the prescribed .412" inches of toe in that you get from misreading the chart in RCVD your results are not too terrible. The outside tire is running 6 degrees of slip angle and defines the corner's arc with its maximum traction at the perfect slip angle. The inside tire needs 2 degrees less slip angle, so it needs 2 degrees less turning angle relative to the true path of the wheel, which was supposed to be 1 degree sharper to begin with. So it requires really one degree of toe in to get 2 degrees less slip angle. Not so bad. Continuing on, you're out of that corner and down the straight and into the hairpin with the 15 ft radius. You cruise into this corner with your .412" of toe in and parallel steer in your Z. Let's see what happens... You need 6.5 degrees more toe out on the inside of this corner, but you have 2 degrees of toe in, because you misread the chart. This time, you're FUBAR. Now with your goal of 4 degrees of scrub on the inside you would need 4.5 degrees of toe out relative to your outside tire to hit your max lateral acceleration mark on the inside tire. But you don't have anything like it. Your car understeers off the side of the track and into a badly positioned corner workers' stand, and is a complete write off. Oh, that sucks! So you can see from this example when static toe in on a parallel steer car works; when the radius of the corner is VERY LARGE. It's going to work well on those super speedways that you always see Z cars running on, which coincidentally, is where you see real racers using AA or toe in. This example disregards the effect of Ackerman at corner entry, which Rouelle would argue is vastly more important than optimizing the toe setting for max lateral acceleration on the inside tire in mid corner. Don't like my explanation? Fine. Don't listen to me. Try it and see how bad it sucks. Toe settings cost nothing but about 5 minutes of your time.

This is one of the things that is so cool about Ackerman vs toe out. Don't turn the wheel as much, and you have less Ackerman. Run a lot of toe out, and you have the wandering front end regardless of whether you need it on a given part of the track. It is always the name of the game to try and reduce weight transfer. Lower cg, wider track, whatever can be done should be done. But this slip angle on the inside tire argument still doesn't take into account where the tire is pointed. In RCVD they literally took an old plane and removed the landing gear and bolted it to the back of a truck. Then they put the tire to be tested on, and turned the tire away from straight at various angles, put a load on it with a nitrogen cylinder and DRAGGED it behind the truck and used force gauges to measure the lateral force generated, and that's how they came up with the ideal slip angle for a vertical load. When you look at the graph that Leon posted, it only tells you what angle and what load produces the highest amount of force. It does not say that the highest load slip angle should be coupled with the lowest load slip angle to produce the best cornering speed. It would be more accurate to say that at low speed with little downforce, the slip angles for maximum cornering traction will be lower than at high speed with lots of downforce. Graph 2.46 has forces that are more reasonable for comparing to a Z, and it shows a 2 degree difference between the tire loaded at 800 lbs vs the one loaded at 400 lbs. Just as running 2 degrees of toe in would be insane and stupid, likewise trying to get the inside tire to point 2 degrees towards the outside in an attempt to maximize it's traction doesn't make any sense at all. The slip angle is the angle that an individual tire travels relative to its own intended path, not related to the other tire or the set divided by 2 (fig 2.33 on p.62 makes this clear). Pointing the inside tire towards the outside of the turn you're trying to make is almost never a good idea. If you have the outside tire determining the radius of the turn you're making, you really do not want the inside tire making its most efficient force while pointing to the outside of that radius. You're going to lose some grip that way. I don't think that bias ply tires favor anti-ackerman. Certainly wasn't the case on that 510.

If you just have the spacer on the bottom the diff you should put some on the top too or just switch to poly and see if that changes things at all.

Do you have the spacers top and bottom? If so, and they're nice and tight, then I don't think the M bar is the source of your problem. Sounds like your clunk is now a clank. What are you running for the stub axles? MM adapter on a stock axle? Any play in the splines there? All bolts tight?

I've dealt with Brian before, he is a good guy. Curious, how does the ps get the car speed? Sensor on the driveshaft? What was the cost? I guess another option would be a 1.5:1 steering quickener and the electric setup, but still have worries about feel and space might also be a concern. Not sure how much power you can get with the electric setup as well. If I'm adding a buttload of scrub and a quickener, will it keep up?

You're getting two issues confused. One is the slip angle at which you obtain maximum grip. The other is whether obtaining the maximum grip with the wheel pointed in the direction that obtains that grip maximizes the corner speed. I don't see how you can get around the idea that maximum grip on the inside tire with a thrust vector towards the outside of the turn is going to tend to give you understeer. Even if the grip level is slightly reduced by adding Ackermann, having the grip be pointed in the direction you want the car to go is better. Again, Smith was mystified by the fact that the cars with heavy downforce turned so much better with Ackerman than without, probably for the same reasons that you're having trouble with it. The simple reason is that the tires are not fighting each other, they are both trying to turn a corner of the same radius. Above and beyond that, steady state maximum cornering power is not necessarily where the best lap times come from. Although I haven't taken his seminar, I have read where Claude Rouelle says that 80% of your corner speed comes from the first 10% of the corner. The importance of getting the front end to respond to that initial steering input is paramount, and that is why Ackerman is so popular with racers and static toe out is popular where Ackermann isn't easy to come by. The benefit is obvious when you've driven the same car with and without Ackerman. You can test the same thing on a stock Z by taking the recommendation of just about every Z racer and running some toe out. It won't cost you a penny, and if you have a course where you know what the car feels like with your normal toe setting, I think you'll feel the difference immediately. It will seem really twitchy, because the front end is suddenly more apt to change direction. Turn the wheel sharply, it reacts better, and there's your first 10% of the corner.

It certainly doesn't make any sense to turn the inside tire less. The outside wheel is the one that controls where the car goes. If you want to turn harder, turn the wheel more. The inside is largely along for the ride, so you can choose to make it turn less or more than the outside wheel. What advantage do you see in turning it less or the same as the outside wheel? Since the inside tire has to turn a sharper radius, even having the wheels parallel would mean that the inside tire is trying to drive a wider arc than would be idea to follow the track of the outside tire, which is again the one that determines the radius of the turn for the most part.

Come back to it when you have the time and we'll hash it out some more if you like. Conventional thinking in the late 70's and early 80's was that anti-Ackerman was the way to go. Anti-Ackerman is in Smith's book Tune to Win, which is probably the most common source for the idea nowadays, but thinking has moved on and now lots of Ackerman is the prevailing theory. Even Smith reversed himself in his later book Engineer to WIn: http://books.google....epage&q&f=false Here's another quote from the same page that deals with slip angles and Ackermann:

No problem, the more ideas that get tossed around the better. Problems with electric steering are that it doesn't quicken the ratio and that I've read some posts from people who felt that it felt totally disconnected from the car.

Forgot to say that I would suspect with the amount of power that you have, you are probably pulling the M bar down so that it hits the washers on the bottom. Those washers have a rubber bumper on them, but I would still guess that this is the source of your clunk. If you replace the bushings with with poly there will be much less movement there. The AZC bar uses poly too, so either way will get the job done. Post when you figure it out, I'll be interested to see if I'm right.

Not really any disadvantage if you're pretty rigidly mounted in front. If you're using a stock front mount, I think aluminum is a bad choice for the mustache bar because it isn't springy and won't allow for the front end coming up, but if you have the RT mount that pretty well fixes the front of the diff, so the aluminum bar doesn't have to deal with a lot of twist.

Are you running poly bushings? Sounds like rubber if you're getting a lot of movement from the bushings. Poly would be a cheap and easy fix.

Make no mistake, I am arguing, because I think your point is wrong. Nothing personal. So if the outside wheel has the larger effect, why can you not just turn the wheel a little more to get the steering angle you want? There is something inconsistent about saying that Ackerman is only in play at very slow speeds, and then saying that static toe out causes understeer at high speeds, because they both essentially do the same thing, which is to turn the outside tire less than the inside tire. I know you're going to have a problem with that statement, but keep reading. OK, follow me here. If you have parallel steer like a stock Z or worse yet anti-Ackerman and you are in a turn, the inside wheel will not follow the track that it needs to. Although it is not as heavily loaded it will still be steering to the OUTSIDE of the turn. I think your problem is you're looking at the toe as if it stays the same regardless of which way the wheel is pointed. Toe is relative. Example: what happens if you take one tie rod, loosen the jam nuts and adjust it 6 turns (either direction), and lock it back down and drive the car? The wheels may be pointed with the right wheel straight and the left wheel toed out 3/8". Regardless, the car will drive STRAIGHT. The wheels are equally loaded, so they don't turn one way or the other because of the toe change. They just split the toe difference and head straight down the road. The steering wheel will be way off center, but the car will drive so that the tires are equally toed out or in, whichever way you adjusted the wheel. Similarly when you are in that high g turn, the outside loaded wheel is the one that "points the car" for the most part and the inside is largely just along for the ride, at least to the extent that weight is transferred off of the inside and that reduces grip. However, instead of putting a smaller thrust vector towards the outside of the turn as it would with anti-Ackerman or parallel steer, it will point that smaller amount of force towards the inside of the turn. Ackermann is most useful at slower speeds, but that's because it does it's thing to a greater extent at a greater steering angle. And here's how it works (this works for Ackermann and toe out): Going down the straight the tires are equally loaded, so the car goes straight. Turn the wheel, and the inside tire turns more sharply than you would have with anti or parallel steer. This puts a yaw force onto the inside tire that swings the car into the corner harder than it would with a parallel steer. Once into the corner that inside tire drives with whatever cornering force it has left after the weight transfers towards the inside of the corner, in the case of a lot of Ackerman or a high degree of slip angle the inside tire actually scrubs, which is almost like the old roundy-round trick of having more brake pressure on the LF caliper. It really helps the car to pivot. What hurts is a lot of bumpsteer. This dynamic toe out of the outside wheel under bump does cause understeer, not because of the relationship between the two wheels but because of the relationship of the heavily loaded wheel in comparison to the direction you want to go. When the wheel you're leaning on toes out after being loaded, you get the effect of understeer. I am also interesting in providing helpful information, and I hope you take this as a friendly debate, because that's how it is intended. Static toe out is a nearly universal setting on a race Z, and Z's are pretty well known to understeer out of the box. I've driven a 510 before and after the steer knuckles were modified for Ackerman. The difference was obvious, and I didn't move my rack closer to the crossmember specifically to get some Ackerman because I wanted less grip in the front end. It really does help, and it's not uncommon to do in all kinds of racing. That said there are some situations where Anti-Ackerman would be called for, but those are not usually the types of situations that you can put a Z car in. You're talking about things like high speed ovals at 220 mph, stability is much more important than ultimate grip as those cars have grip to spare. For the racing that we do, unless you're land speed racing or drag racing, Ackerman (or barring that, some static toe out) helps. Here is a quote from Woodward's tech info: http://woodwardsteer...ion%20guide.pdf "To sum up, Ackermann geometry will make corner entry more positive on both dirt and pavement, and, on dirt, will make the car easier to control in a slide. It is entirely possible that a comparison of these diagrams with the front end layout of your car will suggest certain physical improvements. If so, they are worth doing. Getting rid of reverse Ackermann is one of the most dramatic and instantly rewarding changes you can make to a race car." Competition Car Suspension has a full chapter on the subject and the author describes looking at a Dallara F3 car and seeing huge amounts of Ackermann built into it and then deciding to mess around with it on his own hillclimb car. He opens the chapter by saying he is a "total believer and convert" to Ackerman, and calls it one of the few things that is self adjusting to the precise demand of various circumstances (meaning you need less at high speeds when your steering inputs are smaller, and more at lower speeds where steering inputs are larger). He describes trying 100% Ackermann and then 200%, and says "what had seemed decent turn-in had improved in startling fashion, with the sharper and slower the corner the better even to the extent of a tailhappy tendency." That matches the 510 experience I have, although he went from whatever a 510 has from the factory to 100% Ackerman. BTW both spellings of Ackerman are correct from what I can tell, so I use both so that people searching will find Ackermann too.

Static toe out is a way to mimic Ackerman on a car that has parallel steer like the Z. The toe out helps the initial turn in, and since as you said the inside tire isn't as heavily loaded when in the middle of the turn, it doesn't have as much effect then. If you want more steering angle, just turn the wheel more. Lots of info on Ackerman out there. I think the Millikens went over it, but Competition Car Suspension by Staniforth has a lot of info on running Ackerman and so does the tech page of www.woodwardsteering.com.

You can disassemble the CV and see if the balls are really loose in the joint. If there is a lot of slop, that could cause the noise. Whenever someone says rear end clunk with a Z I'm tempted to say that it's probably a diff mount issue, since that is a known problem with these cars. Search "clunk" here and at www.classiczcars.com and you'll find pages and pages of results. The boot must be coming in contact with something under the car. They normally don't go bad because they aren't doing a lot of turning like a CV in a FWD car. I wonder if a bad diff mount is allowing the diff to move and it's hitting something and tearing up the boot...