TimZ

My money is on cam timing - do you have an adjustable cam sprocket? The stock sprocket will allow you to advance the cam timng by 4 or 8 degrees, which is worth trying. My guess is that you might need to retard the cam timing, in which case you will need a different sprocket. I would recommend using the Nissan Motorsports 8-hole sprocket, rather than the vernier types (Personal preference - I don't like worrying about my sprocket coming apart and screwing up my motor )

Well, yes and no. An inertia dyno measures the acceleration of the roller, whose rotational inertia is known and constant. This is directly proportional to the torque being applied to the roller, but it is not the value that gets reported as the engine's torque, for exactly the reasons that you mentioned above. Instead, the power being delivered to the roller is calculated from the acceleration of the roller (i.e., torque to the roller) and the speed of the roller. This way, no other inputs are needed to get the power figure. Because of this, the gear ratio issue goes away - the torque to the roller is higher, but the speed of the roller is proportionally lower, so the effect is cancelled out. Perhaps you've noticed that they can still give you an accurate power graph, even if they can't get your rpm signal - this is why. The torque value that is reported is calculated from the power figure generated above, and the engine RPM (torque = HP*5252/RPM). This is why they need a pickup for the engine RPM to give you a torque number. Now, frictional losses are generaly higher for shorter (numerically higher) gearing, so all else equal, shorter gearing will probably net a somewhat lower dyno reading, just not for the reasons you were thinking. Also, because the system works by measuring acceleration rates, taller gearing will tend to give more repeatable results, due to the slower rate of change - it's just less noisy.

Because the entire 780 lbs is transferred through the contact patch, the amount of force per square inch will by definition be the same as the inflation pressure. It doesn't have a choice. It sounds like you are making the assumption that the contact patch is always the same shape and just gets bigger and smaller as you inflate and deflate the tire. I am pretty certain that this is not the case. Due to the construction of the tire (I'll assume a DOT-legal radial tire here), the contact patch will change its shape as the inflation pressure goes up or down. In general, lateral adhesion goes up with increasing pressure, longitudinal adhesion goes down with increasing pressure. This has been bourne out through years of practical experience, by both road racers and drag racers alike. In case you are wondering, yes I have done this particular exercise, btw. To answer Bryan's question, you shouldn't really think of using tire pressure as a way to increase your total cornering grip. Yes, the car will pull more lateral g's with the tires at 35psi than it will at 20psi, but you should never try to do limit handling with the tires at 20psi, so the point is moot. The difference in ultimate lateral g capability between 35 and 40psi is probably not going to be that dramatic. You should use it more as a way to fine-tune your handling balance. For starters, I would use the advice that others have already mentioned as far as using chalk marks on the sidewall to determine a good base pressure to use for all four tires. You can then use the tire pressures to fine tune your handling balance - for instance, if you think the car understeers a bit too much, you could increase the pressure in the front and/or decrease the pressure in the rear. Start with small pressure differentials (say 1psi at a time) and see what difference it makes. It helps to not leave lots of time between your evaluation tests - it's really easy to forget exactly how much the car was oversteering or understeering if you don't evaluate back-to back at the same speeds over the same course. Do your tests in a safe place, like a race track or autocross course (legal disclaimer ). Finally, I would not recommend lowering your tire pressure below the manufacturer's recommended pressure for limit handling work. Reinforced sidewall or not, lower pressures will increase the risk of de-beading the tire during hard cornering, which would not be a fun thing.

As exepcted from SCC - more mis-information. They have a few smart guys working there so I wonder how BS like this gets out. I guess I don't see this as being that far off - yes, it's a bit over-simplified, but assuming that you are talking about lateral grip specifically, and that you are starting out with a reasonable tire pressure (say 32psi), this holds up pretty well as a rule of thumb. agreed Now, I hate to do this, but I have to disagree here - this math does not hold up (sorry John ). The psi units refer to the amount of pressure being exerted on all points on the inside of the tire - while there is a relationship, you cannot just say that each psi supports x amount of weight - the units don't match. PSI is in the units of force per area, so for the tire to exert a force on the ground in order to support the weight of the car, it must do so through the patch of tire that contacts the ground. So, I believe that what happens here is that the pressure applied across the area of the contact patch is what exerts the force on the ground. For instance, using the numbers above, 780lbs being supported by the tire inflated to 28psi would result in a contact patch of: 780lb/(28lb/in²)= 27.8in² So, for a given tire, increasing the inflation pressure should decrease the contact patch size accordingly, and vice versa. So how does increasing tire pressure result in better grip? Well, some other things are going on in the tire as well. In general, as the pressure goes up, the shape of the contact patch changes. This is a result of the way that the tire is constructed - the sidewalls generally get stiffer, and the contact patch gets wider (side to side) and not as long (front to rear). While this is helpful for lateral grip, it doesn't do much for longitudinal grip, which is why decreasing the pressure on the driven wheels can help you get traction when drag racing. Think of it more as adjusting the size and shape of the contact patch. Remember that the tire generates force in more than one direction, and the shape of the contact patch dictates how much force can be generated in any given direction. From this, should be fairly clear that the rule of thumb from SCC that started this thread is just a rule of thumb - increasing the tire's pressure will get you more lateral grip for a while, but at some point the decreasing contact patch size will start to dominate, and you will lose grip. Conversely, if you let too much pressure out, at some point the sidewalls will not support the tire sufficiently and bad things will happen. Yes, there is still more to it than that, but hopefully this will give you a better picture of what is going on...

Bleeders go on top

...Then don't. I've heard enough stories from people whose opinions I trust that I really don't have much faith in anything he says. He doesn't have anything that you need that you can't get elsewhere anyway' date=' so why bother? Ummm, yes it has been answered. ANTI-SWAY BARS. That is specifically what they are there for. It's their job. Strut tower braces will not do diddly for your body roll. If your anti-sway bar and/or end link bushings are bad this could definitely have an effect. Body roll issues aside, your suspension bushings will have by far the most noticeable effect on how your car feels and handles, especially if your old bushings are shot. You should not be screwing with anything else if you have bad bushings - it's simply a waste of time and money. I can't emphasize this enough. Yes, it's pretty labor intensive and you will probably end up spending a fair chunk of change if you have someone else install them for you, but without them your other mods will be pretty much pointless. Probably mostly because they just spent a pile of money on them, and they really want for there to be a difference. The strut tower bars will help provide some additional body rigidity - even the single bar type. It's just that if your unibody is in good shape already it gets pretty difficult to quantify how much they are helping - I seriously doubt that there are more than one or two people (if anybody) on this forum who could tell the difference that anybody's strut tower brace makes in your current setup in a double blind test. If you have a super stiff suspension (WAY stiffer than the Eibach setup) with huge anti-sway bars, then you will see more benefit from a setup like rc240 is offering.

Assuming I understand your intent correctly, I'd have to say that the strut tower braces are going to have minimal (if any) effect on your body roll characteristics. You should invest in anti-sway bars (maybe that's what you meant?) long before worrying about tower braces. Since you are already using a pre-packaged solution for your spring rates and shocks, I'd just go with something similar for the sway bars, and you need to get them as a set. Also, don't go overboard with the bar sizes, as the really stiff front bars will eventually tear your frame rails apart unless you do a significant amount of fabricating reinforcements. Also, do you have fresh poly suspension bushings? These will also make a much bigger difference in handling than a strut tower brace could ever dream of.

First gear would have resulted in way more than 850 lb-ft, but you're on the right track. The torque number is almost certainly the torque at the roller, which needs to be divded by the gear reduction ratio to get the normally used torque at the flywheel. My guess is that the pull was done in fourth gear (1:1), with, say, a 3.55 final drive gear. 850 / 3.55 = 239 lb-ft. If Simon were using a 3.7 diff, then the torque would come out to about 230 lb-ft.

Okay, I'll bite... Do you know what you are expecting the spacers to do for you?

Just saw this thread... y2k C5 corvette wheels, 17x9.5" Kumho V700 Victoracers 255/40zr17 in the front 275/40zr17 in the rear

Well, not quite... Wider tires can change the scrub radius, which does have an effect on steering kickback. The scrub radius is simply the distance between the center of the contact patch of the steered tire to the point that the contact patch rotates around when steered (they are seldom in the same place). If the center of the contact patch is to the outside of the center of rotation, then you have a positive scrub radius. This, however, is not the same as bumpsteer, and the so-called "bumpsteer spacers" will not have much effect on the scrub radius. Also, wider tires won't have any effect on the bumpsteer characteristics. With bumpsteer, the toe-in changes with suspension travel, and the car's heading can change erratically when you have large amounts of suspension travel. There doesn't have to be much steering kickback in this situation. ...Just trying to keep the terminology straight.

How on earth could you spend $50k on a Spitfire? $49,500 motor? He must have paid someone to do EVERYTHING.

No, because you could be at TDC on either the exhaust or intake stroke. You need to look at the cam when you have it at TDC with the rotor pointing to #1. If both cam lobes for the #1 cylinder are pointing up (valves closed), then you are on the intake stroke and the dizzy is correct. If the lobes are pointing down (valves open) then you are 180 out.

That's definitely not what came on my 78 Z. I'm thinking that the in the pic, the bracket is upside down, and bolted to the wrong side of the compressor - there are mounting holes on both sides.

Agreed. Again, this is most likely a conscious calibration tradeoff between stopping performance and stability. Inducing understeer is generally considered the more conservative approach for the average driver. The Corvete most likely had different priorities. If i had to guess, this probably gets invoked by repeatedly unloading the tires during the slalom. This most likely sends the unloaded tire into much deeper slip than would usually be expected. When the ABS controller sees this more than once or twice, it probably assumes that it's on patchy ice and alters its behavior accordingly. Again this is probably a tradeoff that was made for maintaining stability on icy surfaces.

Well, 'never' is a strong word... As I mentioned before, there are situations where ABS can increase stopping distance - most notably on deformable surfaces (packed snow, gravel, etc). In this case the ABS prevents the formation of the wedge of crap that would normally build up in front of the tire, which would have added additional stopping force. Another instance would be on "Split mu" surfaces (i.e., right side of the car is on dry pavement, left side is on ice). Braking on such a surface will cause a very significant pull towards the pavement side. The abs system will make a calculated tradeoff here to try to regain some amount of stability - namely by reducing the right-left imbalance by reducing the brake pressure to the pavement side. This will increase the stopping distance, but you have a much better chance of staying on the road and not spinning out. All modern ABS systems do this tradeoff to some extent, but the balance between stability and stopping distance will vary from manufacturer to manufacturer. However, in my experience dry or wet pavement is not one of the places where it is easy to out-brake an ABS system.

The extra 10 psi of fuel pressure under boost only maintains the original 36 psi across the fuel injector (remember that the other side is at 10psi). This will allow it to have the same flow capacity, no more, no less.

That is pretty much exactly the opposite of what I have seen. However, this argument is getting a bit off topic - probably my fault. Here is a somwhat recent post that I found that had some interesting info about the pretend ABS thing: http://www.hybridz.org/phpBB2/viewtopic.php?t=19913&highlight=

Oops - just noticed that John was referring to a road racing tire in his post, not a DR. Sorry.

And my reply answered just that. Basically you are building in a LOT of understeer by running stickier tires on the rear. Since the Zs chassis has understeer designed in from the factory, why would you want to significantly increase it? I'm sure it would come back to bite you on a rainy day or in an emergency situation. I have yet to see anything of substance about the lateral force capabilities of any drag radial. It seems to me that these tires are designed to optimize their performance on the longitudinal axis, which probably means that their effectiveness on lateral performance has been compromised. I'd be more worried about generating an oversteer-prone car, if the tires on the front were something like the A032s for example. Maybe 315 drags on the rear would have enough lateral capability, but I've never seen any reputable data on exactly what their performance is, other than for drag racing. It's a wild card, at best. Also, as I recall, these tires are generally not speed rated, and are not designed for sustained high speeds. Again, not a problem for drag racing.

Not to mention being able to control the vehicle. Small detail. The stopping distance argument really only holds true on moderate- to loose-packed snow or gravel (or similar) surfaces. On these surfaces a locked wheel will build up a wedge of snow or gravel in front of the wheel, which helps the stopping distance. It is VERY difficult to out-brake a modern ABS system (a REAL one, not the pretend thing referred to above) on pavement, wet or dry. Even if you can manage to do so, I'd be willing to bet that it would be on the order of one in 20 tries, with the ABS stops performing very consistently in the meantime.