DennisK Posted April 20, 2000 Share Posted April 20, 2000 When I first logged onto this site I thought "wow, GREAT!". After a few days I"ve come to learn many things to help me with my project. The most important thing I've learned, however, is YOU GUYS ARE ALL NUTS! Just like ME! Now for your expertise. I went to the links where you plug in trans, tire size, redline and get speed on a graph. When I put the T56 at 6500 rpm, and 265/50/15 tires top end is a mere 277mph! There are some guys in Indiana that would be interested for next month's get together! I know some of you race and some are gonna show their cars, but for everyday driving, and putting down a Viper or Vette once in a while, is the expense and comlicated installation of the T56 worth it? Yes, I'm the guy who is going to use the Muncie M22, the chart says I'll top out at 160+mph(327, punched,bluprinted,etc.) I'll probably try to get there once(if I Live)or twice, but for the most part, GETTING to speed(however past the limit that might be!)is probably going to be the most fun. Doesn't that mean Less weight? I have a ZF trans that's awfully heavy, do the other 5 and 6 speeds have similar weight? Wouldn't that offset all the money spent to do what we really want to do? Please correct me if I'm wrong. Quote Link to comment Share on other sites More sharing options...
pparaska Posted April 20, 2000 Share Posted April 20, 2000 Dennis, I think the main reason for wanting the overdrive in the Z is because if you keep with the Nissan differential you are stuck with no lower (numerically) than a 3.364:1 ratio which is rare in an R200, a much more common 3.545:1 in the open R200s, and a 3.7:1 or 3.9:1 from the 87.5-88 300ZX T LSD units. (Remember, those 3.15:1 gears are NLA so finding them is like finding hen's teeth.) Of course, you could buy a new ring and pinion set at 3.364:1 (still available?) or 3.545:1 to put in an LSD R200, but it wouldn't be worth the expense (to me anyway). The 3.364:1-3.7:1 diff coupled with a 25-26 inch diameter tire (more would be tough to fit) means that you will be running around in the high 2 thousands rpm range at 60mph. If you drive on the highway much, that can get tiresome and burn a good bit of fuel. That's the reason JTR preaches the overdrive tranny and I think it's sound advice if you cruise the highways much. I don't think that top speed is the reason anyone goes for an overdrive tranny. The loss of mechanical advantage in overdrive usually means that your top speed is limited since less horsepower is available at the wheels in overdrive, and you need HP to get top speed (especially in the moderately un-slippery Z body). Most top speed runs are done at 1:1 gear for this reason, except for maybe Lingenfelter's cars . ------------------ Pete Paraska - 73 540Z - Marathon Z Project - pparaska@tidalwave.net">pparaska@tidalwave.net - Quote Link to comment Share on other sites More sharing options...
Mikelly Posted April 20, 2000 Share Posted April 20, 2000 .....and I wouldn't exactly call the T56 install difficult. The real issue with the T56 is the fact that there is very little info on them. Since I wrote my tech article, a number of things have been disproven, like the widening of the trans tunnel, grinding of the fins, and the mod to the "Skip Shift" solenoid. The trans does have to be widend on the passengers side, but not on the drivers side, and the other mods listed above do not have to be done at all. The two problems I had with the trans were related to the installation of the Clutch kit, and the balancer plate I used behind the flywheel, which caused problems with the clutch fork. If I ever do this conversion again, the trans will be the easiest portion of the conversion. As for why I chose the T56, I wanted a high tech, and bullet proof design in my trans, wanted something that would live with my 3:7 gears, and I wanted as much economy on the highway as a 500HP motor can have. As for that little calculation, I built my car for top end runs through the desert, and I doubt my car will see 200+mph I-F I can keep it on the ground. If I break 180MPH safely I will be very happy! Mike ------------------ "I will not be a spectator in the sport of life!" mjk [This message has been edited by Mikelly (edited April 20, 2000).] Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted April 20, 2000 Share Posted April 20, 2000 Mike..you doubt 200??? With 3.7 gears I would be surprised if you didn't see 200MPH. Are you doubting the speed because of aerodynamics alone or do you know something I should know before preaching to everyone I will have no problem beating 200MPH?? SpencZ Quote Link to comment Share on other sites More sharing options...
Mikelly Posted April 20, 2000 Share Posted April 20, 2000 Aerodynamics alone will be a tough obstacle, and then getting the car stable will also be a big issue. I think just throwing a motor in the car and running some super good gearing alone will not get you where you want to be. Spencz you have a big advantage in the sense that you are re-engineering the suspension and are gonna get the car much closer to ground than I could. Belly pans and a chin spliter will help me, but I still tihnk the car is gonna be fighting a lot of bad air under the car and buffetting the sides... Venturies in the pans are a guessing game unless you get the car in a wind tunnel and I do not have access to one. We'll see..... Mike ------------------ "I will not be a spectator in the sport of life!" mjk Quote Link to comment Share on other sites More sharing options...
DennisK Posted April 20, 2000 Author Share Posted April 20, 2000 I love it! Spenz' first thought is why not 200mph?!!! Yes, I agree with the answers so far. It really does depend on where you are going to use it. I live in the western suburbs of Chicago-no open desert runs for me! I am at the beginning stages of this project, so it'll be a while before I know for sure what's good for me. And, because of YOU GUYS, I've checked out availability of T56 trans in this area. In my set-up 6500 rpm would work out to 277mph. I understand that horsepower is important, but isn't that to get there? If given enough room, and enough time the rpm of the motor determines the speed of the gears. Diameter of the tire, in conjunction with the gear ratio determine top end, regardless of hp or weight. Hp and weight will just get you to top faster? Quote Link to comment Share on other sites More sharing options...
Mikelly Posted April 20, 2000 Share Posted April 20, 2000 Not so. The faster you go, the more dense the air, and the more of a wall of air that causes you to loose HP. It takes considerably more HP to get to 150 than it does to get to 120. The 1st time I broke 130MPH on a motorcycle it felt like I pushed through a wall... then I hit that wall again at 150. The same thing happened the very 1st time I did it my Zcar... Problem is that you will probably need much more than 500HP to get to that 277MPH that the chart calculates... There is no getting around barametric presure and the mass created by air. Remember the Porsche that took flight and did backflips at Road Atlanta last year? Dirty air caused that, and that car was not moving 200mph and had some really good CG numbers..... Barametric presure under hood and under the chassis of the car acts as a mini tornado... which causes pockets of air to build where it gets trapped..that air developes presure and expands and creates lift... that lift will be problem number two to overcome once you get past the HP issues ..... Mike ------------------ "I will not be a spectator in the sport of life!" mjk Quote Link to comment Share on other sites More sharing options...
pparaska Posted April 20, 2000 Share Posted April 20, 2000 Dennis, You need torque to counteract the aerodynamic drag on the car at much over 70 mph. And the torque needed goes up by the square of the speed. Michael is the aerodynamicists, so before I goof this up any more, I'm going to let him chime in . Quote Link to comment Share on other sites More sharing options...
John Scott Posted April 21, 2000 Share Posted April 21, 2000 I got to jump in too. I've seen well over 160 in my stock bodied Z. (5600 rpm 3.54 rear .7 4th gear with converter locked, and still pulling HARD) It didn't take very long to do and even shorter to realize how stupid it was. Yes you can go really fast in a high hp Zcar. Only a few here are taking the time to make sure the cars can be driven at these speeds, not merely attain them. Its fun to know your car can pull the high #s, but next time I'm that far into the triple digits, I want some areodynamics, BRAKES, Z tires, and tighter suspension. Yes the faster you go the more hp it takes. Lots of magazine articles state "areodynamicly limited" to the top speed #s. Most of the top end shootouts w/6 speeds are done in 5th. Unless you have the hp to pull it, the .5 ratios are just to let your engine relax between showdowns. John Scott Quote Link to comment Share on other sites More sharing options...
Michael Posted April 21, 2000 Share Posted April 21, 2000 Well Pete, since you threw down the gauntlet... Gearing constrains how fast the car can go in principle, without exceeding the engine's power band. So let's assume that we have tall enough gears in the differential, and sufficiently many gears in the transmission, that any speed from 0 to 300 mph is allowable by a gearing/rpm calculator, like that web site that people have been referring to. So, what limits the top speed of the car? The balance between power available and power required. That's true for any vehicle, be it your bicycle or a jet airplane. Power = force*speed. On level ground and in calm air (none of this talk about going downhill in a hurricane!), the "force" in that equation is aerodynamic drag and rolling resistance. Mechanical friction of the drivetrain's internal parts is also important, but we'll budget that as a tax on power available (rear wheel hp vs. crank hp, etc.) So, we have: rear wheel hp = (aero drag + rolling resistance)*speed with a proportionality constant thrown in to make the units work out. Experience shows that for passenger cars, rolling friction is definitely of secondary importance compared to aero drag, when the speed exceeds 80 or so mph - again, on level ground, on smooth asphalt or concrete. The formula for aerodynamic drag is: Drag = 0.5*(air density)*(speed^2)*area*coefficient, where air density is about 0.00238 slugs/ft^3 at sea level. Density DOES NOT vary as the car speed varies. As far as this formula is concerned, it's only a function of atmospheric conditions. The area is the car's cross sectional area. For Z's, it's about 20 ft^2, roughly. And the "coefficient" is the all-mighty drag coefficient that everyone talks about. For Z's, it's about 0.45. So, to a good approximation, we have: power required = 0.00006*speed^3, in horsepower, for a Z, with speed expressed in mph. Thus, to go 100 mph, you'll need a whopping 60 hp. Maybe around 70 hp when you factor in rolling resistance. My stock 1978 Z would top out at around 120 mph, at which point it needs 103 hp at the rear wheels. That's somewhat of a low estimate, but not unreasonable, considering driveline losses, unaccounted rolling resistance, etc. Now, according to this formula, to go 150 mph, you need about 200 hp. And to make it all the way to 200, you'd need 480 hp. But again, that's 480 hp - by this LOW estimate - at the rear wheels. So it's maybe 600+ hp at the crank. Probably 650 hp to be safe. My mildly built big block is expected to make around 350 hp. If that's around 280 hp at the rear wheels, the car has enough power to reach 167 mph. But, the way my car is geared, I'll run out of rpm at around 125 mph. It's just that I'll reach it very quickly Horsepower by itself says nothing about how quickly the car reaches top speed; that's more a matter of the entire torque band, and of course, the weight of the car. And weight, by the way, has almost no effect on top speed over a smooth level road. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted April 21, 2000 Share Posted April 21, 2000 This is a very interesting thread. Aerodynamics has always been of great interest. When I was a kid I used to read everything I could get my hands on regarding aircraft design. As it has been pointed out, the aerodynamic drag on the vehicle will be the biggest obstacle to overcome. Drag on the vehicle does not increase in the same manner as the speed of the vehicle increases. The drag on the vehicle increases exponentionally (sp?). For example, if the vehicle travels at a constant speed of 50 mph then the speed is doubled to 100 mph the aerodynamic drag has increased four times as compared to the drag at 50 mph. If the speed is increased to 150 mph then the drag has increased nine times compared to the drag at 50 mph. As far as the aerodynamic design of the Z car, well I would have to say, as Pete put it, it is modest. It is really the reverse of what one would consider to be aerodynamically efficient. For example, the most aerodynamically efficient shape is a drop of water falling through the atmosphere. Lets think about a drop of water, it is large and rounded in the front and tapers off towards the rear, really the reverse of the Z car. As Mike stated, there are also a great many parts of the Z car, or any car for that matter, that produce "dead air". "Dead air" is really what causes drag as it produces a vacuum. Think about the air moving around the control arms on the suspension, over the moldings around the windshield, rolling off of the back of the rear hatch, etc...all of the air immediately behind these objects on the car is "dead air" because it is not moving. The pressure in these "dead air" spaces is lower than the pressure of the air around them and that is what causes drag and slows the vehicle down. When vehicles are tested in a wind tunnel they attach all of those small streamers all over the body of the car. What they are looking for is trying to keep those streamers moving with the flow of air over the body. If the streamers are not moving then they have found a "dead air" space and aerodynamic drag. I had my 73 240 up to 145 once and that is as fast as I care to go in a stock bodied Z car. Now with the proper aerodynamics I think it would be a great deal of fun. Remember, lift and downforce are forms of aerodynamic drag, downforce equals fun, lift equals, well you remember the example Mike gave. Chris Quote Link to comment Share on other sites More sharing options...
Mikelly Posted April 21, 2000 Share Posted April 21, 2000 Michael and Chris....Move to the head of the class.. Dennis, hope this helps clear that up. Aerodynamics make my head hurt and I have a feeling real soon I'm gonna find out that I need about 700HP to get where I want to at the speed I want to go at! Mike ------------------ "I will not be a spectator in the sport of life!" mjk Quote Link to comment Share on other sites More sharing options...
DennisK Posted April 21, 2000 Author Share Posted April 21, 2000 All points well taken, and quite knowledgble. I know in the real world all it takes to get top end speed, however , what I never really understood was pretty much what that graph/chart was saying. the engine turns(rpm) the trans turns(whichever gear) the driveshaft then the diff to the wheels. If the tire is 30" dia. the travel for one rev is the cicumference, 94.248". If the trans is in a 1:1 gear shouldn't the tire rotate at the ratio(say here 3.54) of 35% of total? Again, I know of aerodynamics and all, but it seems to me that the tires would be skidding as they were trying to go forward, and dirty air, drag etc. was pushing it back? I really do believe you guys, and know from personal knowledge, but this is fun to discuss! Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted April 21, 2000 Share Posted April 21, 2000 Dennis...the whole concept doesn't work as logically and rationally as you aer suggesting. Aerodynamic forces do not act like the trailers on the NHRA tractor pulls...you won't get wheel spin at 180 MPH!!! Go push against a interior house wall and you will get a better idea...push harder...anything happening? Now go get your drinking buddy "Killer"..yeah...300 lb Killer...and have him push on the wall..bye bye wall! Now take killer to a brick wall and have him push...anything happening? "Push harder killer..harder..harde...uh oh...Killer just ruptured something...get another drink and ponder other stuff because this conversation has just hit rock bottom and Killer has a headache. SpencZ Illegible after 11:30 PM EST Quote Link to comment Share on other sites More sharing options...
DennisK Posted April 21, 2000 Author Share Posted April 21, 2000 Yessir!!! I did post another question, and it was BEFORE the extra beers! Thanks for all the input, I really do enjoy this site! Quote Link to comment Share on other sites More sharing options...
John Scott Posted April 21, 2000 Share Posted April 21, 2000 I was going to say something about a Bentton(sp) BMW race car that had less than 1.5 litres, over 1000 hp that achieved wheel spin at 179 mph,...but nevermind. John Quote Link to comment Share on other sites More sharing options...
Guest RON JONES Posted April 21, 2000 Share Posted April 21, 2000 This is great reading.I,m wondering if any of you watch any Nascar racing?Like maybe some of the biger tracks,where they run wideopen and realy don,t use the brakes.I,m no expert,but don,t these cars have over 700HP on tap.They don,t break 200mph?Just something to think about. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted April 21, 2000 Share Posted April 21, 2000 Remember...NASCAR has restrictor plates...they would easily be over 200MPH and yes...they do have engines with a possible 750HP...but not with 2" air inlets. SpencZ Quote Link to comment Share on other sites More sharing options...
Guest RON JONES Posted April 22, 2000 Share Posted April 22, 2000 Ah yes,restrictor plates.I was just talking with my buddy,who informed me the power is more like 450 to 500 with the plates. Quote Link to comment Share on other sites More sharing options...
Mikelly Posted April 22, 2000 Share Posted April 22, 2000 500 with the plates and they are running close to 200.... Maybe I'm not too far off from my original dream... My buddy up the street had his 55 chevy with blower and double carbs out today... I was amazed at how easy he broke loose the 30 inch tires on the rear of his 4500# car.... That little 355 is huffing big time! Mike ------------------ "I will not be a spectator in the sport of life!" mjk Quote Link to comment Share on other sites More sharing options...
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