johnc Posted October 21, 2005 Share Posted October 21, 2005 What I'm getting at is that it is indeed dependant of setup and where you put everything, but if you have a 2 foot long 400lb motor, and a 3foot long 500lb motor and have no plans of cutting the firewall that 3foot long motor will have more weight closer to the front of the car than the 2footer, period. After reading this again, I think you have a small misunderstanding regarding weight distribution. When we talk about weight distribution we're talking about percentages of the total weight of the vehicle. If we have a 2,000 car that has a 50F/50R weight distribution then 1,000lbs are on the front axle and 1,000lbs are on the rear axle. In your above example the longer engine has some mass farther forward but that extra 12" of mass only moves the CG of that 36" long engine forward 6" (compared to the 24" long engine and assuming its a solid block of metal). And, because the weight is always being distributed through all 4 wheels the net affect on weight distribution is smaller then we think. So, let's do the math again: 2,000 lb vehicle (400lb. 24" long engine) - 50F/50R WD. 2,100 lb. vehicle (500lb 36" long engine) - 50.2F/49.8R WD. Both of the above were calculated with Longacre software assuming a few basic things. That addition 100lbs made a difference of 2/5 of 1% in the weight distribution, although overall weight went up by 5%. Is that difference significant? Would it require some changes in suspension tuning? Probably not because much bigger changes are compensated for when using up fuel in a fuel cell hung out behing the rear axle. Quote Link to comment Share on other sites More sharing options...
crazy280 Posted October 23, 2005 Share Posted October 23, 2005 John, I think you misplaced the decimal. It should be .52/.48 For example: a car with 1000 lbs on each axle has a weight distribution of 1000/2000 for the front and 1000/2000 for the rear, which is .50/.50. Whereas a car with 1100 lbs on the front axle, and 1000 lbs on the rear axle has 1100/2100 for the front and 1000/2100 for the rear, which is a weight distribution of .5238/.4762 (roughly .52/.48 ) which is a significant change in weight distribution for a road-race car. Please correct me if I'm wrong. Quote Link to comment Share on other sites More sharing options...
Mikelly Posted October 23, 2005 Share Posted October 23, 2005 I'm sorry, I missed the bell... I didn't realize class was in session and Mr. C. was schooling you kids again! Bottom line to remember is any powerplant is just that, a source of power. Any Zcar is still going to suffer the same issues with regards to chassis stiffness, suspension design, braking, weight balance. John C., thanks for the morning read! Mike Quote Link to comment Share on other sites More sharing options...
johnc Posted October 23, 2005 Share Posted October 23, 2005 For example: a car with 1000 lbs on each axle has a weight distribution of 1000/2000 for the front and 1000/2000 for the rear, which is .50/.50. Whereas a car with 1100 lbs on the front axle, and 1000 lbs on the rear axle has 1100/2100 for the front and 1000/2100 for the rear, which is a weight distribution of .5238/.4762 (roughly .52/.48 ) which is a significant change in weight distribution for a road-race car. Please correct me if I'm wrong. No. Again, an additional 100 lbs. added forward of the vehicle CG does not equate to exactly 100 more pounds on the front axle. The mistake is that some people think of the vehicle CG are a pivot point in a see-saw. Its not. Adding weight forward or back of the CG moves the CG in that direction by some amount. That same amount is always less then you would think. Quote Link to comment Share on other sites More sharing options...
MusPuppis Posted October 23, 2005 Share Posted October 23, 2005 Great read. Thanks for the book recommendation as well. Tossing that on the list with Maximum Boost anda few others I need to buy and commit to memory, lol Quote Link to comment Share on other sites More sharing options...
rudypoochris Posted October 23, 2005 Share Posted October 23, 2005 I'm still racking my mind on how to complete this idea. Get a small V6 that you can get a centrifugal blower on to get to 500HP without an intercooler' date=' get the motor as far bas as possible modifying the firewall need be to get to the point you can't go back farther due to interior space, then modify the front end so there isn't so much nose overhang. A R230 should add some weight to the backend. Put in a cage and weld the roof to the cage to drop the roof line slightly. Rake the windshield back a bit for areo. Put in all speedglas type windows. You should have an ultra low CG with a good rear weight bias to get a really good base to tune with. Granted it would be alot of work for a small difference, it would be dang fun to do.[/quote'] Bah just put in a flat 6 from an svx or b9 tribeca if you really want to go sixes. Wonder if it fits though.... it might with some movement of the steering shaft. Quote Link to comment Share on other sites More sharing options...
Gollum Posted October 23, 2005 Share Posted October 23, 2005 Saw a nice V6 S30 at the brisbane show today, really confirms my ideas about a 6 banger. With as small as pushrod V6 motors are i'm surprised more people havn't done them. The entire engine seemed to sit behind the wheels, as well it should, with the motor only being 3 cylinders long. Quote Link to comment Share on other sites More sharing options...
Nismo180 Posted October 24, 2005 Share Posted October 24, 2005 After reading this again' date=' I think you have a small misunderstanding regarding weight distribution. When we talk about weight distribution we're talking about percentages of the total weight of the vehicle. If we have a 2,000 car that has a 50F/50R weight distribution then 1,000lbs are on the front axle and 1,000lbs are on the rear axle. In your above example the longer engine has some mass farther forward but that extra 12" of mass only moves the CG of that 36" long engine forward 6" (compared to the 24" long engine and assuming its a solid block of metal). And, because the weight is always being distributed through all 4 wheels the net affect on weight distribution is smaller then we think. So, let's do the math again: 2,000 lb vehicle (400lb. 24" long engine) - 50F/50R WD. 2,100 lb. vehicle (500lb 36" long engine) - 50.2F/49.8R WD. Both of the above were calculated with Longacre software assuming a few basic things. That addition 100lbs made a difference of 2/5 of 1% in the weight distribution, although overall weight went up by 5%. Is that difference significant? Would it require some changes in suspension tuning? Probably not because much bigger changes are compensated for when using up fuel in a fuel cell hung out behing the rear axle.[/quote'] ah, I see, so essentially my lack of knowledge of the stigmas surrounding this platform and incorporating those of my own platform(RBs, 20 or bigger, in a 240sx is more than enough to require spring rate changes to compensate for a much more nose heavy car) has changed my answer from downright correct to, moderatly agreeable, but not that important. Fair enough Quote Link to comment Share on other sites More sharing options...
crazy280 Posted October 24, 2005 Share Posted October 24, 2005 Well, if what you say is true, and it is only 2/5 of a percent weight on the front axle, that would mean putting 100 pounds more in the front of the car only adds 4 pounds more to the front than the rear. Maybe the decimal got misplaced, remember, .02 means 2 percent. What if you put 100 pound heavier axles in front? Would that also only change the weight distribution .2 percent? Quote Link to comment Share on other sites More sharing options...
johnc Posted October 24, 2005 Share Posted October 24, 2005 What if you put 100 pound heavier axles in front? Would that also only change the weight distribution .2 percent? No. When talking about weight distribution we are really talking about the longitudinal location of the CG. Also, putting heavier axles on a car is not a good analogy for this discussion because we are talking about spring weight (the chassis). If you have a live axle car and make the live axle 100 lbs. heavier then yes, that end of the car just got 100 lbs. heavier. But, if you put 100 lbs. in the chassis directly over the axle then that end of the car will not get 100 lbs. heavier. Again, the sprung weight (the chassis) gets spread over all 4 wheels. I don't know how to state this any better. Quote Link to comment Share on other sites More sharing options...
johnc Posted October 24, 2005 Share Posted October 24, 2005 ah, I see, so essentially my lack of knowledge of the stigmas surrounding this platform and incorporating those of my own platform(RBs, 20 or bigger, in a 240sx is more than enough to require spring rate changes to compensate for a much more nose heavy car) has changed my answer from downright correct to, moderatly agreeable, but not that important. I know there's a lot of emotion and ego tied up with everyone's builds and, as said in a post above, I'm not knocking what people are doing (this is HybridZ for God's sake). I'm not implying anyone is ignorant, stupid, mistaken, etc., I'm just trying to let people know what I've learned from building and racing 240Zs since 1998. Ya know, I try, and sometimes I wonder why I bother. Quote Link to comment Share on other sites More sharing options...
crazy280 Posted October 25, 2005 Share Posted October 25, 2005 No. When talking about weight distribution we are really talking about the longitudinal location of the CG. Also' date=' putting heavier axles on a car is not a good analogy for this discussion because we are talking about spring weight (the chassis). If you have a live axle car and make the live axle 100 lbs. heavier then yes, that end of the car just got 100 lbs. heavier. But, if you put 100 lbs. in the chassis directly over the axle then that end of the car will not get 100 lbs. heavier. Again, the sprung weight (the chassis) gets spread over all 4 wheels. I don't know how to state this any better.[/quote'] I get the concept of a sprung chassis. But I find it hard to believe that adding 100 lbs directly above the front axle ends up with 48 (almost half!) of those 100 lbs over the rear axle (according to that "Longacre" program). I looked up some stats as a reference, and according to "Road and Track" (august 1965) the big block vette (396) had a 51/49 weight distribution, while the small block vette (327) had a 48/52 weight distribution. I think this is a perfect analogy for what we are discussing, because the article quoted the 396 engine as 150 lbs heavier than the 327, which in the same car changes the weight distribution by 3%. Engine placement in each car was very close to the firewall, with no relavent changes to the chassis other than the engines. I hope I don't come off as argumentative, I'm just trying to discuss. Believe me, I appreciate this site alot for allowing me to learn from people (such as yourself) who have much more experience than I do Quote Link to comment Share on other sites More sharing options...
johnc Posted October 25, 2005 Share Posted October 25, 2005 I hope I don't come off as argumentative, I'm just trying to discuss. You're not coming off that way. In my example above I figured that the additional 100lbs. was behind the front axle not directly above it. Basically I assumed that the 24" engine was up against the firewall and an additional 12" was added forward of that. You BB/SB Corvette example is interesting. I wonder about engine position, transmission differences, and other itmes. But its probably a good example for this discussion. Quote Link to comment Share on other sites More sharing options...
getoffmyinternet Posted March 6, 2008 Share Posted March 6, 2008 For what it's worth, as a spectator of an apparently dead topic, it seems that part of the confusion is coming from interchanging the idea of simply "adding weight" and "putting weight on the axle." If the engine increases in weight, not all of that weight is transfered to the front axle we can all agree, yes? It is true that if you put 100lbs literally on top of the front axle, that axle receives all of the added distribution, but consider if you added 100lbs directly over the center of the car between the two axles. Your distribution changes exactly 0%. On the other hand, if you added weight forward of the front axle, the weight distribution change is two fold. First, all of the new weight is supported by the front axle, and second, that weight now has leverage over the rear axle since the front axle becomes the fulcrum. To put it oversimplified, weight added forward of the front axle is not only added to front distribution, but partially subtracted from rear. It's like on big city busses--barely any weight is over the front tires because of the enormous ass hanging out the back of the rear axle. Consider this in lieu of all that, and without me going out and taking all sorts of measurements to be able to apply it to the real world difference between these two engines or plug them into any software. Say you have a 2000lb car distributed over an 6ft axle distance at 50/50. You add 100lbs on the chassis one foot rearward of the front axle, at the 17% station. Your new distribution should be closer to 51.6/48.4. This is because the weight is distributed 83% to the front and 17% to the rear, making the balance 1083lbs/1017lbs. To get the actual change in weight you would have to plug in exactly how much weight is being added and at what relative distance between the axles it is being added. Now if we supposed that all of that extra 100lbs is being added right on the front axle of a 2000lb car, the difference is obvious: a 2% forward weight distribution adjustment. The actual difference, because the weight is not added directly over the axle, will be slightly less, but couldn't be a whole lot. Really, a 2% difference in distribution is more like a 1% adjustment, because what is subtracted from the weight of one axle is added to the other. If you have a 2000 lb car and your distribution is 52/49, you only need to get 20lbs from the front axle to the rear to be balanced. So is 2% that big of a deal or not? Methinks it depends mostly on the car and the driver. Perhaps your personal diet has more effect on your car's distribution than which engine you choose to put in it. Actually now that I think of it, if you're in a car that weighs 2100lbs with a distribution of 52/48 and you're sitting like a third of the way between the front and rear axle, getting out of the car wouldn't even be enough to even it out. The front would have 1092lbs on it and the rear would have 1008lbs on it, a difference of 84lbs. That means you'd have to lose 252lbs altogether to make the weight over the front and rear balanced at 924lbs each, unless my windows calculator is malfunctioning. Try feeding your car celery... I think the point here, if there is one, is that adding or subtracting weight has a much less significant of an effect on distribution than actually redistributing weight, ie. taking it from one side and putting it on the other, such as in this example where instead of having to cut out 252lbs of meat from the cockpit, a weight redistribution of 42lbs from front to back could be made. Much more attention should be payed to actual placement of the engine and associated parts than its actual weight versus another one. But like it was stated earlier, if the smaller engine is used, associated parts can also be shifted closer to the center as well. Sure a track friendly rb can be done, but you've got a slightly smaller, slightly lighter, slightly cheaper option in a 4banger that already comes with slightly more torque than it's rb equivalent and should rev slightly higher due to the fact that it is slightly shorter and would suffer slightly less harmonic issues. Hmmm... Quote Link to comment Share on other sites More sharing options...
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