Savage42 Posted January 2, 2007 Share Posted January 2, 2007 I wanted to make a comment about the idea of welding the rear diff. A young guy who is a member of the local Auto-X club drives a 240SX with a welded rear diff (he set it up for drifting) and he has problems keeping the rearend behind him. The car has an SR20DET so it's got power similar to a V8 Z which makes it a resonable example. Speaking from experience with both welded diffs and turbo cars and autocrossing, here's what I've experienced. Welded diffs seem to work better with cars with slicks. Bias ply tires must have enough give to make it work better than stiffer radials. As for turbo cars, they are far from the best setup for autocrossing. The quick transitions and short bursts make them far from ideal. Just because the SR20DET has the same HP levels as a V8, it's how it makes that power that is key. Torque is king in autocrossing and linear power of a V8 will always trump the turbo "on-off" switch power band in that game! I had a VG30ET in my 510 and it was much better at the hillclimbs than autocrossing, as I was always afraid to "stab the gas" while accelerating & cornering, as boost would hit and the car would come around on me. A welded diff would make it worse, as they make the car push until they loose grip and then you get sideways. Finess, balance of handling & power and smooth driving is the key to going really fast. Of course, sequential turbo cars, like the 3rd gen RX7, aren't as bad, but if you are cornering on the limit right between the transition of the 2 turbos, the same problem can occur with a spike in boost! It's always something! Driving style, vehicle type and course layout always add variables to the whole equation. Quote Link to comment Share on other sites More sharing options...
lbhsbZ Posted January 6, 2007 Author Share Posted January 6, 2007 OK, I think I have the motor situation sorted out....I found a 4 bolt 350 up in the pallet rack at work....asked around and nobody claimed it, so I did. I had it x-rayed and it looks like a good block. Its at the machine shop right now getting prepped. I'm running .030 over 12.5:1 with about a .650 lift roller cam and a set of Brodix -11 heads I picked up. It should be good for at least 550hp. Damn this is getting expensive. In the morning I'm heading back down to the shop from whom I bought the car to show them the old motor and try to either get some money back from them or get some more parts....like a R200 diff and some spare axles and hubs or ????. Is there anyway to ID a R200 from a R180 without taking the cover off? About the diff, I may try my luck with a $350 OBX helical diff from ebay or go with the Powerbrute...not sure which yet. I'm making progress though. Quote Link to comment Share on other sites More sharing options...
240zV8 Posted January 6, 2007 Share Posted January 6, 2007 r180's are rectangular looking from the back, the r200 is more rounded like a stop sign. check these http://www.geocities.com/MotorCity/Garage/6212/diffswap/diffswap.htm http://www.geocities.com/madmanadam/Z-car/r200swap.html Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted January 6, 2007 Administrators Share Posted January 6, 2007 It's impossible for me to say for sure from here why his car reacts that way, but in theory the car with the V8 mounted further back should be the better turning car. According to Milliken and Milliken, increasing front weight distribution normally improves turn-in. Page 401... "Turn-in will be improved as the CG is moved forward and the front tires do more of the cornering" I suspect the issue with this guy's car was one of setup, but again, impossible to say for sure. I am familiar with the car/driver that Savage is refering to... he's beat me more times than I have beaten him, unfortunately Agreed, set-up is KEY. There is more than what's obvious in this post, but thats true of virtually every developed car. Look at just about any modern front engine/rear driver sports car and you'll see the same thing... S2000, Vette, etc. Engine is stuffed way in the back of the it's compartment in an attempt to get the PMOI to a minimum. They certainly don't do that to make them easy to work on... The C5/C6 has the transimission coupled to the diff so the PMOI is somewhat arguable in this case. Quote Link to comment Share on other sites More sharing options...
lbhsbZ Posted January 6, 2007 Author Share Posted January 6, 2007 According to Milliken and Milliken, increasing front weight distribution normally improves turn-in. Page 401... "Turn-in will be improved as the CG is moved forward and the front tires do more of the cornering" M&M are absolutely right.....but what good does turn in do you when the back end of your car just passed you? There is a happy spot, which changes depending on the degree of acceleration or deceleration that the car is experiencing....which makes said spot and even finer happy spot. Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted January 6, 2007 Administrators Share Posted January 6, 2007 M&M are absolutely right.....but what good does turn in do you when the back end of your car just passed you? I think thats why the word "balance" was invented Quote Link to comment Share on other sites More sharing options...
A. G. Olphart Posted January 6, 2007 Share Posted January 6, 2007 I would think that if the "PMOI" gets too small (everything concentrated around the CG) in a short wheelbase car, that it would be a real handful to drive hard. Should snap spin in a fraction of a second. The most comfortable road car I've ever had was a 58 Desoto (the Chrysler sized model). Whilst traveling from Montana to Texas, I drove it through Kansas (top to bottom) on glare ice. Had the roads pretty much to myself. Nice long wheelbase, lots of time to catch a skid, and there weren't many of those. (You can tell I've not owned any recent vehicles). <> Quote Link to comment Share on other sites More sharing options...
lbhsbZ Posted January 6, 2007 Author Share Posted January 6, 2007 Damn, I had a much better post written up, but the interweb ate it. Weight distribution is like drinking....moderation is key. When you get to the extremes with it, bad things can happen. Up to only a bit more than 60/40, in one direction or the other, is generally managable. I (was drunk one night and ordered a very expensive set of scales online) will put the car on the scales when I get the engine back together and in. This motor has aluminum heads, a single plane aluminum intake, aluminum water pump, and the rest is iron. I can weigh the complete engine before it goes in too. Does anyone know the weight of a fully dressed stock 240 motor? Quote Link to comment Share on other sites More sharing options...
wheelman Posted January 6, 2007 Share Posted January 6, 2007 Just for reference I weighed my 240 with an iron head LT1, T5, R200 and 2001 Camaro fuel tank (15 gallon plastic construction) at our local track last year. The scale was a single pad so I don't have individual wheel weights but we got reasonable front/rear weights. I wasn't in the car, the tank was 1/2 full and the engine is mounted in the JTR position and set back as far as I could get it. Total weight: 2540 lbs Front: 1320 lbs Rear: 1220 lbs 52/48 distribution Turn in is great and the rear is not squirrelly unless I jump on the throttle mid corner or lock the rear brakes which is nearly impossible with the stock drums. I have spun the car twice by shifting from 3rd to 2nd and dropping the clutch mid corner without matching the engine revs to car speed. It effectively locked the rear tires and the car swapped ends, fortunately for me I was auto crossing at the time so had plenty of room to spin and not hit anything. I'm running the MSA sway bars, Tokico springs and struts so the suspension is not tuned or very stiff. The car is very neutral but oversteer can be induced with the throttle. Wheelman Quote Link to comment Share on other sites More sharing options...
240zV8 Posted January 7, 2007 Share Posted January 7, 2007 you wanna drive up to bellingham and let me drive ur car? ^ lol Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted January 7, 2007 Share Posted January 7, 2007 OK, I think I have the motor situation sorted out....I found a 4 bolt 350 up in the pallet rack at work....asked around and nobody claimed it, so I did. I had it x-rayed and it looks like a good block. Its at the machine shop right now getting prepped. I'm running .030 over 12.5:1 with about a .650 lift roller cam and a set of Brodix -11 heads I picked up. It should be good for at least 550hp. Damn this is getting expensive. In the morning I'm heading back down to the shop from whom I bought the car to show them the old motor and try to either get some money back from them or get some more parts....like a R200 diff and some spare axles and hubs or ????. Is there anyway to ID a R200 from a R180 without taking the cover off? About the diff, I may try my luck with a $350 OBX helical diff from ebay or go with the Powerbrute...not sure which yet. I'm making progress though. More like magnafluxed, not x-rayed. Your muncie will be in little itsy bitsy pieces in no time flat no matter how easy you are on it with that combination. Quote Link to comment Share on other sites More sharing options...
lbhsbZ Posted January 7, 2007 Author Share Posted January 7, 2007 No, I had it X-rayed. My machinist builds mostly race engines and he sends all blocks out for X-ray...at least all of them that plan on making horsepower. Magnafluxing will only show cracks on the surfaces that you can see. Anyway, its coming along rather well. I went to see the guy I bought the car from today, and talked him into giving me a R200 diff since he screwed me on the motor. I also ordered an OBX center for it, I'll try my luck and post some pictures once I receive it. I ordered the M22 gearset in hopes that it may make my gearbox live. I have most of it sorted out. My only concern now is what wheel/tire package I want to get. I was thinking about getting some Nascar wheels because they're dirt cheap, but I can't fit very big brakes under 15" wheels, and aside from Nascar tires, they're isn't much out there in terms of wide race rubber for a 15" wheel. 17" seems to have the most tire possibities. I found a set of Mustang wheels, 17x10.5s in the back and 17x9s in the front, brand new, for under $400, with only about a 1 inch offset. I plan on converting to 5 lug anyway, so these may be the ticket. I imagine I'll have to do some more flare work and turn up some wheel spacers, but it might work. 5 lugs also opens up my brake options considerably. I've started gutting and plan on beginning the cage next weekend. Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted January 7, 2007 Share Posted January 7, 2007 No, I had it X-rayed. My machinist builds mostly race engines and he sends all blocks out for X-ray...at least all of them that plan on making horsepower. Magnafluxing will only show cracks on the surfaces that you can see. Anyway, its coming along rather well. I went to see the guy I bought the car from today, and talked him into giving me a R200 diff since he screwed me on the motor. I also ordered an OBX center for it, I'll try my luck and post some pictures once I receive it. I ordered the M22 gearset in hopes that it may make my gearbox live. I have most of it sorted out. My only concern now is what wheel/tire package I want to get. I was thinking about getting some Nascar wheels because they're dirt cheap, but I can't fit very big brakes under 15" wheels, and aside from Nascar tires, they're isn't much out there in terms of wide race rubber for a 15" wheel. 17" seems to have the most tire possibities. I found a set of Mustang wheels, 17x10.5s in the back and 17x9s in the front, brand new, for under $400, with only about a 1 inch offset. I plan on converting to 5 lug anyway, so these may be the ticket. I imagine I'll have to do some more flare work and turn up some wheel spacers, but it might work. 5 lugs also opens up my brake options considerably. I've started gutting and plan on beginning the cage next weekend. Must be nice to live in the big city where that's available. Here we just turn on the 40 watt hipo bulb and look for cracks! :lmao: If we have money then we go to our big city (Yay!!!) and all we can get is magnaflux and sonic testing! (Yay!!!) Back in the day, crap I'm old, the BW T-10 and the M-22 were the hot ticket. A hot sbc or a good bbc were all it took to scatter either of those into lots of little pieces with no warning. Neither muncie will hold up to that kind of power IMHO, at least not for very long. If your going to keep the slush box look into the jerico or TKO. Quote Link to comment Share on other sites More sharing options...
lbhsbZ Posted January 7, 2007 Author Share Posted January 7, 2007 Yeah, the only thing nice about L.A. is that everything is here within a 40 mile radius....it just takes you 4 hours to get across town cuz of the damn traffic. As I was making my gearbox choice, I called up all the V8 boys that I race with in Mexico and discussed it with them. One runs a 425hp crate motor in a 3200lb camaro with an M21 transimission and some kind of hipo clutch, and breaks them constantly. One runs a 3rd Gen RX-7 that weighs about 2600 lbs, with a T5 out of a 5.0 camaro and a stock clutch, and hasn't broken anything in 4 years. I figure my car will come in at less than 2400lb, because I'm cutting out everything that doesnt' need to there. The same engine in a lighter car will put far less stress on the driveline than it will on a heavy car. I remember breaking M21s in my old big block nova that weighed 3200 something lbs, but in my T-bucket, with a blown small block in it, I never head issues with an M20. I guess we won't know until we try it. A Jerico is not in the budget right now. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted January 7, 2007 Share Posted January 7, 2007 According to Milliken and Milliken, increasing front weight distribution normally improves turn-in. Page 401... "Turn-in will be improved as the CG is moved forward and the front tires do more of the cornering" To a point maybe, but then you run into the nose heavy car's dart like performance. Similarly, I've often said that driving a 911 is like throwing a dart backwards, and that is why so many Porches are seen headed off the track ass end first. Racing stockish Mustangs on the other hand is like throwing a dart forwards, is why you see so many Mustangs understeering off the side of the track, and why the fast ones move the engine back. There is a happy medium, and turn in can be affected by a lot of factors other than weight distribution. Have you ever seen the posts where Cary is trying to convince me to move the alternator and radiator to the back of my car? Maybe he has the wrong idea??? All I'm saying is that if I had a blank slate to design a Z it wouldn't have a 60/40 distribution, it wouldn't even have a 50/50 distribution. I'd shoot for something more like 45/55. The only guys I know of that race with a front heavy car on purpose are the front drivers, and I bet if they could move weight back they would too. Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted January 7, 2007 Administrators Share Posted January 7, 2007 Jon, I Apologize if I came across as antagonistic. I generally agree with your statement. I even went so ar as to move an L6 reward 14"... I was just trying to make the point that there can be favorable traits to a front biased car. Quote Link to comment Share on other sites More sharing options...
tube80z Posted January 8, 2007 Share Posted January 8, 2007 According to Milliken and Milliken, increasing front weight distribution normally improves turn-in. Page 401... "Turn-in will be improved as the CG is moved forward and the front tires do more of the cornering" See number 4 on page 393. Sometimes I think you need a owners manual for this book. The only thing I can add is that I don't think it's possible to build a Z car that has so little PMOI it is undrivable. That will be tested when my car runs as the engine sits completely behind the firewall. Cary Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted January 8, 2007 Administrators Share Posted January 8, 2007 See number 4 on page 393. Thats refereing to turn-in on the brakes which could be a different scenario? To use an example... slaloming in an autocross vs. corner entry on a road corse. Seems like two different types of turn-in... am I looking at it wrong? Sometimes I think you need a owners manual for this book. Cool... I'm glad I'm not the only one that feels that way Quote Link to comment Share on other sites More sharing options...
bry593 Posted January 22, 2007 Share Posted January 22, 2007 i have a '72 240z with a v8 chevy. the chevy mounts are centered on the original datsun risers (these are my own mounts, had never heard of scarab when i built them). the car handles pretty well and is gravy to work on. the weight bias is about 51/49 with a half tank of gas.... you can definitely get better than 50/50 with the setback position. -bry Quote Link to comment Share on other sites More sharing options...
wheelman Posted January 22, 2007 Share Posted January 22, 2007 Bry, What is the weight of your car? Do you have aluminum heads, water pump, intake manifold, etc.? How did you weigh it to determine the weight distribution? What transmission are you running? Wheelman Quote Link to comment Share on other sites More sharing options...
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