auxilary Posted February 1, 2004 Share Posted February 1, 2004 yesterday we dropped the rotary onto a crossbeam of the Z that sat on the frame rails, attached to the tranny. The car went down about 3/4" max. I stood on hte radiator support (i'm about 175lbs) and it went down another 1/2" still leaving about a 3" gap between tires and wheel well. When I had the stock L24 in there, it had a little under 1" gap. Engine is couple of inches (or more) behind front strut towers in what is now a mid engine configuration. Transmission is mounted and not moving. I'm running NON-SECTIONED stock strut housings with illuminas and 10" 200lb/in springs all around on Ground Control coilovers. For reference, the motor without turbo/intake manifold, misc. accessories, with transmission (no clutch/flywheel) weighs a little under 300. About 180 for the motor, 100 or so for the tranny (we move the motor around by hand, to/from engine stand!) I am going to guesstimate that my total Z weight will be under 2200lbs (it was 2400lbs even without the rollbar and with a full tank of gas). What would you guys suggest for springs? I have another set of 175 lb springs I need to grab from Dan Juday, but I think those won't work too well either. Should I downgrade the front to 150lb springs, or maybe even lower? I will probably have more rear weight bias, so I will leave the rear 200lb/in springs in there. They will be running with a 3.7 lsd, slightly undersized tires than stock (it equates to about 3.9:1 with smaller tires), and a 3/4" rear sway. Quote Link to comment Share on other sites More sharing options...
Guest Nic-Rebel450CA Posted February 1, 2004 Share Posted February 1, 2004 Hey Aux, I have a high performance handling handbook (not really a handbook, it's over 150 pages) that has some excellent information on calculating optimal spring rates. The chapter for shocks and springs is about 13 pages. I could scan them and email them to you, or since you live close, I could mail the book to you and you could mail it back when you are done with it. Quote Link to comment Share on other sites More sharing options...
DavyZ Posted February 2, 2004 Share Posted February 2, 2004 You know, it hit me right after you left my house the other night... Just install some cast iron weight in the front end! Dude, I have a lot of weights I can let you borrow to get that front end planted like a normal car! By gosh, we'll get it done. I'm thinking you could weld in some rebar to hold the weights in place and viola, you're just about there Davy Quote Link to comment Share on other sites More sharing options...
Guest ON3GO Posted February 2, 2004 Share Posted February 2, 2004 dont feel like sectioing your struts with some 8in or so springs? i no its extra money but it might lower your Z enough. if its that much of a gap i doubt 175 springs will do much... man thats a light Z... wish mine was like that. mike Quote Link to comment Share on other sites More sharing options...
Guest Thurem Posted February 2, 2004 Share Posted February 2, 2004 You can judge springrates by sag. The car sitting on the suspension should compress the spring a certain amount. By measuring the length of the compressed (ie. rideheight) spring and comparing it to the free length of the spring, you get how much how the spring compressed (this figure is RC ). Now measure how much more travel is available (at rideheight.) ie. when does the strut collide with the top springmount. Add these two figures together and you have a figure that tells you how much the spring is compressed at full suspensionmovement (this figure is FC). Now, RC/FC x 100% = RS is a good figure for comparing stiffness of springs. An RS about 33% would indicate a stiff ride (my assumption), which would absorb a 2G bump, an RS of 50% would only absorb a 1G bump and would be more comfy. So if you could figure the old (desired) RS (call this RS1) and compare it to the present RS (RS2) with the lighter engine, you could figure the best (desired) springrate (DS desired springrate, PS present springrate). RS2/RS1 x PS = DS So, for example, if your spring was, with old motor, compressed 3" and you had 4" of travel left your RS1 was 3/(3+4) x 100% = 42.85% Now, with the new motor you have 1.5" and 5.5" figures RS2 is 1.5/(1.5+5.5) x 100% = 21.43% 21.43/42.85 x 200#/" = 100#/" Please repeat with the actual figures from your car!!! I'm pretty sure this a good way of figuring this out, please correct me if I'm wrong. And this does not account for the effects of rollcenter and height of CG, but the wheelgap and the bumpreaction should be the same. Thure Quote Link to comment Share on other sites More sharing options...
ZROSSA Posted February 2, 2004 Share Posted February 2, 2004 Aux, I dont think spring rate has anything to do with your ride height problem. The installed lenght of the spring is just to long. It sounds as though you have coil overs and i take it you are at the end of your ajustment. You just need shorter springs or modifiy how they are mounted. Lower the bottom spring purch, Get ride of the isolaters and run camber plates, Shorter springs with a helper spring, section the stuts and run a shorter spring. You could run a super soft spring but that wont cut it in the corners. Douglas Quote Link to comment Share on other sites More sharing options...
auxilary Posted February 2, 2004 Author Share Posted February 2, 2004 thurem: thanks, i'll check that out nick: i may take you up on that in a little bit zrossa: they're the same springs I've been driving around on for over a year, and since the only variable that changed was weight, a lower spring rate will compress more easily under the current load. (weight's also repositioned, most of it is towards the rear) I'm also considering sectioning my strut housings and running shorter illuminas to lower the front, but springs are cheaper and easier to replace at the moment Quote Link to comment Share on other sites More sharing options...
ZROSSA Posted February 2, 2004 Share Posted February 2, 2004 Aux, Using the spring rate of 175 lbs roughly means that for a 2 inch ride height gain you would have lost 700 lbs of the front end. This seems unlikely to me. What has probably happened is that the tire are stuck high in there travel after the car has been on the jack stands. A bit of bouncing can get them back down, or a bit of a drive around. Douglas Quote Link to comment Share on other sites More sharing options...
Modern Motorsports Ltd Posted February 3, 2004 Share Posted February 3, 2004 I assume you're at the bottom of your adjustment? Seems odd with 10" springs and typical sleeves, must be high on your strut? You didn't state why you want to change.....25 lbs here/there won't make the change you want. I'm not familiar with your resources but how much work for you to drop your threaded sleeves/re and re the lower perch? My custom lower pieces make for an easy install, I could flash 4 out to you for less than a single spring. What top hats do you have on your coilovers? Thin ones (ie. 1/4") or 1"...if thin then go with 8's or section, 8's cheaper and far easier IMO. If you have thick tops, my custom 1/4" thick tops would drop your car the difference in thickness of your tops and mine (ie. some are in excess of 1" thick). I'm not sure which ones Ground Control set you up with. Some options for you. Quote Link to comment Share on other sites More sharing options...
johnc Posted February 3, 2004 Share Posted February 3, 2004 Its not the springs. Shorten your struts, install a coil over setup, and install camber plates. Quote Link to comment Share on other sites More sharing options...
BillZ260 Posted February 3, 2004 Share Posted February 3, 2004 can you weigh the front of the car, and try to make a change in springs based on that? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted February 3, 2004 Share Posted February 3, 2004 All I have to add is that when you get this thing done you HAVE to get it on some scales. I'm really interested to see where your weight is and what your weight is... Jon Quote Link to comment Share on other sites More sharing options...
ZR8ED Posted February 4, 2004 Share Posted February 4, 2004 Auxilary.. you are now in the same boat I'm in... Stiff springs are lost on our cars with the reduced wieght up front... (though yours sounds much lighter than even mine...) Anyways...I upgraded my rear springs to allow a bit more clearance for the rear tires and to fight the massive squat from the extra torque of my new power plant..I thought I needed to upgrade my front springs as well... NOT... I have my stocko springs original "ala" 1978 with 4 coils cut approx (can't remember its been way too long) I do recall some calcs and it was approximiated that my front springs were in the 150 lb range.... Stock is very low 100's.. I want to reduce mine even further to correct my understeer..(which has come back since I widened the rear track 6" ++)... go figure I didn't catch in your post if you had coil overs or not.....you may want to look into stock springs, and cut to get your ride height... If you have coil overs.. then you need a much lighter spring up front.. 25lbs less is not very much.....50-75lbs sounds much better.. Corner weighting the car as some people have mentioned is the correct method... mine is the low budget method of educated guesses from past experience of poor guesses....hehehe Quote Link to comment Share on other sites More sharing options...
johnc Posted February 4, 2004 Share Posted February 4, 2004 From a handling perspective, don't use springs to adjust ride height. Springs are selected to control mass, load transfer, and load transfer rate. Quote Link to comment Share on other sites More sharing options...
auxilary Posted February 4, 2004 Author Share Posted February 4, 2004 oh, I didn't imply springs to adjust ride height. I'm considering switching to 150lb springs in the front because of such light weight. I have coilovers right now, but I'm not running sectioned strut housings, so I'm limited to how much I can lower the car without sacrificing suspension travel. Strut sectioning was my first choice, but I need to figure out how much I can go down before my oilpan is dangerously low. Thanks for your input, guys. Quote Link to comment Share on other sites More sharing options...
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