Doug71zt Posted July 9, 2008 Share Posted July 9, 2008 I am building a street/strip 280Z with a 2JZ/TH400 combo. My current car (3.0 L turbo/Z31T 5spd) has 10" long coilover springs (175F/200R) with shortened struts, and doesn't transfer weight very well at the strip. My thinking is that a softer, longer spring help get the car to transfer weight on the line. I am thinking around 140-160 area. Obviously, this car will not be running around a road course but will be street driven a fair bit. I will not be shortening the struts on this car. Anybody running something similar? Doug Quote Link to comment Share on other sites More sharing options...
JustinOlson Posted July 11, 2008 Share Posted July 11, 2008 Are you going to use a trans brake on the new setup? I'm in the same boat trying to figure out spring rates and struts for my 2JZ/TH400 build. Justin Quote Link to comment Share on other sites More sharing options...
thehelix112 Posted July 12, 2008 Share Posted July 12, 2008 I'm guessing its a very fine line you're walking, and as johnc would point out, everything is a compromise. If you go with long-travel, very soft springs, then you are gaurunteed a lot of camber change during launch, which at a guess, will reduce grip. If you go with limited compression suspension on the rear, you run the risk of overloading the tyre's and reducing grip also. Maybe a potential solution is to run 15s with larger sidewalls, let the tyre deal with the compression, and keep the suspension you have for now. Dave Quote Link to comment Share on other sites More sharing options...
tube80z Posted July 12, 2008 Share Posted July 12, 2008 I am building a street/strip 280Z with a 2JZ/TH400 combo. My current car (3.0 L turbo/Z31T 5spd) has 10" long coilover springs (175F/200R) with shortened struts, and doesn't transfer weight very well at the strip. Weight transfer has nothing to do with the springs. I'm not following how that's going to work. I'm not a drag racer so maybe I'm missing something. Cary Quote Link to comment Share on other sites More sharing options...
thehelix112 Posted July 13, 2008 Share Posted July 13, 2008 Weight transfer has nothing to do with the springs. Cary, I assume you're referring to the fact that the suspension system has no effect on the amount of weight tranfer that happens? I am relatively confident that the suspension system does have a pretty large influence on how the total transfer is applied. I'm not a mecheng, but from my limited understanding, the stiffer the suspension, the faster the transfer occurs. While I know next to nothing about tyre loads, or drag racing, it would seem that if you are asking the tyre to give you longitudinal force, whilst it is in the midst of deforming horribly due to a large shock load, it might just say `no'. Dave Quote Link to comment Share on other sites More sharing options...
datman Posted July 13, 2008 Share Posted July 13, 2008 Surely the length wouldn't make any difference unless the coils were binding? If the LB rating was less it would just need a little more preload to get the same ride height. You could just run a softer spring of the same length if it's softer you're after. Quote Link to comment Share on other sites More sharing options...
tube80z Posted July 14, 2008 Share Posted July 14, 2008 I assume you're referring to the fact that the suspension system has no effect on the amount of weight tranfer that happens? I am relatively confident that the suspension system does have a pretty large influence on how the total transfer is applied. It's probably just semantics then. I'm thinking weight transfer based on wheel base and Cg height. I guess going to a lot lower spring rate will cause the front to rise and the rear to squat but the overall Cg height isn't going to change that much is it? I'm not a mecheng, but from my limited understanding, the stiffer the suspension, the faster the transfer occurs. While I know next to nothing about tyre loads, or drag racing, it would seem that if you are asking the tyre to give you longitudinal force, whilst it is in the midst of deforming horribly due to a large shock load, it might just say `no'. This is more what I was thinking and I call this load transfer. So I'd agree stiffer springs will increase the load transfer. And I'd agree softer springs will slow it down. But at the rates mentioned I have a hard time believing there will be any advantage based on the suspension moving a lot more and having camber change that works against you. My thought would be that this would be better controlled using shocks since what it appears we're looking for is based on suspension movement. Maybe softer rear compression and less front rebound. My own experience shows a slight gain in performance when running 450 pound rear springs that when my car was running 175s. But these were not using drag tires (FA rears). It seems like there are some people on this forum that are going really fast with the independent rear. And if I recall correctly one of those cars was using bumpstops to limit the rear compression. That will increase the rear spring rate fairly quickly. So I think the rear tires can handle a lot more than we give them credit for. Quote Link to comment Share on other sites More sharing options...
Doug71zt Posted July 16, 2008 Author Share Posted July 16, 2008 Thanks for the analysis - I've been buried at work for a couple days. As for camber change hurting traction, I'm going to be running 15 inch DOT drag tires (Hoosier QTP or M/T ET Streets). With an outside diameter of 26 inches, and a really soft sidewall, I don't think that camber change will be a real issue. My question came from watching stock suspension S30's running at the strip VS cars such as my 240 with a more road course oriented suspension. The stock, softly sprung cars pitch up and seem to transfer weight to the rear tires, whereas my car seems to bring up the front end to the limit of travel (maybe 3 inches) while not really compressing the rear suspension all that much. I'm happy with my 240 suspension as a compromise for what that car will now be doing, but the 280 will have a different purpose and I am not so interested in going around corners fast with it. I will be running a longer bump-stop with a progressive action, to avoid what ZGad gets into on his SEZ Video, where the car hooks, squats and then bottoms out hard and bounces. The tear rebounds fairly hard and spins at that point. Do you think that having a longer, softer spring with it preloaded at full extension (stock situation) will be a lot different than having a shorter/stiffer spring that is unloaded at full droop? Thanks again for the discussion. Doug Quote Link to comment Share on other sites More sharing options...
JustinOlson Posted July 21, 2008 Share Posted July 21, 2008 What strut are you planning on running? I would shoot for a spring rate that doesn't bottom out the strut on the bump stop. If you are using a trans brake it will make the rear squat more on launch, necessitating a stiffer spring. Justin Quote Link to comment Share on other sites More sharing options...
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