More 240z Suspension Questions

[TomL]

Paul -
I realize you can move the center of travel a bit by adjusting strut tube length and the size of the spacer (or not using one) under the insert. I just don't see how that is influenced in any way by the length of springs you use, which was the original question. Or was I reading to much into your response - that centering the shock is a good thing in general (and you weren't addressing the spring length question?)

[pballance]

TomL and Tom, my last response about centering the shock was more for TomL than TomD. Too many Toms around here I guess we just need some "Harry's". I'm not going looking for "Richard's"

TomL, I think maybe I wasn't clear enough and maybe you read a little too much into it. Get the shock where you need it, then figure out the length of the spring from that based on your artificial (mocked up assembly) ride height. If you have a delta that might allow you to use springs of 2 length's, let's say 9" or 10" and still get ride height and adjustability, then go with the shorter i.e. lighter of the 2 springs.

TomD, I have only seen different length springs on struts that used the OEM perches for the lower mounting point of the springs. Some tubes had been sectioned, others not. If I were in your shoes, and could use 4 springs of equal length and get the car set, that is what I would do. Otherwise SHUT UP AND DRIVE! didn't we have that conversation?

[kthomas]

If I were in your shoes, and could use 4 springs of equal length and get the car set, that is what I would do. Otherwise SHUT UP AND DRIVE! didn't we have that conversation?

That.

The natural frequency of the suspension springs for the rates and dimensions commonly used on 240Z's is inconsequential. Now you want to talk about spring harmonics when it comes to valve springs on and L24 and we have something worth discussing. We always used 10" free length springs on cars I prepped because I didn't have to worry about stack up for any reasonable rates, and it put the spring perches in convenient places relative to the strut tube to not cause any issues or clearance problems.

We won a ton of races back in the day with rates under 250 on both ends. Big springs, remember, are going to require more consistency and precision on the part of the driver, and may not be as much fun to drive, or drive well, depending on how regular your track days are.

[Tom Donnelly]

We won a ton of races back in the day with rates under 250 on both ends. Big springs, remember, are going to require more consistency and precision on the part of the driver, and may not be as much fun to drive, or drive well, depending on how regular your track days are.

Keith,

Glad you're still around! My plan was lower spring rates and increase them as my track time, consistency and precision goes up. The lower spring rates are more forgiving right? And not necessarilly slower. I need to run newer than 8 year old tires too.

Tom

[kthomas]

Keith,

Glad you're still around! My plan was lower spring rates and increase them as my track time, consistency and precision goes up. The lower spring rates are more forgiving right? And not necessarilly slower. I need to run newer than 8 year old tires too.

Tom

That, gentlemen, is a man who don't let ego get in the way of good decision making.

Higher rates are ultimately faster on paper because the aid to roll control gives a better contact patch provided the shocks are up to the task, however, you've heard me say that a softer car is faster sooner- meaning if you aren't driving a lot (twice a month+ may be enough for an ITS driver to be on his game) you may be faster in a softer car, and faster earlier in each track weekend because you acclimate sooner. Now if the car is wallowing all over the place because the shocks don't work then softer won't help, but you know what I mean.

Chet and I ran front row ITS times at Roebling one weekend in a $300 240Z with a 150k bone stock motor and some old race pads and tires with the old Bob Sharp street Koni package on it- about 115 lb/in springs up front and about 140 in the rear. Some of the most fun I ever had on a track ('course a lot of that was because we were kicking major Porsche butts with a $300 car, but I digress) because it was balanced and the shocks matched the springs well. Blast to drive, went where you pointed it, and recovered predictably when you got out of whack. Wasn't as fast as our ITS car mind you (which I hear ran 117's at Roebling a couple years ago, Holy $h1t!), but I'd venture to guess that most of an ITS field would be faster in that $300 car for a Saturday qualifying than their own race car.

[Ron Earp]

Wasn't as fast as our ITS car mind you (which I hear ran 117's at Roebling a couple years ago, Holy !),

Is that correct? If so I think that would have the ITS record. The fastest Z that I've seen down there in the last few years at the SARRC weekends has been John Williams' car in the low 1:20.xx. As far as I know Jeff or I haven't missed a SARRC weekend down there.

[kthomas]

That was according to the current owner, Bobby Bitterman in AL. The car now races vintage, but is still in IT trim, tires, and the Sunbelt IT motor that was sold with the car. Not sure what if anything might have been out of IT spec other than the RR shocks. I could be wrong, but I'm pretty sure he told me he turned laps in the 1:17's. It was captured by the data acquisition system on board so perhaps there's proof.

No doubt in my mind that car would be faster than John Williams. 1:17's? I dunno.

[Tom Donnelly]

[quote=kthomas;294658]Not sure what if anything might have been out of IT spec other than the RR shocks./quote]

Keith and Ron,

I know Keith said same tires but slicks are allowed in vintage. He probably ran slicks. Which would help close the gap between ITS and EP times. That would be close to the same setup in Grayson's old car I think. Then 1:17's would be real doable. Don Ahrens ran a 1:17 last year in EP at Roebling in a 240z.

Tom

[Tom Donnelly]

Hey, how come my quote stuff didn't work?

[specialtyautomo]

Actually it was a 118 and small change. The car was on dot's and the only thing not ITS legal is the rr shocks. Great weather and good drafting partners a (gto and a 914-6). Three laps were in the 118s. There is alot of set up difference between Johns car and mine. Most of the lap time came from turn one and two. Enough corner speed that I stayed in 4th gear from the front straight untill turn 4. I have learned that Z cars are very alignment sensitive.
Bobby Bitterman

[Charles Perry]

Ok Bobby, you know someone was going to ask! What did you do alignment wise to get through 1 and 2 so well??? Z car guys want to know!

[specialtyautomo]

The easiest way to put it is that Keith took full advantage of the rules when it came to strut housings. I am lucky enough to have two sets (one set for each car). Most, if not all Z cars have bent strut housings to get the proper camber. Having had a set of those in the past and compairing them to what I now have thats not the way. My experience has been that Z cars want all the camber that you can get and then some. 3-4 degrees isnt enough, closer to 5 will get you in the ball park. The only difference in the car from when purchased is the alingment and the driver. I am nowhere near the driver Chet is, I would bet his time would be even faster. I can say that that alingment does not work as good for RA though. It works at Barbers and Roebling.
Bobby Bitterman

[gira]

Good Day folks,
My two cents on this topic real quick. First off, a coil spring is only considered 36% unsprung weight, so buying an IT spring with this as the main criteria might not be that great. Some people think a longer spring produces more reliable results. I like trying to use the same size springs so that I'll have more choices to change my chassis setup. Once the front tubes are sectioned, changing the shock body length and shimming up and down inside the tube could only change your droop travel since the top of the strut and the bump stop will not change location. Once you get the components in the right location at your normal ride hide, you shouldn't have to change it that much. We use 10's and 12's I believe and incorporate a 2" space sometimes.
Hope this helps.

greg ira

[dspillrat]

Is that correct? If so I think that would have the ITS record. The fastest Z that I've seen down there in the last few years at the SARRC weekends has been John Williams' car in the low 1:20.xx. As far as I know Jeff or I haven't missed a SARRC weekend down there.

Jeff/Ron......This series one 240z "Keith is refering to" ....Blue/Blue car wasn't super fast...in a straight line, but handled quite well..I was privileged to be a passenger in with Chet driving that weekend back in 1999/2000 maybe.... I remember well cause Chet done blowed my engine up that weekend telling me to go faster :eek:.......Damn V-8...
Many moons ago......

Ready to try some extreme camber at the SIC........Hmmm...

David Spillman.......