Chassis Setup (corner weights)

[74_5.0L_Z]

I just got back from a local racer's shop where we set the corner weights on my car. My car is a 1974 260Z with a 1989 Mustang 5.0L and T5. The 5.0L has edelbrock aluminum heads, the car has a full tubular front end and an extensive cage.

 

Here are the results with 16 gallons of fuel and me (190LBs) in the car:

 

LF = 648 Lb RF = 607 Lb

 

LR = 751 Lb RR = 710 Lb.

 

Total = 2716 Lb

 

Here are my percentages:

 

(LF + RF)/ Total = (648 + 607)/2716 X 100%= 46.2 percent on the front

 

53.8 % on the rear.

 

(LF + RF)/ Total = (648 + 751)/2716 X 100% = 51.5 % on left and 48.5% on right.

 

 

my diagonals are equal ie..

 

(LF + RR) = (RF + LR) -> (648 + 710) = (607 +751) = 1358.

 

I am pretty happy with these numbers.

 

Here's a question for johnc, Jmorstensen, RossC, et al...

 

What rate springs would you run based on these scale readings, and is it worth adding ballast to the right to try and equalize things left to right?

 

I current am running 250Lb springs in the rear and 200 Lb springs in front. I have a 1" front sway bar and no rear bar.

[JMortensen]

I wouldn't add any ballast. If the diagonal weights are equal, call it good. If you were racing in a class that required more weight, then I'd add it as low as possible wherever it would even out the corners the most. But the crossweights are what will really affect your turning left vs turning right. You should see my old racing buddy's crossweights. Prepared 510 at 1900 lbs last I heard with a ~230 - 250 lb driver, depending on how much he rides his mtn bike... pretty funny stuff. When he got in he was 10% of the weight of the car.

 

I would think you are a little undersprung, but I suppose it depends on how far you want to go and what you're doing with the car. My Z was perfect 50/50 and diags were within 10 lbs the first time I scaled it. Just got lucky I suppose. I'm running the same springs you are with 1" bar in front and 7/8" bar in back, and I had a bitch of a time getting the push out of my front end. Ended up setting caster at 5* and camber at -3.5* front. That ended the push.

 

I've seen your pics, you should be able to do the same, but I'm wondering if you're ever going to be able to tune out all the push without a rear bar. Maybe the extra weight in the back will help to swing it around???

 

I have only a very limited conception of how the rear weight bias is going to affect the car, from working on Porsches years ago. We used to go with lots of toe in in the back, I would think you should have at least a little. I would also try to take some weight off the rear if possible. Fiberglass hatch, Lexan, etc. You should be able to brake REALLY LATE AND HARD the way it's set up though...

 

I always did cornerweights with 1/2 tank fuel, which is what 6.5lb/gal? That would affect your front/rear bias a little.

 

From the pics anyway your car looks like a BLAST to drive! I hope it drives as good as it looks!!!

 

Terry might be able to help you a little too. I think he has rear bias as well.

 

Jon

[blueovalz]

These numbers look good. Mine is close, but I've got about a point or so more toward the front than your numbers show. I'm running 265 rear/225 front, and am quite happy with these rates. Not too stiff, but enough, with a 7/8" bar front and 3/4" rear to satisfy me. I am going to reduce the effectiveness of the rear bar though by moving the body mounting points closer toward the middle (just outside either side of the differential) and attempt to mimic a 1/2" sized bar.

[CruxGNZ]

I am going to reduce the effectiveness of the rear bar though by moving the body mounting points closer toward the middle (just outside either side of the differential) and attempt to mimic a 1/2" sized bar.

 

Sorry to get off subject, but Terry, you are going to move the mounting points inward so the bar see's not only twisting, but more bending (up and down movement) to mimic a 1/2" bar? I had to sit here and think about how moving the chassis mounting points inward would make the bar less effective. Didn't make sense at first. Did you do any calculations to figure out where the mounting points should be or are you just going to shoot from the hip?

 

!M!

[jt1]

I would guess you're a little soft, but probably not by more than 50 #/in. I'm running 250F/275R at about the same weight, but with very close to 50/50 F-R. The main thing with stiffer springs is to get a shock that can damp the stiffer spring. The Tokico 5 ways can only damp up to about 300#/in from what I can learn. To get much stiffer than that you have to get into the high dollar shocks like the penske's. I would probably run the car like it is before making any changes, so you'll have a better idea of what you need.

 

John

[blueovalz]

!M!, your thoughts are correct. This is another advantage of having the long continuous plate behind the differential that the bar is mounted to. In practice, I could eventually move the body mounting points together to act as a single point directly behind the differential, thus nearly eliminating any effect of torsion the bar would normally provide. Any yes, it would be trial and error (at least for me anyway)

[JMortensen]

I mentioned before my spring rates but I didn't mention the total weight of the car, which was 2350 at the time.

 

Also, as to shocks there are the Koni Sports which are revalvable and cheap and good for higher spring rates, and I recently found out that you can get Carrera to make struts for you with custom valving. Not too familiar with this at all, but a friend of mine got shocks for the rear of his 510, and he's about to order Carrera strut inserts for the front. Supposedly not adjustable, but you can pick your valving and they'll build it that way. He said Winston Cup runs 4 and he picked 5 for the back (stiffer), and was going to get the same in the front. The best part is they're CHEAP. 5 would be like hardcore roadrace/autox valving.

 

I already knew about their shocks, but anyone else ever run a Carrera strut insert or hear of someone running Carrera inserts??? JohnC?

 

Jon

[johnc]

Wayne Burnstien (sp?), an ITS racer back east, runs Carreras and he's very happy with them. Regarding spring rates for 74_5.0L_Z's car: what do you intend to do with it?

[74_5.0L_Z]

Thanks for the responses guys.

 

The car is used for autocross and track days mostly. Its does see occasional street and dragstrip duty.

 

I was thinking about moving the 250#/in springs to the front, and getting 275#/in or 300#/in springs for the rear. I have the old Koni Reds on the car.

[JMortensen]

Yeah, I'd swap out the springs if I were you. You may also want a bigger difference in the front to rear springs. Like a 250F/325R or something like that. IF you don't care about ride quality driving around town. I'd like to move up to a similar spring rate in my car, just don't have the $$$ for new struts and springs right now...

 

The only question I have is how heavy a spring can the red Konis deal with?

[74_5.0L_Z]

Ok guys,

 

Based on the above discussion(and the fact that one of my front cartridges has died), I have decided to get some new struts. I have been looking at Koni 8610-1149 single adjustable struts.

 

Has anyone gotten a Koni 8611 double adjustable to work in a Z?

 

What other struts would you suggest for 250 - 300 lb/in springs?

[clarkspeed]

I think my springs are in the 250-275 range if I remember correctly and car weighs around 2450 empty. Springs are just a little stiff for auto-cross work, a little soft for hard track work, and torture for street drive. Just the right compromise for me.

 

I run Carerra's and love them. Non-adjustable, but it's one less thing I need to worry about. Mystrut nut came loose at Sebring and the thing slapped around in the tube at weird load angles for 20 minutes. I took it out and still couldn't push the rod down with my hand. My struts are 8 years old, with a lot of abuse, and they are still like new.

[260DET]

Ok guys' date='

 

..............................................

 

Has anyone gotten a Koni 8611 double adjustable to work in a Z?

 

What other struts would you suggest for 250 - 300 lb/in springs?[/quote']

 

I've got a pair of 8611 double adjustables on order for the front. For ultimate track performance a lot more shock bump is required than is usually available with street type shocks, even Koni Sprts, IMHO. But we'll see because that is where my suspension is headed.

[preith]

It seems most guys I've seen who have Ground Control's Advance Design shocks are happy with them. What's the general consensus here?

[gramercyjam]

Tom Holt has them in his car - he is very happy (and very quick). All of the cars I've seen them on are very quick. I have heard heard that they aren't any good 3rd hand from some race car builders - most likely because they are putting Penskes and Ohlins on cars. There is no comparison dollar-wise between Penskes and Advance Design.

[JMortensen]

Am I just being completely naive when I think that the best way to get a good cheap strut for racing is to get a Koni or a Carrera valved how you want it. The Carreras are supposedly super cheap and you can get them valved correctly before they even ship them to you. They are cheaper than Illuminas from what I hear. If you have it valved correctly, then you don't really need to make adjustments all the time. I guess what I'm saying is that there is a "right" bump and rebound valving for the unsprung weight and the spring rate, and changing it is not the best idea.

 

I should point out that I have Illuminas and I like the adjustability now because so far I've been driving to events in the car. So I crank them down to 1 and drive there, then put them up to 4. I have used them to adjust the handling of the car, but I'm increasingly convinced that at the track adjustments to the balance of the car shouldn't be made with the struts, but with sway bars instead, and major adjustments should be made with suspension angles. When I stopped trying to rely on the struts and started adding some serious negative camber and positive caster I made huge improvements.

 

The people buying Advance Design struts or running 300 in/lb plus probably aren't driving to events (I think), so my use of the adjustable struts to make it comfortable on the street wouldn't really be an issue any longer.

 

Am I way off base here?

[gramercyjam]

I think you are correct. I don't see very many purpose built race cars being driven to events. I think you will see a lot of different ways to adjust setup on cars, alignment, springs and sway bars being the primary way to do it.

[johnc]

Am I just being completely naive when I think that the best way to get a good cheap strut for racing is to get a Koni or a Carrera valved how you want it. The Carreras are supposedly super cheap and you can get them valved correctly before they even ship them to you. They are cheaper than Illuminas from what I hear. If you have it valved correctly, then you don't really need to make adjustments all the time. I guess what I'm saying is that there is a "right" bump and rebound valving for the unsprung weight and the spring rate, and changing it is not the best idea.

 

True, but you do adjust suspesnion, shocks, etc. for specific tracks and for track conditions. You can tighten up compression and rebound on a glass smooth track but on a bumpy track you better back off compression or the car will be skipping. For asymetric tracks (like WSIR) you adjust shocks and camber to help the car turn (right for WSIR). ANd, if you're running in the rain you'll want to soften everything up as much as you can.

 

Being able to adjust the car to the conditions and track gives you a little edge over the competitor who had non-adjustable stuff.

[JMortensen]

Mmm... I thought I might be oversimplifying it a bit. I know rain would be the biggee.

 

Still thinking I might just go Carreras when I eventually up spring rates, just for the $$$.

 

Thanks for pointing that out though John.

[Savage42]

I ran the Carrera coilover setup on the rear of my 510, and we've put them on several other 510s locally. The rears were adjustable with 3 settings that varied the compression/rebound rates. Of course, the rear 510 stuff is not an insert, but a stand alone shock with coilover sleeves on them. I'm not familiar with their inserts, as I ran KYB adjustables in the front w/ ZX struts. They will build them for the rate that you run, and they were in the neighborhood of $100 each. Hope that helps.