Complete front and rear subframe swap

[tube80z]

I wouldn't change the donor's geometry at all, no matter which donor I choose. If necessary, the wheelbase may be shortened by a couple inches. This will cause one problem I read about called bucking, but a change of only a couple inches should not cause it. I'll make the body match the suspension, not the other way around. The suspension will expect a lot more weight, so the shock and spring rates will have to be reduced.

 

Sounds like a reasonable plan. It would be helpful to have an idea what the stock CG was on the doner cars compared to the Z. There are a number of spreadsheets floating around on the internet that you can use to get things in the ballpark for the new car. If you need suggestions we're always full of opinions

 

Re: RonTyler

You are absolutely correct, and this did not escape my attention. I have two books on race car chassis engineering that I periodically reread. From these books, I know what problems to watch for. The new subframes will probably have to be mounted to a rollcage that will act as a tube frame. I only decided this after starting this thread - thanks to the group's input.

 

Back before I decided to take the EMOD plunge I was going to build a street legal autox car. After thinking about a cage for a long time and not really wanting to deal with that on the street I really looked hard at creating a backbone frame that could be put in the Z and connect front and rear subframes. I think if you went down this path you could get close to the same torsional strength as a vette and keep the weight very similar to the Z. A cage is great in a race car but I don't think I'd want to live with it on the street and there's the issue of your head and how close the cage tubes are.

 

Re: Pop N Wood's question:

The Supra MkIII (and many other new suspensions) are double A Arm and was designed in 1985 or 1986. The Supra is a high end car and built of expensive components. The original Z car was built to be economical, and was built of cheaper components.

 

I don't really want to turn this into a a-arm/mutli-link versus strut debate but I've been surprised at how well I've made struts work. I've driven a 510 that was converted from struts to a-arms using a plan very similar to yours by people who know what they are doing. And the difference wasn't as much as you'd expect. It was mostly easier to steer but didn't have any more grip than when it was strut based.

 

I do think you're right about getting good components from a donor to save a lot of potential dollars. Just make damned sure you can use everything before you end up buying all the pieces over. Spend the time up front to do all the research. I've played this game far too many times myself.

 

Good luck and hope to see some pics,

 

Cary

[ThreeDeadZs]

Re: Corvettes

It's true that I do not know anything about Corvettes. However, I looked back at the records and in raw times only one out of the five corvettes in all categories beat me, and I was in a borrowed racecar that I was driving for the first time (I owned two of the same car and was in the same club, so he entrusted me with his baby!). The owner of the car I was driving (we each did three runs) almost matched the best raw time of the best Corvette, with my 200lbs in the passenger seat. One guy was allowed two sets of three runs, and he hit an average of two cones per run; I would be afraid to volunteer on the track with that guy driving. Many other types of cars were matching us and the Corvettes. Perhaps these were five Corvette owners who didn't know what they were doing? The car doesn't make the driver! This was an SCCA SOLO2 autocross in 1998.

http://www.sfrscca.com/solo2/Results/1998/Slush/round6.html

(note that some cars finished in 40 some seconds, but that is after it started raining and they were only allowed one lap instead of two. We and the Corvettes raced before the rain)

I was driving a completely BUILT 1984 Supra MkII in E Street Prepared. However, I'm certain that on a larger, faster track there's no way I could have matched the Corvettes in that car, but someone could in a Supra MkIV Turbo.

 

Re: cG

Oh crap, I forgot! But if I use subframes from a heavier car (lightening it's body as far as the suspension is concerned) wouldn't my cG be lower than the donor car? Therefore, quoting Chassis Engineering by Herb Adams, "It is easy to see why a lower center of gravity will result in less roll angle." Any thoughts?

 

Re: Struts vs. A Arms

I'm sure every type of suspension can be well done, I'm not really comparing the types necessarily. However, I expect a design penned in the 80's or 90's will be an improvement over one penned in the late 60's, no matter which type of suspension is selected.

 

Re: tube frame vs. roll cage vs. backbone frame

ABSOLUTELY! Thank you! I'll use a backbone frame.

[BRAAP]

Re: Brapp

I would say the Supra MkIII is like your description of the Corvette C5 in point 4, except the vette likely outmanouvers the best stock Supra. I believe point 5 in incorrect. I wouldn't change the donor's geometry at all, no matter which donor I choose. If necessary, the wheelbase may be shortened by a couple inches. This will cause one problem I read about called bucking, but a change of only a couple inches should not cause it. I'll make the body match the suspension, not the other way around. The suspension will expect a lot more weight, so the shock and spring rates will have to be reduced....

 

 

As you stated, if you do not “alter” or “modify” the donor suspension in any way, then what you said does hold true.

 

As for what I stated in #5, I was spot on spot. What I stated was “modifying”, of the stock donor suspension so that it would fit “within” the stock Z body. I probably should have also stated, “not WIDENING” the NARROW Z cars body, which I did just now. In “altering” or “modifying” the donors suspension by shortening the control arms and/or sub frame, that WILL adversely alter its geometry.

[ThreeDeadZs]

Re: Brapp

I misspoke. Yes modifying the suspension to fit would not work well. Thus modifying the body is the only way to go.

[260DET]

Hey Richard (260DET)

I just noticed that your recommendations do not include how you are doing your current project car. How well is your S13 suspension working out? Effectively, you've done exactly what I'm talking about - using the complete front and rear subframes and equipment from a donor car. Now that I see you have done exactly this project, I'll put very serious consideration into the GTR and Z32 subframes as you recommend. Which engine will you use in your project? Or is the car on the road yet?

 

If I chose to copy your project, would you be forthcoming with the details? I really like your photo gallery. There's a small shadow at the center of one of your pictures that is extremely enticing!

 

Mine is a 280ZX (S130) though, not a S30, which is why it wasn't mentioned. The tension rods on both the 280ZX and the S13/14/15 go forward, not back as on the S30. Using the S13/14/15 entire front suspension assembly on a S30 would require modification in regard to the tension rods at least, which then defeats the original purpose doesn't it

 

My site is updated every now and then with pics of the 280ZX that show significant progress.

[RTz]

Re: Corvettes

Perhaps these were five Corvette owners who didn't know what they were doing? This was an SCCA SOLO2 autocross in 1998.

http://www.sfrscca.com/solo2/Results/1998/Slush/round6.html

(note that some cars finished in 40 some seconds, but that is after it started raining and they were only allowed one lap instead of two. We and the Corvettes raced before the rain)

 

I’m not following you...

 

If you’re speaking of the 5 entrants in SS (the above link), they were all clearly driving in the rain... they were running 80+ seconds vs. 40+ earlier in the day.

 

Coincidentally, you happened to pick a driver that I know pretty well. Don Mckenna is my uncles father. At that time he was driving a bronze C4. You may remember it...

 

 

 

 

Don has more trophies than you can shake a stick at. From first hand exerience, I can assure you that Don’s driving abilities are not lacking. He *is* National caliber. The SFR SCCA has a small salute to him on thier website, next to the above picture.

 

“Don McKenna is one of the smoothest drivers in SFR, some say. It's clear that he can make cars do things that many believe to be impossible. Don has passed this historic vehicle on to a new generation of McKenna drivers, and now drives a blue Gran Sport.”

 

A C4 has got to be one of the WORST cars ever built for the rain... I have to dismiss the above link.

 

 

As for National trophies in Corvettes, I thought I would find a few years worth of records for you. I stopped at the first records that I found (2004) becuse, well, I think that one year makes the point on its own.

 

Super Stock

Top 14 positions are all C5’s

 

A Stock,

First and Second place, C4

 

A Street Prepared

First and Second place, C5’s

 

B Street Prepared

First 4 positions, C4’s

 

Keep in mind there were over 1200 drivers entered that year and that these 4 classes make up THE fastest times of ANY street legal cars.

 

 

Enough about Vette’s. Your Supra idea is interesting reading... keep it up.

[ThreeDeadZs]

Re: Corvettes

Actually, it's the other way around. The Corvettes, Lotuses, Open Categories, and in my case E Street Prepared all raced shortly after sunrise, just after we layed down the track in dry weather and it started to sprinkle lightly. We knew the rain was coming but the track was still fairly dry. It only began to pour midday and the classes that still had to race were only allowed to drive one lap so the event would be over before the rain got heavier. That's why you see non-competitive cars getting 40+ seconds later in the day (in one lap) and the best cars getting 80+ seconds earlier in the day (in two laps).

 

One factor I never accounted for until now: The E Street Prepared Supra I drove had brand new (I forgot the brand) sticky racing tires that are normally slicked but he kept the treads for the moment. The suspension was completely worked by a professional race car builder, specifically as a dedicated autocrosser, and the owner paid $10k on just one session. I expect any moisture on the track would not have bothered this particular Supra MkII, but would have made the Corvettes squirrely. Please note I'm not even comparing my own driving to anyone. This was my first attempt in a car I didn't know and my times were just acceptable. I also didn't want to push it and damage someone else's car.

 

I have no doubt Don McKenna could wipe the floor with me in any type of race, even if he drove a stock Citation and loaned me his Corvette! HOWEVER... He had to take two sets of runs, and knocked two cones down each on four of his six runs. He only beat the owner of the car I was driving once in raw times, even though he was the only competitor allowed two sets of runs that day. There may have been a factor we are not considering, like an equipment problem or that he was pushing himself extremely hard therefore hitting more cones. I've no beef with Corvettes, so I'll try to let this subject about Corvettes end peacefully. In short, I'm sure Don McKenna is a far better driver than I'll ever be, and any car I build will still not match his... but that day his squirreliness was scary! On careful review of the results, I find that he's the only Corvette that hit any cones. Ask him, maybe he'll remember why.

 

I would guess that any well built race car with a budget of the price of a stock Corvette C5 would get at least comparable results, if not superior though without the luxury. To have a great stock car, all you need is money. To have a great homebuilt racecar, you have to have dedication, knowledge, imagination, tenacity, and do a lot of research, and spend months to years building it. Not to mention the trial and error. It's kind of like apples and oranges. Granted, stock Corvettes are great racecars, especially in the right hands. I find much greater satisfaction reading about custom work like yours, Ron Tyler! I thumbed through some of your posts, and really love the detail of your custom work. Off the shelf stuff (like a whole C5 Corvette) doesn't really interest me, if you know what I mean.

 

PS. This is strange to end up taking this position, because I always wanted a Corvette, and would still love to have one.

PPS. Let's stick to the subject at hand... What Nissan/Toyota/Mazda, etc would make the best donor for subframes for a 240Z autocrosser? Additionally, which do well in the rain?

[ThreeDeadZs]

Mine is a 280ZX (S130) though, not a S30, which is why it wasn't mentioned. The tension rods on both the 280ZX and the S13/14/15 go forward, not back as on the S30. Using the S13/14/15 entire front suspension assembly on a S30 would require modification in regard to the tension rods at least, which then defeats the original purpose doesn't it

 

My site is updated every now and then with pics of the 280ZX that show significant progress.

 

Thanks, I'll look into front tension rod designs...

 

I just got out my photos of my old 87 Supra's suspension and discovered something new. As far as I can tell, there are NO tension rods. The entire front end suspension is built as one system, and as far as I can tell from the photographs, only connect to the body in three ways:

Subframe->frame rails

Rollbar-> frame rails

Struts -> Shock towers

The function of the tension rods must be handled within the front subframe itself. Can anyone with first hand experience with Supras 86.5-98 (3rd and 4th generations) confirm or refute this?

 

Another thought on center of gravity: The subframes will be much heavier than stock as will the backbone frame I'll need to build. All of this weight is on about the plane of the floorpan. Little or no reinforcement will exist above 24" off the ground, since I'm abandoning the idea of a rollbar/rollcage and the Z body and glass is much lighter than a Supra. Anecdotally, wouldn't this give a slightly lower cG than a Z, and much lower cG than a Supra? Is there such a thing as too LOW a center of gravity?

[BRAAP]

Before you know it, you will have built and will be driving that Supra you long for…

Keep us posted on what you find in regards to the suspension...

 

[Pop N Wood]

Yeah. Let us know how you enjoy your Supra.

[ThreeDeadZs]

Let's stick to the subject at hand... What Nissan/Toyota/Mazda, etc would make the best donor for subframes for a 240Z autocrosser? Additionally, which do well in the rain?

[RTz]

Additionally, which do well in the rain?

 

Nearly all of the compromises you make for a dry car work against you in the wet, and vice-versa.

 

Ask Braap about the time I raced a pack of Vette's in a bone stock Celebrity.... in the rain. Red faces and good times!

[ThreeDeadZs]

Bummer! How do I get a good comprimise between autocross and wet weather driving?

[tube80z]

Bummer! How do I get a good comprimise between autocross and wet weather driving?

 

Tires make a big difference. And I've found the biggest single factor for my car is the roll bar. When it's wet you need a lot less roll stiffness because you can't generate the same level of lateral accelleration. For me spring rate made little difference.

 

Cary

[ThreeDeadZs]

Ron, are you saying that for wet weather driving, I'd be better off not reinforcing the Z body except as required to mount the subframes? I'd like to hear more about why the Celebrity was able to perform so well, and your interpretation of what to do to build a Z strictly for wet weather driving safety. Tires are obvious, but I've never read anything about how to make a wet weather car.

 

Cary, are you saying that adding your roll bar made your car worse for wet weather driving?

 

Let's ignore autocrossing and my idea of using Supra equipment for the moment. How should I build this car for slippery mountain roads? Perhaps I'll build two Z cars, one as my main transportation in the mountains, and one to play on dry mountain roads and autocross.

 

Thanks for all your help guys,

Matthew

PS. I'm not exaggerating about the roads around here. Currently, I'm snowed in and expect to be for at least a week because I do not have a 4WD. All nearby highways are closed!

[ThreeDeadZs]

From the Supra forum, I received the following advice from Jeff Mohler, which seems extremely accurate and complete. Please comment on this approach:

-----------

"Well..wet driving is more of a suspension setup issue as well, a good suspension for dry use will cause issues in wet use.

 

Tire selection..is huge, next is compliance. front swaybar..make it softer, if you can losesn the endlinks (mk3s you cant). [He's referring to 86.5-92 Supras] Set struts to as soft as you can, rear end..same thing, remove swaybar possibly as well. Tire pressure..5-10psi (depending) lower than dry performance cold PSI.

 

Driver..dont do quick snappy things."

------------

I'm starting to think I cannot have it both ways, forcing me to choose wet or dry. Therefore, I'm considering adjustable struts (like Tokiko 5 ways, or a Toyota TEMS system), two sets of tires, and two sets of anti-sway bars. But is there a shortcut to allow me to have extreme performance in both wet and dry conditions without rebuilding my car every spring and fall? It's just a hunch, but I'd bet BMW's are made for all conditions... I can't afford a BMW donor, but perhaps I can copy whatever approach they use. Does anyone know?

[trippintl0]

I think Tein produced some struts / shocks that were adjustable, and could be controlled by electronic actuators. You could adjust them from inside the car. Kind of like mounting a small motor on top of the adjustment knobs or something.

[Careless]

I think Tein produced some struts / shocks that were adjustable, and could be controlled by electronic actuators. You could adjust them from inside the car. Kind of like mounting a small motor on top of the adjustment knobs or something.

 

Tein with EDFC (electronic dampening force controller)

 

It's basically a small stepper motor and a control unit.

if you could find someone who had just the EDFC, and someone who has the stepper motor model number or part number, you could probably kit it together a lot cheaper, but I think you would need to find a collar to mount the motor the the adjustment knob on the top of the strut

[ThreeDeadZs]

That Tein system sounds just like Toyota's TEMS system (Toyota Electronically Modulated Suspension) which I could get salvage off a Supra MkIII. A computer senses any harsh movements and sets the system to "sport." There's also controls on the center console.

 

Okay, we've covered tires, tire pressure, and adjustable shocks, but what else can be done to make a wet and dry use sportscar?

 

Again, am I choosing the right donor, or is there something better than a Supra MkIII for this purpose? (Supra MkIII's are affordable when dead, Supra MkIV's probably are not)

[tube80z]

Ron, are you saying that for wet weather driving, I'd be better off not reinforcing the Z body except as required to mount the subframes? I'd like to hear more about why the Celebrity was able to perform so well, and your interpretation of what to do to build a Z strictly for wet weather driving safety. Tires are obvious, but I've never read anything about how to make a wet weather car.

 

Think about it. A vette has wide tires and a relatively stiff suspension. A celebrity has skinny tires and normally handles like a ♥♥♥♥ barge. In the wet where your maximum lateral acceleration potential goes from 1g to something maybe no higher than 6 tenths so this isn't that great a factor.

 

Cary, are you saying that adding your roll bar made your car worse for wet weather driving?

 

For wet weather I don't need a rear bar and use a front bar about the size of stock. If you want to be able to play with the same car in both wet and dry you'll want two front bars and a way to quickly turn the rear bar off (pip pin on one rear down link for instance).

 

Cary