240SX IRS Swap

[Drax240z]

My 2 cents here... Tim is absolutely correct in saying if you move any of the mounting points at all you are asking for a world of hurt. There aren't many people here that have the tools available to analyse a multilink suspension to the point that they can be sure the movement isn't hurting the suspension.

 

On the 240sx vs 240z rear suspension issue, having driven a lot of both, I find the 240sx a great deal better in street driving. (yet to drive a 240sx on the track) Better traction, larger sweet spots and the ability to get power down being big advantages. A well designed multi-link setup will hold toe and camber much more consistant through the normal driving ranges than the 240z/chapman strut setup will. 240z's (even in like-new condition) have enough toe change under accelertation on the dyno for it to be visible. Also a well designed multi-link is going to have a more consistant camber curve in most cases. (ie: -ve camber gain is more linear)

 

Just my 2 cents.

[Ed260Z]

The swap it self doesn't call for any modification of the multi link arms, or their placement. I think that if you can get the sub frame placed on the same Horz. & Longi. plane as on the 240SX you should be able to maintain it's ride charecteristics. I'm no expert in any sence of the imagination on this, but ut sounds about right to me.

[BRAAP]

This is in response to a post that was apparently removed by the Moderator. It was a bit of a flame on the whole concept of this swap. But this is a forum where we discuss ideas of hybriding the Z. (Hence the name).

 

 

 

That was me that wrote that post. My post was talking bout the Nissan Multi link rear suspension in a very negative light. I deleted on my own as I didn’t feel there was any reason to try and sway peoples opinion on whether or not they should use something that, (in my mind), won’t work any better than what’s in their car already, (from a performance stand point), because if they want it bad enough, they’ll justify the reason why they think it needs to be installed no matter if it helps with any issues that they perceive exists with the existing suspension or not.

Any how, it really isn’t my place to make the comments I originally made. I would be more than happy to give my “opinion” and from what little experience I do have with the Nissan Multi link rear suspensions I’ll post here. I was working at Nissan in Riverside CA, (Quaid Auto Expo), in 1988 when the 240 SX hit the showrooms and was also fortunate enough to go to the unveiling of the new 240 SX, Z-32 and Axxess in Anaheim. The Nissan MID-4 was also on hand. (what a cool looking contraption that was.)

 

I have personally removed 2 complete rear multi links including the cradles from S-13’s. They are heavy, not sure if they are heavier than the Chapman set up of the earl Z but they are heavy. I also own a ’96 Infiniti Q-45 that has this suspension design under the rear. The Q is much softer than the Z-32, S-13, and S-14 and as such goes through quite a bit of travel between bump and droop while driving it aggressively, even with the brand new Tokicos installed. The rear end of the car is all over the place, very unpredictable and at any thing past 8-tenths, the car is scary. Like I said, the Q is SOFTER than the Z-32 and S-13/14 so the Z-32 and S-13/14 cars will have a much more “controlled” feel as the suspension doesn’t go thorough as much motion as the Q. When the multi link moves through its travel, it goes through some pretty aggressively camber, caster ,toe, and roll-center changes. I’m sure someone has mapped it out and that info should be readily available.

 

I personally don’t see the multi link as a vastly superior design.

Ask any performance sports car chassis designer what he/she thinks about Semi Trailing arm in a truly high performance application? Chances are they would much rather choose an alternative design. The Datsun 510 and 280 ZX utilize the Semi Trailing and are fairly competitive on some race courses. These same cars are also so stiff that the semi trialing doesn’t move much so its inherent geometry woes don’t show up. The down side, is on a rough course or rough road, these same cars are taking a back seat to cars with properly set up double A-arm or equivalent suspension designs that don’t have to be that stiff to “hide” its geometry woes. What I’m getting at here is the Nissan Multi link can be made to handle great like the semi trailing arm, but it has to be made REAL stiff so that it doesn’t go through too much wheel travel. Nissan pushed the Multi link as some engineering marvel and that it was designed on the Cray super computers of the time. Sure, having your suspension designed on the Cray super computer is a engineering marvel and gives you a heads up at the bench racing venue, but it doesn’t make the car handle any where near what the modern BMW’s, Vettes, Vipers, S-2000, NSX, etc. These car are world class handling machines and you can bet they don’t utilize a multi link like the Nissan design. These same cars don’t use the Chapman strut either. My point is, if the design doesn’t TRULY improve your cars handling over its existing design, then why install it, unless it is a show car, cause that multi link does look sweet. Think about this for a moment. This suspension was designed in the late ‘80’s, (high tech bells and whistles was the name of the car game back then whether these bells and whistles did anything to make the car faster or not) and this multi link suspension is to go under mass produced cars for Joe Blow. The demographics, the same guys and gals that might consider the Camaro Z-28, Mustang GT, Dodge Stealth, Mitsu Eclipse, Ford Probe, etc. . Compromises need to be made so that Jane Blow will also feel comfortable behind the wheel. This suspension wasn’t designed for the discerning sports cars racer like Mario Andretti. High performance handling was not on top of the list of design goals, that you can be sure. If it were, then we should see more Multilink suspended cars at the top of national level ranks of most racing events. In Solo II on a national level, the Prepared and mod class cars, you wont find the 240 SX or Z-32 running as fast the Prepared or mod class S-30 cars. I’m not saying the rear suspension s is slowing the cars down, but I am saying it isn’t helping them go scary fast either. The Early Z with its Chapman strut, (and this is my opinion), offers LESS compromise from a performance stand point than the Multi link does.

Now if you install stiffer bushings in the Multi link, you will cause the suspension to be in “bind”. Even with the OE Rubber bushings, the suspension has a great deal of rubber friction from the twisting binding motion of the control arms. You try and move the suspension through its travel with the spring/strut removed and OE rubber bushing and you’ll see what I mean. I would bet it takes over 100 lbs to get the suspension from full droop to full bump with OUT the strut/spring combo. This is not good. You want to the suspension to be able to articulate with as little friction as possible so the spring and damper can do their respective jobs without in other influence, say from the bushings. Heim joints might be a different matter all together. The Heim joint might allow the suspension to articulate without binding, but I’m not 100% sure on that.

As for the short nose diff. Well it fits the Multi link cradle so no sense swapping it out. Though I’d stay away from the Viscous versions. They are really no better than the open diffs. I’ve driven quite a few Nissans with the Viscous LSD, my Q included, and it really doesn’t offer much of any appreciable or even noticeable advantage over the open diffs. Save your dollars and purchase the open diff and install a Quaife or NISMO clutch pack center section and that issue is solved.

 

 

 

Now as for reasons why I think that suspension “should” be installed in an early Z car? It looks VERY trick especially with the A/M tubular arms etc. Great for a show car and just to be different. It already has the 5 lug hub and disc brakes. For a race car or high performance street car, I feel the Multi link is a step backward or at best, is no better than what is currently under the car even after made the huge financial investment and after how much time and labor spent modifying the car to accept this really cool suspension?

 

That is my $.02

[260DET]

Interesting and informative post Paul, it prompts a few comments.

 

First, the stock S13 etc rubber bush cradle mounts need to be replaced with either poly or solid substitutes for much improved handling. Second, S13/14's perform very well on the race track, apparently due to an excellent chassis as much as anything else although the suspension seems to play its part. Three, consider the Z32 which uses similar suspension and of course was designed as a high performance car. But I don't know how the Z32 performs in racing, maybe someone else can comment on that.

 

In my limited circuit track experience, once you build in some adjustability the S30's rear suspension performs very well, its the front which is the weak end. Aside from not being able to play around much with Ackermann due to the location of the steering rack, the S30 typically drags the inside of the tyre edge on the inside wheel in a corner. 'Typically' because that seems to be characteristic of strut suspension. Yet very few seem concerned with replacing the front suspension on a S30 for some reason or other.

 

My S30 in the pic is pretty well set up, see how flat its sitting in a high G corner and how flat the rear wheels are sitting, yet note that inside front wheel angle

[Gollum]

if you're gonna do all that work to put in a different IRS setup why not go withsomething that's double wishbone type? There are many cars to choose from.

 

But the suspension of the S13 has really proven itself. They're some of the best cars for tight & technical courses (ie mountain racing). But it call comes down to money. They're not great out of the box and needs lots of modifications just like anything out there.

 

Personally, I'd be looking at miata suspentions. Dual wishbone on all 4 corners. As long as it's strong enough it would be great. It's probly about as light of a setup you'll find too.

[Ed260Z]

One big problem that you have with the stock S30 Rear is the excesive camber changes through the suspensions travel. Welding some camber plate will correct the static set up, but as soon as you start moving the suspesion you get the effect again. The S13/S14 multi link does not suffer from the same amount camber changes through it's motion.

 

I'm not saying that this would be the best IRS you could ever put in a S30. But it is a very cost effective way to get alot more. Not just a better suspension. (Even if it's only a bit better.) You get 5 lug hubs, and bigger brakes. And the short nose LSD diff are alot cheaper than the Long nose.

 

If I wanted to spend $6-8K I could get one hell of a custom IRS built for my car.

 

Interesting and informative post Paul' date=' it prompts a few comments.

 

In my limited circuit track experience, once you build in some adjustability the S30's rear suspension performs very well, its the front which is the weak end. .........................Yet very few seem concerned with replacing the front suspension on a S30 for some reason or other.

 

[/quote']

 

I agree with you. I wish that more people would look into "fixing" the S30's front suspension. I looked into the Skyline, and a few other cars front suspensions, but I was told that none of them would work. And a custom job is big $$$$$$.

[BRAAP]

Yes, you all have hit on the S-30’s weak link, the front end. Adding caster helps to BAND-AID some of its turn in issues, but it still pretty much blows. The rear suspension on the other hand, isn’t great, but it does work fairly well on many levels. For lack of a better description, the rear suspension on the early Z car is a good Jack of all trades, master of none.

 

 

I would also agree that he 240 SX is competitive, “in its respective class”. Now compare the 240 SX times to comparably set up early Z cars around the same track and there really is no comparison.

 

I would like to believe this comparison would help shed some light on which car might have a better suspension for all out handling. These are the current 2006 SOLO-II classifications as per the 2006 SCCA Rule Book.

In the street prepared category, for those not familiar with SOLO-II, the cars are typically very nicely set up street legal cars with full interior, street tires, and only limited mods allowed. The 240 SX falls into “D” street prepared class and the early Z falls into “B” street prepared, (DSP and BSP respectively). In the “Prepared” category, the 240SX falls into “E” prepared and the early Z falls into “F” prepared. The prepared categories are WAY more lax and allow monster slicks, full roll cages, gutted interiors, but the car must retain similar engine config, etc. Now the SCCA has gone to great lengths to class cars within a certain class so as not to bias the class to a particular car in order to keep the competition stiff and fun. They adjust these classes every year to make up for any nuances that arise and to make space for the new cars that come available.

Any how, I’ll let you the readers decide which car you think makes a better or at least has the potential to be a faster car based on the SCCA’s classification and what other cars surround these cars in their respective classes.

 

 

DSP;

Acura Integra, BMW 2002, Geo Storm, GM J, L, N, and X body, Dodge Neon, Dodge Colt, Ford Contour, Mercury cougar, Ford Probe, Hnda civic, Hyundai Tiburon, Mitsu Galant, Nissan 200 SX, 240 SX, Maxima, Sentra, Pontiac Vibe, Saturn, Toyota Camry, Toyota Supra 82-85, Volvo 240 series.

 

BSP;

Corvette up to ’96 incl ZR-1, Pantera, Honda S-2000, RX-7, Datsun 240, 260, 280 Z, Supra Turbo 93+, Sun Beam Tiger, Subaru WRX STi, Saleen S281E

 

Based on the mildly modified “Street prepared category, the S-13/14 is in pretty sedate company compared the group of cars in the Z car class…

 

 

 

 

Now lets look at the race only versions and see what their respective competition is…

 

EP;

Datsun/Nissan, B210, 210, 310 510, 610, 710, 810, Pulsar, Sentra, 240-SX, Chevy Vega, Dodge Colt, Dodge Shadow, Ford Escort, Mustang II, Mazda 323, 626, Toyota Paseo, Corolla, VW Jetta, Scirocco.

 

 

FP;

BMW 3 series, Datsun/Nissan 240, 260, 280 Z and ZX, Ferrari, Honda S-2000, Lotus Elise, Mazda RX-7, Mitsu Eclipse AWD Turbo, Porsche 911, ALL, 914-6, 924-S, Toyota Supra 93-98, MR-2 Super charged.

 

 

 

 

At the national level, BSP cars are substantially quicker than the DSP cars and the FP cars are substantially quicker than the EP cars.

From this point of view, the Z cars Chapman strut rear suspension doesn’t look to bad, now does it, even if it does have EXCESSIVE camber gain?

 

Something else to keep in mind. When Nissan campaigned the 240 SX in GTU, and the 300 ZX in GTO, Nissan didn’t retain the multilink on either end of either car. It was double wish bone on all four corners, and they did that for a reason and it wasn’t because rules said they couldn’t use the multi link.

 

I probably should bow out of this one at this juncture before someone launches an RPG at my shop, LOL

 

 

 

Merry Christmas and a wonderful new year to All of you…

[JMortensen]

The man speaks the truth... even if his screen name is an onomatopoeia for burping.

[Ed260Z]

OK, so what your saying is that the S13/S14 rear is not going to give any real preformance gain over the stock S30 IRS.

 

What IRS would you go with?

 

The only other IRS that I know can handle the power would be a Jag style IRS. But that is around $3-4K. I do have a tight budget and the RB26DETT will be sucking up most of it.

 

I'm not looking for a racecar, altough the occasional run through an Autocross event is not out of the question. I want a well balanced machine. And I want to do it as cost effectivly as possiable.

 

There seems to be a hang up on doing this swap just for the "better" suspension. What about the other benefits?

[johnc]

There's an effort to reclassify the 240/260/280Z from BSP to DSP. The 240Z is completely outclassed at the national level in BSP and with the speed and power of the E36 325i in DSP the 240Z looks like a good match.

[BRAAP]

There's an effort to reclassify the 240/260/280Z from BSP to DSP. The 240Z is completely outclassed at the national level in BSP and with the speed and power of the E36 325i in DSP the 240Z looks like a good match.

 

 

 

John,

I agree with you on Street prepared class change. It is about due. For that level of competition, the Z is becoming out classed. You don’t see to many Z in the top ranks at the national level in BSP any more. Back when the Z was pulled from ASP and put into BSP, there was one guy, I forget his name, any how, he would dominate the class at nats in his Street prepared 240 Z. If memory serves, he was also doing pretty well when he was running it in ASP.

Hmmm… Putting the Z in DSP sure would shake things up, that’s for sure. In doing I’m sure there will be other DSP drivers that will argue for a more thorough class restructuring.

 

BTW, Have you heard any rumors about possibly reclassifying the Z out of FP? FP, on the national level, seems to be “Z” Prepared, i.e. the Z ‘s pretty much dominate.

 

Thanks for your insight John, much appreciated.

[tannji]

I am one of the people comtemplating the 240SX IRS swap... but had not considered the down-side, other than the difficulty of properly doing the swap itself. If the 240SX set-up is not much of an improvement, what is? I am not up to date on this, but someone mentioned the Mazda MX5/Miata double wishbone suspension, which I think is front and rear... I know that some people put some decent horsepower into those cars. Is it on basically stock suspension? What are the limitations? It's is beginning to sound like in order to do this properly, you would have to tube the front clip and start from scratch, which is probably a bit more than I ever want to do. = ) The only thing I have ever read specifically on the MX5 ride handling was in a comparison between the Miata and it's new competitor, the Solstice. If I recall correctly, the writer seemed to think that both cars were basically competent, if not much more, as far as suspension and ride were concerned.

[rudypoochris]

The only other IRS that I know can handle the power would be a Jag style IRS.

 

Why does everyone assume the 240z IRS (i guess 260z in this case) can't handle power? How much are you planning on putting through that RB26??

[87Kevin]

I am in no way a suspension expert, but I have swapped the 240sx IRS into my z31. This suspension is loosely based on a "double wishbone" setup. Most of the pros and cons have already been discussed, and the debate of multi-link vs semi-trailing will go on forever. But from personal experience, everyday street driving as well as the occasional trip to the strip, it is a world of difference. It really feels like a different car in a good way. That was before I replaced the cradle bushings with solid aluminum - the best susp mod i've evar done. And the car doesnt take a poop every time I shift! But seriosly, weight wise, the cradle is heavy, but so are those huge control arms they replaced, and also, i'd bet the short-nose is lighter than the long-nose. This rear suspension design has been used on every rear-drive nissan 89 and newer, and I've never heard and bad reviews on it, so it must be doing something right.

[BRAAP]

OK' date=' so what your saying is that the S13/S14 rear is not going to give any real preformance gain over the stock S30 IRS.

 

What IRS would you go with?

 

There seems to be a hang up on doing this swap just for the "better" suspension. What about the other benefits?[/quote']

 

Ed260Z,

If you are in search of a different rear suspension for the Z, I suggest getting together with someone that is “suspension design” savvy such as Cary, aka “Tube80Z” or even Ron Tyler, etc, and consider a nice Double A-arm. These guys are very knowledgeable about suspension design and also take into account what takes place “dynamically” within the suspension design, not just “static” issues.

For the DIYer, maybe get a good close look at the C-5 and C-6 Vetter rear suspension as well as the later Vipers. If you ever get the chance to ride in, or even drive one of those cars on the track, and then on the road home in stock or street prepared trim, you’ll know what I’m talking about. Those cars offer absolutely phenomenal handling on D.O.T. tires with out much compromise in passenger ride comfort. Those cars are able to get the power down to the ground pretty well, corner on street tires better than some dedicated race cars do on race tires, (just look a the results from NATS) and the ride quality is adequate for taking Granny to the Grocery store without causing her to pee in the seat. Of course all these wonderful driving attributes aren’t JUST because of the double A-arm set up they are running, it is also the fact that those cars have a very LOW CG with a WIDE track and longer wheel base, i.e. less CG movement for a given cornering load, especially compared to our beloved Z cars.

Anyhow, my point is, if you mimicked the Later Vette, Viper rear suspension and made the appropriate adjustments to compensate for the Z cars narrower track, wheel base, wheel loading at maximum effort cornering etc, you should end up with a nice upgrade from the Chapman strut.

Other wise, you could always try and find ways to “lighten” up the Chapman strut design with lighter weight alloys replacing the heavy steel parts and maybe even try designing your own “longer” lower control arm.

 

 

In my opinion , you should just leave the rear end alone for the time being, other than struts, bushings and/or other slight geometry enhancements, ie. Terrys and JonMortensosns adj rear toe, (great projects by the way guys, nice work), and focus on redesigning the front suspension so that it can at least keep up with the rear, bringing the car into a better balance, handling wise. Everyone here at this point all agree that the Z cars front suspension is the weak link from a design stand point, and needs attention before the rear does. After getting the front end some what sorted out and you are wanting to get REALLY nuts with the car, you would attack both the entire car as a whole.

 

Double A-arm up front would be a nice starting point… Maybe these pics will add a little motivation…

Here are a few pics of a Ron Tyler’s’ Double A-arm front end for his 240 Z that he designed and built a little while back. The idea was to get wheels the same size as the C-4 Vette under the Z with as little compromise in handling as possible and also get the car to “turn-in” with more authority and eliminate, or at least reduce, some of the other negative issues the Z front end suffers from and still be able to fit a Small Block Chevy in the engine bay. I remember him struggling most with not wanting such short control arms, but to keep the Z cars front track relatively normal, and fit the suspension around the V-8, this was, in his opinion, his best option. A custom built front cross member held an Oxendale style Ford PWR steering rack etc. He had it all finished up and attached to the car and then abandoned the project to build his own “scratch built, mid engine car” using a Taurus SHO engine in the back, complete with scratch built Double A-arms, front and rear etc. I currently have most of control arm parts from the defunct 240-Z front A-arm project in these photos including the custom T/C rod hiem pick up.

 

 

 

 

Here is the scratch built car he was working on. This project is now on hold and the front end is hanging from the rafters in my shop while he currently is working on his E-30 M-3 project.

 

 

 

 

And the front spindle/hub assy…

 

[BRAAP]

I am in no way a suspension expert, but I have swapped the 240sx IRS into my z31. This suspension is loosely based on a "double wishbone" setup. Most of the pros and cons have already been discussed, and the debate of multi-link vs semi-trailing will go on forever. But from personal experience, everyday street driving as well as the occasional trip to the strip, it is a world of difference. It really feels like a different car in a good way. That was before I replaced the cradle bushings with solid aluminum - the best susp mod i've evar done. And the car doesnt take a poop every time I shift! But seriosly, weight wise, the cradle is heavy, but so are those huge control arms they replaced, and also, i'd bet the short-nose is lighter than the long-nose. This rear suspension design has been used on every rear-drive nissan 89 and newer, and I've never heard and bad reviews on it, so it must be doing something right.

 

Very cool. I commend you on your efforts. For a stock to stock comparison, I think the multilink set up is a nice improvement for the Z-31. I bet the launch squat is GONE!

Did you have to do much cutting, fabricating and/or welding to get the cradle under the car?

So what other mods have you done to your Z-31?

[tube80z]

Something else to keep in mind. When Nissan campaigned the 240 SX in GTU, and the 300 ZX in GTO, Nissan didn’t retain the multilink on either end of either car. It was double wish bone on all four corners, and they did that for a reason and it wasn’t because rules said they couldn’t use the multi link.

 

I don't really have much to add to this thread. I got to talk with Trevor Harris once and asked this question. His answer at the time was they didn't have adequate tools to figure out the suspension and what to change for racing. We're pretty spoiled with the apps we have now and can run on a PC.

 

Cary

[BRAAP]

The only other IRS that I know can handle the power would be a Jag style IRS. But that is around $3-4K. I do have a tight budget and the RB26DETT will be sucking up most of it.

 

As for the OE Datsun R-200, U-joint half shafts, and the Chapman strut rear suspensions toughness, I offer you this crazy nuts Z car in the links below. The first link below links to videos of this S-30 Z car doing WHEELY’s that would make street bikes jealous, and it does it over and over all with the original greasy grimy R-200, U-joint half shafts and OE Chapman strut rear suspension. Even a 1000 HP RB won’t deliver those kind of “shock” loads to the drive train as the boost as to build first at the drop of the clutch or release of the trans brake. This car has ALL of its 700+ HP available IMMEDIATLEY at launch! That is “shock” loading on a grand scale.

This is just one of many RADICALLY powered Z cars that are testament to the durability and survivability of OE rear ends, half shafts, and suspension under extreme abuse. The OE parts are in essence BULLET proof for pretty much any “street application” we mere mortals would ever afford to build within the Datsun S-30 shell.

 

 

 

Here is the link with the video footage…

http://forums.hybridz.org/showthread.php?t=105587

 

 

Here is a thread with pictures of the OE rear suspension, half shafts, control arms, etc under this crazy nuts wheel standing Z car.

http://forums.hybridz.org/showthread.php?t=104179

 

 

 

Hope this puts to rest the notion that the OE parts are weak or not up to the task of street abuse…

[BRAAP]

I don't really have much to add to this thread. I got to talk with Trevor Harris once and asked this question. His answer at the time was they didn't have adequate tools to figure out the suspension and what to change for racing. We're pretty spoiled with the apps we have now and can run on a PC.

 

Cary

 

 

Thanks for the info Cary.

 

I hope you don't mind that I gave up your name as being fluent in performance chassis design.

 

Thanks again,

Merry Christmas an Happy New year to you and yours,

[tube80z]

I hope you don't mind that I gave up your name as being fluent in performance chassis design.

 

No, I don't mind. But in all honesty I just hold a degree in advanced bench racing, which means believe half of what I say and even less of what I do.

 

Cary "back to welding to make some heat ..."