Front Suspension Swap? Anybody done one

[seattlejester]

I think with the modern trend of "I know what I am doing" by maybe some that are not as knowledgeable taking over the land scape asking questions are a good measure to check yourself. Whether there is merit in the response, or the questioner will follow solid advice will always be determined. 

 

Chances are people have different perspectives, priorities, and experiences, the benefit of the forum is that it brings people together. Some might have extensive track experience, others may have extensive autocross experience, others may know the intricacies of stance, and others may know the world of drifting. Suspension/steering for these activities are quite different depending on the course and layout. 

 

The caveat is always how much do you let the information influence your decision. Some may be bench racing, others may be suspension engineers, everyone is going to have an opinion. 

 

I think a good exercise is to entertain the options, that usually helps lay out your priority. Like maybe a double wishbone setup is the most stable with great camber characteristics and adjustability, but if adding additional suspension pickup points is out of your time/budget/etc then the priority obviously falls into limiting to something of a similar nature ala strut with single lower control arm. You don't have to act on every suggestion, but looking into it can help focus your own goals. 

 

 

[Ben280]

On 6/7/2018 at 3:34 PM, Leon said:

I used Ben's statement as a jumping-off point as he decried struts as the sole reason the Z isn't competitive anymore which I don't agree with. It could be (is) a myriad of factors that all add up. It's not a malicious jab but a friendly argument, and he redeemed himself afterwards saying that in spite of the apparently non-competitive struts, his car handles fine, wizard-like even. And this is coming from someone that is actively competing

 

Leon, you are correct and I would be remise to claim that the only reason for the Z's not being on par with newer cars is its strut suspension. All that is meant to imply is that at peak driver performance, a SLA front end WILL outperform a strut front end. Can mere mortals get to that point in driving? That remains to be seen. 

 

Going off topic, but the bigger issue for competition (for my case at least) is the lack of power. I'm at minimum class weight and with a 8.5/10 motor build, about 9lbs/whp, with the guys at the pointy end of the field closer to 6-6.5 lbs/whp. 

 

For auto-x the Z has a lot going for it; light weight, excellent weight distribution, narrow even with monster tires on it, and lots of space to modify and add parts. The class I race in allows for most of the foils in the suspension to be fixed, and the excellent aftermarket support these cars have found recently makes it easy to get the adjustable parts. I'm getting closer with the car, and still believe that the nut behind the wheel is the limiting factor. Once that ceases to be the case, I'll be sure to post pics of my front suspension conversion. 

 

I will say that doing a front end conversion like this is a fabulous way to add years of development to a car, if not well thought out, or completely ruin a good car if it's not thought out at all.

[rabrooks]

OP is back. Thanks for all the input. I wasn't expecting so much discussion and diversity. So let me try to explain my purpose for the thread and my idea of a suspension swap. 

 

The strut arrangement is a good setup when all the geometry is right. My problem is I don't like the fact that the spindle is fixed to the strut. So the suspension will always be at an angle based on the rotating position of the lower control arm. If the suspension is a double a arm setup I feel like I will have  more adjustability. I like the idea of setting camber and having built in geometry that the camber remains under compression. So the shorter upper a arm, attached to the chassis at a more outboard point allows negative camber  to remain and can be better dialed in. Also, I feel like the suspension will move around less as a double a arm setup.

My previous track car was an 09 c6 z06. It was an awesome track car. I found the car to be unparalleled in high speed corners and of course the straights because of the power. Slow corners, I was unable to hang with the good Porsche's. Since I started this thread, I found something in the aftermarket that is for the Z and it is an awesome setup. I can't share anymore than that because I promised I wouldn't share the information. Keep your eye on Apex Engineering.

 

After looking more closely at the rear suspension and fender well of the car, it appears I will have to cut out the inner fender well and move it inward in order to create an attachment point for the upper a arm. The lower one is fine as is. Please share your thoughts on this. I want to do this because of my comfort in double a arms and because of the statement below about roll centers.

 

On a different tangent. I have some roll center questions. Determining roll center is easy enough for front and rear. It seems most cars are set up with a lower roll center in the front and the rear is typically higher. So that puts a roll center axis thru the car front to back not being level. So is that the best set up or is the best setup for cornering and tire wear to have the roll center level. Keep in mind, I realize roll center is dynamic. But is seems if the roll centers were more level it would be a better setup. Having said that, maybe a good cage  and stiff chassis with a roll center high in the rear would put alot of pressure on the front outside tire. maybe too much causing a huge push

 

Thanks

Roger

Edited June 19, 2018 by rabrooks

[Leon]

6 hours ago, rabrooks said:

So is that the best set up or is the best setup for cornering and tire wear to have the roll center level

 

You used the b-word...

 

If I may summarize your post, you want to convert the front and rear suspension in your 280Z from struts to dual A-arms because you feel like you'll have "more adjustability" and "the suspension will move around less"? And because your Corvette couldn't keep up with Porsches in slow corners? Then some stuff about roll centers that showed a fundamental lack misunderstanding of what roll centers do.

 

Quote

But is seems if the roll centers were more level it would be a better setup.

 

You might as well say, "if your anti-roll bar rates were more equal, it would be a better setup". Roll centers are just one component of anti-roll which itself is just one component of vehicle handling.

 

It's all a system. You will be frustrated and lost if you're only looking at single characteristics in isolation.

 

You have to understand the problem first, ask yourself the right questions, research and execute. In reality, that's an iterative loop. Currently, there is a lack of understanding and lack of clarity as to your wants and therefore needs. I've seen the Apex kit and while nicely crafted, it represents the above statement.

[caperix]

The z can have camber change under compression as well with the factory struts. Use roll center spacers to keep the control arm at a downward angle. The arc of the arm will have camber gain until you are past the level point of the arm, then will start loosing negative camber.

[rabrooks]

3 hours ago, Leon said:

 

You used the b-word...

 

If I may summarize your post, you want to convert the front and rear suspension in your 280Z from struts to dual A-arms because you feel like you'll have "more adjustability" and "the suspension will move around less"? And because your Corvette couldn't keep up with Porsches in slow corners? Then some stuff about roll centers that showed a fundamental lack misunderstanding of what roll centers do.

 

 

You might as well say, "if your anti-roll bar rates were more equal, it would be a better setup". Roll centers are just one component of anti-roll which itself is just one component of vehicle handling.

 

It's all a system. You will be frustrated and lost if you're only looking at single characteristics in isolation.

 

You have to understand the problem first, ask yourself the right questions, research and execute. In reality, that's an iterative loop. Currently, there is a lack of understanding and lack of clarity as to your wants and therefore needs. I've seen the Apex kit and while nicely crafted, it represents the above statement.

My posts seem long to me so I do my best to condense in an effort to shorten the post and provide the viewer the info needed. In doing so it may seem that I am just rambling, especially when talking about suspension because it is all a large component and it is all dynamic. It is true, I don't fully understand all that I should but that's why I'm here. Educate me

You may not have seen the apex component I'm referring to. Its not yet introduced and isn't on they're website. Its currently in testing.

Thanks

Roger

[rabrooks]

I agree that the Z suspension is a good setup. But I have never thought that a strut setup is a setup that could be adjusted to most situations. IT has some limitations. All suspensions have limitations. I believe the double a arm suspension offers more options with less trade off. So while i have the car completely stripped, I'd like to make any improvements that I can. At least until I learn more, it seems that the lower control arms on the car are good and I am looking at what it would take to add an upper arm and what its advantages may be.

All suggestions are welcome. Just don't beat me up too bad.

Roger

[jpndave]

On 6/8/2018 at 4:36 PM, seattlejester said:

Regardless of OP's likelihood of execution I think the spirit of discussion is quite useful. 

 

I'm not sure the motivation in trying to kill the discussion. The question was vague, yes, but the replies were interesting. We're no strangers to swapping parts here especially from other makes, and I also think we have members who have shown we don't just stick on components with bubble gum and duct tape. The scope of the suspension as a whole may not be executed perfectly given we don't know much about the OP, but a discussion of alternative setups I imagine would be useful. Mark's corvette or sc300? I forget which, but that conversion comes to mind as a well executed example.

Agreed, I started reading this and particularly JMortensen's posts including the one on the double joint front had me intrigued. So I'm thinking cool, a healthy discussion on SLA front suspension! Then suddenly I'm wading through muck. At that point I'm m not sure I even want to chime in, not cool. Generally this forum is great to have healthy discussion on topics that often can translate to my car being a better design. I would appreciate going down the road this started to head. Or if the OP wants to continue a different direction we could take it somewhere else.

 

Is a SLA suspension required for good handling? Not necessarily. Can the Z be made to handle with the stock design? Sure. Is a strut superior to a double arm if both are executed correctly? No way. The reason they run struts is cost or packaging and I suspect the Z was done that way for both reasons, fairly light, cheap, easy to package. If your car is in decent shape and you're not doing an intensive build with tools and skill set to get it right the struts are probably best left there. I've got to rebuild the entire front subframe along with the new engine, brakes, etc. and for me going to the better designed SLA makes sense. I'm intrigued by that double joint lower and want to explore if it may solve some scrub. I'm looking at a relatively clean sheet but would like to use readily available stock pieces wherever possible. Anyone up for a Healthy discussion?

Edited June 25, 2018 by jpndave

[JMortensen]

I've started my own thread on the dual ball joint setup, going to see how feasible it is because I have serious issues with scrub with 15x14 wheels. 


 

[rabrooks]

Thank you for bringing positivity to the discussion and waking up the thread.

I realize how easy it is to hear a comment about what someone might do, and speculate that it will never happen. But I can assure the naysayers, if I can create a better setup without a total butcher job, I will get it done. My track experience has taught me alot. But I know there's alot to learn, hence the reason for the tbread. Feel free to teach me

[rabrooks]

For the sake of further discussion,  I've decided to install the GM 3.6l doc v6 with 60 degree v and 340 lbs and 323 hp in stock form. And no need for heavy exhaust manifolds. This engine is in the camaro and caddy. A twin turbo version is in the caddy making 465 hp. 

 

I have looked at the chassis works front beam and suspension. I believe I can modify the beam set up to build in better adjustment and add to the rear of it to provide engine mounts for the short v6 and keep it as far back as is reasonable.

 

But as I mentioned earlier, Apex engineered has a new deal about to be introduced. I won't do anything g til I see that setup in completion 

[seattlejester]

In Leon's defense and I surmise his main point is that it looks like you are looking for an out. There are fixes to the niggles that you mention as ben mentions. If it is difficult to address these issue in stock form grafting on a new system would potentially be a cause of concern as trying to trouble shoot a grafted system is going to be far more difficult. Looking to swap out the front suspension here to apply hyperbole would be to change the engine because the spark plugs are fouled. Granted a huge precursor is if this is strictly in the realm of discussion aka bench racing, then the discussion of theory is at our imaginations limits.

 

Unfortunately one of the points of this forum per JohnC is that this isn't automotive 101. The fact you state you need to learn is awesome, it is a huge first step that many people are too prideful to take, but it would be more appropriate to search and find a few systems and ask specific questions, the breath and depth of the subject of suspension and chassis dynamics is quite vast.

 

And the use of the "b word" is quite frowned upon here, as stated there are different bests depending on time, location, finances, etc trying to find that without providing any info would be an exercise in futility. 

 

To keep things going though, if a fixed knuckle is a concern, the 240sx knuckle is quite modular. I've looked and noticed you could run them flipped in the front with the driver on the passenger and vice versa (the 240sx is rear steer, the 240z is front steer), standard coilover and a custom top, and you have a knuckle with quite a bit more aftermarket options in terms of brakes and coilovers. Granted the benefits I don't know would outweigh the effort involved.

[rabrooks]

So someone help me with a question I asked earlier in the thread. Concerning Roll Centers. It seems under many circumstances the rc is low in the front and high in the rear. If I undestand Mt geometry correctly, as the roll center is low and dynamic under compression aren't I adding extra weight to the front outside tire as I turn. And does lowering the rear to match the front balance the potential traction. Or have I got that backwards. 

I know the rear will squay on exit which may be better for roll center to work in my favor. So is that why most cars seem to have a high rear rc

[JMortensen]

General rules:

Front engined cars usually have lower roll center in front and rear RC is slightly higher than front. 

For performance, low front roll center is best. If it's too high what it does is force the wheels to move outwards in order for the suspension to compress. This can really make it hard for the outside suspension to work under load. Conversely, an underground RC will want to compress the suspension more than it would otherwise with cornering forces.

Higher roll centers can be used to allow softer spring rates.

 

If you spring the car stiff enough, you can run low roll centers and not have excessive roll and reduce the jacking forces.

As a kind of rule of thumb, 80% of the turn happens in the first 1/10th of the turn. This is why the minutia is important. If the car won't turn in the instant you turn the wheel, then you're not getting around the turn very well, regardless of what it will do once it changes direction and is in a steady state corner. Again, as a general rule, the end of the car with the lower RC will tend to grip better, so RC is a way to change handling balance. This is why you have a lower RC in front. Solid axle cars have a hard time with high rear RCs and they use different solutions to lower the rear RC to improve handling. Not really germane to this convo, but here is a link to a discussion of a Mumford link, which is a modified Watts link that can lower rear RC: 
http://www.locostusa.com/forums/viewtopic.php?t=77

[jpndave]

3 hours ago, rabrooks said:

For the sake of further discussion,  I've decided to install the GM 3.6l doc v6 with 60 degree v and 340 lbs and 323 hp in stock form. And no need for heavy exhaust manifolds. This engine is in the camaro and caddy. A twin turbo version is in the caddy making 465 hp. 

..... 

Is this the LLT (and subsequent versions) direct inject you're referring to? Do you have the engine? I ask because I had one for a different project and sold it due to logistics and abandoned the project in favor of building my 240Z. I still have photos, dimensions somewhere along with an imported Australian 4L60E bellhousing and either a flexplate or the flywheel.

 

On paper sounds great, in reality not a good choice for a ton of reasons. I'd be happy to share but if you want suspension here maybe a different engine thread to not derail this further. 

[rabrooks]

35 minutes ago, jpndave said:

Is this the LLT (and subsequent versions) direct inject you're referring to? Do you have the engine? I ask because I had one for a different project and sold it due to logistics and abandoned the project in favor of building my 240Z. I still have photos, dimensions somewhere along with an imported Australian 4L60E bellhousing and either a flexplate or the flywheel.

 

On paper sounds great, in reality not a good choice for a ton of reasons. I'd be happy to share but if you want suspension here maybe a different engine thread to not derail this further. 

Yes, I am referring to the same engine. The one I'm after is the LFX or the LGX. I'd like to run a t56 behind it but I think it will actually be a AY6

[jpndave]

10 minutes ago, rabrooks said:

Yes, I am referring to the same engine. The one I'm after is the LFX or the LGX. I'd like to run a t56 behind it but I think it will actually be a AY6

So improved power integral exhaust manifold version that's a little lighter (basically the weight of the exhaust). 

 

Downsides - REALLY tall. I'll find my measurements. The Voodoo (Coyote) I'm using is bad but a low profile race pan is available making it possible . Not so here and it's structural. I don't think it will even be close to fitting in a Z. It is extremely short but the all up weight is not much less than an aluminium LS. The accessories are in the way of the steering. Electronic support should be there on later models. That early one used an oddball Bosch ECU that at the time I couldn't find support for. Wiring is doable and I had the harness really cleaned up nice ready for wrapping. The direct inject pump is right rear cam driven so shouldn't be a problem. Normal FI pump feeding it from the tank at normal pressures. Goofy bellhousing pattern (that's why I posted that rear photo) so you'll want a manual transmission donor full pull. 

[jpndave]

HTH some on the engine. First photo is the factory GM and the rest are of the engine I had. 

[rabrooks]

1 hour ago, jpndave said:

HTH some on the engine. First photo is the factory GM and the rest are of the engine I had. 

 

[rabrooks]

Since there is a secondary fuel pump. Will I need to create a fuel return line to the tank or does the secondary pump recirculate