I drove R3 and S1 back to back on track before
The steering feedback on R3 is amazing , I think due to age of chasic, but one thing Mather a lot could be foam injection subframe
As u can see on my pic, Mazda already try this setup on JDM special edition model
On the pic it say, this change improve 20%of stiffness !!! Sounds too good to be true
Wonder any member try to do this mod on their S1 8 ?

 

Pic loose on post....

 

Here u can see the special edition Mazda debut in S1.5 area

 

It does literally nothing for the vast majority of usecases.
The difference you're feeling are the shocks and sway bar differences.

Think about it, most of the cornering force is stored in the spring/bumpstop/sway bar and never makes it to the crossmemeber.

And if you did stiffen it, given the suspension geometry, you would get less camber gain on compression, so... I dunno I would not put any time into this.

 

R3 not just foam fill subframe, the S2 whole sheet metal is thicker and come with extra brace~ thus the extra weight
so I am pretty sure the torsion stiffness is stronger then S1

 

Accoarding Rx-7 magazine issue 38(one of best season magazine for rx7/8)

The S2 chassic is more then 100% stronger, by thicking shee metal of front suspension area 1.4-1.6mm and front windshield .65-.75mm along with more spot weld and foam fill subframe

So I think is very obious that S2 R3 have very different body structure, which S1 can only envy about, all we left mabe try to foam into the subframe to see any steering feeback can be improve!!!

 

Ok go ahead. See how that works out.

Or you know, work on the suspension which is actually what determines steering feedback.

 

Find this on quick search, seen like this is what BMW put on E46 rear subframe
wonder how this will work out~

 

BMW only did it as a repair kluge to offset subframes that were prone to cracking

you seem fixated on this like it’s some kind of magic elixer that will suddenly transform your RX8 to be superior to those without. As per my reply in your other duplicate thread, Mazda already did this on the S1 Shinka. It was probably one one of the most bloated, slow RX8 models offered except for maybe the early base 4-port RX8 automatics.

You’d be better off looking for an undamaged Shinka front subframe from a recycling yard. Adding weight didn’t make an S2 superior in reality regardless of the theoretical paper analysis, just heavier and slower. Specifically to the R3 model, I’ve yet to see any results where it suddenly showed up in any race class and started whomping on the S1. Kind of the opposite. Same for all those engine mods that were going to improve Renesis durability that didn’t really pan out in reality either.

.

 

The Shinka and anniversary trims included the foam filled subframe on the S1 here in the US. I haven't come across anyone who mentioned grabbing those for their cars but you could always try swapping them out.

 

I imagine it would be also difficult in DIY conditions to fill in an uniform way, regardless if it actually"does anything"

 

I’d tend to think they had a special fixture for it to be under vacuum during filling just for that reason.

 

That picture actually says "lateral deformation down by 20%", which is related to stiffness, I suppose. I can't read too much Japanese.

The foam for S2 is an R3 only thing, and I recall 9k(Shinka also has the foam) saying it's basically just a way to market the car better. It's not really a huge deal and I'd rather spend the money on some better rubber(OEM ones are terrible from what I have heard).

IDK, if you are pulling the engine, you could get a Shinka subframe at the same time to try it out. Again, not worth the investment IMO.

Edit: this is the thread I was thinking of. Again, same idea as this thread.

https://www.rx8club.com/series-i-whe...ricing-182511/

 

Straight off the Mazda website:

Wasn’t even mentioned in the 2009 service highlight manual. Of course it had already been used on the S1, so maybe because it wasn’t anything new. I might question where the info on the Japanese text came from actually and possibly it’s accuracy.

 

That's what I was going to say, I searched through the Service Highlights and I just can't find anything about it. Maybe even Mazda thinks it doesn't make a huge difference?

And from what I have looked up, some people do it on some other cars, but exactly how much it helps is a bit debatable, and the density of foam used is also an issue, as some people mentioned in the thread I linked.

OP do you Autocross or track the car? I Autocross and I desperately need some driver mods LOL. I am not concerning myself with suspension mods yet. I mean FFS, there was a guy in a bone stock 03 Ford Focus that went faster than a bunch of people in way nicer cars(including mine). That's just the power of driver mods.

 

Injection foam is not thing new
Many car manufacturers and race car had done it, I try it on My Miata back in early 2000 with big success ~
The problem is finding right foam, at that time I test seversal formula ~ most people fail because they might get their foam from Home deport 😂

 

What do you consider big success?

I still fail to see why, given the track experience you have, you're attaching so much importance to the foam in the R3 and not the choice of wheel, tire, tire pressure, stiffer shocks and front sway bar over the S1 you drove.

 

Just like dont judget book by its cover, and Judget my track experience by how many I post is same thing

I have lots experience on road race
Here are just small clip that I race my FD3S among newest Factory back race car in my cpuntry

 

My approach to upgrades has always been that you try to improve your current bottleneck. For example, my tires were garbage beforehand, and even with my not-so-great skills, they are limiting me with the grip. That's the bottleneck, and I have upgraded my tires. Now my skills are holding me back, so I am not going to get better suspension until I can be up there with some of the frequents in terms of time.

So in your case, is the front subframe the bottleneck? Or is there something else? Tires, suspensions, skills, etc. would all likely come before the foam.

 

I just would like to point out that even assuming you managed to succeed in filling the subframe with the correct kind of foam AND filled it as good or better than Mazda did from the factory, you are still talking of obtaining the claimed 20% rigidity increase of only ONE component (and realistically the number is probably less)

Adding salt to the wound, youre also significantly increasing the weight of the subframe by filling it with foam.

You mention driving both a S1 and a S2 R3, did you ever consider that the S1 being older likely had much more worn suspension and steering components resulting in it feeling more sloppy and loose?

It seems pretty clear you have a boner for the S2 R3, so just get an S2 R3.

Like TeamRx8 said, IF the S2 really was better then no competitive race team would ever pick the S1 as the starting chassis for their race builds.

 

Actually I read your thread on 7club and was commenting specifically on your track experience. There was no sarcasm or post count involved.
You're been doing this for a while, you should know how different components influence car behavior.

So again, what are you trying to accomplish? What is the big success you had with foam in Miatas that you mention?

 

I have filled subframes with Home Depot foam for years in my cars. I don't notice a difference steering feel, but I do notice a nice difference in NVH, especially in the rx8. Road noise is reduced a perceptible amount, in my opinion, which I why I continue to do it in my cars. I started on a 1981 GPz550 that would begin a weave when cornering over 100mph. I tried many of the conventional methods to remedy at the time, (not going to waste your time here), and spent money, but what finally fixed it was injecting the frame tubes and swingarm with Home Depot foam.

I was running out of ideas, so I said why not...

It may improve steering feel in a track car... I would think there are other things that would make a bigger difference, but I could be wrong. It might contribute that last few percent?

I am a street driver, so that observation is way beyond my experience. Foam can add stiffness to a hollow weldment, sometimes quite a bit, depending on the part, its shape, its use, and a million other variables. I don't see much downside to this, other than retaining moisture in a hollow somewhere and causing rust, or stiffening a part that is meant to flex and causing a stress riser somewhere that forms a crack.

Its worth a try at least.

 

My target for my track day Rx8 is Budget
Before I start my Rx8 project , i have no track able car I can run in rain ~
And Rx8 with its Rotary power , great handeling , superior brake balance , affordable price fit my target !!!

As Two part foam injection, this seen so much cheaper and lighter compare any tower bar or under brace
And offer 20% rigidly approved by Mazda
Which I think is worth to try

 

I've been running my car without the front shock tower bar and haven't noticed any ill handling as a result.

Granted I have a different front subframe, but I highly doubt the filled front subframe does much for performance. The bigger improvement is probably in NVH. Regardless I really don't want any extra weight out over the front wheels and anyone looking at using the car in a competition environment won't want weight there either.

 

Not to mention that OP was pointing out parts of the S2 that have thicker sheet metal than the S1, however those parts have nothing to do with the front subframe so I have no clue how those points would apply at all (and why I made the comment that I did)

This thread just feels like so much trolling