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I test drove a Shinka a good while back for northzone as he was interested in one in my area. While I wasn't pushing it in terms of handling, I don't think it felt that different from my S2 GT, even in terms of NVH... The bigger difference between the 2 IMO is the transmission feel. S1 Aisin is smoother while S2 Mazda is more mechanical.
I imagine it would be also difficult in DIY conditions to fill in an uniform way, regardless if it actually"does anything"
I don't think that this would be a huge issue. Just run a PET or PP tube (whichever is resistant to the chemical reaction) into the frame that is cut to a pre-ran length, and pull away while you fill it. Maybe maybe make a mess but a good approach. Also if you can get a cheap thermal camera, you would be able to track the fill and determine where an air pocket it and fill it separately with a small drilled hole.
I am not sure why there is so much trolling on this idea. It isn't uncommon and it should ideally help with some sort of structural integrity as well as feedback harmonics.
Two part urethane foam isn't very heavy so the argument of weight is pretty ridiculous. Obviously density is of a concern but I bet a 1/2lb density foam would have a... different steering wheel feel. But if rigidity comes with that then that could be good and bad.
Originally Posted by kevink0000
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.
I agree 100 percent with Kevin, that this should add rigidity no matter how you slice the subject. My big concern again what Kevin brought up is that moving stress to a weak area causing cracks.
My final thought though is should you be chasing pure rigidity? Or you trying to concentrate sway to purely suspension components? I am no track star just a street driver so I am here to learn as well as give my opinion.
There’s no trolling; gave my opinion and reasoning. He seemed determined to do it regardless, so ok. Think I’d try to find a factory one first rather than diy, but it’s his deal.
TeamRx8: to be clear, i meant i felt like the OP is the troll. Not sure if you were responding to my comment in your statement but just wanted to clarify that.
I feel like the next thread to get created by OP will be about header power gains on a Renesis
I was responding to the prior post comment from Fickert.
The RX8 is substantially stiffer than the FD3 so you can’t really expect comparable results between the two.
So 20% stiffer; instead of moving 0.12mm it only moves 0.10mm (7/10000”)? The point being, you have no real reference of how much it flexes; on it’s own or as compared to bushings etc. which may be substantially more. Also no valid way to measure it. Just the ol’ butt dyno method. It’s his deal though. Have fun.
The stiffer suspension in the R3 introduces more vibration to the chassis. The foam is used to help dampen the vibrations so they are not transmitted to the steering.
Well
With 20% increase stiffness by injection foam to subframe is lighter and cheaper then most aftermarket tower bar or under chassis bar
So why not try it ?
And is not fair to compare shinka to say this mod work or not ? Shinka is full load car with more then 100lb hever then sports model
Sure-~
If u just happend to drive two similar S1 S2 at same day, mabe u can bit more open mind on it
Originally Posted by trackjunkie
it's like the one hood vent company that claimed their vents increase down force by 400%. 400% of what, 1 lbs?
This is from Mazda Japan, not some random shop
As for me, I Have always race car with very low torsion stiffness 13BPP SA22C, 13Bbp FC3S
I am pretty used to that , not until I pop in a Rx8
That really is day and night different the chassis just have way more torsion stiffness then rx7
But when I drive R3 back to back on track
I know this is definitely some thing very different
I would try to find right urthene foam for the job
And find the way to do a Back to back test
how will you quantify the test, other than just personal opinion and feel at the butt.
i personally feel there are better low hanging fruits on the rx8, and i'm still pretty new with the rx8 platform.
I am still
Thinking about it
Friends have unwanted subframe on ground
So I might just use it , as test bed ?
I am think to hydraulic press on it to see how much deform it will get under same force one side with foam one with out it ~
The key is find right foam, those home deport stuff never work.....,
I am very new to Rx8 too, although I been mess around Rotary for quite a while
Sorry, without the rest of the S2 chassis mods you have no idea how it plays out on an S1, but in general you seem to be overlooking the obvious. If it was such an improvement for the S1, then why did Mazda only offer it on the most bloated, fully optioned models not likely to be raced? Why did we never hear anything from Speedsource or other race teams about it? Do you honestly think they wouldn’t have access to that knowledge or equipment?
if it lacks density then how is it rigid enough to offer a substantial stiffening benefit? I’m not saying it does nothing (the previous reply was a joke), but your night vs day scenario seems unlikely. What seems more likely is it changes the steering feel due to vibration isolation that you’re misinterpreting as some kind of handling increase. That’s how a butt dyno works and why it can’t be relied on.
Sorry, without the rest of the S2 chassis mods you have no idea how it plays out on an S1, but in general you seem to be overlooking the obvious. If it was such an improvement for the S1, then why did Mazda only offer it on the most bloated, fully optioned models not likely to be raced? Why did we never hear anything from Speedsource or other race teams about it? Do you honestly think they wouldn’t have access to that knowledge or equipment?
if it lacks density then how is it rigid enough to offer a substantial stiffening benefit. I’m not saying it does nothing, but your night vs day scenario seems unlikely. What seems more likely is it changes the steering feel die to vibration isolation that you’re misinterpreting as some kind of handling increase. That’s how a butt dyno works and why it can’t be relied on.
Like I mention earlier, my race experience
Is all on low torsion stiffness car
I believe even with full on weld cage , SA or FC 's torsion stiffness still no match to stock Rx8
And of course I still clocking much faster lap time compare to Rx8, so fast lap time don't need to have great torsion stiffness
The car I started to feel it's body torsion stiffness
Is 996 cup car I once co drive in one hour endurance few year ago
that car with torsion stiffness and precious steering feedback really impressive me compare to Rx7
Because with this advantage u can really know limit on the tire !!! without it RR 911 wil be almost impossible to drive on limit
But I still don't like Porsche rotary for life
To answer why race team don't use it , because
Is much easier for them to spot weld the subframe~ but not easy for us ......
And I think why Mazda Try foam injection on S1 sinka model
Is to have similar feel like Europe's car feel to target different buyer group
seems to me you're better of foaming these parts of the chassis then to concentrate on the subframe. the rx8 has a big gaping hole in the middle because of the rear suicide doors and no B pillar.
Last edited by trackjunkie; 07-03-2019 at 02:36 PM.
06-27-2019, 01:12 PM
rotary for life 
