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dgross7's STF build thread

47K views 244 replies 24 participants last post by  dgross7 
#1 · (Edited)






Using this thread to document/share my progress both as a driver and of my car.

Improvements to date:

Chassis
Koni 8611-1256 race inserts
Corksport plates
Hypercoil 400f/650r
Goodridge ss lines
SPC rear arms
EBC yellowstuff
Tripoint RSB
AWR endlinks

Engine
Mazdaspeed CAI
Vibrant Headers/HFC
Racing Beat exhaust
SU trans mount
cp-e passenger motor mount 60 duro
cp-e rear motor mount 65 duro

Wheel & Tire
Rota Slipstream 15x7.5
205/50/15 RE-71r

O.Z. Alleggerita 17x7.5
225/45/17 Michelin PSS (travel tires)
 
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#36 ·
True, though how much the gains any of these car airflow/exhaust systems see in a bubble, by themselves, I'd be interested to know more definitively. A bottleneck anywhere along the line might keep you from realizing the full gains you're supposed to be getting from one component or another. But then again there, you don't want to decrease back pressure by too much either for our small CI NA engines.

Then there's the logistics of a header. Depending on where you live and the laws and the strictness of emissions testing in the area, an aftermarket header could get you in trouble. Especially a catless one, which most are. And the one catted one that I've seen, the gains didn't seem all that stellar. Plus, they're noisy!

An exhaust on the other hand, the sound alone can be worth the price of admission never mind the power gains. But if you're going for a performance exhaust I do believe that it's probably a good idea to also increase your air intake to see most of those gains.
 
#37 ·
Ok so I'm trying to decide what suspension I want to run for the 2014 season, and this is me trying to document all my thoughts:

I currently have koni yellows and eibach pro-kit (SHIT). I definitely want to switch over to a coilover set-up just to have the spring rate options.

1) custom valving on my current yellows by koni-na. then figure out how to run coilover springs. I talked with koni and they said the OD of my yellow struts are 52mm and the spring perches they sell are 50mm. So that would be problem number 1. I'm probably going to get camber plates to mount the struts, bumpstops and upper spring perch shouldn't be an issue.

2) koni race inserts (8611-1257). two options with these, try and figure out if they will fit in the stock strut housing, or see if I can still order the AWR strut housings. again, probably camber plates and everything else up top should be straight forward (i'm hoping).

3) keep it simple and buy KW/MS coilovers. Only issue with this is that I really like koni shocks and I think I can create a better set-up with the koni route. Pros to this set-up: simplicity and rear spring perch.

The other problem with the first two options is the rear spring perch, I have emailed tri-point about it, not sure if I'll be able to get any (waiting for a reply from them). I guess I would be ok getting oe style springs in the rear, I know swift makes 250# springs that will fit in the back. Not the most ideal spring rate, but I figured it could do for the time being.

I think that covers it. Feel free to add any wisdom or point out a mistake in any of my ideas :)

Oh I also have been using information on home-made koni coilovers from this website, which is actually an awesome reference for autox-ers

http://farnorthracing.com/autocross/konis.html
 
#39 · (Edited)
I called Ground Control recently and they told me they do have a coil-over conversion kit for Mazda3 struts now. The kit also comes with rear spring hats. They quoted me $450. Springs and camber plates are separate of course.


I have my plan down to two options and I'm in a similar spot as you. 1. Get a custom valve on my existing Bilsteins, hack the spring perch off, and buy the G/C kit + 2.5" Eibach springs + camber plates or 2. Buy some Bilstein PSS9's + Camber plates (Pss9's do not come with them) + 2.5" Eiback springs and ditch the springs that it comes with.

Still shopping around on custom revalves for the Bilstein struts. I think Bilstein may actually have the best price or a very competitive one at least, gonna call today and verify, but I believe all 4 cost around $400-500 last time I asked and since they do make the things it should be done right.

Option 1 which is the custom valve + ground control really has more appeal to me for a few reasons. One is cost, it should be less expensive than the PSS9 route. 2. Say for instance I buy 500 in/lb springs. I can tell Bilstein the spring rate, give them the motion ratio of my suspension and I'll have a nicely matched up set of converted coilovers and rear shocks to my springs. If you take any single or double adjustable coil-over (doesn't really matter the brand, KW, Bilstein ect) and just slap it on the car with the springs of your choice you're really just twisting the knob or knobs until it feels about "right." Not as ideal even on high end shocks that actually have damping adjustments that work as they are supposed to (most don't). In other words you are completely in the dark. Adjustable shocks are really kind of over-rated (according to suspension Guru's like Dennis Grant) and I think the custom valved non-adjustable Bilsteins may be a better setup out of my 2 options. Here is what the Far North Racing Guy (Dennis Grant) says:


"Note that I consider knobs on shocks as ways to get the forces to match on the dyno, or to rough in forces while testing; I never, ever, ever muck with the shocks during competition. I've run hundreds of shocks on my shock dyno and the repeatability of shock adjusters is downright horrible on anything except the highest end shocks (and even these have their quirks). When you have the damping right, it's right - unless you do something to change the natural frequency. Changing the shocks to try and change balance is an act of desperation - or of a Stock class car, which has few other options."
 
#40 ·
Mmhhmm. I think my KW/MS kit is great but if I could go back and do my suspension again Bilstein B16 PSS9's would get a good long look. Can't beat the price either for a plug-and-play, easy button option.

I was told by a friend that FatCat Motorsports have vast experience rebuilding/revalving Bilsteins PSS's. They are a good reputable outfit.
 
#41 · (Edited)
Yeah, off the shelf coil-overs definitely have their fans because it is easy (just order them up and bolt them to the car) and some people might be impressed by fancy knobs. It is tempting to just order up some PSS9's with a few clicks and get them the next week. I haven't ruled out that option yet. People also typically pay more for the "convenience" and it's more expensive than the ground control route especially if you already have Koni's/Bilsteins. Going the custom valve route is more of an inconvenience because you have to pack your shocks up and send them off somewhere and wait 1-2 months typically. Also you have to do your homework ahead of time because if you want to change spring rates later on, the shocks are no longer matched to the springs.

I emailed Shak over at FatCat on a quote for a custom valve job and he never got back to me. I hear he does good work but he's also way over-priced. I'm sure Bilstein does good work on their own stuff too, and I'm thinking they charge around 1/2 as much as Fatcat. I may call up there and get a quote on the phone because I'm just curious. As the name suggests go with Fatcat if money is no object. ;)
 
#42 · (Edited)
Getting your shocks matched to your spring rates to get the natural frequency at 1 to 1.5 or whatever you want is the key, that site strongly urges it lol. This is part of the reason I am leaning towards the koni route, with both options, i'm going to ensure they are valved appropriately from the springs I'm going to run. (that too is also still up in the air. I was thinking something in the ballpark of 450f/375r)

What spring rates are you guys running/planning on running?

EDIT: I just called GC too (just to confirm/double check) and they said they have them and should be available within the next month. Front and rear spring perches with springs (eibach presumably). This means I'll be checking the site pretty regularly over the next few weeks lol. This also might have been a deciding factor. Have koni north america custom valve my yellows, order camber plates and gc sleeves. then order the springs I want. (unless the kit can come with spring rates I want)

Nifty.
 
#43 ·
You may also want to match your spring rates to sway bar stiffness, I believe. But don't take my word for it, I'm not an autoX guy or anything. I've just had somebody mention something to that effect to me once before.
 
#45 ·
Oh is spring rate adjustable with these coil overs? Because the guy who mentioned it to me before said that the upper stiffness of the CS bar was approaching too stiff with his springs, and CS's upper stiffness level is below the lowest of the Tri-Point I believe.
 
#46 ·
spring rates are adjustable in a sense that you can take out springs that are too stiff or too soft, and put in a different spring with a different rate. There is not a knob to adjust spring rate on the fly or something.

My guess is he had really stiff springs as well. Like I said, sway bars can counter lack of spring.
 
#47 ·
Ahh, I see what you're saying. Though, I thought stiffer sways actually made it seem like you had stiffer springs and that the two had a cumulative effect with each other.
 
#48 ·
Spring and sways do have a compounding effect, but only in the lateral direction.

Higher spring rates will resist body roll in both directions(for/aft and side to side). In doing so, it will lesson brake dive and squat when applying power, as well as lateral body roll when turning.

Sway bars(obviously) only come into play laterally. TECHNICALLY, you could generate enough roll stiffness with springs alone, but nobody does because then spring rates wouldn't allow enough weight transfer for proper brake balance. Even purpose built race cars (F1 for example) use sway bars.


Sent from my iPhone with Tapatalk.
 
#52 ·
Yeah I don't think koni is too expensive either, I expect the turn around time to be about 2 months though.

You guys missed my question earlier, what spring rates is everyone thinking? I'm thinking 450f/375r. That might not be enough though taking to others
 
#53 ·
You guys missed my question earlier, what spring rates is everyone thinking? I'm thinking 450f/375r. That might not be enough though taking to others
Not sure yet on spring rates, but will report back once I know something. I have a few local autocross friends who have backgrounds in engineering and mathematics who can help me determine what a good spring rate and ride height will be.
 
#56 · (Edited)
^ So is that aiming for a frequency of 2?
Yes that was for desired frequencies of 2 on the front and 20% higher in the rear at 2.4.

Also, if my RSB stiffness is at 640, is that the same thing?
Good question. No. This formula is independent of sway bars. Bars only contribute to roll stiffness (side to side motion), whereas, spring stiffness and frequencies have to do with pitch angle (front to rear motion). Simply we are assuming the left and right wheel hubs on the axle travel the same distance (no roll), so therefore the sway bar has no stiffness.

I wonder how you figure overall stiffness with sway and springs? Any idea?
Another good question. Sway bar stiffness is a factor of diameter, material, blade length, and solid/hollow (wall thickness). Sway bars act by torque (twisting). I could give you all the formulas to calculate bar stiffness too, but I will some it up with bigger diameter, shorter blade, harder material, and thick wall hollow bar equals really stiff. All of these factors act dependently on each other. This means as one of these factors is decreased, the whole system's stiffness is decreased. More important than that is where the bar is attached...again motion ratio. The bar on our cars is at a lousy 0.4-0.5 ratio. If your bar has 1600 lbs of force, only 40-50% (640-800 lbs) of that actually gets to the tire. Perfect example of this is the difference between the Focus ST and the Mazda3 RSB. They both have the same solid diameter, but yet the ST exerts a lot more torque on the wheel. It simply comes down to the ST having the sway bar attaching right next to the hub, whereas, the Mazda's bar attaches much farther inboard. To "sum" it up, the stiffness of the spring and sway bar do add together for overall stiffness when the car is rolling.
 
#57 ·
^ Ah OK, thanks. I'd probably be shooting for a frequency of 1-2 for my purposes of being a DD.

I knew about most of the controlling factors that give a sway its stiffness (though not the blade length bit because it seems like a shorter blade would increase stiffness, not a longer one), but what I really wanted to know is how to formulate optimal stiffness between the springs and the sway. Of course this would vary depending on what you're looking for from your car as you stated above. If it's simply just adding the spring's lbs per inch (spring rate?) to the sway's professed lbs per inch then that's pretty easy to calculate. Or is factoring in the 0.4-0.5 ratio necessary when looking at what manufacturer's claim their bars provide and dividing it by that? Or is trying to calculate it this way just wrong altogether? Trying to balance roll stiffness with squat and dive (I think those are the terms) has gotta be difficult, especially if you throw an aftermarket sway into the mix.

As far as the ST that's pretty interesting. That must be the main reason that car has some oversteer. It basically has a stiffer RSB stock just due to its position.
 
#58 ·
I knew about most of the controlling factors that give a sway its stiffness (though not the blade length bit because it seems like a shorter blade would increase stiffness, not a longer one)
You are right. I was thinking in terms of an applied force, whereas this is a case of deflection. Meaning if you have a fixed vertical deflection, then the shorter arm will create a larger twist angle and effectively more torque (and force). Thanks for straightening me out!

but what I really wanted to know is how to formulate optimal stiffness between the springs and the sway. Of course this would vary depending on what you're looking for from your car as you stated above.
It would vary depending on what balance you are looking for, and autocross balance (especially in a fwd car) gets wacky. Not sure how one would formulate the optimum though.

If it's simply just adding the spring's lbs per inch (spring rate?) to the sway's professed lbs per inch then that's pretty easy to calculate. Or is factoring in the 0.4-0.5 ratio necessary when looking at what manufacturer's claim their bars provide and dividing it by that? Or is trying to calculate it this way just wrong altogether? Trying to balance roll stiffness with squat and dive (I think those are the terms) has gotta be difficult, especially if you throw an aftermarket sway into the mix.
I believe it is as simple as adding them together. Something I've never thought of before...where and how does the manufacturer measure their bar's stiffness...at the tire, at the endlink? Do they consider the ratio? How much deflection are they considering? You nailed it, the end goal is balance. And we haven't even considered the most complicated puzzle piece...shocks!

As far as the ST that's pretty interesting. That must be the main reason that car has some oversteer. It basically has a stiffer RSB stock just due to its position.
Because of its position is the key. It's not necessarily a physically stiffer bar, but its effective stiffness is much greater because if where it mounts. If the rear tire deflects 1", the ST bar's blade will deflect 1" whereas the Mazda blade will only deflect 0.4"...that is effective stiffness (and where motion ratio is critical). Here's some good links showing pictures and probably explaining it more clearly than I:
Regular Focus
Gen2 Speed3
Focus ST
As you can see the only real difference in the entire suspension design is the mounting point of the RSB. So don't let your friends tell you their ST rear suspension is sooooo superior to your Mazda. Stick a bigger RSB on your 3 and you will get the same "ST oversteer effect".
 
#62 · (Edited)
To me it would boil down to return on your investment. How much to re-valve your current Koni Yellows vs 8611's and what is the potential performance gain of the more expensive option. 8611's cost around $300 a piece so you're looking at $1,200 for shocks plus whatever the housings may or may not cost you to pick up. I'm guessing you can re-valve those Yellows for around the price of one 8611. I think there is a possibility you may get as much or even more ultimate performance out of custom valved Yellows compared to fiddling with knobs on the 8611's.

It's a little long, but check out Shaikh's video on "Playing with Knobs."

 
#63 ·
I should have clarified. The 8611s would only be on the front, the rear yellows would still get valved appropriately. Second, the 8611s would also be valved to my spring rate choice and i wouldn't dare touch the knobs. I worked out the difference to be somewhere around 600 to 700 dollars difference between having the koni race shocks up front versus the yellows
 
#64 ·
Quick update:

Purchased AWR housings for koni 8611 inserts

Planning on purchasing:
BC rear spring perches
hyperco 350f/600r 2.5" ID
corksport camber plates (once April 1st rolls around........................ugh)
then obviously the koni 8611-1256 inserts (hoping to have these dyno'd by koni-na since they won't be on the car until after April anyway.....)

Maybe corksport will surprise us and release the next batch sooner than posted.

As far as my wheel/tire options, I'm still in debate on wheel options. Pretty sure I've settled on the O.Z. Alleggerita in 17x7.5 of course, with 225/45 dunlop z2s. The tire I'm sure of, I really like my z1s so I plan on sticking with 'em!
 
#70 ·
They will handle 2k more than they are valved for. They are valved for 14k front and 16K rear. ;) So they can handle 16/18 rates...aka 896F/1008R is the outter limit of their adjustment range.

The adjustment range on them is HUGE so I'm happy. As they are now, if I put the rears on full compression we couldn't move the rear more than about 1/4" with 2 of us jumping on the ledge of the trunk. LOL that's about 400lbs jumping. At full soft it's a very well mannered setup, firm over big bumps but smooth on most highways. :)
 
#71 ·
So being bored at work I began thinking to myself about the motion ratios on the rear. Since I have settled at around 650# for the rear spring, just brain storming here, I would need to get them valved would be for a spring rate lower than the spring rate. Since the spring is set more inboard than the shock the motion ratio takes the same affect on the shock so I would probably only need to revalve the rears at 500# or so. And then I began thinking if it's really even necessary to revalve for 500#... on the rear suspension... of a fwd, front bias car (weight distribution).
 
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