Budget Street/Autocross/Track 2.5 NC Project!

Miata Parts, Intakes, Superchargers, Headers, Exhausts, Shocks, Springs, Sway Bars, Brake Kits, Autocross and track mods.
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Brian
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Re: Budget Street/Autocross/Track 2.5 NC Project!

Post by Brian »

MitchC635 wrote:Not sure a diffuser is necessary, but getting rid of the drag generated by the rear valance scoop in the rear bumper cover is something that could be done on this car. It should also help with cooling flow under the car and cost little, although some racing rules might restrict such a mod.
rear valance mod.jpg


I've seen the attached mod as well as a video where the entire lower dark grey valance was removed - somewhere in between may be the sweet spot. Would like to see what affect the mods would have on track, and it would allow the world to see the true art of your exhaust creations as well as honor Ryan Passey's proven fast assless Miata form in a more street acceptable look. Know you would find a way to do it right and make what looks like a useful mod less scary for those of us unwilling to do raw experimentation on our NCs.

Although you haven't seen enough demand for a center exit muffler to justify going that way yet, if you perfect this valance mod to make it easy, you should be able to generate significant demand for a center exit muffler and create a signature GWR look in the NC community in the process. Center exit single would look significantly better than off center exit IMO. The attached double center exit exhaust shows a little different way of reducing the rear valance drag and gives a hint of how good a center exit single could look.
Got a design idea we are playing with for Helmholtz version of RoadsterSport RSII, call it RSIII that gets the helmholtz at the rear in such a manner that we fill the gap and leave a lot less space for air to get up under the bumper. Picture pushing the 'can' for RSII back into the gap far enough to put Helmholtz can in parallel right off the muffler entry flange, result two cans at same level and no big gap for air to get up under that bumper. At the same time we do "Max Midpipe" update to our current classic RoadsterSport NC Midpipe with fiberglass resonator, rather like we did with ND that gets us a 5 inch converter in the midpipe (60 percent more flow than 4 inch all the current choices use). Will update this post with pic of the idea once we get proto versions welded up...but I like the idea of not allowing that big 'air catch' rear bumper. Will look down the road at stage II of this project at doing something like Verus Motorsports ND Rear Diffuser for NC, but will start with just better filling the gap with new exhaust design.
Brian Goodwin
Good-Win Racing
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MitchC635
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Re: Budget Street/Autocross/Track 2.5 NC Project!

Post by MitchC635 »

Filling the gap to get back towards factory aerodynamics on the back bumper probably works too.

Wonder if that back bumper actually creates as much drag as it looks like it would when the muffler area is no longer filled. Disturbed airflow affects aren't always predictable like that.

Might be worth doing a few fast laps to get avg lap times for the car, then dropping the back bumper cover and doing it again to see if there is a noticeable difference. Easier than getting wind tunnel time, and should be much more entertaining.

Could test back brake heat at the same time to see if they are affected by the change as well, but that would take more effort to control all variables. Would need same starting brake temps, same track temps, and same number of laps to have any relevance.

If lap times are faster, or brake temps are lowered without the bumper hangover, it might be worth a little extra effort to fill the gap and/or develop a diffuser
LateNights
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Re: Budget Street/Autocross/Track 2.5 NC Project!

Post by LateNights »

Brian wrote: RoadsterSport Race Springs (to be developed on this car) 400 lb/275 rates ~$178

KONI SPORT shocks $596
Would you guys consider developing the new set-up with helper springs?
Brian
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Re: Budget Street/Autocross/Track 2.5 NC Project!

Post by Brian »

LateNights wrote:
Brian wrote: RoadsterSport Race Springs (to be developed on this car) 400 lb/275 rates ~$178

KONI SPORT shocks $596
Would you guys consider developing the new set-up with helper springs?

Not talking about coilover springs that could use separate helper springs. Full diameter springs here, full length, the helper spring section is essentially built into the design with some close coils at one end.
Brian Goodwin
Good-Win Racing
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erikv
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Re: Budget Street/Autocross/Track 2.5 NC Project!

Post by erikv »

Brian wrote:
LateNights wrote:
Brian wrote: RoadsterSport Race Springs (to be developed on this car) 400 lb/275 rates ~$178

KONI SPORT shocks $596
Would you guys consider developing the new set-up with helper springs?

Not talking about coilover springs that could use separate helper springs. Full diameter springs here, full length, the helper spring section is essentially built into the design with some close coils at one end.
Curious: Will the off the shelf Koni shocks have enough range to handle the higher spring rates?
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Brian
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Re: Budget Street/Autocross/Track 2.5 NC Project!

Post by Brian »

erikv wrote:
Curious: Will the off the shelf Koni shocks have enough range to handle the higher spring rates?
The spring rate was chosen to work with the KONI Sport damping profiles, there are THOUSANDS of Miata owners out there running these springs rates on Koni SPORT shocks in the NA/NB generations. It's ground well covered and well understood.
Brian Goodwin
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LateNights
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Re: Budget Street/Autocross/Track 2.5 NC Project!

Post by LateNights »

Brian wrote: The spring rate was chosen to work with the KONI Sport damping profiles, there are THOUSANDS of Miata owners out there running these springs rates on Koni SPORT shocks in the NA/NB generations. It's ground well covered and well understood.
From what I'm reading "helper" springs aren't generally considered a performance upgrade anyway - seemingly they're more to do with extra control where needed - as you say, most often springs have that functionality built in...

(I'd assumed they were a performance upgrade due to their use on certain coilovers, and I guess technically they are in a sense)

I also heard mention of "tender" springs - but couldn't find much about them - any ideas what the difference is?
Brian
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Re: Budget Street/Autocross/Track 2.5 NC Project!

Post by Brian »

Heavier rates of assist (often called Tender) springs are higher rate helper springs and used to fine tune the rebound travel of the shock. But again, that's easier to understand in the coilover application where it is actually a separate spring from your main spring. As the rates get higher in a standard length spring we envision here we need to build in helper/tender/assist sections that has more than one rate. That's what folks typically call 'dead' coils when it appears as part of a full length spring because with the car parked the helper/tender/assist section springs may be fully or nearly compressed at static height, though they come into play once the system is in motion and the system extends over potholes or during hard cornering, and that's when it can both keep the spring seated and help prevent loss of traction due to inside wheel lift in hard cornering.
Brian Goodwin
Good-Win Racing
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AZ Sun Lover
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Re: Budget Street/Autocross/Track 2.5 NC Project!

Post by AZ Sun Lover »

Hmm...
Brian do you really think a stock Koni shock is going to last with that much spring rate?
FM had Koni increased the valving for their springs.
Plus I've had a few Koni's go South and the first thing Koni asked me was what springs I was using.
Another member here (RPMChris) had a company cut off the spring punches and make the Koni yellows into an adjustable coilovers so he could use 2.5" coilover springs. I do not recall the spring rate he was using but the stock internals didn't last. He then had the Koni's rebuilt with stiffer valving. Then put the rebuilt Koni's up for sale. I really wanted to buy the Koni's but was nervous that the shocks would be too stiff for the springs I wanted to run. I just wanted them for height adjustably. I've done Auto-X, I didn't like standing around most of the day just to get in 3-4 runs that may last 90 seconds if that. I much rather ride my quad all day in the Dunes or ride a MTB all day up in the mountains. MTB cross country racing is hard training but it's fun to eat a half gallon of ice cream and not worry about gaining weight. As a matter of fact I had to eat like a pig just to stay above 150 lbs.

AZ
Brian
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Re: Budget Street/Autocross/Track 2.5 NC Project!

Post by Brian »

Doing this in consult with KONI, and really no different than THOUSANDS of Miata owners do every year on NA/NB with standard Ground Control kits (375/250), I ran that setup myself for SCCA STS for many years. Don't bring up FM's efforts on NC anything unless you want laughter in reply, they have NEVER done a fast NC, don't have a clue. Nobody at FM races anything, particularly an NC, in contrast I set all the early NC track records and took home hundreds of top finishes in the NC over the last dozen years for both track and autocross events. FM has zero credibility on the topic of how to make an NC fast, because they have never done it.
Image

While Instructor for BMW Autocross event this past Saturday I drove a student's Miata with setup 'by FM" and it was worst handling Miata I have driven in recent history, plowing understeer until it went into snap oversteer, will be helping that guy fix his Miata so it actually works. As I already said further up the page, this ground very well covered, not something radical or untested for us. Nonetheless, may still retreat on the project to something softer like 300/200 we did on ND to keep more comfort in the combo, and we already have high rate Progress Sways as an option for even more roll resistance in the setup. Also still some debate in our team about whether we should just use a low cost coilover like so many customers start with, since that has some obvious advantages like allowing more height control, corner balance ability, etc. As always, will test in measure, will take the project to competitions and only go forward with what actually works and wins.
Brian Goodwin
Good-Win Racing
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