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engiekev
engiekev HalfDork
2/16/22 8:26 a.m.

Lots of good ideas and discussion!  Sounds like a Koni w/ coilover sleeve wouldn't be a bad place to start.  For rallycross this is all probably overanalyzing the problem; its all about the tire and making the tire work.  A worn out stock suspension car is probably just as fast if not faster with the right tire choice.  Detroit region has entered its spring lull, so I have some time to play with setup before any chance of a first event.

It doesnt sound like theres a lot of mileage on the Paco Rallycross coilovers in actual rallycross events, some verbatim from events suggest its setup far too high.  Fairly price as well, that buys a few sets of re-tread cheater tires!

https://grassrootsmotorsports.com/forum/grm/miata-rallycross-questions/135485/page1/

Spring rate is (somewhat) independent of the damper choice in this case, I'd be interested in putting together a list of what other GRM'ers have run in miatas for rallycross spring rates (and the damper used) for comparison.   It would be interesting to see where this falls in the spring rate chart relative to % of OEM and how the F/R ratio differs.  Obviously lots of other inputs going on here like tire spring rate, sway bar, chassis stiffness (rusty=floppier? hah) but still some good data points.

EvanB
EvanB MegaDork
2/16/22 8:39 a.m.

My suspension has been through:

Mazdaspeed Bilstein dampers and springs (F215/R158): Felt great until the dampers were shot and needed rebuilt. 
Revalved Bilsteins with mazdaspeed springs: Very harsh on compression, felt good at speed but jarring on the road and uncomfortable.
KYB AGX with mazdaspeed springs: Decent feel, much less harsh on compression but still felt controllable for rallycross, fronts lasted a couple events before blown (they were used before I put them on, unknown miles. The rears are still on and doing fine)
Stock 1.6 shocks and springs: Way too soft for good transitions with no sway bars, better than bouncy blown KYB though. 

engiekev
engiekev HalfDork
2/16/22 8:42 a.m.

I've only ran my rusty NA with KYB GR2 and NA springs, and it was far too soft for the rough detroit region events.  Especially with sway bars disconnected, lots of body movement and oversteer which was fun but not fast.

cghstang_chris
cghstang_chris Dork
2/16/22 8:43 a.m.

A long time ago, EvanB was running oem mazdaspeed miata springs. 

For one more data point, I once used my NA on FM lowering springs/tokico illuminas (?) to evaluate a soybean field course as safety steward and that combo felt pretty good.

If you're taking votes, I'd say start with the FM springs and no rear sway bar. Disconnect front sway bar for low grip surfaces, keep it hooked up for high grip surfaces.

 

engiekev
engiekev HalfDork
2/16/22 9:40 a.m.
cghstang_chris said:

A long time ago, EvanB was running oem mazdaspeed miata springs. 

For one more data point, I once used my NA on FM lowering springs/tokico illuminas (?) to evaluate a soybean field course as safety steward and that combo felt pretty good.

If you're taking votes, I'd say start with the FM springs and no rear sway bar. Disconnect front sway bar for low grip surfaces, keep it hooked up for high grip surfaces.

Another curve ball, this NB has FM sway bars so there is some added stiffness, and another variable since they are adjustable (2 and 3 end link positions on the bars).  Depending on the first venue location, I could try out rear disconnected and then experiment with both disconnected in the afternoon sessions.

FooBag (Forum Supporter)
FooBag (Forum Supporter) Reader
2/16/22 1:11 p.m.

In reply to engiekev :

I wouldn't put too much stock in Kyle's info there.  That was early in his/the car's rallycross life. I believe he ended up going to softer rates later and then eventually Flatout coilovers (suprisingly had good luck with these).  When the car trophied at Nationals, it was on the Flatout setup.

I've texted Kyle to see if he wants to get in on the discussion.  He's been out of the rallycross world for a few years so we'll see.

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
2/16/22 1:20 p.m.

It should be noted that dirt actually increases grip with load transfer up to and including carrying a tire.  Obviously this is no good on the drive axle, or hardpack surfaces that act more like lumpy concrete, but still.

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
2/16/22 1:22 p.m.

It should be noted that dirt actually increases grip with load transfer up to and including carrying a tire.  Obviously this is no good on the drive axle, or hardpack surfaces that act more like lumpy concrete, but still.

Going really soft on the front suspension just makes the car roll more before you start cornering, and unloads the inside rear tire so tire spin is easier.

 

Kylini
Kylini Dork
2/16/22 1:39 p.m.

I'm pretty sure we've won local events on completely blown shocks so.....run whatever you want. I recommend Spec Miata takeoffs.

For springs, 8 inches is ideal in front and 9 inches is ideal in rear. 10 in rear will work; longer than 10 will coil-bind (I actually tried 12 in early on xD). The best thing about longer springs is you can quickly add in a touch more ride height if you gotta switch to paddle tires like IndySport BRs. I liked keeping the ride height close to stock because the lower center of gravity helps you engage with ruts on the course for free steering assistance (just like the walls and other racers when playing GT4!). Tiny bit of lift for tire clearance + tiny bit of lift for 185/65-15 IndySport SGs == good to go.

Because I like longer springs, the softest I recommend in the rear is 275 lb/in (softer will coil-bind). If you run 8 in springs, you can go as low as 225 lb/in before bottoming out. Either way, long bump stops are your friend and I usually don't run sway bars.

At Watkins Glen, which was bumpy as heck, we ran 350 lb/in front and 225 lb/in rear (both 8 in) and definitely bottomed out a few times, but it was fast and fun!

At Nationals, we ran 425 lb/in front (8 in) and 280 lb/in rear (9 in; Swift sells em in metric). This was stiff enough to go fast in the dry, but not so stiff to cause spins in the mud.

We've run as stiff as 700/400 before and completely blew out a set of shocks without noticing (they weren't exactly doing much at that stiffness xD).

Regarding extended lower front ball joints, they're awesome because you'll lose some camber on taller tires. That said, don't run more than -2.5° front camber because the lever forces are higher with taller ride heights and bigger bumps and you don't want to pop your upper ball joints! This camber will also help your tires survive much longer, because otherwise you tend to rub/cut them on your metal fenders (check the latest rules on fender rolling; we weren't allowed to back in the day). 

I'm glad people still remember that car! heart

engiekev
engiekev HalfDork
2/16/22 2:50 p.m.

Thanks so much for adding your knowledge!

Chris Berchin runs a spec Miata in our region with revalved SM bilsteins, I believe he even converted them to take aparts, and he is quite quick in MR. And of course plenty of Miata entries with blown shocks have been through.

That's really good to know that you can package a 185/65r15, was there any fender liner clearancing required? I was sold on 165/70r14 with the light NA wheels, but knowing 15s work I may change course. Unfortunately alpha retreads are only available in 195/65r15, or at least that's what Ben Howe offers. Indysports are a bit harder to come by now I think.

Ironically, this will look pretty similar being a black NB with black hardtop!

AnthonyGS (Forum Supporter)
AnthonyGS (Forum Supporter) SuperDork
2/16/22 10:46 p.m.
engiekev said:
AnthonyGS (Forum Supporter) said:

Every time I've swapped out Bilsteins, I've gotten improved ride quality.  In rallyX you want travel and compliance.  Bilsteins don't do that from what I've seen.  I'd be real curious about Fox since they earned their rep off-road.  They are pricey though.

I'm facing a similar question with my Subaru.   Koni's or someone's coilovers?  

What brand of coilovers? Almost everything out there is going to have terrible damper quality, other than Ohlins or similar, but I'm not familiar with the Subaru market.  Not a lot of current data but Dennis Grant's site still has some very valuable information.

http://farnorthracing.com/autocross_secrets18.html

Are inverted STi struts worth looking into (I thought those were a common swap for the rallycross subaru community)?

That's just it.  For Subaru coilovers I'm not seeing any brands I trust for the price.  Bilstein makes a B16 setup....  KSport..... Yellow Speed....  neither of them are companies I know.  Cusco sells an $8000 set of seperate reservoir rally coilovers.  Feal used to make some rallycross coilovers for the Subaru.  They seem to have a decent reputation.  And then I can do Koni yellow inserts in stock housings with springs of my choice (STI or King).  It really sucks because I don't want to do this 2 or 3 times.  I can get new bars and endlinks from Whiteline so that's easy.  I'm not keen on buying used JDM parts, but that might be the way to go. 

engiekev
engiekev HalfDork
2/17/22 7:31 a.m.
AnthonyGS (Forum Supporter) said:
engiekev said:
AnthonyGS (Forum Supporter) said:

Every time I've swapped out Bilsteins, I've gotten improved ride quality.  In rallyX you want travel and compliance.  Bilsteins don't do that from what I've seen.  I'd be real curious about Fox since they earned their rep off-road.  They are pricey though.

I'm facing a similar question with my Subaru.   Koni's or someone's coilovers?  

What brand of coilovers? Almost everything out there is going to have terrible damper quality, other than Ohlins or similar, but I'm not familiar with the Subaru market.  Not a lot of current data but Dennis Grant's site still has some very valuable information.

http://farnorthracing.com/autocross_secrets18.html

Are inverted STi struts worth looking into (I thought those were a common swap for the rallycross subaru community)?

That's just it.  For Subaru coilovers I'm not seeing any brands I trust for the price.  Bilstein makes a B16 setup....  KSport..... Yellow Speed....  neither of them are companies I know.  Cusco sells an $8000 set of seperate reservoir rally coilovers.  Feal used to make some rallycross coilovers for the Subaru.  They seem to have a decent reputation.  And then I can do Koni yellow inserts in stock housings with springs of my choice (STI or King).  It really sucks because I don't want to do this 2 or 3 times.  I can get new bars and endlinks from Whiteline so that's easy.  I'm not keen on buying used JDM parts, but that might be the way to go. 

KSport are essentially eBay specials, even their "rally" coilovers; expect terrible dampers on anything with an eBay/alibaba flair.

Feal was pretty decent in the rallycross community.  Flatout has questionable reputation, though they changed ownership recently so maybe it has improved. If you must have coilovers bespoke to rally, DMS is an option but parts are getting hard to find at this point.  Samsonas, hotbits, lots of other options for a true rally coilover but that quickly prices out of the typical rallycross budget.

OEM 2004 Sti inverted struts might be a good option, with whatever springs you want.  It doesnt seem like all the subarus that run in the detroit region are on expensive or custom coilovers, most are probably on stock suspension if I had to guess (Can ask around next event).

Dirty Impreza would be the best place to look for info as at least that forum is focused on rallycross or "offroading" subarus:

http://www.dirally.com/forums/forumdisplay.php?96-Rallycross-Preparation&s=e12d85766c5d5bb1cb88a4027ede4cf1

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
2/17/22 8:59 a.m.

IIRC Draco blew out a Feal strut in like one rallycross, in his Evo.

He also has weird luck sometimes, he had a brand new Michelin rally tire delaminate driving five miles between hotel and site at Nationals one year...

engiekev
engiekev HalfDork
2/22/22 7:53 a.m.

1 week to go until I pick the car up, time to get ready!

Megasquirt PNP2 acquired, along with another Ballenger AFR500 wideband for permanent installation in the car.

For the supercharger swap, some assessment of the hardware needs to happen once I get it pulled off the old crusty NA.  Since its a 1.6L "kit" that's on the car, I believe this is what is needed:

  • Mounting bracket
    • Might be able to modify the 1.6L bracket to fit, hard to say.
  • Pulley system & Belt
    • Buying the TDR bracket as I just don't have time to re-engineer a new setup that works with PS and AC
    • Will need to measure with TDR bracket and SC mounted to get correct belt size
  • "Dumby" 1.8L throttle body
    • They don't make the "dumby" throttles anymore, so I'll have to modify an OEM 1.8L throttle for pass through.
  • MAF relocation and IAT
    • With MS, don't need to worry about the MAF.
    • IAT bung will be welded before the intake manifold inlet on the crossover tube
  • "power card" (what came with the JR kits originally)
    • Don't need this, as MS will take care of the tuning aspect
  • Injectors
    • Will attempt with OEM injectors, but may swap to larger if needed based on data
  • Intercooler
    • Nope.
    • Will attempt to keep the supercharger inlet temps down enough by making an airbox for the intake, and TDR manifold heatshield blanket.

Picture of the original kit that came on a 99-05 miata:

1999-05 Jackson Racing M45 Supercharger kit CARB LEGAL! - Miata Turbo Forum  - Boost cars, acquire cats.

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
2/22/22 8:31 a.m.

Would there be any way you can use a bypass valve and blow through the throttle body, instead of having the throttle body 6 feet from the ports?  You don't have to worry about keeping a MAF happy anymore.  The difference in throttle response is pretty significant in both directions.

 

I am a bit biased in favor of response smiley

engiekev
engiekev HalfDork
2/22/22 8:43 a.m.
Pete. (l33t FS) said:

Would there be any way you can use a bypass valve and blow through the throttle body, instead of having the throttle body 6 feet from the ports?  You don't have to worry about keeping a MAF happy anymore.  The difference in throttle response is pretty significant in both directions.

 

I am a bit biased in favor of response smiley

Now that is a good idea!  Sounds like most people try dual TBs if there is an intercooler involved, but volume is volume.  

So the stock throttle body would remain with IAC/TPS etc. in OEM configuration, a second throttle body would be added as a supercharger throttle, and the SC bypass vacuum would have to route to manifold vacuum source. 

For some reason, this approach is much more popular across the pond, these chaps just added a second throttle cam and cable, simple:

https://www.mx5nutz.com/threads/m45-dual-throttle-body-mod-complete.21108/

Keith Tanner
Keith Tanner MegaDork
2/22/22 9:33 a.m.

If you run a single blow-through TB, you will need a significant bypass valve. It's also going to be loud as hell. Other than idle droop problems, that M45 without IC does okay for throttle response with the throttle pre-blower. 

IATs will be high, check the upper temp limit on your sensor. 

You'll probably run out of supercharger before you run out of injector. That M45 isn't all that big, so chasing power hits the point of diminishing returns quite quickly. I wouldn't spend a lot of effort on trying to optimize the blower, just run it in a mostly-stock configuration and concentrate on the chassis. 

engiekev
engiekev HalfDork
2/22/22 9:53 a.m.
Keith Tanner said:

If you run a single blow-through TB, you will need a significant bypass valve. It's also going to be loud as hell. Other than idle droop problems, that M45 without IC does okay for throttle response with the throttle pre-blower. 

IATs will be high, check the upper temp limit on your sensor. 

You'll probably run out of supercharger before you run out of injector. That M45 isn't all that big, so chasing power hits the point of diminishing returns quite quickly. I wouldn't spend a lot of effort on trying to optimize the blower, just run it in a mostly-stock configuration and concentrate on the chassis. 

GM IAT has range up to 135C, I really hope it doesn't max the sensor out!

Keeping it simple with the M45 is definitely my goal (based a lot on your feedback from older posts!).  I likely will not mess with a dual TB setup until much later, if at all, but it might be a fun experiment if there is free time.

I really didn't notice too much of a throttle response lag on the 1.6L with the pre-SC throttle body.

Keith Tanner
Keith Tanner MegaDork
2/22/22 10:12 a.m.

I know the IATs will be over 100C. We used to have an ECU that went into a failure mode at 100C IATs and we couldn't use the sensor post-blower on those.

DeadSkunk  (Warren)
DeadSkunk (Warren) UltimaDork
2/22/22 10:53 a.m.

I've got an NB with the M62 supercharger and throttle response is fine, no intercooler. The idle droop is a PITA sometimes though. I've never measured the intake temperature but it certainly gets hot under there.

Keith Tanner
Keith Tanner MegaDork
2/22/22 11:01 a.m.

The MP62 should have lower IATs than the little M45. Not low, but better.

TVR Scott
TVR Scott SuperDork
2/22/22 11:28 a.m.

A methanol sprayer would be just the ticket to drop those intake temps.

I had a M45 on my old 1.6 and it was lots of fun.  Not crazy power but definitely enough to wake things up.

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
2/22/22 11:33 a.m.

An M45 on a 1.8 seems like it would be overspeeding a bunch...

I have my head in Buicks where they have a built in bypass.

engiekev
engiekev HalfDork
2/22/22 11:39 a.m.

There is somewhat of a bypass valve on the M45, the actuator on mine was sticking open and resulted in 0 PSI Boost. I believe this only really works if the throttle is pre-SC inlet.  Bypass valve normally opens under vacuum.

With a dual TB setup it needs to reference manifold pressure/vacuum, and an additional bypass/blowoff valve would be needed between the manifold TB and supercharger exit.

Keith Tanner
Keith Tanner MegaDork
2/22/22 11:46 a.m.

Yeah, the M45 has a bypass pre-blower. It won't keep you from blowing all the intake plumbing apart on a shift if the blower is ramming air into the backside of a throttle body. I've seen intercoolers break at the seams. That little bypass will allow you to drive the car if the SC belt breaks, but it's really really really down on power :D

An oversize throttle body might actually be beneficial, as the pre-blower TB is sucking unpressurized air unlike a post-blower unit.

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