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engiekev
engiekev Reader
10/21/20 8:13 a.m.

Purchased this one a whim from a SCCA friend who we recently met offroading with our Montero.  All I knew initially was that it was an NA, had a "lift", supercharger kit, high mileage, and came with two sets of winter tires. Oh, and it's terribly rusty! But for $1500, how can you beat that for rallycross fun on a budget?

Upon arrival at home, it was time to start inspecting what I just got myself into.

engiekev
engiekev Reader
10/21/20 8:24 a.m.

Going over the rust bucket in more detail (or as it's now known, the "crusty tuna can") revealed a few things.  

 

 

The "lift" is a Paco 3" lift kit, KYB GR2 struts that appear fairly new (not rusty), and some unknown blue springs.  For rallycross, a lift is really not needed, but this will stay for now as the lift brackets look fairly rusted in place.  I may try to pull one lift bracket off, and see how these unknown springs sit.

The supercharger kit needs some attention. Right now, the supercharger makes decent boost, but during a gear change (when there is a speed difference in the pulleys) the belt slips momentarily. The throttle cable was routed in a not so good way, binding and causing a sticky feeling pedal. 

The belt tensioner is in sore need of an upgrade.  This is a manual non-power steering, with A/C, so it uses the factory tensioner.  However, it appears to be a cobbled together fix, where the through-pulley bolt which is supposed to be threaded is totally fixed and welded to the adjustment tensioner bolt. So to make tensioner adjustments, you need to push down the pulley and then quickly tighten a lock nut on the tensioner bolt.  It looks like these parts are impossible to find now, so I will have to machine the pulley through "t-bolt".  In the original mossmotors kit for non-PS w/ AC, they included a newer ribbed pulley, and "t-bolt" which I will need to fabricate.

 

 

The exhaust, which is a mess of the factory manifold to downpipe, straight pipe where the cat was, and then welded to a stainless cat-back to a "turbo tuff" muffler was ridiculously loud, even for a dedicated rallycross car.  This is addressed in short order.

Overall though, just a few things to address before the next scheduled rallycross, a mixed surface event that promises to be a blast!

engiekev
engiekev Reader
10/21/20 8:28 a.m.

To address the loud exhaust, which was far too loud for backroad messing about and highway driving, the cheapest 2.25" stainless resonator on SummitRacing was ordered.  If you can tell a theme for this build, it's bare minimum.

Plenty of room before the diff, so a 24" AP exhaust 2.25" stainless resonator fits the bill.

A quick mig welding session and it's on the car.  Much quieter, which has an added bonus that the supercharger whine is actually audible now!

engiekev
engiekev Reader
10/21/20 8:30 a.m.

Obvoiusly, the lack of a boost gauge needed to be rectified.  Advance sells Bosch brand gauges for a steal, if you use the online coupon for 20% off, and most stores carry them.  It's like some off brand made in china that's badged as a Bosch unit, but again, bare minimum cost!

This was useful in diagnosing that the supercharger belt is slipping during gear changes, and who doesn't like boost gauges?

engiekev
engiekev Reader
10/21/20 8:32 a.m.

A local GRMer and good friend offered to loan his hardtop for rallycross events, which is another reason for this impulse buy.  Without a hardtop available, buying one for close to what the car itself costs made no sense!

A short trip over and it's ready for the weekend! Unfortunately, the rallycross day I was signed up for got canceled due to rain.

Professor_Brap (Forum Supporter)
Professor_Brap (Forum Supporter) GRM+ Memberand UltraDork
10/21/20 8:43 a.m.

I got the same boost gauge I use for diagnosis. It was jammed under the wiper arm of a focus st this morning

engiekev
engiekev Reader
10/21/20 8:51 a.m.

I can't emphasize this enough, but bare minimum cost. Paint work will consist of Rustoleum Professional enamel, sprayed through HVLP thinned and with some hardener.  I tested this paint method out on a car dolly (also loaned by dear GRMer friend!) and it appered to work just fine!

Since the rust is so bad on the rockers, why not hide it with some paint?

Some quick 'shops later, here's a few ideas. The idea with not painting the wheel's lip is because lets be honest, this is not going to be perfect paint job, and tire shops will just scratch off the paint when remounting tires anyway.  Or, it's a style choice!

 

Option 1: paint below the "beltline" on the doors/rockers, and front and rear bumpers. 

Option 2: Just pain the doors/rockers.

I'm partial to Option 1. Of course due to laziness, I could always paint by panel until it's complete.

 

engiekev
engiekev Reader
10/21/20 8:57 a.m.
Professor_Brap (Forum Supporter) said:

I got the same boost gauge I use for diagnosis. It was jammed under the wiper arm of a focus st this morning

Really can't beat the price, considering there aren't many cheaper gauges even online through Amazon or Summit.

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
10/21/20 10:24 a.m.

Fun!

What's the point of the boost gauge? You can't actually affect the boost with anything other than your right foot, and a SC fails to low boost instead of high. Absolute minimum cost would be no boost gauge at all :) I guess it did help you find a slipping belt, but you can usually spot those from a lack of tension. The Downing/Atlanta aka Sebring aka Moss aka Jackson Racing supercharger was not strong in the belt tensioner area, but all of my experience is with a PS car.

The combination of a lift kit and lowering springs is funny. Maybe the goal is a higher spring rate, but I suspect those blue springs are fairly soft for their ride height and you may have very little actual bump travel. A set of stock springs from a 1996-97 and no lift kit may be a better option.

engiekev
engiekev Reader
10/21/20 10:50 a.m.
Keith Tanner said:

Fun!

What's the point of the boost gauge? You can't actually affect the boost with anything other than your right foot, and a SC fails to low boost instead of high. Absolute minimum cost would be no boost gauge at all :) I guess it did help you find a slipping belt, but you can usually spot those from a lack of tension. The Downing/Atlanta aka Sebring aka Moss aka Jackson Racing supercharger was not strong in the belt tensioner area, but all of my experience is with a PS car.

The combination of a lift kit and lowering springs is funny. Maybe the goal is a higher spring rate, but I suspect those blue springs are fairly soft for their ride height and you may have very little actual bump travel. A set of stock springs from a 1996-97 and no lift kit may be a better option.

It was more for fun than anything else, but yes was to help diagnose the lack of boost. I also have another project car it can be used on, so it will eventually come out.  I didn't notice a large amount of belt dust, though I don't have a tension gauge to properly set tension so who knows how close it is.  It's also extremely difficult to get it tight with the current tensioner bolt being fixed to the pulley bolt.

For the belt tensioner, it looks like Track Dog Racing and others offer upgraded belt tensioner systems but they are a bit pricey for this project and require the power steering pump in place for the bracket (or an additional bracket).  If I can't get the factory A/C tensioner to work, then I may just design and machine a tensioner system to fit off the block.  The belt slip isnt a huge issue for rallycross, there isn't much shifting, and it only appears to happen during hard upshifts.

It is an odd suspension combo! I plan to ask around for some stock springs locally, though I don't think I'll be able to get them in time for Saturday's event.  The rallycross director is a bit miffed by it running a "lift kit", but really with this combo it doesn't appear to sit much higher than a stock NA.

I'm also totally new to the Miata world if you can't tell, excuse my ignorance!

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
10/21/20 11:14 a.m.

If you do look for stock springs, those 1996/97 units are taller than previous so they'd be your rallyx choice. 

Patrick (Forum Supporter)
Patrick (Forum Supporter) MegaDork
10/21/20 11:17 a.m.

Wonder if this is one of joey's old miatae?  I recall he had a rusty supercharged one and is in Michigan 

engiekev
engiekev Reader
10/21/20 11:21 a.m.
Patrick (Forum Supporter) said:

Wonder if this is one of joey's old miatae?  I recall he had a rusty supercharged one and is in Michigan 

It's not Joey's miata, but he's the hardtop and dolly loaner! Small world.

It belonged to Marcus Meredith, who I met through offroading, he's heavily involved in SCCA autocross and is running for area director. 

engiekev
engiekev Reader
10/21/20 11:25 a.m.
Keith Tanner said:

If you do look for stock springs, those 1996/97 units are taller than previous so they'd be your rallyx choice. 

Would a used set of bilsteins also be the shock of choice?  The KYB GR2 are quite stiff, but do look new enough.

psteav (Forum Supporter)
psteav (Forum Supporter) Dork
10/21/20 12:00 p.m.
engiekev said:

For the belt tensioner, it looks like Track Dog Racing and others offer upgraded belt tensioner systems but they are a bit pricey for this project and require the power steering pump in place for the bracket (or an additional bracket).  If I can't get the factory A/C tensioner to work, then I may just design and machine a tensioner system to fit off the block.  The belt slip isnt a huge issue for rallycross, there isn't much shifting, and it only appears to happen during hard upshifts.

 

Oooh.  I'm interested.  I have most of a supercharger setup (less the tensioner) for my Miata project as well; and the TDR piece is $200.  There was an article in GRM in the last couple of years where Carl Heideman's kid built a junkyard blower setup for a Miata, and he wound up adapting the serpentine belt tensioner for an LS series motor to tension the supercharger belt.

https://grassrootsmotorsports.com/forum/grm/salvage-yard-supercharging-ad/136832/page1/

 

engiekev
engiekev Reader
10/21/20 12:11 p.m.
psteav (Forum Supporter) said:
engiekev said:

For the belt tensioner, it looks like Track Dog Racing and others offer upgraded belt tensioner systems but they are a bit pricey for this project and require the power steering pump in place for the bracket (or an additional bracket).  If I can't get the factory A/C tensioner to work, then I may just design and machine a tensioner system to fit off the block.  The belt slip isnt a huge issue for rallycross, there isn't much shifting, and it only appears to happen during hard upshifts.

 

Oooh.  I'm interested.  I have most of a supercharger setup (less the tensioner) for my Miata project as well; and the TDR piece is $200.  There was an article in GRM in the last couple of years where Carl Heideman's kid built a junkyard blower setup for a Miata, and he wound up adapting the serpentine belt tensioner for an LS series motor to tension the supercharger belt.

https://grassrootsmotorsports.com/forum/grm/salvage-yard-supercharging-ad/136832/page1/

 

That's the idea I was looking at, some sort of auto tensioner would be ideal and then it's just down to finding the right belt length.  They used a tensioner from 2003 6.0L GM, AC tensioner pulley.  Likely the bracket would need to be CNC alluminum, or laser cut thick steel that's welded, if it is only one bracket bolting to the block.  Looks like they used a piece of steel plate bolted to the factory manual steering tensioner.

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
10/21/20 1:39 p.m.
engiekev said:
Keith Tanner said:

If you do look for stock springs, those 1996/97 units are taller than previous so they'd be your rallyx choice. 

Would a used set of bilsteins also be the shock of choice?  The KYB GR2 are quite stiff, but do look new enough.

I do not hold Bilsteins in the same esteem as others, and in the Miata application in particular I'd be worried about their control of small wheel movements on rough surfaces. I would prefer the GR2 or the Koni orange. 

engiekev
engiekev HalfDork
10/23/20 7:07 a.m.
Keith Tanner said:
engiekev said:
Keith Tanner said:

If you do look for stock springs, those 1996/97 units are taller than previous so they'd be your rallyx choice. 

Would a used set of bilsteins also be the shock of choice?  The KYB GR2 are quite stiff, but do look new enough.

I do not hold Bilsteins in the same esteem as others, and in the Miata application in particular I'd be worried about their control of small wheel movements on rough surfaces. I would prefer the GR2 or the Koni orange. 

The local RallyX group chatter mentioned that NB suspension has more travel than NA, is that true? The "non sport" springs were also mentioned to give the most height. 

EDIT:

I found this great video, thanks for putting this stuff out there! These video series are super informative and very well produced and presented.  So essentially the only difference with a stock NB suspension, is taller upper shock mounts with better bump stop and shock bushing design?

https://www.youtube.com/watch?v=SkEmgsrJ-Cw

Pete Gossett (Forum Supporter)
Pete Gossett (Forum Supporter) GRM+ Memberand MegaDork
10/23/20 9:03 a.m.

In reply to engiekev :

Lmk when you finally get around to 4g63t swapping it, I might be interested in the drivetrain. ;-)

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
10/23/20 9:30 a.m.

Well produced and presented! It's a guy with an iPhone pointing it at another guy in his home garage rambling on about the subject of the week :) But I'm glad it's useful. Next week, we might try some live in-car commentary while doing suspension testing. That might be interesting.

The "NB has more travel" concept is one that won't go away, but it's primarily down to the stock bumpstop choice. The NB upper mounts are only taller if you choose a specific dimension to measure.

NB shocks and springs with NA upper mounts would give you the tallest ride height. You'll need some spacers at the top of the shock shaft under the nut.

dps214
dps214 HalfDork
10/23/20 10:03 a.m.

The bilsteins on my rallycross boxster were fanstastic both in the dirt and on the street, but I have no baseline for comparison. For all I know the stock struts would have been just as good...not really sure they could have been much better though. But again no baseline, and no experience with the miata application...so take my input for what you paid for it.

irish44j (Forum Supporter)
irish44j (Forum Supporter) MegaDork
10/23/20 10:34 a.m.
Keith Tanner said:

Fun!

What's the point of the boost gauge? You can't actually affect the boost with anything other than your right foot, and a SC fails to low boost instead of high. Absolute minimum cost would be no boost gauge at all :) I guess it did help you find a slipping belt, but you can usually spot those from a lack of tension. The Downing/Atlanta aka Sebring aka Moss aka Jackson Racing supercharger was not strong in the belt tensioner area, but all of my experience is with a PS car.

The combination of a lift kit and lowering springs is funny. Maybe the goal is a higher spring rate, but I suspect those blue springs are fairly soft for their ride height and you may have very little actual bump travel. A set of stock springs from a 1996-97 and no lift kit may be a better option.

This. Years ago I got one for my WRX. I think I looked at it all the time for the first week. Then I think I never looked at again for the next 7 years lol...

psteav (Forum Supporter)
psteav (Forum Supporter) Dork
10/23/20 11:14 a.m.

In reply to Keith Tanner :

Keith...does your lab coat really say "Professor BatE36 M3"?  That's the best thing I've seen today.

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
10/23/20 11:24 a.m.

It does. Warren from Exomotive gave that to me after we finished with the supercharged V8 XXXocet. Presented it to me in a ceremony at Road Atlanta. I like it very much :)

engiekev
engiekev HalfDork
10/25/20 9:28 a.m.

More prep for the Saturday Rallycross, this was going to be a mixed surface event at Milan Dragway. Really an amazing venue find by the region, it supposedly is an old short course an OEM spent to build and it never got used.  Lots of room to change course setup here, and it is also the regions first mixed surface event, inspired by out-east regions like Canaan raceway (anyone from here driven on that course?).

Rough marking of start and finish points, you can see where the last test event was held on the dirt:

Pulling the Paco lift revealed a quite low ride height, maybe too low for rough ruts but I figured with the mixed course surface, lower was better.  These will be swiftly swapped out with some stock NA springs, but I ran out of time for this event.

I also messed about with mocking up a heat shield for the air filter, to promote airflow coming from the headlight area and not the heated air coming from the radiator and radiating from the exhaust area.  I left it in there and did some spirited runs, it didnt melt, so it stays until I can make a metal version with a bit more refinement.  I tested this "ram air" intake with the headlight popped up all the way, and about halfway, with a leaf blower and it did seem to get enough fresh air in that area.  I hope by keeping the supercharger inlet temps down, that will at least improve efficiency as much I as possible without going to an intercooler (too much money and complexity for this project).

I really don't like how this square filter sits, the bottom panel sits on the flat frame area, maybe a MAF adapter to round connection then running that to a filter located near the headlight area would be best, something like this combo but altered a bit, thoughts?

MX5 NA Miata - How to build your own Cold Air Intake and heat shield -  YouTube

My new DIY cold air box/intake heat shield. - Miata Turbo Forum - Boost  cars, acquire cats.

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