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...I ran that same wing, and even when I had no front splitter my car didn't have terminal under steer like that. That wing isn't doing much of anything in those slow speed corners and your car just seems to push. Something else is going on.
Howdy Fire, thanks for the confirmation about the wing there. Like I mentioned in my previous post, losing that bolt in the passenger's ball joint and having the eccentric on the same side come loose is the current suspect for the car's extreme oversteer. When I can get the steering repaired and the differential replaced so I can get the car back on the track we'll see how it handles and go from there.
Many important bits to respond to:
- Happily I've already got the supermiata eccentrics in - I've been reminding Jeff and his crew that those bolts can take more torque - sounds like they're ready to take advantage of that now.
- Got a replacement Torsen ordered through ebay - it's a Type 2 instead of a Type 1 and it's a 3.9 so not really what I was looking for in either case but no one domestically is offering the 3.6 torsens now that PrestigesparesUK is no longer playing and I wasn't getting into 6th much on our teensy Arizona tracks anyway - we'll see how it all shakes out (not that I have much of a choice) and I'll just have to adjust my shifting to the new ranges.
- Gee Emm, another excellent recommendation with that GRM Guide - I actually already have a copy in my Google Drive. I've also got a copy of the new BF Goodrich Performance Driving Guide (curated by Ross Bentley) which has some good info too, although not as much tuning data. The fanciest I've gotten so far is using a pyrometer to check the inner, middle, and outer edge tire temperatures to help identify correct tire pressures and note that everyone goes slower as it gets hotter. GRM's Trackside companion as it sits in my google drive BF Goodrich's guide, also plopped in my google drive
Really, this picture I stumbled across tells the story: It was labeled "Champion Racing Team"
Not exactly F1 levels of staffing but day-um, that's a lot of people to keep the dude in the middle on the track and even collecting some purdy shinies. As we all know, successfully campaigning a car requires a lot of skillsets most of which I lack and many of which I have neither the time nor the inclination to take on.
"But John, how can you expect to do well if you don't at least work to address the most critical items?"
Um, I don't expect to do well?
I finish last in my time trials group. Every time, in fact. Without exception. Do I complain about that? No, I understand why it is happening and I just accept that's how things are right now. I work full time in IT, take care of a household, oversee a few adult children, and throw some battered cars around the track periodically and try to keep the wheels in the right direction. Watching some of the board members do amazing things in such a short period of time is both impressive and disheartening, but I just have to give myself permission to be slow and sucky both on and off the track or I'll stop having fun and I, like hopefully most everyone, am in this for the fun. Unfortunately for me the fun part is doing what that guy in the middle is doing but I'm not rich enough to do the whole arrive-and-drive thing so I do what I can from that mountain of other people, farm out what I can't or won't to others, and watch my bank account shrink. Now that's going fast. ;P
What happened with the old diff exactly? Were you running it and it started acting up or did something go wrong during the rebuild? They're usually pretty stout (not sure if the T1 vs T2 is a massive difference in that regard).
What happened with the old diff exactly? Were you running it and it started acting up or did something go wrong during the rebuild? They're usually pretty stout (not sure if the T1 vs T2 is a massive difference in that regard).
Great question(s)! The car is so noisy on the track with all the creaks, rattles, whooshes, screeching, pops, and everything else partially muffled by my helmet that I didn't hear anything unusual at Firebird West. When I drove it to the shop the other day I thought the amazing howling sound was from the driveshaft grinding itself into oblivion on the exhaust (tolerances are pretty tight with the drop floor in) - turns out that's not the case and it was the driveshaft gyrating harmonically around due to entirely-too-much-play in the failing rear differential. The differential in question was rebuilt with a painfully expensive new 3.63 ring and pinion by Phoenix Rack & Axle Differential a smidge over a year ago with the rather eyebrow-raising results noted here: https://www.miataturbo.net/build-thr...st#post1663441
I contacted them right after the above post to ask about the bearing pieces and strange color of the break-in oil and got absolutely no response... ...
...so with little other option we made sure the tolerances were good at the time and sent it.
I'm of the opinion that the differential wasn't rebuilt properly - I'm not running that much HP, I don't drag race, etc. On top of that, the shop was having significant staffing issues at the time, they were running extremely late, etc, etc. At least the differential was dying slowly enough that we were able to catch it before something really bad/dangerous happened.
Once we get the replacement differential in place I'll decide if I feel like taking a half day off of work to carry it over there and have a little chat with them.
I'm not optimistic.
From my reading the Type 1 Torsens have more bias towards acceleration and the Type 2s have more bias towards braking. The Type 2s are also cheaper to make and might be stronger. A Type 2 is what I can find in the time I have so a Type 2 it is. Honestly if I was really desperate we could yank the 4.1 Type 1 Torsen out of the Red Miata, but I reeeeealllly don't want to go back to a 4.1 rear end on the White Miata - it sucked - and I'm sure as &#%@ not paying to have another 3.63 ring and pinion put in any differential after the last waste of money.
Oh, on a completely different topic, I shipped my old UltraShield belts back to UltraShield to have them rewebbed/recertified - they called me the day after they received them and said, "This hardware is too old. We can't recertify it."
"Oh. Is there a discount or something on a new set?"
"No."
...
I really wish they'd put some sort of information regarding that possibility on the rewebbing form before I took time off of work and paid $20-something bucks to ship them out, but apparently Real Racers just know this stuff.
My new and annoyingly expensive FIA-rated Sabelt GT/Rally Steel 2" Racing Harness gets here tomorrow.
Last edited by JohnnyOTS; May 8, 2026 at 07:35 PM.
Reason: Spelling!
I finish last in my time trials group. Every time, in fact. Without exception. Do I complain about that? No, I understand why it is happening and I just accept that's how things are right now. I work full time in IT, take care of a household, oversee a few adult children, and throw some battered cars around the track periodically and try to keep the wheels in the right direction. Watching some of the board members do amazing things in such a short period of time is both impressive and disheartening, but I just have to give myself permission to be slow and sucky both on and off the track or I'll stop having fun and I, like hopefully most everyone, am in this for the fun. Unfortunately for me the fun part is doing what that guy in the middle is doing but I'm not rich enough to do the whole arrive-and-drive thing so I do what I can from that mountain of other people, farm out what I can't or won't to others, and watch my bank account shrink. Now that's going fast. ;P
A nice grounded perspective on this motorsport thing, that can become an obsession. Do what you can, importantly make sure you are enjoying it, and that it's place in your life doesn't push away other enjoyments and even responsibiliies. As one with a strong competitive streak, that's an ongoing challenge for me.
Bummer about the diff. I have about 0 idea of the history on my diff (type 2 3.6), but it's survived a good deal of abuse. The torsens are known to be pretty tough, so I'd be sceptical of the quality of the rebuild.
Bummer about the belts as well. Honestly I haven't heard of people sending belt in to be "rebuilt" but I don't see why it couldn't be done. Bummer that they turned them away though. I wouldn't expect the hardware to change a ton over the years
I have a car back. The front suspension components have all been reattached, torqued down, and red-Loctited. The ever-cranky passenger's front brake caliber bleed screw has been replaced. It has been aligned yet again. It has a new differential and is now running a 3.9 type 2 torsen because that's all I could get. The transmission oil has been changed to something that might not get so cranky when everything gets super hot so I can continue shifting into 5th and reverse. A Mazda 3 heat shield has been repurposed/reformed into something to try to keep me and the transmission from cooking quite so much. Jeff's mechanic Steve did Brilliant Work on that. New Heat Shield!
The HVAC stuff is out. A temporary (or maybe permanent) tombstone replacement is welded up and bolted in. The car is a complete mess, but it mostly works. Messy but somewhat functional
The only remaining issue of significance is the dash gauges don't work. (Well, except for the speedometer but that's mechanical and isn't even accurate now that I'm running a 3.9 rear end.)
It lights up just fine and the tach twitches when it first gets power, but nothing else.
I checked the Meter fuse - it was good. I replaced the Meter fuse with a new 10a fuse anyway. Twice. Still no gauges.
My digital dash works fine so I know the Megasquirt is putting out data - the digital dash there on the right has a tach, temperature gauge, AFR stuffs - no problem. The gauge cluster doesn't show any of it.
Also of note - I've got that shift light wired into the plugs that go into the back of the gauge cluster (FM had a guide on how to do that - those of you with elephantine memories will recall me grousing about some of the details, but I did get it working eventually!)
The shift light powers on but won't show anything but incoming voltage either, so it seems like the problem is somewhere between the ECU and the gauge cluster. I've made a point of connecting the ground points of the dash harness to what I think are really decent grounds on the chassis itself so I wouldn't think that's the problem.
Not sure if its related, but neither of the idiot lights I had installed work either! Jeff says they have power and signal but neither will light up any more.
Since this car goes on the trailer early tomorrow morning for a weekend of track time at Inde Motorsports Park down in lovely Willcox AZ, I may be shifting by sound (with different shift points thanks to the replacement rear end) and squinting at my really hard to see digital screen in the tombstone area to check for warning stuffs.
Awww, sorry you won't be there Roda! I'm running in the Orange group and HL2 time trials group both days. Hopefully I can keep from breaking the car and/or eating the tires this trip.
That heatshield looks right at home. I wouldn't have known it was repurposed. I'm going to have to keep that one in mind once things start heating up this summer.
That heatshield looks right at home. I wouldn't have known it was repurposed. I'm going to have to keep that one in mind once things start heating up this summer.
I was thinking exactly the same - can give any more information on the model it came from?
It's a Mazda 3 heat shield - Part # BP4K-56-441F
Be warned - it looks nothing like what Steve turned it into!
Further gauge cluster weirdness - the gas gauge works. Nothing else except for the speedometer. Shift light and idiot lights still don't work either. I'll be doing some continuity tests when I get back home after the weekend at the track (assuming the car doesn't end up doing right back to the shop at least!)
I think Moti had a post about using that heat shield in one of his builds a long time ago. Maybe it's in the Morpheus thread? I'm not going to hunt it down, but interested people can do the digging from the breadcrumb I remember.
I think Moti had a post about using that heat shield in one of his builds a long time ago. Maybe it's in the Morpheus thread? I'm not going to hunt it down, but interested people can do the digging from the breadcrumb I remember.
Yes, Johnny's post triggered a memory of a post talking about a Mazda heatshield, but without the when/where/what details.
I used a Mazda heat shield on my car, but IIRC it was a CX-5?? The original idea goes back to Moti's post, but thebeerbaron also used one on his K swap and that's where I got the idea. I got mine off eBay at a pretty big discount.
I also used some of this generic aluminum heat shield from Amazon:
Ouch, $450 for that part here - hard pass! I'll ask around the local wreckers and see what they have, otherwise it looks like Roda's Amazon solution is the go.
I’ll be another to praise the heat shield idea. I’ve got that aluminum/fiberglass-type shielding attached to my tunnel with adhesive and push pins and kinda hate it. Maybe the high end DEI stuff is better but whatever my car came with has started to come apart and will sometimes shower you with fiberglass particles if you tag your hand on it. Doesn’t look nearly as nice either.
Hope to hear the track day at INDE went well and the gearing change wasn’t too jarring!
Last edited by Z_WAAAAAZ; May 26, 2026 at 12:46 PM.
Like I mentioned in my previous post, losing that bolt in the passenger's ball joint and having the eccentric on the same side come loose is the current suspect for the car's extreme oversteer. When I can get the steering repaired and the differential replaced so I can get the car back on the track we'll see how it handles and go from there.
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