How did our V6 Miata fair racing with Lucky Dog at Carolina Motorsports Park this past weekend? It’s a good-news, bad-news sort of situation.
The good news is that the Miata is fast–we were on pole–plus we learned a lot from our first competition outing since swapping in the new engine.
What did we learn? That’s where the bad …
Glad to hear that the car's first outing went pretty well, all things considered. Looking forward to seeing it compete more in the future.
The wrap photographs so nicely. (Says the editor who needs to be aware of these things. 
)
How many horsepower is this thing putting down?
Iirc, a 1.8 miata put down a similar lap during this year's or last year's champcar race. Right around a 1:46.
We put down a 1:48 in a gm 3.5 swapped 2nd gen rx7 with 180rwhp.
I guess what I'm saying is... I thought it would be faster. Is there more performance left somewhere?
I assume they're aftermarket halfshafts (probably from DSS via V8R). Interested to hear if it was the inner or outer CV, and if you're using the stock Miata drive flanges or an aftermarket one (and thus which spec of CV it has).
In reply to wvumtnbkr :
IIRC, the Spec Miata lap record is something like a 1:49 at CMP, and probably wasn't set on an 85-degree day. Don't forget we're also running street tires.
With tuning, we think the car has a 1:42 in it. But we were happy with a 1:45:00 fresh off the trailer after a few years under the knife.
In reply to Keith Tanner :
Aftermarket DSS halfshafts via V8R. Outer CV, with aftermarket outer flanges. The internal CV spline (connecting halfshaft to CV joint balls) is what stripped.
In reply to wvumtnbkr :
They did take pole. The track may not have been all that fast at the time.
Tom Suddard said:In reply to Keith Tanner :
Aftermarket DSS halfshafts via V8R. Outer CV, with aftermarket outer flanges. The internal CV spline (connecting halfshaft to CV joint balls) is what stripped.
I have had problems with DSS driveshaft lengths being not quite right, which leaves you running on a very small length of spline if they're too short. The spline then strips.
It's possible there's a long and a short halfshaft if the diff is slightly offset, and if you get them backwards you can get this failure as well.
Tom Suddard said:In reply to wvumtnbkr :
IIRC, the Spec Miata lap record is something like a 1:49 at CMP, and probably wasn't set on an 85-degree day. Don't forget we're also running street tires.
With tuning, we think the car has a 1:42 in it. But we were happy with a 1:45:00 fresh off the trailer after a few years under the knife.
He'll yes. That IS fast.
Champcar is also on street tires BTW. So it's fairly apples to apples. Also, the race is in June usually so temps the same or higher.
A 142 would be smoking on street tires.
Tom Suddard said:In reply to Keith Tanner :
Aftermarket DSS halfshafts via V8R. Outer CV, with aftermarket outer flanges. The internal CV spline (connecting halfshaft to CV joint balls) is what stripped.
M300 shafts may solve that issue, but then what's the next weakest link?
deaconblue said:Tom Suddard said:In reply to Keith Tanner :
Aftermarket DSS halfshafts via V8R. Outer CV, with aftermarket outer flanges. The internal CV spline (connecting halfshaft to CV joint balls) is what stripped.
M300 shafts may solve that issue, but then what's the next weakest link?
M300 is what? I come up with Chevy Spark driveshafts when I google that :) I'd dig a little deeper, the DSS stuff can handle an LS3 Miata in endurance racing so it's not a fundamental strength problem in the halfshaft.
Endurance racing is an exercise in finding the next weakest link until you get to the end of the race.
300M? Some beefy metal that FD drag racers were using when FDs were "cheap" enough to go drag racing with.
The failure mode suggests to me that the axles had their splines cut, instead of rolled, and you found the limits of cut splines of that size.
Let's wait for a picture of the damaged splines, that may tell us quite a bit. It's likely Tom and co. didn't tear it down all the way when they discovered the halfshaft was rotating inside the CV joint, that's all they really needed to know in the pits.
A SC group managed 1st in C class in a Miata. Their car is slightly less photogenic though.
I had a similar failure in my (at the time) L33 Miata - 350 rwhp or so. My notes say that the spring clip broke and allowed the halfshaft to pull partway out of the CV, but the picture doesn't seem to confirm that. I don't recall much else, it was 9 years ago. I think I broke both axles, because as soon as the first one went all the V8 torque was transferred to the second and it didn't want that. I've still got the parts, I should pull them out and look.
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