Went to the dragstrip today. (protip: don't go to the dragstrip.) - Page 3 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 04-28-2008, 02:00 AM   #41
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A 2.1 60' on street tires is not bad at all.

Looks like the exact same gears went on both of ours. One of those side gears went on mine, and two or three others split clean in half when the whole unit locked up. I wonder if cryo treating would help any?

And for the record, I wheel hopped for the first time the run before I broke mine too, so maybe that has something to do with it.
Uh, wheel hop has everything to do with it! There's no doubt. That's putting 10x the force on the diff, and stuff breaks. Our 7" diff is plenty big. We don't need a 9" rear end. We need to brace the thing to stop wheel hop.

Cryo treating would help, but it's a band aid approach. The diff being weak isn't the problem. It's wheel hop that kills it. Kinda like knock on an engine. Dosn't matter what you have if you have knock, it will break your ****. If we didn't hop our rear ends would be much much better off.

FWIW, I think it needs a pair of frame rails that tie to the factor rails and the rear subframe, and then brace the diff off of these.
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Old 04-28-2008, 02:06 AM   #42
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Our 7" differential isn't the weak link IMO. Well, it sort of is. Wheel hop is what kills ****. Our diff winds up like a spring when you launch it. The front of the diff jumps up and nothing stops it. Look at how the RX7 diff is mounted. Ours needs to be supported just like that, with a brace between the frame rails holding the front of the diff. Stop wheel hop and the diff's would stop breaking.
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I just sold a 1990 RX-7 TII with a LT-1 put 365hp to the wheels and had the worst wheel hop I have ever driven. I used poly on every point and welded the front of the diff to the mount to try and fix the hopping and nothing was fixing it. The RX-7 mount is NOT the answer.
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Old 04-28-2008, 02:10 AM   #43
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You guys dont think an ace hd w/6 puck going from 0 to 7k in an instant has anything to do with diff failure?
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Old 04-28-2008, 02:11 AM   #44
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I don't know RX7's well, but something had to be giving for it to hop. On our miata's, the front of the diff is just not supported. What do you think was giving on the RX7 for it to hop? Again I've been under an RX7 twice, so not real farmiliar with them, but I know they have a brace that holds the front of the diff. Granted, it was all connected with bushings.
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Old 04-28-2008, 02:22 AM   #45
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You guys dont think an ace hd w/6 puck going from 0 to 7k in an instant has anything to do with diff failure?
Please elaborate. Sure it has something to do with it. You put down several hundred ft/lbs of torque to the rear wheels in first gear. The diff can lay down that torque, say 700 ft/lbs. But hop and it goes 700, then 200, then 1500, then 100, then 2100, etc. It beats on it and breaks stuff.
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Old 04-28-2008, 03:03 AM   #46
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someone please define the term "welded diff" for my noobish self....
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Old 04-28-2008, 03:07 AM   #47
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someone please define the term "welded diff" for my noobish self....
It's when you weld up the spider gears in a stock open differential. This locks the differential so that both wheels ALWAYS turn the same speed. Great for drag racing. And that's about it. Sucks in the turns, dangerous as hell in the rain, makes the car push (understeer like a bitch), it's hell on axles, etc. But it will give incredibly predictable and consistent launches.
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Old 04-28-2008, 11:09 AM   #48
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Sav, get some 3.3 or 3.6 gears and have them cryo'd and shot peened, and get some diff mounts. Set your Konis to full stiff in the back, and cross yo fingas! You can track this set up and take it to the strip.
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Old 04-28-2008, 12:07 PM   #49
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Sav, get some 3.3 or 3.6 gears and have them cryo'd and shot peened, and get some diff mounts. Set your Konis to full stiff in the back, and cross yo fingas! You can track this set up and take it to the strip.
Don't you mean full SOFT?
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Old 04-28-2008, 12:22 PM   #50
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R-Compounds aren't very effective for drag racing. The sidewalls are WAY too stiff and most don't have a lot of stick unless they are hot. You'd probably be better off with streets running low PSI.
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Old 04-28-2008, 01:40 PM   #51
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Installing a larger diff. won't solve wheelhop, and that needs to be eradicated.

You all need to look at some of the V8-swap Miata guys and what they've done to reduce/eliminate wheelhop. A few of them have fabricated longitudinal links that connect the lower rear A-arms to the frame rails, and that seems to pretty much eliminate the problem.
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Old 04-28-2008, 01:56 PM   #52
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R-Compounds aren't very effective for drag racing. The sidewalls are WAY too stiff and most don't have a lot of stick unless they are hot. You'd probably be better off with streets running low PSI.
I would also think your tires had a big hand in killing the diff.
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Old 04-28-2008, 01:57 PM   #53
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Don't you mean full SOFT?
maybe, I never made a pass, I though that full stiff will keep you from being too bouncy? Maybe? And maybe reduce wheel hop...? But what do I know.
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Old 04-28-2008, 01:57 PM   #54
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Brian, can you think of anyone's build specifically? Having a hard time searching for it, but the m.net server seems to be going on and offline.
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Old 04-28-2008, 03:15 PM   #55
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Originally Posted by bripab007 View Post
Installing a larger diff. won't solve wheelhop, and that needs to be eradicated.

You all need to look at some of the V8-swap Miata guys and what they've done to reduce/eliminate wheelhop. A few of them have fabricated longitudinal links that connect the lower rear A-arms to the frame rails, and that seems to pretty much eliminate the problem.
I've seen pics of that before. It made me wonder. I kind figured our factory 4 link wasn't the problem, but it could be. Perhaps supporting the front of the diff as I described and some long arms supporting the Lower A arms would do it. FWIW I've also seen people box in the 4 corners of the lower sub frame. That might help a little to.
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Old 04-28-2008, 04:21 PM   #56
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Originally Posted by jayc72 View Post
R-Compounds aren't very effective for drag racing. The sidewalls are WAY too stiff and most don't have a lot of stick unless they are hot. You'd probably be better off with streets running low PSI.
It was either the 225/45 NT-01s or my 185/60 Falken 912s. The NT-01s typically hook up in a straight line better than the 912s do.
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Old 04-28-2008, 05:54 PM   #57
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Originally Posted by jayc72 View Post
R-Compounds aren't very effective for drag racing. The sidewalls are WAY too stiff and most don't have a lot of stick unless they are hot. You'd probably be better off with streets running low PSI.
yeah, because the car really had trouble with traction when the diff exploded
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Old 04-28-2008, 07:28 PM   #58
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I think he was thinking, as am I, that softer sidewalls and less air pressure would limit the wheel hop which is speculated to be the killer here, not traction.
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Old 04-28-2008, 10:33 PM   #59
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Brian, can you think of anyone's build specifically? Having a hard time searching for it, but the m.net server seems to be going on and offline.
Yes, V8Nutz's is probably the nicest example, as I recall: http://www.cardomain.com/ride/398122/3

Al Cooper was the first I remember seeing, but it looks like the pics are all broken on his cardomain site: http://www.cardomain.com/ride/291686/3
He does talk about it in post #4 here: http://forum.miata.net/vb/showthread...oper+wheel+hop

There's one other I've seen, but I can't think of the guy's name. I'll post when I find more.
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Old 04-29-2008, 09:02 AM   #60
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Yes, V8Nutz's is probably the nicest example, as I recall: http://www.cardomain.com/ride/398122/3
Damn, that's a nice car.
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