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Old 10-06-2007, 11:00 PM   #1
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Default Speedo accuracy

Went from 4.30 to 4.10 gears today, and now I'm wondering if I need to do something about my speedo. I'm curious if anyone's tried checking their speedo with GPS. I'd think that it reads 5-10% high (like pretty much every car on the road) so with my taller gear, it's probably pretty close to being right.
I'm going to try to check it against GPS tomorrow.
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Old 10-06-2007, 11:03 PM   #2
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I'm curious as well. When checking my car against my buddies Jetta my car read 5 mph slow. Not sure if that was the 17" wheels or what causing that.
How does the 4.10s feel compared to the 4.30s. I'll be doing the same swap soon with my torsen. Hoping 1st gear is a bit more useful and 2nd gear gets me to 60mph.(Think it gets me to like 57mph now, could be mistaken and full of **** on that one.)
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Old 10-06-2007, 11:05 PM   #3
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My 99 reads high from the factory. I've never checked it against gps, but I figure when it shows 75, I'm really doing 70. Trap speeds at the local 1/8 mile also verify the speedo reads optimistic. Most fords speedo's are dead nuts.
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Old 10-06-2007, 11:21 PM   #4
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it's probably closer than it was before. I know mine is very close with 195/60/14 azenis and 4.10 rear. I'll check it against the gps tomorrow.
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Old 10-06-2007, 11:26 PM   #5
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so far its baller. I noticed the taller gear right away, the first time I put the car in 1st and started from a stop. The car took more throttle to get moving. The 3rd time I started from a stop, I was used to it.

the car seems more relaxed, more so than the slight change in gear would indicate. at very light throttle openings, the car isn't as quick. at moderate openings, I can't tell a difference. I'd suspect that the additional load just results in additional boost, essentially canceling out acceleration lost due to the gear change by forcing the motor to produce additional torque.

the mazda comp diff mounts made all the difference in the world as far as shift quality. gears are actually where they're supposed to be. shifting no longer feels forced. the 2-3 shift especially. i also must have had some front to back slop in the driveshaft/diff before, which is gone now. Or perhaps the old diff mounts were toast.

this rx7 diff has a lot of lock up. the pedal feels much more connected to the back of the car when cornering, meaning mild changes in throttle position result in more change in yaw than I was expecting. I'll have to seriously adjust my driving habits.

I haven't seen more than partial throttle, partial boost yet. I've got my original ignition on the car, which won't fire the plugs. It's like hitting a rev limiter at 8 psi. (took the COPs off the car as the model to mock up another). I'm going to put the COPs back on the car tomorrow and see what's up.

oh, I'm running 205-45-16 tires
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Old 10-07-2007, 04:20 PM   #6
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Mine reads 6-7% high according to my gps with stock gearing and stock diameter tires.
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Old 10-07-2007, 04:27 PM   #7
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Quote:
Originally Posted by Ben View Post
this rx7 diff has a lot of lock up. the pedal feels much more connected to the back of the car when cornering, meaning mild changes in throttle position result in more change in yaw than I was expecting. I'll have to seriously adjust my driving habits.
What was it before, stock 1.6 open?
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Old 10-07-2007, 04:44 PM   #8
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1.6 vlsd
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Old 10-07-2007, 06:01 PM   #9
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Mine was pretty dead at at 50 or so mph as far as those little radar gun your speed is this trailers is concerned. I was kinda surprised cause i changed the speedo gear to a 4.1 but my tires are 225-50-15 this is almost an inch taller than stock.
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Old 10-07-2007, 06:11 PM   #10
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i verified mine with a police "you're going this speed" sign.

195/50/15 - 4.10 rear.

25 matched, 35 matched, and 50 matched.
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Old 10-07-2007, 06:19 PM   #11
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If you grab a speedo gear from a '94-'97 gearbox that should set everything right. Assuming that stock is right that is.
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Old 10-07-2007, 07:51 PM   #12
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GPS confirmed:
0-30 mph no variance
30-70 mph, car speedo lower than gps reading by 1 mph
70-90 mph, car speedo lower than gps reading by 2 mph
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Old 10-07-2007, 08:20 PM   #13
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How hard are the mounts to get in the rear end...and where the hell do you find them?

I'm thinking the ones I have in the torsen I swapped are SHOT.
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Old 10-07-2007, 08:30 PM   #14
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get some good mounts from MMR

mmr-direct.com
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Old 10-07-2007, 08:40 PM   #15
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MMR mounts are cheap but the motor mounts are not for the faint of heart.
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Old 10-07-2007, 08:53 PM   #16
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you get get them from mazda or mazdacomp.
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Old 10-07-2007, 09:09 PM   #17
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Well, it took 3 hours to change the mounts out, if that tells you anything. However, we got the second side done much more quickly than the first.

Best method:
Use a hole saw to knock the mount centers out. Use a deep 1 3/4" (44mm) saw. Then use a press to push the outer casing of the bushing out. Grease up the carrier good and press the new bushing in. I bet that if I had to do it again, it would only take an hour or so.
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Old 10-07-2007, 11:58 PM   #18
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FYI You can get the speedo verified (had to do this to get out of a ticket) mine showed abuot 4.5mph faster than what I was doing on the rollers. Cost ~50$ if you really wanna find out or if ya need to get out of a ticket ;-)

Last edited by mtncrvr; 10-08-2007 at 11:11 AM.
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Old 10-08-2007, 11:32 AM   #19
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Quote:
Originally Posted by mtncrvr View Post
FYI You can get the speedo verified (had to do this to get out of a ticket) mine showed abuot 4.5mph faster than what I was doing on the rollers. Cost ~50$ if you really wanna find out or if ya need to get out of a ticket ;-)
thanks, but that only works the first few times :gay:
ask me how i know, lol
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