Few questions on mph/tuners and clunking ques.

[joker21705]

So i recently bought my car ( 04 cobra ) and discovered it has upgraded gears in it i'm thinking they are 3:73 i am leaning towards 4:10s though, if i'm cruising at 65 the RPMS are about 2500 just under and for example when the speedo says 55mph my GPS says i am going about 63 mph i thought i may have been going faster then it's been saying i confirmed that this morning.
The real question is if i get an SCT tuner can i correct that myself without getting it professionally tuned, as i didnt plan on bringing it to get tuned until next year, and when you bring it somewhere to get tuned don't you need a SCT tuner anyways?

On to the clunking ques when i am in say 3rd/4th gear cruising if i lightly step on the gas and let off you sometimes hear a clunking noise and idea what that may be?

 

[apex svt]

Personally wouldn't do 4:10's unless you are just going to stay a pullied eaton forever, it's just a lot of gear for a car with a ton of bottom end. If you go anywhere to get tuned you will need your own hand held tuner. Sorry I'm unsure about the rest

 

[Rich'sTRsvt]

If your speedo is reading lower then what you are going then it is assuming you have shorter gears then you have got. Like it is adjusted for a 4.10 but you really have a 3.73. As far as the clunk it could be the typical cobra clunk. It can usually be fixed with new diff bushings and the correct front IRS subframe bolts. It could also come from too much backlash in the diff.

 

[joker21705]

So driving home today I noticed my GPS said I was doing 65 rpms were just above 2,000 maybe 2100 but my speedo said I was doing 57. So maybe I don't have gears car just thinks I do for some reason?

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[03' White Snake]

Your car could have a chip tune in it already. What size wheels and tires are you running? That could be why your speedo is off too.

Do yourself a favor and bring the car to Pete at Performance Dyno in NH. He is the best tuner around.

Jack the back of the car up, put a mark on driveshaft and on a tire. Rotate the driveshaft counting rotations, follow the line on the tire. If its half a turn they are 3:55's, 3/4 turn 3:73's, ect. This is the easiest way to tell if there are gears or not without opening the cover.

The clunk could be a few things, warn gears, warn diff bushings, loose pinion nut, bad u-joint ect. Mine does it a little too, had a near pinion seal installed and it helped a lot.

 

[Rich'sTRsvt]

At 65mph today I had about 1850rpm, I am guessing you have 3.73's.

 

[joker21705]

At 65mph today I had about 1850rpm, I am guessing you have 3.73's.

Your car could have a chip tune in it already. What size wheels and tires are you running? That could be why your speedo is off too.

Do yourself a favor and bring the car to Pete at Performance Dyno in NH. He is the best tuner around.

Jack the back of the car up, put a mark on driveshaft and on a tire. Rotate the driveshaft counting rotations, follow the line on the tire. If its half a turn they are 3:55's, 3/4 turn 3:73's, ect. This is the easiest way to tell if there are gears or not without opening the cover.

The clunk could be a few things, warn gears, warn diff bushings, loose pinion nut, bad u-joint ect. Mine does it a little too, had a near pinion seal installed and it helped a lot.

I have 305/35/18 between that and possibly 3:73 gears maybe that's why the speedo is off so much definitely need to go get it tuned though just not going untill next year.

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