3.15 TO 3.73 SWAP

Looking to do a 3.15 - 3.73 swap gt manual. Just going to by the whole assembly and be done. Question is 1) Do i need a tune for the swap? 2) If not will it void my power train warranty? May seem like stupid questions to some but this is the first modern stang I've own as well as one I bought new with a warranty.

A tune cannot modify the settings necessary to accommodate the change in gears like in previous mustangs. The setting is contained with the BCM.

In order to modify the setting you can either,

1. Purchase the Whipple flare tool
2. Refer to the as build modification in the DYI section

The as build modification will be cheaper, is not locked to your VIN and has a lot more options.

I'm not sure on the warranty part.

Before you purchase you should post up as there are folks with 3.73 who would be interested in swapping parts for parts.

Yes it would void your powertrain warranty and it's an expensive thing to do for no performance gain.

If your car is a manual transmission you don't have 3.15's.

Ok let me fix some bad info.First u can adjust the speed calibration for these cars,if its not a big gear change the abs will relearn the speed through the wheels sensors,if the gear change is beyond the relearn strategy of the bcm the Sctx4 does recalibrate the speedo,i just did this when i switched from 373 to 331's.I am tuned by lund but my x4 is not locked wheir i cannot use the gear/tire calibration.This just my opinion a naturally aspirated car will have significant gains from a gear swap.U might have to check to see what gears are available for the 315 rear if its an auto.I verified my speedo was correct using 2 different gps app and it was dead on.

Tommy V said:

This just my opinion a naturally aspirated car will have significant gains from a gear swap.

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Incorrect. Been there done that with a gear change on my auto. Saw absolutely no improvement at the track. It was a waste of money.

I'm sorry guys I'm dumb I have a manual with 3.31 been doing a lot of research and got numbers mixed up when I started the thread. Thanks for the responses tho

Back in the days of 3 and 4 speeds, gear swaps really helped. Now with 6 speeds, not so much...

Deaner44 said:

I'm sorry guys I'm dumb I have a manual with 3.31 been doing a lot of research and got numbers mixed up when I started the thread. Thanks for the responses tho

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If you are absolutely sure you are not going with any type of FI or a all out NA build then the switch will make the car much funner to drive. If you drag it and run the 1320' you will have to shift into 5th to get there which provides a slower ET. I liked my 3.73's until I went FI...that's why we buy a manual ...right..to shift it.