6cylndermaddness

Hi I have a 1999 3.8L mustang. It has about 91,000 miles. I have put a lot of work and time into the car and when the 3.8 kicks the bucket I would like to drop a new 4.0L in it so i can have a 0 mile engine start and eventually put more work into and not have all the work i have already done go to waste. I was wondering if it was possible to put a 4.0 in it and if so would i need new trans or rear end or new wiring harness ect. i figure if a 4.6 can fit in it a 4.0 can i didn't want to do a 4.6 swap because its way too costly. but if anyone can give me any advice it would be appreciated.

If it's possible my main goal is to buy a new forged 4.0L block get aftermarket heads and upper and lower intake, supercharge it and put in a new rear end and transmission.

Thanks All.

fallfast90

It would be a waste in my opinion. Go over to supersixmotorsports and pick up a brand new forged 3.8/4.2. Once you do that, throw on the boost and enjoy. That simple.

LilRoush

Agreed, you'd spend a TON more for less power if you did a SOHC 4.0L instead of a nice fresh pushrod 4.2L from SSM.

mudvayne1

It wouldn't cost much more to convert it to an v8. 91000 miles isn't alot either. I wouldn't worry about finding a replacement for another 100,000 miles. Or until it starts burning oil or knocking.

quiksilver00

plusone on the comment about mileage.

3.8s are pretty reliable. Do a compression test and you have some options. Build it, Boost it, M112 it, or build it and add some FI

NeoTokyo

+1 SSM 4.2/4.3L (Its the same as your splitport 3.8L but with a steel 4.2L crank, forged 4340 long rods and forged 0.030 over pistons to make it a 4.3L (4.2L if you dont bore it.)

indisposible_teens

Have to agree. It just costs way to much money to put the 4.0L into our SN95 chassis to be worth it.

Lunarink

Will a 3.8 intake fit a 4.0? My 3.8 went and I found a cheap 4.0 but it needs an intake. And will it bolt up to the stock transmission?

NeoTokyo

Welcome to the forums.

No, the intake will not fit a 4.0L, they are two completely different engines.

jimkaray

Unless you really want a unique project I would consider a built .8.4.2 or a 4.6. First off there are no motor mounts for this application. Second is the drive by wire throttle so you'll need to either convert it or add the electronics. Your trans may bolt up to the bell housing but i would expect possible differences in the input shaft length and splines. Going with the 4.0 trans would raise issue of shifter set being different and electronic speedo sensor if you aren't doing the full elelectronics swap. Then there's potential issues matching up to the SN95 crossmember.