4.6 Engine swap help please..

1999gt · July 15th, 2009, 04:53 PM

I have a 1999 Mustang GT,
I am able to purchase a 2003 Mustang GT motor. My shop is telling me that because my 1999GT is setup for a windsor motor, that the 2003 Romeo motor will not fit due to balancing issues and some other stuff...
What all will I need to make this swap work? Or is that BS and will it be just as easy as putting in a Windsor motor?
Thanks guys.

1999gt · July 15th, 2009, 05:52 PM

will the electrical all be the same or will i need new harness + ecu etc?

liljojo4711 · July 15th, 2009, 06:00 PM

if its a complete motor im pretty sure it is a direct swap and u can use all the electrical from the 99

1999gt · July 15th, 2009, 06:03 PM

yes it is complete motor he has everything, just was told because it is a romeo and my car was setup for windsor it wouldnt work.

Dolbs4082 · July 15th, 2009, 06:26 PM

If they're both 4.6L v8 they will be the same, the difference will be the crank. yours will have an 8 bolt crank where as the romeo will have a 6 bolt (i beleive) which means that your clutch might not match up to the new flywheel. also means that if your getting the motor make sure to get a new flywheel because the one u have now will NOT work.

When building my motor (01 romeo) we put a windsor crank in it, and i had to buy a new flywheel. luckily the clutch worked. wiring wise tho, everything should be the same.

SWEET2KSTANG · July 15th, 2009, 07:42 PM

everything is a direct swap. there is minor differences with the long block itself, but thats it. the flywheel is a 6 bolt in a romeo, so all you would need is a corresponding flywheel. a stock 01+ clutch kit will be 11in, if you want to stick to a 10.5 kit, you will need to get an aftermarket flywheel that will take either. there are a couple campanies that make a flywheel for either, i got an xtd for mine, it takes either. we put one in a mach as well not too long ago. intake, electrical, etc will bolt up.

1999gt · July 15th, 2009, 08:12 PM

ok cool, i already have a 6 bolt flywheel and an 8 bolt flywheel lying around... I wont even need to swap the electrical? Just need different clutch? this has been really helpful guys!

JasonT1124 · July 15th, 2009, 10:58 PM

Originally Posted by 1999gt

ok cool, i already have a 6 bolt flywheel and an 8 bolt flywheel lying around... I wont even need to swap the electrical? Just need different clutch? this has been really helpful guys!

No need to swap any electrical. Just make sure any sensors you get or use are from the 99 if you want to be sure... but everything should all be the same as far as that goes.

casper gt · July 15th, 2009, 11:31 PM

Originally Posted by JasonT1124

No need to swap any electrical. Just make sure any sensors you get or use are from the 99 if you want to be sure... but everything should all be the same as far as that goes.

all the electrical parts need to come from the 99. the coil's are diffrent, the IAT is diffrent, the MAF is diffrent, the alt mount's & wiring is diffrent, you guy's already adressed the flywheel issues. basically you'll use the complete romeo motor with intake, alt, & alt mount (you will have to fabricate some alt wiring from both motor's), all the rest of the accesories will have to come from the '99.

1999gt · July 16th, 2009, 02:53 AM

Originally Posted by casper gt

all the electrical parts need to come from the 99. the coil's are diffrent, the IAT is diffrent, the MAF is diffrent, the alt mount's & wiring is diffrent, you guy's already adressed the flywheel issues. basically you'll use the complete romeo motor with intake, alt, & alt mount (you will have to fabricate some alt wiring from both motor's), all the rest of the accesories will have to come from the '99.

Ahhhh, im so confused lol its always some people saying one thing the others saying different. So I do need to use all the electrical off the 99? I am unable to do any "fabricating", that is going ot be a problem? and the computer is different as well???? oh no

SWEET2KSTANG · July 16th, 2009, 04:52 AM

Originally Posted by casper gt

all the electrical parts need to come from the 99. the coil's are diffrent, the IAT is diffrent, the MAF is diffrent, the alt mount's & wiring is diffrent, you guy's already adressed the flywheel issues. basically you'll use the complete romeo motor with intake, alt, & alt mount (you will have to fabricate some alt wiring from both motor's), all the rest of the accesories will have to come from the '99.

huh? coils are the same, alt mount is the same but the top bracket is different because of the intake manifold, wiring is pretty much the same minus the MAF/iat. installing the actuall motor needs no fabrication.

ForestGRN_Ghost · July 16th, 2009, 01:16 PM

Regulator · July 16th, 2009, 01:42 PM

He's saying you have to use the coils off the 99, because the 99 wiring harness has a different plug that you cannot use 00+ coils on.

The valve covers are different, so the wiring harness won't sit on the motor the same as it did before, but everything should plug up just fine. Use your old alternator and bracket if you can, and I believe the coolant neck on the intake faces a different direction on the romeo vs. windsor, but they are interchangeable. If the motor is out of an automatic, make sure you put a pilot bearing in the crank.

jdq5947 · July 16th, 2009, 01:56 PM

I just completed this exact same swap in April. I bought an 03 motor and tranny and the swap was pretty smooth. The motor was complete though from wiring harnass to oil pan.... didn't come with the accessories though (ie AC, starter etc) The issues that I ran into were that the alt. bracket is different which I modified with new hole locations and the coolant sensor plug is on the engine harnass of the 99 and the chasis harnass of the 03. Other than that it was plug and play. As was stated previously if you are not putting 3650 tranny in you will need a different flywheel. Any questions PM me. Good Luck

July 15th, 2009, 04:53 PM	#1
1999gt Newbie Join Date: Jul 2009 Posts: 5	4.6 Engine swap help please.. I have a 1999 Mustang GT, I am able to purchase a 2003 Mustang GT motor. My shop is telling me that because my 1999GT is setup for a windsor motor, that the 2003 Romeo motor will not fit due to balancing issues and some other stuff... What all will I need to make this swap work? Or is that BS and will it be just as easy as putting in a Windsor motor? Thanks guys.

July 15th, 2009, 06:00 PM	#3
liljojo4711 Regular Join Date: Mar 2009 Location: dallas Posts: 358	if its a complete motor im pretty sure it is a direct swap and u can use all the electrical from the 99 __________________ 5.4 2v swap soon

July 15th, 2009, 06:26 PM	#5
Dolbs4082 Hardcore Enthusiast 2001 mustang steeda gt 13.4 Join Date: Dec 2008 Location: kansas Posts: 1,748	If they're both 4.6L v8 they will be the same, the difference will be the crank. yours will have an 8 bolt crank where as the romeo will have a 6 bolt (i beleive) which means that your clutch might not match up to the new flywheel. also means that if your getting the motor make sure to get a new flywheel because the one u have now will NOT work. When building my motor (01 romeo) we put a windsor crank in it, and i had to buy a new flywheel. luckily the clutch worked. wiring wise tho, everything should be the same. __________________ 324.2 rwhp and 350.2 tq, on a conservative tune. Time for Nitrous!!!

July 15th, 2009, 07:42 PM	#6
SWEET2KSTANG mm's nitrous mod 2000 mustang gt 11.79@115.83 Join Date: Oct 2006 Location: N.W. AR Posts: 9,469	everything is a direct swap. there is minor differences with the long block itself, but thats it. the flywheel is a 6 bolt in a romeo, so all you would need is a corresponding flywheel. a stock 01+ clutch kit will be 11in, if you want to stick to a 10.5 kit, you will need to get an aftermarket flywheel that will take either. there are a couple campanies that make a flywheel for either, i got an xtd for mine, it takes either. we put one in a mach as well not too long ago. intake, electrical, etc will bolt up. __________________ right now, she is a jackstand warrior if the car was a horse, i would shoot it!!! project warhorse under construction being built by MP2 Performance

July 16th, 2009, 01:16 PM	#12
ForestGRN_Ghost Enthusiast 99 mustang GT Join Date: Apr 2009 Location: spokane Posts: 710	__________________

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July 15th, 2009, 05:52 PM	#2
1999gt Newbie Join Date: Jul 2009 Posts: 5	will the electrical all be the same or will i need new harness + ecu etc?

July 15th, 2009, 06:03 PM	#4
1999gt Newbie Join Date: Jul 2009 Posts: 5	yes it is complete motor he has everything, just was told because it is a romeo and my car was setup for windsor it wouldnt work.

July 15th, 2009, 08:12 PM	#7
1999gt Newbie Join Date: Jul 2009 Posts: 5	ok cool, i already have a 6 bolt flywheel and an 8 bolt flywheel lying around... I wont even need to swap the electrical? Just need different clutch? this has been really helpful guys!

July 16th, 2009, 01:42 PM	#13
Regulator Regular 1999 Mustang GT Join Date: Nov 2008 Location: Louisville, Ky Posts: 177	He's saying you have to use the coils off the 99, because the 99 wiring harness has a different plug that you cannot use 00+ coils on. The valve covers are different, so the wiring harness won't sit on the motor the same as it did before, but everything should plug up just fine. Use your old alternator and bracket if you can, and I believe the coolant neck on the intake faces a different direction on the romeo vs. windsor, but they are interchangeable. If the motor is out of an automatic, make sure you put a pilot bearing in the crank. __________________ '99 GT FS/FT. Click here for details! "And I heard a voice in the midst of the four beasts, I looked and behold: a pale horse. And his name, that sat on him, was Death. And Hell followed with him."

July 16th, 2009, 01:56 PM	#14
jdq5947 Newbie Join Date: Dec 2007 Posts: 7	I just completed this exact same swap in April. I bought an 03 motor and tranny and the swap was pretty smooth. The motor was complete though from wiring harnass to oil pan.... didn't come with the accessories though (ie AC, starter etc) The issues that I ran into were that the alt. bracket is different which I modified with new hole locations and the coolant sensor plug is on the engine harnass of the 99 and the chasis harnass of the 03. Other than that it was plug and play. As was stated previously if you are not putting 3650 tranny in you will need a different flywheel. Any questions PM me. Good Luck

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