Thread: 1998 Grand Prix GT engine swap

Hi,

I am new to this forum and have a question about a motor swap to a supercharged GTP motor. I am sure you have all answered this before, but my limited ability to search the forum did not find the answers I need.

I have a 1998 Grand Prix GT that I have owned since it was new. It is a nice car and I do enjoy driving it, but I have always regretted not getting the GTP when I bought the car. But those were different times and I got what I could get at the time. Anyway, I am now fixing the car up from 11 years and 122,000 miles of use. I just got the car out of the paint shop and it looks great! Now I am waiting for my new headlights and tail lights to show up and then it is going in for new struts, tires and an alignment.

Now, I have an opportunity to purchase the motor out of a 2000 GTP that is a good runner because the car got rearended. The comparison that I have done leads me to believe that all I would need is the complete motor and the Engine computer. Does anyone know if that is correct? The wiring harness in both cars look identical to me, so I am thinking I would not have to change the harness. I did find on this forum that the transmissions are different, does anyone know if my exisitng transmission will work or do I have to change the trans also?

If anyone can help me out with these answers or offer any other thoughts and advise I would appreciate it.

Thanks.

Ok, noob here to but going to try to answer the best I can and see if my research is paying off!!

From what I understand by reading up in here is that the wiring is the same except for I think two plugs... I know the MAP sensor is different.. Your N/A 3800 has the MAP sensor on the rear upper intake opposite of the throttle body. The S/C motor's MAP sensor is located near the rear of the engine bay by the firewall I believe mounted on the bracket where the front O2 sensor plug is. Several 3800 performance online stores sell extension pieces that you would splice into your harness to extend your harness back to the correct location for the new MAP sensor.. Or since you are getting the whole motor you could cut the plug off the GTP harness about a foot back and use it instead. Not sure the color wires are the same but probably so.. Since you are using the stock GTP computer (GT computer has to harsh of a tune) it would be good to hook stuff up as stock. There are a couple of vac lines (evap I believe) are slightly modified as well..

Your GT transmission is typically the same if not a hair better except if you do lots of hard launches.

What I would do (well I am doing to my car eventually) is just swap the top end of the motor (heads up) onto your motor. You will get more power and it's just as reliable. There are some good "Top Swap" threads in here to read up on about that but probably the better option if you want the extra power but you'd want to slightly mod your exhaust as well.

I hope this helps and I do hope I'm not giving bad info!!

Plenty of GREAT info in the forum just take the time and search!!

Originally Posted by dbextreme

Ok, noob here to but going to try to answer the best I can and see if my research is paying off!!

From what I understand by reading up in here is that the wiring is the same except for I think two plugs... I know the MAP sensor is different.. Your N/A 3800 has the MAP sensor on the rear upper intake opposite of the throttle body. The S/C motor's MAP sensor is located near the rear of the engine bay by the firewall I believe mounted on the bracket where the front O2 sensor plug is. Several 3800 performance online stores sell extension pieces that you would splice into your harness to extend your harness back to the correct location for the new MAP sensor.. Or since you are getting the whole motor you could cut the plug off the GTP harness about a foot back and use it instead. Not sure the color wires are the same but probably so.. Since you are using the stock GTP computer (GT computer has to harsh of a tune) it would be good to hook stuff up as stock. There are a couple of vac lines (evap I believe) are slightly modified as well..

Your GT transmission is typically the same if not a hair better except if you do lots of hard launches.

What I would do (well I am doing to my car eventually) is just swap the top end of the motor (heads up) onto your motor. You will get more power and it's just as reliable. There are some good "Top Swap" threads in here to read up on about that but probably the better option if you want the extra power but you'd want to slightly mod your exhaust as well.

I hope this helps and I do hope I'm not giving bad info!!

Plenty of GREAT info in the forum just take the time and search!!

Also HD differential might be worth picking up.

Ok, that is good info so far. I thought about just swapping the top end, but I looked up the pistons for the two engines and they are different. I was assuming this was for lower compression on the supercharged version, but that was an assumption. Anyone able to verify either way on that?

Is the HD diff worth the trouble? Seems like it would be easier to change the whole transmission if I go that route then to open up the differential.

Thanks guys, keep the info coming.

http://www.grandprixforums.net/f17/t...lots-7763.html

The tranny's aren't different cept for the final drive ratio and the differential.

NA: 3.29 and 9.4:1
SC: 2.93 and 8.5:1