Mustang?

[oldschooleco]

Hello everyone,I picked up an 1989 mustang gt back in november.It is the hatchback and ill post pics later on. I was wondering if you guys could give me any tips to make the old girl do the best on gas. Heres the trick,I'm building a 351w motor for it. High flow aluminum heads,Longtube headers edelbrock cam Ect ect and a 5 speed.(400-500hp) My plans are to lower it and add a vacuum gauge and lighten the car up to a point where it'll be under 3000 lbs. I still want it to look like a mustang!lol no boatails or fender skirts sorry!Im willing to listen about air dams kammbaks and spoilers though.This car will spend 85% of the time on the highway, and I'm spinning at about 2000 rpms at 70mph. Let me know your thoughts,thank you!

[Hersbird]

Can't help you in the aero but will tell you I spent a lot of time drooling over those late 80s early 90s 5.0 GTs as I graduated high school in 1988 and went in the Navy. My wife and the budget got us a used 5.0 86 Cougar instead, still pretty cool for 1988.

[Baltothewolf]

Electric fan
Underbelly paneling
Underdrive pullies
Bigger amp alternator (140amp minimum)
LED lights everywhere

The LEDS will probably help a lot. The car uses a ton of incandescent lights that suck a lot of power.

[2000mc]

How does the bigger alternator help?

[mcrews]

Originally Posted by oldschooleco

Hello.This car will spend 85% of the time on the highway, and I'm spinning at about 2000 rpms at 70mph. Let me know your thoughts,thank you!

There is the key!
85% hiway!
Look at some of my 02Q45 posts, especially on tires.
You need to get a scangauge. Then get out on a freeway and get rpm for 50,55,60,64,70.
and record the rpm(from the scangauge) and mpg for each.
Now you have a base line.
THe sweet spot on the 4.5liter V8 (340hp) in the Q45 was around 1724.
I increased the tire diameter to help get to that. 2000 rpm MIGHT be to high to maximize mpg.
since you are doing so much hiway drivng, losing a little of the line wont matter.

[oldschooleco]

Originally Posted by 2000mc

How does the bigger alternator help?

Because the under drive pulleys will spin the alternator slower? i think?Im skeptical of them for that reason and they also spin the water pump slower…Which will make a 450hp V8 heat up rather quickly in traffic.Everything else i totally agree with.Thank you

[Baltothewolf]

Bigger alternator means it will run at a lower cycle rate which means it doesn't pull as much from the engine. Testing will be needed for Underdrive pullies, but if you go a high flow water pump and a good radiator (like you should) then it shouldn't be a problem. I gained 1mpg when I upped my alternator to a 140amp from the pathetic 80A that's stock on my '91. Not to mention my lights don't dim at night anymore.

Also, I would run like 12-14° timing if possible, I gained like 2mpg when I bumped my timing to 14°. Cruising was way easier as was my acceleration. Idk with a 351 if you will be able to run that high of timing without knocking. Again, testing will be needed.

Still, I think stock you can get 19-21 on the freeway, if you do some other mods you can probably get 25ish


How high of compression are you running?

[aerohead]

You might peek at the MUSTANG SVO.
It was aero optimized a bit with a patented bi-wing rear spoiler.The wheels are lower drag.
A NASCAR-type nose would improve drag and lift.

[dirtydave]

http://www.streetlegaltv.com/news/de...speed-mustang/

cdn.streetlegaltv.com/image/2014/03/photo-24-Custom1.jpg

cdn.streetlegaltv.com/image/2014/03/IMG_1942-Custom.jpg

http://www.speednik.com/files/2014/0...om-640x426.jpg

cdn.streetlegaltv.com/image/2014/03/IMG_1918-Custom.jpg

[darcane]

Originally Posted by mcrews

You need to get a scangauge. Then get out on a freeway and get rpm for 50,55,60,64,70.
and record the rpm(from the scangauge) and mpg for each.

That's going to be a challenge because...

Originally Posted by oldschooleco

Hello everyone,I picked up an 1989 mustang gt back in november.
<snip>
Heres the trick,I'm building a 351w motor for it. High flow aluminum heads,Longtube headers edelbrock cam Ect ect and a 5 speed.(400-500hp)

'89 Mustang with a 351W? There's no OBDII in 1989 and most likely the engine swap means it's carbureted now too.

Sounds to me like the OP is building a race car with outdated technology but would like modern fuel economy. Aero and gearing will help some, but mostly this is putting lipstick on a pig. Keep the car a "5.0" with a Coyote motor and a 6-speed, and you can probably hit the same power with significantly better mpg.