Trans Am build thread
 

I decided I should start a new thread for any further mods I do on my car instead of posting to my intro thread.
A little background, I typically get 18.5~19 mpg. 20.5-21 mpg if I really, really tried. After sealing up gaps at the front of the car, and extending the front air dam, it's up to 21.7 and 21.5 without too much effort. My next mod was side skirts.

Anyway, I have a couple of pictures to post of the rain gutter side skirts I finished last night.

https://scontent-a-lax.xx.fbcdn.net/...71920109_o.jpg

https://scontent-a-lax.xx.fbcdn.net/...82387017_o.jpg

https://scontent-a-lax.xx.fbcdn.net/...46752699_o.jpg

They started out white, but a can and a half of black plasti-dip fixed that. I also made up an inner pair of skirts to go up to the inside edges of the tires, but I don't have any way to mount those yet.

All told, I have less than $25 in them. When I installed them last night I had about 220 miles on the current tank. After today's commute to work and back there are 265 miles on the tank. Probably will see no difference until I have a full tank with these on here.

How did you seal the gaps up front? Foam?

Joggernot

have you thought about going with a T56 (Manual 6 speed)?
it's got a double overdrive

would probably make a difference
but with those 3.23 rear gears, you may need to go 75mph to get peak mpg



my 4,000+lb GTO with a 400HP 6.0L (when stock)
was getting 30-32mpg on the highway (if I could keep the speed up about 70-75mph)
and that's with 3.46 gears

now, she gets about 23-24mpg highway

btw,

your front tires are on backwords?
are those Mich Pilot Sport A/S?

https://scontent-a-lax.xx.fbcdn.net/...82387017_o.jpg

Yes I used a strip from front to back between the skirt and rocker panel.

I have considered a T56 but those cost their weight in gold around here, and I have been planning a 6L80 swap with 2.73 or numerically lower ratio rear for a while now anyway.

Yes and yes. I swapped them a while back to diagnose a problem pulling to the right and have yet to swap them back.

If the l480 and l680 use the same first gear then using a 2.73 rear is going to be slugish.

What kind of wheels are those?
And are they lighter than the factory wheels?
The factory iroc alloy wheels weigh 22lb.

The 4L60 has a 3.06:1 1st gear and the 6L80 has a 4.03:1 1st gear. For a reference, the C6 08+ Corvettes with the 6L80 come with a standard 2.56:1 ratio or an optional 2.73:1 'performance' ratio.

With the torque this 406 already makes, I am tempted to try the 2.56:1 rear with the current 4L60 trans.

And these are C5 Z06 replicas 17"x8.5" front, 18"x9.5" rear. I have them to clear the future brake upgrade. The factory wheels won't clear the front rotors I'm looking at getting.

Do you think front 17 inch vette wheels will fit all 4 corners of a 3rd gen?

They will for sure. But this a dual purpose car of sorts haha

Call me crazy but this is sort of my quest to build the poor man's Z06 which is a 427 (7.0L) rated 505 hp and returns 28 mpg at 75 mph. If it can do it, I feel I should be able to get close. It has 18" front and 19" rear and they are wider.
I'm sure it's considerably less frontal area than my car, and I know it sits lower, but I don't think it's THAT much of a difference. But I could be wrong. Lol

The thing is the last body style of hyundai sonata the v6 has very simular weight, frontal square footage and Cd as a 3rd gen. The hyunda gets up to 8mpg better than the old V8 80s car.
So its possible for car of that mass and aero profile to get mpgs in the high 20s. The difference is all engine, engine management and gearing.

You need to be aware that some models had different offsets for the front wheels and rear wheels, I know my 86 with the B&W 9 bolt rear did.

Note the air dam on my Civic, LOL!

http://i107.photobucket.com/albums/m.../my2beasts.jpg

Off sets are 99% of the problem.
GM used 2 bolt pattern on cars, 5 on 4.5 on small cars and 5 on 4.75 on full size cars that includes older half ton chevy trucks too. With more than a few off sets.

Engine management is already taken care of (2003 Corvette PCM, fully sequential EFI, distributorless individual coil-near-plug ignition, months of fine tuning with HPTuners). The engine is about as low-friction as it can get (it will be getting a roller cam soon to replace the flat-tappet). Only thing left is gearing. I see a 400 small block having no problem moving a 3200 lb. car with 2.56:1 gearing.

I have been wondering if the headers are skewing the O2 sensor reading. They are heated sensors but the header tubes let out a ton of exhaust heat. I wonder if wrapping them would have a positive effect? It's a common problem with long tube headers, where the O2 sensors don't get hot enough and cause a car to run pig rich. These are shorty headers, but with as mild a cam as it has, the EGT isn't going to be high at all.

Everything on the 3rd gens were narrower than the newer cars, so you just need to figure out how thick of a spacer you need. I had an iroc w/ different fr + r offsets I put 4th gen wheels on

On mine I had 2" spacers all the way around. Since swapping the 4th gen rear I only have the spacers on the front. Rear end came from a 1997 trans am with disc brakes.

97s must have been good for getting wrecked, mine was out of a 97 firebird too, idk if it was a TA, but it was disc. I was swapping it out because parts weren't available for the oe 9bolt. With 4th gen wheels, the only thing that wasn't a simple bolt up was the parking brake cables

Really cool project you got there

wheels/tires
 

I think that your wheels and tires are going to ruin your chances for 28-mpg.
The TA originally had 205mm rubber,the MOON-esque wheel covers,and the rear spoiler,for Cd 0.315.
With John Shinella's secret wheel covers and narrower tires (195s),the drag could be Cd 0.283.
*The original airdam was too low to begin with,but WAS optimized aerodynamically.
*The side skirts were optimized as well.
*The 'widening' of the C7 Corvette,with the Z06 package degrades the Corvette's drag ,from Cd 0.29,to Cd 0.37.
*Your TA already has a frontal area challenge compared to the 'Vette.
*If you were to have a chance at the mpg,my opinion would be that you'd have to lose the wheels and tires and restore the car to stock spec,and add "narrower" rubber.
*I don't know how you'll be able to keep the airdam on the car.North Texas streets are littered with the originals.Same for the Corvettes:o.