New in Louisiana - Trans Am
 

Hi all,

Figured it was time to sign on and introduce myself. Been lurking here for a while getting ideas for my daily driver.

1982 Trans Am with the typical go-fast parts (heads, cam, intake, exhaust, etc.)
No aero mods yet, but ideas are taking shape. Looking at a more aggressive front air dam, adding tire spats, LeMans style side skirts, full belly pan, and rear diffuser.

I'm not sure what else to add so if you have questions, please feel free to ask.

Welcome !
Raise the psi in the tires to 40plus.
Get a gauge ( see link in my signature)
Adjust the nut behind the wheel

Welcome,

If you haven't read these, do so.

100+ Hypermiling / ecodriving tips & tactics for better mpg - EcoModder.com

65+ Vehicle modifications for better fuel economy - EcoModder.com


If your car is carbureted, a vacuum gauge would be helpful. If injected a MPGuino.

Like mcrews said "Adjusting the nut behind the wheel" will give the best results.



>

If you're going to do an underbody, don't bother with an air dam. Air dam increases frontal area so the mess underneath experiences less air- if the bottom is totally smooth, then there is no point in increasing frontal area.

Welcome!

What is your baseline MPG? What are your goals?

Wow. Reading your rig's data is more a stat sheet for a weekend strip fighter, not an ecomodder.

406 SBC under the hood, blimey. If you have something smaller lying around and a free weekend, you might want to screw in a mill that's got perhaps a few less cylinders? But that's probably not a viable option.

You could consider reflashing the ECU to something more economy-minded. Your stat sheet indicates you installed the tune that's in there, so coming up with something thriftier should be well within your skill set.

That generation of Firebird was one of the most aero products GM was making at the time, right at .3 CDa if I recall. I don't doubt there are improvements to be made though. Why, for instance, do no manufacturers offer rear wheel skirts even as an option? It's so simple, so obvious.

For my own part, whatever Ultarc says I would second. He's got over 300hp on tap and still knocks out over 40mpg. I don't know precisely what the heck he's doing but he's seriously dialed in on that Mustang.

What's the RPM at 60 MPH? Big engine in a small car needs low RPM for MPG. Think down around 1400 RPM and tuned for efficiency at that RPM. And one of those wide ratio six speeds so the first gear is low enough to get it rolling without burning out the clutch.

Thanks for the warm welcome. I didn't expect replies this soon. Lol

I run the front tires at 36, rears at 32. If I go any higher the ride is hell and the rears wear in the middle of the tread.

I can use a scan gauge it will show as a 2003 Corvette 5.7. But until I upgrade to LS3 injectors with known injector data for the PCM it will show mileage about 4mpg high. For now I check by the odometer. I have verified it with gps.

Point taken on the air dam vs. belly pan. If doing only one, which would make the most improvement?

My baseline average is 21 mpg about 75% highway. Goal is 28. Our '03 corvette coupe frequently knocks down 30-32 mpg in the same conditions. New Z06's frequently do 28 hwy.

The .70 OD and 3.23 rear end have me at 1600 rpm at 55 and 2100 rpm at 70. Planned is a 6L80 auto with .67 OD and 2.56 rear end. More fun and more fuel efficient.

I feel pretty confident with my hypermiling techniques. I took a 2011 Suburban 5.3L from Alexandria to Shreveport and averaged 28.8 mpg. It could have been better I'm sure but this was a bone stock vehicle.

Thanks again for the warm welcome, everyone.

89 Iroc I had would overheat / make the fans run going 55mph or higher without an air dam. Also the air dam from my the iroc and other later 3rd gens w/ lower ground affects might be larger than the earlier 3rd gens

Correct, these cars are bottom feeders. Also GM had two designs for the air dams, a two piece like I have and a revised, more aggressive three piece. If a belly pan is more effective than an aggressive air dam, I will be replacing the one I have with a new one since this one is warped from age.

I forgot to add I have previously done pop-up deletes on the car. Link to the build thread will be added when I have more than 5 posts :cool:

I'd look at the mods made to Bonneville race Trans Ams; IIRC Hot Rod Magazine did a write-up on theirs and went on at length about the aero aspects of it.

You're starting with an excellent cd of ~0.29, so that thing will be super slippery after aero mods. Sounds like a blast to drive too!

I will look into the firebirds that ran at the salt flats.

Today I started looking for ways to seal up body gaps on the front of the car. Lots of potential there. My cool weather average (not much of a winter here in Louisiana) is usually 18 mpg. After somewhat repairing the front air dam and today's sealing of a few body gaps, I filled up and showed 19.8mpg. Before the changes I had 108 miles on the tank. Filled up at 295.6 miles with 14.9 gallons. This is about 75% highway so I don't consider those to be glorious numbers. Lol

Link to pop-up delete build thread on TGO: Pop-up deletes that look good - Third Generation F-Body Message Boards

Going back to the air dam and belly pan, which one would yield the greater results? Which would do more for reducing lift at high speeds?

I know people who have dedicated road race cars and some who road race their daily drivers. They run belly pans with the addition of a rear diffuser because it reduces lift and supposedly reduces air turbulence behind the car. Would this equate to cleaner air behind the car and lead to better fuel economy, or am I dreaming? My thinking: these things help them achieve higher top speeds so they must have drag reduction effects.

Less frontal area, less hitting the wind.

Less drag under the car, less slowing you down.

Underbody > Air Dam
Air Dam> Nothing

Is this why I never see a car with air dam and belly pan? Now that I think about it, I only see either aggressive air dam alone, or belly pan with a front splitter.

*Edit: the C7 Corvette has under body paneling and also a front air dam.

C7 as in 2015, or is that a different model? Is that all of the C7s with underbody panels and air dams or just certain editions?

What I've gathered so far is the C5, C6 and base coupe C7 all have front air dams and all have a large amount of panelling underneath. C5 are bottom feeders like my car for cooling and the C6 has a front grille but needs the air dam to create that low pressure area behind the radiator to draw air through it. But the C7 has a nice front grille and vents radiator heat through the hood vents, reason for radiator tilted forward. However, after further reading, the C7 with the Z51 performance package does not have the air dam which I found puzzling. The base coupe doesn't need the air dam for cooling since it vents through the hood.

I have read a quote supposedly from a GM exec that by removing the air dam and allowing air to flow under the car, the hood vent was able to pull more of that up and over the top, increasing downforce. I'm unsure of if that works or not. Seems logical with the Z51 package being more track oriented.

Please excuse my rambling. Lol. Just for reference, C5 1997-2004, C6 2005-2013, C7 2014+

I will try to remember to check my NAIAS images from this year and last year. I have started taking underbody images at the show, very few actually had underbodies connecting to their very elaborate diffusers.

Cleveland Auto Show is Saturday, hopefully I will remember then, and take some images. I am about 15,000 images behind in processing, so it will be a while to find if they are not readily available lol.

Progress
 

I made some progress this week. I had about 225 miles on this tank when I extended the front air dam. I did change up my driving habits a little bit as well.
I've attached some pictures of it. ~4.5" ground clearance and this tank netted 21.68 mpg with 322 miles total on the tank; highest it's ever been. Movin' on up!

Got my rain gutter side skirts plasti-dipped and put on the car tonight. 220 miles on this tank so probably won't notice any mileage difference until the next tank. I did go for a drive and it did seem to coast better, but I could just be wanting it to be better. Next couple of fill ups will tell.