What can I do TODAY on my Sunfire? (mods for 2000 mi round trip)

[GMPG]

I've been reading and lurking here for a number of months now but I haven't done any aero-mods yet. I'd intended to get my 2000 Sunfire 2.2 5spd to hit 40mpg and with tuning mods and driving changes I have hit a peak of 36.5mpg with an average of about 33mpg in combined but mostly rural driving.

Early in the summer I lost interest when I replaced the car (2002 Jetta 2.0 Wagon) and I haven't done much with it since. Well the time is almost here to get rid of the spare car and I'm about to head out on a roughly 2000mi round trip to GA and back tomorrow morning. I have materials at hand and a list of mods I plan to do and some optional ones. If anyone wants to chime in with suggestions about which mods may be best or may not be worth doing I'd appreciate it. All my packing is done so I've got all day to play on the car.

Correction, I have done two mods. I deleted the rear wing and I installed a small 1.25in lip under the front bumper which is a few inches behind the leading edge.

Here is a list of mods I plan to do with approximate times:

Front air dam to 3.5-4in ground clearance. (1.25 - 2hr)
-Heavy MDPE garden edging attached to previously mounted 1.25in MDPE edging "lip". I'll have to look more closely, I may be able to move the lip forward so that the airdam will be at the leading edge of the bumper but I think due to the contours of the car this would make it jut forward in the center. The existing lip and the airdam will follow the contours of the bumper but are about 3in from the leading edge at the deepest and come closer towards the corners.

Cowl at rear of hood in front of wipers. (45min)
- The wind seems to hit right at the base of the windshield, I'm already attaching some stiff rubber moulding that will project up about 1in and lay back at a slightly higher "angle of attack" than the windshield. I'm hoping this will bounce air over the wipers without causing worse problems.

Headlight covers (1-1.5hr)
- Sigh... GM was in the ballpark with the aero headlights on this car, they just stayed at the back of the field. The headlights are set well back of the leading edge and instead of blending they create more opportunities for turbulence. I'm attaching temporary plexiglas covers to blend them with the hood line.

Grill blocks, upper and lower. (1-2hr)
- Coroplast covers for the upper and lower grills. Upper will be a 100% block, lower will probably have some opening for cooling to the radiator although I may incorporate an opening in the top of the air dam and a coroplast scoop behind it to push that air up towards the radiator.

Optional Bonus Round:
Rear wheel skirts (2-3hr)
- Coroplast over a steel former, blended with the wheel opening at front and overlaying it at the rear. I've got all the materials for this and from other experience I think I can fab up the first one in a bit over an hour and knock out the other side quicker.

AND/OR

"moon" covers in coro for two or four wheels. I've got 16" 5 spoke wheels and I think I can cut out circles and zip-tie them on with two per spoke and call it done.

With testing and not going past my time estimates I've got a pretty full day coming, anyone think any of these ideas are worth dropping from the list? Grill block and air dam are going to be the next projects, then headlight covers and finally rear wheel skirts if I have time.

Thanks for any input! I'm going to put a followup quickly with an overlay of the car profile.

-GMPG

[GMPG]

Here is an image of the car profile with aero curve overlaid. (Thanks for that tool whoever made that!!) This is how the car looks now with the...addition of the deletion of the rear wing.

Is there anything I can do at the top of the rear window/roofline to help the flow? I haven't been reading lately but I think the rear window drops away too fast so attached flow might be good? No real time for tuft testing that one although maybe on the road I'll have time to experiment on the trip back.

As a note for other Sunfire owners: Removing that wing didn't do anything I could measure for mileage but it made the interior a LOT quieter at highway speeds. A rear parcel shelf and 3rd brake light from a Cavalier fits fine but you need to trim the edges (Cav sedan wider) and remove most of the brake light. Attach the trim and red plastic lens/bulb holder to the parcel shelf directly and it fits and looks fine.

The most obvious noise is now coming from the mirrors on the highway but a delete there falls outside the scope of this project. I'm going to run about 38psi, maybe 40 but I'll probably leave the whip antenna on for the trip. May shorten it and wrap a 6-8in stub with the right length of wire.

[scivicblu83]

i think grill block (watch the engine temps), passenger mirror delete if you have one,rear skirts(cause they look cool and they work) and headlight covers.
keep up the good work, it pays off nicely.

[GMPG]

A quick note on the windshield cowl, holy cow! I took the car out for a few minutes to get baseline downhill coasting and coast down speeds while I warmed it up for an oil change and.. HOLY COW!

No idea what it will do to/for mileage but the noise from the mirrors is cut by half or more. I couldn't believe my ears so I tucked it under the hood on the passenger side and sure enough there was a lot more turbulence noise on that side again.

Thanks for the thoughts, Scivicblu, but no mirror delete for this car. Everything I'm doing can be undone with a pair of side cutters, a couple of wrenches and an hour or less. I'm planning to sell this car when I get back from this roadtrip so this is kind of a final thrust towards 40mpg before I return the car to mostly stock and sell it. Don't worry though, the Jetta will be getting some love too as I get more familiar with working on it.

[MetroMPG]

I'm wondering about that factory rear wing - it's interesting. I'm not convinced deleting it is best! The "effective" rear angle of the car is much closer to ideal with it in place.

But sounds like it's too late to spend time doing testing to confirm or not.

Aside from that, your list looks good.

EDIT: I'd put the headlight mods at the bottom of the list, priority-wise though, and put the grille blocks near the top.

Please post pics & road trip results!

[GMPG]

Originally Posted by MetroMPG

I'm wondering about that factory rear wing - it's interesting. But sounds like it's too late to spend time doing testing to confirm or not.

Aside from that, your list looks good. Please post pics & road trip results!

I was hoping you'd chime in!

That wing is an ugly piece of carp is what it is... several tank to tank tests over the same route (several round trips per tank, Ultra gauge and pump calculation) show no difference I can spot in overall MPG or MPG over the same stretch of road at the same speed. If it makes a difference it's too small for me to tell but it does make a BIG difference in cabin comfort to have it deleted.

Are there any tricks to get the air to reattach to the rear window that "should" work? As I said, no time for tuft testing. I can tell you that as it is rain runs straight down the middle and bows in towards either side somewhat at highway speeds. I'll probably just leave it alone unless someone has an idea I can slap on there today or next week on the way back.

I don't know if I'll have time to post up pics at the end of the day but I will take some, and more along the way and post them up in early October when I'm home. Maybe from the road if I get a chance.

[UltArc]

When people come here, ans say they have been lurking, I always wonder if they really have been. And then some people make a comprehensive list of their plan, ideas, so on, and it is evident they have been, and are genuinely interested.

So I can whole heartedly say welcome, we are glad to have you.

I once did a LOT of changes, and noticed a huge change, so now I try to do one change at a time. But that is me, I like to know exactly what is going on. I just finally did a speed chart to see my stats, so I will know what my changes are doing.

But if you get those changes done, you should see huge results. I PERSONALLY would do the airdam first, then rear wheel skirts. Then, instead of building the wiper thing, I would just put them in your car for the trip, maybe get some rain x. And a friend of mine here noted that his wheel covers did nothing for him. He did extensive testing. Please note that this does not mean they do not work, rather they might not make a calculatable change over your current rims.

But your plan sounds good, I look forward to reading the results.
EDIT:
I just saw your join date, CLEARLY you have been lurking for a while lol

[MetroMPG]

Originally Posted by GMPG

That wing is an ugly piece of carp is what it is... several tank to tank tests over the same route (several round trips per tank, Ultra gauge and pump calculation) show no difference

That's the difficulty of tank-to-tank comparisons.

It sure would be interesting to study it more though. Given the poor angles/shape of the rear of the car, it's definitely not a slam dunk which would be better.

Are there any tricks to get the air to reattach to the rear window that "should" work?

Not really.

The common solutions when you have early separation at the rear and want to make a smaller/more organized trailing wake are:

1) make a kammback
2) raise the entire decklid height
3) properly positioned/angled spoiler

Just for kicks, I'd also add to your list: taper & square off the rear corners of the bumper to promote clean separation there. This aero mod is turning up on lots of higher-efficiency designs, like the Prius, Volt, Honda Fit EV. Position them so there's some taper (~10 degrees would be safe) leading to the added "corner".

20 minutes to make with duct tape & some rigid bendable material.

EG: Honda Fit's rear bumper:

[GMPG]

Just a place marker with coastdown speeds and "hill coast" speeds which I'll check again after mods and before filling up (1/4 tank now) or packing the car.


Coast down:
42.56 seconds from 60mph to 35mph.
-------
45.24 seconds from 60mph to 35mph with mods
-mods, upper and lower grill block, air dam, hood cowl.

So 2.68 seconds longer to coast down

This is on as level a stretch of road as I can find locally, four timed runs in each direction and I threw out the high and low outliers. It's not science but it's something...

Hill Coast:
Entry marker 55mph
Mid point 62mph
Exit point 55.5mph

Hill coast with mods as above in this post.

Entry marker 55mph
Mid point 63mph
Exit point 57.5

Up 1mph at the mid point and 2mph at the exit. I also was rolling several mph faster when I hit the 35mph sign coming into my town that I normally hit right at 35mph while coasting.

This is a regular coasting spot for me, I usually coast out of gear but I can shut off the engine and coast about 1.5mi down hill, back up and down again to the next stop. The uphill even puts me right at the speed limit for the final downhill leg! (35mph)

Metro: I also used my ultragauge to try and test the real world MPG over the same road at the same speeds etc and could not see a difference as closely as I could measure it. I may or may not hurt or help but either way it isn't much of a difference. If I was keeping the car I'd think about a shallow kam back but rear visibility leaves much to be desired on this car as it.
Rear visibility was actually the main reason I removed the wing. I always hated the look of it but it also made backing up a rear pain because you couldn't really locate the rear of the car. I'm tall and it was an issue, for someone under 5'8" or so it might as well be a panel truck back there!

Next update will be post mods.

[TheEnemy]

Spend some time optimizing your route. I did that for a trip or two, even though the road speeds were slower we shaved off 30 minutes, saved a few gallons and even had a more plesant drive (back road through the mountains vs freeway).