seeking aero advice

[philip1]

I have a 2003 Saturn LW200 2.2 4-speed auto. I am trying to squeeze every mpg I can out of this car.

Here's what I have done so far:
warm air intake (I may convert it to a hot air soon)
2.25in exhaust from engine back
lowered suspension
((I used to race this car so these were done for power not economy))
upper grille blocked (I'm planning a lower grille block soon)
small lip spoiler (trip strip) on tailgate
tire pressures at 44 psi (max rating on sidewall)

I guess my questions are where to go next and have I done any aero damage with additions (such as the lip spoiler).


I am looking at a belly pan. The window screen thing has my complete attention. I am also looking at fitting a hard tray between the bumper and radiator support so the air sent to the radiator goes there and not anywhere else.
I am hoping to see 40+ mpg

[SL8Brick]

Re: the rear lip spoiler...

I have one of these on my Volvo wagon...http://www.jcwhitney.com/autoparts/Product/tf-Browse/s-10101/Pr-p_Product.CATENTRY_ID:2011299/p-2011299/N-111+10201+600001926/c-10101
http://gallery.newbug.org/albums/volvo/20070612_161754_3072x2048_57590.thumb.jpg
I have the 1" high version. They're very flexible and can be easily bent to contour to a rounded rear roof line. They can also be profesionally painted to match. Personally, I like the practical benefits and anti-lift characteristics of the rear lip when applied to a two-box...but I'm sure there are others here who will disagree with that.

[philip1]

yep thats the one

[SL8Brick]

yep thats the one

Any close-up photos of yours?

[philip1]

I'll have to get some when it's light out

this is the best I have so far
http://216.77.188.54/coDataImages/p/Groups/335/335411/folders/262132/2098637PICT2510.JPG

[kamesama980]

2.25" is way bigger exhaust than you want. 2.25" is perfect for my toyota 3l revving engine. Your domestic 2.4 will probably do better with a 2" (quality exhaust!!) or so unless you get the revs up. reason is you'll lose exhaust velocity and low-down torque meaning you'll have to use more gas. basically, exhaust size determines peak torque point and powerband distribution. 2.5 collector to axle to a 2.25 axle-back on my 3l puts the power peak OVER 6k rpm. 2" with cat and both mufflers put it about 4.5-5k. You want the peak efficiency to be where you spend most of your revving time: in an economy mindset, at or around acceleration and highway rpms.

Course then again maybe the ecotechs are wierd sobs and do best with a big big exhaust.

I suppose I should also qualify that it depends on how good the exhaust system is. if you use a free flowing cat and muffler with mandrel bent pipe, you'll want 2" or less. if you get regular press-bent with wrinkles, crimps, and normal mufflers, 2.25 might be necessary to make up for the inefficiency of the system itself.

[philip1]

I used to race this car incase the photo was not a total give away. this exhaust size was determined by several factors.
1. VE at 5800rpm needed flow conducive to 2.25in pipe
2. 16 valve head flows more than 8 valve
3 10:1 compression
4. Dyno results indicated a 5-7hp gain across the board

this means nothing to FE unfortunately just a loud drone

BTW: I can't remove the roof rack due to the factory installed curtain airbags.

[Dynamically Aero]

Here's another source (http://www.buyautotruckaccessories.com/product.cfm/cf-bin/pn.jsp-katana-lip-spoilers) for the spoilers.

[kamesama980]

Like I said, I don't have experience with the ecotechs.

well if you're looking for 5800 rpm power, go for it. I've seen people do too big exhaust on cars and lose (usable) power and mileage because they shifted the exhaust velocity peak above redline. Drive an Infiniti G20 with open downpipe vs full ehxuast...revs great and huge power on the highway and crazy high rpms but you can't drive with it under 3k rpm. put the exhaust back on and you can chirp the tires at 2k rpm.

[philip1]

if I could I would go back to a stock cat back at least

[philip1]

OK now that we have established my exhaust is too big how about some aero help....
I am looking at the area directly behind the bumper it is open to the ground so the air intended for the radiator is free to go wherever it pleases. I think I'll close the open space under the nose and then block some of the lower grille

[brucepick]

OK now that we have established my exhaust is too big how about some aero help....
I am looking at the area directly behind the bumper it is open to the ground so the air intended for the radiator is free to go wherever it pleases. I think I'll close the open space under the nose and then block some of the lower grille

Sounds good. "Clean-sheet" it from the lower bumper edge to as far back as you can get it. For me that meant near the front axles line, due to the steering and suspension gear there. Coroplast is good; I used really thin lauan plywood; 2.7 mm. Plenty of airflow so it stays dry + doesn't rot. Or prime with oil base house paint.

See if there was a baffle or deflector to grab air from center vents at lower bumper and direct it up to the radiator (if needed for your car's layout). They get lost sometimes. A friendly dealer service shop might tell you. Or check in junkyards.

[philip1]

I purchased the car new and I did ask about that. I was told it never had one and never was intended to have one. after crawling under the car I am tossing the BS flag. I will make one out of luan or aluminum and then block the grille a bit.

[philip1]

I have the grille block done upper and 90% lower I noticed that the heater has more affect on the engine temp so I may open it up a touch till I get the tray done.

[philip1]

I have screened in the belly of the wagon and if nothing else the wind noise is reduced. I am currently above 1/2 tank and 210 mi which is far better than the car has ever done in the past. I am cautiously optimistic that I may see 450 mi on this tank.

[Hasbro]

Pics?

[DRW]

'Screened in the belly?'
I haven't heard of this before. Is it as simple as it sounds? Just attach a layer of household screen door/window material to the underside of the car?

[philip1]

I used industrial aluminum window screen. I got the idea from this site and this thread... http://www.gassavers.org/showthread.php?t=5613


I will post photos of mine after it stops raining

[SD26]

I've thought about using screen too. Would it just make enough turbulence to develop kind of a "air wall" that air would just continue flowing past cleaner? Would like to do under my trailer, maybe the bus.

[brucepick]

I've thought about using screen too. Would it just make enough turbulence to develop kind of a "air wall" that air would just continue flowing past cleaner? ...

See the thread quoted two posts above.

You can paint the screening and omit the paint around the exhaust or any other parts that might need ventilation. The paint fills in the gaps in screening. I found some latex/acrylic paint for aluminum and galvanized steel; I used it on stainless for another project and it bonded very well in spite of the fact that almost nothing bonds to stainless. I hope to "screen" the bottom of my car this coming spring.

[philip1]

for those who requested photos they are up in my garage profile. TBH I'm not totally happy with the screen but I think it is due to the exhaust at the rear of the car being lower than stock. I am currently planning to re-do the front in something more solid. and I am looking for a stock exhaust so I can get rid of the BUMP under the rear of the car.
http://www.gassavers.org/garage_images/l23czc4muk69u594xups.jpg

[ChrstphrR]

I used industrial aluminum window screen.

Phil,

Could you let us know where you got hold of that screening? It looks like from your pictures, that it spans continuously. Most of the sources I've looked for screening at don't have very large widths (usually 36 or 54 inches wide).

I like the look of it, and I hope you have good results from that next tankful. :)

[philip1]

I bought it at a ma and pop hardware store local to me. I had never seen it in 60in widths till then so I bought 20ft. if I make it back to the store soon I'll find out the brand and such.