Modding a Scion Xa

[MTXA]

I'm waiting on warmer weather too to start conjuring higher mpgs out of my XA. I have a round trip drive to work of three miles, max mph 25, and am averaging 23.7 one way mpg. My XA stays in open loop 2/3 of the trip. Recently I took a trip of 90 miles round and averaged 42.5 mpg. This was on mildly hilly two lane country blacktop with about 3 miles of town driving. Not too shabby considering I was burning winter grade E10 and the outside temp was around freezing. I never exceeded 52mph and drove with load, coasting on the downgrades. I know it could have been better but I was plagued with tailgaters that messed with the neutral coasting on downgrades. I have a manual trans XA and find the mpg sweet spot at 52mph @ 2250 rpm, usually in the mid 50 mpg range.

So far, the XA is stock with the addition of an Ultragauge and 40 psi in the tires. Possible mods include aero improvements -smooth the nose, drill the rear bumper cover (pure parachute!), air dams, outside mirror delete; mechanical mods - tank heater, battery tender, fuel pump relay toggle switch, warm air / cold air intake, alternator cut out and whatever else looks promising.

I'm looking forward to see what kind of improvements this thread bears.

[nbleak21]

MTXA, if you have a heated garage, or install a block/coolant heater, you can get that number up higher. I have 1.5mi of city travel prior to hitting the interstate, and have noticed quite a gain from the combination of parking the Acura in my garage (iat approx 65F) as well as the trickle charger overnight. Those two changes alone have brought me up from 17-19mpg to 23-25mpg during that 1.5 mile portion of the trip.

I like your list of proposed mods... I'd include a grill block, which has several possible benefits: slight aero, quicker warm ups, and helps aid in wai applications.

I am curious to the fuel pump relay mod... I've heard of people doing such as an anti-theft device, but have yet to come across reasons for FE... What is the reason behind this?

[sustainable sam]

I am averaging about the same on my 2.5 mile commute. Have you consider a rear underbody panel instead of drilling the bumper?

[MTXA]

To answer nbleak21: I garage the XA at home but I don't heat my garage. I'm looking at a 750 watt tank heater at the local Farm & Fleet coupled with a timer for my commute to work. I work second shift and pull the car into the shop a couple of hours before the end of my shift so it is warmed up (if I didn't I'd be almost home before I could defrost the windows).

Some good friends of mine run an automotive upholstery business and I'm going to see if they could sew up a full nose bra that has vents that I can open when the weather gets warmer. I'm also considering building grill shutters controlled with blend door stepper motors. I've been looking for a damaged grill to build it with.

The fuel pump cut out will be a normally closed switch that will control the ground circuit of relay so I can shut off fuel during coasting without shutting off the ignition. That will keep me from potentially locking the steering wheel by using the ignition switch and also keep my short trip data stream alive

Answering Sustainable Sam: I've put the XA up on the shop hoist a couple of times to do an engineering study on a belly pan. If I went that route, I would prefer to use sheet aluminum that has been louvered to dissipate heat. The sheet aluminum I can find easy enough but I don't know of anywhere local that has a louver press though I suppose I slice and peen it. Because most of my driving is non-highway, I'm considering just making an air dam and side skirts out of heavy duty landscaping edging and drilling the rear bumper cover with large holes to vent it. My XA spent its' first seven years in downtown Chicago where they park by feel, so the bumper covers are already pretty dinged up. Right now, I'm mainly seeing what others have done so I can pilfer their good ideas. I've been looking for a decent book on automotive aerodynamics but so far it is pretty slim pickins.

[nbleak21]

Originally Posted by MTXA

To answer nbleak21: Some good friends of mine run an automotive upholstery business and I'm going to see if they could sew up a full nose bra that has vents that I can open when the weather gets warmer.

That is an excellent idea!

I have considered the louver idea as well, but ROI just wasn't worth it with the setup I wanted to do.

The fuel pump cut out will be a normally closed switch that will control the ground circuit of relay so I can shut off fuel during coasting without shutting off the ignition. That will keep me from potentially locking the steering wheel by using the ignition switch and also keep my short trip data stream alive.

I would consider a fuel injector cutoff over fuel pump, unless they are on the same circuit.

Cutting the fuel pump alone would cause all the residual pressure to still be released during injector firing, this can cause overly lean firing, fuel pooling, air in the fuel system, etc... Furthermore, for correct operation upon reignition (via bump starting or clutch) the fuel system needs to be at proper PSI, meaning after fuel pump shutoff, the pump will have to re-prime the system, causing the same problems describe above, except under load, which is definitely not good.

[MTXA]

Shutting off the fuel pump should result in only a second or two of lean running before the engine stalls. The system should re-pressurize in a second or so when the relay is grounded again. The biggest problem that I would be concerned with is on the restart the 02s would likely command rich so the savings may not be worth it. I could also open the grounds in the injector circuit to maintain fuel pressure but I would be concerned about spiking the ECM from the field collapse.

[Sven7]

Originally Posted by MTXA

I'm considering just making an air dam and side skirts out of heavy duty landscaping edging and drilling the rear bumper cover with large holes to vent it. My XA spent its' first seven years in downtown Chicago where they park by feel, so the bumper covers are already pretty dinged up. Right now, I'm mainly seeing what others have done so I can pilfer their good ideas. I've been looking for a decent book on automotive aerodynamics but so far it is pretty slim pickins.

Go with the air dam and side skirts. The rear bumper actually holds in a high-pressure bubble of air that provides a "phantom" belly pan against the surrounding low-pressure air moving past the car. It's much like the benefits of keeping the tailgate up on a pickup truck.

Drilling out the bumper invites all that low-pressure air to go swirl around the bumper area and creates extra drag. If you're worried about that area, design a partial belly pan that starts at the rear axle and goes back from there (level to the ground for a hatch/wagon profile).

This is the ecomodder's aerodynamics Bible. Aerodynamics of Road Vehicles - SAE BOOKSTORE Whenever someone mentions "Hucho", they're referencing this book.

[sustainable sam]

I don't think the xa would benefit much from an airdam, the front already extends to the lowest point of the car. I picked up two sheets of coroplast today. I think it will be wheel covers and wheel skirts to start and then I will work on reducing the wake with a kammback.

[sustainable sam]

I made a little progress with some wheel covers.

Before:


After:


Overall I think they look pretty good and they are wife approved. I am not sure how many mounting points are needed. I accidentally poked holes for each spoke. I have had no luck finding the image with the effect of wheel covers on cd. Anyone have an idea? I still think the wheel arch gaps are awful on this car especially the back. This will be the next thing I tackle.

What do you guys think?

What do you guys think?

[MTXA]

Here is a link to a thread with A-B-A testing of full wheel covers: http://ecomodder.com/forum/showthrea...-6-a-4368.html

I noticed the bumps on the rim between the spokes. They look like an excellent attachment point for the covers if you drill & tap them for screws. It would look a little more hot roddy too.

The rear wheel arches on the XA are going to be difficult to close up. After giving the arches on my XA the scrutinizing squint, I'm inclined to make the rear skirts over a stressed skeleton frame made from light gauge aluminum flat stock. That is the only way I can see to fill the whole arch due to the curvature.