Quote:
Originally Posted by MetroMPG
Great - added a few pics and links to your YouTube vids in post #1.
What an impressive build - congratulations.
As for the goal of better highway economy, have you compared the Miata's CdA (drag coefficient x projected frontal area) with the Metro's? Aero losses outweigh everything else above ~25-30 mph.
FYI, the default values in the aero/rolling resistance calculator here are for a Metro of the same specs as your engine donor: Aerodynamic & rolling resistance, power & MPG calculator - EcoModder.com
I saw you mention the hard top option as a potential aero gain. If you're talking about the tapered aftermarket "fastback" hard top I've seen in pics of some racing Miatas, it will likely help. The OEM hard top, probably not so much. |
Thanks for all the interest! I see I have a lot of questions. Hopefully I can answer most. If I miss something ...ask again.
Hardtop and aero mods...
According to the Miata folks... there is a MPG increase when the factory hardtop is installed. I seem to recall the increase is about one - two MPG. A used hardtop generally cost $500-$800. An aftermarket fastback looks great but is very costly. I can justify the expense of a factory hardtop because I have a 2nd Miata that I want to get a hardtop for.
The Miata sort of looks aerodynamic but is not an optimized shape for speeds greater than 40 MPH. Drop the top and it gets worse.
Probably not a good car to start with but I like Miatas ...so I centered my project on this chassis.
I realize my choice of body-style and drivtrain configuration will limit the results and 60 MPG @ 65 MPH is probably impossible.
Quote:
Originally Posted by MetroMPG
It makes a noticeable difference in low-end torque. I added an XFi camshaft (OEM fuel economy cam similar to 3tech's economy version) to my car. Though I didn't try to measure the change in fuel consumption (too difficult to get an accurate A-B-A comparison). http://ecomodder.com/forum/showthrea...leted-102.html
In combination with switching to the tallest possible final drive (for reduced highway cruising RPM) they made for a good combination. http://ecomodder.com/forum/showthrea...-gain-107.html
But my driving environment is very different from yours: I never take the freeway. Always secondary roads, so I'm rarely above 55 mph. |
FXi camshaft
I'm really interested in a FXi camshaft experiment. The car currently has a 3tech 6* cam sprocket and the car seems to run better at highway speeds.
You probably read about the 3tech cam sprocket experiment I did. The results were more or less inconclusive because of the winter fuel reformulation. I eventually decided the 6* cam sprocket was better than stock but I'm going to do the experiment over when the summer blend is back on the market.
Another reason I'm unsure about the whole 6* cam sprocket is I discovered my GPS is flaky. The GPS crashes and the touch screen is always detecting phantom touches.
I did manage to get a few good numbers from the experiment that leads me to believed the sprocket may be a benefit.
I had an additional mishap and lost the sensor for the vehicle speed. Something really bad happened underneath the car and I haven't had a chance to look.
So... back to the FXi cam......
You indicate I may see some improvement with an XFi cam and taller tires or a lower gear ratio. Sort of use the torque and not HP to move the car. I can see your reasoning.
Lowering the car....
I'm sort of in a tough spot with this car right now. This Miata was perfect for the original experiment but it is almost imposable to alter. Rust is the issue that I have to deal with ... and everything on this car is rusted solid.
I want to lower the car 1-2 inches but I fear bad things will happen once I start to disassemble the suspension. This is an issue I'm debating and the only real answer is to get another Miata to drop the three cylinder engine into.
Emissions.........
I worked many years in an emissions laboratory and I'm familiar with the rules manufactures need to adhere to. NOX, HC, CO... and the balancing act to get it all to work.
I'm just not a rule follower.
Perhaps someday I'll sort it out.
Money....
nobody asked, but I'm cheap. Playing with cars is a hobby. Realistically I can spend lots of $$ and get outstanding results. .... but I'm in it for the adventure and challenge.
The other car....
I'm very happy with the G10 Miata but I decided to do a second build with a slightly bigger engine. This second build has put the G10 sort of on the back burner. What I'm saying is I'm delaying transplanting the three cylinder engine into a nicer car.
I continue to drive the G10 and experiment with it but unfortunately it will remain a rusty car for a little while longer. I really need to get a show on Discovery Channel or something.... seems like everyone else has one.
Anyway the other Miata I'm building has a 1.3 Ford Festiva engine. the link is
Project B3 STEALTH. A 63HP Festiva powered Miata - MX-5 Miata Forum
I did a lot of research and prep work to make the B3 project something that can be duplicated.
Jim