alfadriver wrote: Porting, sure, but I'm not sure that LS Juan is an answer for an car that the engine was downsized from a 4v 1.6l to a 2V 1.3l engine just to get fuel economy. Unless, of course, the LS can get 45mpg in a Miata....
I do a lot of work on motors just like these, and would be surprised if that swap netted anything other than less power with no gain, and possibly a loss in fuel economy.
Some of you don't seem aware of this build thread- https://grassrootsmotorsports.com/forum/build-projects-and-project-cars/1994-miata-mpg-project-b3-stealth-mk-ii/61007/page1/
He has gotten 40mpg, and is looking to make it better.
One other note- I've done some thinking along the same idea- trying to get some real FE out of a Miata.
One of my ideas was using a gear set from an RX-7 that had a very tasty ratio set plus the lowest final drive available to fit in a Miata rear end. Numerically, that would resulted in engine to wheel rates that were very similar 1-3 for my current car, 4th that was taller based on the FD change, and 5th that was quite a bit lower. It would have resulted in a little over 1000rpm drop for my drive cycle.
Step 2 would be a 1.6 turbo build that would not be hugely boosted- but enough that a 5th gear crowd at 3000rpm would be the same as a 5th gear crowd at 4000rpm with my 1.8.
Going down that path is very effective at getting a lot of fuel economy- there are a number of turbos where the actual performance improvement isn't what the engine itself should have delivered, as it was re-geared to get a lot of fuel. Some really nice packages out there with a nice power increase and a nice FE increase at the same time.
So all of that dreaming and a few spreadsheets I did makes me quite interested in this build. Especially with the drive I have right now- I probably used WOT less than 100 times in the 14 years of commuting.
As far as fuel economy... original AE86 GTS was "corrected" rated @ 28 highway. I currently managed low 30s... while one of the race shops in Japan has managed to get mid 40s!
plus if you add in a bit of economy driving.... I currently have 2 friends who can managed upper 30s in an almost stock AE86
I've been involved in hundreds of economy builds, and in almost every case, there were little to no gains in using either more overdrive, or a taller final drive. More often than not, it resulted in less (sluggish) performance, and worse fuel economy. I'm not saying it wouldn't work here, but you know better than most that more gear doesn't usually equate to better fuel economy.
The 1.6 16V to 1.3 8V swap seems backwards in practically every single way, based on my experience. A little work on the 16V, and better fuel and ignition management would, in all likelihood, be a far superior combination.
Zomby Woof wrote: little to no gains in using either more overdrive, or a taller final drive
Without mods to support those changes, you won't see much gain unless the car was geared way too short originally. However, if you make aero improvements, taller gearing at highway cruise will get engine loading back into a more efficient range (better aero = less power needed to maintain speed, so you gear taller to get rpm down and throttle back up into a more efficient range). If you gear it tall enough to spend a lot of time in fuel enrichment, you'll gain nothing, but otherwise, more load is generally more efficient.
Zomby Woof wrote: I've been involved in hundreds of economy builds, and in almost every case, there were little to no gains in using either more overdrive, or a taller final drive. More often than not, it resulted in less (sluggish) performance, and worse fuel economy. I'm not saying it wouldn't work here, but you know better than most that more gear doesn't usually equate to better fuel economy. The 1.6 16V to 1.3 8V swap seems backwards in practically every single way, based on my experience. A little work on the 16V, and better fuel and ignition management would, in all likelihood, be a far superior combination.
Go read his build thread, I have had a couple different 1.6 Miatas over the years and I never got over 30mpg no matter how I drove. This guy is getting over 40mpg with I believe no aero mods to speak of.
chiodos wrote:Zomby Woof wrote: I've been involved in hundreds of economy builds, and in almost every case, there were little to no gains in using either more overdrive, or a taller final drive. More often than not, it resulted in less (sluggish) performance, and worse fuel economy. I'm not saying it wouldn't work here, but you know better than most that more gear doesn't usually equate to better fuel economy. The 1.6 16V to 1.3 8V swap seems backwards in practically every single way, based on my experience. A little work on the 16V, and better fuel and ignition management would, in all likelihood, be a far superior combination.Go read his build thread, I have had a couple different 1.6 Miatas over the years and I never got over 30mpg no matter how I drove. This guy is getting over 40mpg with I believe no aero mods to speak of.
I don't know what you were doing, but even with 4.30s, my 1.6L Miata gets 35mpg on the thruway
I was getting mid 20's in my 1.6 Miata, then I replaced the front wheel bearings and I was back at 30-32 mpgs. I wonder if I replaced the plugs and wires when I did the bearings...
whatever you do, please revisit the intakercooler/hot air intake!
In reply to alfadriver:
I didn't describe what I was envisioning in my mind with trying to keep the runner cross-section as similar as possible from the plenum to the port. My line of thinking was something like "the best flow that will keep fuel off of the port walls is going to be as laminar as possible" and having some kind of constriction could result in air "backing up" at the area of the constriction, resulting in turbulence and increased heat in the air/fuel gas stream reaching the cylinder.
Plus I really don't think that making the intake runners larger is going to help that much if Ford/Mazda/Kia didn't think it was needed. Does the above make sense?
I wonder what kind of help some more aero work could do for this car. Has underbody aero been touched yet?
In reply to pres589:
Got it- I was wondering what you meant.
I'd have to go re-read the thread, but with the aero changes on the nose, I seem to recall the idea of putting in a full belly pan.
In reply to Zomby Woof:
I know a lot depends on a lot of other things.
But I also know that having an engine spinning at 4000rpm cruising down the road can be improved on greatly. That's what Miata's do at 70mph.
And I also tested the Solstace Turbo, which was considerably better on fuel than the NA car was- a lot of it had to do with the gearing matching with the increased performance.
Like was already posted- go read the thread. He is getting 40mpg. Better than I ever got.
Wow, I missed a lot of this discussion... sorry, its been some long days at the office.
For the folks not familiar with the project, the car gets 40+ mpg without doing any special driving tricks... just jump in and drive. The mpg vary depending on air conditioning or other nonsense but the car never dips below 40. Sometime I see 45...not too shabby.
The car was built to commute and is surprisingly quick off the line. The engine develops all its torque at a lazy 3000 rpm and when coupled to the Miata transmission this works out great. The transmission has been modified with an RX7 5th gear but 1st through 4th are still fun gears. The most recent HP calculation indicate the engine is producing only 74HP... meh it could be worse.
The goal is to get the average up to 50 mpg. I got a lot of problems sorted out just before it started snowing and the goal may actually be achievable this year.
Doc Brown wrote: The goal is to get the average up to 50 mpg. I got a lot of problems sorted out just before it started snowing and the goal may actually be achievable this year.
Get another head... 1) CAREFULLY port/blend the bowls and seats. 2) Check all combustion chambers for poor quality casting, improve chambers, and equalize chamber volumes. 3) perform a multi-angle valve job on the seats, and back cut the valves.
What you are doing is improving what is already there by taking a mass produced part and improving its efficiency, and capability.
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