lets face it. gas prices suck and our beloved FC's suck way more gas than they should for the power they put out.

so.... i wanted to start a discussion about fcs and fuel effeciancy, what we can do to improve it, what the effeceincy ceiling may be for an RE, and also discuss the mods im going to be trying on my car over the summer to maximize my MPG.


to my knowledge, the things that make for a more effecient engine almost always make for a more powerful one.

this would include:

minimizing pumping losses by reducing the restriction of intake and exhaust.

running as close to stoichiometric or as lean as possible before risking detonation

insuring full ignition of the charge by keeping plugs/coils in top shape or upgraded.

geting cooler air into the engine.

granted, moding your engine to make 400hp is gona kill effeceincy, but i geuss the whole point is to make it EASIER for the engine to ingest about the same amount of air, not necissarily ingest lots MORE air.


ok, that aside. here are the plans for my car.

what i have that matters:
stock block s5 na motor at about 35k miles
running premix.
RB header and exhaust
recently made CAI (picks up just inside the fender below the old airbox)
all emeision removed
no p/s a/c or air pump pullies (less drag)
functional 5/6 and vdi
royalpurple oil in tranny and diff.
generaly well maintained, a good strong engine.

and what i plan to add:
-denso iriduim leading plugs, ngk platinum trailing.
-an msd box and some blaster coils on the leadings.
-some minor intake/tb porting and polishing. mostly just gasket match and polishing, polishing primarily before the injectors)
-get the undertray back on.
-do a full tune up
-drive eaiser (this will go a long way, but the mods are gona help too)

and the real kicker: an SAFC.

now i know you can make good power gains by leaning out the upper rpm range, but has anyone tried to use one to gain MPG by leaning out the lower rpm/partial throttle settings?

how good is the stock EMS at doing closed-loop feedback during crusing conditions? could anything realy be gained here?

could the safc be butt-dyno tuned until the power starts to fall off (thus leaning out beyond stoich.) in cruising conditions, or do i still need a wideband to do it right and not risk dmamge?

im getting about 18-20 mpg mixed right now (as long as i dont go out and do hot laps on my favorite roads, hehe)
i want to get up to at least 22-24 mixed mpg and am going to shoot for 30mpg on the highway.

can it be done? is this a good way to get there?

any thoughts or comments welcome.

-andy

 

i run about that on a street ported TII (even with a couple time up to .8bar)

so i think there is some room for improvements

 

beat you to it, I installes a s-afc when i put my nitrous in, but I've since taken out the nitrous (not the s-afc)

I've notice very good gas milage, but what strikes me even more, is that I get good gas milage, when I'm cruising at 90 + miles an hour on the florida turnpike.

Seems to be a really effecient car now, especially for long trips.

I followed a friend of mind in his turbo fc and when we got to our destination he had 1/4 tank of gas, and I was still on 3/4!!

Very good idea, and an easy cheap upgrade. It really does pay for it'self!! (no infomercial reference intended)

 

btw 30 mpg easy using cruise control, I'd say it'd even be better using a s5 because of the better throttle position sensor.

 

huh, yeah i didnt think of that. i should put my cruise back in, but i think im pretty good about keping the gas steady when im cruising on the highway. well, when i want to.

 

So an S-AFC makes that much of a difference even on a N/A? cool maybe i'll have to pick one up sooner than planned...

 

Me to. yheeiii

 

how bout improvements on a T2?....i cant stand paying 2.05 per gallon but the t2 also doesnt run without gas....

 

Make sure your tire pressure is at 32 psi. And you have an alignment. Those two things could hurt your gas mileage.

James

 

You would think Mazda would build every possible improvement into the Renesis. Why does it get such terrible mileage if you guys can squeeze 25+ mpg out of your s4s and 5's?

 

Tune it with a wideband!

I plan on doing that with an AFC (not purchased yet) and an Innovative LM1 I picked up cheap from www.SPLparts.com this weekend...

Use light wheels/tires with proper pressure, great alignment, windows up, no AC, cruise control on, etc.

 

I get about 17-18 MPG mixed, but thats with plenty of spirited driving. I've been doing a lot of highway driving lately because I was looking for/moving into an apartment in Killeen (about 30 miles from my house). I was getting 20-22 with mostly highway, but that still included some spirited driving. That last time I filled up, I got over 25 MPG, so I know its possible. Once I get an s-afc it should get even better. Also, why are you getting Denso leadings and NGK trailings?

 

those of us with 6 port N/A,

pineapple racing sleeves

 

well the pinaple sleves would only help (maybe) if you are going over 3800 rpm. but thats not exactly the best way to save gas, so i dont think they would realy affect it much.

 

we got 25ish in a ported t2 with a full t4 on the freeway.
hell the 20b gets 19 on the freeway.

make sure the 02 sensor is good, and the ecu stays in closed loop and you're good, or go standalone and tune it leaner

 

I get 25 mpg on the highway in my 86 n/a. I have an MSD on the leading coils, RB header and presilencer, 2.5" pipe to a single muffler, K&N, stuff removed, TB mod, and a couple other small things i'm sure most have.
I got a little better mileage in my 88 that was everything above plus ported intake, advanced timing, and modified MAF.

 

Man all u guys are lucky i get about 14-17 mpg on average and i even have a new intake and exaust. gas just hit $2 here so i love griving my RX vs my 83 chevy pickup truck which got adout 1/2 the gas milage my RX gets. but im just going to stop driving once gas hits $2.50 here lol problem solved

 

Before Baby turned into a smoke bomb she was getting a consistant 19 MPG in the city. Pretty good for a 15 year old 216,000 mile car.

 

1) going from a 100:1 ratio down to 85:1 on the premix saved me about .2 to .3 gal per 200 miles, but I learned your rotor oil seals have to be in good shape, or your engine oil tends to "collect" the gas/ premix more than the 100:1. Definite fuel economy improvement, though, I kept track of mileage through 8 fillups, now back to the 100:1 due to the excessive blowby, the rebuild is soon...
2) if you're n/a and have control over the 5/6th port opening pressures, open them sooner, at 3000 or so, and the secondaries won't kick in 'till later (about 4500) when you really want 'em to, instead of that annoying 3800 surge right before the shift during "normal" driving (because of the secondaries kicking in when ya really don't want 'em to- how much gas has that wasted over the life of our cars?)

 

i have changed the o2 recently. how would opening the 5/6 early keep the secondaries from comming on?

 

Good question- I can only speculate... when the ports open early, the manifold vacuum drops due to the extra air. The boost sensor sees this drop, and since the numbers don't agree with what the ECU thinks should be there at that RPM, I get a boost sensor code every time I romp on it (no prob, doesn't affect performance). Anyway, since the boost pressures just dropped, the engine has to rev even higher before the "right" boost pressures are sensed by the ECU to fire up the secondaries (that 4500 point I was talking about)...I don't know if I really like it set up this way or not, but I know I didn't like 'em kicking on at 3800 (I like shifting around 4K)- it's a waste of gas...which is the topic, right?

 

Boost sensor code? I thought you were refering to an N/A. Just curious becuase I have an N/A, and building an rpm switch soon...later

 

The N/A's have boost sensors, the T II's have a pressure sensor..


No, i'm not kidding.