cam overlap, engine preformance

[silvermazda]

Small introduction, I have had a 1.8L mazda miata for 3yrs and its given me fair mileage over the years, but am thinking of improving it.

Back on topic:
I sorta am getting into diesels...I know disapointing, but I dont wanna sell the miata. I really dont like the suspension on FWD's or how they feel, though havent tried a manual FWD.

I got a quesition, is there a way to lean out AFR's on the stock ecu (obd2). I'm looking to limit myself to 30% max power about 80% of the time (horrible city traffic) and then flick a switch (if circuit based mod) to go back to stock. Is there such a thing? Should I be concerned about burning valves?

2.Feel free to add suggestion for RWD sports cars, I can find to many that help.

thanks and keep on

[Stacygifford]

I have never really seen it done on a Miata however, if you have the time to wire in a wideband o2 sensor I don't see why you couldn't do it. Innovate motorsports makes a digital wideband that you can program to act as a narrow band that has a switching point other than 14.7 to 1.

this is assuming that the car uses a narrow band from the factory. I have never really worked on the Miata, but most Mazdas and most cars in general have a narrow band o2 sensor. I don't see why you couldn't wire in a switch that you could alternating between the two of two sensors. Of course this would have to be a dual position switch. With the switch wired in such a way the signal wires are selectable.

The only problem is if you go too lean you will throw a code for the secondary o2 sensors.
If you go even more lean... kaboom. By-by engine. .. i would never go leaner then say... 17 to 1, 16 would be safer.

Here is a link to the o2 sensor I am using on my track car.

Innovate Motorsports 3844 MTXI WDEBND UEGO GAUG KT

All this being said. I feel like a 5speed would be a more cost effective upgrade.

[silvermazda]

Thanks, I've been using a mtxl for the last 2yrs and if the aftermarket ecu wouldve worked..I'd have a different story to tell.

Yes its a narrow band. When I only installed the wideband and needed the car the ecu picked up on it and set a factory preset map. I'm guessing I can trick a sensor with a resistor or rheostat to adjust to my liking. If I were to use the narrow band output on it it would set a code. I hope keeping it dumb or without signal would allow me to go as down as 18/20:1 as there is less power down there, hopefully I could run more open throttle (reducing pumping losses), and reducing heat as there's less gas to burn hence less heat to burn valve. On the cat temp/ect you're right; a leaner burn will burn slower and maybe peak temps will be seen at the cat, but then my cat is 15yrs old and barely passed emissions, so as I see it I will be trying mods with this and the next one will have a happier life once I got decent figures/values dialed up. (might have to find a lean burn cat off a insight)

[silvermazda]

Main Post


Here's my plan right now:
-Do mods to allow for more open throttle/detuning
-Adjust intake camshaft to mimic what the prius "atkinson" engine is doing, which is pumping out air out of the piston to burn less, though I thing my ecu would have a hard time not pumping in a decent amount of fuel-aka misfires because fuel gets squirted in with the air, then its being pumped out to the intake manifold.
-Cover up the large mouth opening as my miata doesnt need a 30" radiator opening, just a 6" circle when autocrossing/spirited driving, with my granny driving I'd say 4" would be sufficient.
-Adjust cooling capacity for 180*F thermostat, the factory 192 keeps it hot and makes it prone to jumping to 215*F where factory ecu dumps fuel to cool artificially. Dyno testing has proven 200*F coolant temp for ideal hp/torque figures AKA piston rings working their best.

Already done:
-removed jack and spare tire 20+5.4=25.4lbs
-AC system approx 40lbs
-smaller batter 7lbs vs stock 21lbs =14lbs
-removed a panel or two =10lbs
-exhaust manifold iron vs steel =18lbs
-removed PS pump =10lbs
-parts store brake rotors cheaper =12lbs
-no PS AC belt (friction points)
-one belt running WP/Alt
-Mobile 5000 conv oil 5w-30

Planned:
-10lbs wheels [current 13lbs]
-13lbs tires 175/60-14 ~400 thread wear (insight had 165/65 that weighed similar, but these are more cost effective, federals FD2) [current 18lb 300 threadwear]
-partial grill block


Aero: 18ft sq frontal area x
-.37Cd with convertible up
-.44Cd with top down
-.3XX with hardtop option (approx 3mpg highway know improvemnt)

[cRiPpLe_rOoStEr]

Originally Posted by silvermazda

Adjust intake camshaft to mimic what the prius "atkinson" engine is doing, which is pumping out air out of the piston to burn less, though I thing my ecu would have a hard time not pumping in a decent amount of fuel-aka misfires because fuel gets squirted in with the air, then its being pumped out to the intake manifold

Some folks claim that it ends up acting like a "chemical intercooler".

[Stacygifford]

I would highly highly advise against running 20 to 1 air fuel ratio s on that engine. The only reason the Hondas are capable of running so lean is because they are designed to do so. Running under any form of acceleration or any load at all for that matter on an engine that is not designed to do so will cause catastrophic failures. I'm talking burning holes all the way through the top of the pistons.that is not to say that it can't run slightly lean, but that is an entirely different story.

if it were on a system to where it would switch between lean and a normal air/fuel ratio based upon engine load ( map sensor readings) that would be completely doable and in fact, it would probably be relatively easy to wire up if you had a wideband o2 sensor and a standard o2 sensor you can switch between.I don't want to sound like a negative nancy or a jerk I'm just speaking from experience lol.

As for your adjustable cam gears you could very well just advanced the intake a few degrees and really optimize low rpm cruising by giving your engine valve overlap. and by doing that with an adjustable cam gear you could even potentially get rid of the need to retune your ECU.

of course, retuning the ECU would be optimal. However, it may not be completely necessary with minor timing adjustments.wild teen cream with a 1.8 liter dual overhead cam Honda I found that getting rid of some cam overlap in the low rpms help tremendously with low rpm torque and driveability. it did lose some high rpm power though.

[Stacygifford]

either advanced your intake cam by the one and a half or two degrees or retarded the exhaust cam by the same amount you would just have to test and see. This is under the assumption that that card is not already have a variable cam timing system.

[iveyjh]

Originally Posted by Stacygifford

I would highly highly advise against running 20 to 1 air fuel ratio s on that engine. The only reason the Hondas are capable of running so lean is because they are designed to do so. Running under any form of acceleration or any load at all for that matter on an engine that is not designed to do so will cause catastrophic failures. I'm talking burning holes all the way through the top of the pistons.that is not to say that it can't run slightly lean, but that is an entirely different story.

if it were on a system to where it would switch between lean and a normal air/fuel ratio based upon engine load ( map sensor readings) that would be completely doable and in fact, it would probably be relatively easy to wire up if you had a wideband o2 sensor and a standard o2 sensor you can switch between.I don't want to sound like a negative nancy or a jerk I'm just speaking from experience lol.

As for your adjustable cam gears you could very well just advanced the intake a few degrees and really optimize low rpm cruising by giving your engine valve overlap. and by doing that with an adjustable cam gear you could even potentially get rid of the need to retune your ECU.

of course, retuning the ECU would be optimal. However, it may not be completely necessary with minor timing adjustments.wild teen cream with a 1.8 liter dual overhead cam Honda I found that getting rid of some cam overlap in the low rpms help tremendously with low rpm torque and driveability. it did lose some high rpm power though.

I have been running up to 22.4 to 1 AFR in my 2000 Metro for a couple of years with none of problems you speak of. I run an EGT sensor and have found that running lean actually decreases the combustion temps. A little lean from stoich under load produces hotter temps.

[vskid3]

Have you considered doing a Prius engine swap instead of trying to make your current engine emulate one?
http://ecomodder.com/forum/showthrea...fxe-27266.html

[Stacygifford]

Originally Posted by iveyjh

I have been running up to 22.4 to 1 AFR in my 2000 Metro for a couple of years with none of problems you speak of. I run an EGT sensor and have found that running lean actually decreases the combustion temps. A little lean from stoich under load produces hotter temps.

An EGT gauge/sensor would be a must have. The temps under load is the concern. For normal causing (for someone who drives economical) it wouldn't cause a problem.

However the problem arises whenever aggressive driving styles come into play.