RkTek 858 a/f ratio numbers to aim for?

Sunvang · Jan 19, 2015

Hi.

I know there are alot of rktek 858 threads out there. But can't find any recommendations for a/f ratios, besides WOT.
What numbers for what rpm is recommended?
Ive tuned several Boondocker turbos before, but this is my first big bore, and want to know what to aim for.

I use my sled for 50/50 trail crusing and boondock playing.

Thanks.

Sunvang · Jan 25, 2015

Nobody?

Sent from my iPhone using Tapatalk

die hard poo · Jan 25, 2015

I strive for 14:1 from idle to 5500rpm, 13ish:1 from 5500 to 8500rpm.

inspector01 · Jan 26, 2015

Desired AFR doesn't change just because you have a big bore.

Sunvang · Jan 26, 2015

inspector01 said:
Desired AFR doesn't change just because you have a big bore.

It did with a turbo kit, thats why I asked.

And im not safe with running any performance parts at stock afr.

Look in this video of a stock 2013 Pro Rmk with a afr wideband mounted. Can't see it beeing safe running these numbers with performance parts added.

https://www.youtube.com/watch?v=bGn6pGlFPV0

die hard poo · Jan 26, 2015

My O2 sensor is also located on the pipe, about 12" away from the cylinder and not on the end of the pipe where you could have some air being sucked back through the pipe end. I use the NGK afr gauge and it seems to work better than the innovative or aem gauges. Much smoother reading.

die hard poo · Jan 26, 2015

My O2 sensor is located in the pipe here:

And I use a NGK AFR gauge. Way smoother than the AEM or Innovative i have used in the past.

inspector01 · Jan 26, 2015

Sunvang said:
It did with a turbo kit, thats why I asked.

And im not safe with running any performance parts at stock afr.

Look in this video of a stock 2013 Pro Rmk with a afr wideband mounted. Can't see it beeing safe running these numbers with performance parts added.

https://www.youtube.com/watch?v=bGn6pGlFPV0

A turbo kit and big bore are vastly different in tuning theory, no comparison.

Why would "any performance parts" require a richer (or different) AFR? There are many factors in tuning, but just adding parts does not necessarily require you to tune to a different AFR.

Sunvang · Jan 26, 2015

inspector01 said:
A turbo kit and big bore are vastly different in tuning theory, no comparison.

Why would "any performance parts" require a richer (or different) AFR? There are many factors in tuning, but just adding parts does not necessarily require you to tune to a different AFR.

Didnt know that, thats why im asking what is a good afr for this setup.

I know how to tune a turbo, but never did any big bore, or other performance adds. Thats why im asking.

Thanks for your answer tough, so in theory i can tune this to the same afr like in the video?

Sunvang · Jan 26, 2015

die hard poo said:
My O2 sensor is located in the pipe here:

And I use a NGK AFR gauge. Way smoother than the AEM or Innovative i have used in the past.

Ive tried both AEM and Innovate, most happy with Innovate. Never tried NGK, will do so in the future.

Here is my mount location.

Sent from my iPhone using Tapatalk

inspector01 · Jan 26, 2015

Sunvang said:
Didnt know that, thats why im asking what is a good afr for this setup.

I know how to tune a turbo, but never did any big bore, or other performance adds. Thats why im asking.

Thanks for your answer tough, so in theory i can tune this to the same afr like in the video?

I didn't watch the video, but you should be fine to tune it to the same AFRs as you would any other similar N/A engine with similar fuel/compression/etc. (General starting numbers for most engines on gasoline- ~15:1 at idle/low load, tranisitioning to ~13:1 at WOT).

FYI: WBO2's are pressure sensitive, if your sensor sees pressure, it won't be reading correctly.

Sunvang · Jan 26, 2015

inspector01 said:
I didn't watch the video, but you should be fine to tune it to the same AFRs as you would any other similar N/A engine with similar fuel/compression/etc. (General starting numbers for most engines on gasoline- ~15:1 at idle/low load, tranisitioning to ~13:1 at WOT).

FYI: WBO2's are pressure sensitive, if your sensor sees pressure, it won't be reading correctly.

By looking at the video, it actually starts lower in afr, thern it peaks at around 6-7000rpms, at one point its up at 17.

You think this would effect my reading where i mounted it? That i should move it?

DynojetResearch · Jan 26, 2015

Sunvang,

The most important thing to remember is that you are tuning your engine to obtain a chocolate brown plug color and good wash. Your "sensor" might need to see that 14.6:1 based on it's location, engine/pipe dynamic, etc., but the burn is optimal there - a reading to shoot for is irrelevant, the condition inside the engine is important.
I've installed an O2 bung in that exact location of a Polaris and the gauge did read lean all the time (about like yours). Plus it had very little deviation from the ~14.2-15.2ish range and was very hard to get it to dip under 13.0 even when adding large amounts of fuel. The locations illustrated by die hard poo or near the factory EGT probe produce more "real" readings of what is actually going on in the engine. The location way out near the silencer permits too much free air inclusion/turbulence toward the sensor which skews readings on the gauge.
If you wish to rely on the gauge reading and want it to be down in the 13's just for peace of mind, consider moving your O2 bung closer to the combustion chamber to avoid the funky readings displayed by your gauge.

~T.J.

Sunvang · Jan 26, 2015

DynojetResearch said:
Sunvang,

The most important thing to remember is that you are tuning your engine to obtain a chocolate brown plug color and good wash. Your "sensor" might need to see that 14.6:1 based on it's location, engine/pipe dynamic, etc., but the burn is optimal there - a reading to shoot for is irrelevant, the condition inside the engine is important.
I've installed an O2 bung in that exact location of a Polaris and the gauge did read lean all the time (about like yours). Plus it had very little deviation from the ~14.2-15.2ish range and was very hard to get it to dip under 13.0 even when adding large amounts of fuel. The locations illustrated by die hard poo or near the factory EGT probe produce more "real" readings of what is actually going on in the engine. The location way out near the silencer permits too much free air inclusion/turbulence toward the sensor which skews readings on the gauge.
If you wish to rely on the gauge reading and want it to be down in the 13's just for peace of mind, consider moving your O2 bung closer to the combustion chamber to avoid the funky readings displayed by your gauge.

~T.J.

Thanks for your input. Im oposite of your experince, according to the gauge im to rich, and the sled feels rich in the midrange also. But i will changed the position of the bunge, and i do check the plugs once a while for safety. Still to dark, but im getting somewhere.

Kcjepperson · Jan 26, 2015

I agree with dynojet,

I have tuned off of my ngk wideband for the last two years and had the mapping really good where the afr's where running 14.6-14.8 at idle and then decreasing to 12.8-13.0 at WOT, and though it was perfect. Then pulled the plugs and noticed the plugs and wash were indicating everything was rich still. Leaned it out alittle more and it's ran more crisp on the bottom end and the plugs look a lot better.

Use your afr's number as a gauge but check was and spark plugs for accuracy.

geo · Jan 26, 2015

Nothing really changes. No easy shortcuts to tuning something different.

Still plugs and wash in the field.

champyfz450 · Jan 26, 2015

Sunvang said:
Thanks for your input. Im oposite of your experince, according to the gauge im to rich, and the sled feels rich in the midrange also. But i will changed the position of the bunge, and i do check the plugs once a while for safety. Still to dark, but im getting somewhere.

If you're referring to the gauge in the video you posted, you're way lean my friend not rich. And according to where your bung is mounted I'm inclined to say that you just may be in the safe zone. But you won't get accurate readings til you mount in the location described by dynojet and die hard poo.

Sunvang · Jan 26, 2015

champyfz450 said:
If you're referring to the gauge in the video you posted, you're way lean my friend not rich. And according to where your bung is mounted I'm inclined to say that you just may be in the safe zone. But you won't get accurate readings til you mount in the location described by dynojet and die hard poo.

The video is not my sled. It a stock 2013 Pro Rmk 800. I know it looks really lean, but that how it comes from the factory.

On my sled, im getting reading 15 at idle and down to 11.5 wot, but i still hear and notice it beeing a little rich.

champyfz450 · Jan 27, 2015

Sunvang said:
The video is not my sled. It a stock 2013 Pro Rmk 800. I know it looks really lean, but that how it comes from the factory.

On my sled, im getting reading 15 at idle and down to 11.5 wot, but i still hear and notice it beeing a little rich.

Ok I got ya. Yeah, you're correct, 11.5 wot is really rich

voodoo · Jan 28, 2015

We typically put the AFR at the stinger as it reads more consistently. To close to the engine and you get weird readings. Look at Dynotech, they shove the afr stinger up the muffler and compare it to actual calculated AFR readings from the dyno fuel and airflow gauges and it's pretty accurate.

BTW, the NGK is nice. Iv'e run the Innovate and prefer the NGK

RkTek 858 a/f ratio numbers to aim for?

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