AFR Tuning questions

RobertTrivanovic · Nov 11, 2013

So Im going to be tuning my M8 turbo over the next few weeks using a PC5 and an AEM AFR. I know that 14.7 is considered perfect, but I have been reading a bunch and from what I see people keep talking about wanting to be at around 11.8 wot. So what numbers should I tune for in my RPM ranges? Leaner around idle and cruise RPMs then richer at wot? Am I on the right track thinking this? And why not just tune for 14.7 all around?

Thanks in advance guys!

Tony skagen · Nov 11, 2013

A boosted motor will not live at 14.7 or even 13.7. Adding more fuel will keep it cooler and fight detonation. 11.5. - 12.0 is as lean as I would run at wot. And yes you can run it leaner at lower Rpms. Theses are afr's I run in my race boats.

Duraslut · Nov 11, 2013

U will melt down at 14.7 . We're did u get that number from? I'm guessing from the automotive industry cause that's wat optimal afr is on a 4cycle motor. A 4 cycle motor can run alot leaner then a 2 stroke. I run my turboed 8 at 11.8 at wot. Mid range and idle will always be hot on a 2 stroke turboed sled. That's y they say to "chop" "blip" the throttle when riding at cruising speed. U can get the afr down a bit on cruise but u will see that when u cruise without blipping it, it will nvr stay at 11.8or even 12. I tune mine so the mid range is still crisp and my wot is at 11.8. I'm not a pro at tuning but I did alot ov reading on here to learn my afr gauge and to tune with it. I've had one whole season trouble free.

RobertTrivanovic · Nov 11, 2013

Duraslut said:
U will melt down at 14.7 . We're did u get that number from? I'm guessing from the automotive industry cause that's wat optimal afr is on a 4cycle motor. A 4 cycle motor can run alot leaner then a 2 stroke. I run my turboed 8 at 11.8 at wot. Mid range and idle will always be hot on a 2 stroke turboed sled. That's y they say to "chop" "blip" the throttle when riding at cruising speed. U can get the afr down a bit on cruise but u will see that when u cruise without blipping it, it will nvr stay at 11.8or even 12. I tune mine so the mid range is still crisp and my wot is at 11.8. I'm not a pro at tuning but I did alot ov reading on here to learn my afr gauge and to tune with it. I've had one whole season trouble free.

When you say you tune for the mid to still be crisp what numbers are you tuning to in the mid?

Duraslut · Nov 11, 2013

I have a dobec based fuel controller. I'm pretty sure I was just tunning the mid by how it ran. Riding in snow mid throttle and seing how responsive it was. I started with the mid rich and went down from there till the midrange cleaned up. I'm not worried about cruise on the trail. I blip the throttle lots which causes the afr to go way down. I know wat settings I run when I get to elevation. So on trail ill turn up the green(bottom end) and yellow (mid range) just for better peace ov mind and I don't even look at afr cause it bouncing all over from me blipping it.

Snopro_69 · Nov 12, 2013

^^^^^^ what he said

Snowmow · Nov 12, 2013

I've talked to Ovs and boondocker they both recommend 14.5 cruse and 12.5 WOT

carlc · Nov 12, 2013

I have always aimed for no higher than 16 idle 14 cruise and 12 for wot.

RobertTrivanovic · Nov 12, 2013

Think im going to tune my idle to 14.7 cruise to around 13(ish) ill get it so its crisp so that might be leaner or richer, and my WOT at 11.8-12, those all being starting numbers of course.

Thanks for all the info guys!

RACINSTATION · Nov 12, 2013

11.8 to 12.5 is a good guideline for wide open. Each sled is different. On the M8 12.0 to 12.2:1 is OK on wide open. You will FEEL what is right too. It'll be doggy at 11.5 or so and you will fee it clean up leaner. ALWAYS check wet line and plugs to verify your tuning and then use that for a guideline.

DynojetResearch · Nov 13, 2013

RACINSTATION said:
11.8 to 12.5 is a good guideline for wide open. Each sled is different. On the M8 12.0 to 12.2:1 is OK on wide open. You will FEEL what is right too. It'll be doggy at 11.5 or so and you will fee it clean up leaner. ALWAYS check wet line and plugs to verify your tuning and then use that for a guideline.

Thank you RS for interjecting the only true way to know what Your engine should run at -- checking plugs and wash.
Numbers are only a number without knowing what that correlates to inside your cylinders.
A value of 11.8 used from other people's engines/setups is heresy and may not work for your engine at all. A 12.8 value might be more appropriate for your engine based on probe placement to get a solid burn in the combustion chamber.
An '09 Turbo M8 of mine liked to see 12.2WOT, and 1250* EGT -- for chocolate brown plugs.
My '12 Turbo Pro likes 11.8WOT, and 1140*EGT -- for the Same chocolate brown plugs.
Why the difference?? Probe placement, turbo setup, engine style, fuel mix, etc.

~T.J.

RobertTrivanovic · Nov 13, 2013

Thanks for the info guys! I'll definetly be checking plugs and wash when tuning.

What are you guys tapping into for the minimum 10v power to run these things? Sleds a 2007

Snowmow · Nov 13, 2013

This is how the twisted kit works.

Accessory plug powers capacitor, capacitor powers high output fuel pump. Stock fuel pump plug is used for afr gauge and attitude box. If your using a electric oil pump for the turbo that was also Drawing from the capacitor.

RobertTrivanovic · Nov 13, 2013

Snowmow said:
This is how the twisted kit works.

Accessory plug powers capacitor, capacitor powers high output fuel pump. Stock fuel pump plug is used for afr gauge and attitude box. If your using a electric oil pump for the turbo that was also Drawing from the capacitor.

I might try to run from the accessory plug but its probably pretty close to being maxed out right now since its running a fuel pressure accelerator that runs my fuel pump and oil pump at the moment, stock fuel pump plug also runs into the fuel pressure accelerator so that plug is being used as well. No capacitor.

Snowmow · Nov 13, 2013

Great Scott!!!

That circuit is prolly drawing 1.21 gigawats!! Which would be enough to send Michael J fox back In time and hopefully find a cure for Parkinson's.

RobertTrivanovic · Nov 13, 2013

Snowmow said:
Great Scott!!!

That circuit is prolly drawing 1.21 gigawats!! Which would be enough to send Michael J fox back In time and hopefully find a cure for Parkinson's.

I think I see where your going with this...

Snowmow · Nov 13, 2013

Even if it all works at idle. Won't the accelerator demand more voltage with higher RPM's?

I would think that to reliably run everything you will either need a capacitor or the updated CCU

RobertTrivanovic · Nov 13, 2013

Snowmow said:
Even if it all works at idle. Won't the accelerator demand more voltage with higher RPM's?

I would think that to reliably run everything you will either need a capacitor or the updated CCU

I rode the sled once and the tuning was way off making it almost impossible to actually ride but the sled ran the whole time so it was clearly getting fuel, and my oil pressure never dropped according to the gauge. A turbo oil pump shouldnt be drawing all that much power?

Snowmow · Nov 13, 2013

No. Not much draw. But if your getting close to the max. Every bit helps.

RobertTrivanovic · Nov 13, 2013

Well im not sure but id think im getting close to max, which is why I dont want to wire my AFR into that.

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