how lean can i go at low boost levels?

H

hendrixgr

Registered
Hi.
I would like to ask if anyone knows of course, how lean can i go at say 5000 rpm (actually 4600-4800 rpm) and 2psi of boost without risking any damage to the engine?
Right now i am at 14.7:1 but i have tried up to 17:1 for 10 seconds (always with steady throttle cruising) with no ill effect on engine smoothness or acceleration performance.
I don't know for sure but i am thinking that nothing bad can happen at max 5000 rpm and max 2 psi of boost...
As you might have guessed i am trying to increase mileage although i don't really need to, there is something inside my brain that won't let me relax :laugh:
Chris
 
Just as low as your pockets are deep, those gas pennies really add up when you're talking a $5K motor, just saying......

Experts should be along soon :poke:
 
On the RCC website it says A/F should be 11.5 - 11.8 under boost. But I am no expert, they should be here shortly.

-D
 
This guy would stay away from anything over 13.5 while building boost at 5k. Though It would probly be hard to burn that motor at 5k short of running it without oil.
 
Thank you all for your help.
I am sure that it i am stretching it at 17:1 but i would think that 14.7 is tolerable at maximum 2 psi and 4800 rpm for a low compression (9.5:1) motor.
In any case i will leave it to 13.2 -13.5 for now just to be safe.
For a strange reason i just can leave my perfectly running turbo Hayabusa and my mind in piece.
Chris
 
hendrixgr said:
For a strange reason i just can leave my perfectly running turbo Hayabusa and my mind in piece.
Chris
Click to expand...

That thinking may change if you ever end up toasting a motor because you couldnt leave well enough alone. That peace of mind will vanish and you might end up saying "damn,it ran perfect why did I have to F with it?!?":laugh:
 
oldgixxer said:
That thinking may change if you ever end up toasting a motor because you couldnt leave well enough alone. That peace of mind will vanish and you might end up saying "damn,it ran perfect why did I have to F with it?!?":laugh:
Click to expand...
You never know what you have until you loose it, i know...
I just finished programming the ecu for a fat 13.5:1 AFR on that range but it would be nice to know if there it is really dangerous
to run lean at those very low boost and rpm levels.
For sure it will not be good for the engine but can it melt pistons, burn valves etc?
After all the stock ecu runs closed loop at 14.7:1 for up to 4800 rpm (on European gen1 models)
Chris
 
hendrixgr said:
You never know what you have until you loose it, i know...
I just finished programming the ecu for a fat 13.5:1 AFR on that range but it would be nice to know if there it is really dangerous
to run lean at those very low boost and rpm levels.
For sure it will not be good for the engine but can it melt pistons, burn valves etc?
After all the stock ecu runs closed loop at 14.7:1 for up to 4800 rpm (on European gen1 models)
Chris
Click to expand...
Im surprised that Rob@ Boosted Cycle or Powerhouse hasn't replied yet:dunno:
 
I am at 14.5 on the highway at 4700 rpm with probably a .5, maybe .3 boost or so the logs appear at 80mph or so fixed TPS. I would not go any leaner than that. I ride that to my reserves 100 miles 1 way, 2 days in a row. I tried putting brand new plugs in and seeing what they looked like after. They looked great to me. They looked good enough to me to not want to mess with it any more. Now, my IAP and low throttle and WOT needs tweaked but my highway IMO is great. if 14.5 works, it aint broke. Talking highway cruising speed. Nothing else. When I can verify anything else is good via how the plugs look, I would comment on that.
 
My MAP sensor is not calibrated well, I admit that but I think the boost pressure is slightly above 0 at that rpm/load. It may go up to 2psi on aggressive passing but that is a different TPS and the AFR dramatically changes along with that.
 
Kevin Jones said:
My MAP sensor is not calibrated well, I admit that but I think the boost pressure is slightly above 0 at that rpm/load. It may go up to 2psi on aggressive passing but that is a different TPS and the AFR dramatically changes along with that.
Click to expand...
When i said max 2 psi boost i really meant 1.3 to 1.6 psi...
i also think that max 14.7:1 for cruising won't hurt the motor at such low rpm and boost levels
Chris
 
oldgixxer said:
Im surprised that Rob@ Boosted Cycle or Powerhouse hasn't replied yet:dunno:
Click to expand...

It's been a busy day...

Anyways, with small turbos it's not uncommon to see 1-2psi at fast highway speeds. The turbo is doing its thing when at 5-6k in a steady state. At 90mph on my old bike it would sit right at 1psi.

That being said, don't get hung up on ideological afr numbers, you need to give the engine what it wants/needs. However running the bike at 17:1 it has to run like crap. These engines love fuel in comparison to a lot of performance cars/trucks. Part of by business is tied in to the performance automotive world, and usually when I discuss with other car guys the types of afr's theyre usually shocked at how much fuel these engines actually need.

Never, in all my years of building and tuning these bikes have I ever allowed a bike to run at 17:1afr. In my experience anything over 14.0 the engine almost always starts breaking up, running rough, and had a noticeable sputter and even popping much past that. I like to tune part throttle lean to an extent, but while maintaing a smooth running and responsive engine. Typically I'll tune to 12.8-13.1 for going down the highway at sustained speeds. That's a good trade off point between fuel economy and engine smoothness and responsiveness.

Other things to consider when you're running that lean you're creating more heat in the combustion chambers. Ignition timing in that portion of the map is generally pretty high, which further adds to heat, I'm willing to bet it's detonating too at that point. Higher egts also result in the turbo spooling. I'm willing to bet if you bring the afrs down to 13.0 you'll notice at the same point you were seeing 2psi cruising, it will be between 0-1 psi because you aren't pumping so much heat in to the turbo. It's the same concept as antilag like you see on prostreet bikes. Retarding the timing and throwing in a ton of fuel so it's still burning going in to the turbo causing it to make boost without any load on on the engine.
 
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hendrixgr said:
I don't know but my instinct says that 20 rwhp sound somewhat low, i would say based on nothing that 2 psi at 4800 rpm equals about 40 hp.
Chris
Click to expand...

If the bike was at wot, this would be true. Need to remeber pressure (boost) and air volume (how much) play a roll here in this scenerio. Boost is essentially a measurement of resistance. Assuming your gauge is attached underneath the throttle blades, yes you may be seeing 2psi, however because your throttle is only open 15-20% you're not getting the full volume of air because it's being slowed down or "restricted" by the throttle blades. You can confirm the by looking at your fuel map. Your injector pulse widths will be smaller at 15% throttle at 2psi the at the same rpm at 100% throttle and 2psi. You need fuel to make HP.

If you put a gauge on the plenum you'll see more pressure on the plenum side of the blades verses the gauge hooked to the underside of the blades. This pressure diffriental will only spread more the higher the boost level assuming you can somehow make more boost at that throttle percentage. But the pressure on both gauges will read the same at wot.
 
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As always the best description-explanation i could hope for!!!
Btw at 17:1 afr indicated the motor was running very very smoothly (go figure...) but i do realize that i am pushing it too far.
I will leave it to 14.7:1 which i think is a good trade off.
Chris
 
hendrixgr said:
As always the best description-explanation i could hope for!!!
Btw at 17:1 afr indicated the motor was running very very smoothly (go figure...) but i do realize that i am pushing it too far.
I will leave it to 14.7:1 which i think is a good trade off.
Chris
Click to expand...

Trust me, if you really pay attention from 14.7 or 17.0 to 13.0 you'll see the difference. Again don't get hung up on numbers like stoichiometric. These engine need fuel.
 
hendrixgr said:
As always the best description-explanation i could hope for!!!
Btw at 17:1 afr indicated the motor was running very very smoothly (go figure...) but i do realize that i am pushing it too far.
I will leave it to 14.7:1 which i think is a good trade off.
Chris
Click to expand...

Boosted Cycle Perf said:
Trust me, if you really pay attention from 14.7 or 17.0 to 13.0 you'll see the difference. Again don't get hung up on numbers like stoichiometric. These engine need fuel.
Click to expand...

I'd just assume listen to the professional who does this for a living,why take a chance?
 
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