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Limit power and increase fuel efficiency in tune


turbogrill
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Hi,

 

I need to reduce the top power on our NC Miata to save fuel for COTA (and downgrade to GP3 for WRL).

 

What is the best way to increase fuel efficiency and reduce power in a tune? Is it to lean out and cut back timing?

 

So let say that our current AFR is 12.2 at 6000 RPM with an advance of 25 degrees. Let say that gives 165 whp

Should I increase AFR until I reach my power goal of 155 whp and then cut back some timing to be safe?

 

What happens if you run ~14 at full load and high RPM?  Would it knock it self to death or would it just cost power?

 

Car has knock sensors.

 

I don't want to short shift, I just want to flatten out the power a bit up top. 

 

 

 

 

 

 

 

 

 

 

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You would melt things at WOT and 14 AFR.

 

Depending on the efficiency of your head design, you can likely lean it out some safely.  I would guess a modern 4-v head can support 13.0 afrs.

 

Pulling timing will help reduce power also

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Assuming you have computer controlled variable valve timing, reduce the valve opening overlap in the high power window. 
 

Assuming drive by wire, make the throttle close a bit as you reach the highest power section of your powerband to flatten it out.

 

Add restriction to the throttle body opening to reduce peak airflow.

 

Engage your electrical generator in the high power area of the powerband to bring the power down a bit. Use that electrical energy on your hybrid drive motor when you aren’t in the peak power window. 

Edited by enginerd
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4 minutes ago, Huggy said:

You would melt things at WOT and 14 AFR.

 

Depending on the efficiency of your head design, you can likely lean it out some safely.  I would guess a modern 4-v head can support 13.0 afrs.

 

Pulling timing will help reduce power also

 

Pull timing would only reduce power and do nothing for fuel efficiency? It would still squirt in same amount of fuel but it will "burn" in a suboptimal way?

 

2 minutes ago, enginerd said:

Assuming you have computer controlled variable valve timing, reduce the valve opening overlap in the high power window. 
 

Assuming drive by wire, make the throttle close a bit as you reach the highest power section of your powerband to flatten it out.

 

Add restriction to the throttle body opening to reduce peak airflow. 

 

With the VVT stuff, would that help fuel efficiency since less air/fuel is being drawn in?

 

Ideally I would like to have a RPM programmable TB. That way I could have 100% throttle up to 5000 RPM and then maybe 80%.

 

A restriction to the TB would reduce power all over the curve right? I want max power/torque up to 5000 and then start to limit stuff.

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Thinking about it, wouldn't a restrictor plate (or throttle limitation) only "cap" airflow? So the restrictor would only affect high rpm?

 

Or limit the throttle 90% instead of 100% might do the trick?

 

The dyno graph between a restricted and non restricted should be the same up to specific point?

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Lowering timing and leaning it out would make the egt’s high and like previous stated lowering timing will not gain more “mpg”. Less air into the engine is the only way to get what your after and the engine live. Either they vvt or a restrictor plate. Depending on our fuel burn rate we will most likely add a restrictor  plate to our new build. 

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I tune the engine for best efficiency then tune the driver for best fuel usage.

 

12.2 is quite rich for a port injected engine, go to at least 13.0, set the timing for best mean power then back off a couple of degrees.

 

My pushrod 2 valve minivan engine did very well at 13.5:1 afr @ WOT and was relatively insensitive to timing changes.

 

Reducing the throttle opening mechanically (restrictor, brick under the gas pedal, etc.) or by backing off takes the engine out of its most efficient range (WOT). 

Image result for bsfc graph"

Short-shifting the final gear change on the long straights is the best way to cut back on fuel usage while minimally affecting lap time. 

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1 hour ago, turbogrill said:

Hi,

 

I need to reduce the top power on our NC Miata to save fuel for COTA (and downgrade to GP3 for WRL).

 

What is the best way to increase fuel efficiency and reduce power in a tune? Is it to lean out and cut back timing?

 

So let say that our current AFR is 12.2 at 6000 RPM with an advance of 25 degrees. Let say that gives 165 whp

Should I increase AFR until I reach my power goal of 155 whp and then cut back some timing to be safe?

 

What happens if you run ~14 at full load and high RPM?  Would it knock it self to death or would it just cost power?

 

Car has knock sensors.

 

I don't want to short shift, I just want to flatten out the power a bit up top. 

 

 

 

 

 

 

 

 

 

 

Take you foot off the go pedal. 

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1 hour ago, turbogrill said:

So let say that our current AFR is 12.2 at 6000 RPM with an advance of 25 degrees. Let say that gives 165 whp

Should I increase AFR until I reach my power goal of 155 whp and then cut back some timing to be safe?

If you lean it out enough to drop 10 whp you'll likely end up burning valves. From where you are you'll probably gain a few whp as you get close to 13.0 and will likely be well into the 14s by the time it drops to 155. Don't do it, even on the dyno! Hard to say what the timing will do without knowing what the engine likes but 25 degrees sounds a little on the low side already. I'd go the other way to find best power first.

 

If you have to limit your power to 155 whp, use your rev limiter.

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Turbocharge it and have the boost vary inversely with RPM such that you get a flat power ‘curve’.

 

(All this fun is somewhat moot, though. The question was about detuning to meet WRL class gp3, and WRL will slap you with a penalty of sorts if your dyno shows a flat power curve.)

Edited by enginerd
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22 minutes ago, karman1970 said:

Swap in a TDI.

 

I am at 495 pts....would Bill Strong notice an engine swap in a Miata?

 

 

image.thumb.png.429abb6bb7368fabd698c113b5a03c7f.png

 

Blue line is what I have, red is what I want. 

 

If I sort shift at 6000 RPM I will end up at 4500 or so where our engine is like a NA Miata.

 

Maybe just try to change the throttle pedal to 95% and see what happens.

Edited by turbogrill
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48 minutes ago, shanehutton said:

I don't understand why you would want to go to this trouble vs just laying off the gas pedal a bit or shifting earlier.  Both will reduce fuel consumption and shifting earlier will reduce the beating your engine is taking.

He’s talking about building the car for WRL gp3. They require dyno sheets and I assume they would baulk at a dyno plot that showed an early lift. 
 

Also, short shifting causes a huge drop off in power for the next gear. It’s better to have an engine which reaches peak hp, nose over, then shift rather than one that is climbing and hasn’t yet reached peak power by the time you shift. 

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I leaned out my Miata to improve economy and the car suddenly ran 20 degrees hotter.  Keep that in mind.  Adding water wetter and wrapping the exhaust mandrels and downpipe got those 20 degrees back (and then some). 

 

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On 1/14/2020 at 11:53 AM, turbogrill said:

Hi,

 

I need to reduce the top power on our NC Miata to save fuel for COTA (and downgrade to GP3 for WRL).

 

What is the best way to increase fuel efficiency and reduce power in a tune? Is it to lean out and cut back timing?

 

So let say that our current AFR is 12.2 at 6000 RPM with an advance of 25 degrees. Let say that gives 165 whp

Should I increase AFR until I reach my power goal of 155 whp and then cut back some timing to be safe?

 

What happens if you run ~14 at full load and high RPM?  Would it knock it self to death or would it just cost power?

 

Car has knock sensors.

 

I don't want to short shift, I just want to flatten out the power a bit up top. 

 

 

 

 

 

 

 

 

 

 

There is a much more effective way to save fuel and I have not really shared it until now, but the huge gas tank cars are winning a lot and have a huge advantage so I will give up a secret for us small gas tank guys.  Sure, lean it out a little bit helps, which I have also done, but this will also help and be a much more effective way to save fuel.  I never found short shifting to actually save that much fuel at all.  You are still on the throttle and still using fuel.  The real way to save on fuel is to not use fuel and that is the key, but how do you not use fuel? That it the real question. 

 

Example.

1:30 stint length.

2:00 min lap times.

50 seconds of WOT.

3 straightaways.

You will do 45 laps.

2250 seconds total at WOT, or 37.5 minutes.

On the straights you let off the gas at braking marker 3, hard on the brakes, corner, apex speed and back on the gas.

 

Instead, brake prior to the 5 and coast for 1 second, before braking on all three straights.

This saves 3 seconds of WOT per lap.

You use 2115 seconds of fuel or 35.25 minutes of WOT.

You saved 6% of your fuel.

You can now go 1:38 minutes

You extended it 8 minutes.

When you let off the gas and coast you are really not losing that much time at all as you are not acceleration that much at that high of speed.  You slow down some, but adjust your braking.  You will actually brake much better and hit the apex faster due to a controlled braking period.  Your lap times will actually increase. Funny how that works. Almost all drivers, no matter how great you think you are, over brake and slow down to much, myself included. Data confirmed.

 

Now here is where it gets interesting.

Now if you do 2.7 seconds of coasting it will cost you about a second a lap, but saves you 16% fuel.  Now you can go 1:55 minutes instead of 1:30 and pit every two hours. In that 1:55 minutes would have gone 57 laps at WOT.  If you give up 1 second a lap you would go 56.5 laps and are only half a lap back. Pit 3 times and that is 1.5 laps lost due to the 1 seconds.  Drive WOT and pit and extra full stop and that is 2.5 laps.  You saved yourself 1 full lap, plus give yourself the opportunity to gain a pit stop under FCY at the 2 hour mark.

 

The other option is to go WOT and pit and extra time and hope to get two FCY pits when others get green pits. This would basically equal out and if you get an extra FCY stop you would gain laps, but 3 pits under FCY and later in the race when you need them can be very very hard to get, ask me how I know that as it does not happen often anymore.  

 

This is strategy type we use to go longer now and it really does work and the funny part is that coasting has made me a better driver as I can really focus on my corner entry speed and apex speed.

 

Math is fun.

 

Enjoy

 

Troy

 

 

 

 

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6 hours ago, MR2 Biohazard said:

There is a much more effective way to save fuel and I have not really shared it until now, but the huge gas tank cars are winning a lot and have a huge advantage so I will give up a secret for us small gas tank guys.  Sure, lean it out a little bit helps, which I have also done, but this will also help and be a much more effective way to save fuel.  I never found short shifting to actually save that much fuel at all.  You are still on the throttle and still using fuel.  The real way to save on fuel is to not use fuel and that is the key, but how do you not use fuel? That it the real question. 

 

Example.

1:30 stint length.

2:00 min lap times.

50 seconds of WOT.

3 straightaways.

You will do 45 laps.

2250 seconds total at WOT, or 37.5 minutes.

On the straights you let off the gas at braking marker 3, hard on the brakes, corner, apex speed and back on the gas.

 

Instead, brake prior to the 5 and coast for 1 second, before braking on all three straights.

This saves 3 seconds of WOT per lap.

You use 2115 seconds of fuel or 35.25 minutes of WOT.

You saved 6% of your fuel.

You can now go 1:38 minutes

You extended it 8 minutes.

When you let off the gas and coast you are really not losing that much time at all as you are not acceleration that much at that high of speed.  You slow down some, but adjust your braking.  You will actually brake much better and hit the apex faster due to a controlled braking period.  Your lap times will actually increase. Funny how that works. Almost all drivers, no matter how great you think you are, over brake and slow down to much, myself included. Data confirmed.

 

Now here is where it gets interesting.

Now if you do 2.7 seconds of coasting it will cost you about a second a lap, but saves you 16% fuel.  Now you can go 1:55 minutes instead of 1:30 and pit every two hours. In that 1:55 minutes would have gone 57 laps at WOT.  If you give up 1 second a lap you would go 56.5 laps and are only half a lap back. Pit 3 times and that is 1.5 laps lost due to the 1 seconds.  Drive WOT and pit and extra full stop and that is 2.5 laps.  You saved yourself 1 full lap, plus give yourself the opportunity to gain a pit stop under FCY at the 2 hour mark.

 

The other option is to go WOT and pit and extra time and hope to get two FCY pits when others get green pits. This would basically equal out and if you get an extra FCY stop you would gain laps, but 3 pits under FCY and later in the race when you need them can be very very hard to get, ask me how I know that as it does not happen often anymore.  

 

This is strategy type we use to go longer now and it really does work and the funny part is that coasting has made me a better driver as I can really focus on my corner entry speed and apex speed.

 

Math is fun.

 

Enjoy

 

Troy

 

 

 

 

Troof.  I use about 80% of the fuel in @E. Tyler Pedersen car when I am conserving fuel.  My fast lap is about a second slower, but my lap times end up being within tenths of each other because it is easier to hit the markers when you are coasting into the corners versus waiting til the last second.

 

I was faster through the stint at Sebring, had a longer stint, and used less fuel.

 

I was doing exactly what troy said.

Edited by wvumtnbkr
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On 1/18/2020 at 12:50 PM, MR2 Biohazard said:

 

Instead, brake prior to the 5 and coast for 1 second, before braking on all three straights.

This saves 3 seconds of WOT per lap.

 

 

This is very effective at saving fuel, and is one of the best methods pro teams use to save fuel. 

 

In oval racing where you are in top gear all the time (can't short shift), the 4 methods commonly used are 

 

Delay WOT application on exit by some time

 

"Peak and hold", driving hard to a max rpm limit and maintaining it.

 

"Lift early", picking a spot on track and lifting there. Brake at brake marker, but just throttle lift and coast early.

 

"Lift and stab", a timed throttle lift mid straight for x seconds. 

 

As Troy pointed out, the most efficient strategies get the car up to speed at max effort, and take the speed penalty\lift at the very end of the straights. Mathematically the later you wait to do your lift\reduced power the shorter the distance that you will be "slower" over. The method he pointed out is generally considered the best....

 

You missed your calling in pro race strategy.....

Edited by Black Magic
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On 1/14/2020 at 2:15 PM, turbogrill said:

 

I am at 495 pts....would Bill Strong notice an engine swap in a Miata?

 

 

image.thumb.png.429abb6bb7368fabd698c113b5a03c7f.png

 

Blue line is what I have, red is what I want. 

 

If I sort shift at 6000 RPM I will end up at 4500 or so where our engine is like a NA Miata.

 

Maybe just try to change the throttle pedal to 95% and see what happens.

 

Reviving the original question...

1) what is the max % of total horsepower that you could safely/reliably 'detune' from optimal in an engine (assume no restrictor plate, and only timing, TPS, and fuel were available parameters to modify).

2) What method would you use to get there?

 

-Thanks

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