[nelson]

Hi I'm considering ordering a G80 and trying to get up to speed with the modern tuning approaches for these cars.

I've been reading through the threads on the DME unlock vs piggyback and want to understand the different options for me tuning at ~5k feet altitude with possibility to drive to 8k-9k feet altitude on a regular basis.

I guess the first question is either option particularly risky at my altitude or when driving to the mountains? I have regular access to 91 pump gas. and E85, so I guess I could mix (have separate questions on how do you get the mix exactly right if E85 is variable and the tune calls for E40 for example)

Alternatively I could go back to stock when driving to the mountains but what If I forget lol!

It seems the piggyback keeps some stock safetys - is this the better option for me? I just don't want to be running too lean or too rich and not know it. Same consideration for cold weather I guess. Do the piggyback or regular flash tune compensate for bad AFRs or super low or high temps?

thanks in advance for the education session

[GixY2K]

I used the RC year round @ level7 here in Colorado Springs with a change of elevation from 6,000 to 7,200; no issues. Well worth it if you can buy one used for ~$300.

Full disclosure: "I'm not a tuner expert"
Having said this, when I had my GTR and tuned it for this elevation, my tuner said that he had to close (or was it open) the wastegates 100% because my turbos were running out of steam at this elevation. Conversely, when I took my GTR to sea level, he had to re-tune it so I wouldn't over boost.

I guess what I'm trying to say is that high elevation should not be an issue. But if you want your car/S58 to run as efficient/powerful as possible, I'd suggest getting your DME(ECU) unlock and get a good tuner to tune your car for those elevations specifically.

[vetteflier]

Altitude has virtually nothing to do with performance from a turbocharged car. The car makes its own air and will adjust to higher density altitude. You don't need to do anything with a wastegate. Air is metered--and corresponding fuel needed, by several different methods in different cars. Don't know about GTRs, but the M4C loses--at worst, maybe 5 hp at 7000' where I live. Garrett has some very good writeups on turbos and altitude. https://www.garrettmotion.com/news/n...0air%20density. When you consider the car is putting out 550 or so stock, a few hp means nothing. Now on a Vette, 100hp loss on my C7 here. You won't find any NAs at the Pikes Peak Hillclimb.

[cleaningup]

Originally Posted by vetteflier

Altitude has virtually nothing to do with performance from a turbocharged car. The car makes its own air and will adjust to higher density altitude. You don't need to do anything with a wastegate. Air is metered--and corresponding fuel needed, by several different methods in different cars. Don't know about GTRs, but the M4C loses--at worst, maybe 5 hp at 7000' where I live. Garrett has some very good writeups on turbos and altitude. https://www.garrettmotion.com/news/n...0air%20density. When you consider the car is putting out 550 or so stock, a few hp means nothing. Now on a Vette, 100hp loss on my C7 here. You won't find any NAs at the Pikes Peak Hillclimb.

This is not true when we are talking about tuning. Altitude has absolutely everything to do with performance. BMW leaves a lot of room, and we can run near sea level times at 5000' on a stock tune due to how much room BMW leaves, but you are losing a lot more than 5 hp--even stock. You are also moving your torque curve further up the powerband because your turbos need to spin faster to pump more air up here and this happens at a higher RPM compared to sea level. In any case, stock Ms perform well at altitude. Like .5ish off the 1/4.

However, there are less oxygen molecules in that air which is the reactant in combustion. Turbos can force more air into the combustion chamber, but they do not create oxygen. When we are talking about tuning, they max out very fast at altitude. There is always nitrous which would make up for altitude. Injecting more oxygen molecules vs compressing more air into the cylinder. I digress.... I cannot hit the same boost pressure that a tuned car could hit at sea level because the air is less dense at my altitude. Less dense=less pressure. The article you linked showed 22PSI of boost on a 500hp car. Those are weak numbers compared to what people are doing on this platform. I know I already started, but don't even get me going on torque curves and gearing. There is so much more that goes into it.

To answer OPs question, I am FBO and port injection in Denver. I'm running 1.5 seconds slower 60-130s than guys running my setup at sea level at 90% wastegate duty cycle. I cruise up to 14,000'. It's fine, you just won't hit boost targets. It's not dangerous for the engine if you are not hitting boost. Your turbos are going to hate you, but they are going to hate you anyway when tuned.

I personally do not care for piggybacks. You are tricking your ECU. This sounds like adding unnecessary complexity. I do not know about keeping stock safeties. How would you keep them if you are tricking your DME? Flash tunes flash the DME and allow it to control your car as intended. It will compensate for AFR via fuel trims just like it would stock. You can keep all safeties in place. I vote you tune it.

[LongBeachDinanFan]

The JB4 has compensation for elevation in its tuning since it's taking in a ton of engine data via CANbus. I wouldn't run a dumb piggyback up there, might run lean.

[cleaningup]

Originally Posted by LongBeachDinanFan

The JB4 has compensation for elevation in its tuning since it's taking in a ton of engine data via CANbus. I wouldn't run a dumb piggyback up there, might run lean.

Hmmm, I did not know that they had canbus access. I still don't like adding complexity. Says the guy with a reflex controller on his car, lol.

[LongBeachDinanFan]

Originally Posted by cleaningup

Hmmm, I did not know that they had canbus access. I still don't like adding complexity. Says the guy with a reflex controller on his car, lol.

If you're going to use a piggyback JB4 is hands down the best one. Lots of user customization and great data logging also to the app if you're in to that sort of thing.

[GixY2K]

Originally Posted by vetteflier

Altitude has virtually nothing to do with performance from a turbocharged car. The car makes its own air and will adjust to higher density altitude. You don't need to do anything with a wastegate. Air is metered--and corresponding fuel needed, by several different methods in different cars. Don't know about GTRs, but the M4C loses--at worst, maybe 5 hp at 7000' where I live. Garrett has some very good writeups on turbos and altitude. https://www.garrettmotion.com/news/n...0air%20density. When you consider the car is putting out 550 or so stock, a few hp means nothing. Now on a Vette, 100hp loss on my C7 here. You won't find any NAs at the Pikes Peak Hillclimb.

Again, not the expert here, but when I went to dyno one of my turbo cars here in Colorado Springs (6.5k ft. elev.), the tuner explained that he was going to use 15% power loss factor as opposed to 25% he uses on N/A engines to obtain results that are "roughly" close to sea-level numbers.

Also, when I drive to the top of Pike Peak (14k ft. elev.), I do feel the engine running extremely sluggish. I guess it can be attributed to the ECU not compensating near real-time.

[nelson]

Thanks everyone for your posts its really helpful for me to understand.

Originally Posted by cleaningup

I personally do not care for piggybacks. You are tricking your ECU. This sounds like adding unnecessary complexity. I do not know about keeping stock safeties. How would you keep them if you are tricking your DME? Flash tunes flash the DME and allow it to control your car as intended. It will compensate for AFR via fuel trims just like it would stock. You can keep all safeties in place. I vote you tune it.

So for context on this specific comment I talked to the JB4 guys and understand that it doesn't trick the ECU for critical things like AFR, overboost, etc. so the standard throttle cuts and/or limp mode can I apply if I get bad gas or there is an overboost situation. I'm not sure if those things still exist with an ECU tune or not.

[Info@mad-us.com]

Originally Posted by nelson

Thanks everyone for your posts its really helpful for me to understand.



So for context on this specific comment I talked to the JB4 guys and understand that it doesn't trick the ECU for critical things like AFR, overboost, etc. so the standard throttle cuts and/or limp mode can I apply if I get bad gas or there is an overboost situation. I'm not sure if those things still exist with an ECU tune or not.

I believe you can if you use the custom maps but the pre-made maps or auto tuning maps have all that safety built in.

Thinner air at elevation will definitely require more work from the turbo to make the same power.

[Hendo741]

Being tuned then going to higher elevations is safe because the air gets less dense, turbos have to work harder, and you make less power. Getting tuned at elevation, then going closer to sea level is where things could get dicey. If you car is tuned to the razors edge at 7000 feet, when you go down in elevation it's going to be over boosting and could create issues.

A piggy back would be perfectly acceptable, but I would just use one of the less aggressive maps for safety.

[Bostro]

And here are results you can expect with RC (no other mods) in Colorado. Fort Collins precisly. G8x for aure make huge difference on how its operating on high elevations, because with my previous m4 2020 the difference was very noticable. You will not regret!

[nelson]

Originally Posted by Bostro

And here are results you can expect with RC (no other mods) in Colorado. Fort Collins precisly. G8x for aure make huge difference on how its operating on high elevations, because with my previous m4 2020 the difference was very noticable. You will not regret!

In the 10s at altitude with just a tune - that is wild. Is this on 91?

[vetteflier]

Originally Posted by cleaningup

This is not true when we are talking about tuning. Altitude has absolutely everything to do with performance. BMW leaves a lot of room, and we can run near sea level times at 5000' on a stock tune due to how much room BMW leaves, but you are losing a lot more than 5 hp--even stock. You are also moving your torque curve further up the powerband because your turbos need to spin faster to pump more air up here and this happens at a higher RPM compared to sea level. In any case, stock Ms perform well at altitude. Like .5ish off the 1/4.

However, there are less oxygen molecules in that air which is the reactant in combustion. Turbos can force more air into the combustion chamber, but they do not create oxygen. When we are talking about tuning, they max out very fast at altitude. There is always nitrous which would make up for altitude. Injecting more oxygen molecules vs compressing more air into the cylinder. I digress.... I cannot hit the same boost pressure that a tuned car could hit at sea level because the air is less dense at my altitude. Less dense=less pressure. The article you linked showed 22PSI of boost on a 500hp car. Those are weak numbers compared to what people are doing on this platform. I know I already started, but don't even get me going on torque curves and gearing. There is so much more that goes into it.

To answer OPs question, I am FBO and port injection in Denver. I'm running 1.5 seconds slower 60-130s than guys running my setup at sea level at 90% wastegate duty cycle. I cruise up to 14,000'. It's fine, you just won't hit boost targets. It's not dangerous for the engine if you are not hitting boost. Your turbos are going to hate you, but they are going to hate you anyway when tuned.

I personally do not care for piggybacks. You are tricking your ECU. This sounds like adding unnecessary complexity. I do not know about keeping stock safeties. How would you keep them if you are tricking your DME? Flash tunes flash the DME and allow it to control your car as intended. It will compensate for AFR via fuel trims just like it would stock. You can keep all safeties in place. I vote you tune it.

I never mentioned tuning. I spoke only of stock turbo loss at higher DA vice NA. And I specifically mentioned 7000' AGL, not the top of Pikes Peak. Plus, I think I'll stick with Garrett for opinions. And the article I referenced was very clear on altitude for turbos.

"Turbocharging at elevation is an efficient way to minimize horsepower loss due to elevation and lower air density. At high elevations turbochargers compress more air into the engine cylinders making up for the lower air density allowing the engine to produce power as if it was at sea level. This extra tunability is found only in turbocharged applications."

Seems pretty clear to me. As to the 'benefits' of tuning at altitude, no question they help--just like at SL. Agree completely on that.

[Bostro]

Originally Posted by nelson

In the 10s at altitude with just a tune - that is wild. Is this on 91?

Yeap, 91 Octane. And Zits just Raceachip so if you want to call it tune, your call
Imagine what can happen if I replace RC piggyback with real DME tune

[Mapper]

Originally Posted by cleaningup

This is not true when we are talking about tuning. Altitude has absolutely everything to do with performance. BMW leaves a lot of room, and we can run near sea level times at 5000' on a stock tune due to how much room BMW leaves, but you are losing a lot more than 5 hp—even stock. You are also moving your torque curve further up the powerband because your turbos need to spin faster to pump more air up here and this happens at a higher RPM compared to sea level. In any case, stock Ms perform well at altitude. Like .5ish off the 1/4.

However, there are less oxygen molecules in that air which is the reactant in combustion. Turbos can force more air into the combustion chamber, but they do not create oxygen. When we are talking about tuning, they max out very fast at altitude. There is always nitrous which would make up for altitude. Injecting more oxygen molecules vs compressing more air into the cylinder. I digress.... I cannot hit the same boost pressure that a tuned car could hit at sea level because the air is less dense at my altitude. Less dense=less pressure. The article you linked showed 22PSI of boost on a 500hp car. Those are weak numbers compared to what people are doing on this platform. I know I already started, but don't even get me going on torque curves and gearing. There is so much more that goes into it.

To answer OPs question, I am FBO and port injection in Denver. I'm running 1.5 seconds slower 60-130s than guys running my setup at sea level at 90% wastegate duty cycle. I cruise up to 14,000'. It's fine, you just won't hit boost [...]

Not quite correct. If you create a set volume of air from sea level and conpress to 15psi then collect air from 8000ft altitude or even 20000 ft and compress to 15psi . (Aka the manifold) You will have the same amount of oxygen in the set volume from any altitude. 15psi of air contains Approximately 21% of oxygen. Doesnt matter where its collected from.
Air is 21% oxygen no matter what pressure / altitude.

The difference is the required turbo rpm to attain 15psi in the manifold whic takes more turbine passes at high altitude.. usually drifts outside the optimal turbo map. Increase heat cones into play. And the power band shifts... the oxygen content is the same. 15psi of air is 15 psi of air= same oxygen molecules. Moles

[Mapper]

Originally Posted by Hendo741

Being tuned then going to higher elevations is safe because the air gets less dense, turbos have to work harder, and you make less power. Getting tuned at elevation, then going closer to sea level is where things could get dicey. If you car is tuned to the razors edge at 7000 feet, when you go down in elevation it's going to be over boosting and could create issues.

A piggy back would be perfectly acceptable, but I would just use one of the less aggressive maps for safety.

It shouldn't overboost. Wastegate controlled turbos target a manifold pressure it doesnt care from what elevation. The idea that the engine would suddently add 2.5psi in the manifold going from a DA with 85kpa to 101kpa ambient isnt true on a wastegate controlled turbo. The whole reason turbos are advantageous going up in elevation. Same manifold pressure = same oxygen mole per volume