High-altitude tuning question

mgranic

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I need to understand what I'm being told here (in layman's terms) and I was hoping that someone on the forum, with expert knowledge on this subject could explain the following quote to me.

BTW, I live in the mile-high city of Denver...

Living so high you should start thinking about VNT17 soon. With atmoshpere pressure about 820 the stock turbo should not exeed 2070mbar absolute pressure in the manifold, that is not much more then a stock pressure at see level. With 2070mbar absolute pressure there won't be much power increase if you don't want to smoke. With a vnt17 you could run at about 2400mbar absolute pressure at your altitude.
Are there other people who have had successful high-altitude tuning?
 

jackbombay

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I'm 1,000 feet higher than you:D

And to answer your question, yes, it was one of the main reasons I wanted a custom tune. Unfortunately there are no compressor maps available for the 17 so Aligator started with the stock map from the PD 150, the car for which the VNT 17 is the stock turbo and we changed it slightly, took a little off the max boost at low RPM (I'd rather be safe than sorry when it comes to surge, which is different than spiking) and added a little through the mid and upper RPMs. I rarely ever exceed 4000 RPM though to stay away from "choke". I have about 20k miles on it so far.
 

mgranic

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jackbombay said:
I'm 1,000 feet higher than you:D

And to answer your question, yes, it was one of the main reasons I wanted a custom tune. Unfortunately there are no compressor maps available for the 17 so Aligator started with the stock map from the PD 150, the car for which the VNT 17 is the stock turbo and we changed it slightly, took a little off the max boost at low RPM (I'd rather be safe than sorry when it comes to surge, which is different than spiking) and added a little through the mid and upper RPMs. I rarely ever exceed 4000 RPM though to stay away from "choke". I have about 20k miles on it so far.
That sounds fine for a VNT17 turbo, but what about a stock turbo? What are the options there?
 

jackbombay

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The same approach could be used for the 15 as far as boost limits are concerned (check the stock maps for your altitude) and the tune
adjusted to keep spikes under control depending on how your turbo responds at your altitude.
 

slotracer577

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So far I have run a RC 1+ for about 7000 miles and then an alligator tune for the last 2000 or so. I commute from Monument hill to Denver every day. Car is an 06.5 PD with a 5 speed.

I am going to start out with this disclaimer, when Jeff programed my ECU he felt I had an issue with something in the car since it is really dead when rolling into the throttle. We also found water in the intake. I then sent the ECU back to him after running it for about 7000 miles and he flashed it back to stock so I could take it in to the dealer. The dealer said, car runs fine, could not find any issues. I guess I will have to spend more $$ to figure out what is up. I put in the alligator tune with the Q-loader to try it out.

Here are my observations: RC 1+ Faster than the Alligator, pulls harder up top, lots of smoke at higher RPM, some times I wanted less smoke. Milage dropped by about 2 mpg per tank. I was a little disappointed with the HP increase, expected more based on what people say about tunes and what I get in my ford PS. Did not dyno car to get real #'s.

Alligator tune is less hp than RC 1+ and less smoke. Milage is same as stock tune ~ 45 on my commute. Waiting to get some time with a vag com to log runs so Alligator will adjust program.

So far I am not sure which program I will stay with long term. I want more HP than the RC 1+, but with stock bottom end, less smoke than the RC 1+ and the milage of stock. There doesnt seem to be such a solution yet.

John
 

doc_m

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you can also get the tune adjusted to suite your needs like the rc one just as the tuner.
 

mgranic

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slotracer577 said:
So far I have run a RC 1+ for about 7000 miles and then an alligator tune for the last 2000 or so. I commute from Monument hill to Denver every day. Car is an 06.5 PD with a 5 speed.

I am going to start out with this disclaimer, when Jeff programed my ECU he felt I had an issue with something in the car since it is really dead when rolling into the throttle. We also found water in the intake. I then sent the ECU back to him after running it for about 7000 miles and he flashed it back to stock so I could take it in to the dealer. The dealer said, car runs fine, could not find any issues. I guess I will have to spend more $$ to figure out what is up. I put in the alligator tune with the Q-loader to try it out.

Here are my observations: RC 1+ Faster than the Alligator, pulls harder up top, lots of smoke at higher RPM, some times I wanted less smoke. Milage dropped by about 2 mpg per tank. I was a little disappointed with the HP increase, expected more based on what people say about tunes and what I get in my ford PS. Did not dyno car to get real #'s.

Alligator tune is less hp than RC 1+ and less smoke. Milage is same as stock tune ~ 45 on my commute. Waiting to get some time with a vag com to log runs so Alligator will adjust program.

So far I am not sure which program I will stay with long term. I want more HP than the RC 1+, but with stock bottom end, less smoke than the RC 1+ and the milage of stock. There doesnt seem to be such a solution yet.

John
I'm in an interesting situation where I have an upgraded fuel pump and PP520s (so I have an increase in fuel) but with the altitude I have decreased air pressure. To compensate for the thin air, the turbo has to spin faster to get more volume, but can only safely spin just so fast.

Can some other high-altitude guys chime in here as well? I'd like to hear how other tunes have done at high altitude.
 

juicy bits

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I don't have a tune but I did live in Ft.Collins for 3yrs. with my 2000 Jetta automatic. I would go to Vail to ski alot and I did get about 4 limp modes going up the passes, and after I moved to Boston I got another limp mode so I took it to Mr.Chill out here and he found play in the turbo shaft.

Chris's thought was the high alt out in CO was causing the turbo to spin too fast due to lower air pressure. I now have the 17 installed. I am not sure about tuning but I think the atmosphere at that altitude can break the vnt-15. Maybe a boost valve could help but I don't know if that would help if the turbo is spinning too fast?
 

jackbombay

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slotracer577 said:
I want more HP than the RC 1+... ...less smoke than the RC 1+ ...

There doesnt seem to be such a solution yet.

John
You will need to upgrade your turbo to accomplish that goal, there is no other solution.
 

jackbombay

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juicy bits said:
Maybe a boost valve could help but I don't know if that would help if the turbo is spinning too fast?
Boostsvalves have no place under the hood of a TDI and will not prevent turbo overspeed anyway. Overspeed/choke occurs at WOT and high RPM, don't exceed 4,000 RPM and you won't have to worry about it.
 

KROUT

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My boost valve isn't doing anything but it is still under the hood hooked up. I will leave it there just in case. No harm in having it if the boost never hits high enough to open it. Aligator has got my boost spot on no spikes.
 

jackbombay

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Kabin said:
I read some spiking was desirable as it reduces smoke upon instantaneous increases in fueling.
Maybe I'm missing something, but AFAIK at WOT you're up against the smoke map so the spike itself causes the instantaneous increases in fueling.
 

hgeittmann

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As I drove from home A (5000') to home B (9000') this evening, I pondered this very question. I don't know jack about tuning, but I was thinking about what's different w/ altitude... if a tune boosts Xpsi at sea level, it should(?) boost the same gage pressure (X) at high altitude. However, the compressor map is all about pressure ratios. At higher altitudes, the pressure ratio across the compressor will be higher (sorry don't have CB's MaxBoost in front of me to get all the terminology right and I'm just an arm chair engineer here) because ambient pressure is lower. For example, 1 bar boost at 1 bar ambient, PR = 2. 1 bar boost at 0.8bar ambient, PR = 2.25 ((1 + 0.8)/0.8). So at altitude, it's probably always less efficient to generate X amount of boost. Bummer. And yes, pressure at compressor is not simply ambient, but ambient - some pressure drop due to air filter and plumbing. But assuming said pressure drop is approximately the same regardless of ambient pressure... probably a decent assumption assuming MAF is similar, but obviously for a given gage boost pressure, MAF will be a little lower. Ok, now my brain hurts.

I also wonder about timing. Less partial pressure of O2 probably also means combustion occurs slower, iow timing is effectively retarded. If this is true (and I have no idea, so I hope someone with some real knowledge will chime in), then we're double screwed because anyone who's read anything about VE pumps knows that timing is limited to 18deg advance and then looked at their timing on a WOT run can see their aint no room for more advance... so what happens? High EGT's and smoke. What's the limit for PD's (dunno, even though I own one)? CR should help here if it's truly an issue.

So what does tuning for high altitude really mean? Obvisously de-rating it. What I'd be curious to see is how does a "high altitude tune" work at sea level??? What gets left on the table?
 
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woofie2

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jackbombay said:
Boostsvalves have no place under the hood of a TDI and will not prevent turbo overspeed anyway. Overspeed/choke occurs at WOT and high RPM, don't exceed 4,000 RPM and you won't have to worry about it.
Exactly! but boostvalves do save those who spike the turbo, I can get mine to work very easily.
Boostvalve will save the turbo from shearing the vanes off trying to make more boost pressure but not from flying apart trying to spin fast enough to compress thin air.
IIRC- the RallyVW team lost a turbo on Pikes Peak >12k feet, and it was a broken shaft.

As for tuning, keep the max boost requests down for the turbo, because running full PSI boost will cause the turbo to overspeed and detonate.
make sure you are running a thicker weight oil (oil viscosity will keep the turbo speeds slower. 15W40 synthetic)
Also get chip that has a switchable program, so you can go to stock or a lower power map for winter, a Diesel makes more power naturally, the air is thinner(worse turbo overspeed problems), as well as less power is needed to slip the wheels on a wet, snow or ice covered road.
 

woofie2

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hgeittmann said:
I also wonder about timing. Less partial pressure of O2 probably also means combustion occurs slower, iow timing is effectively retarded. If this is true (and I have no idea, so I hope someone with some real knowledge will chime in), then we're double screwed because anyone who's read anything about VE pumps knows that timing is limited to 18deg advance and then looked at their timing on a WOT run can see their aint no room for more advance... so what happens? High EGT's and smoke. What's the limit for PD's (dunno, even though I own one)? CR should help here if it's truly an issue.
you are partially correct, but
with boost pressure raising the intake pressure to X value, the MAF measures the amount of air passing it's grid, so the computer can squirt less fuel because it knows there is less air to burn in the cylinders.
Which is why you have little or no power below 2000 RPMs for climbing.... (I stalled three times pulling out of the trail ridge visitors center, the car needs boost to drive!)
 

jackbombay

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hgeittmann said:
What I'd be curious to see is how does a "high altitude tune" work at sea level??? What gets left on the table?
Nothing, because the car knows by the batrometric pressure sensor that it is at sea level.
 

hgeittmann

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jackbombay said:
Nothing, because the car knows by the batrometric pressure sensor that it is at sea level.
Yep, so what in the world does it mean to be tuned for high altitude then? Is there some sort of scalar or vector applied to the maps that represents ambient pressure, or what in the world are you talking about when you mention your elevation (you mention it often) and how it relates to your tune???
 

Roller

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woofie2 said:
...the MAF measures the amount of air passing it's grid, so the computer can squirt less fuel because it knows there is less air to burn in the cylinders.
I live @7K feet and am interested in a tune, so thanks for the info here! I was wondering if you could help me understand; why would there be a less partial pressure of O2 in the intake manifold when boost is on? 15psi at the intake in Santa Fe should still be 15psi at sea level, no? It seems that since there's a pressure transducer in the IM, this would be the best measure of the mass of O2 to calculate the mass of fuel injected... Just pontificating... Also, why would we need a MAF measurement to begin with; for calculating emissions/ EGR control maybe? Thanks!
 

Roller

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hgeittmann said:
Yep, so what in the world does it mean to be tuned for high altitude then? ?
I'd like to understand this better, too. In my mind (lonely in there...), it seems that since the turbo provides whatever psi at the manifold that the ECU requests (or at least tries to), the only concern with high altitude is the higher RPM the compressor has to turn in order to achieve a given IM pressure; to acheive 2 bar in the IM, the turbo would not have to spin as fast at sea level since ambient pressure is already closer to 2 bar than at higher elevation; or in short, what hgeittmann said in his earlier post.

So does that mean a high altitude tune would, among other things, lower the max boost pressure to prevent the turbo from pulling too high of RPMs? We'd need to find the max safe RPM of the turbo at a given elevation and see what boost pressure that translates to and use that as an upper boost limit. :confused: Thinking way too hard, need caffeine...
 

Roller

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hgeittmann said:
15psi is gage pressure, meaning 15psi more than ambient.
ohhh, thanks! So, that means there's an absolute pressure transducer elsewhere (to measure ambient pressure), then a differential one measuring IM pressure relative to ambient; gotya. Will VAGCOM let you read both of those? I really need to get one to help me work this stuff out better, thanks!
 

hgeittmann

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The pressure sensors are all absolute pressure sensors, but everyone talks about Xpsi boost as a boost gage shows the differential pressure. The baro sensor sits somewhere in the engine bay. For my '96, the intake manifold transducer is in the ECU. Newer cars put the sensor in the plumbing and route wires back to the ecu instead of tubing. You can read both sensors with VAGCOM. MAP is channel 11. Barometric pressure is channel 10 I believe.

I'd like to understand the tuning better too. I have an idea which I'm sure is either partly or completely incorrect. Basically there are maps for fuel, timing, and boost. Now there could be a boost map for different barometric pressures, but I kind of doubt it. More likely there is a factor related to barometric pressure that modifies the requested MAP. Possibly fuel as well. Or it could be that simply modifying requested MAP causes lower MAF, which in turn decreases the fueling.

So IF this is approximately the way it really works, tuning for altitude would simply be modifying the scalar(s) that are related to ambient pressure. That doesn't really seem like that big of a deal to me.

Some people might want to push the throttle response to be lighter at low go-pedal values and kick in only past 1/2 throttle or something. That's not necessarily tuning for altitude, that's just changing the way the car drives at all elevations. If the motivation for that is related to taking it easier on the turbo when it's spooling (vehicle accelerating), that's fine, but I just don't see that as tuning the vehicle for higher altitudes.
 

jackbombay

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hgeittmann said:
Yep, so what in the world does it mean to be tuned for high altitude then?
Turbos spool at different rates depending on altitude, I want the response (requested boost) to be mapped for my altitude so that I don't have spikes or undershoot.
 

hgeittmann

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jackbombay said:
Turbos spool at different rates depending on altitude, I want the response (requested boost) to be mapped for my altitude so that I don't have spikes or undershoot.
If you were to take your car w/ the tune for your elevation to sealevel, do you think the ecu would compensate and deliver the same tight boost control? If boost could be increased at a faster rate at lower altitude, then the tune is de-rated, which is fine as it simply illustrates what must be done to operate safely at higher elevations. If the ecu compensates and performs flawlessly, then this discussion is pointless... there is no need to tune for elevation per se, rather tune for proper boost response.
 

TDiaght

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Hey guys Im new on the forum, but been reading all your posts especially these about alltitude. Im from South Africa, Johannesburg and we are at 6000ft here and our tempretures are very rarely below 15 degrees C... Can you guys give me some advise on how to get rid of the lack of power i often feel in these conditions!!
 

jackbombay

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hgeittmann said:
If you were to take your car w/ the tune for your elevation to sealevel, do you think the ecu would compensate and deliver the same tight boost control? If boost could be increased at a faster rate at lower altitude, then the tune is de-rated, which is fine as it simply illustrates what must be done to operate safely at higher elevations. If the ecu compensates and performs flawlessly, then this discussion is pointless... there is no need to tune for elevation per se, rather tune for proper boost response.
Given the number of blown turbos TDI are suffering from at Pikes peak this past week I am still glad my car was tuned at altitude :).

I do think that tunes need to be derated at altitude, but that shouldn't affect their sea-level performace.
 
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otbBlaine

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Roller said:
I live @7K feet and am interested in a tune, so thanks for the info here! I was wondering if you could help me understand; why would there be a less partial pressure of O2 in the intake manifold when boost is on? 15psi at the intake in Santa Fe should still be 15psi at sea level, no? It seems that since there's a pressure transducer in the IM, this would be the best measure of the mass of O2 to calculate the mass of fuel injected... Just pontificating... Also, why would we need a MAF measurement to begin with; for calculating emissions/ EGR control maybe? Thanks!
Pm me, I'll show you what the Upsolute tune feels like....

ps. do you have a laptop? I've got a VAG-COM but can't get it to work on the mac and I need to re-check my IQ after doing the hammer mod.
 

Syncrogreg

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Hello I'm headed to pikes peak with my TDI bug and I was wondering if there is a genius out there that would know some rough numbers on how many degree timing it takes per thousand feet???

I have punched some numbers approximately in my ECU bit I know they are not correct.... More of an eyeball .

Let me know.

Greg
 
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