altitude and timing

[jimi87-t]

I had to go pick up a new timing light today, apparently mine got lost in the move. So the guy at the parts place said, "You know you need to add 1 deg of timing for every 1000 ft of elevation."

I have actually heard this from many people up here. I have been living in CO now for about 2 years at 6500 ft elevation. And have no clue if this is true or not, especially on a boosted car that is not effected as much by the altitude.

I do know they have lower octane gas up here compared to what we had in TX. Highest octane here is 91, in TX it was 93. I guess the altitude effects the octane rating. But, what about on a boosted engine?

I would think that on a boosted engine, under boost, there would be no difference for the timing and the octane.

Anyone know about high altitude tuning? :1zhelp:

 

[sthmstr]

Cool to see another Supra in Co.!

I have heard the same figure for timing adjustments and have alot of experience adjusting it when I go 4 wheelin. I live in Denver and try to be in the mountains at least once a week. I notice huge power gains when I advance the timing. Most times in Denver I run about 5 degrees advanced.

With a boosted car it kinda depends on how much boost you are running. Sometimes when runnin large amounts of boost you will want to retard it accordingly. How modified is your car?

 

[jimi87-t]

At the moment I am running stock boost, but in the next month or so I will be finishing the build which is just basically a different turbo and running around 12psi and installing my Maftpro with RC 550s.
What is done so far you can see in my build, but the main things are, a FFIM with 70mm TB, large FMIC, 2.5" IC piping, 3" DP and full 3" exhaust.

 

[sthmstr]

Sounds like a great setup. I don't think you'll have to wory about retarding the timing at at all to compensat for boost. Just start factory timing, then add about 3-4 degrees. Run it a bit and bump up as needed according to idle from there. If you're at 6500ft then I don't think you need to really go crazy advancing it. I always set it then go on the highway for a few miles. I fit feels like you have lost any top end you've advanced too far and should back it off a bit.

 

[Poodles]

Turbo car isn't effected, plus it's fuel injected so it should adjust accordingly anyway.

As the pressures seen by the engine are dependant on temp and the pressure from the turbo, it's only going to effect off boost power, and could lead to issues under boost.

I remember a story about a guy beating up on a Viper in CO in a Supra that most people didn't think had enough mods to beat it. Altitude is a bitch to N/A's...

 

[jimi87-t]

Thats what I was thinking, because the ECU has an altitude sensor, so it must be able to correct for it.
My thought is that the timing/altitude thing came from carbureted engines/ pre EFI.

 

[Poodles]

Paging jetjock!

 

[sthmstr]

Any and all combustion motors are affected by altitude. Having a NA motor on average looses 35% power in our altitude. A forced induction car only looses 15%. Granted these are very general terms and there are many cars either way that have better or tougher times compensating. My Samurai is fuel injected and soon to be boosted, but used to be carbureated, so I have experience in all of those fields with just that car. not to mention others. I have driven Audi's that are fantastic at altitude and also have been absolutely disgusted by every LS1 or LS2 I've driven in colorado. Just depends on that vehicle's ability to properly meter. Really there is no way on paper to tell you the exact timing to set it at. I recomended the 3 degree bump because with a stock motor that still does most of it's power form the motor and not form the power adder/ pre OBD-I computer you will not have a vehicle that does quite as well as say a WRX or Terminator Cobra.

The key part is to start for stock then work your way up according to how the car feels when you drive it. I do believe you will end up advancing your timing from stock but how high will be completely up to the feel of the car.

As to success stories of boosted cars in Colorado spanking Vipers, etc.....Very common!
Try 93 MR2 with 275 at the wheels destroying 1. I swapped a JDM 7m into a 90 supra last year and ate a LS2 GTO for breakfast. Stock except for intake and exhaust. Easily done. Bottom line is at altitude forced induction is king!

 

[jetjock]

Paging jetjock!

Not me. There was a time I'd have answered something like this quickly but after the tire pressure thread I'm holding off for the entertainment value. I pleased to see it's already getting up there

 

[sthmstr]

Fair enough. I'll step away.

 

[jetjock]

No need. I didn't say you were entirely wrong. All comes down to whether we're talking in general (you did mention that) or about this particular car. Besides, I'm sure they'll be input from others...

 

[jimi87-t]

Well I personally am only concerned with the supra, as my other car has no timing adjustment
But I'm in the process of getting ready to fire up the supra as we speak, as in the next 30min to an hour. And my goal is to set timing and fuel psi.
So for now I will just set to 10deg as per TSRM.......until the dust settles....

 

[jetjock]

No timing adjustment eh? Imagine that.

Set it to spec or a little more if you like. Not because of altitude but because some people do it to squeeze out a little more power. I understand why but stock is fine too. After all the ESA system has been carefully designed to provide correct timing under all conditions. Btw the HAC sensor is there mainly for fuel correction. It's there along with the IAT sensor because the stock AFM is volumetric, not mass flow. The only part it plays in timing involves idle stabilization at altitude.

I don't wish to get into a big discussion about this but fwiw I can tell you ignition timing on piston aircraft engines (turbo, N/A, carbed, fuel injected, doesn't matter) remains unchanged regardless of altitude and the manufacturers of those things work hard to eek out every bit of power they can because in aircraft marketing performance is everything. There's no speed limits up there (well, actually there is but I won't go into that) and those engines are usually run at 75% power for hours on end. Fuel delivery (mixture) is the only thing adjusted with altitude while timing stays the same (set internally for max power) all the way up to the aircraft's service ceiling, which can be over 25,000 ft for a turbo engine...

 

[grimreaper]

he cracked! good info to understand from a different point of view. Is it safe to say the added timing would be to make up for the altitude power drop?

 

[Poodles]

Knew I paged the right person

I'd be curious to see what a Supra would dyno at at sea level and at that elevation (uncorrected), as under boost it shouldn't really matter but I've heard differently. Unless compressor map issues come into play I don't see it effecting it, at least in theory (and I know turbocharged aircraft where king during WW2).

 

[IJ.]

Knew I paged the right person

I'd be curious to see what a Supra would dyno at at sea level and at that elevation (uncorrected), as under boost it shouldn't really matter but I've heard differently. Unless compressor map issues come into play I don't see it effecting it, at least in theory (and I know turbocharged aircraft where king during WW2).

Change that to "forced induction" 2 stage Merlin springs to mind

I have no input on altitude tuning as our biggest mountain is a speed bump so it's not something I've ever had to learn.

 

[suprarx7nut]

I have always wondered what my NA would feel like at sea level. I imagine it'd feel like a free 10-20 horsepower, but unfortunately I've never driven it below ~4000ft.

My beat to hell turbo last summer was MUCH faster than my NA and it was bone stock with poor compression so it only feeds my opinion that turbo is the only way to go at this altitude...

 

[Poodles]

Turbo auto adjusts for altitude, superchargers don't

P-38 Lightning comes to mind with the Allison engine

 

[IJ.]

2 stage does

 

[jdub]

Turbo auto adjusts for altitude, superchargers don't

P-38 Lightning comes to mind with the Allison engine

Pretty sure the Allison V1710 used in the P-38 was turbo-supercharged.