- Thread starter SVcummins
- Start date
Oregon Tractor Jack
Member
Yes it does. International used to offer the letter series tractors with a high altitude option. I believe it was designed for tractors that would operate at 5000ft and above. I don't remember exactly how much it upped the compression but it was at least one point. There just isn't as much air at higher altitudes. You can only compress what you have to start with.
OTJ
OTJ
The compression ratio stays the same, but you start with less pressure. Sea level atmospheric pressure is 14.7 psi. 10000 ft is 10.1 psi. So if you have an 8:1 compression ratio, at sea level your theoretical cylinder pressure would be 102.9 psig. You would only have 70.7 psig at 10000 ft.
guido
Well-known Member
Hello svcummins,
Horse power goes down, not the compression. Less air available for combustion, also a 1% less h.p. for every 10* above rated temperature. NOW that holds true for naturally aspirated engines as well as supercharged engines.
For turbocharged engines the elevation H.P. loss is 4% for each 1000
feet of elevation. Latest SAE H.P. I have stated is for 2005, could have changed, when I went
to school the SAE specs were different then 2005,
Guido.
Horse power goes down, not the compression. Less air available for combustion, also a 1% less h.p. for every 10* above rated temperature. NOW that holds true for naturally aspirated engines as well as supercharged engines.
For turbocharged engines the elevation H.P. loss is 4% for each 1000
feet of elevation. Latest SAE H.P. I have stated is for 2005, could have changed, when I went
to school the SAE specs were different then 2005,
Guido.
MarkB_MI
Well-known Member
- Location
- Motown USA
Compression ratio is unaffected by altitude, because it's fixed by the mechanics of the engine. Power, on the other hand, not.
The greater the density of the air-fuel mixture, the greater the power output of a given engine. The density of air is affected by altitude, temperature and humidity. Pilots are well aware of this effect and routinely calculate "density altitude" to predict aircraft performance.
As density altitude increases (meaning air density decreases), the engine becomes less prone to detonation. So the engine may be operated with lower octane fuel or with greater spark advance. If you travel from Kansas or Nebraska into Colorado, you'll notice the octane rating posted on gas pumps drops when you cross the Colorado state line. That's because states at high elevations are allowed to sell lower octane gasoline than is sold in neighboring states. And back in the day, before computerized engine control, we would run our engines with a few degrees extra advance beyond factory spec when we were at high altitude.
The greater the density of the air-fuel mixture, the greater the power output of a given engine. The density of air is affected by altitude, temperature and humidity. Pilots are well aware of this effect and routinely calculate "density altitude" to predict aircraft performance.
As density altitude increases (meaning air density decreases), the engine becomes less prone to detonation. So the engine may be operated with lower octane fuel or with greater spark advance. If you travel from Kansas or Nebraska into Colorado, you'll notice the octane rating posted on gas pumps drops when you cross the Colorado state line. That's because states at high elevations are allowed to sell lower octane gasoline than is sold in neighboring states. And back in the day, before computerized engine control, we would run our engines with a few degrees extra advance beyond factory spec when we were at high altitude.
Bob Bancroft
Well-known Member
- Location
- Aurora NY
Interesting discussion.
I recall reading, [for what it's worth] about the DT466 engine I used to have, that it would maintain HP up to 10,000 feet MSL.
I don't know if that means it was producing considerably more than advertised HP at sea level?! But the claim was the turbocharger compensated for altitude[air density]
I recall reading, [for what it's worth] about the DT466 engine I used to have, that it would maintain HP up to 10,000 feet MSL.
I don't know if that means it was producing considerably more than advertised HP at sea level?! But the claim was the turbocharger compensated for altitude[air density]
MarkB_MI
Well-known Member
- Location
- Motown USA
> I don't know if that means it was producing considerably more than advertised HP at sea level?
I don't know about that particular engine, but it was once common to "turbo-normalize" aircraft engines to a flat rating from sea level on up to some specified altitude. Since the engine is not supercharged above sea level atmospheric pressure, the engine components don't need to be beefed up from their naturally-aspirated equivalents.
I don't know about that particular engine, but it was once common to "turbo-normalize" aircraft engines to a flat rating from sea level on up to some specified altitude. Since the engine is not supercharged above sea level atmospheric pressure, the engine components don't need to be beefed up from their naturally-aspirated equivalents.
Texasmark1
Well-known Member
Interesting. I went to Arizona some years back and being used to 87 octane here at 800+ feet. Went to fill up and the octane ratings were a point or two lower. Got me to wondering....now I know.
Ok, moving along with this, you buy a widget. Look in the operator's instructions and it says 89 min. Daaaaa. Does that mean if in the Rockies your chain saw, not just MIGHT work better with premium, MUST have premium to meed design performance specs???????
Ok, moving along with this, you buy a widget. Look in the operator's instructions and it says 89 min. Daaaaa. Does that mean if in the Rockies your chain saw, not just MIGHT work better with premium, MUST have premium to meed design performance specs???????
MarkB_MI
Well-known Member
- Location
- Motown USA
> Ok, moving along with this, you buy a widget. Look in the operator's instructions and it says 89 min...
First off, the recommended octane ratings for outdoor power equipment are generally given as Research Octane Number (RON). But pump numbers are not RON; they're the average of the Research and Motor Octane Numbers for the fuel. This inflates the rating by a couple of points. So if your equipment specifies 89 octane and you use 87, you're probably OK. And of course if you're at a five thousand foot elevation, you can probably chop off a couple more points, meaning 85 octane would be fine.
That said, it never hurts to use a higher octane than specified in the manual.
First off, the recommended octane ratings for outdoor power equipment are generally given as Research Octane Number (RON). But pump numbers are not RON; they're the average of the Research and Motor Octane Numbers for the fuel. This inflates the rating by a couple of points. So if your equipment specifies 89 octane and you use 87, you're probably OK. And of course if you're at a five thousand foot elevation, you can probably chop off a couple more points, meaning 85 octane would be fine.
That said, it never hurts to use a higher octane than specified in the manual.
rlp in Co.
Well-known Member
Thanks for that explanation moresmoke. Took me a while to figure out why you subtract the original atmospheric pressure to get the gauge pressure! Ha.
Ok, another question. Why does it take several revolutions to reach the top pressure when using a compression tester?
I actually answered my own questions after I thought about them for awhile.
Ok, another question. Why does it take several revolutions to reach the top pressure when using a compression tester?
I actually answered my own questions after I thought about them for awhile.
Texasmark1
Well-known Member
Got me confused on this answer of yours. What do you mean? On "read the manual", if you are implying that I don't, I was quoting from them so I must have read them. What got me interested in octane posted in the manuals was listening to "Jeffcat" and following his advice on irridium plugs, replacement carbs, and premium gasoline for small engines, BS V twins in particular. He has been dead-nuts on with his recommendations.....obviously he has BTDT and passed on his findings.
Texasmark1
Well-known Member
"First off, the recommended octane ratings for outdoor power equipment are generally given as Research Octane Number (RON).".........
Based upon on what references? "(Research+Motor)/2" has been the standard method of rating as I know it since Ethanol came out down here. Since Ethanol is mentioned in the manuals also, why would they post octanes based on RON numbers?
Based upon on what references? "(Research+Motor)/2" has been the standard method of rating as I know it since Ethanol came out down here. Since Ethanol is mentioned in the manuals also, why would they post octanes based on RON numbers?
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