cam for high elevation
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From: Maricopa, AZ
OP, have you figured out what cam you are going with?
So maybe the best way to build a cam for elevation is to find out the max you can get away with at the lowest DA it will be running in and build around that? So your you it's 5000ft DA, for me it's <1,000 ft DA. Which really sucks cause most of the year I'm over 3500ft DA.
TECH Addict
Joined: Dec 2010
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From: Maricopa, AZ
TECH Addict
Joined: Dec 2010
Posts: 2,610
Likes: 4
From: Maricopa, AZ
Slightly off topic from the specific cam at altitude, but the best thing you can do with elevation is add boost. You make pretty much the same power as everyone else this way and it gets rid of the inconsistencies that come with elevation.
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From: Maricopa, AZ
But not nearly as bad as NA is effected. One day I may just go that route though.....
It still varies based on DA, but not as drastically because the pressure on the intake charge stays relatively the same. But, the efficiency of the motor is still not as good because it has to work harder to compress the air to the same boost. So the thinner the air the more compression needs to happen and the less efficient the motor will be, that's assuming the turbo is powerful enough to compress the air to it's regulated maximum pressure. On top of that the Turbo will produce less pressure in the same amount of time as it would with lower DA's so power across the entire RPM band is decreased and delayed.
But not nearly as bad as NA is effected. One day I may just go that route though.....
But not nearly as bad as NA is effected. One day I may just go that route though.....
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Verdad Gallardo TECH Addict
Joined: Dec 2010
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From: Maricopa, AZ
Yes, it's amazing the amount of technological advancements made in the last 10 years in Turbo technology. Some turbos are so efficient that they can be used with non-turbo specific cams. Those cars I have no doubt will hit that mark, but it'll take more fuel to do it. So still less efficient. That's not to take away what they have done, it's impressive and I look forward to more advancements in the future.
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Many years ago I lived at 9,600 ft elevation and spent a lot of time driving between 5,000 and 8,000 ft in a Chevy pickup with a Gen I 350. When I moved there from Texas, the engine had a fairly mild 204/214 cam that worked fine in the lowlands. But at high elevation it became a real dog below 3,000 RPM. I leaned out the Edelbrock carb which helped some, but what really changed things was a new cam.
After speaking with a Crane Cams tech, I bought a very unusual flat tappet cam from them: their #114112 at 194/204 with a 104 LSA. That cam closed the intake valve a lot sooner (around 18 crankshaft degrees as I recall) than the old cam, making more cylinder pressure. Bottom line was a LOT more torque and better throttle response in the 1500-3000 RPM range, and being able to use one gear higher when driving around switchbacks up the mountain road to my house. Downside was the engine pretty much gave up at 4000 RPM, but, hey, it probably spent 98% of the time at 1500-3000.
Anyway, when I moved back down to around 800 ft elevation, I re-jetted the carb and drove the truck with that little cam for several more years. Never heard any detonation, even on very hot days, but that was probably due to the lame ~8.0:1 static compression.
So, I'd suggest you focus on the intake closing angle to make more power at altitude. But your power band is only going to be so wide, so any gains at low-mid RPMs will cost you at higher RPMs. But you also have to be realistic about how much time your engine spends at high RPMs.
After speaking with a Crane Cams tech, I bought a very unusual flat tappet cam from them: their #114112 at 194/204 with a 104 LSA. That cam closed the intake valve a lot sooner (around 18 crankshaft degrees as I recall) than the old cam, making more cylinder pressure. Bottom line was a LOT more torque and better throttle response in the 1500-3000 RPM range, and being able to use one gear higher when driving around switchbacks up the mountain road to my house. Downside was the engine pretty much gave up at 4000 RPM, but, hey, it probably spent 98% of the time at 1500-3000.
Anyway, when I moved back down to around 800 ft elevation, I re-jetted the carb and drove the truck with that little cam for several more years. Never heard any detonation, even on very hot days, but that was probably due to the lame ~8.0:1 static compression.
So, I'd suggest you focus on the intake closing angle to make more power at altitude. But your power band is only going to be so wide, so any gains at low-mid RPMs will cost you at higher RPMs. But you also have to be realistic about how much time your engine spends at high RPMs.
Last edited by MikeBr; Aug 3, 2014 at 08:46 AM.
Teching In
Joined: Dec 2012
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From: Albuquerque
Very interested in this convo.
I too am in Albuquerque - a low DA (beginning/end of season) is in the low 6000's, where during the warmer months DA is quite often over 8000ft. I mostly go to the track in the ~7000ft range (give or take 500).
Speaking of cams, I initially installed a BTR Stage 2 cam and *lost* power, quite a bit (~50rwhp). I swapped it out to a GT9 cam and got my power back, with only about a 15rwhp gain over pre-cam dynos. Most people at sea level seem to be picking up around 40rwhp with similar mods.
BTR Stage 2 - 227/242 .614"/.592" 122+6 LSA
GT9 - 215/247 .629"/.656" 121 LSA
Could any of you explain why the 2 above cams (Especially the 1st one) would do so badly? I notice quite a bit of split in both cams, would that be a bad thing?
Car: 2009 CTS-V, 13-15psi (at elevation), stock heads, stock manifolds, cat delete, e85.
I made 620-630'ish rwhp before cam (depending on day and dyno goblins), currently making 650rwhp with more pulley (about 1-2psi) and the GT9 cam.
I too am in Albuquerque - a low DA (beginning/end of season) is in the low 6000's, where during the warmer months DA is quite often over 8000ft. I mostly go to the track in the ~7000ft range (give or take 500).
Speaking of cams, I initially installed a BTR Stage 2 cam and *lost* power, quite a bit (~50rwhp). I swapped it out to a GT9 cam and got my power back, with only about a 15rwhp gain over pre-cam dynos. Most people at sea level seem to be picking up around 40rwhp with similar mods.
BTR Stage 2 - 227/242 .614"/.592" 122+6 LSA
GT9 - 215/247 .629"/.656" 121 LSA
Could any of you explain why the 2 above cams (Especially the 1st one) would do so badly? I notice quite a bit of split in both cams, would that be a bad thing?
Car: 2009 CTS-V, 13-15psi (at elevation), stock heads, stock manifolds, cat delete, e85.
I made 620-630'ish rwhp before cam (depending on day and dyno goblins), currently making 650rwhp with more pulley (about 1-2psi) and the GT9 cam.
Formerly 2001c3driver-7/31/10
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From: Santa Fe New Mexico
Wow- learned a lot by reading this thread. Have the same problem living at 7,000 feet, Santa Fe NM. the truck feels sluggish with 3.42 gears like a loose high stall converter but, just went to Chicago for a memorial, and OOFA!- this thing ran like a scalded cat! Everything was right there right now. My first endeavor is to swap in some 3.90 gears, and then think about a cam if necessary because- as illustrated you can really cam it up for this elevation and blow it up when going to sea level...........
Speaking of cams, I initially installed a BTR Stage 2 cam and *lost* power, quite a bit (~50rwhp). I swapped it out to a GT9 cam and got my power back, with only about a 15rwhp gain over pre-cam dynos. Most people at sea level seem to be picking up around 40rwhp with similar mods.
BTR Stage 2 - 227/242 .614"/.592" 122+6 LSA
GT9 - 215/247 .629"/.656" 121 LSA
Could any of you explain why the 2 above cams (Especially the 1st one) would do so badly? I notice quite a bit of split in both cams, would that be a bad thing?
BTR Stage 2 - 227/242 .614"/.592" 122+6 LSA
GT9 - 215/247 .629"/.656" 121 LSA
Could any of you explain why the 2 above cams (Especially the 1st one) would do so badly? I notice quite a bit of split in both cams, would that be a bad thing?
If the valve closes early, like 10*ABDC, then you'll get a lot of cylinder pressure in the lower rpm ranges. But it will tend to give up some power at the top end. And the opposite is true.
You can easily lose power by choosing the wrong cam for your combo. You'll need to look at the cam card for the details.
Wow- learned a lot by reading this thread. Have the same problem living at 7,000 feet, Santa Fe NM. the truck feels sluggish with 3.42 gears like a loose high stall converter but, just went to Chicago for a memorial, and OOFA!- this thing ran like a scalded cat! Everything was right there right now. My first endeavor is to swap in some 3.90 gears, and then think about a cam if necessary because- as illustrated you can really cam it up for this elevation and blow it up when going to sea level...........
I have 3.42s in a 5.3l truck at 700ft elevation and will tell you 3.73-4.10 is a great idea, truck tire height makes a world of difference.
Most f-body guys opt for 3.73 well to get the same effective ratio with a truck 265/70/17 you need 4.45.
Basically 3.42s are equivalent to 2.93s in an f-body when you consider tire size.
How many folks are rushing around to put 2.93s in their f-body?
I got the truck tire size from my 2005 Sierra and am using 26.5" as f-body size if anyone has a problem with my math.
Most f-body guys opt for 3.73 well to get the same effective ratio with a truck 265/70/17 you need 4.45.
Basically 3.42s are equivalent to 2.93s in an f-body when you consider tire size.
How many folks are rushing around to put 2.93s in their f-body?
I got the truck tire size from my 2005 Sierra and am using 26.5" as f-body size if anyone has a problem with my math.
Formerly 2001c3driver-7/31/10
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From: Santa Fe New Mexico
Math is good. Also- the proposed camshaft is great, too. As always with cam trimming it's a delicate balance attempting to retain precious vacuum and other parameters. I'm just saying at this point for me I'm choosing to go the ring and pinion route as it's pretty hilly in my locale as well. But the biggest thing I've observed is staying on the bubble on the power band and that it still exists here in the stratosphere it just takes a lot more work to get to, after the 3.90's if I think I can still use more I'll look at camshafts; prolly something on the 113 LSA. in observance of the camshaft mentioned above- it looks great(according to what I know) as the lift may seem up there, keep in mind you're spending a very short amount of time at max lift and the bulk of time spent should be focused on where the heads flow best- yes, I've spent many a sleepless night pondering the perfect camshaft.
So in a nutshell- I'll start off with 3.90 ring and pinions...............
So in a nutshell- I'll start off with 3.90 ring and pinions...............