How DA affects Compression?
Originally Posted by Old SStroker
As you increase altitude your Indicated Airspeed drops, but your True Airspeed stays the same or increases. Indicated Airspeed can be thought of as the number of molecules you plow thru in a period of time, while True Airspeed is how fast you pass each molecule.
A jet transport that cruises at 650 mph (true A/S) at altitude would have trouble going that fast near sea level.
A jet transport that cruises at 650 mph (true A/S) at altitude would have trouble going that fast near sea level.
Originally Posted by BlackHawk T/A
Actually Houston is under 2000, even being as insanely humid as it is right now, if the numbers are correct. Looks like elevation plays a much bigger role than humidity. In comparison i'm sitting at about 3000 DA.
11 Second Club
iTrader: (20)
Joined: Sep 2002
Posts: 2,684
Likes: 3
From: Albuquerque NM - The Land of 8000ft DA
Originally Posted by AOC
Wow, 8,000 DA??? And I thought we had it bad when we reach 3000 DA. lol.
pfft, I wish would could get that.
We've had a fluke of cold weather here in Albuqueruqe. I about shat my pants when I found out the DA was 7400ft. Usually around this time of year its 9000ft.
Was able to run a 12.51@107.9 on a 1.68 60'. Full bolt on 3100lb car with 4.30 gears.
easily an 11 second car at sea level
From what I understand, I actually lose about .5 points of compression living here in the Denver area. Less air to compress.
Makes that 12.64/115 look decent.
Stock gears, stock rear, crap launch, etc.
Makes that 12.64/115 look decent.
Stock gears, stock rear, crap launch, etc.
TECH Resident
Joined: May 2005
Posts: 983
Likes: 0
From: 8000DA Land
Originally Posted by sscam68
pfft, I wish would could get that.
We've had a fluke of cold weather here in Albuqueruqe. I about shat my pants when I found out the DA was 7400ft. Usually around this time of year its 9000ft.
Was able to run a 12.51@107.9 on a 1.68 60'. Full bolt on 3100lb car with 4.30 gears.
easily an 11 second car at sea level
We've had a fluke of cold weather here in Albuqueruqe. I about shat my pants when I found out the DA was 7400ft. Usually around this time of year its 9000ft.
Was able to run a 12.51@107.9 on a 1.68 60'. Full bolt on 3100lb car with 4.30 gears.
easily an 11 second car at sea level
yeah, guys crying for 12s at real low DAs crack me
On The Tree
Joined: Jun 2006
Posts: 120
Likes: 0
When building an engine for high altitude you can really up the compression. If the air is 20% less dense, you can up the compression by 20%.
You can also cut your exhaust duration down because you are puting 20% less air(lbs/hr) into the engine. You treat the engine a lot like you do a restrictor plate engine.
The only thing you need to change is to put a bigger radiator on the car, because there is less air to cool it.
You can also cut your exhaust duration down because you are puting 20% less air(lbs/hr) into the engine. You treat the engine a lot like you do a restrictor plate engine.
The only thing you need to change is to put a bigger radiator on the car, because there is less air to cool it.
11 Second Club
iTrader: (20)
Joined: Sep 2002
Posts: 2,684
Likes: 3
From: Albuquerque NM - The Land of 8000ft DA
Originally Posted by CamKing
When building an engine for high altitude you can really up the compression. If the air is 20% less dense, you can up the compression by 20%.
You can also cut your exhaust duration down because you are puting 20% less air(lbs/hr) into the engine. You treat the engine a lot like you do a restrictor plate engine.
The only thing you need to change is to put a bigger radiator on the car, because there is less air to cool it.
You can also cut your exhaust duration down because you are puting 20% less air(lbs/hr) into the engine. You treat the engine a lot like you do a restrictor plate engine.
The only thing you need to change is to put a bigger radiator on the car, because there is less air to cool it.
I was wondering how a cam grinder would look at our situation. Given our altitude a lot of the "off the shelf" grinds I don't think would work really well up here.
I'm thinking about a cam but would like something designed for our particular application. Got any recommendations?
Last edited by sscam68; Jul 8, 2006 at 11:46 PM.
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo
Originally Posted by Old SStroker
DA @ 200 miles up must be hard to figure, huh?
So why are they going ~18,000 mph? Why not ~24,000?
So why are they going ~18,000 mph? Why not ~24,000?
Breaking free of the Earth uses up almost all of the fuel.
TECH Fanatic
Joined: Jun 2002
Posts: 1,979
Likes: 3
From: Upstate NY
Originally Posted by white2001s10
If we had a space-based refueling station they would go faster than that.
Breaking free of the Earth uses up almost all of the fuel.
Breaking free of the Earth uses up almost all of the fuel.
What happens below about 18,000 mph to a craft launched from Earth?
What happens above about 24,000 mph to a craft launched from Earth?
On The Tree
Joined: Jun 2006
Posts: 120
Likes: 0
Originally Posted by sscam68
I'm thinking about a cam but would like something designed for our particular application. Got any recommendations?
PM me with all your specs and I'll get you a recommendation.
I've made a bunch of racing cams for high altitude, I'll just need to know if your planning on running it at lower altitudes also.
On The Tree
Joined: Jun 2006
Posts: 120
Likes: 0
Originally Posted by Wnts2Go10O
think of it this way. at sea level you have 14.7psi of natural boost. the higher up you go the less natural boost you have hence less power.
Normal N.A. cams and engines are designed for 14.697psi of boost, and if you don't have that much boost you need to change the design.
Originally Posted by Speed Density
Just wondering why in higher DAs you have to run less compression, wereas in lower DA you can run much more.
11 Second Club
iTrader: (20)
Joined: Sep 2002
Posts: 2,684
Likes: 3
From: Albuquerque NM - The Land of 8000ft DA
Originally Posted by CamKing
I'm sure I can figure it out.
PM me with all your specs and I'll get you a recommendation.
I've made a bunch of racing cams for high altitude, I'll just need to know if your planning on running it at lower altitudes also.
PM me with all your specs and I'll get you a recommendation.
I've made a bunch of racing cams for high altitude, I'll just need to know if your planning on running it at lower altitudes also.
In my particular app. the DA ranges from 9000ft in the summer (worst case scenario) to 6000ft in the winter.
In general, how would the cam design differ? What would be the design considerations? Mind you this is more of strip app. than a street. What kind of a static compression would work better? A lot of people with AFR combos are having the heads milled and ending up with a static compression of 11:1
(roughly). According to what you posted, if I were to up the compression 20% I would end up with a 13.2:1 static compression
. Maybe it's just me, but isn't that just a tad too high?Not to go to far off on a tangent, would the port design, both intake and exhaust, differ greatly for a high altitude app?
Frank
On The Tree
Joined: Jun 2006
Posts: 120
Likes: 0
Originally Posted by sscam68
According to what you posted, if I were to up the compression 20% I would end up with a 13.2:1 static compression . Maybe it's just me, but isn't that just a tad too high?
. Maybe it's just me, but isn't that just a tad too high?Some of the differences in cam design would be more area on the intake and less on the exhaust.
For me to figure out what you need, I need the Bore, Stroke, Rod Length, Peak HP RPM desired, RPM you want to launch at, Injector throttle body size, Comp ratio, Port Flow #'s, and Rocker Ratio.
Not to go to far off on a tangent, would the port design, both intake and exhaust, differ greatly for a high altitude app?
TECH Regular
Joined: Oct 2005
Posts: 430
Likes: 0
There is compelling logic to the argument that valve events need to be altered to best utilize the reduced air pressure at higher altitudes, but... Several books I have read on turbocharging say that for a well-matched system (in which exhaust back pressure is about the same as boost, unlike a typical bolt-on where the ratio can be as high as 2:1) there is essentially no change required to valve timings.
If no change is required for say plus 20 psi, then surely the same holds true for minus 3 or 4?
If no change is required for say plus 20 psi, then surely the same holds true for minus 3 or 4?
On The Tree
Joined: Jun 2006
Posts: 120
Likes: 0
Originally Posted by MadBill
Several books I have read on turbocharging say that for a well-matched system (in which exhaust back pressure is about the same as boost, unlike a typical bolt-on where the ratio can be as high as 2:1) there is essentially no change required to valve timings.