Useless Spoolup Info

[motorhead]

True or false. Higher compression ratio produces more exhaust velocity and more heat...thus quickening spool time.

Really it depends.  If the cam and ignition timing, fuel, and architecture of the engine (and drivetrain) are not optimized for it: no.  The whole engine must be designed as a package to perform as such.

10 seconds on Goofle later...
http://www.xcceleration.com/cr-boost%20101.htm

http://energy.gov/sites/prod/files/2014/07/f17/ft016_heywood_2014_o.pdf

https://www.physicsforums.com/threads/high-compression-turbocharged-engines.646362/

Garrett still wants you to run low compression and a big turbo:
http://www.turbobygarrett.com/turbobygarrett/compression_ratio_with_boost

[Steve Wood]

http://speedtalk.com/forum/viewtopic.php?f=1&t=39166

My experience is that more compression (with no change in the cam) will raise the dynamic compression ratio creating more cylinder pressure so that the car spools faster.  Now, according to the above link, the exhaust temp may go down and that makes sense when I think about it.  On the other hand, I am guessing the velocity will actually increase.

[larrym]

Hmm why do higher compression motors run hotter if the exhaust temp is lower?

[Steve Wood]

because they release more heat into the cylinder to drive the piston downward and this heat is absorbed by the coolant passages and the oil....

[larrym]

I'm still confused how can there be cooler exhaust then? Would there not be more heat in the exhaust gas also.

[Steve Wood]

There is a more complete burn within the combustion chamber so the gas temperature that emerges should be less if the tune is correct.

Remember that an engine is essentially a heat pump.  Adding compression builds more heat because the heat is contained better in the cylinder due to the completeness of the combustion.  If the timing is reduced too much, then we get more heat out the exhaust valve...and we get less power

[Steve Wood]

and add to the above that the act of driving the piston down absorbs quite a bit of the heat generated by combustion so there is less left to exhaust


a compressed gas cools when allowed to expand

[earlbrown]

Let's keep this thread rolling. True or false. Higher compression ratio produces more exhaust velocity and more heat...thus quickening spool time.

Static or Dynamic?

[earlbrown]

I'm still confused how can there be cooler exhaust then? Would there not be more heat in the exhaust gas also.

10% cooler and 12% more of it.

Lower temp in degrees, but more heat in total.


(those numbers aren't exact)

[good2win22]

It's widely accepted that cooler air can make more power because the air is more dense. 
 
The earth's atmosphere contains 78% nitrogen, 21% oxygen and 1% other gases of which .03% is carbon dioxide, the composition and percentages of those gases remains constant no matter what the elevation is but the pressure decreases as the elevation increases.
 
With that being said, at sea level, what temperature would we see a negative benefit on power increases due to the density of the air?
 
Also, what would be the ideal temperature and elevation (density altitude) to get the most benefit from the turbo before getting the compressor wheel into blade compressiabili ty?
 
One other thing, in the aviation community engines are spec'd for the power they can make on what is called a "standard day."  A standard day being at sea level, 15 degrees C (59F) and altimeter setting of 29.92 inHg (1013.25 mbar).  How does the automotive world spec their engines?  I mean I can dyno an engine at Pike's Peak and get some numbers and then go to Galveston and dyno the same engine and get completely different numbers.

[Steve Wood]

There should be a dyno correction applied to bring the readings to standard....NH RA used to, and probably still does, apply a density altitude correction to compare cars from different venues as I recall.

I don't know if there is a tipping point, but we do everything we can practically to get the intake air as cold as possible to obtain the densest air going into the engine and, of course, we add fuel to keep the a/f where we want it.

Bigger intercoolers, intercoolers submerged in ice/water or alcohol, spraying the intercooler with co2 out of bottle, alky injection both post and pre-turbos, etc.  I would say the colder the air the better as long as the air is dry as possible.

As humidly increases, the less the "air" going into the engine.

[Steve Wood]

many articles out there discussing dyno corrections... here is one   http://www.superchevy.com/how-to/ghtp-1109-fact-and-fiction-of-dyno-correction-real-wheel-horsepower/

[Forzfed]

The earth's atmosphere contains 78% nitrogen, 21% oxygen and 1% other gases of which .03% is carbon dioxide, the composition and percentages of those gases remains constant no matter what the elevation is but the pressure decreases as the elevation increases.

Correct, but why mention % since all calculations are done with pressure and volume?  I do realize the last portion kind of explains that.  For me I always use the diameter formula for calculating volume, not radius because you don't buy pipe by radius even though it does give you the same answer.

[Steve Wood]

The earth's atmosphere contains 78% nitrogen, 21% oxygen and 1% other gases of which .03% is carbon dioxide, the composition and percentages of those gases remains constant no matter what the elevation is but the pressure decreases as the elevation increases.

Correct, but why mention % since all calculations are done with pressure and volume?  I do realize the last portion kind of explains that.  For me I always use the diameter formula for calculating volume, not radius because you don't buy pipe by radius even though it does give you the same answer.

You must stop eating Quibbles and Bits for breakfast!

[Forzfed]

I only mention that because of the practical aspect of it.  You don't go out and order radius pipe, so you divide by 2 then multiply by 2 again when you order it.  Just Monday, I used the steam tables to cross reference what temperature a coil should have at a given pressure, it was bang on for one and the other was off 20'C which is telling me the control valve isn't opening up all the way.

Steve, I only mention that because a really smart person mentioned it to me once and when you think about it, he was totally right.  Makes calculating and ordering of parts much easier, with less likely hood of ordering the wrong part because of something like I need a 6" diameter pipe but I accidently ordered 3" because I was thinking of radius.  This is why you stick with a practical standard.