Im not so sure about this. I know elevation has a huge impact on atmospheric air density which is directly related to boost pressures. I have read articles that if you do drop from elevation to sea level you will gain significant HP, in upwards to 20% just from the 6,000ft im at. I actually wanted to put this to the test and take my Z up to pikes peak (the highest paved road in the continent), which is at 14,000ft, to see if my levels drop. But I honestly am not sure on the physics of it all.

In the equation for compound boost I am only expecting to see around 13psi. However this may be skewed because at the 7.5psi i was hitting i was only at 315whp. Now if i ran 7.5 on a turbo I would expect to see closer to 415. I have no idea what this compound will do in terms of hp per pound. Cant wait to get it on the dyno to see what happens. But if i hit anything 20+ its game over and ill have to wait another couple of months to rebuild with stronger internals.

SuperZ is driving his and hasnt mentioned anything about cranking out rediculous amounts of boost. (he hasnt mentioned anything really except that it works, its fun, and hes driving it daily). And im guessing he is pushing alot more than 4psi out of his turbo.

I wish he would throw out some numbers already. I wonder if hes waiting for me.

 

I have raced up Pikes Peak three years during the PPIHC with 928 Motorsports. You need to keep in mind that boost pressure and horsepower are not the same thing. A turbo will always spool fast enough to maintain pressure regardless of air density. It is true a car at X psi will have less power the higher it goes but pressure will remain constant on turbo vehicles hence why Pikes Peak cars tend to be turbocharged. Superchargers will see a loss in pressure due to air density and a fixed rpm curve.

It appears as though you are forgetting that compound boost is not additive. 8psi on your supercharger and 8psi on your turbo will not net 16. It will net much higher than that because the supercharger rating for the pulley is based on the inlet seeing only atmospheric pressure. Your setup will actually have positive pressure at the supercharger inlet and therefore your supercharger will flow more.

Again, you will need to be very cautious at such a low boost as the waste gate is typically not designed to bypass that much exhaust gas on a stock turbo kit.

 

I see. But overall with altitude your power goes down, in relation you have a less chance of mechanical failure. Hence if you went to sea level your power goes up and theres a higher chance of mechanical failure. Im not too concerned about this as i never plan to use my Z on a trip to the coast but good to know regardless.

Quamen, I fully understand that the compounding is not a function of addition. Im not quite sure where your drawing your implications that i assume it is. You must not have read this forum in its entireity as I have stated this multiple times and have even placed the formula for compounding in here somewhere.

To save some searching if your wondering:
((((6+14.6)/14.6)*((4+14.6)/14.6)))*14.6)-14.6=11.35psi

Props to you for racing up pikes peak. The documentary is sick. I am going to that this summer.

 

Your formula is correct. I misread one of your previous posts and apologize. I have read thru your entire thread and am aware that you have done calculations and commend you on not blindly going into this. The only thing I think may be different is that the supercharger pulley may actually net the psi it was rated for now. Either way I am excited to see your results.

SuperZ does need to post some numbers though

 

so we're all on the same page, that twin charged lotus got rear ended by a porsche who fled the scene.

nice progress OP.

 

Iwas able to find some more info on that lotus and it has a 6262 turbo, MP62 supercharger and 44mm waste gate. For the most part the same combo as for the Z which is good. The biggest difference is the 1.8L compared to our 3.5L.

 

There's ALOT more to that story.....ALOT more!!

http://www.lambopower.com/forum/inde...pic=62336&st=0

 

i agree definitly use map but i prefer map for anything personally. then use a aftermarket air temp sensor post somewhere mayby after the turbo intercooler or in one of the intake runners in the lower intake(stillen still uses that right?) thats why i went with a kinetix intake, easier to mount a iat sensor after the direct port meth. granted not a option with this.

T1(honda place) makes a tiny intake air temp sensor that responds as quickly to temp changes as the gm one. i went with it to prevent much protrusion into the intake with a bung welded on.
also topgun if you have a open dump try and angle it to the ground or get one custom made to angle it at the ground. thats what i did and cant even hear it over the straight pipe exhuast even though its directly under my seat pretty much.

 

Well at least we know and it is proven that this combo works. It is not a bottleneck as many had posted (out of pure speculation). Even though the engine is half the size the engine will still see quick and responsive boost. Im excited.

So just for fun here is a max calculation using the equation if i were to crank them both up.

((((8.5+14.6)/14.6)*((15+14.6)/14.6))*14.6)-14.6 = 32.22psi

Its funny though that they say "a 280 hp supercharger" in the video. Out of a MP62..really?

 

That's crazy if the minimum boost you can get is in the 20-30's... boost cut is going to be activating every time you mash it.

 

Great info. 280HP was prob running that same gas/alcohol set up snd massive timing

 

What? Minimum is 11. Maximum is 32. You must have misread.

 

I know this end of the conversation is dead already but in my nifty SAE school book it said that on a NA engine for every 1000ft above sea level you were you lost 3% overall engine power (assuming it meant torque and HP) but if you were turbo charged you could alleviate this problem. I was wondering if based on this concept that turbo charging a car that is already at altitude (meaning it started with less power due to elevation) would bringing it down gain it power or since you are now FI would that alleviate the total loss of I want to say he said he was at 7K feet so 21% of base power? Basically once you slap on that turbo you no longer lose power off the NA and you also gain the power of the boost, so would it be safe to bring it down to sea level without building the motor assuming the turbo/waste gate was only going to stop at a predetermined boost level. I wish I could verbalize this better as in my head it makes sense but I am having trouble putting it on paper.

 

Yeah. Thats where I said a 20% power loss. It says right in the manual for the stillen that if you have low boost readings...it could be belt slip or elevation.

Now what makes simple sense is that what burns is fuel plus air. Whats in the air that burns is the oxygen. Oxygen gets thinner and thinner as you gain altitude, hence the reason climbing Mt. Everest is such a feat. So therefore there is less oxygen to burn to create a bigger combustion.

 

Turbos automatically compensate for altitude inherently by design...the problem is density at high altitude but once the turbo compresses you now have high density air. Unless you're saying the oxygen is displaced by other stuff like nitrogen or co2...

 

This is a concept that confuses me that I think I will never understand until I actually see it. I may have to slap a turbo on my car here and dyno it and then drive up into the Sierra Nevadas and Dyno it again just to see what it does. lol. Waste large sums of cash....For Science! lol The US government does it all the time, why not me?

 

I mean think about it... the turbo is gonna work as hard as it needs to in order to get 5psi (or whatever the spring is set at). So at higher altitude it works harder to achieve the same PSI (density of air) in the intake manifold. Assuming your turbo isn't outside it's efficiency range it's output shouldn't be affected too much by altitude.

 

The further away from sea level you are, the pressure of the entire atmosphere decreases so in effect, there is less air. Less air means less oxygen. Now, after all my searching I have discovered that atmospheric pressure at 5280 ft is 12.1 psi and not 14.6.

SOOO...to confuse the living **** out of everyone more. Lets place this into the compound equation.

((((6+12.1)/12.1)*((4+12.1)/12.1))*12.1)-12.1 = 11.975psi

remember that at 14.6 using the same boost numbers i would have = 11.35psi

What is going on here??

 

But superchargers are affected since they cant "work" any harder since they are only working as hard as the engine speed. An engine doesnt compensate for altitude..only your foot does. So essentially the boost will be constant on a turbo yet fluctuate on a SC with altitude changes.

 

wont there be more lag on the turbo as it still will build up to 5psi or whatever you have it set at, but with less dense air it will take longer for it to boost up to that point? Im talking negligible differences probably but it stands to reason, at least in my head, with thinner air it would take longer to condense the same amount of air as at sea level. Now here is my turn to **** your brain, what happens in death valley? You are under sea level, is the air more dense or less?