wanklin

iTrader: (2)

anodize all the way

wanklin

iTrader: (2)

robbing this from the other thread...

PV = nRT

P (pressure) = constant (example 10PSI)
V (volume) = manifold = constant

n = amount of air (dependent on temp)
R = constant
T = temperature

Kento

How would a big turbo pushing only 10 psi be less safe than a small turbo nearing the edge of its efficiency curve pushing 10 psi?

NissanConvert

iTrader: (1)

Okay I still can't get this. (sorry)

All other things staying the same i don't see how a larger compressor housing *can* make more power than a small one. I understand that if you increase the efficiency of the whole system (larger diameter intake, intercooler, etc... downpipe, cat/midpipe, etc.. how more flow could be achieved

but if the flow rate stays the same and the pressure stays the same then how does a larger compressor move more air? Imagine pushing positive pressure into a jar at sea level: you use a small compressor so it takes a while to fill the jar but ultimately you manage to cram the jar with 24.4psi (14.4 atmospheric +10psi) of air. Since the compressor is already spun up the next jar won't take nearly as long to fill.

When you use a larger compressor it doesn't have to spin up as much to move the volume of air that brings the atmospheric pressure inside the jar to 24.4psi.

Both jars ultimately will contain both the same pressure and the same total volume of air (at atmospheric pressure) unless one compressor overheated the air- bringing me too.....

But compressor efficiency doesn't make a big difference unless one of your compressors is out of it's efficiency range.

I hope you all followed that.

Mahjik

iTrader: (1)

The flow rate isn't the same, that's just it. If the rate is the same, then a large turbo wouldn't really be producing any more power than the stock twins. Take a look at the first post here:

http://forums.nasioc.com/forums/arch.../t-359824.html

They demonstrate the air movement differences between a few different setups.

Have you ever looked at computer CPU/Case fans? Start comparing the fan size, with the rpms and the CFM it moves; similar concept.

NissanConvert

iTrader: (1)

Yes, but with Case fans you're really only worried about the size and the rpm. There aren't any serious restrictions in the case or in the atmosphere.

So if i were to take a gt42r and strap it on a bone stock car reduce the compressor outlet to stock and run 10psi how would i make more power than the stock twins at the same manifold pressure?

calculon

iTrader: (29)

yes, dubulup, i agree 100%. That's what I was trying to say, you just said it much more eloquently.

for some reason, I literally chuckled out loud when I read big dog rizza, I love that my screenname/avatar serves its intended purpose, I think I wanna to change it though.

ryan

wanklin

iTrader: (2)

denser air+less backpressure = more power = kaboom

Fritz Flynn

iTrader: (263)

The charge temp from that gt42 will be much colder

NissanConvert

iTrader: (1)

When you say "much" what do you mean? On my twins at ~80mph i see IATs about 20c over ambient.

Kento

Just because you're making more power doesn't mean you'll blow the engine. I'd say the chances are greater with a small turbo working hard near the edge of its efficiency range heating up the intake charge and forming a more enticing environment for detonation to occur.

wanklin

iTrader: (2)

smartass response withdrawn.

Fritz Flynn

iTrader: (263)

I have no idea but bolt one on and ask your ***.

wanklin

iTrader: (2)

it was really just an arbitrary response to an arbitrary question. Are we talking about a stock ECU, proper tuning or what? tell me the determinants and I'll stop with the half-as responses. lol

Kento

Detonation doesn't care how much less air/fuel volume is in the combustion chamber. It does care how much higher the intake temps are, which is what you get with the smaller turbo.

EDIT: Not trying to be an *** here. Just clarifying what can be a very misleading statement.

Kento

Try asking the guys who have medium-sized singles on their tracked FDs about the differences in power at basically the same boost levels (like, um, hey...Fritz Flynn!). There's a big difference in turbo efficiency/IATs between just running along at 80 mph, and constant full throttle whippings through the gears for 20-30 minutes straight. Not sure if any of them have compared IATs, but I'm sure if they did, there would be a drastic difference.

wanklin

iTrader: (2)

Ignore that BS above as I understand how detonation works, I was just giving a BS reponse to an ambiguous question, and made myself look like I don't know what the hell I'm talking about. lol. I really agree with you on all counts this thread just brought me back to a previous one started by some guy who wanted to run a GT35R on a stock ECU. Run a larger turbo on a stock ECU and you lean out. That was my thought process.

detonation cares about ratio and temperature (not volume) as you kindly pointed out.

Kento

No worries, not trying to fart all over your thread. Although, sorry man, one more : Actually, detonation does care about temperature. If the intake temperature is high enough, it doesn't matter how much fuel you dump into the combustion chamber; once the pressure rises to a certain point, kaboom...

wanklin

iTrader: (2)

shoot. lol another typo. I meant to say that it cares about temp and fuel/air ratio, not volume (as corrected above). lol. I give up ;/

sweet bike BTW

Montego

iTrader: (1)

lol we are gonna have a tough time figuring it out using a physics book, since the ideal gas law is covered in chem... Man talk about making a simple scenario complicated.

PV=NRT: It is a relationship between pressure , Volume, molecules, and temperature. And really applies more to intercooling rather than turbos.

for this application:

P= NRT1/V = 10 lbs
P= NRT2/V = 10 lbs

temperature goes down the N (number of molecules) has to go up in order to maintain the same pressure. More oxygen molecules in combustion chamber = more power.


Just so you all know comparing 10 psi single Vs 10 psi twins is apples to oranges.

Single turbo:
Pressure at the manifold = 10 psi

Twins:
Pressure at the manifold = 10 psi

CFM of single > than CFM of twins

Using a single, the end result is alot more oxygen molecules at the COMBUSTION chamber due to a higher CFM. In the combustion chamber: Pressure using a single does not = the same pressure as using the twins.

its are all about CFM. PV=NRT directly applied at the manifold, where the pressure is measured, does NOT depent on how much air is moving through it.

wanklin

iTrader: (2)

The engine isn't really seeing 10PSI, it's seeing whatever the turbo can get into the intake ports before they close. That's why flow matters. A large turbo will move more air in that short window of time. If the engine was getting 10PSI boost internally with both setups flow wouldn't mean squat. Flow means nothing once the ports are sealed.

FDNewbie

iTrader: (10)

That's where you're incorrect. Reason being is you're speaking in abstract talk. Once the turbo is spooling it IS making boost. So "sufficient boost" is completely relative based upon what you're comparing or trying to achieve.

For example, the stock twins are considered spooling until 10psi, right? And at 10 psi they make 255hp, correct? If you stuck a GT40 on a 3rd gen for example (which is capable of much higher boost than the stocker), and saw the power output at 10psi, you'd see it'll make MORE than the stockers' 255hp, despite it still being IN SPOOL. Why? Because your reference point (when you're out of spool) has changed.

In simple terms, just b/c a turbo is in spool does NOT mean it isn't creating enough power. A spooling turbo produces boost, and ANY level of boost creates power. No nothing's null and void here

Again, that's where you're missing the point. At the same psi (which is what you've been comparing all along), a smaller turbo will be FULLY spooled while a large turbo will STILL be spooling. BOTH will be creating boost, BOTH will net in greater power. Yet despite the pressure rating being the same, the larger turbo will make MORE power at that same psi, despite it being in spool, simply b/c that VOLUME of air being compressed to reach that psi is LARGER than the volume of air being compressed by the smaller turbo.

Not accepting it

Theoretically, sure. But NOT at the same PSI!!! Which is what your original question was after, was it not?

Sure it does, but not in the way you're thinking. Engine speed (rpm) determines how much exhaust gas is coming out. Spool is nothing more than the engine speed (rpm) needed to create enough exhaust gas flow to spool the turbo. But given that you're trying to compare different size turbos, the rpms necessary to spool to X psi or X hp will ALWAYS differ. So it's a variable you can do without. No need to complicate your life RPM will become MUCH more important when you're comparing similarly sized turbos and trying to determine turbo LAG (which is different than spool), as lag is a turbo-specific characteristic. It'll also help in determining shift points, tuning, and other points for your individual setup, but not so much for comparison purposes. There's a reason why there are a ton of guys on the forum who run larger turbos w/ very large spool up times, yet they're very happy w/ them, since they run 'em at low boost (and that's what they got 'em for). More power, greater efficiency, lower temps (as Kento mentioned), and a simplified engine bay.

If two differently sized turbos were rotating at the same speed, while the LARGER turbo would compress more AIR (ie volume), BECAUSE of it's greater volume (and that area is in the denominator in the pressure equation), the psi it would be running at would be LOWER. Ie, the SMALLER turbo would indeed be compressing a SMALLER volume of air, yet it's PRESSURE (psi) would be HIGHER. And that's the fundamental point I'm trying to get ya to see. PSI is NOT NOT NOT directly related to turbo area; in fact it's *inversely* related.

The very last part I agree w/. The first about charge velocity and backpressure...I'm not even getting into those. That's involving WAYY too many variables. Agree and bang out the core details before expanding and including compounding factors and variables. It'll make life much easier Rob

~Ramy

NissanConvert

iTrader: (1)

I think we've established that more CFM = more power and that a larger compressor will deliver more CFM at a given MAP. However, if the rest of the system does not allow for the increase in flow how does it?

Kento

If the "system does not allow for the increase in flow", then, well, there won't be more flow. What's your point? It's already been noted that (well, you have to search for it in the thread with the drunken late night rant) that if you don't have the peripheral components to support the increase in efficiency/flow that a larger turbo provides, then you won't realize the full benefits. The thread is comparing turbos themselves, not any and all ancillary system possibilities.

If you're referring to the stock twin setup, all you have to do is look at the people with BNR Stage 3 setups (or those lucky enough to have the old M2 BB twins, or the even rarer Australian SP versions) to see that even with the restrictive stock exhaust manifold design, you'll still see an increase in power relative to boost, and that's even with turbos that are only slightly larger than stock. Does this mean you can just fab a Cummins diesel-sized huffer onto each end and you'll end up with more power? No, of course not. But all else being equal...

CarbonR1

iTrader: (2)

You guys are making it way more complicated than it needs to be. The ideal gas law doesn't apply, and equations aren't going to simplify it at all.

A large turbo at a given boost pressure supplies more mass of air per time than a small turbo at a given boost pressure. That's why they are different, pressure does not tell you how much air you are getting, and neither does volumetric flow (CFM) by itself although they can give you an idea.

Kevin