how much psi can the stock motor hold?

[Jaden]

Originally Posted by billwot

You can't. You can't "flow more air at the same pressure".

The only way to get more air into a fixed volume (the space above the piston) is to increase its density (pack more air into a smaller unit). And air density is directly related to pressure, and inversely related to temperature. So to increase air flow into the engine, you either increase the pressure, or decrease the temp.

That's the whole basis of FI. The more you pressurize the intake air charge, the more fuel/air charge you can push into the cylinder.

To increase power, you need to increase the mass (weight) of air, not the volume.

LOL I don't know, some people on here seem to be under the impression all you have to do is get a bigger turbo that flows more air...lol I had long running arguments about this very topic trying to convince people of the truth that you can only fit so much air into the cylinder at a given boost...

Jaden

[toast]

No.

You don't flow more air at the same pressure, you can flow more air at less pressure.

A larger turbo pushes the same volume of air without having to compress it as much. Without compressing it the air stays cooler, so it is more dense. A better way to think about it is not with volume and temperature, but air mass. A larger turbo will deliver more air mass per minute. Also, a larger turbo will generally have a larger turbine wheel which acts as less restriction in the exhaust flow, resulting in a higher VE for the motor.

Run 10 psi of boost on one of our motors with a disco potato turbo (GT2860) and then with a GT3076. Which one generates more power?

[armstrom]

Wow, this is an old thread... But suffice it to say there's some misinformation floating around. The main factor in making power is the number of oxygen molecules in the combustion chamber at the time of ignition and injecting an appropriate amount of fuel to combust using the available oxygen. Yes, ignition timing is a big factor as well, but that's another discussion...

You can get more oxygen into the combustion chamber in one of three ways:
*Inject it in the form of Nitrous (so-called "chemical" supercharging)
*Increase the pressure of the air entering the engine (Boost due to turbo/supercharging)
*Increase the Volumetric Efficiency (VE) of the engine

If we set aside Nitrous as an option, VE, combined with the displacement of the engine is the primary factor you need to consider, even when talking about boosted applications. What is boost, after all? The turbo or supercharger does not "make" pressure... It flows air... That's all. If the compressor is flowing more air than the engine can consume for a specific load/rpm point, then that airflow "backs-up" in the intake piping causing the air pressure to increase.

So, how can a big turbo flow more air at the same pressure? Easy! Most "big turbos" are comprised of a larger compressor section AND a larger turbine section. The turbine is where the magic happens. When you increase the size of the turbine wheel and housing you remove exhaust restriction which increases the overall VE of the engine (The engine flows more air). That means the same flow rate that produced, say, 10PSI before may now only produce 7-8PSI... But the wastegate control on turbos is based on pressure, so the turbo will continue to make 10PSI like it did before, it will just have to flow more air to do so. Of course, all of this has limits based on the compressor map of the turbo, and things are slightly different for superchargers which tend to flow proportionally to engine RPM rather than dynamically as controlled by as wastegate.

The short version? A big turbo will flow more air than a smaller turbo at the same boost level because the larger turbine increases overall airflow through the engine.
-Matt

[Jaden]

Originally Posted by armstrom

Wow, this is an old thread... But suffice it to say there's some misinformation floating around. The main factor in making power is the number of oxygen molecules in the combustion chamber at the time of ignition and injecting an appropriate amount of fuel to combust using the available oxygen. Yes, ignition timing is a big factor as well, but that's another discussion...

You can get more oxygen into the combustion chamber in one of three ways:
*Inject it in the form of Nitrous (so-called "chemical" supercharging)
*Increase the pressure of the air entering the engine (Boost due to turbo/supercharging)
*Increase the Volumetric Efficiency (VE) of the engine

If we set aside Nitrous as an option, VE, combined with the displacement of the engine is the primary factor you need to consider, even when talking about boosted applications. What is boost, after all? The turbo or supercharger does not "make" pressure... It flows air... That's all. If the compressor is flowing more air than the engine can consume for a specific load/rpm point, then that airflow "backs-up" in the intake piping causing the air pressure to increase.

So, how can a big turbo flow more air at the same pressure? Easy! Most "big turbos" are comprised of a larger compressor section AND a larger turbine section. The turbine is where the magic happens. When you increase the size of the turbine wheel and housing you remove exhaust restriction which increases the overall VE of the engine (The engine flows more air). That means the same flow rate that produced, say, 10PSI before may now only produce 7-8PSI... But the wastegate control on turbos is based on pressure, so the turbo will continue to make 10PSI like it did before, it will just have to flow more air to do so. Of course, all of this has limits based on the compressor map of the turbo, and things are slightly different for superchargers which tend to flow proportionally to engine RPM rather than dynamically as controlled by as wastegate.

The short version? A big turbo will flow more air than a smaller turbo at the same boost level because the larger turbine increases overall airflow through the engine.
-Matt

THE VOLUME of the engine is the primary determinant of how much airflow the engine can handle.

A larger turbo flows more air at less pressure, YES, however, the engine is limited on how much it can take in. There ARE things that you can do to increase the flow of air the engine can receive. Reduce exhaust restriction, increase valve size, duration, port heads etc...

Adding a larger turbo will NOT by itself increase the airflow of the engine. At least not past the point that the volume of the engine can allow.

Anyone who thinks that's not the case, I invite them to put a t-trim vortech s/c in place of the stock one that came in their vortech kit and let us know how much more power they make on the same boost level.

Jaden

btw, you're wrong about the turbo or s/c compressing the air. In a twin screw or lobe type, it is the lobes coming together that compress the air, in a centrifugal type compressor in a turbo or cent s/c, it is the compressor wheel forcing the air through a smaller space than the inlet. In a linear compressor, (as those seen in jet engines), it is fan blades forcing air into a tighter and tighter space. In ALL cases it is the actual compressor of the charge source that creates the compression and boost of the air, it has little to do with the charge piping between the compressor and the intake.

[Jaden]

Originally Posted by toast

No.

You don't flow more air at the same pressure, you can flow more air at less pressure.

A larger turbo pushes the same volume of air without having to compress it as much. Without compressing it the air stays cooler, so it is more dense. A better way to think about it is not with volume and temperature, but air mass. A larger turbo will deliver more air mass per minute. Also, a larger turbo will generally have a larger turbine wheel which acts as less restriction in the exhaust flow, resulting in a higher VE for the motor.

Run 10 psi of boost on one of our motors with a disco potato turbo (GT2860) and then with a GT3076. Which one generates more power?

no, sorry, you CANNOT flow more air through an engine at the same IAT AND less boost.

The turbo will flow more air at less boost, the ENGINE will NOT. It is possible to flow more air at the same or less boost IF the smaller turbo is not capable of as efficiently pushing the amount of air you're trying to flow into the engine AT that boost level. This is only because of a cooler more dense charge, it has NOTHING to do with the amount of air the turbo can push at that boost level, and it is FINITE.

It is only up to the amount of airflow the engine is capable of ingesting at said boost level.

Jaden

I can do the math and within 2% TELL you exactly how much more power your stated example will produce based on the compressor maps of those turbos alone based on the efficiencies of those turbos at that boost level without seeing a single dyno.

Here's the kicker, the only reason that the 3076 will make more power at 10psi is that at it's peak efficiency of ~75% it is STILL within the limits of the engine's ability to ingest air. At the engine's ~limit the 2860 is only at 68% efficiency so the charge will be hotter and less dense.

Here's a question for you. If you now take a gt3582, will it make more power than the gt3076? How about if you take a gt4088? Forget about spool time, it's irrelevant for this discussion, it only has to do with the advantages of using one turbo over another not peak airflow.

[toast]

Your next to last sentence was the point of my post. I never suggested sticking a turbo sized for a Peterbilt on our engine. A more efficient compressor will provide colder air delivering the same mass of air at less boost pressure. A larger turbine will increase the VE of the motor. Saying boost pressure and volume are all that matter leaves out the last variable in the ideal gas law.

Edit: where are you measuring IAT? If it is post compressor, then fine, we are saying the same thing. I never said the temperatures were the same after the compressor, the fact that they can be different is entirely the point.

[Jaden]

Originally Posted by toast

Your next to last sentence was the point of my post. I never suggested sticking a turbo sized for a Peterbilt on our engine. A more efficient compressor will provide colder air delivering the same mass of air at less boost pressure. A larger turbine will increase the VE of the motor. Saying boost pressure and volume are all that matter leaves out the last variable in the ideal gas law.

Edit: where are you measuring IAT? If it is post compressor, then fine, we are saying the same thing. I never said the temperatures were the same after the compressor, the fact that they can be different is entirely the point.

No big deal, it's just that a problem arises when people just look at the flow rate of the turbo and think that's what their car will flow.

People forget that a car can only flow what it can flow at a given boost level and get stuck on mowr turbo...thinking that airflow of the turbo means airflow of the engine. Power generation is a direct correlation of ENGINE airflow, not TURBO airflow and engine airflow is a direct correlation of ambient airflow versus boosted airflow in regards to FI, (for the most part with some exception regarding valve overlap etc...)



Jaden

[nemesis_frs]

I've been running 12 psi with the vortech kit and a tune by ft86 speedfactory . I've never had an issue . Going 3 years strong

[86 South Africa]

Originally Posted by nemesis_frs

I've been running 12 psi with the vortech kit and a tune by ft86 speedfactory . I've never had an issue . Going 3 years strong

Boosted mileage??

[Fd3sr2]

Originally Posted by Jaden

no, sorry, you CANNOT flow more air through an engine at the same IAT AND less boost.

The turbo will flow more air at less boost, the ENGINE will NOT. It is possible to flow more air at the same or less boost IF the smaller turbo is not capable of as efficiently pushing the amount of air you're trying to flow into the engine AT that boost level. This is only because of a cooler more dense charge, it has NOTHING to do with the amount of air the turbo can push at that boost level, and it is FINITE.

It is only up to the amount of airflow the engine is capable of ingesting at said boost level.

Jaden

I can do the math and within 2% TELL you exactly how much more power your stated example will produce based on the compressor maps of those turbos alone based on the efficiencies of those turbos at that boost level without seeing a single dyno.

Here's the kicker, the only reason that the 3076 will make more power at 10psi is that at it's peak efficiency of ~75% it is STILL within the limits of the engine's ability to ingest air. At the engine's ~limit the 2860 is only at 68% efficiency so the charge will be hotter and less dense.

Here's a question for you. If you now take a gt3582, will it make more power than the gt3076? How about if you take a gt4088? Forget about spool time, it's irrelevant for this discussion, it only has to do with the advantages of using one turbo over another not peak airflow.

yes but when solving for N using the ideal gas law equation, p and v being equivalent, and t being lower via a compressor running at a higher efficiency- you yield a higher N value. N being moles of the gas means you are fitting more air in the cylinder. Just as you said the 68% eff vs the 75% eff yields a lower density, and with static volume lower density means less mass ie less air
as in DV=m. I know this is very generalized as it is more complex to calculate v with VE having a hand in that dynamic value as opposed to a static one, but the point is the same. Mixing in VE is a whole other can of worms.

[GsxrMe]

I was running 8PSI on 93 for the first year and 12PSI with e85 for the past year on the stock block. I was told by my tuner not to push more than 400HP without a built block. I check for knock every now & then and so far its been perfect.

How do I feel with 12PSI with 93? Well I hate it. Once you go e85 you'll never look back nor want to put it in your tank.

Get ready for 1500 mile oil changes with e85 with 24/7 use.

[revaholic]

Newb question: I'm wondering, if you're not making crazy power, like with the Jackson Racing C30 or Sprintex 210 kits, is there any detriment to keeping the stock headers on with the exception that you're not getting as much power as you could? Would the restrictiveness of the stock header cause problems for the engine?

[tyler_win_photo]

Originally Posted by revaholic

Newb question: I'm wondering, if you're not making crazy power, like with the Jackson Racing C30 or Sprintex 210 kits, is there any detriment to keeping the stock headers on with the exception that you're not getting as much power as you could? Would the restrictiveness of the stock header cause problems for the engine?

No... but if you're already spending a couple grand you might as well go all the way to get the most out of it. The gains are definitely noticeable between stock and catless header

[Bfranklyn86]

Originally Posted by revaholic

Newb question: I'm wondering, if you're not making crazy power, like with the Jackson Racing C30 or Sprintex 210 kits, is there any detriment to keeping the stock headers on with the exception that you're not getting as much power as you could? Would the restrictiveness of the stock header cause problems for the engine?

There's 15-20bhp on offer for supercharged cars swapping out the stock header, so can be good 'bang for buck'.

Also there have been a couple of failures of the stock manifold over here that I have heard of, so not a bad idea to swap it out anyway. I run the stock manifold on my SC car with no issues for over a year but am swapping it soon.