"PSI" level is not directly relative to cylinder pressures??!!!!!!!!!!

[Marceldsm]

"PSI" level is not directly relative to cylinder pressures??!!!!!!!!!!

i saw a stock 7 bolt run 32 psi on stock everyting .....made 417 fwhp


the question is ..........is that engine still alive or not
apparently they did a compression test after
the engine is OK


I WHAT MORE INFO ON CYLINDER PRESSURE AND BOOST


TANKS IN ADVACE

I REALY WHANNA UNDERSTAND THE TECHNICAL PART

stock 7-bolt block and head (even stock cams). I'm also still on the stock intake manifold and throttle body
* Acceleration from 3100 to 7100
* Absolute barometric pressure: 28.90 in. Hg.
* Vapor pressure: 0.4 in. Hg.
* Elevation: 997 ft. above sea level
* T3 50-trim @ 27.6 psi (spikes briefly at around 32 psi)
* peak timing advance: 21.4 degrees
* Injector duty cycle: 69.0% (850cc)
* Air-to-fuel ratio: 12.3:1 (on 110 octane Sunoco)
* Airflow: 47.5 lbs/min
* Peak power: 403.4 WHP
* Peak torque: 356.9 ft/lbs

 

[habitatguy187]

What exactly do you want to know? More boost will increase cylinder pressures of course, bigger cams will increase cylinder pressure, detonation will increase cylinder pressure.

Our cars can handle a lot of boost with a bone stock motor if everything else is setup and tuned correctly.

 

[dsm-onster]

Talk about about the mad hatter asking the march hare for more sugar!

But you actually are pointed in the right direction to solving all of this simplicity. IT IS ABOUT FLOW ANd EFFICIENCY, NOT PSI.

deal is. . . There would have been more power with more cylinder pressure, regardless of boost pressure. That is all you SHOULd worry about. You need not hassle yourself with boost pressure; or as they say, pee es eye. Just focus on how to get the highest cylinder pressure with the least amount of knock. More mass into the chamber, more thermal efficiency, less losses bringing that massflow to full burn rate (pumping loss), etc. Figure out how too keep your intake manifold temps cool enough for the fuel you are using while increasing the boost enough to reach your goal, KNOWING that your efficiency in burn and pumping and volume flow are as high as you need them to see the full use of the compressor at ANY boost it can sustain.

 

[Ceddy]

Boost will increase the Effective Compression Ratio.

8.5:1 @ 32 psi = 27:1

Effective Compression Ratio Calculator

 

[dsm-onster]

Run you n/a motor on 27:1 static CR (static CR = effective CR at 100% VE) and it will knock with race fuel before you get to way less than 90% VE

 

[92AWDTalonTSI]

Talk about about the mad hatter asking the march hare for more sugar!

Spoon!

 

[habitatguy187]

Run you n/a motor on 27:1 static CR (static CR = effective CR at 100% VE) and it will knock with race fuel before you get to way less than 90% VE

So why can we do it?

 

[TunaTalon]

So why can we do it?

With a boosted/intercooled engine the heat of compression from the boost is mostly removed by the intercooler.

With a NA engine all of the compression takes place in the cylinder and the heat of compression raises the charge temperature and pressure far beyond what would be expected from the static CR alone.

 

[habitatguy187]

With a NA engine all of the compression takes place in the cylinder and the heat of compression raises the charge temperature and pressure far beyond what would be expected from the static CR alone.

So it's almost like the compound turbo effect right? The air that's entering the cylinders is already compressed, then the pistons multiply that compression. Is that correct?

 

[TunaTalon]

Yes the external compression of the turbo is in series with the internal compression of the piston but the point of my comment is that the heat of compression from the turbo does not reach the cylinder. Most of the comments here about boost and tuning talk about flow and pressure but temperature is also an important tuning variable.


My best effort to describe this concept was in the BOOST IS GOOD section of http://www.kidzuku.com/StrokeOrNot.pdf.

 

[viperlp01]

I ran about 24psi on my holset with 110 race gas flowing like 43-44lbs/min completely stock and I just ripped the engine down and it looked good. I am just going to build it with new rings and bearings for a customer.

Main thing here. TUNING is the key!!

 

[knochgoon24]

Lots of good info here:

The cooling of the charge with the intercooler is one reason why people DROP compression ratio so they can run more boost. Then they use the intercooler to pull some of that heat out instead of having it in the cylinder during the compression stroke.

I found a really good source that compared N/A and turbo engines and how the difference in compression ratio affects compression pressure and temperature, but I can't find it right now.

 

[Marceldsm]

people here in canada can`t belive a small 2L CAN DO THAT

so ya even me the most boost i whent is 22 psi and my oil stick just went flying

anyway
tanks for the info , i realy apreciate it

is very tecnical for my me can you guys explain it in more simple terms ?

 

[floader]

Its mostly about Lbs/min, not PSI

if you have two motors that are the same displacement ( say 2.0) and they are both making 25 psi, but one flows 35Lbs/min and the other 40lbs/min, then the one with the higher flow rate is making more power....... even if a motor was only building 20 psi at 40lbs/min, its gonna make more power. Its all about flow

 

[knochgoon24]

When you run your air compressor for shop tools, you notice that the tank gets warm. As you use the air out of the tank, it cools off. This temperature increase and decrease generally follows the ideal gas law:

P*V = n*R*T

where:
P = Pressure
V = Volume
n = amount of stuff
R = Ideal Gas Constant
T = Temperature

In your engine, the as the piston moves up in the cylinder, the amount of air in the cylinder (n) stays the same. The volume also decreases.

So P1 * V1 / T1 = P2 * V2 / T2

Rearranged:
V2 / V1 = (P1 * T2) / (P2 * T1)

Compression ratio = V2/V1

If the temperature were held constant (T2=T1), then:
V2 / V1 = P1 / P2

The pressure would have to increase (P2>P1) as the the cylinder compresses the air, and this pressure would increase inversely with change in volume. A 10:1 CR engine would compress a 20psia charge to 200psia.

But actually, there is still some heat in the engine from the combustion stroke of the last revolution. So since T2>T1, P2 has to increase more than the inverse of the volume change. That 20psia charge could now be 210psia. [There are much more complex equations that would account for this, but you wanted it simple. I'm trying.]

Now volumetric efficiency (VE) also plays into all of this. Your engine doesn't "suck" in exactly 2.0L of air/fuel mixture for every revolution. The ratio of the the actual amount to this "perfect" amount is the VE. A VE of 90% means you're engine is sucking in 90% of 2.0L, or 1.8L. Since you're now only compression 90% of the total volume, your 10:1 CR piston only has an effective compression ratio of 9:1, and you'll see a cylinder pressure of about 180psia.

This can be a good thing, or a bad thing. In the 60's, some cars used an 11:1 CR piston, but had a low VE at low RPM due to a late closing intake cam profile. This kept cylinder pressures low at low RPM to decrease the risk of knock, and increased cylinder pressures at higher RPM where the air mixed with the fuel better and the chance for knock was lower.

--------------------------------------------------------------------------------------------

With the stock cams, the VE of his engine at higher RPMs is lower than it could be. To combat this, he increased the intake pressure. Essentially, this was like running a cammed car at a lower boost level. I'm guessing this car also had an intercooler more substantial in size than the stock side mount.

--------------------------------------------------------------------------------------------

In a nutshell, it's all about flow (VE in combination with boost level), not just boost level.

I wish I could dumb it down more, but it can get very technical very fast.

 

[Marceldsm]

Its mostly about Lbs/min, not PSI

if you have two motors that are the same displacement ( say 2.0) and they are both making 25 psi, but one flows 35Lbs/min and the other 40lbs/min, then the one with the higher flow rate is making more power....... even if a motor was only building 20 psi at 40lbs/min, its gonna make more power. Its all about flow

When you run your air compressor for shop tools, you notice that the tank gets warm. As you use the air out of the tank, it cools off. This temperature increase and decrease generally follows the ideal gas law:

P*V = n*R*T

where:
P = Pressure
V = Volume
n = amount of stuff
R = Ideal Gas Constant
T = Temperature

In your engine, the as the piston moves up in the cylinder, the amount of air in the cylinder (n) stays the same. The volume also decreases.

So P1 * V1 / T1 = P2 * V2 / T2

Rearranged:
V2 / V1 = (P1 * T2) / (P2 * T1)

Compression ratio = V2/V1

If the temperature were held constant (T2=T1), then:
V2 / V1 = P1 / P2

The pressure would have to increase (P2>P1) as the the cylinder compresses the air, and this pressure would increase inversely with change in volume. A 10:1 CR engine would compress a 20psia charge to 200psia.

But actually, there is still some heat in the engine from the combustion stroke of the last revolution. So since T2>T1, P2 has to increase more than the inverse of the volume change. That 20psia charge could now be 210psia. [There are much more complex equations that would account for this, but you wanted it simple. I'm trying.]

Now volumetric efficiency (VE) also plays into all of this. Your engine doesn't "suck" in exactly 2.0L of air/fuel mixture for every revolution. The ratio of the the actual amount to this "perfect" amount is the VE. A VE of 90% means you're engine is sucking in 90% of 2.0L, or 1.8L. Since you're now only compression 90% of the total volume, your 10:1 CR piston only has an effective compression ratio of 9:1, and you'll see a cylinder pressure of about 180psia.

This can be a good thing, or a bad thing. In the 60's, some cars used an 11:1 CR piston, but had a low VE at low RPM due to a late closing intake cam profile. This kept cylinder pressures low at low RPM to decrease the risk of knock, and increased cylinder pressures at higher RPM where the air mixed with the fuel better and the chance for knock was lower.

--------------------------------------------------------------------------------------------

With the stock cams, the VE of his engine at higher RPMs is lower than it could be. To combat this, he increased the intake pressure. Essentially, this was like running a cammed car at a lower boost level. I'm guessing this car also had an intercooler more substantial in size than the stock side mount.

--------------------------------------------------------------------------------------------

In a nutshell, it's all about flow (VE in combination with boost level), not just boost level.

I wish I could dumb it down more, but it can get very technical very fast.

MENNNNNN .........IM A NOVICE MECANIC WHAT YOU SAID THERE MAKES ME LOOK LIKE I HAVE NO IDEA WHAT THE HELL IM DOING WHIT MY ENGINE

GUESS I NEED MORE STUDYING

ANY SITES THAT EXPLAIN ALL THESE IN DETAIL ?

TANKS GUYS

SO ITS ALL ABOUT Flow temperature compression if i get it right

 

[knochgoon24]

It's all about getting as much air into the engine as possible. One way it to increase boost (stuff a lot of air through a little hole using pressure). The other way it to increase the efficiency of the engine (make that hole bigger and get the same amount of air though the hole using lower pressure). The problem is that as you compress air the temperature increases. If the temperature gets too high it's enough to ignite the gas just like a spark. Bam. Pre-detonation. You have to walk that fine line.

I got a little carried way with that last post. Sorry. All I deal with in my classes is air being compressed, it's temperature, and how it interacts with stuff.

 

[Marceldsm]

it's all about getting as much air into the engine as possible. One way it to increase boost (stuff a lot of air through a little hole using pressure). The other way it to increase the efficiency of the engine (make that hole bigger and get the same amount of air though the hole using lower pressure). The problem is that as you compress air the temperature increases. If the temperature gets too high it's enough to ignite the gas just like a spark. Bam. Pre-detonation. You have to walk that fine line.

I got a little carried way with that last post. Sorry. All i deal with in my classes is air being compressed, it's temperature, and how it interacts with stuff.

tanks honesty for all that info

so you just have to find a whay to lower that temperature
right ???

 

[knochgoon24]

Yes. That's where intercoolers and meth/water injection come into play. That's also why you need to run low/mid 11 AFR up top with high boost instead of 12.5 AFR on pump gas. The extra gas cools the air as the liquid gasoline evaporates. That's the same way meth and water injection work. You really aren't looking to burn the meth, you're just looking to cool the air down as the liquid meth evaporates.

When the compression temperatures get to high, you knock.


Air expands as it's heated. That's why a larger turbo can flow more at 20psi than a smaller turbo might as 25psi. The smaller turbo heats the air more.

When you look at a compressor map, you'll see the islands that show it's efficiency. The center ring on this map shows 77% efficiency. This means that 77% of the energy from the spinning compressor goes into compressing the air, while the other 23% heats the air. When choosing a turbo, your aim is to have it be efficient where you need it, so you don't end up with extra heat in the intake air charge, that you'll want/need to remove with an intercooler or water/meth injection.

You must be logged in to view this image or video.

Here's a nifty little calculator that will show you just how much the air gets heated by the turbo.
http://www.stealth316.com/2-turbotemp.htm

For example. This is for my small 16g at that peak efficiency island:
Input Temperature 85ºF (under-hood temperature)
Input pressure 14psi (use absolute pressure: -0.5 psi/1000 ft elevation)
Output pressure 22psi (gauge pressure: usually 1-2 psi more than plenum pressure)
Compressor efficiency 77% (typically 60-75%)
Output temperature 302ºF

It does intercooler efficiencies too:

IC input temperature 302ºF (Turbo discharge temperature)
IC Efficiency 70 percent (example: enter 80 for 80%)
IC pressure loss 2 psi (greater than or equal to 0)
Ambient temperature 80ºF (outside air temperature)
Plenum temperature 147ºF

Now you see why turbocharged cars use intercoolers. The 147ºF intake temperature is much less likely to knock than the 302ºF air coming out of the turbo.

 

[Marceldsm]

so meth injection is there just to coll down the air not to exand it ( coller air is denser ) ?

 

[knochgoon24]

Exactly. You aren't looking to burn the meth (though it does burn). You're looking to use it mostly for it's cooling effect as it evaporates. That's why there is a certain distance from the throttle body suggested. That's so there's enough time for the meth to evaporate. That's also why some people use water. It will also evaporate and pull heat out of the air charge.

Colder air is denser and colder air is less likely to detonate. Both are very good things.

 

[Marceldsm]

Exactly. You aren't looking to burn the meth (though it does burn). You're looking to use it mostly for it's cooling effect as it evaporates. That's why there is a certain distance from the throttle body suggested. That's so there's enough time for the meth to evaporate. That's also why some people use water. It will also evaporate and pull heat out of the air charge.

Colder air is denser and colder air is less likely to detonate. Both are very good things.

tanks these tred helps 100%

 

[99gst_racer]

"PSI" level is not directly relative to cylinder pressures??!!!!!!!!!!

i saw a stock 7 bolt run 32 psi on stock everyting .....made 417 fwhp


the question is ..........is that engine still alive or not
apparently they did a compression test after
the engine is OK


I WHAT MORE INFO ON CYLINDER PRESSURE AND BOOST


TANKS IN ADVACE

I REALY WHANNA UNDERSTAND THE TECHNICAL PART

stock 7-bolt block and head (even stock cams). I'm also still on the stock intake manifold and throttle body
* Acceleration from 3100 to 7100
* Absolute barometric pressure: 28.90 in. Hg.
* Vapor pressure: 0.4 in. Hg.
* Elevation: 997 ft. above sea level
* T3 50-trim @ 27.6 psi (spikes briefly at around 32 psi)
* peak timing advance: 21.4 degrees
* Injector duty cycle: 69.0% (850cc)
* Air-to-fuel ratio: 12.3:1 (on 110 octane Sunoco)
* Airflow: 47.5 lbs/min
* Peak power: 403.4 WHP
* Peak torque: 356.9 ft/lbs

Those stats sure do look familiar. You pulled those off of my youtube video, I take it?

Yes, that same engine lived until the following summer when I overboosted 40+ psi by accident, and then I finally bent all 4 rods. I rebuilt it after that, but I'm still rocking the same block, crank, and head. These engines can handle some crazy cylinder pressures, and will hold together fine as long as your tune is in check.

"PSI" level is not directly relative to cylinder pressures??!!!!!!!!!!

'PSI' is only relative to the turbocharger itself. The engine only cares about air mass, which is not measured in 'PSI'.

Think about this; Assume you have a T25 running at 25 psi, and a GT42r running at 20 psi. Even though the T25 is running more boost, the 42r is flowing more overall air and will allow for more cylinder pressure due to it's larger compressor wheel. This is why comparing PSI numbers between turbos is useless. It would be more appropiate to compare mass flow numbers, as that is what the engine cares about.

 

[JEFFREYCASTGSX]

Heres another explanation:

PSI is just a measure of restriction, as PSI increases there is more air, and thus more pressure/restriction. You up the boost to get more air into the engine, but there is more pressure due to more air. For example, a stock 4g63t with X turbo, at 20psi that makes Xwhp, but its still on stock cams and intake manifold, add some good cams and short runner/high flow intake manifold then you will make Ywhp on the same boost and make Xwhp on less boost, because some restriction is removed. Now lets say you have 2 cars one with a 16g and with a 35r, both cars running 25psi. The 16g will make less power but will have more heat and CAN have more pressure, thanks to this SOMETIMES running a smaller turbo and pushing it to the limit can be dangerous, BUT under PERFECT conditions the pressures on the 35r car will be way higher due to more air being pressurized into the intake. This also explains why a bigger engine will make the same power on less boost, thanks to more area in the intake and cylinders, BUT lets say that theres a stock 4g63 and stock LS2 and both make 600whp on the same turbo, but the 4g63 will have to run 30psi, and LS2 will use 10psi thanks to the higher displacement, BUT both engines will be flowing 60lbs/min of AIRFLOW. This isnt EXACTLY how it will work but is a very close example.

 

[TunaTalon]

Those stats sure do look familiar. You pulled those off of my youtube video, I take it?

Sure enough; as uploaded September 19, 2006.