home register FAQ memberlist calendar

Go Back   Turbobricks Forums > Mechanical > performance & modifications

Reply
 
Thread Tools Display Modes
Old 02-09-2018, 11:41 AM   #76
SlowRide
Cold War Crumple Zones
 
SlowRide's Avatar
 
Join Date: Aug 2008
Location: FLORI-DERP
Default

Quote:
Originally Posted by Sjeng View Post
The ideal gas law is an approximation anyway.

At higher pressures, the volume of the molecules can no longer be ignored in calculations. This leads to the ideal gas law giving inaccurate results. For this reason, I use the Redlich-Kwong equation of state in my calculations. You would be surprised in the difference this makes. I cannot believe people do not take this into consideration.

While in reality I'm just another drunk who bolts together mismatched parts of 1980's technology.
At high pressures, no you cannot ignore the molecular volume, but then you’re existing in combustion dynamics. In an intake runner or all four overall? At the intake valve as it opens? The exhaust valve at full excursion? Between pulses, at a non-smooth curve in the exhaust manifold?

Without breaking a turbo charged gasoline engine into component parts—which is what this thread would love to accomplish, but cannot—one would be hard pressed to find an EOS that works from MAF to exhaust tip. This aint rocket science, literally. Unless we are talking about single stroke 240’s...

Broad strokes, experimental data, trial and error. As you said, 80’s fuel injection... not ideal. Y’all can go pervert equals nert quietly in the corner.
__________________
- Justin
1980 242 DL
240 Junk for Sale
Feedback

Last edited by SlowRide; 02-09-2018 at 11:48 AM..
SlowRide is offline   Reply With Quote
Old 02-09-2018, 12:03 PM   #77
NotSoFresh
Sick ****** T-Brick Prick
 
NotSoFresh's Avatar
 
Join Date: Aug 2008
Location: gangcouver
Default

After a day of pondering, I came up with this:
Its a semi closed loop system. The amount of exhaust effects the amount of intake. How do we improve the efficiency of this system, to get more power? Find the current worst bottle neck and eliminate it. The goal is a balanced system.

If the intake is a drinking straw, it doesn't matter what size turbo is there, you can only move so much air at a given pressure. Increase the size of the straw and a point is reached where that no longer is the bottle neck in the system. Keep increasing the intake flow capabilities and you get no more results because something else is now the restriction. Perhaps the next bottleneck is the cam dynamics, and the cam is not suited to a performance turbo motor. Install a cam better suited to a turbo motor, flow goes up and now the bottleneck is the exhaust. Its not converting enough exhaust energy to intake charge. Port the exhaust to allow the exhaust turbine to better use the exhaust energy, and you will see improvement until the turbine is the new source of restriction to the new flow levels of the rest of the system. It can't handle the flow the engine is capable of, and instead of converting it to intake energy, it maxes out and heat is the result. Install bigger/higher flowing turbine and the restriction is now moved to the compressor. Up the size of the compressor to match the turbine, and you will now see the power gains. Balance.
If the components are sized correctly to each other, the system should be working in balance, at a new hp level. There will always still be a small bottleneck somewhere. Want more power? you need to adjust the whole system to a higher balance point.

I realize I never included heat, at least not directly. Too much heat is evident in a system that is not in balance. Something along the way is causing resistance. Heat is a product of inefficiency. Ideally all the exhaust energy directly equates to intake charge. This is not true and the difference is heat. Heat should not be a factor in a system designed in a balanced and efficient manner. Heat is an indicator of inefficiency. You can't get away from the heat that is created when you compress a gas, That is physics. You can however reduce any additional heat applied to the air by the inefficiencies of the system by achieving balance.
What are intercoolers for? To reduce the heat you can't get away from. It is not for reducing the heat created by mismatched components.
This requires looking at each part separately, and seeing if it is the current bottleneck in the system as a whole.

Quote:
Originally Posted by linuxman51 View Post
If volume is the sole dictator of performance, all 2.3L turbo engines would make the exact same power at the exact same boost levels.
But this is not the case, is it. Ford 2.3 turbo guys struggle to get "big numbers". 2.0 mitsu engines throw down big numbers.
1.6L hondas, big numbers.
Ergo, volume cannot be considered static.
The volume IS static. The volumetric efficiency varies. Those motors all have different stroke/bore ratio, head configuration, rotating assembly mass, compression ratio, valve size, cooling, oiling, etc.......All of these factors play into the VE of the engine and why those engines do or do not make power at a given displacement.
NotSoFresh is offline   Reply With Quote
Old 02-09-2018, 12:06 PM   #78
SlowRide
Cold War Crumple Zones
 
SlowRide's Avatar
 
Join Date: Aug 2008
Location: FLORI-DERP
Default

Quote:
Originally Posted by NotSoFresh View Post
What are intercoolers for?
So far as I can tell, they’re for collecting oil...
SlowRide is offline   Reply With Quote
Old 02-09-2018, 12:25 PM   #79
linuxman51
BRANDSCHUTZVORSCHRIFTEN!
 
linuxman51's Avatar
 
Join Date: Dec 2002
Location: mont, AL
Default

Quote:
Originally Posted by NotSoFresh View Post

The volume IS static. The volumetric efficiency varies. Those motors all have different stroke/bore ratio, head configuration, rotating assembly mass, compression ratio, valve size, cooling, oiling, etc.......All of these factors play into the VE of the engine and why those engines do or do not make power at a given displacement.
Which was my point. Swept volume may be static, but for what we're discussing, it's largely meaningless by itself. You don't consider the static displacement of the engine to be the end all be all when you're playing with the turbo calculators (whether you realize it or not).. on a very basic level you plug in VE, displacement to get a comparable number, and then plot it against various rpm points on the compressor map based on the calculated amount of air going through the engine. (be it cfm or lb/min, whatever). (that sounds contradictory eh)

swept displacement matters most if you're comparing two identical engines except for that, e.g. b21 vs b23 or b200 vs b230, that sort of thing.. where your VE based on head performance is going to be fairly similar.

(I'm not trying to suggest that displacement matters not at all, don't get me wrong)

Quote:
Originally Posted by SlowRide View Post
So far as I can tell, they’re for collecting oil...
yeah, sometimes it seems that way eh
__________________
"They bum rushed them in their own crib, they drank all their beer, they partied with their ladies and they left with the trophy"

Now with in-house Dyno tuning!

Megasquirt Tuning!
Plug and play LH 2.4 Megasquirt, now with stealth mode!
linuxman51 is offline   Reply With Quote
Old 02-09-2018, 12:41 PM   #80
linuxman51
BRANDSCHUTZVORSCHRIFTEN!
 
linuxman51's Avatar
 
Join Date: Dec 2002
Location: mont, AL
Default

that explanation is a bit problematic (I had to rush it, caught a cramp if you knowwhatImean)... anyway, you caught what I was getting at before.
linuxman51 is offline   Reply With Quote
Old 02-09-2018, 12:46 PM   #81
bobxyz
Board Member
 
bobxyz's Avatar
 
Join Date: Aug 2014
Location: Boulder, Colorado
Default

Quote:
Originally Posted by JohnMc View Post
Now I vaguely want to hook a PSI gauge to my exhaust manifold and see how high the PSI gets when it's making 20 psi of boost.

Not enough to actually DO anything about it, mind you.
Quote:
Originally Posted by linuxman51 View Post
I haven't done this yet either, but it's on the list of things to add to racecar V....whatever version it is.
I'd really like to see some different plots showing intake/cylinder/exhaust pressure versus rotation for a turbo engine and a few different operating points (idle, cruise, max boost).

Somewhere (maybe Heywood?) I remember seeing a plot that showed the expected blowdown pressure peak, followed by flat-ish presure for the rest of the exhaust stroke, but then a jump in pressure (to intake boosted level) at overlap. No reversion at all. If anyone knows where to find some example plots, that would be great.

Not to digress too far, but how do I account for an intercooler when using a compressor map to size a turbo? I know there will be some pressure drop across the intercooler, so the PR needs to be bumped up over what's desired on the boost gauge. For flow, the intercooler is going to drop temperature and condense the air so that the compressor needs to supply extra CFM to the intercooler to keep up with the engine CFM. Is there a standard way to scale compressor CFM for the estimated cooling?
__________________
'85 245glt aw71 k-jet -> ms
bobxyz is offline   Reply With Quote
Old 02-09-2018, 01:04 PM   #82
linuxman51
BRANDSCHUTZVORSCHRIFTEN!
 
linuxman51's Avatar
 
Join Date: Dec 2002
Location: mont, AL
Default

You can set things up such that the pressure on the exhaust side is lower than the pressure on the intake side (then, with overlap, you might end up blowing some of the charge out, something the swedes occasionally talk about).

you could take before and after pressure readings on the intercooler to see what it's doing, it's been my experience though on a decently sized cooler, you don't start to see a significant pressure drop until you start closing in on it's max flow capacity (so that is to say, it depends on a number of factors, there's not a say... .01 multiplier or something to factor that in)

in real world terms, unless it's a really poor intercooler, it generally would just move the dots up a little and over a little.
linuxman51 is offline   Reply With Quote
Old 02-09-2018, 01:13 PM   #83
BDKR
Section 9
 
BDKR's Avatar
 
Join Date: Nov 2003
Location: Horizons Cave
Default

Quote:
Originally Posted by Dirty Rick View Post
...15psi is 15psi no matter what turbo is pushing it.
You're right. 15PSI is 15PSI no matter the turbo used. HOWEVER, psi IS NOT A MEASURE OF MASS. Wiki does a very good job of getting down to the bottom of this in just a couple of sentences.

Quote:
Originally Posted by From Wiki
The pound per square inch or, more accurately, pound-force per square inch (symbol: lbf/in2;[1] abbreviation: psi) is a unit of pressure or of stress based on avoirdupois units. It is the pressure resulting from a force of one pound-force applied to an area of one square inch. In SI units, 1 psi is approximately equal to 6895 N/m2.
In other words, how much air is crammed into that square inch? Larger turbos tend to cram more air into a square inch than smaller turbos. And try to keep in mind that turbos do this by "compressing" that air.

Quote:
Originally Posted by linuxman51 View Post
Threads like this continue to underline the fact that none of yall are ever actually going to catch me.


Quote:
Originally Posted by linuxman51 View Post
We *know* that it is based on mass air flow
Clearly this is where everyone get's it tossed!
__________________
Quote:
For all you Dijkstra fanboys:

Knuth also cites a letter sent to him by Dijkstra, in which the latter adds some nuance to this earlier statements: "Please don't fall into the trap of believing that I am terribly dogmatical about [the go to statement]. I have the uncomfortable feeling that others are making a religion out of it, as if the conceptual problems of programming could be solved by a single trick, by a simple form of coding discipline!"
BDKR is offline   Reply With Quote
Old 02-09-2018, 01:15 PM   #84
bobxyz
Board Member
 
bobxyz's Avatar
 
Join Date: Aug 2014
Location: Boulder, Colorado
Default

Thanks for the intercooler info.

Quote:
Originally Posted by linuxman51 View Post
You can set things up such that the pressure on the exhaust side is lower than the pressure on the intake side (then, with overlap, you might end up blowing some of the charge out, something the swedes occasionally talk about).
There was a MS thread a couple years ago about a weird ridge in the VE map. I think that this was exactly what was happening, and when coupled with injection overlapping with the intake valve opening at higher RPMs, some of the injected charge went straight out the exhaust causing a need for extra fuel to get back to desired AFR.
bobxyz is offline   Reply With Quote
Old 02-09-2018, 03:49 PM   #85
apachechef
Burnt Sierra Madre
 
Join Date: Jan 2009
Location: Letterkenny, ON
Default

Quote:
Originally Posted by linuxman51 View Post
in all seriousness, where I was going with my comments and remarks was to make things obviously disproportionate enough to force a re-think. Part of the reason is I feel like some amount of effort needs to be exerted on the part of those inquiring, and the other part is cynical in nature--this very subject has been beaten to absolute death on this forum and others, and yet the insipid notion remains that the *only* reason bigger turbos exist is to run higher boost and/or cooler charge temps, and that that is the *only* reason they make more power. Its a discussion so old and worn out at this point I have a hard time not having fun at other people's expense. May not be the right way to deal with that, but horses and water and what not.

t.
Thanks for teaching some anyway.
I feel your pain, when trying to explain other basic concepts like evolution and origin of life, I remember some very over simplified points you tried to inject that we're cringeworthy to me, but would have been answered with a moment's thought or bio 101.
It's hard to handle neophytes politely, I'm very guilty of that myself. I appreciate you sticking around enough in threads beneath your level so there really less of them.

I wasn't trying in any way to put Delta T as the only, not even a big factor in trbo choice.
I can see why you thought I might be though, hard to specify what you are talking about sometimes.

What got me thinking was this notion (not tours)that
"Bigger turbo flows more at same psi" go back and see the peppered in the early thread. I quoted you because I knew you'd know how to explain, because that just seemed to be a terrible weirdness in a bad way. I'm sure you agree that that is a bad phrase. The dynamic system can't be explained like that, when the cylinder gulps a set volume, a stable cfm in a way you can't say it flows more in cfm.
Wasn't accusing you of that stuff, was hoping to clear that up.
Problem I saw was higher flow, same psi, in a system that had constant flow limited by the rigid volume of the cylinder. Saying that turbo 'flows" more makes zero sense to me, nor you, I'm sure. Was primarily objecting to that, not trying at all to saying turbos are only different in temp.



I think we know that turbos and ICEs are hypercomplex, dynamic machines, with so many variables that narrowing down static shots are less valuable.
Thanks bearstronaut for pointing out that TLDR, I know your pain as well. Post a pic of some of the systems you work with, love big stainless industrial octopus things.

Next up, I have a built up 2.5L redblock waiting for a turbo choice, which since I'm not looking for one by temp change at 18psi I will need help learning to pic a good match turbo for it.
I hope you guys help, despite the neophytism
.
__________________
Quote:
Originally Posted by lummert View Post
Dammit, Lummert.
Quote:
Originally Posted by Jesse8931 View Post
Well keep us updated on how your dumbass plan goes.
apachechef is offline   Reply With Quote
Old 02-09-2018, 03:59 PM   #86
JohnMc
PV Abuser
 
JohnMc's Avatar
 
Join Date: May 2004
Location: St. Louis
Default

I guess a different way to say it is that the bigger turbo has to flow more air to make the same PSI, because the engine can use more of it at a given PSI with a bigger turbo on the exhaust side.
__________________
'63 PV Rat Rod
'93 245 16VT Classic #1141
JohnMc is offline   Reply With Quote
Old 02-09-2018, 04:09 PM   #87
CAPT_BLOTTO
#Crush It
 
CAPT_BLOTTO's Avatar
 
Join Date: Jul 2005
Location: Kansas City
Default

So how psi a stock can support depends on of CFM, T, volume, cats, intake valve size, humidity, and the price of rice in China?
__________________
Hello My Glorious!

Junkyard Parts request thread!
Mesquite FB page! Constant updates!

Da Yellow Sold | $800 245 | 77 244
CAPT_BLOTTO is offline   Reply With Quote
Old 02-09-2018, 04:10 PM   #88
JohnMc
PV Abuser
 
JohnMc's Avatar
 
Join Date: May 2004
Location: St. Louis
Default

Are they using the rice to make ethanol?
JohnMc is offline   Reply With Quote
Old 02-09-2018, 04:19 PM   #89
CAPT_BLOTTO
#Crush It
 
CAPT_BLOTTO's Avatar
 
Join Date: Jul 2005
Location: Kansas City
Default

Sake flavored ethanol
CAPT_BLOTTO is offline   Reply With Quote
Old 02-09-2018, 04:21 PM   #90
JohnMc
PV Abuser
 
JohnMc's Avatar
 
Join Date: May 2004
Location: St. Louis
Default

A sip for me *hic* and a slosh for the car *glug*.
JohnMc is offline   Reply With Quote
Old 02-09-2018, 04:34 PM   #91
EivlEvo
Board Member
 
Join Date: Sep 2012
Default

How much PSI a stock can support?
EivlEvo is offline   Reply With Quote
Old 02-09-2018, 04:58 PM   #92
linuxman51
BRANDSCHUTZVORSCHRIFTEN!
 
linuxman51's Avatar
 
Join Date: Dec 2002
Location: mont, AL
Default

Quote:
Originally Posted by apachechef View Post
Thanks for teaching some anyway.
I feel your pain, when trying to explain other basic concepts like evolution and origin of life, I remember some very over simplified points you tried to inject that we're cringeworthy to me, but would have been answered with a moment's thought or bio 101.
It's hard to handle neophytes politely, I'm very guilty of that myself. I appreciate you sticking around enough in threads beneath your level so there really less of them.

I wasn't trying in any way to put Delta T as the only, not even a big factor in trbo choice.
I can see why you thought I might be though, hard to specify what you are talking about sometimes.

What got me thinking was this notion (not tours)that
"Bigger turbo flows more at same psi" go back and see the peppered in the early thread. I quoted you because I knew you'd know how to explain, because that just seemed to be a terrible weirdness in a bad way. I'm sure you agree that that is a bad phrase. The dynamic system can't be explained like that, when the cylinder gulps a set volume, a stable cfm in a way you can't say it flows more in cfm.
Wasn't accusing you of that stuff, was hoping to clear that up.
Problem I saw was higher flow, same psi, in a system that had constant flow limited by the rigid volume of the cylinder. Saying that turbo 'flows" more makes zero sense to me, nor you, I'm sure. Was primarily objecting to that, not trying at all to saying turbos are only different in temp.



I think we know that turbos and ICEs are hypercomplex, dynamic machines, with so many variables that narrowing down static shots are less valuable.
Thanks bearstronaut for pointing out that TLDR, I know your pain as well. Post a pic of some of the systems you work with, love big stainless industrial octopus things.

Next up, I have a built up 2.5L redblock waiting for a turbo choice, which since I'm not looking for one by temp change at 18psi I will need help learning to pic a good match turbo for it.
I hope you guys help, despite the neophytism
.

At the base level, a bigger turbo does flow more at a given pressure ratio than a smaller turbo. This is clearly mapped out on compressor maps.. there's a range, and a surge line.. and if you size your stuff wrong and end up left of that line, reality changes (and not in a good way), but this is what gives us "ranges" for various turbos. As others have said above too, it's still somewhat of a "grey" area and very much application specific as to whether a given turbo in a given range will work better than another in the same range, etc. I think, again, in this specific thread, part of the problem is that a 13c, while villified, is not some order of magnitude smaller than a 15g. If you took max-effort setups for both, sure, 240-250 hp from the 15g is a reasonable upper limit (not a hard limit), whereas you might expect a max effort 13c to belt out 220. (cue the people who've done better with both lmao). In both cases however, I would posit that you've gone past what you should be doing, you need to step up again.

The problem with simply looking at swept volume in a more or less fixed point is that you're missing literally thousands of points all around it. Volumetric efficiency gets tossed around but in terms of what we're doing, changing the turbo setup on the car changes it's VE. Bigger housings breathe better, etc.
So.. at say, 15psi and 3000 rpms with either turbo you may see very little difference in performance, as the amount of air the system is moving now vs what its moving with the smaller turbo may or may not be exceeding the ability to exhaust this air. Where your differences start to come in to play, and where your fuel system starts to take it in the shorts is higher and higher (and 3k is really just an arbitrary number), as the speed and overall amount of air to make the same amount of torque goes up.

A somewhat common example of this can be seen across the pond with the "budget" 8v turbo setups a lot of swedes run around with.. big cam, springs, port the head, very large turbo, and a relocated powerband.. the 13c/15g car is effectively "out of steam" before this thing even gets going, and yet we're still talking about essentially the same engine in terms of swept volume (but not in terms of output obviously)

So, in the sense of how a given system performs, saying that a turbo flows a given amount makes complete sense to me. Remember, at the end of the day, power and fuel consumption are tied directly to airflow. Superchargers and turbochargers force more in. Talking about it in terms of flow is a lot like talking about it in terms of how much power it supports, be it CFM, lb/min, or just "hp". A lot of is somewhat lazy and knowing the platform at this point, and a fair amount of direct experience over the years lol.
linuxman51 is offline   Reply With Quote
Old 02-09-2018, 05:01 PM   #93
apachechef
Burnt Sierra Madre
 
Join Date: Jan 2009
Location: Letterkenny, ON
Default

Quote:
Originally Posted by linuxman51 View Post
.
Thanks
apachechef is offline   Reply With Quote
Old 02-09-2018, 05:48 PM   #94
linuxman51
BRANDSCHUTZVORSCHRIFTEN!
 
linuxman51's Avatar
 
Join Date: Dec 2002
Location: mont, AL
Default

hope some of it made sense. one thing im not good at is teaching lol. anyway, going forward, don't be afraid to ask questions even if they may be dumb. everyone's been there, and while we might have some fun at your expense its usually meant with good intentions.
linuxman51 is offline   Reply With Quote
Old 02-09-2018, 06:25 PM   #95
VB242
These Pipes Are Clean!!
 
VB242's Avatar
 
Join Date: Sep 2011
Location: Virginia Beach
Default

Nobuddy sed ennything bout negative cam overlap for turbos.
__________________
1980 primer JDM flares franken-242DL, 1989 silver 780 sienna rear spring nivomat delete
VB242 is online now   Reply With Quote
Old 02-10-2018, 12:02 PM   #96
EivlEvo
Board Member
 
Join Date: Sep 2012
Default

Regular hotdogs and footlong hotdogs have the same PSI on their casing, but one has more meat.
EivlEvo is offline   Reply With Quote
Old 02-10-2018, 12:07 PM   #97
NotSoFresh
Sick ****** T-Brick Prick
 
NotSoFresh's Avatar
 
Join Date: Aug 2008
Location: gangcouver
Default

Quote:
Originally Posted by EivlEvo View Post
Regular hotdogs and footlong hotdogs have the same PSI on their casing, but one has more meat.
But can you cram it in the hole any faster? Like how many hotdog inches a minute can you gobble?
NotSoFresh is offline   Reply With Quote
Old 02-10-2018, 12:19 PM   #98
EivlEvo
Board Member
 
Join Date: Sep 2012
Default

To the meat store!

EivlEvo is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump


All times are GMT -4. The time now is 08:09 AM.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2018, vBulletin Solutions Inc.