byzan a4
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« Reply #30 on: December 26, 2012, 01:42:40 PM »
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deleted, cos it was pointless
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« Last Edit: December 26, 2012, 04:44:03 PM by byzan a4 »
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prj
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« Reply #31 on: December 26, 2012, 02:03:42 PM »
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It's not special, It's a built engine running 9.25CR without problems and without it self destructing No one ever said it will self destruct. I simply stated that with lower CR it will make more torque/power throughout the range any time you are WOT. Do you disagree then? Explain to me how a larger capacity engine with higher CR will possibly have poorer spool and off boost performance? Because your fuel is only 97 or 99 RON, it's not 120+ RON. When you floor the car from 2000 RPM, your high compression engine will make significantly less torque due to the fact that it will be knock limited, and the lower compression engine will not be. Your high compression engine will not be able to extract as much power from the same amount of gasoline, as it will be operating at a reduced ignition angle, thus lowering the very efficiency, you are searching for. Because the high compression ratio engine will make less torque, the revs will rise slower. Because the revs rise slower, you will get up to boost slower. What's so hard to understand? This is really the basics. The *only* downside for say 8.5:1 on V-Power or Momentum would be slightly decreased fuel economy. And the reason for that is, that at low load, the high compression ratio engine will not be knock limited, so it can run optimal spark advance, and the lower compression ratio engine will lose out on efficiency. If you saw any kind of gains for a higher CR anywhere (off boost or on boost) at WOT, then something else was at fault. |
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« Last Edit: December 26, 2012, 02:06:15 PM by prj »
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matchew
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« Reply #32 on: December 26, 2012, 02:05:41 PM »
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What physical facts, all i have seen here is you stating it won't work, when others here have plainly seen different.
He said its not the ideal way. I have personally tuned none, I have however been present when many engines have been tuned, including low and high CR engines. Viewing the logs and interpreting the information I have not seen what you speak of in real life.
So you have personally seen (not tuned or been involved with tuning) 2 identical setup engines just with different compression ratios? At what power level are you talking? Explain to me how a larger capacity engine with higher CR will possibly have poorer spool and off boost performance?
Explain to me what makes a turbo spin? |
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« Last Edit: December 26, 2012, 05:09:19 PM by matchew »
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nyet
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« Reply #33 on: December 26, 2012, 02:46:57 PM »
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In my experience, all things being equal, a low compression 2.7t makes more torque and spools faster than a stock 2.7t on pump gas (regardless of the turbos), for all the reasons prj outlined. As he said, the limitation isn't VE related, but rather knock related.
Silly VE tricks (like "cold air" intake games) are for people stuck with N/A motors. For some reason, a lot of their voodoo explanations for things (unfortunately) leaked into FI tuner strategies.
YMMV.
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byzan a4
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« Reply #34 on: December 26, 2012, 05:02:08 PM »
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what you say makes some sense, but is opposite to what ive seen. Hybrid 1.8t's on 9.0-1 making 20 BHP less than the 9.5 CR Variant given the same spec turbos, LP heads,same add odds and the same results from several tuners.
In any case, I apologise for my rant.
I personally much prefer to be able to drive my car around at less than WOT it's not all about maxboost and power, higher cr=lower boost and earlier torque in the cars i have experienced personally.
I don't have my plot and logs to hand to show what mine is doing as my valve guides need doing so I am rebuilding the head shortly, will have details then as I had the tuning aborted due to excessive overrun smoke( guides)
it was around 283 hp@ 1bar and 350 torques from memory at 5 k ish , It's late now I'd have to double check, but i'm sure it's not miles from that.
Can someone explain the US fuel then, I thought you had a fuel "worse" than out std 95 ron stuff then almost the same and your next one being around 97 not 99 like V-power.Ignoring super race fuels and the like
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ddillenger
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« Reply #35 on: December 26, 2012, 05:08:30 PM »
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We have 91 on the west coast, 94 on the east coast (octane, not RON), and a hodgepodge in between.
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Please, ask all questions on the forums! Doing so will ensure the next person with the same issue gets the opportunity to learn from your experience!
Email/Google chat:
DDillenger84(at)gmail(dot)com
Email>PM
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prj
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« Reply #36 on: December 26, 2012, 05:15:10 PM »
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what you say makes some sense, but is opposite to what ive seen. Hybrid 1.8t's on 9.0-1 making 20 BHP less than the 9.5 CR Variant given the same spec turbos, LP heads,same add odds and the same results from several tuners. Well, then their spec was different or the tune was different, very simple. Or let me guess, you are taking numbers from random dynos on different days? Or do you think that Audi also went to 9.0 CR from 9.5 with K04, just for shits and giggles? Why am I even bothering replying to you. You do not understand anything about what goes on in the combustion chamber, you just regurgitate "I have seen" "Others say" over and over and over again. It's getting old and you are starting to sound like a broken record. It doesn't work like you say it does, period. No matter how many times you repeat it, it's not going to magically come true. Read a book and educate yourself, you really need it. Stop just repeating and looking at others, figure things out yourself, understand how and why things work. I don't need to look at what "others say" and "others do". Because I have personal experience with these things and understanding why something works the way it does. Lots of it. More than a couple things you have seen here and there from some "tuners" or read on some forum. You already said you have zero experience mapping an internal combustion engine. I've done 100's. Why are you still here arguing? You are yet to counter a single fact that was posted. Your claims are in complete opposition of physics. To someone who understands the combustion process you are basically claiming that the world is flat. That's how outrageous it is. |
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« Last Edit: December 26, 2012, 06:11:57 PM by prj »
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AARDQ
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« Reply #37 on: December 26, 2012, 05:20:36 PM »
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Dynamic compression ratio, as opposed to mechanical compression ratio. sqrt((boost+14.7)/14.7) * CR = effective compression ratio. Dropping CR allows a greater effective CR (therefore greater oxygen with which to combine with fuel). Say you drop from 9:1 CR to 8:1, which allows an increase in boost from 15 psi to 18 psi without detonation onset and all else being fairly equal. You've lost 3-4% in power potential as a result of the decrease in mechanical compression ratio, but you've gained 10% in absolute potential, for a net increase of 6-7%. Could be wrong, but I doubt most people could tell the difference in throttle response in off-boost situations between 8:1 and 9:1. There is a point where a lower CR will not be enjoyable in off-boost conditions, but I don't think 8:1 or 8.5:1 is it.
Interesting discussion.
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prj
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« Reply #38 on: December 26, 2012, 05:31:02 PM »
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@AARDQ,
Don't forget, that if your engine was knock-limited before at a load site, then by dropping compression ratio you will lose those same 3-4% from it, but gain back 10+% from being able to advance the timing and actually use the fuel to push the piston, compared to blowing it as heat out of the exhaust.
The reason behind this is, that the more you compress, the hotter the charge gets, so the likely the fuel is to start detonating instead of burning normally.
This is where most people go wrong, they always think they are running a perfect fuel. And if you had an imaginary fuel with infinitely high octane rating, then you would always gain when increasing compression, however no fuel has an infinitely high octane rating, so it's always a tradeoff.
Where that breaking point is depends on the fuel used and on combustion chamber design.
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« Last Edit: December 26, 2012, 05:51:32 PM by prj »
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rob.mwpropane
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« Reply #39 on: December 26, 2012, 07:21:40 PM »
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What turbo are you planning to run?
My hopes and dreams are a 2.0 conversion, and currently I own, but have yet to install a Garrett GT2860RS. 93 Oct, and at the track E85 or 104 Oct. I'm really glad this got brought up. This discussion, especially with the examples given, has painted a more vivid picture of what happens in the (FI) internal combustion engine. Even thanks to those who pissed off prj, without you I'm not sure he would have explained the process so in depth to prove you wrong.  (and I mean that, no sarcasm) |
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This has nothing to do with cars but you can see my glorifying job at, www.MWPropane.com |
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AARDQ
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« Reply #40 on: December 26, 2012, 07:39:15 PM »
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@AARDQ,
Don't forget, that if your engine was knock-limited before at a load site, then by dropping compression ratio you will lose those same 3-4% from it, but gain back 10+% from being able to advance the timing and actually use the fuel to push the piston, compared to blowing it as heat out of the exhaust.
The reason behind this is, that the more you compress, the hotter the charge gets, so the likely the fuel is to start detonating instead of burning normally.
This is where most people go wrong, they always think they are running a perfect fuel. And if you had an imaginary fuel with infinitely high octane rating, then you would always gain when increasing compression, however no fuel has an infinitely high octane rating, so it's always a tradeoff.
Where that breaking point is depends on the fuel used and on combustion chamber design.
Absolutely true. An engine is a system; everything must be considered in concert. |
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carsey
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« Reply #41 on: December 26, 2012, 08:37:24 PM »
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Seems everyone is saying that boost makes the power in these engines?? I've seen less boost applications make more power than those with higher levels of boost and the power made from timing?
Either way, soon see what happens when I blow 30psi through it and if it makes power.
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AARDQ
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« Reply #42 on: December 26, 2012, 08:55:56 PM »
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Seems everyone is saying that boost makes the power in these engines?? I've seen less boost applications make more power than those with higher levels of boost and the power made from timing?
Either way, soon see what happens when I blow 30psi through it and if it makes power.
Boost in concert with proper timing for the fuel. Not boost ignoring everything else. |
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Bische
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« Reply #43 on: December 27, 2012, 12:36:29 AM »
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No, it's not that simple. Put it on a dyno, and you will know.
But from my experience if you go WOT on a GT35R at 3000 RPM on a dyno, where absolutely nothing happens boost wise then at the resulting load site then your MBT is still knock limited even at 8.0:1. Yes, I figured that. I just got the feeling from your posts regarding MBT that the "threshold" is much lower than I thought, and maybe I could get a better ballpark than my current. Take a look at the graph I attached, pretty much anything over 70rl on my setup and we are in boost. Thanks, that only confirms it, was that 35R on straight pump gas? Im going to visit a dynapack in the new year, is it even viable to tune non-knock limited MBT without an emulator? I mean, sure it ~can be done flashing, but I would imagine it would take many hours to do 2 timing tables properly. Regarding power vs. CR, I did read a very good line a couple years ago: It is all about where you compress the air. |
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littco
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« Reply #44 on: December 27, 2012, 02:45:04 AM »
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what you say makes some sense, but is opposite to what ive seen. Hybrid 1.8t's on 9.0-1 making 20 BHP less than the 9.5 CR Variant given the same spec turbos, LP heads,same add odds and the same results from several tuners.
In any case, I apologise for my rant.
I personally much prefer to be able to drive my car around at less than WOT it's not all about maxboost and power, higher cr=lower boost and earlier torque in the cars i have experienced personally.
I don't have my plot and logs to hand to show what mine is doing as my valve guides need doing so I am rebuilding the head shortly, will have details then as I had the tuning aborted due to excessive overrun smoke( guides)
it was around 283 hp@ 1bar and 350 torques from memory at 5 k ish , It's late now I'd have to double check, but i'm sure it's not miles from that.
Can someone explain the US fuel then, I thought you had a fuel "worse" than out std 95 ron stuff then almost the same and your next one being around 97 not 99 like V-power.Ignoring super race fuels and the like
Reason hybrids make more power on higher compression is because you are limited by the max boost the hybrid can make at redline. Typically the k04 hybrid will hold a max of 21psi ( or for another want, x amount of lbs of air or flow) at 7200rpm. With this, where you can't add more boost/flow into the engine you can only increase cr to squeeze more power out. |
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