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PassatWorld Staff
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Discussion Starter #1
I removed my "suitcase" resonator two weeks ago, replacing it with two 90-degree-3"-radius-2.5" elbows. No other mods. Comparing trendlines (omitted for clarity) I'm now down 10 ft-lbs peak TQ in addition to losing a lot of area under the curve. And while peak HP is pretty much the same, the peak occurs higher in the RPM band (expected) but again I've lost a lot of area under the curve.



WTF? One important piece of data is that in the process of wrestling with the exhaust system one of my downpipe bolts came out. It was out for a few days before I found the problem (the car, of course, sounded like sh*t, and I thought it was due to removing the res, and I was bummed), but the bolt is back in, everything is tight, and it sounds great. Maybe the ECU freaked with the exhaust leak and I just need to reset the ECU and maybe do a TB adaptation? I've got some other ideas, too, but I'd love to hear yours.

Thanks - Rusty

P.S. More important pieces of data:

1) Timing is being pulled (compared to before) - two degrees @3000, up to a max of 10 degrees @4800.
2) I'm getting plenty of fuel. Trims are +5.5/+1.6. Before removal they were +5.5/+4.7. Odd that they dropped - I would have expected them to increase. And I'm not hitting the 16.32 msec ceiling.
3) O2 sensor voltage is the same as before at .855 volts, which is about 13.5:1 - not great, but par for a stock ECU and the same as before.
4) Boost has not varied, still peaking and holding at 14 psi, except that it used to drop to 7 psi @6000, and now it holds 9-10 at 6000 - again an expected result.
 

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You're building those graphs based on ECU's load calculation, right?

I'd consider invalid measurement as a prime source of the discrepancy...

Are you saying the ECU pulled 10 degrees of timing :shock: Or that's the total from the trims? Even having pulled 2 degrees is rather significant. Bad gas? Hotter ambient temps from previous test? And quit trying to measure AFR with your narrow band before I come over and slap you :poke: I assume the +1.6 part of "+5.5/+1.6" is short term? I don't think changes to STFT's are going to affect your open-loop fueling at all.
 

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PassatWorld Staff
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Discussion Starter #7
You really think two 90's is more restrictive than the resonator? Plus, if it were more restrictive, I think I wouldn't have picked up the extra boost on the top end...

But to answer your question directly - no, I can't replace the two 90's - not without too much money and time spent. This was supposed to be an easy, almost "free" mod - a friend had two leftover elbows. These are mandrel-bent, 2.5" dia. I can see losing a bit of velocity as the pipe transitions from 2.25 to 2.5 and back to 2.25, but this shouldn't cost me any power... should it? :???:
 

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Discussion Starter #8
Macabre said:
You're building those graphs based on ECU's load calculation, right?

I'd consider invalid measurement as a prime source of the discrepancy...

Are you saying the ECU pulled 10 degrees of timing :shock: Or that's the total from the trims? Even having pulled 2 degrees is rather significant. Bad gas? Hotter ambient temps from previous test? And quit trying to measure AFR with your narrow band before I come over and slap you :poke: I assume the +1.6 part of "+5.5/+1.6" is short term? I don't think changes to STFT's are going to affect your open-loop fueling at all.
The graphs are built from Ross-Tech Andy's dynoplot4.xls, and are acceptably accurate as-is. I have modified it to make it more convenient to use, and have added scotty_passat and SAE correction factors, and have compared it with "real" dynos, and am confident in the accuracy of these plots relative to each other.

The ECU pulled the timing. I log MAF, Fuel injector cycle, timing, and IAT on all my dyno runs. The data is omitted on the comparison graph for clarity. I'll download the complete graphs and you can take a look.
Also, not mentioned above, MAF is down slightly.

The trims on these Bosch ECU's are not long term/short term. They are additive/multplicative. And there's still some debate about whether or not these trims are added to the maps used when in open loop. Some people say they are. My experiments to determine whether or not have been inconclusive, but seem to indicate that they are not.

Excerpted from http://www.clubb5.com/forums/viewtopic.php?t=47402 :

"Add" means additive trim, which is addressing an imbalance at idle. When the ECU is using additive trim, it is telling the injectors to stay open a fixed amount longer or shorter. The malfunction (e.g. vacuum leak) becomes less significant as RPM increase. For additive adaptation values, the injection timing is changed by a fixed amount. This value is not dependent on the basic injection timing.

"Mult" mean multiplicative trim, which is addressing an imbalance at all engine speeds. The malfunction (e.g. clogged injector) becomes more severe at increased RPM. For multiplicative adaptation values, there is a percentage change in injection timing. This change is dependent on the basic injection timing.


Temp - It's definitely hotter ambient temps than the "before" run, by 10C. I suppose this would be enough to cause the timing to be pulled - but that damn much? It was about 50F for the B4 run, about 70F for the "after". Both dry-as-hell Albuquerque days.
 

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A properly tuned exhaust will give you more power than a straight pipe because the exhaust pulses are tuned by the geometry of the system. If you modify it, it's entirely possible that you're creating resonances in the wrong place (part of RPM band) and/or adding non-beneficial ones elsewhere.

There's more to an exhaust system than just removing back pressure.

All this being said, I'm sure the exhaust pulses are pretty much hosed up on a turbo car.. so it probably doesn't matter as much. In this situation, I would say that reducing backpressure would let the turbo spool quicker and easier...
 

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They are based on the ECU's load calculation though, right? I.e. they don't do any actual measurement of anything, they just convert the load reference to lb-ft? I would not use that to calculate horsepower because there's a lot more to horsepower than how much mass is passing through the MAF housing and that could be contributing to your mixed readings, but that's me. Your graphs still indicate that your engine is sucking in less mass but that the diff between 50F and 70F could certainly contribute that. What kind of difference in g/s readings are you seeing? About 5% in the mid range and none up top? I would say that indicates your exhaust free'd up the top end a lot but conditions are poorer.

I think "Add" and "Mult" is just another way of saying long and short term trims just using how they're applied as a naming convention rather than how they're determined, but it doesn't matter. Is the +1.6 your "Add" or "Mult" ?
 

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PassatWorld Staff
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Discussion Starter #11
Yeah, with a turbo you're not tuning pulses (except in the manifold); you just want to get rid of as much backpressure as possible while maintaining velocity.

OK here's the raw charts:

Before 2/26/04, ambient temp 6C/43F:


After 3/19/04, ambient temp 18C/64F:
 

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Discussion Starter #12
Macabre said:
They are based on the ECU's load calculation though, right? I.e. they don't do any actual measurement of anything, they just convert the load reference to lb-ft? I would not use that to calculate horsepower because there's a lot more to horsepower than how much mass is passing through the MAF housing and that could be contributing to your mixed readings, but that's me. Your graphs still indicate that your engine is sucking in less mass but that the diff between 50F and 70F could certainly contribute that. What kind of difference in g/s readings are you seeing? About 5% in the mid range and none up top? I would say that indicates your exhaust free'd up the top end a lot but conditions are poorer.

I think "Add" and "Mult" is just another way of saying long and short term trims just using how they're applied as a naming convention rather than how they're determined, but it doesn't matter. Is the +1.6 your "Add" or "Mult" ?
dynoplot4.xls takes a log of time, engine speed, vehicle speed, and the car's weight, calculates the kinetic energy difference between each data point (work), and converts to HP (time rate of doing work).

+5.5/+1.6 = add/mult.

My MAF g/sec readings don't make sense because I have the equivalent of a larger-than-oem MAF assy to compensate for my larger-than-OEM injectors.

I have been modding and plotting for months now, through several weather changes. Everything has correlated and been as-expected through every mod. This one has thrown me for a loop.

Here's another piece of info: Shifting. I have a Tip w Tip Chip. Before the resonator mod, it would surge forward under power with every shift. Now, when it shifts, it pauses, feeling like timing retard, then "catches up".

If someone put a gun to my head and forced me to put forth a theory here, I would say that I'm on the ragged edge of the stock ECU's ability to handle things, and removing the resonator put it over the edge, and I'm just getting boost too efficiently for the ECU to keep up...
 

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You sure did lose a lot of timing there.. maybe a bad load of gas, too?

Anyways it looks like your g/s and horsepower numbers are reduced by a reasonable amount at the low-mid range given the temp difference. I did a very rough calc and came up with ~3% correction for the temp diff which seems to match your data. What do you think?
 

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Rusty said:
dynoplot4.xls takes a log of time, engine speed, vehicle speed, and the car's weight, calculates the kinetic energy difference between each data point (work), and converts to HP (time rate of doing work).
Ahh, that's better. I remember there was an old one around that just used the load reference from the ECU.

Here's another piece of info: Shifting. I have a Tip w Tip Chip. Before the resonator mod, it would surge forward under power with every shift. Now, when it shifts, it pauses, feeling like timing retard, then "catches up".
Good luck with that one.. :suspicio:
 

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Discussion Starter #15
Macabre said:
You sure did lose a lot of timing there.. maybe a bad load of gas, too?
yeah, that could be it, although I always use Chevron. Well, there's an angle I haven't thought of - it's transitioning from winter to summer here (we don't get much Spring) and it could be that the warmer weather plus the "winter" gas (ethanol-diluted) could be causing this.

Macabre said:
Anyways it looks like your g/s and horsepower numbers are reduced by a reasonable amount at the low-mid range given the temp difference. I did a very rough calc and came up with ~3% correction for the temp diff which seems to match your data. What do you think?
Your correction for the temp diff - is this separate from and additive to the standard SAE correction? 'cause it's already SAE corrected for temp.
Maybe I need to get my arse out of bed early enough to get to the "dyno" area while the air is still cold...
 

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no it's not seperate from the standard correction but I was thinking more about your g/s reading than horsepower (ignore what I said about horsepower now that I see you're using a reasonable tool to measure it). I think you could just call the losses on the "dyno" results a result of the pretty significant timing retard from 3.5-6k. All in all with the data available it looks like your mod was a success, IMO, if you ignore the possibility that exhaust mods are causing your timing issues. I agree that it could be the case but I wouldn't make that judgement yet.. maybe mix in some higher octane or toluene to check the gas theory and make a run with colder ambient temps like you suggested
 

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Discussion Starter #17
OK I think I see what you mean about Timing. In sum (please correct me if I'm wrong):

1) The retarded timing is definitely causing the loss in power.

2) The retarded timing may or may not be a result of the exhaust mod. It may be the result of bad gas, or simply the hotter day, or the exhaust, or some other factor we don't know yet.

Here's another bit of info, one DTC which I noted on the dyno day 3/19. I ignored it since I had no idea of when it occured, and since I just had an exhaust leak at the downpipe I figured I'd have a code or two:

DTC
16486 - MAF Sensor (G70): Signal too Low
35-10 - - - Intermittent
 

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Rusty,

I think that more exhasust out is only benificial if more air is going in. Have you modified the intake? Maintaining a balance is key I believe.

I had my resonator removed and a mandrel bent pipe spliced in with great results by the bum dyno. :lol: I Coloradoed my air box and put in a K&N panel filter :thumbup:

:beer: ,

Malcolm
 

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Discussion Starter #19
My airbox is already Colorado'd, K&N'd, and heat-sheilded, plus I have a port-matched intake manifold and New South powergasket...
 

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I wonder if the transition form 2.25 to 2.5 and back is acting the same way an expansion chamber works on a 2 stroke. When I was into motocross the expansion chamber could do all kinds of weird stuff.. back pressures and odd resonanaces. Eg as the exhaust gases enter the 2.5" they scatter around .. flow is disrupted

Just a thought
 
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