Got Boost ? (part 2).... Ramblings, tests and confusion
10-15-2002, 07:01 AM
#1
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Got Boost ? (part 2).... Ramblings, tests and confusion
The Boost gauge is driving me crazy!
First - I did make sure the chip was on. : ) It was. Wow, was that evident. Per your advise, in stock mode, the boost stops right before 15 psi and the car felt "heavy" and slow. Turned the chip back on and zoooommmmm. Psi peaks were now in the low 17's. I saw the needle bounce to 20psi for an "instant" on a couple romps.
What makes me nuts is this. When accelerating (under load i.e., up a long incline)I see boost jump up to 15 - 17+ and then quickly drop off. I "SEE" the drop off. I do not "FEEL" the drop off. The pulls hard all the way to redline. I do not think boost is going away.
I tried another test. I turned the chip back off and rolled the power on (flooring it in 4th gear) while on a LONG straight uphill road. At 5500 RPM, the power just went away... It was as if I'd hit a rev limiter or something. It was terrible.
I turned around and duplicated the test. I switched the chip back on, was in 4th, rolled the power on (floored it) and WOW... Strong power and acceleration well past 5500 to redline. There was no surging or flat spot. The gauge showed the same odd results. Psi was up (15 - 17+ range) for a second or 2 and then it drops off.
Is it possible I have an incorrect vacuum/pressure source?
Is this what boost gauges do? I've never used nor seen one (in action) before.
I know I do not have a leak. The gauge holds a perfectly steady 22 inches of vacuum @ idle and more on decel.
Sean you mentioned you were seeing 22-23 to redline.
What say ye boosters?
First - I did make sure the chip was on. : ) It was. Wow, was that evident. Per your advise, in stock mode, the boost stops right before 15 psi and the car felt "heavy" and slow. Turned the chip back on and zoooommmmm. Psi peaks were now in the low 17's. I saw the needle bounce to 20psi for an "instant" on a couple romps.
What makes me nuts is this. When accelerating (under load i.e., up a long incline)I see boost jump up to 15 - 17+ and then quickly drop off. I "SEE" the drop off. I do not "FEEL" the drop off. The pulls hard all the way to redline. I do not think boost is going away.
I tried another test. I turned the chip back off and rolled the power on (flooring it in 4th gear) while on a LONG straight uphill road. At 5500 RPM, the power just went away... It was as if I'd hit a rev limiter or something. It was terrible.
I turned around and duplicated the test. I switched the chip back on, was in 4th, rolled the power on (floored it) and WOW... Strong power and acceleration well past 5500 to redline. There was no surging or flat spot. The gauge showed the same odd results. Psi was up (15 - 17+ range) for a second or 2 and then it drops off.
Is it possible I have an incorrect vacuum/pressure source?
Is this what boost gauges do? I've never used nor seen one (in action) before.
I know I do not have a leak. The gauge holds a perfectly steady 22 inches of vacuum @ idle and more on decel.
Sean you mentioned you were seeing 22-23 to redline.
What say ye boosters?
10-15-2002, 07:16 AM
#3
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I tapped into the fuel pressure regulator line.
The gauge lookes dead on accurate for peak boost. It just will not display it "holding boost". It seems odd to me.
PS. I did flip the DV. (you knew I had to as soon as I got home). I really felt no difference. It feels the same to me.
PS. I did flip the DV. (you knew I had to as soon as I got home). I really felt no difference. It feels the same to me.
10-15-2002, 07:30 AM
#4
comparing it to the Stg 3 is kinda difficult because
the efficiencies of the turbos are different, on the K03 and K04 most tuners will ramp up the boost and then slowly pull it down in order to keep EGT's etc in check. Once the K series turbo go out of the effeciency range, they produce more heat instead of more boost. Tuners are taking advantage of the turbos effeciency range at the lower rpms...
The GT-25 does not suffer this same effeciency problem, it can flow more air at higher RPM's and APR does not need to lower the boost since the turbo is designed well within the needed air flow requirements.
As for why you are seeing the boost fall off but not really feeling the fall in chipped mode but seeing and feeling the fall off in stock mode...
My theory would be this, there is a lot of other factors (other than just boost) that determines power. My thought is that not only is APR changing boost levels, they are also changing timing / fueling etc. These also help in producing power.
Also looks like you are pulling a bit more vacuum than I am as well, I only get to -22hg if I am coasting on the road in gear....at idle I am only at 20hg's
The GT-25 does not suffer this same effeciency problem, it can flow more air at higher RPM's and APR does not need to lower the boost since the turbo is designed well within the needed air flow requirements.
As for why you are seeing the boost fall off but not really feeling the fall in chipped mode but seeing and feeling the fall off in stock mode...
My theory would be this, there is a lot of other factors (other than just boost) that determines power. My thought is that not only is APR changing boost levels, they are also changing timing / fueling etc. These also help in producing power.
Also looks like you are pulling a bit more vacuum than I am as well, I only get to -22hg if I am coasting on the road in gear....at idle I am only at 20hg's
10-15-2002, 07:34 AM
#5
I agree with you on the accuracy thing but please explain to me
why he should not be seeing drops like that? All chips for stock turboed 1.8T's that I know of all drop boost in the upper rpm range.
If your boost is not peaking/spiking and dropping off, it is because there is something that you have modified to keep it from doing this...N75 valve perhaps?
If your boost is not peaking/spiking and dropping off, it is because there is something that you have modified to keep it from doing this...N75 valve perhaps?
10-15-2002, 07:39 AM
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I could understand if chip tuning was pulling down the boost to deal
with EGT's etc. I would "feel" it being pulled down (i would think). What I'm "seeing" is boost falling off asap ! It's the same thing in each gear regardless of load (well that's not really true as partial load "shows" no boost at all)
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10-15-2002, 07:40 AM
#8
Right spot for the tap....>>
<center><img src="http://images.fotki.com/v12/photos/7/7305/130918/postmod-vi.jpg?1033847549"></center><p>Drop off is more noticeable in the lower gears. I notice it more with the 110, but in a 4th gear roll, here's what I have. Nice and flat. (this is with lots of intake restrictions removed though)
10-15-2002, 07:48 AM
#9
I think what you are experiencing is just the difference in stock and
chipped mode.
Keep in mind that in chipped mode you are now *leveling* down to what the stock car peaks/spikes at, that is a considerable difference in power and/or boost, as much as 4-5psi.....
I dont think that you are feeling the drop off in power as exaggerated in the chip mode because you are looking at the difference in boost levels
Keep in mind that in chipped mode you are now *leveling* down to what the stock car peaks/spikes at, that is a considerable difference in power and/or boost, as much as 4-5psi.....
I dont think that you are feeling the drop off in power as exaggerated in the chip mode because you are looking at the difference in boost levels