Boost limits / spikes

What are considered safe spikes for these turbos:

VNT15 -- sustained 19psi max --- safe spike= ?
VNT17 -- sustained 23-25max --- safe spike= ?
17/22 -- sustained 28psi max --- safe spike= ?

Is the 'safe spike' usually the same amount of psi over the max sustained boost for every turbo, or do some turbos handle larger spikes then others?

Also, when adjusting the boost valve with a compressor, do you set it so that the air just starts 'seeping' out at the max sustained boost or a few psi higher?

Depends on rpm

KERMA said:

Depends on rpm

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Doesn't most spikes happen in the 'early' rpm band and then settle back down to the sustained boost levels? ---around 2500rpm? (unless your doing some 'drag race' launches)

gogobug said:

What are considered safe spikes for these turbos:

VNT15 -- sustained 19psi max --- safe spike= ?
VNT17 -- sustained 23-25max --- safe spike= ?
17/22 -- sustained 28psi max --- safe spike= ?

Click to expand...

These boost numbers are a little high.. VNT-15 should sustain 18.0 max. and spike no more than 21.0 PSI in a typical 1,500RPM-redline 3rd or 4th gear test.

28 PSI for 17/22? Seems a bit high. 26 PSI sustained was recommended by the original VNT-17/22 distributor a little while ago, and even that's a little high. 28 PSI is also close to the limit of 3 bar MAP. It's still ultimately the owner's decision though.

So far all of the VNT17/22 I tuned only have 0-1 PSI spikes above sustained. No boost valves.

More importantly the spikes should be brief, lasting no more than a second. Some people mistake a 2-4 second overboost for a normal "spike."

Just get a proper remap and there are no spikes!

When adjusting the boost valve with a compressor, do you set it so that the air just starts 'seeping' out at the max sustained boost or a few psi higher?

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It depends on the boost valve. Some boost valves bleed boost early before they can effectively control max. boost.

Just pay attention to your boost gauge or VAG-COM and adjust the boost valve until desired result. You'll be accelerating and pulling over to adjust the valve often. If you have a hand pump you can use that to speed up your valve adjustment a bit more quickly, but you'll probably still need to fine-tune it on the road.

You shouldn't have boost spikes with a proper tune and a clean VNT system. I've always said that a boost valve is a band-aid solution, but it's still useful as cheap insurance for your turbo in case your VNT/N75 control deteriorates over time (if it helps reduce overboost at all.. but if you have sticky vanes you're out of luck).

Boost High

Ok, so i am driving at 75 mph, 2200 rpm roughly, cruise control engaged and my MAP reading on the OBD scanner i am looking at says 223 KPA when it starts to accelerate up a grade..

~32psi~ ??????

on a 2004.5 BEW powered automatic Jetta, EGR delete and a few other mods but no tune.. What gives?

ig109 said:

Ok, so i am driving at 75 mph, 2200 rpm roughly, cruise control engaged and my MAP reading on the OBD scanner i am looking at says 223 KPA when it starts to accelerate up a grade..

~32psi~ ??????

on a 2004.5 BEW powered automatic Jetta, EGR delete and a few other mods but no tune.. What gives?

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That 32psi may include ambient (if that's the right word) pressure which should be about 14.6psi, meaning ~17.5psi booooooost. Confused me quite a bit when I first read my Group 008 logs of about 30 psi on my stock VNT-15!

quadcomm said:

These boost numbers are a little high.. VNT-15 should sustain 18.0 max. and spike no more than 21.0 PSI in a typical 1,500RPM-redline 3rd or 4th gear test.
28 PSI for 17/22? Seems a bit high. 26 PSI sustained was recommended by the original VNT-17/22 distributor a little while ago, and even that's a little high. 28 PSI is also close to the limit of 3 bar MAP. It's still ultimately the owner's decision though.
So far all of the VNT17/22 I tuned only have 0-1 PSI spikes above sustained. No boost valves.
More importantly the spikes should be brief, lasting no more than a second. Some people mistake a 2-4 second overboost for a normal "spike."

Click to expand...

I think there's been quit a few Garrett 17/22's around here running 28psi without any issues. Ask Oliver

Hi. What is the maximum boost for a vnt22 (gt2260v) on a 2.0 tdi engine?
For now i am running with ~ 30 psi (3000-5000 rpm) on turbo gauge and i'm wondering if it's safe for the turbo or engine. What do you think?

avionu said:

Hi. What is the maximum boost for a vnt22 (gt2260v) on a 2.0 tdi engine?
For now i am running with ~ 30 psi (3000-5000 rpm) on turbo gauge and i'm wondering if it's safe for the turbo or engine. What do you think?

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If you are running stock nozzles/injectors, you will never need the max boost that turbo can do.
I would run max of 2bars at 4000rpm with that turbo

I have seen 240bhp with "only" 1.75bars at that engine ....

ArturCosta said:

If you are running stock nozzles/injectors, you will never need the max boost that turbo can do.
I would run max of 2bars at 4000rpm with that turbo

I have seen 240bhp with "only" 1.75bars at that engine ....

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So the engine interns can handle 2 bar of boost? I would like to run with ~2 bar of boost till ~4800-5000 rpm and i`m not sure that the engine and turbo can handle it. Any suggestions?

You say that you have seen 240bhp at 1.75bars but what kind of modifications did that engine had?
Thanks

Only 2256 , better clutch and exhaust.
FMIC is nice , the only thing that you really need at that power is a fuel cooler.

Regards

WVU TDI said:

That 32psi may include ambient (if that's the right word) pressure which should be about 14.6psi, meaning ~17.5psi booooooost. Confused me quite a bit when I first read my Group 008 logs of about 30 psi on my stock VNT-15!

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How does one find out what the "ambient pressure" is that you have to subtract off of the numbers you see when you do a channel 011 log in vcds? I found a converter online to convert from mbar to psi http://www.translatorscafe.com/cafe/units-converter/pressure/calculator/millibar-%5Bmbar%5D-to-psi-%5Bpsi%5D/ but according to my vcds log, my maximum mbar is 2437 which equates to 35.5 psi which is definitely not correct!

SheeB said:

How does one find out what the "ambient pressure" is that you have to subtract off of the numbers you see when you do a channel 011 log in vcds? I found a converter online to convert from mbar to psi http://www.translatorscafe.com/cafe/units-converter/pressure/calculator/millibar-%5Bmbar%5D-to-psi-%5Bpsi%5D/ but according to my vcds log, my maximum mbar is 2437 which equates to 35.5 psi which is definitely not correct!

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Unless you're in the middle of some major hurricane or something like that, ambient pressure is about 1000mbar, give or take 20mbar. Even in the most extreme storms may drop pressure to 900mbar, but that's about it.

After goggling for a bit I managed to calculate my specifc ambient pressure which is 1004 mbar. Your answer was right on the money!

WVU TDI said:

Unless you're in the middle of some major hurricane or something like that, ambient pressure is about 1000mbar, give or take 20mbar. Even in the most extreme storms may drop pressure to 900mbar, but that's about it.

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Not where I live...

KERMA said:

Not where I live...

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Excellent point. Mile highish should be what, 850s or something?

Also, one of the VCDS groups logs ambient pressure, but I can't remember which one it is and I'm not sure if it's accurate. I believe it reads across RPM, ambient pressure, and absolute MAP pressure (same as group 11 actual pressure), this would proabably give you a more accurate boost reading (assuming it's ambient figure is correct.

Here in tooele at 5000ft, it's about 865kPa, and in the eisenhower tunnel at 11,000 ft, it's 650 or so

I've got a few customers with high-end tunes who make that commute every day, live at 8500 ft, drive to 11,000 ft, down to 5000 ft, then back every day. Makes for some interesting tuning issues that the sea-level guys don't have to deal with. While there are a few altitude dependent maps, the stock tunes really don't deal with that adequately, either. Take a look a the pressure ratios when your atmospheric is 700 mbar and requested is 2100 (16-17 psi at sea level) pressure ratio of 2.1 at sea level becomes 3.0 at that altitude! Stock turbo is turning well over 200,000 rpm to make that boost. Of course, on the gage, it will look like 21 psi (ish) IF the request was a kept at 2100mbar absolute, BUT the ecu does a good job of keeping the gage boost fairly constant over altitude changes, but the PR still increases dramatically, even if the gage says the same "boost". (when I say gage, that's not vag-com, which reads in absolute)

When I tune for the high altitude guys, I try to keep the PR more or less constant between high altitude and low altitude, for turbo safety. "hey, why does my boost gage read lower at altitude"

the problem is compounded (pun intended) by lower mass flows at altitude, so a greater propensity for compressor surge... now, about those compound turbos...

gogobug said:

I think there's been quit a few Garrett 17/22's around here running 28psi without any issues. Ask Oliver

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I know a guy that's been with a 17/22 for a couple years now with 39psi on a ALH

Do you also know this thread is from 2009?

Yourbuddysatin said:

Do you also know this thread is from 2009?

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thank you Paul Blart

Uh huh

10yr old post