Larger Turbo and Auto w/o new tune?

FirstOrbit84 · Dec 9, 2009

Hi guys, I've already got the engine mods in my sig which as of right now are RC2, sprint 520s, and a mufflerectomy. At WOT I'm pushing 18psi constant, with a 21psi spike. When I punch the throttle (and don't let the boost build up) I get a ton of soot, but when I gradually roll onto it I still go fast but not nearly as much soot if any.

My question is: Will a larger turbo such as a VNT17 or 17/22 hybrid give me any appreciable power gains without changing anything else?? Or will I have to get retuned, but have to hold back because of the auto trans??

What other mods would I need besides a 5-speed swap, larger injectors and a retune to fully support the capabilities of the larger turbo?? 3-bar map sensor??

Bush Hopper · Dec 9, 2009

your having tuning issues, and those should be resolved by the tuner. 18 psi on auto tranny is to much, that's why your having spike issues. When the tranny makes a shift, the flow or exhaust is still constant, and it causes over boost. Its normal, and the only ways to prevent the spikes is to turn down the boost to about 16.5 psi max, or get a ghetto boost valve, or get a 5 speed tranny.

You need to upgrade your tranny sooner or later for a big turbo.

FirstOrbit84 · Dec 9, 2009

Flying Kasper said:
your having tuning issues, and those should be resolved by the tuner. 18 psi on auto tranny is to much, that's why your having spike issues. When the tranny makes a shift, the flow or exhaust is still constant, and it causes over boost. Its normal, and the only ways to prevent the spikes is to turn down the boost to about 16.5 psi max, or get a ghetto boost valve, or get a 5 speed tranny.

You need to upgrade your tranny sooner or later for a big turbo.

thanks for the response. not sure if i completely understand what you mean by "When the tranny makes a shift, the flow or exhaust is still constant, and it causes over boost."

Then right after you say that "Its normal" but I want to prevent it??

If spikes are normal, then why do I want to prevent them? I was under the impression that the VNT15 could handle 19psi sustained, and that spikes of up to 21psi for only a fraction of a second would not hurt it. I was told by the tuner (Jeff) that boost controllers are only for failing turbos and that the ecu controls the boost levels, so I didn't need to run one.

Plus I can only really hit the full 18psi sustained in 3rd and 4th gear at WOT after creeping up to it from about 15-16psi. Around town and in normal conditions my spikes are around 18psi and sustained is around 15-16psi... So, I don't really think I have much of a tuning issue...

Back to my question, though: Would adding a bigger turbo, ceteris paribus, give me any more power??

vwmikel · Dec 9, 2009

FirstOrbit84 said:
thanks for the response. not sure if i completely understand what you mean by "When the tranny makes a shift, the flow or exhaust is still constant, and it causes over boost."

Then right after you say that "Its normal" but I want to prevent it??

If spikes are normal, then why do I want to prevent them? I was under the impression that the VNT15 could handle 19psi sustained, and that spikes of up to 21psi for only a fraction of a second would not hurt it. I was told by the tuner (Jeff) that boost controllers are only for failing turbos and that the ecu controls the boost levels, so I didn't need to run one.

Plus I can only really hit the full 18psi sustained in 3rd and 4th gear at WOT after creeping up to it from about 15-16psi. Around town and in normal conditions my spikes are around 18psi and sustained is around 15-16psi... So, I don't really think I have much of a tuning issue...

Back to my question, though: Would adding a bigger turbo, ceteris paribus, give me any more power??

The automatics always spike when they shift. A boost valve isn't just for a failing turbo. They can be a very cheap insurance policy as well. A larger turbo by itself probably won't net you any power improvement on it's own, but it paves the way for other upgrades. I think the stock auto (in good condition) has a little more in it than just 18 psi on the stock turbo, but I wouldn't go dropping in Race 520's either....

Joe TDI · Dec 11, 2009

FirstOrbit84 said:
Back to my question, though: Would adding a bigger turbo, ceteris paribus, give me any more power??

We dropped in my 17/22 alone and it gave it almost ZERO extra power.... I mean, maybe a few HP due to increased airflow, but you'll need a re-tune to optimize a larger turbo....

FirstOrbit84 · Dec 14, 2009

Joe TDI said:
We dropped in my 17/22 alone and it gave it almost ZERO extra power.... I mean, maybe a few HP due to increased airflow, but you'll need a re-tune to optimize a larger turbo....

thanks... this is the answer i was looking for

but considering the fact that i already have a tune, and it puts out a good bit of soot at full throttle, does that mean that i'm already over-fueled and the increased airflow might actually give me more of a gain than if i were to drop it in a stock-tuned engine??

Joe TDI · Dec 27, 2009

FirstOrbit84 said:
thanks... this is the answer i was looking for

but considering the fact that i already have a tune, and it puts out a good bit of soot at full throttle, does that mean that i'm already over-fueled and the increased airflow might actually give me more of a gain than if i were to drop it in a stock-tuned engine??

I already had a tune & nozzles (RC3 & Sprint 520's) when we dropped in the 17/22..... Didn't make much of a difference with anything, smoke or power....

Don't put in an expensive turbo and not optimize it by not getting it re-tuned... You must re-tune after a turbo upgrade.... You could probably go to RC3+ on your setup with a VNT17 or 17/22 hybrid.

I'd start thinking about a downpipe and exhaust too.... you'll need it.

dec942 · Dec 30, 2009

I also have an auto tranny, and just installed the VNT17, no power difference alone. I do plan to re-tune which will make use of the larger turbo, however as much as some people may like the smoke and soot all that is, is unused fuel going out the tail pipe.
I'm going to put this to the test by going to stage 3 and keep my .205's and keep smoke and soot down and see what happens. With the stock vnt15 I'm at about 130-140hp, 0-60mph in 7.5-8.0secs.

Larger Turbo and Auto w/o new tune?

FirstOrbit84

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Bush Hopper

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FirstOrbit84

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vwmikel

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Joe TDI

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FirstOrbit84

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dec942

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