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I was doing some research but I’ve been seeing needing a tune and not needing a tune for the same bolt on mod. I just got my 91 vr4 running after 8 years of sitting and after half a year of replacing parts and doing maintenance on it I’m ready for some performance upgrades. I live in Hawaii and there isn’t any dynos for AWD so your help would be much appreciated
 

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Basically once you start messing with injectors, you need a tune. You can do the following without a tune: intake, exhaust, intercoolers, boost controller. Just keep the boost under 14ish PSI and you won't over run the stock injectors. My first suggestion is get a Y style downpipe(like from 3sx) and test pipe, then gut your pre-cats. The difference just doing that makes is huge.
 

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Sounds like rossb is echoing what i have been telling everyone who asks this question recently, lol.

Exhaust is not necessary though. Stock catback is fine to ~500whp. Gut precats (free with labor), get a test pipe ($50 or so). Thats significant in itself. Downpipe is also big, but its expensive if you go 3sx or any good, non-ebay one. If it were me, i would gut the precats, get a test pipe, get a aluminum Y-pipe (more preventative than performance), get a good filter to replace stock airbox, and get a boost controller to up boost a little. That will be a significant improvement over stock. You can also hotwire your fuel pump to give you a little more fueling headroom. If you still want more after that, then add downpipe.

Stock ICs arent great but they are expensive to upgrade and should be fine for stock turbos.
 

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Discussion Starter #4
Basically once you start messing with injectors, you need a tune. You can do the following without a tune: intake, exhaust, intercoolers, boost controller. Just keep the boost under 14ish PSI and you won't over run the stock injectors. My first suggestion is get a Y style downpipe(like from 3sx) and test pipe, then gut your pre-cats. The difference just doing that makes is huge.
Yeah I’ve seen a thread somewhere that they said you’d need a tune for a downpipe due to running too lean or something like that. I also seen a page where it shows a breakdown of upgrades you can do and they were categorized from Bolt on and the following pages are the ones you need a tune but I don’t know how credible the page is.
Here’s the page
 

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Sounds like rossb is echoing what i have been telling everyone who asks this question recently, lol.

Exhaust is not necessary though. Stock catback is fine to ~500whp. Gut precats (free with labor), get a test pipe ($50 or so). Thats significant in itself. Downpipe is also big, but its expensive if you go 3sx or any good, non-ebay one. If it were me, i would gut the precats, get a test pipe, get a aluminum Y-pipe (more preventative than performance), get a good filter to replace stock airbox, and get a boost controller to up boost a little. That will be a significant improvement over stock. You can also hotwire your fuel pump to give you a little more fueling headroom. If you still want more after that, then add downpipe.

Stock ICs arent great but they are expensive to upgrade and should be fine for stock turbos.
I’m just tired of my friends with STIs and then bragging about their Cobb upgrades lol. I kept up with a 2020 stock sti till around 3rd gear and he started to pull about a fender or a car. So I was thinking it’s time to show them what an old 91 3000gt can do with some light upgrades.
 

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Assuming all your maintenace is good, gut the precats and get a test pipe. Minimal cost, just some labor, and im sure you will be happy with the result.
 

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Assuming all your maintenace is good, gut the precats and get a test pipe. Minimal cost, just some labor, and im sure you will be happy with the result.
Won’t taking out the cat make my car run too lean?
 

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Won’t taking out the cat make my car run too lean?
Uh, why? The ECU will compensate for any additional air; these cars run a MAF. There's no closed loop fueling under boost, but the car can easily handle the small changes caused by going catless, especially at the same boost level.
 

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Uh, why? The ECU will compensate for any additional air; these cars run a MAF. There's no closed loop fueling under boost, but the car can easily handle the small changes caused by going catless, especially at the same boost level.
Okay thank you
 
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