BEW VNT17 upgrade

stevenszack

New member
Joined
Aug 24, 2024
Location
Canada
TDI
MK4 golf BEW
First post, iv always checked the forms when I needed a question answered but this time im at a loss. I have a 05 golf bew with a stage 2 tune. my kp39 was on its way out so I replaced it with a new vnt17 turbo just the other day and my car is gutless. The turbo hardly spools in 1,2 or 3 and then 4 & 5 it’s about 26-2800 rpm’s when you can feel it actually start to pull. I checked the actuator and it starts to move at 2-3Hg and then stops close to 18-19Hg. When I log my actual boost vs my target it takes about 4 seconds for my actual to catch up to my target in but by the time it catches your already up into the 3000 rpm range. My old kp39 that was coming apart when it would work would boost 10 times better then my “upgraded” turbo. I did check the cam today. It is showing signs of wear on 1 one and the edges chamfer if wore off the edges but is no way are they flat spotted or anything. I see cams in ar work that are just cooked and they don’t really have any noticeable performance issues and my car would pull really well right up until I put the new turbo on.
Any help would be appreciated.
 

Tristan265

Active member
Joined
Jan 5, 2024
Location
Minnesota
TDI
2004 Jetta manual tdi BEW
The Vnt-17’s are bigger turbos they do tend to spool at a higher engine rpm, but it shouldn’t have crazy boost lag. I would check for any vacuum leaks and check n75 valve functionality. Another possibility is that you may need to get your car retuned for the bigger turbo.
 

stevenszack

New member
Joined
Aug 24, 2024
Location
Canada
TDI
MK4 golf BEW
It takes about 4 second for my turbo actual to reach the target pressure and by then I’m already in the top of the rpm range. When I had my kp39 on it was very quick through the first 3 gears it pulled good and hard now 1,2 and 3 you couldn’t even spin the tires if you tried. Is a stage 2 not enough to get any kinda performance out of the vnt17. Also what should I be getting for vacuum in inches mercury at idle
I keep seeing different number but with my car idling and a vac gauge connected under 18hg
 

Tristan265

Active member
Joined
Jan 5, 2024
Location
Minnesota
TDI
2004 Jetta manual tdi BEW
Ok, that’s not normal. Check vacuum at the turbo actuator, you should see 18-20 hg at idle.
 

stevenszack

New member
Joined
Aug 24, 2024
Location
Canada
TDI
MK4 golf BEW
I get 18Hg at idle and sorry for the mistake it’s a gt1749v. Everything worked perfectly before putting this turbo on minus the fact the kp39 was on its way out cause here on the east coast of Canada what happened is the manifolds rot out of the actual lip on the chra rots and splits right around the actuator and that’s what happened to mine. I have in inlet pipe off now getting the size as I am about to go to get the supplies needed to make a boost leak tester. I can not hear one when the car is running even using a hose to my ear to check connections but that doesn’t mean I don’t have one
 
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