Turbo Lag on VNT-17 vs. VNT-15

Hi,

2003 ALH. I need to replace my VNT-15. Thinking about a VNT-17, DLC520s and Malone stage II. Clutch will be the LUK 17-050

I know I don't need the VNT-17 for 15 PSI stage II however I was told the 17 is a sturdier unit and an upgrade over the stock 15.

I was wondering how bad the turbo lag is vs. the stock turbo?

It all depends on tuning and how much time/effort you want to put into it. I've seen 15's slower than 17's and vice versa. Theoretically a 17 should be slower, but practically speaking there isn't a difference if tuned properly.

An exhaust pressure gauge is your best friend here. For a 15 psi tune I would recommend a pressure range of 30 psi. It's very easy to built this kind of pressure on the exhaust side. Start slow/easy on the throttle and get a feel for where it wants to go. If it starts heading off the end at a high rate of speed - back out of the throttle, get back home and adjust the actuator (or the tune) to reduce the spike. A ~20-25 psi spike on the exhaust side during spool up that drops very quickly to ~match the boost pressure is a good goal to shoot for. You'll get a feel for it. If exhaust is lower than boost or there is very little spike you'll see that it's laggy. Too much exhaust pressure will make it laggy too (and send your 30 psi gauge to the peg). I recommend that you not use a MAP based tune (MAF Delete).

These from Hewitt are pretty nice and moderately priced. Fill the tubes with engine oil to damp out pulsations and eliminate water build up which will kill the gauge in the winter.

https://hewittindustries.com/product/108-10x/

You can use the EGR port on the exhaust or drill/tap the manifold. A short (6") piece of stainless tube will isolate sufficiently from the heat

CleverUserName said:

Hi,
2003 ALH. I need to replace my VNT-15. Thinking about a VNT-17, DLC520s and Malone stage II. Clutch will be the LUK 17-050
I know I don't need the VNT-17 for 15 PSI stage II however I was told the 17 is a sturdier unit and an upgrade over the stock 15.
I was wondering how bad the turbo lag is vs. the stock turbo?

Click to expand...

I don't think the 17 is that much sturdier than a 15. The later 15s use the same base Garrett part number, even (GT1749).

Personally, if I did not plan on going to a stage 4 tune and all the mods that support it (clutch, bigger than 520 injectors, 3 BAR MAP along with the VNT17), I wouldn't bother upgrading the turbo at all.

You'd be better off going with the Borg-Warner BV39 if you NEED to replace the turbo and just want a slight upgrade while you're doing it, which is very similar spool to the stock turbo, but the extended tip design of the compressor wheel would safely support more boost, just shy of VNT17 levels without sacrificing spool when you don't yet have the tune and fueling upgrades to make the 17 spool adequately quick.

A 17 will spin up very quick if you have the fueling and tune modifications to go along with it. But if you're not going to mod it to the point of being able to add that much fuel that fast to help spool, there really isn't a point of going with the 17.

CleverUserName said:

Hi,

2003 ALH. I need to replace my VNT-15. Thinking about a VNT-17, DLC520s and Malone stage II. Clutch will be the LUK 17-050

I know I don't need the VNT-17 for 15 PSI stage II however I was told the 17 is a sturdier unit and an upgrade over the stock 15.

I was wondering how bad the turbo lag is vs. the stock turbo?

Click to expand...

i mean in all honesty if your only going stage 2 I would not buy the vnt 17 as you will be no using close to what it worth, but if you are going with the vnt 17 it is a upgrade for sure compared to the vnt 15 but sided with nozzles even 11mm pump and a tune higher then stage 2 or its not worth. id say almost same reliability of vnt 15 and more power.

CleverUserName said:

Hi,

2003 ALH. I need to replace my VNT-15. Thinking about a VNT-17, DLC520s and Malone stage II. Clutch will be the LUK 17-050

I know I don't need the VNT-17 for 15 PSI stage II however I was told the 17 is a sturdier unit and an upgrade over the stock 15.

I was wondering how bad the turbo lag is vs. the stock turbo?

Click to expand...

but to answer your question when I installed my vnt 17 and tuned it the boost was climbing very slowly until I added more fuel im not sure if stock injector nozzles would beable to produce enough for the turbo to have a decent ramp up time apposed to the vnt 15

Boost lag or boost spool time? 2 completely different things.
Everyone uses the words boost lag wrong. Boost lag is NOT the time it takes to build boost from idle, it's the time it takes to spool up the turbo to full boost between shifts.
Turbo spool time refers to going from a idle to full throttle, how soon (at what rpm) will the turbo start making full boost.
I assume you want to know both. Basically it all comes down to your fuel map and other upgrades.
Going to a turbo from a 15 to a 17 like you want, you wont notice much at all difference. It's not peak power, it's the area under the curve at specific rpms. That's all based on your fuel tune, nozzle size, and other supporting modes like more boost, cam ect......
Just budget for what you want, build it to that and dont future proof anything other than your clutch.