Most boost from a VNT Daytona??

[93DaytonaR]

What is the most psi you can get from a stock VNT??

[sdac_guy]

I know that 18psi is easily attainable on a stock turbo, but the turbo won't last long doing that. The rotational speeds on the VNT's are much higher to produce the same level of boost as the regular T1 or T2 turbos. This means that at high boost levels the bearings (and seals) in the VNT turbo are stressed to nearly the point of failure.

The general rule of thumb, is that on a VNT, if you want the turbo to have any longevity at all, keep the boost below about 15psi.

Barry

[93DaytonaR]

Would 15 or 16 psi be ok to make it last a while??

[pkpturbo]

Kind of a dumb question from a novice: Could you add a blow-off valve and limit the boost to about 15 - 16psi fairly easily? Is this even a good idea?

PKP

[93DaytonaR]

Sorry for asking about something I dont know about but I thought that is what this forum was for. I always thought that turbos were for ricers til I bought my Daytona and learned about turbo Daytonas.

[90DodgeVNT]

**Kind of a dumb question from a novice: Could you add a blow-off valve and limit the boost to about 15 - 16psi fairly easily? Is this even a good idea?


No question is ever dumb, especially when you are new to the turbo game. By adding just a BOV, you can't control the boost as it's function is entirely different then a bleed or a grainger.

Look at Gary's site for the information on how to bleed a VNT, but just make sure you don't go nuts and run out of fuel at the same time.

[sdac_guy]

As I understood the message, pkpturbo was commenting on his own question, not on anyones else's.

But to address the other items brought up since my last post.

The limit of the stock electronics to control or monitor boost is 14.7 psi, as that is the upper limit of the stock MAP sensor range. So keeping boost below that level, most likely will avoid turbo problems, and the engine will know how much boost there is so that proper fuel and timing can be controlled. Boost above that level can damage the turbo in fairly short order, and the ECU has no way of seeing boost above 14.7 psi so it cannot tell how much fuel to add or timing to run. There is more to it than what I am saying here, but this covers the basics.

A purpose of a BOV is to relieve the built up boost pressure when the throttle is closed returning to idle. It comes stock on all the 1990 VNT's already (built into the airbox assembly).

While the BOV does aid in adding longevity to all turbos, in the VNT, it is the high shaft rpm speeds that destroys the seals and bearings, and the BOV doesn't affect those at all. Getting 16-18 psi out of a stock VNT turbo is fairly easy to do, but it shortens the life of the turbo every time it is done, the shaft speeds are just too high ...

Barry

[93DaytonaR]

Ok another question, and by the way sorry about the confusion pkpturbo im quick to take offense sorry bro. I read on another thread that they were talkin about making a switch or taking the wastegate arm off so that it would only run low boost could you make the VNT push 18psi at the the flip of a switch or the turn of a key then back to low boost when in the off position?? Hellofa question huh?? lol

[sdac_guy]

The vacuum plumbing for the VNT control is fairly complex compared to the standard Garrett controls. There are 3 VNT solenoids, but for normal Garrett turbos only one is used.

And the vane actuator has 2 ports, both a boost port AND a vacuum port, while the normal Garrett turbo wastegate actuator only has one port with the wastegate being controlled by boost only (though early T1 cars used a two port actuator as well).

Let me be clearer on the high boost issue. Last spring I had to replace my VNT turbo on my 90 Daytona because for a little over a year it was boosting to the turbo limit (18-20psi) because of a vacuum line leak. The oil seals were damaged because of the high shaft speeds. It was smoking pretty bad by the time we got around to changing it out.

So if you ask me whether there is ANY way to safely run more than about 15 psi on a VNT without damaging the turbo, my answer will always be NO.

There may be a few folks that have gotten away with it, but with the expense to replace a VNT turbo, I don't think it is worth the risk.

Barry

[DirectConnection]

Quote:

Originally Posted by pkpturbo Kind of a dumb question from a novice: Could you add a blow-off valve and limit the boost to about 15 - 16psi fairly easily? Is this even a good idea? PKP

I see that nobody answered his question so I will as I see a problem with his idea.

Yes, a BOV could be used to limit the boost, but that is a VERY bad idea to do. Say you want 15psi, and the turbo is having a problem trying to control that boost and is boosting to 18psi instead. If the BOV is open and venting that additional boost (3psi) and you are getting 15psi on your guage, your turbo is still overspinning itself to 18psi which is still very bad(probably even more as it's fighting for 15psi now and including pressure drop from the cooler, etc). You may be controlling the amount of boost so you won't run out of fuel and detonate, but now that extra backpressure is going to cost you alot of HP since the turbo is spinning much harder than it should. That will also reduce your turbo's life expectancy.

[sdac_guy]

Quote:

I see that nobody answered his question so I will as I see a problem with his idea.

Well actually there were two answers already given. It appeared he was confusing the BOV with a type of boost controller. So the use and operation of the BOV was explained to a point (twice).

But even then, nearly all BOV's I've heard of operate off a vacuum source. How would it be operated to bleed off boost, even in your example (which was absolutely correct otherwise)?

Barry

[DirectConnection]

Quote:

Originally Posted by sdac_guy But even then, nearly all BOV's I've heard of operate off a vacuum source. How would it be operated to bleed off boost, even in your example (which was absolutely correct otherwise)? Barry

Some of the aftermarket BOVs also have an adjustable spring for the diaphram. I assume loosening this too much would allow it to blow off the seat rather easily to whatever you set it for. (Greddy type s for instance)

[pkpturbo]

Yep - I was referring to myself as a novice-with-dumb-question. Sorry about the confusion.

PKP

[DirectConnection]

Quote:

Originally Posted by pkpturbo Yep - I was referring to myself as a novice-with-dumb-question. Sorry about the confusion. PKP

Don't worry about it. Everyone starts out at the same level. I know I have asked noobie Q's in the past on the sdml years ago... and even here from time to time.

Asking "ricer" type Q's deserves a flame, though

[1fastsleeper]

So exactly how do you get more boost from a VNT car? I have a 90 daytona and i just wanna play around with it for a bit since i have a super 60 waiting for me..