VNT IC Upgrade Q's

[TurboDodge]

Finished mounting the intercooler and started fabbing up the pipe runs. Should have the install complete by T-Day. Will post more pics then. Core is 11"x12"x3".

[GLHNSLHT2]

ahh how cute :)

[The Pope]

LMAO, really though it is very popular in the old days to do a "dual core" IC and this is the copy of that. I would have got one a little longer but not a total need.

One thing I'd consider is cutting the tank on the passenger side and flipping it. A thing to consider also is a VNT feeding it, a huge IC would spike the turbo harder too. I looked at this one for an L body for size a while back.

[GLHNSLHT2]

spike the turbo harder?

A higher flowing FMIC is going to allow the turbo to fill the intake sooner and hit it's boost goal in the intake sooner requiring less rpms from the compressor. Found this interesting over on the other site when comparing stock intercoolers.

"VNT = 4.2 psi drop at 18psi

That means that a VNT is getting beat up at 22psi to make 18psi at the intake and for a turbo that's at 179,500RPM at 14psi this means pre-mature seal leakage and ultimately bearing failure."


So yes you should get boost in the intake sooner, but it'll spin less rpms so it should be easier on the turbo.

[The Pope]

the turbo over spins filling is what I ment

By lowering the drive PSI in the exhaust, more like 10 PSI for 4 in the intake your really allowing the VNT to breath. They have a problem with over boosting, lowering the drive pressure really helps. There are a million intercooler choices today, so having many different ideas of what others would do is normal lol.

So if the stock IC costs you 4 PSI intake, at 2.5 times for drive pressure your dropping exhaust pressure 10 PSI. That is a pretty big number really with over lap etc.

It would be nice to have a bigger IC, but the VNT doesn't move huge volume and your pressure drop is delt with. So in this case the shorter less volume IC is a pretty good choice. Maybe a T28 compressor mod next then? Would lower shaft speeds a bit.

[GLHNSLHT2]

I have to disagree, even if he had an i/c twice the physical size it would not come close to equaling the volume of the intake manifold. Allowing the air to get to the intake sooner will keep the rpms of the turbo lower than stock. You have to spin 4psi more worth of rpms just to get 0psi at the intake.

[TurboDodge]

I finished the intercooler install today. +1 on this IC basically being like the two stock core mod of old...but this one was only $70 and no cutting and welding required lol! Also added an RFL BOV, K&N Filter, and an oil catch can. Funny you mention the T28 mod Rob...I installed a T28 turbo at the same time doing this IC install. I had one of the Ebay VNT25 units fail in just over 2k miles so it was the perfect time(I guess) to splurge for a VNT upgrade unit. This setup sounds great and the car pulls strong. I haven't really flogged it yet because I just replaced the transmission with a 91 large spline 568...so I had to install a new clutch.... So far I haven't seen any overboosting or boost creep...but again I haven't wound the thing out like WOT at 5k+ RPM and the like. I will report back after clutch is broken in and the punishment can start. Some pics...

[The Pope]

funny how huge that turbo mod looks in the little VNT cover lol. You should have a lot less drive pressure, which should mean a lot better flow without spike. Even though it is a little small for the typical aftermarket install it flows I bet 2.5 times better and cools the same better lol.

Only thing I think I'd do different is add a hard pipe to the coupler on top and run 1 flex coupler by the rad. I would bet it flops around a bit much with the soft line.

[GLHNSLHT2]

couple of small things for more flow. Port the outlet of the turbo like this.


It'll help with throttle response.

Next, time for some 3" piping and a bigger air filter like this: Cold Air Intake

It'll also help with throttle response, and put you lower in the flow map by lowering the pressure differential at the compressor. Which means lower turbo rpms for the same boost level.

[TurboDodge]

The intercooler piping is secured to the core support. You can see it in the first picture I posted. The use of the original upper VNT IC hose isn't the best looking but it doesn't flop around too much. It isn't permanent. I need another piece of aluminum piping with a mild bend like 22 degrees to go there. Just needed to get the thing back on the road and the stocker upper hose slapped right in there. I am not sure I believe increasing the size of the intake tubing will help the performance. The inlet on the turbo is 2.25". Wouldn't the same theory about not needing piping larger than the ID of a throttle body apply here as well? The intake piping used on this intake is 2.25 to match the turbo inlet. And the K&N filters I think can keep up with the demand of the turbo. I have tried so many different intakes over the years on my TD's and it isn't really where I saw very noticeable gains. Even from stock airbox with a drop in k&n to a 3 inch pipe intake with a k&n cone, which I have installed on the drag Daytona but it uses a GT series DBB turbo. I've also tried ported turbo outlets on stocker turbo units and I wasn't able to tell a difference. Not saying you are wrong, we all have our own opinions. I'm just talking about my experience with the said mods. And thanks to all of you who have participated in this thread. I'll report back after clutch is broken in.

[GLHNSLHT2]

You want to FEED the turbo with lots of low restriction air. So you go very big on the filter and tube to it. Right now you're worse than stock. Suck through a pixie straw then suck through a Mickey D's shake straw. See the difference. You're trying to lower the rpms of the turbo to make the same amount of boost. By lowering the restriction in front of the turbo it puts you lower on the compressor map, requiring you to turn less rpms of the turbo for the same amount of boost.

My experience, I went from Just the early T1 2.5" ID smooth hose mounted on my MP Plus turbo sucking in hot unfiltered air at the track to a 3" with a big 3" K&N Extreme filter sucking in hot underhood air and found 1mph consistently at the track. That's 10hp. Plus lower shaft speeds.

Lower shaft speeds to achieve the same boost also means you get to your boost goal quicker since the turbo doesn't have to spin as quickly.

Just trying to lower shaft speeds to keep the VNT under control. A VNT spins 179,000rpms to make 14psi, a T2 turbo is like 110,000 to make the same boost with much larger bearings.

[Fox]

Quote:

Originally Posted by GLHNSLHT2 couple of small things for more flow. Port the outlet of the turbo like this. It'll help with throttle response. Next, time for some 3" piping and a bigger air filter like this: Cold Air Intake It'll also help with throttle response, and put you lower in the flow map by lowering the pressure differential at the compressor. Which means lower turbo rpms for the same boost level.

looks good, do you do that kind of port work ?

[TurboDodge]

I understand that you want low restriction but I don't see how my current setup is worse than stock or that it is restrictive for that matter. The piping isn't smaller than the size of the turbo inlet. Air flows similar through passages like water. If I were to connect a 3" water hose to a 2" spout, the spout will limit the amount of flow. Or to parallel your analogy using straws, blowing into a larger straw that chokes down to a smaller diameter straw is no different than just blowing air through that small straw by itself, the same amount of air gets through. I also don't believe that the filter I chose can't keep up with the air demand of the turbo or that the stock air box with a paper filter is less restrictive than this intake. But it is obvious that we disagree here so we are just spinning our wheels debating it. I still respect you and your opinions. Again, I will report back with the final answer to the original question I had in this thread after the clutch break in, which was...Does upgrading an intercooler in a VNT car cause overboost or boost creep? But, I have gone and screwed with the test by switching out the turbo unit simultaneously to a T28 wheel unit. So my final result won't be what happens when adding an aftermarket intercooler to an otherwise stock VNT car. Thanks again for everyone's input.

[GLHNSLHT2]

Because up until the turbo inlet you have a nice low pressure area that the turbo can use to grab as much air as it can.

3" water hose to a 2" spout doesn't work because either the water is under pressure and pushing it's way through or it's on the other side where the water is coming out into the 3" hose and cavitating because the 3" flows so much more.

Now say we have a fire hose hooked up to a hydrant with a nozzle on the end that has a turbine that will spin. Pressure forces water through the nozzle. What happens when we reduce that pressure? Not as much water flows out right? Keep reducing the pressure and pretty soon the turbine has to start powering itself to try and shoot water out instead of the water pressure pushing it's way through.

Take a 1ft section of garden hose and blow through it. Now take 50ft of the same garden hose and blow through it. The length requires are larger cross section to flow the same. So 3" right to the filter means only 1-2" of 2.25" at the venturi section of the turbo which helps to speed all that air into it.

Look at compound turbos. Two smaller turbos used to make tons of boost. Both set to a 2:1 pressure ratio aka 14lbs of boost. But what comes out of the 2nd turbo is 28lbs of boost in the intake. Why? because it got fed with 14lbs of boost at it's inlet and doubled it.

Same goes for your intake air filter setup on your turbo. If you can feed it atmospheric pressure (0psi) and you need 179k rpms to make 14psi you'll get 14psi out. Now you get full vacuum (30" of HG or -15psi) in your intake tube. How fast does the turbo have to spin to make 14lbs of boost? Infinately because it get's no air. It might have to spin 300krpms if you allow it say 10" of vac in the intake tube. Have to figure it out on a compressor map for exact #'s but I think you should get what I'm getting at.

The stock intake pipe on a VNT flows more than what you currently have. Just because the inlet on the turbo is only 2.25" id doesn't mean that having the same size pipe isn't causing a restriction.

[GLHNSLHT2]

Quote:

Originally Posted by Fox looks good, do you do that kind of port work ?

I've done it for myself, I don't have access to tools all the time to be able to do it for others.

The Pope does though. He's posted in this thread.