16V Twin-VNT Conversion? (Long)

http://www3.telus.net/braun/16v.html - I'll try to add updates to this link on my site and add some pictures as I get them done.

I've toyed with this idea a lot, but never looked that seriously at it because of money. I'm curious how cheaply this could be done, while still maintaining a solid setup with some reliability.

The Problem:

1990 TIV 2.2L Engine: 160-175hp depending on who you talk to, and 210-225lb-ft depending on who else you talk to.

The actual theory behind the VNT is terrific, but the final product released in 1989 and 1990 by Shelby and Chrysler isn't ideal for tuning and upgrading. As most of us know, the 2 limiting factors are the size of the VNT housing (smaller than a T1 Mitsubishi), and the restrictive flow of the head and exhaust, which is somewhat necessary on a VNT to prevent overspooling in milder and colder weather.

Unlike the comparable Turbo II application, the VNT does not use a wastegate to control exhaust flow. Taking advantage of the nature of the VNT, the computer uses a similar looking device, an external vane controller and actuator. Using pressure supplied to the diaphram in the vane controller, the actuator moves, opening and closing the vanes accordingly, to limit boost.

Herein lies the ebb and flow of the VNT's success. The VNT turbo, being small and quickspooling, power was easy to come by, and came earlier than other turbo applications. However, to limit overspooling the turbo, boost was kept low, to about 12 psi, by means of a restrictive exhaust.

Overboost cutout is at about 14.7 psi, but doesn't cut out immediately. I've spooled my VNT to over 18psi in the cold and not cutout because I let off the throttle quickly.

Due to its size, the stock VNT25 is limited to about 200hp, topping out around 230hp in free flowing, high spooling setups (this drastically shortens the life of the turbo).

Running an open exhaust and ported head on the VNT allows for more flow, and more power, but also more overspooling. The solution is to simply install a wastegate, or run a controlled amount of boost to the vacuum side of the vane actuator to help control the boost.

By now, you've either spent a lot of money on increasing the flow and then controlling the VNT from the extra exhaust flow, or realized that the VNT just isn't made for tuning. There are two other VNT turbos available for TIV cars.

The most common is the VNT28, which has the same turbo housing and is a bolt on upgrade, using a larger compressor wheel to allow for safe boost up to about 18psi (VNT25 is safe to about 14.5psi).

The S60-VNT which uses the super60 turbo compressor is good for over 25psi, and provides more flow at 12psi than a VNT25 supplies at 16psi, hence more power at lower boost.

Both turbos are expensive, hard to come by, and require aftermarket or custom ECU calibrations to run effectively. An upgraded VNT turbo with the appropriate calibraion, a flowing head and less restrictive exhaust will cost you in the range of $1000, and might only net you an extra 50hp if you're conservative, which leads to my idea: 16 Valve Twin-Turbo VNT 2.2L 4 Cylinder.

The Plan:

Most people by now are probably bored and scoffing at me for using Twin Turbo in the same sentence as 4 Cylinder. Fair enough, it's not common, and requires a lot of custom fabrication, but could allow for much higher net results, and more HP per Dollar than simply upgrading an existing VNT.

The Dodge Turbo III cars sport a hefty 220hp stock, and benefit from two main advantages (and others, like distributorless ignition) over the slightly older Turbo IV setup: 16V DOHC Head, and a larger Turbo. An upgraded Turbo IV car with the stock VNT25 probably won't be competetive with a TIII car as it just can't meet the HP numbers easily. However, a Turbo IV car coverted to Turbo III status, while maintaining it's Turbo IV wiring and vacuum setup, should yield better driveability and more power than a modified TIII.

The VNT25 is rated for 150-200 horsepower, so two of them should be able to provide 300-400 horsepower, while spooling faster than a conventional turbo.

Converting a TII engine to TIII almost always means a custom intake manifold, which is beneficial to the twin turbo idea, as we'll have 2 sources of boost, but only one intake manifold to receive it.

On the exhaust side, running 2 custom headers, from cylinders 1/3, and 2/4, allows for 2 downpipes, and therefore, 2 turbos. Even a ported 8V head won't be able to flow enough exhaust to spool even the tiny VNTs quickly when using half the exhaust ports. However, a 16V head would provide ample flow to spool the VNT turbos, which are suited for slightly smaller engines than standard turbos of the same size.

Using 2 headers, 2 downpipes, and 2 turbos, leads to the obvious conclusion of using 2 exhausts (:thumb: Dual Exhaust), which will eliminate some of the backpressure in the system, and allow the turbos to spool more easily.

Intercooling will only help our purpose here, and our choice of intercooler will depend greatly on how we choose to supply boost to the intake manifold. Unlike a true Twin Turbo, like the Stealth R/T or Nissan 300ZX, we only have one intake manifold, so running 2 throttle bodies to it poses the problem of keeping the boost consistent on both turbos.

Running a large Front Mount Intercooler (Think Custom Welded Multicore) with large inlets and outlets on the endtanks should provide enough flow and cooling for the entire application.

Since both turbos will be facing the same direction, it will be easier to "Y" both turbo outlets to the same inlet on a single intercooler. Since we're using stock VNT25s (or VNT28s if you want to upgrade a bit for some extra power), it makes sense to use their stock turbo outlets, and Y them into a larger, 3" intercooler inlet. This setup is space efficient, and cost efficient as it eliminates the need for an extra intercooler, throttle body, intake manifold port, and a lot of front end custom fabrication to fit it all.

Running the intercooler outlet to whichever choice of intake manifold you choose should be no different than a normal 16V conversion. Since we're already doing so much custom work, it won't be much more to tie in some extra boost control, vane actuator control, and maybe even a boost bleed for some extra fun along the way.

Obvious roadblocks and drawbacks:

Custom Calibration will be necessary
Boost Control will be more difficult than with a single turbo
The fuel system will need to be upgraded
Engine internals will also need to be upgraded to handle these boost levels.
A great amount of custom work is involved, as this is no longer bolt-on work.

This is obviously a job for someone who loves custom work and wants to try something a bit different. I thought about this idea for a while, and being a VNT guy, I think it's the ideal turbo for this setup on our engines, as it's one of the only turbos that will spool quick enough to be effective in a Twin Turbo application, and it's small enough that it won't be as difficult to find room for it.

I'll try to add replies with some drawings if I can get any done before things get really busy around here. Very curious to hear some input on what will and won't work with this idea.

Whorse

http://www3.telus.net/braun/16V/16VTemplate.jpg

Neat idea and the TT concept has been tried and proven to work on our engines. It was twin Mitsus in that case.
One question though, didn't Garrett continue with the VNT idea after Chrysler dropped the VNT cars? I think I remember runing across a VNT turbo on Ebay that was used on some kind of diesel.
It seems to me that it would be an easier way to go to adapt a larger single vnt turbo from a different application to work on your engine.
That with the 16v setup would be really neat to see.

That's an awesome idea, you really put alot of thought into that. I think on a hybrid 16v engine, it'd be pretty easy to do with one of the weld-it-together-yourself log manifolds. Just ask for a second turbo flange when you buy it. Granted, that'd let the exhaust kind of flow any way it wanted, or you'd have to run one turbo off 1 and 2 and the other off 3 and 4.. Another idea to add to your proposal.. Twintercooler.. Twin intercoolers, one for each turbo, Y'd together to go into the single TB.. Or twin inlets on a large intercooler, and a single large outlet.

I liked the twin intercooler idea at first, as it sees less pressure drop, but I think it would make it much more likely to see differences in pressure between the two turbo lines, which could potentially weaken the setup. With one large intercooler both pressure sources meet before anything happens, and the total pressure remains the same in both lines.

I dunno, just something I thought of. That said, a couple of nice spearcos would work great.

Here is an easy way to do it. Just get Warren Stramer to build it;)

Alan

I thought about this a couple weeks ago while talking to a guy with a mid engine Omni. Here's one more idea though. The VNT's are limited at their compressor flow so 12psi is about it before you drop efficiency. Ok so what to do. Run them in series or staged like a diesel :) 12psi out of one, into the other and you've got 24ish psi in the intake :) Run it through a big efficient i/c and you're set :) Also thought about doing it with twin Mitsu's. Look at the ATB? Vdub Golf that was making the magazine rounds a couple months ago that was twin turbo'ed and made 450hp. Now they didn't run them in series but still would give an idea on how to mount them up.

Running them in series is not going to work. The air out of one would go through the other.. So your completely defeating the idea of doubling the air flow, as they both have to flow ALL of the air.. In parellel, they only have to flow half the air the engine needs. So think of them as being on a 1.1 or 1.25l engine.. Suddenly the turbo isn't too small anymore, and because it's max flow isn't being reached, it can create far more than 12-14psi.. I'd imagine you could get 20-25psi safely out of them.. Half the engine, double the boost safely..

not neccesarily true. granted you cut the flow in half and moved the point of efficiency closer to the center of the island. I used to have a comp map of the VNT but I can't find the bookmark at the moment. Anyway you could be off the map to the top of the island or into the surge zone. By running them in series you're right in the middle of the island because each turbo is only compressing at a 2.0 pressure ratio. It makes them far more efficient by keeping shaft speeds down which is the vain (pun not intended) of the VNT turbo.

ahh there it is. at 2.4 pressure ratio (20psi) and 20 lb/min airflow which is approximate to 200hp (300-400hp 16v divided by 2) you're turning 167 THOUSAND rpms! Wanna run them at max efficeincy? Run each turbo at 8psi and 14lbs/min Now in series you can make 16psi and I'm gonna assume double the flow. I need to go back through my tech articles and see if the flow does double. I cannot remember if that holds true or not at the moment. Anyway a VNT really sucks for making power. It's off the map at 23lbs/min and it might make 220hp if you can do it at 18psi on a stock motor. Now you're close to 160k rpms on the poor thing. It's choked off at the exhaust and can't flow at the compressor. Upgrading the comp isn't the right fix as you're still choked at the exhaust although you could lower shaft speeds and help it out a bit but what does the big comp wheel and the tiny exhaust wheel do to the stress on the small bearings. Of course on this application you only have to flow half the motor through them so it might work ok. The small bearings and shaft speed is what you'd have to watch out for.

I think the theory is the same, that as long as you have 2 sources of boost going into the same intake, they only have to do half the work. Being that the engine output is divided in half, to about 1.1L, it would make the VNTs nicer for low end spooling, just not as good for top end. I think we all know that if you want a lot of boost and a lot of top end, a big turbo is the way to go. This is more of a fun way to get some interesting and efficient use from a VNT.

reading this brought to mind mazda's sequential turbos. i think the dual VNT would be a great idea, but heres another variation. use the VNT for low boost low RPM useage to keep its shaft speed down and in the efficiency island, but also use a larger turbo that kicks in after the VNT maxes out. this way the VNT takes care of the larger turbo's lag, giving you lower boost (less traction problems) until the bigger non-VNT turbo spools.

I just re-read this. Some of my stuff isn't quite accurate as I didn't know nearly then what I do now.

Sequential turbos like the later RX7s have are definitely cool, but it's sometimes tricky to spool that bigger turbo and find room for it.

How about....2.5 hybrid with 4 VNT turbos on it :p

Quote:

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Originally Posted by GLHNSLHT2

ahh there it is. at 2.4 pressure ratio (20psi) and 20 lb/min airflow which is approximate to 200hp (300-400hp 16v divided by 2) you're turning 167 THOUSAND rpms! Wanna run them at max efficeincy? Run each turbo at 8psi and 14lbs/min Now in series you can make 16psi and I'm gonna assume double the flow. I need to go back through my tech articles and see if the flow does double. I cannot remember if that holds true or not at the moment. Anyway a VNT really sucks for making power. It's off the map at 23lbs/min and it might make 220hp if you can do it at 18psi on a stock motor. Now you're close to 160k rpms on the poor thing. It's choked off at the exhaust and can't flow at the compressor. Upgrading the comp isn't the right fix as you're still choked at the exhaust although you could lower shaft speeds and help it out a bit but what does the big comp wheel and the tiny exhaust wheel do to the stress on the small bearings. Of course on this application you only have to flow half the motor through them so it might work ok. The small bearings and shaft speed is what you'd have to watch out for.

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8+8PSI=16PSI. I did not think that was how it worked, even with staged turbos.

No, it doesn't. I learned a few things at work and realized how dumb I must sound in my original post. 8psi @100cfm + 8psi @100cfm with no loss would equal 8psi@200cfm.

Quote:

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Originally Posted by Whorse

No, it doesn't. I learned a few things at work and realized how dumb I must sound in my original post. 8psi @100cfm + 8psi @100cfm with no loss would equal 8psi@200cfm.

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Glad that hasn't changed lately.

HAHAHA, ya the world would be pretty wacked right now! LOL

Well if you've never learned about this kinda stuff it's hard to grasp at first, even though it's so simple. I have avoided this thread because I knew I looked like a dummy but you guys just haaaad to bring it back :p

HAHAHAHA. Dude, been there done that. The best things about mistakes is what you do with them. You idea was pretty good. Have you had thoughts about continuing this project? There is some new VNT stuff out there now.


Frank

I have thought about it a lot to be honest. I have some ideas for controlling them in either series or parallel, and my biggest setback is money. If you have any thoughts about it I would love to hear them because maybe one day down the road I will be ready to do this. I actually have an extra VNT turbo here just for that in case I ever need a spare or want to do this.