For VWRacer re your race car

[TDIMeister]

Hi,

You were not completely forgotten over the past weekend as I was putting in the SDI manifold into may Passat at the Dorchester GTG.  :wink:

I felt that I should amend some comments I made previously in TDIClub about my feeling that, well, I'll let my original post do talking:

I have serious doubts anything can be done to make a VW Diesel engine rev to 6000 RPM and make any kind of usable horsepower up there (not to mention survive a race at those RPMs).

Shortening the stroke will not significantly allow an increase in RPM. This is because the VW Diesel engine is not limited by mean piston speed (i.e. a function of stroke). At rated power (~4000 RPM), the 1.9 TDI with a 95.5mm stroke has a mean piston speed of about 12.7 metres/second, which is low in the world of modern automotive-scale engines. Gasser engines routinely exceed 16 - 20 m/s, but that is no comparison to a Honda S2000 engine, which has a mean piston speed exceeding 28 m/s at redline!  

Reducing the stroke from 95.5mm to 86.4 results in a decrease in mean piston speed of about 10.5%, which will not automatically translate to a possible 10.5% increase in max. engine speed. That's because in a Diesel engine, RPM is limited by fuel injection and mixing rates, and this is a function of time rather than of piston speed / crank angle as in a spark ignition engine.

Direct injected engines like the TDI are similarly mixing-rate limited, hence the lower redline than IDI Diesels. If high RPMs are a priority, then the IDI is preferred. They have a stock redline exceeding 5000 RPM.

In general, IDI Diesels have higher air-utilization rates than DI, which means for a given amount of air-flow, more fuel can be burned before reaching the threshold of excessive smoke. This, in combination with higher RPM is the formula for higher power density in a Diesel which is important in a race car.

My concerns surrounded (and still do) prolonged operation of a Diesel engine at upwards of 6000 RPM in an endurance race trim.  The theory I established above with regard to mean piston speed and Diesel combustion being limited by fuel injection and mixing rates is sound, but it appears that through some pump wizardly, it is indeed possible to run a VW 1.6 Diesel to that targeted 6000 RPM level -- how long is another question entirely...

One very important thing I would advise you to do while developing the engine is to monitor EGTs.  Especially at high RPM, high load conditions, EGTs will be at their peak.  I would advise lowering the compression ratio via two ways: installing the thickest possible head gasket (3-hole) and very slightly -- and carefully -- opening up the swirl chamber passageway throat.  This will reduce the flow velocities across that throat and hence reduce heat transfer.  Cold start being a non-issue in a race car and in light of your geographic region, it's probably acceptable to drop the compression ratio from the current 23:1 by as much as 3 points or so.  

Next, what I would do is carefully lighten and balance the pistons and rods.  Not something for an amateur to try...  This will reduce reciprocating mass and inertial loads at high RPMs, and reduce power-robbing and engine-killing unbalanced forces, which increase to the square (or cubed -- I can't remember) of RPM.

Next is to have all the combustion chamber surfaces treated with a thermal barrier coating.  This would include piston crowns, cylinder head "hot-sides", valve heads and swirl chambers.

Speaking of cylinder heads, a 1.9 AAZ head has larger diameters on both intake- and exhaust valves, and much better larger / better port geometry.  ARP/Raceware stud kits for the head, main bearings and con rod big-ends would be obligatory, and while at it, if your engine uses 11mm bolts, it would be a perfect time to modify them to accept 12mm ones.

Use a runnered intake manifold, unlike the sorry OEM ones used on the TD and TDI.  You don't need an extra long one like my SDI since the engine will live at a high RPM constantly; an 8V gasser manifold will bolt up (may require match-porting) and should do the trick.

For turbocharging, since I understand that your engine's final displacement will be 1.6L, IMO a GT17-49V will give plenty of flow capacity to your engine's 6000 RPM redline and peak at upwards of 2.5 bar boost absolute (23 PSIG) peak.  It will be a very fast responding turbo, and the VNT design and high turbine A/R will reduce exhaust backpressure (good for power, efficiency and EGT), and overall turbo efficiency will be improved such that you can be operating at a positive pressure delta (i.e. compressor boost pressure greater than turbine backpressure).  A possible alternative would be a GT17V/GT20 hybrid as KERMA has done and posted about on TDIClub.  Incidently, I have a complete GT17-49V (S2) turbo with integrated exhaust manifold for sale, or I have a source for new GT20 turbos costing as little as $570 US.  I am not a fan of the older-generation Garrett T-series or KKK K-series turbos because they are relatively dated designs and lack the low-inertia, fast spool-up and high efficiency of the Garrett GT-series turbos.  Finally, it would be good to put a thermal insulating wrap or coating around the exhaust manifold.  It results in more energy to drive the turbine, and it also acts as a heat shield from warming up the intake charge.

Oh, and it may interest you to know that I'm working on a custom profile camshaft for the TDI that would also work on the TD....  My design achives a so-called "Miller cycle" effect in that the expansion ratio is greater than the compression ratio by closing the intake valve later from BDC in relation of exhaust opening.  Some numbers I've crunched suggest it's possible with this strategy to have the effective expansion ratio as much as 1.5-2 points higher than the compression ratio.  Therefore, the geometric (static) expansion ratio can remain at, say, 20:1 to retain good thermal efficiency, while the effective compression ratio is reduced to 18-18.5:1 to reduce peak cycle pressures and EGTs.

[TDIMeister]

double posted somehow?

[VWRacer]

Thanks for the great post. I enjoyed reading it, but it'll be tomorrow before I can reply. I flew all day today and am dragging my tail feathers... :wink:

[VWRacer]

TDIMeister,

I certainly agree that there are considerable challenges to be overcome if one is to successfully race a diesel engine for 25 hours. You have identified most of the big issues, but I am confident that I can overcome them sufficiently well to achieve my goals.

To reiterate, I have two principal goals for the race: to survive the 25 hours and then to win the ESR class. Winning overall is not a realistic goal. The winning cars from the past 3 races have all gone on to podium at the 24 Hours of Daytona just 2 months later -- I don't think that a victory against them is feasible in an 80 hp car. However, the ESR class has been won each year by a Spec Racer Ford (SRF); a 1650 lbs, 105 hp slug that's stone reliable if ugly and slow. FWIW, my car weighs 1350 lbs fully loaded, so I expect to have a slight power-to-weight advantage.

SRF's run 2:06 laps and have to refuel about every 45 minutes. With its gas engine, my car is 10 seconds per lap faster than a SRF. On diesel it can go twice as far between refuelings. Hence, my plan is to make this a tactical race...match their speed and reliability and beat them on fuel efficiency. If we turn out to be quicker than them, great! But 25 hours is a long time, and to finish first, first one has to finish...

With that homily in mind, I am concentrating on reliability and economy rather than outright speed. Ensuring the gearbox and engine survive are the keys to making it to the finish, so the engine and gearbox will be thoroughly prepped, and the gearbox will have an added cooler to keep temps in check. Mk9's routinely survive the Baja 1000, so getting one to live for 25 hours on smooth asphalt ought to be routine.

The strength and reliability of any racing engine lies in the bottom end, and the TD shines in this regard. Everything in the lower end is first rate, with a marked emphasis on durability. Some things need to change in a racing engine to further improve on a great starting point (like dry sump oiling, balancing, and quality fasteners), but the basics are all there. It's not like prepping a Toyota 4 AGE, where one starts by throwing away everything save the block and head castings.

I need to finalize details, but have arranged to purchase a 1.9 head to go on the 1.6 block, following in Dr Diesel's footsteps. If a GTI intake manifold won't work (I know the holes line up, but the ports are so different that it may not work), I'll make my own from aluminum or carbon fiber. The 1.9 head is totally superior to the 1.6 head at high RPMs, and since it is a straight forward swap, I will take the advantage it offers.

I am very interested to learn more about your cam and turbo. Please PM me with more details and pricing. If the GT17 turbo will require any electronic control, I may need help as I am no expert with the 'trons...  :roll:

You bring up some good theoretical points, too, but we differ in the details. While I do agree that ignition delay is time-based, everything I have read (from Richaro on...) notes that diesel's combustion rate (once ignition is initiated) is proportional to piston speed, just as in SI engines. Now that Giles and others have developed injection advance mechanisms capable of meeting any arbitrary mechanical advance, it is a straight forward exercise to determine how far injection needs to be advanced to ensure peak pressure is obtained at the optimal point ATDC. In short, I see no technical reason I cannot expect conventional combustion events at RPMs VW never envisioned.

Can we reasonably expect a TD engine to last 25 hours flat-out? I see no technical or practical reason why not. Last year a Mk1 GTI with a completely stock engine made the distance revving to well past 6000 RPMs with a wet sump. While some of its engine internals are lighter than the TD's, they are also not as strong, and they lack the "cushioning" afforded by turbocharging. Even though turbocharged, my engine will run cooler and be putting out less power than the GTI with essentially the same components, so the somewhat higher stresses with diesel will be partially offset by lower power stresses.

However, I haven't thought of everything, so keep those ideals and comments coming. I would hate to overlook something important!

Thanks again! Stan

[DVST8R]

It seems like to me, that I read somewhere way back when you were first talking about this that you mentioned that "tail pipe" somke was heavly frowend upon, or even outlawed by the powers that be. If this is the case I would be thinking about a twin setup, to take advantage of both excellent spool up as well as top end power, with out smoking like a frieght train. Now some of this is still untested in the VW motor, but is becoming an everyday thing with the truck guys (cummins, power stroke ect...) Now living across the street from one of the biggest diesel performance shops in north america (BD Diesel), and on a few minutes drive from one of the best diesel performance shops in the world (piers). I have had a chance to view, ride and even drive some big single and twin setups.  Now the closest comperison of similar trucks both 97' 2500 dodge ram 4x4, short box regular cab. both with the 12V motor, auto trans by DTT, both at about 500HP. Now when you hope in the big single soot grinder (hx40), and mash the throttle the first thing you notice, is that this thing moves pretty good for this big of a truck, next thing you notice is that the pyro is just about, redlining and the intersection behind you has disapeard into a balck haze, now all of the sudden you hear a whistle like a jet spooling up and things really start to happen, your pyro is dropping just about as fast as it was climbing earlier and the black smoke has just about dissapeard and you are gaining ground on the vette in the lane beside you, and you are well over any speed limit and are whistling like a lunch break steam whistle. Now a ride with the twins is a bit differn't, I wish I could have raced the same vette, but you can't always pick your races, so a mustang svt supercharged will have to do. Same thing you mash the throttle at the green no a little differnt secnario, you have a litle puff of smoke, follewed by smoke screeching and quite a bit of smoke (silly me the tires are spining and the mustang is getting away) my buddy brian (owner of the truck) says if I knew that is what you were planing I would have told you to flip it into 4x4 for the first bit. Anyway the tires stop pretty shortly and everything else is in check the pyro has moved up but is still green and the tubo's are whistling but not as loud, and everything is quite smooth, just one continuess accelaration, very linear. The guy in the mustang thinks he has you beat as he has jsut about a car lenght on you from the silly smoke show at the intersection, but he looks in his rear view to see how much he is going to beat you by, and just sees you box, as you have moved up to his quaterpanel you can now see the look of terror as you move up even with his window and he is searching for more from the go peddle, but thats it, and without anyother comotion you pull right on by him and are through the traps in 12.91 sec.

Now the single setup is my buddy dans truck, it is his work truck and he pulls 15,000 lbs + with it everyday, it can be a handfull to drive as you have the tipacle turbo ride. That and if you get on it to much too early while pulling you risk frying the turbo. Now brians twin setup is actually his wifes daily driver, drives verymuch like stock just alot quicker stock.

The only con I see of the twins is cost and fab work, and in your case possiblly fitment, as I am assuming from the pics that you have fairly limited space to work with. Now I am not a trubo guru in anyway all of my work is trial and error (a slow costly way to do it.) But from what I have learned I think that if money isnt an object of concern you get a garret gt ball barring turbo about the same size, mabey slightly bigger then the 1.9TD turbo as the ball barring turbo's do spool quite a bit quicker then non. and then something in the k24/26 hybrid range, or even up to a k26, but again in a garret gt ball barring turbo, have both of the hot sides ceramic coated and run header wrap between them and on the down pipe. And I think that you would have one of the quickest diesels ever seen. Or for more of a budgeted way get a 1.9TD turbo I'm sure there a lots of people with there 1.9TD that would happliy trade for a 1.6 Turbo, and then a k24/26 Hybrid from an audi, rebuild them both and have the hotside treated and wrap the conection and down pipe with header wrap and you set.

Like I said before I am sure there are lots of people on this board who can decipher a turbo map, and woudl be able to correctly match you a pair of turbo's so if any of them would like to chime in I would like to here what you have to say as well.

Lastly there is not much point in having all of that fuel the giles can provide if you cant burn it :twisted:

(I am sure there are countless spelling errors and gramatical errors, but I don't think that I could pick the right ones out on a spell checker even if I had one so you will have to live with it  :wink: )

[VWRacer]

Funny you mention the twin turbo route, DVST8R, because I had been thinking along those lines since reading s thread about the K03 turbo, which came on some VWs. IIRC, didn't someone identify them as the smallest turbos to come on VW diesels? And really too small for the TD?

Well, maybe one of those being fed by a k26 would be just the ticket to both prevent smoke while assuring full power at high RPMs. I am hoping TDIMeister and others will weigh in with some analysis...

[TDIMeister]

Twin turbos is a great idea.... if you have a six- or eight- or more cylinder engine.

The problem with twin-turbos in a 4-cylinder engine in a parallel arrangement is that you would have to pair the exhaust from cylinders 1&4 to one turbo and cylinders 2&3 to the other.  There are two HUGE problems with this: One is that the turbos will be receiving exhaust pulsations every 360 degrees CA, leading to extreme windage periods and the highly unsteady exhaust gas flow that will lead to poor efficiency.  

The second problem is that each turbo will be effectively servicing the airflow needs of half of the 1.6 litre, 4 cylinder displacement.  This will put the turbo operating into surge, and being that the K03 and GT15 are already among the smallest automotive turbos you can find, you can't find a decent turbo pair to match well with such a small displacement engine.

Setting up a twin-turbo system in a sequential arrangement has potential, especially for a wild setup with extremely high boost pressures, where a single turbocharger stage cannot efficiently (if at all) generate those boost pressures.  However, in a race car setup were every pound of weight is important, you have to ask yourself what it the true value of another 30 pounds of turbo and its associated additional plumbing and complexity.  Will you make extra HP to more than offset the extra weight to have any benefit? -- and also the potential loss of response and added backpressure of effectively having two restrictions in series in the exhaust?

Unless you plan on running more than 30 PSI or more boost, forget the idea of twin-turbos: MHO.  For all its perceived weaknesses, the GT17-49V setup would be kick-ass in your application!  An efficient, properly matched, single-stage turbo system will spool reasonably quickly, more than supply the airflow needs for a modified 1.6L engine, and be good up to about 22 PSI with a GT17, (or over 28 PSI for a more exotic turbo).

[DVST8R]

Well I don't know about stan, but I know for myself that I am planing on runing over 30psi, as it seems that dr.d is runing 30psi and it is still smoking as black as coal, and the only way other ten with propane or n20 ect... that I know of to burn off that excess is with more boost. I completely agree that the motor would have a tough time with parellel turbo's, but I think that it would be well worth the extra pounds in a sequential setup, esspetialy one that will see more then 6000rpm's with full fuel, but I guess the only real way to know is to try :wink:

[addautomotive]

Have you considered running biodiesel in order to lessen smoke? I can understand that MAKING biodiesel is just another layer of logistics that you don't need for a project like this, but surely there must be someoen nearby that makes good, clean biodiesel. Anyone I know running the stuff notices a dramatic reduction in smoke. I haven't heard of anyone dyno testing, so I'm not sure about power advantages/disadvantages.

It'd also be cool.

[VWRacer]

It should be fairly clear from my post above that I am only considering a sequential setup. If anything, TDIMeister understates the challenges of running a parallel setup on one of these engines. I still have an experimental setup from a 10,000 RPM Toyota 1.6l 4AGE engine that couldn't be made to work, so am not about to try it on a slow-turning TD.

OTOH, a sequential setup might work to both reduce lag as well as help ensure little or no visible smoke. On this question TDIMeister and I differ. Under normal circumstances he would be correct to say that the only reason to use two turbos is to build very high boost. But for my needs, low-RPM boost and smoke avoidance, a sequential setup is still on the short list if I cannot find a proper single turbo setup. Nothing more should really be read into it than that...  

Now, addautomotive has gone and let the cat out of the bag, so to speak. I say that because we are getting ready to approach the commercial biodiesel makers here in Cali for sponsorship in the form of (hopefully) free biodiesel. Not only does it reduce the smoke signature, but cuts down on a primary race expense. We shall see!

Cheers! Stan

[type53b_gtd]

But for my needs, low-RPM boost and smoke avoidance, a sequential setup is still on the short list if I cannot find a proper single turbo setup.

This sounds like a VNT application to me.  You're not likely to find a single turbo that spools faster than a VNT15 while flowing as much air at higher rpms.  If you need more than that, VNT 17.  The time and effort spent developing or adapting a boost control system would have to be less than that spent on developping a reliable sequential turbo system which is not going to perform any better at low rpms than a VNT would.

[TDIMeister]

OTOH, a sequential setup might work to both reduce lag as well as help ensure little or no visible smoke. On this question TDIMeister and I differ. Under normal circumstances he would be correct to say that the only reason to use two turbos is to build very high boost. But for my needs, low-RPM boost and smoke avoidance, a sequential setup is still on the short list if I cannot find a proper single turbo setup. Nothing more should really be read into it than that...  

I have no issues against a sequential turbo setup in a Diesel; BMW has shown a 6-cylinder (presumably) 3L displacement motor with twin-sequential turbos with something like 272HP FROM THE FACTORY   :shock:

IMHO I have based everything I have said on your desire for a durable endurance racer that needs to last a 25 hour race.  That precludes stupid amounts of fuelling and stupid amounts of boost, especially when you will be starting out with a motor with a 23:1 compression ratio.  It will not take much of the combination of fuelling, boost and high compression to exceed the designed gas-pressure and thermal loading limits of the engine components.  The strategies to making power is markedly different between modding a street engine that will only see peak power for short, relatively infrequent bursts, to an endurance race engine that will be operating near the ragged edge nearly 100% over the course of a 25 hour race.

Smoke output is irrespective of the physical turbo arrangement, whether a single, dual parallel or dual sequential, etc.  I would only advise you consider that a sequential setup will add lag and transient delays from the simple fact that the same exhaust gas stream that would only need to drive one turbine now has to drive two, and each turbine acts as a restriction and has its respective associating inertia.  What IS important is where the operating regime of mass flow and PR (pressure ratio) would be on the map(s).  If the operating conditions make it more efficient with a dual sequential setup, that's great, go with that.

Also, you should not be surprised that as an example, if a single turbo stage can generate a PR of 2.25 at a conservative efficiency of 70%, it would STILL be more efficient than a dual-sequential setup operating at a much more efficient point of 80% to achieve the same overall PR: each stage would operate at a PR of 1.5 (1.5*1.5 = 2.25), and the overall efficiency would be 0.80*0.80=0.64 < 0.70.

And yes, if it's not already obvious, the complexity of matching a sequential turbo setup has been WAAY underestimated...  :?

In a race, the one who wins is not the one who has the fanciest setup.  The one who wins is the one who crosses the finish line first (in fact, if he crosses the finish at all, that would be a small victory).

[VWRacer]

Great post, TDIMeister. FWIW, I don't think we're all that far apart. I've just carried on a conversation about turbo options, and while I have always assumed that the first and most desirable option is a single turbo setup, I have also left the door open to a sequential twin setup if that appears to be a better choice. Like I wrote, there isn't really anthing more to be read into it than that.

Please believe me that I have not underestimated the difficulty of matching a sequential setup, and that I am not looking for "bling" points... OTOH, if we get kicked out of the race for unacceptable levels of smoke because our fuel and boost curves are mismatched, that would be a major bummer, as well.

Back Monday...!

[lord_verminaard]

Here's a crazy idea- how about a supercharger/turbo setup?  Someone on the darkside (VWVortex) just got his Scirocco with the G60 engine running- but he's not using the G-lader charger.  Try an Eaton M90.    He said that it makes boost at idle (3-4 lbs @ 950 rpm) and has his bypass valve set at 15 psi- he cant go any higher because it leans out.  I know Toyota did a few charger-turbo setups with limited sucess, and of course Detroit Diesel had a monster V8 (two stroke, I think?) supercharger-turbo that made a stupid amount of horsepower.  This would be something to think about- and would probably be easier to run than messing with two different sized turbos.  Here's the topic on the 'Tex: http://forums.vwvortex.com/zerothread?id=1458638

It sounds like a siren when he really gets on it..  with that charger and a turbo it would be one noisy Diesel!    M90's are easy to come across, you see lots of them on ebay just about any time.  Crazy idea yes, but man that would be cool.  

Brendan
84 Scirocco 8v
00 Camaro L36

[DVST8R]

Well after doing some research I have come up with a few ideas :idea:  First for controling the vnt turbo by boost I fond this (I wish I could take credit it for somthing like this but it is not mine) it is based on the VNT25 that are found in 90-92 chrystler products, but should function the same on any VNT setup.

"CUSTOM APPLICATIONS

    So, What engines are candidates for a VNT 25? The answer is not so much engine size, but power. This turbo should work on an engine that can produce 150-200 hp with 8-15 lbs of boost. I am aware of a 1600cc VW installation that is very responsive. Twin VNT's on a 400 hp Porsche should be outrageously more driveable than the stock big single turbo. Another candidate for a twin would be a Buick 3.8 liter V6. This turbo should also work on high rpm 1 liter motorcycles, but the turbine housing is fairly large from a packaging standpoint. Remember that these application suggestions are just that, not guarantees. These units have standard late model Chrysler turbine and compressor housing connections and use standard Chrysler gaskets. As far as using the VNT on a custom application, the flange dimensions and bolt patterns are not the same as any other turbo, but adapters can be made with the dimensions shown

OIL SUPPLY

    This turbo needs .3 gpm of oil @ 30 psi. minimum at full power. Any oil that you can use in the engine will work for the turbo. The oil drain uses one bolt and seals with an O ring. A flat flange with a gasket will also work. A .5 inch minimum inside diameter oil drain is recommended and must be within 30 degrees of vertical with no "sink traps" that will allow oil to puddle.

CARBON SEALS

    The unit uses a carbon seal and therefore be used with a carburetor upstream in a draw through installation,although the Chrysler was fuel injected. Except for the VNT turbine, this unit is very similar to a standard Garrett T25. The compressor, bearings and seals are interchangeable with T25 turbos.

WATER CONNECTIONS

    The water cooling is intended for passenger car applications where the turbo is bolted to a heavy cast manifold withlittle airflow and many miles of stop and go service. The water cooling is not needed on a race car that isn't driven daily. Likewise, the water is not needed when the turbo is mounted on headers that don't store heat like a casting can. The water fitting is designed to mate with a steel tube flare nut. These can be removed and a different adapter can be threaded directly into the pipe threads and in the housing. Remember that the water is only for cooling during shutdown, the oil cools the bearings when the engine is running. When the engine is shutdown the heatstored in the cast exhaust manifold "soaks back" into the turbo causing the water in the center housing to boil.

    When this happens it is important that the bubble that forms can escape upwards causing water to flow in from below and allowing the cycle to repeat itself. The upper hose should connect to the engine at a higher point than thelower water connection. The water flow direction while the engine is running is not important. It is when the engine stops that the boiling occurs.

TEST INSTALLATION AND VNT CONTROL

    To determine the ease of controlling the actuator and to discover any installation problems in general, the author installed a VNT25 on his sandrail (Dunebuggy). The engine is a 2 liter German Ford. To keep the installation assimple as possible, the turbo was mounted on an old Roto-Master cast iron manifold that was intended for a T04B. Drilling the bolt holes out to 9/16" allowed the turbine to fit 3 of the 4 bolt holes and sealed acceptably for the test. The turbo pressurized a Motorcraft 121 two barrel carb in a simple "blow through" configuration. The pressure side (small tube) of the VNT actuator was connected to the hose fitting in the compressor housing.

    The results were instant boost and easy wheelstands in 1st and 2nd gear. The vanes were closed at idle and it was very quiet, even without a muffler. The VNT limited the boost to 12 psi without any further controls during thequick " around the block" bonzai runs. (This control point is a function of engine size and flow and may be different for your application.

    The addition of paddle tires and some steep dunes, however, changed things. The engine was not fully loaded onsuch a light vehicle on flat pavement. On a steep incline the boost would rise to over 20 psi as the engine became fully loaded. The solution was to install a conventional wastegate to control boost when the flow range of the VNT was exceeded. This is recommended for all VNT applications.

BOOST CONTROLS

    Chrysler did not need a wastegate because the backpressure of the stock exhaust limited turbine power. TheSandrail used a very low backpressure 2.5" exhaust system. The Sandrail installation simply ran a hose from the compressor housing to the pressure port of the actuator. Do not make the mistake of assuming that the larger 1/4" port is for pressure because it is the same size as the fittings on the compressor housing. The 1/4" port is for vacuum. The smaller 3/16" port is for pressure. Pressurizing the vacuum port forces the vanes closed at all times.

    They will eventually plug up with carbon, causing the " potato in the tailpipe" effect. If your engine runs poorly or won't start again after your first test run, check the actuator hoses. The boost setting can be mechanically adjustedwithin a limited range by shortening the rod length. Make sure the diaphragm does not bottom out before reaching the full stroke. It can also be adjusted with an electronic adjustable boost control system that is designed to control a conventional wastegate.

    A pressure regulator can also be used as a "boost over boost" control to raise the actuator pressure control point just as it is used on a wastegate. In a nutshell you run a controlled amount of boost to the "wrong" side of theactuator to cancel out part of the pressure on the boost side. Each psi put on the back of the diaphragm raises the boost setting by 1 psi and so on. This is plumbed by hooking up the actuator pressure port to a boost signal (i.e. the fitting on the compressor housing) directly as usual. Then hook up a second from the same boost signal to a pressure regulator and then to the vacuum side of the actuator. Setting the pressure regulator to 1 psi raises the boost `1 psi etc...

    In an off road or race only application this simple system will suffice. As a minimum a " part throttle open" controlcan be easily achieved by connecting manifold vacuum through a check valve to the vacuum side ( big tube) of the actuator. The check valve is to block boost. To prevent any pressure from being trapped between the check valve and the actuator, a .030" bleed orifice to atmosphere should be used. This will open the nozzles when vacuum is present at idle and part throttle.

    This has some important benefits:

    1. It cycles the vanes every time the throttle is depressed which helps them stay free of carbon.
    2. It prevents excessive EGR due to higher then normalbackpressure which affects idle quality.
    3. It improves fuel economy by eliminating backpressure caused by the turbo.
    4. It prevents part throttle boost which heats the intake air unnecessarily.
    5. It provides a more linear feel to the throttle pedal position."

Now with that being said I think that either a pair of the gt17VNT turbos, or a pair of these VNT25's in a sequential hot, and parellel cold would be an amazing ride. My other thought to this is have a gt17VNT (i think there is another name that they go by but I'm sure you all know what turbo I'm refering too. :? ) in sequince with a big gt28r disco patato, or k26, or a holset  hx35/hy35w with the 9cm housing would flow some serious air, starting at a very low rpm, and flowing right through the 6000+ rpm probley even enough to compress all of that fuel that giles is supplying :twisted:

My last thought is on camshafts, a subject I know even less of then turbos :oops: However the little that I do know is that if you get the exhuast valve to open a little sooner you get the benifit of that hot expanding gas to sping the turbo up quicker. I'm sure that there are people on this board with some good info and advise as far as a custom cam goes, but that is mabey better left to its own thread. Well I hope this helps someone I know it has me leaning in the direction of a VNT at least for my primary. (I am still stuck on twins as my car is a street vehical and there is some cool bling factor to the twins :lol: .