Turbo choices

[Christ]

Can someone describe a simple relationship between a/r numbers and turbo sizing? I've read a bunch of stuff, but it seems like it might be a thing you just learn from doing.

[euromodder]

Originally Posted by Christ

Ok, that's a lie, but it involves a high pressure fuel pump and some electronics.... PITA.

On combined gas/diesel systems, the CNG or LPG goes into the air intake AFAIK, so the pressure is rather low.
You can work with the pressure in the CNG/LPG tank to overcome turbo pressure - and a pressure differential sensor to block the gas if the pressure in the gas tank drops too low.


BTW : Why not get a VW turbo off a junked 1.6 TD ?

[cleanspeed1]

Originally Posted by Christ

Can someone describe a simple relationship between a/r numbers and turbo sizing? I've read a bunch of stuff, but it seems like it might be a thing you just learn from doing.

Got off the phone with a Garrett distributor, and unfortunately there isn't a simple correlation. Too many variables involved.

Saw the map for a GT1544 ( have two versions ) and it seems that from a flow standpoint, it's good, but based on the variables it places the intersecting points on the edge of the island. Looks like a hybrid would be good for something like this, but it'll have to be made.

[Christ]

Originally Posted by euromodder

On combined gas/diesel systems, the CNG or LPG goes into the air intake AFAIK, so the pressure is rather low.
You can work with the pressure in the CNG/LPG tank to overcome turbo pressure - and a pressure differential sensor to block the gas if the pressure in the gas tank drops too low.


BTW : Why not get a VW turbo off a junked 1.6 TD ?

The high pressure pump is to change the internal pressure of the injection pump to cancel the dynamic advance mechanism, so the propane/CNG doesn't cause premature ignition.

Dynamic advance is based on the difference between inlet and internal pressure in the IP. If I pump in fuel to the vane pump at 50psi, it basically cancels the advance mechanism altogether.

Regardless, it's not really something I'm looking into right now, just a light minded idea.

As far as the VW turbo, sure, I'd do that, but I'm not likely to find one anytime soon for a reasonable price. As it sits, the GT15 seems to be on the edge of capability for my requirements, and the k03/T25 seem like good candidates. If they end up not soiling lure enough, I can always see about mods to fix that situation.

[Adandos]

Our calculator does great turbo sizing for your engine demands and target power goal and 'good' estimation of aspect ratio sizing ...

Our aspect ratio calculator has two main factors in it, one is your redline and the other is your peak PSI ...

to illustrate this simply

A low boost, high rpm engine such as a turbocharged motorcycle (hyabusa for example) still needs an oversized A/R to give good flow at high rpm to allow for good flow in those RPMs (would be pretty stupid to take a motorcycle that makes all it's power between 14000 and 16000 rpm and choke it off with a smallish A/R turbo).....

A high boost, low rpm engine will also need a higher than Average A/R because the flow through the turbine area at full boost will vary for the same turbine from A/R to A/R ... so when you're running a turbo at high boost you'll need the larger A/R to compensate for the exhaust flow corresponding to that boost level.

So our equation looks at those factors, redline , spool rpm, peak boost and comes up with two numbers one for spool and one for peak flow and so gives you a recommended aspect ratio between 0.8 and 1.0 A/R for example (Depending on what your parameters are) ... rather than giving you a simple single number.

If you care more about spool, go with the lower number. IF you care about peak flow and top end power, go with the higher number. If your buildup is an average RPM engine with an average Boost level, you'll see a tighter gap between the two numbers. If your engine is something ludicrous like 1000 rpm, 35psi motor you'll see a much larger gap between the two numbers.

So we leave the final decision to the user, but we give them good information about what the right ballpark is.

edit: can't post links ...

Horsepowercalculators dot net ... look for our turbo calculator on the home page...

[jtbo]

My car has 1.9l turbo diesel motor with Garret T2 turbo, these were made with similar sized KKK too, but below 1700rpm there is not much life unless lead foot, 50mph is 1850rpm and any lower rpm would require lead foot to get on boost and to get car going.

Hills would be much easier to climb with more speed as maximum torque is 2250rpm from my memory and it is about where can get max boost.

T2 is tiny turbo, but still boost is coming quite late, this makes me bit skeptical that it would be possible to make good boost at idle without wasting fuel to just make it boost, however I really interested of how such could be done as I would love to get my motor to pull well 500rpm lower than it does now.

[cleanspeed1]

Originally Posted by jtbo

My car has 1.9l turbo diesel motor with Garret T2 turbo, these were made with similar sized KKK too, but below 1700rpm there is not much life unless lead foot, 50mph is 1850rpm and any lower rpm would require lead foot to get on boost and to get car going.

Hills would be much easier to climb with more speed as maximum torque is 2250rpm from my memory and it is about where can get max boost.

T2 is tiny turbo, but still boost is coming quite late, this makes me bit skeptical that it would be possible to make good boost at idle without wasting fuel to just make it boost, however I really interested of how such could be done as I would love to get my motor to pull well 500rpm lower than it does now.

Getting a turbo to boost at idle is impossible because the velocity of the gasses and the lack of heat don't supply enough energy to get the party going, and the turbo you have is a fixed geometry unit. The factory pump settings are to keep it from puffing smoke on initial application of the throttle so fuelling between idle and maximum boost makes the engine feel soft.

The thing I would suggest is to take the car to a chassis dyno ( rolling road ) and find out exactly what the horsepower and torque curves look like, and then based on what you see, decide what would be the most cost effective way to achieve your goals.

The simple things like the piping in the turbo system can have a profound effect on boost response. Look at the factory piping and see about making the piping larger ( you don't have to go overboard on size, just make sure it has great routing with no kinks and smooth bends ), a low restriction exhaust system ( turbos do not like backpressure ) with an upgraded downpipe from the turbo if it has kinks and poor bends.

The main thing with your combination is to remember that a 500 rpm drop is huge with the factory camshaft timing and injector pump calibration. Now comes the time when you have to ask how far do you want to go, because to get there may get expensive. I'll never discourage someone from doing something, just be committed and be wide eyed about the realities.

You need more torque below 2250 rpm, which means either making the fuel come on hard before then by calibrating the pump delivery and timing that way, spooling the turbo ( you do that by flooring the throttle now ) or building more cylinder pressure preboost with a cam swap. Find out if there was a commercial version or industrial version of your engine made and see where the torque peak is because the cam timing is usually milder for these engines and a lower torque peak rpm. If not, you'll have to get something ground that will put peak torque at 1750 rpms. I know someone here that can do something like that, and as long as you can get the info he needs, he'll give you what you want. Maybe Piper or Kent can do the same over in the UK; I am just not familiar with the camshaft specialists over on the Mainland that are closer to you.

If you combine the cam swap and the injection system mods, you will get where you have to go. The increased cylinder pressure will spool the turbo up harder and earlier, reducing lag and increasing fuel efficiency, while at the same time eliminating the need to change turbos. The turbo is optimized for what you have now.

[jtbo]

Originally Posted by cleanspeed1

What kind of injection system are you running? Mechanical rotary, inline or electronic?

Mechanical, but maybe rotary, that I have never studied so much.

Maybe pic will help? It is not even same brand car, but engine is same and pump more or less same.


It is like Christ's car, dumb mechanical injection without any fancy stuff, however that 1.6l VW engine should have pump that is lot easier to play with.

[Christ]

Should be same pump... Bosch mfg. Rotary mechanical injection.

[cleanspeed1]

Yep, looks like Bosch rotary pump. Something just occurred to me, you should give those crazy Finns over at Myna Diesel a call. They do wonderful things with injector pumps.