Turbo Optra - Now on tuned Haltech @ 225whp

[exist3nce]

As promised, here are some dyno clips:

http://www.youtube.com/watch?v=zu3JQBFnpRU

[benzino]

Sounds awesome. Love the extra spool noise.
That seems like a shit load of exhaust backpressure though... where was the reading taken from?

[exist3nce]

Sounds awesome. Love the extra spool noise.
That seems like a shit load of exhaust backpressure though... where was the reading taken from?

thanks man! The reading was taken right at the turbine inlet (made a tiny bung right in the collector).

The pressure does get excessive at my high boost setting, which is why we stopped from going any higher. My boost controller was not maxed out, I could have gone more... but as you can see the turbine was starting to choke pretty bad. It is of no surprise tho... its quite small. A stock Subaru STi turbo would make a nice upgrade

[benzino]

so the reading was taken before the turbine? wouldn't that affect the reading? I thought you were meant to take it from after the turbo

[gse_turbo]

The type of 'back-pressure' talked about through most forum does refer to post turbine resriction. Like a dam in a river it restricts the free flowing ability of the turbo. Generally, this type of back-pressure will affect spool time and the ability to produce boost pressure if really bad. Ideally this type of pressure needs to be as low as possible.

When it comes to 'turbo tuning' or fine tuning your turbo selection, back-pressure inside the manifold is the most important. I could use a deeper lesson but from what I understand a ratio between 2:1-3:1 is good for street us, or 20-30psi in the turbo manifold for every 10psi in the inlet manifold.
A high ratio like 4:1 means the turbine housing is too small for high RPMs and is chocking the exhaust flow and is limiting the boost output. A larger turbine housing or larger wastegate can help fix the problem. Porting an internal gate is a good option as opposed to going external but comes with other boost control dramas.
A low ratio like 1:1 means the turbine housing is larger than needed for street use. Its good for full race applications that don't see low RPMs often as there will be a great deal of boost lag.

I'm a huge fan of smaller turbine housings and large external waste-gates. The holly grail of turbo tuning is a digressive turbine pressure ratio that idles at 3:1 and drops to 1:1 at full boost.

Regardless of the turbo system, you always want exhaust pressure after the turbo to be as low as legally possible.

[exist3nce]

so the reading was taken before the turbine? wouldn't that affect the reading? I thought you were meant to take it from after the turbo

The type of 'back-pressure' talked about through most forum does refer to post turbine resriction. Like a dam in a river it restricts the free flowing ability of the turbo. Generally, this type of back-pressure will affect spool time and the ability to produce boost pressure if really bad. Ideally this type of pressure needs to be as low as possible.

When it comes to 'turbo tuning' or fine tuning your turbo selection, back-pressure inside the manifold is the most important. I could use a deeper lesson but from what I understand a ratio between 2:1-3:1 is good for street us, or 20-30psi in the turbo manifold for every 10psi in the inlet manifold.
A high ratio like 4:1 means the turbine housing is too small for high RPMs and is chocking the exhaust flow and is limiting the boost output. A larger turbine housing or larger wastegate can help fix the problem. Porting an internal gate is a good option as opposed to going external but comes with other boost control dramas.
A low ratio like 1:1 means the turbine housing is larger than needed for street use. Its good for full race applications that don't see low RPMs often as there will be a great deal of boost lag.

I'm a huge fan of smaller turbine housings and large external waste-gates. The holly grail of turbo tuning is a digressive turbine pressure ratio that idles at 3:1 and drops to 1:1 at full boost.

Regardless of the turbo system, you always want exhaust pressure after the turbo to be as low as legally possible.

I'm glad this stirred up a little discussion, but yes there are two points to measure backpressure we can talk about:

Post-turbine: Garrett is correct on this in that the pressure should be as little as possible so that the exhaust "wants" to flow quickly out of the turbine. Flow will always happen when there is a pressure difference, and therefore the less pressure after the turbine means the exhaust will want to escape easier. Again high restriction here such as a clogged cat or severely bent/deformed exhaust will kill spool, limit the amount of boost you can make, and kill power. In my case we didn't measure this because I won't be changing up the exhaust at this time anyways - my setup likely has some restriction here as I am using a factory Lexus IS300 muffler to keep noise down.

Pre-turbine: Garrett I feel that you are a little off on this one. I have observed first hand hundreds of cars with vastly different setups being tuned from 100whp - 1500whp and also lucky enough to have had a chance to discuss the results/theories and gains/disappointments with the tuner. Generally speaking normal or ideal should be around the 1:1 ratio - so 1psi of pre-turbine exhaust pressure for every 1psi of boost pressure. This is to say that a well designed reasonably efficient setup should be able to achieve the 1:1 ratio. There are actually a bunch of factors that can affect this pressure, and not JUST the physical sizing of the turbine and turbine housing. Once you start getting significantly higher like 2:1, 3:1 etc it is considered excessive and you are losing out on potential power that would have been gained through the efficiency of lower pre-turbine pressures. The engine has to work harder to push the exhaust out of the cylinders (adds to extra heat around the exhaust ports/valves) and if you are running any kind of aggressive cams with overlap you now have potential for exhaust reversion !! Think EGR at WOT.... not good. So now think of the opposite of that - a ratio of less than 1:1. Take for example 1:0.7. I have seen this on very efficient setups - and no it does not mean the car is laggy at all, it will actually be very responsive. Now think of what happens with boost being higher than exhaust backpressure - we can actually take advantage of some of the scavenging effects and it will be easier for the engine to expel the exhaust and allow less heat to linger around in the head. As it applies to my setup I am still running stock cams with non adjustable cam gears so the high backpressure isn't hurting me as much as it could. However you can really see where power just takes a nosedive and that is also around the same place the backpressure skyrockets. I can even feel how choked it is at the very top when driving. But this was an experiment to see how much power we could get out of that tiny turbo - and it was a success as we made around half of what two of these turbos make on a Supra

[gse_turbo]

Good write up. I think we're saying about the same thing in a different way. What's most common when talking about pre-turbine:inlet pressure ratio is considering the ratio as a static figure at WOT and full boost. These being 1:1-1:0.7 as an ideal like has been mentioned.

I like to see how the ratio acts from idle (negative inlet pressure) up through full boost and WOT. I strongly suggest that anyone getting into this look into Zietronics ZT-2 data logging system. Any monetered system can be graphed and overlayed ontop others. I like to see MAP/WOT/Pre-Turbine on top of each other. Ive considered pre-throttle pressure sensor as well to see how well the BOV or Recirc valve are working but never done it.

If Im not mistaken, the ratio at idle should be around 2:1 with the WG closed and BOV open and move to 1:1 or lower with WG open and BOV closed at WOT.

[benzino]

Wow, very interesting guys. Thanks for taking the time to explain.
I had no idea pre-turbine backpressure was measured, now the results in the video make a lot more sense!

[exist3nce]

If Im not mistaken, the ratio at idle should be around 2:1 with the WG closed and BOV open and move to 1:1 or lower with WG open and BOV closed at WOT.

Just something further to consider.... you won't be able to measure any tangible pre-turbine exhaust pressure at idle. If you have backpressure at idle - then you've got some serious restriction issues going on lol.

If you look in my video at the pressure test you can see this before the pull starts - the gauge is sitting at 0.

Wow, very interesting guys. Thanks for taking the time to explain.
I had no idea pre-turbine backpressure was measured, now the results in the video make a lot more sense!

You are welcome

[gse_turbo]

I seem to keep putting my foot in my mouth. I guess 'idle' wasn't the word to choose. I'll have to post a graph of what I'm talking about when the car with this system is back together.

Existence, would you like this conversation to remain on you thread or split and start a tech post?

[exist3nce]

Yes I would be interested to see that when you get a chance.

As for the conversation, I would like it to remain here - but you can make a breakout thread with a copy of all the relevant posts if you want, as it might make it easier for people to read / search. Perhaps all the posts from the "dyno results" onwards and maybe include some of the turbo pictures so people would have an idea of the physical size of this turbo.

[PrecisionBoost]

Quite an interesting setup, why did you decide to put surge ports on your compressor ?

[benzino]

Quite an interesting setup, why did you decide to put surge ports on your compressor ?

forgive me if I'm jumping in on this, but from on earlier post it seems like they're for anti surge and increased turbo spooling sound

[exist3nce]

Quite an interesting setup, why did you decide to put surge ports on your compressor ?

Benzino is right, it was mostly for the sound improvement (I like loud turbos). But I was also hearing some occasional surge at low RPMs and considering there are no compressor maps for the CT12 this was a nice fix.

[PrecisionBoost]

To the best of my knowledge the closest match to the CT12B is the T3 "45" trim, which should not exhibit surge unless you are closing the throttle body without a BOV.

I am curious about your progressive boost curve vs dyno graph data, you made far less power/torque than I would expect for 11psi so I can only assume you were running relatively low boost for most of the RPM band.