Si turbo on non-Si

Hollywoo0220

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The Si turbo is only 1mm larger in the Exducer with the same compressor. It flows about 7 more CFM. The difference in thought of power “gained” isn’t all coming from the turbo however. The Si’s compression is a bit lower as are the piston head design. That is reason that more boost can be run on the Si as opposed to the Non and yet gain a bit more power up top.
Since the Non-Si does have a slightly higher compression, you can see that 16.5psi (stock) and the Si 20.3 (stock) are only 20hp (at the crank) apart.
Now, the belief that you can extend the power band a bit more to the right is true - For another 300rpm and then you are back in to exhaust pressure is greater than boost and the choke is back.

Slippery slope turbos are; to include Compression and Piston head design (for fuel) differences.
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Myx

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The Si turbo is only 1mm larger in the Exducer with the same compressor. It flows about 7 more CFM. The difference in thought of power “gained” isn’t all coming from the turbo however. The Si’s compression is a bit lower as are the piston head design. That is reason that more boost can be run on the Si as opposed to the Non and yet gain a bit more power up top.
Since the Non-Si does have a slightly higher compression, you can see that 16.5psi (stock) and the Si 20.3 (stock) are only 20hp (at the crank) apart.
Now, the belief that you can extend the power band a bit more to the right is true - For another 300rpm and then you are back in to exhaust pressure is greater than boost and the choke is back.

Slippery slope turbos are; to include Compression and Piston head design (for fuel) differences.

Excellent points! This all makes sense. Remember, I never recommend anyone do what I do. Go with the status quo. 27Won turbo is built for efficiency and topend power. Stick with that and you are golden. Look at how many people are happy with the 27Won turbos.

To be honest, I'm absolutely happy with my stock, non-breathing, no topend turbo (104mph = No Topend? :rofl:). This is supposed to be an economy CVT right? Works for me! I'm just being greedy now and sharing the why's as to what I'm doing. No expectations as usual. Just testing stuff. Great points as always @Hollywoo0220
 

Myx

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BTW guys.....please don't delete your posts if I run in the 12.9-13.3 range by October-December. On street tires! Be fair! We all know this won't happen though. :)
 
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r.camlin

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Since the Non-Si does have a slightly higher compression, you can see that 16.5psi (stock) and the Si 20.3 (stock) are only 20hp (at the crank) apart..

Slippery slope turbos are; to include Compression and Piston head design (for fuel) differences.
Exactly why I think the turbo alone isn't enough (for what I want to do, at least). To truly maximize the benefits of the larger turbo (in both efficiency and power) you need to also consider exhaust and air flow and compression ratio.

JE sells pistons for our cars. I plan to pair the W1 (or other larger turbo) with the 9.5:1 CR pistons to reduce ignition retard and yield more effective power from the turbo while alleviating excessive torque where it doesn't need to be. That way, I hypothesize that you would be able to maintain similar boost levels with a smoother curve and more aggressive top end when boost peaks. All the while staying cooler and less stressful for the engine components.
 

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Exactly why I think the turbo alone isn't enough (for what I want to do, at least). To truly maximize the benefits of the larger turbo (in both efficiency and power) you need to also consider exhaust and air flow and compression ratio.

JE sells pistons for our cars. I plan to pair the W1 (or other larger turbo) with the 9.5:1 CR pistons to reduce ignition retard and yield more effective power from the turbo while alleviating excessive torque where it doesn't need to be. That way, I hypothesize that you would be able to maintain similar boost levels with a smoother curve and more aggressive top end when boost peaks. All the while staying cooler and less stressful for the engine components.
Be mindful of the natural Bore/Stroke of the engine. Also, since using Premium fuel then going lower than an Si’s piston CR is really only going to NET less power.
As long as you are using Prem Fuel with the 1.5L’s Bore and Stroke and a CR no greater than 10:6 and no lower than 10:3 you will be able to maximize timing and fuel and generate better strength in the power band.
 


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Yes. A Si turbo was bought used for fun and placed on a non-Si a small gain last year. There is a thread on it. I do not think there was dynos to show a quantified change from the swap.
 

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I agree @charleswrivers , the compressor is the same and the slight variation of the exducer reaches a little higher in the RPM (about 300).
 

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BTW guys.....please don't delete your posts if I run in the 12.9-13.3 range by October-December. On street tires! Be fair! :) We all know this won't happen though. :)
Maybe with full weight reduction
 

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Yes. A Si turbo was bought used for fun and placed on a non-Si a small gain last year. There is a thread on it. I do not think there was dynos to show a quantified change from the swap.

I need to find this thread. Thanks!
 

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r.camlin

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Yes. A Si turbo was bought used for fun and placed on a non-Si a small gain last year. There is a thread on it. I do not think there was dynos to show a quantified change from the swap.
Just read the thread. It's purely anecdotal, and still, he does say that he noticed an improvement. It's unfortunate he never updated. The physical differences may be small, but any difference is enough to warrant a change in performance and behavior.

I think it sounds promising, and I'm anxious to see some real numbers and a dyno plot.
 

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The Si turbo is only 1mm larger in the Exducer with the same compressor. It flows about 7 more CFM. The difference in thought of power “gained” isn’t all coming from the turbo however. The Si’s compression is a bit lower as are the piston head design. That is reason that more boost can be run on the Si as opposed to the Non and yet gain a bit more power up top.
Since the Non-Si does have a slightly higher compression, you can see that 16.5psi (stock) and the Si 20.3 (stock) are only 20hp (at the crank) apart.
Now, the belief that you can extend the power band a bit more to the right is true - For another 300rpm and then you are back in to exhaust pressure is greater than boost and the choke is back.

Slippery slope turbos are; to include Compression and Piston head design (for fuel) differences.
Ok. When raising the Non-Si PSI to the levels of the Si - you’ll see the same HP. The Si Turbo does have 1) Less blades, 2) Slightly larger exducer and 3) different CR with piston top design. It is designed that way because they are running +3.8PSI more than the Non-Si.
In essence, they are EQUAL in their design.
 
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Myx

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So what is the expectation with installing a stock Si turbo in a non-Si?

Nothing? A loss of hp/tq and slower 1/4 mile times? The same 1/4 mile times? I just want to be clear on this.

I'm reading that just changing the turbo out gains nothing. And even tuning for the Si turbo the same result because they are not that different. Am I correct?
 

Hollywoo0220

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So what is the expectation with installing a stock Si turbo in a non-Si?

Nothing? A loss of hp/tq and slower 1/4 mile times? The same 1/4 mile times? I just want to be clear on this.

I'm reading that just changing the turbo out gains nothing. And even tuning for the Si turbo the same result because they are not that different. Am I correct?
For you @Myx , what you will gain isn’t coming from the turbo alone. You have a pretty open exhaust channel already and you will notice that slightly extended RPM peak; this extending your power a smidge longer. Perhaps another 8hp & tq above 4000rpm; where the non-si begins to build higher back pressure.
The difference of 2.2% in exducer size and less blades with the same bore and stroke and similar CFM, and slightly higher compression are contributors to what I would gauge you at.
Granted we are measuring at the same PSI. Of course, you can increase that + fueling and achieve more - but it is a Non-Si engine without the stronger Rods and with a CVT.
 
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Just read the thread. It's purely anecdotal, and still, he does say that he noticed an improvement. It's unfortunate he never updated. The physical differences may be small, but any difference is enough to warrant a change in performance and behavior.

I think it sounds promising, and I'm anxious to see some real numbers and a dyno plot.
I made a Vit turbo upgrade from Comp Turbo using an extra SI turbo I had previously. I since then sold that to a buddy of mine who has a manual hatch sport and is etuned by DRob on flex with FBO, LSD installed, and spec stage 2 or something clutch and flywheel. Now that's a turbo that is worth having since it holds power to redline as Vit intended it to. Only thing was the hatch sport internals are not as good as Si from what DRob said hence knock control and some other stuff are more sensitive to more boost and runs out of air sooner than the Si too. My buddy is getting an Si inlet installed on his hatch sport even though DRob said you'll gain some air but don't expect much at all.
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