200SX S13 ~ Turbo Conversation Exclusive

Question A
How does a different size of turbocharger running the same boost be pushing out different BHP in an S13?

Reply A
To understand that, one must have basic knowledge in turbocharging. Turbocharging falls under the same category as Forced Induction, meaning that you are forcing either air/fuel into the combustion chamber. For example, a stock car running a stock turbo say a T25 turbocharger pushing 220BHP running 1.2 bar of boost, however after a turbo(T28) changed and of course ECU programming, the car pushing out 280BHP with 1.2 bar of boost. Same boost but different BHP ratings. Why is that so ? First of all, we have to understand the units of air that is generated by each different A/R rating turbo going into the same engine. That means, per unit volume, there is more air. How can this be? Because pV=nRT where p is the pressure, V is the volume n is the number of moles, R=0.0821 L atm mol-1 K-1 (that is, R is the gas constant), and T is the temperature. Sorry that I didn’t want to start a Chemistry lesson on Ideal Gas Law.

Meaning that, if you have a stock turbo, you will see a mass increase of the charged air, when you use this equation, PV=nRT since your pressure meaning the boost pressure of 1.2 bar is constant, temperature is not constant, meaning bigger turbo, less stress on the turbine, lesser heat, R is always constant, that’s the universal gas constant in Ideal Gas Law equation. The variable, V or Volume changes, meaning the volume of the air changes, because of the a/r ratio of the turbocharger. Bigger A/R means bigger volume of air can be pushing into the combustion by the bigger turbocharger but running the same boost pressure of the stock turbo. So if you varies the n(Moles of air), you can change other variables in the equation. Thus you will understand why.

The reason why most people run bigger turbo is to minimize temperature and boost pressure which is a deterrence factor to Horsepower building as excess heat is a nuisance in turbocharging. You can push 350bhp on a x rated turbocharger running a 1.2 bar of boost pressure, but you can push 500bhp on a y-rated turbocharger running a 1.2 bar of boost pressure, with lesser heat generation.

Well that’s very basic. One need to understand the turbocharger’s compressor map to understand more on which turbocharger is efficient on your engine. It does not mean bigger the turbocharger, the better it is.

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Question 1
The HKS T2540 ur were mentioning comes in two AR, 0.6 and 0.86. so is it better to get a higher AR value. what's the compromise. is HKS T25 series and the T28 series ball bearing?

Reply 1
Different A/R will have to match your fins angle and size. Also have to depend on what application you are building your wagons/cars to which level (BHP/Torque) Range. Eg. you car makes 400BHP and my car makes 280 BHP, but mine's faster. Why ? It's the area under the curve of BHP/Torque Curve vs the RPM.For example, people modified the A/R mostly by changing the Turbo housing. A slightly bigger A/R gives better BHP but reduces response as surface area is bigger. The older T25 and T28 are not ball-bearing, they are trust bearings. The newer HKS GT-Series are ball-bearing and they have a very special fin design, in our turbo terms, "Q" Trim fins or "GT" Fins.
Looking at normal turbo fins, it's of all same shape with a little tilted angle, however "Q" Trim or "GT" has same features but with addition bend or high degrees and more aerodynamics to "Capture" more air that's why the fins will spool faster at low revs and reduce turbo lag. In addition the turbo has ball-bearings to further reduce turbo spooling tim to minimal.

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Question 2
Also i notice the spec are quoted as "GT2835 48T A/R 0.86 " , the T48, is it the turbine size, and what does A/R stands for?

Reply 2
For turbo ratings, for example, Mistubishi or Apexi Turbos they used, TD series...such as TD06 SH 25G.
The TD is the code, 06 is the size of the housing, SH is normally the bearings, 25G is the inlet compressor fins size.
For example, HKS GT 2835 48T with 0.86 A/R decoded as GT Is the model of the turbo with ball-bearings, 2835 is the turbo housing size as according to HKS Spec, 48T is usually the fins size (Hmmm...quite a big fins actually) 0.86 is the A/R or Air Flow Ratio.
Different manufacturers has different turbo size and specs, it's all depending on your target BHP for your car. Such as you want to build a 500BHP CA18DET S13, you will most probably need a HKS T51R Turbo rated for close to 600-700 BHP ratings, or a Trust T-66 Turbo for close to 650 BHP. You need to give allowance for the turbo BHP range in order to increase the life of the turbo.

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Question 3
What are the things i should take note when choosing a turbo that will fit to my current manifold?

Reply 3
Standard Manifold for turbo car is not as good due to the inability to maximise exhaust flow presure, most car manufacturers make the exhaust manifold with cost-effective and easily to make. That's why they are cast iron. I do recommend a manifold change for smooth boost response and better upgradability in changing bigger turbos later on.
Remember a normal T-28 ball-bearing garrett turbo makes close to 300BHP to 320 BHP at the max limit however a HKS T28 Turbo may makes up to 400BHP due to it's fins and housing designs. As HKS T28 Housing are similar from the outside in shape but the internal diameter of inlet are different and the flow rate is better.

Difference in T25 and T28 is the compressor size and fins size as wll as it's internal wastegate is different, T25 is standard for CA18DET, T28 is for SR20DET. T25 is smaller of course and it's usually non-ballbearing and max output of around 240BHP which is peanuts.

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Question 4
You were mentioning that a T28 (from S14 I presume in this case) is capable of up to 300 to 320HP at max out, in that case is it possible to tune the S14 using stock for 300HP?

Reply 4
To be honest due to my experience and understanding, stock S14 turbos are just a T28 thrust bearing and IT IS NOT BALL-BEARING. A claim of 320BHP using a S14 Turbo is like running close to 1.8bar of boost thus running the risk of blowing the turbo. Unless you run the new face-lift S14 Turbo (or T28BB for ball-bearing), You can get close to around 280 plus to 300 BHP possible. For the old T28 (S14) you cannot even touch 280 BHP to be honest. I heard the new S15 Turbo is slightly larger than the T28BB and is a hybrid turbo from Nissan a little similar to HKS GT25 series turbo. Of course HKS GT Series is better. Remember it is better to make more BHP using as low boost as possible is better. That's why people upgrade their turbo. Eg. By running a GT2840 turbo using 1 bar of boost, the car makes 300BHP is better than using a T28BB running 1.6 bar of boost making 300BHP. Higher the boost = the faster the engine/turbo blows.

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Question 5
I was under the impression that if a SR20 S14 engine is only able to meet ard 240HP at 1bar, is it possible that a bolt on T28 on CA18 S13 able to see even close to that value of HP??

Reply 5
To be honest....Be realistic in the figures.... I remember a guy I used to know claimed his 200SX S14 to make 400BHP, it lost to a 300 BHP WRX on quartermile. Besides S14 uses SR20DET (2 litre) with an variable inlet timing thing from Nissan called NCVS and the CA18DET (1.8 litre) uses a butterfly type inlet on the manifold that is being controlled by the Solenoid which is linked to the MAP sensor and ECU, trick is to "lock" the butterfly to increase air flow. In addition, the manifold design of the SR20DET is much better than the CA18DET but not as lasting as the CA18DET. To be honest, 240BHP on the wheels is taken in the account that for rear wheel drive car that's a close to 25% power lost in transmission, FWD has 15% power lost while 4WD has up to close to 55-60% powerlost.
If that car makes 240BHP at the wheels, it will make 369.2 BHP on the engine...on a T28 or even T28BB....HOW CAN THAT BE ? MUCH MORE THAN THE MAX LIMIT OF THE TURBO....end of the day, you still have to change the turbo to a bigger size like Garrett T3G, or T04 or T04R, then the power output of 240 seems more possible.

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Question 6
You also mention that a 280HP car can be faster than a 400HP car, it all depends on the area under the BHP/Torque Curve vs the RPM.
So base on graph below ( theoritically) an S13 using a HKS GT2510 will outrun a HKS GT2540 under the 6000rpm range ? anything above 6000rpm the GT2540 will take over?

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