GT Motorsports: 370Z Supercharger system development

Buddy Revell

Question: On the various 350Z forced induction systems, why was there such a wide variation in peak hp numbers from roots SCs, centrifugal SCs, and TT kits even when at similar boost levels?

kdoske

has nothing to do with the car but the different FI options. They all create boost differently. Roots having boost the quickest, then Centrifugal SC, then TT. Sometimes Centrifugal SC and TT produce boost at around the same time though.

Buddy Revell

But if boost is boost, then they should all have similar peak numbers at the same boost level on the same engine, right?

kdoske

I definitely don't know all the reasons why boost doesn't actually translate that way but I do know that TT is the efficient boost option. It is essentially free energy because it is using the actually exhaust of the engine to spin the turbine. The only problem is you have to wait for the exhaust pressure to build for the TT to spool. SC on the other hand uses engine HP because the turbine is spun by the engines belt system which, while creates boost, also takes HP to do. Typically the main benefit of SC over TT is earlier boost times. The disadvantages is that you will typically not have as high gains from SC then you would a TT. Main reason being is becuase the engine itself it working harder just to spin SC.

Like i said above, sometimes Centrifugal SC and TT produce boost at around the same time though.

roplusbee

With those thoughts in mind, the Centrifugal SC setup should cost less than the Roots SC and TT setups. Especially if the "spool time" is relatively similar on the Centrifugal SC and the TT setups. I would say Roots SCs have a different application (like as close to direct response as possible) as compaired to the other 2 options. I could be off in left field, but that is not how the ball bounces though. I have seen a few Mustang guys get Roots SC systems with everything necessary to make a beast for a few grand. Although their suspension setup sux big time (barring the latest models).

I have stayed away from SCs because I have always run higher revving 4-bangers and I do my best to stay in the sweet spot (in boost) so that I maintain that instant throw-you-back-in-the-seat response. I guess having a 6 cylinder is lilke having a jack of all trades kind of deal.

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Minicobra1

This is caused by the friction and drag from the supercharger and belt, some have more then others which will result in HP loss to the rear wheels.

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KEVTEX

There is no free energy. All of the power required to spin a turbine and compress inlet air comes from the engine. Belt driven off of the crank or back pressure on the exhaust stroke, the power requirement is the same.

Solus

Kevtex... I have read your posts and for the most part agree with all of them except this one. The power requirement is not the same to get it from a belt as it is from the exhaust. When you take it from the belt you will suffer a larger power requirement due to the parasitic loss etc and you are taking power to make power. Gaining it off of exhaust gasses doesn't cost anything. The engine is shooting out the exhaust gasses whether the turbos are there or not so you are not taking any power from your engine to make the extra power (boost).

RCZ

^ There is more back pressure with a turbo than without one therefore you are taking some power away. The parasitic losses from a turbo are negligible when compared to the losses from a supercharger though. The SC takes a much much bigger toll on power than the tc.

KEVTEX

With a turbo, the engine has to work harder to get the exhaust out because of the increased back pressure the turbo provides. The same amount of extra work is required if you take the power from a crank pulley.

RCZ

Not at all because the sc has to move gearing and a belt while the tc only has to spin. We aren't arguing for the sake of argument, we know this is and has always been the case. In modern days, parasitic losses from the sc have been greatly reduced through new designs, but its still takes a bigger toll on the engine to make the power.


Also, guys, the whole bigger turbo makes more power thing.... From what I understand its not because it flows more, we know that 5psi is 5psi. What matters is the charge density of that 5psi. According to what Silo posted, a turbo that is in its peak efficiency zone (or island if you've ever seen a turbo flow chart) will create a more dense 5psi than one that is not. Think of it this way... colder air is denser, air particles are more compact therefore there is more oxygen to burn therefore you make more power. The same apparently goes for a turbo operating at peak efficiency vs one that isnt. The one operating at peak eff. somehow produces a more dense charge (at the same temperature) as the one that is out of its efficiency zone.

The post by silo didnt explain why, but I have a feeling it has something to do with how the air is compressed in a more efficiently sized tc than a less efficiently sized one. Efficiency relating to the size of the engine and the amount of psi you are targeting.

I'll do some more research and let you guys know.

Silo

That was my point. A larger turbo, and i have to state more specific, at a given psi might be more efficient, which means will it heat the charge less, hence more oxygen in that charge.

One simple factor is that it has to "shovel" less. You have a larger shovel you will dig that whole more efficiently than with a spoon. The other factor might be that the exhaust side is larger and therefore pumping loss is reduced. The larger turbo might still be less efficient at a lower psi but usually we compare the peak operating psi range.

kdoske

I see what kevtex is saying. Laws of physics will tell you the same amount of energy is used to create say 6lbs of boost whether it be by pulley or exhaust. I totally agree with that, but the energy used by the exhaust while exactly the same as the energy used by the pulley does create different effects on the engines HP/TQ output. I still say using the exhaust pressure is more efficient for the engine to create boost and not have such and adverse effect on the current HP output, but yes, it does exhaust the same amount of energy on an atomic level as with the pulley.

Solus

I have to disagree with you on that one kev... just my personal stance doing more research right now to provide valid documented points.

StillenZ

Hope that birdy wasn't kiddin....

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