Turbocharged vs supercharged

[Irace86.2.0]

Originally Posted by CSG Mike

18G

Specifically a GReddy T518Z

The FMIC doesn't cause any boost drop; the Garrett FMIC actually increased flow.

The turbo has a giant hot side, with a relatively small cold side. Your picture above isn't too far off from the actual size of the cold side.

I think most folks have a good idea of the size of the OEM throttle body diameter. Use that as a frame of reference compared to the turbo. In particular, look at the outlet size of the turbo. It's smaller than the outlet of a Rotrex C30-94. https://www.instagram.com/p/BbYKuqwhwzB/

Ok, maybe I read the post wrong. It sounded like you were saying the turbo hits a boost limit under the threshold of your wastegate, so the wastegate is always essentially closed. It sounded like you were saying the turbo was such a small compressor it couldn’t flow enough air to hit higher boost levels. I assumed you modified a turbo with a restrictor plate or changed the compressor wheel or housing. The 18G can hit much higher boost levels than that, and so do smaller turbos.

[Calum]

Originally Posted by Irace86.2.0

Ok, maybe I read the post wrong. It sounded like you were saying the turbo hits a boost limit under the threshold of your wastegate, so the wastegate is always essentially closed. It sounded like you were saying the turbo was such a small compressor it couldn’t flow enough air to hit higher boost levels. I assumed you modified a turbo with a restrictor plate or changed the compressor wheel or housing. The 18G can hit much higher boost levels than that, and so do smaller turbos.

Boost pressure is a measure of restriction to flow, nothing more. A turbo breathing through a relatively low restriction engine/exhaust/etc. won't make much boost, but can still be flowing at or near its max flow rate.

[CSG Mike]

Originally Posted by Irace86.2.0

Ok, maybe I read the post wrong. It sounded like you were saying the turbo hits a boost limit under the threshold of your wastegate, so the wastegate is always essentially closed. It sounded like you were saying the turbo was such a small compressor it couldn’t flow enough air to hit higher boost levels. I assumed you modified a turbo with a restrictor plate or changed the compressor wheel or housing. The 18G can hit much higher boost levels than that, and so do smaller turbos.

Boost =/= flow.

I can certainly make observed boost higher, but that would come at a power loss.

Try blowing as hard as you can through a coffee stirrer, vs a mcdonalds straw, vs a boba straw. Note the inverse correlation between boost (how hard youre blowing through the straw) vs flow (how much air is going through the straw). This is one lungpower of boost/flow through various straws.

[Irace86.2.0]

Originally Posted by Calum

Boost pressure is a measure of restriction to flow, nothing more. A turbo breathing through a relatively low restriction engine/exhaust/etc. won't make much boost, but can still be flowing at or near its max flow rate.

I'm just saying, other 2.0L vehicles and 86's running this turbo or smaller turbos hit higher boost. The turbo will do 25 psi I bet. Maybe more. It might be out of its efficiency range, so heat would be high, and there would be no gains in power, but that isn't my point. He said his turbo was so small the wastegate was always closed, which essentially is like running with the vacuum line removed. People overboost in that situation. I'm sure he has fuel/spark/throttle cut to avoid overboost anyways, so the point is moot. This is why I asked earlier if he had boost drop across his massive FMIC, which drastically reduced temperatures, so pressure dropped or something, but I still feel like he shouldn't have enough drop to justify having such a low boost ceiling.

This guy has a EJ205 WRX and the same turbo at 20 psi.

https://forums.nasioc.com/forums/sho....php?t=2465521

https://www.ft86club.com/forums/show...&postcount=107
https://www.ft86club.com/forums/showthread.php?t=68154

Not really sure why it says wastegate then he is saying his wastegate is always closed. I'm just confused.

[Grady]

Max boost of a turbo is at zero flow, Max flow of a turbo is at zero boost. Nether of these numbers are going to tell you how a turbo will interact with the engine in the middle.

This feels like Groundhog Day!

[Irace86.2.0]

Originally Posted by CSG Mike

The turbo does not. The stuff I added beyond the kit gives me some control.

I don't have a "kill" mode. My wastegate effectively runs permanently closed, and the power i make is all i make.

A supercharger can also have any number of maps for various octanes and circumstances.

Originally Posted by CSG Mike

SC's bleed boost; TC's generally build less boost, for the type of control you're talking about.

I spool to 7 psi, rising to about 10.5 psi.

I'm effectively dead even with an Edelbrock or Harrop kit on a standard pulley + ethanol and tune.

Yes, I spent a lot more money to end up at a SC powerband. I can make a meatier powerband, and used to, but it just doesn't make sense to.

Originally Posted by CSG Mike

It's simple physics.

- small turbo, so small it's maxed out, and doesn't actually need a wastegate to run safely
- maxed out turbo = out of efficiency island, vs say, a TVS1320 which is in the meat of its powerband
- known data that on a FA20: Whether JRSC, Edelbrock, or TVS, on 91, they make the same power whether you're seeing 9psi or 12 psi

- to supplement my maxed out turbo, I also run a giant giant Garrett intercooler rated for more than double what I need, complete with ducting
- If you saw my pre-intercooler charge temps, you'd probably shit your pants

- I make no more power going higher than 7psi on a 91 octane map, due to diminishing returns on boost vs iat vs octane, so my 91 map peaks at 7 psi. My 91 map at 7 psi (or 10.5 psi if you want to get technical) makes roughly the same power as a JRSC/Edelbrock/Harrop on their standard pulleys.

You're welcome to extrapolate my power using videos.

Originally Posted by CSG Mike

Because with the current setup, I literally, cannot overboost. Stuck wastegate? no problem. Wastegate failure? no problem. My goal is reliability and sustainability, not pure output.

Enabling more power and/or efficiency is just a matter of swapping on a larger turbo, but why? I can't use any of that extra efficiency/overhead without going back into constantly-breaking-transmissions territory.

I don't care to total my car with a CD009 swap, and don't care to swap in a PPG gearset.

If I just want more power, there are other more powerful cars I can drive.


At the end of the day, I went turbo because I wanted to prove that a turbo setup can be done reliably. It just so happens a supercharger can put out just as much power at roughly half the cost.

Modern superchargers are far more efficient than I think you may give them credit for.

Again, I'm just trying to understand these statements.

A wastegate that is permanently closed is one that never opens, so it never allows exhaust gases to bypass the turbo's exhaust turbine. As such is the case, the turbo is free to flow as much air as it can, which will be a byproduct of how fast an engine can spin the exhaust turbine that will spin the compressor turbine, and how much air the compressor turbine can grab. That is a limit of the size of the fins, the speed of the fins and any offloading limits, so the size of the housing.

Considering the above, it sounds like you are saying the turbo is so small that even without a wastegate the turbo will not overboost on your setup, and what happens is boost rises fast to 7psi, but then it rises more slowly where it hits its limit at 10.5 psi before hitting redline or falling. Ok, so if that is the case, and we know other 2.0L platforms and 86's hit higher boost, while still using their wastegate to not overboost, what are you doing to keep your pressure down? The only answer I can think of is IATs being dramatically lower, but I don't think a giant FMIC would do it. I could be wrong.

Maybe you misspoke, and your wastegate is opening at a predetermined boost level of 7psi, which is where your wastegate spring is at, but you have an EBC tuned to bleed off boost from the vacuum line running to the wastegate, so you can slowly ramp up boost to a peak of 10.5 psi.

I'm curious. I would love to see someone remove the pressure line going from the turbo's compressor housing to the wastegate actuator, so the wastegate never opens and run this turbo to redline.

[tomm.brz]

and how did csg mike make the engine flow so super good that a t518z turbine at maximum with wg closed all the time makes only 0.72bar of boost? extreme amount of valve overlap blowing everything out of the exhaust? modified heads?

[Grady]

Originally Posted by tomm.brz

and how did csg mike make the engine flow so super good that a t518z turbine at maximum with wg closed all the time makes only 0.72bar of boost? extreme amount of valve overlap blowing everything out of the exhaust? modified heads?

Ancient Chinese Secret possibly?

[Ultramaroon]

Originally Posted by CSG Mike

The turbo has a giant hot side, with a relatively small cold side.

This is THE way to do it.

[Irace86.2.0]

Like the opposite is possible. Match a large turbo to a proportionally small wastegate, and there can be boost creep. This is when the wastegate opens, but the engine still produces more air than the wastegate can reject, so as rpms rise, exhaust gases eventually spin the turbine faster.

Similarly, someone could remove/leave the wastegate open. With a wide open wastegate bleeding off only a fraction of the exhaust, the exhaust could eventually generate enough flow to spin the turbine and boost could rise. It would likely have a low boost ceiling. I don't know anyone who does this. I also don't know the efficiency of said setup.

[Grady]

Originally Posted by Irace86.2.0

I'm curious. I would love to see someone remove the pressure line going from the turbo's compressor housing to the wastegate actuator, so the wastegate never opens and run this turbo to redline.

Yes, did that, AVO turbo with stock exhaust. Boost would build to just under 10psi around 6k rpm then drop to around 7psi at red line. Yes there was more airflow at 7psi then there was at 10.

[Irace86.2.0]

Originally Posted by Ultramaroon

This is THE way to do it.

I don't know if he was saying he modified the hot side or if he is saying the hot side is naturally large. It doesn't look large:

[Irace86.2.0]

Originally Posted by Grady

Yes, did that, AVO turbo with stock exhaust. Boost would build to just under 10psi around 6k rpm then drop to around 7psi at red line. Yes there was more airflow at 7psi then there was at 10.

So you plugged the port on the wastegate or left it to atmosphere, and you plugged the bung on the turbo, so you weren't bleeding boost to atmosphere, and you took the car to redline to see what the turbo would do, and 10 psi was the max? All you had was an AVO kit on the car?

Uhhh, really?

[Ultramaroon]

Originally Posted by Irace86.2.0

I don't know if he was saying he modified the hot side or if he is saying the hot side is naturally large. It doesn't look large:

Basically, the compressor is geared low for the displacement so it becomes the limiting factor in the system. It spools later in the game but when it does, it's super responsive and is literally unable to overspeed the compressor. The combination is tuned for play above the vvt crossover speed.