turbo efficiency

[bboyt3nsk]

I looked for this topic and it came up with a bunch of way off topics for this and i searched through about the first 25 and i couldnt find this question...Is the stock turbo on a SR20 (91-93) a T25 or T28? and whichever one it is how much boost until it is past its efficincy range? and if i did get a wastegate would that help the effeciency range at all or just allow more boost?

God bless your soul if you can respond to all these question...bles you if you even respond at all!

thanks alot

[GRiDRaceTech]

It's a T25.
How much boost? I'd guess between 15 and 18psi.
Wastegate would not help. If you wanna run lots of boost, you'll have to increase the size of the turbo.

[bboyt3nsk]

When would a upgraded wastegate help?

[180fan]

The stock t25, I wouldn't run past 17psi. The wastegate will not increase efficiency. A wastegate only opens at a specific amount of boost and lets it stabilize at that boost number. All an aftermarket wastegate will allow you to do is keep your turbo from spooling more than it's supposed to. The stock wastegate does leak. I forget the number though. I'll try to dig it up later.

[f8ldzz]

The wastegate's sole purpose is to control boost levels by the turbocharger.
An "upgrade" wastegate implies larger wastegate.
A better wastegate controls boost better.
Inferior wastegates cause boost creep - this is due to the turbocharger overrunning the (too small) wastegate, which causes overboost and boost creep.
Boost creep can kill engines due to the uncontrolled nature of the boost levels.

[bboyt3nsk]

Goodstuff I love this forum

[240LoVeR]

what about a BOV? when would it help if at all?

[Parry]

No.

A BOV vents air pressure from the intake tract to keep from stalling the turbo when you close the throttle.

[f8ldzz]

Originally posted by 240LoVeR
what about a BOV? when would it help if at all?

The sole responsibility of the BOV is to prevent "compressor surge".

What is compressor surge?
This is when airflow tries to "backpeddle" over the compressor wheel section.
Normally, the turbo sucks in air and then spits it out into the intercooler / engine.
If there is a spike in pressure after the turbo, the airflow suddenly stops and sometimes actually travels backwards!
If this happens, it's called compressor surge.
You can sometimes hear this as a "fluttering" sound.
Compressor surge is BAD.
You basically try to make a 50,000RPM to 150,000RPM turbo (compressor) wheel stall to a dead stop or even spin in reverse.
In mild circumstances, this puts tremendous load on the thrust bearing on the turbo.
In extreme circumstances, it will tear the compressor wheel off of the shaft.

So why this dangerous situation?
When boosting hard, everytime to lift of the throttle (i.e. to shift on a manual transmission), the throttle plates on the throttle body snaps shut.
The turbo cannot stop on a dime, so it's still trying to pump air into the engine.
But the throttle body slammed shut?
What happens?
There is a huge pressure spike in the entire system between the turbo and the throttle body.
This is where the BOV comes in.
By triggering the BOV, positioned between the turbo and the throttle bodyt, to act like a relief valve in between the throttle body and the turbo, this sudden pressure spike is relieved.
This is why you hear the loud WHOOSH; it is this pressure spike being relieved.

So the BOV is not just there to make "cool noises".
It's there to prevent damage to the turbo from compressor surge.

[LOVMUFN]

Sport Compact Car did a BADA$$ article in one of their issues about turbo effeciency. If I can find it in my collection I will post the issue number and if it is legal I might post it on my web site (giving proper credit where due) and link it here.

[malcolm]

when we first started running an 87 turbo FC3S, we had only one BOV, and the turbo lasted about 10 laps (mind you, it was the original turbo, so road racing the thing was probably the last straw for it).

We put on two stock BOV's, and the turbo lasted about a year running on 14 psi (that's about the best you can hope for with the cheap Hitachi turbo... the turbo was from the same manufacturer as my microwave!). For a turbo FC3S (I know this is a little off-topic), I would suggest either two stock BOV's, or one, big, quality, aftermarket BOV. With that, you'll get approximately the following turbo life:

7 psi - probably 5 years
10 psi - about 2 years
14 psi - about a year
17 psi - every three or four races (a "race weekend" is about 2 hours of track time)

Once you go above 12 psi, you'll need either big injectors, or plumb in a third injector upstream of the intake that comes on for any boost over 12 psi.

Yeah, this is a little off topic, but I included this just from what I learned from my car, and the cars of a few of my friends. Moral of the story: BIG blow-off valves are essential. (and they sound cool too!)

[240LoVeR]

thanks guys, keep this thread going its really informative!!

[kaosman]

Originally posted by malcolm
when we first started running an 87 turbo FC3S, we had only one BOV, and the turbo lasted about 10 laps (mind you, it was the original turbo, so road racing the thing was probably the last straw for it).

We put on two stock BOV's, and the turbo lasted about a year running on 14 psi (that's about the best you can hope for with the cheap Hitachi turbo... the turbo was from the same manufacturer as my microwave!). For a turbo FC3S (I know this is a little off-topic), I would suggest either two stock BOV's, or one, big, quality, aftermarket BOV. With that, you'll get approximately the following turbo life:

7 psi - probably 5 years
10 psi - about 2 years
14 psi - about a year
17 psi - every three or four races (a "race weekend" is about 2 hours of track time)

Once you go above 12 psi, you'll need either big injectors, or plumb in a third injector upstream of the intake that comes on for any boost over 12 psi.

Yeah, this is a little off topic, but I included this just from what I learned from my car, and the cars of a few of my friends. Moral of the story: BIG blow-off valves are essential. (and they sound cool too!)

Yeah the stock Hitachi turbo sucks, but for what it was designed to do, its decent. 14 psi is a LOT of boost for that turbo and even with a great BOV its gonna die a glorious death after not too long.

12 psi with an AIC & injector isn't a good idea...due to the nature of the FC's engine management you'd need to run a FCD to get boost above 8.6. So basically at 12 psi you're running timing maps set at 8.6 psi. This leads to a dead engine. For the FC, you really need a standalone to push more boost than 11-12 psi reliably.

[malcolm]

perhaps, but with our car, we ran 14 reliably, and just had to change that cheap turbo once a year. Also, a friend of mine was running 17 psi, and he got about four races out of his before he would rebuild/replace them. He was the guy running a third injector, before the manifold. I am not sure how he configured or operated it, but it worked well for him. Next time I see him, I'll ask him how he did it, and post on here.

[kaosman]

Originally posted by malcolm
perhaps, but with our car, we ran 14 reliably, and just had to change that cheap turbo once a year. Also, a friend of mine was running 17 psi, and he got about four races out of his before he would rebuild/replace them. He was the guy running a third injector, before the manifold. I am not sure how he configured or operated it, but it worked well for him. Next time I see him, I'll ask him how he did it, and post on here.

Oh no I don't doubt it, wasn't stating that it was impossible. Just a bad idea, thats all. With the additional injector you could get it pig rich and compensate for the lack of timing *Censored**Censored**Censored**Censored**Censored**Censored* at those boost levels and the car will run decent. But with an EMS, you can get the timing right and drop fuel down a little bit for more power.