When is a Turbo too Big?

I've always considered spooled the point where boost stops rapidly climbing.

 

So when you hit target then.

 

Pretty much yea. Right now I don't really have targets to hit though since zero WGDC.

 

I miss spooling that low.

 

Hop on the twinscroll train! Be a hipster, it's the next up and coming trend.

 

I'd rather hop on the "not in debt up to my eyeballs due to buying car parts" train. Even more hipster around here; literally NOBODY is doing it!

 

Isnt part of "spool" about where you start too? I can hit 20+ psi at 3200 with my turbo if I start at 2500. if I start at 2800 it moves up. I guess I have never understood how the whole "spool" thing works.

 

Spool is roughly equivalent to the distance between a mic and speaker; spooled would be when you hear the feedback. Incidentally, feedback is pretty much how turbos work, with the wastegate bleeding off excess energy (which could be expressed as sound, since pressure waves do come out of the exhaust) in order to control how much energy is imparted back into the engine as compressed air.

The way I've been using terms is as follows:
Spool is the time it takes to go from WOT to spring pressure measured in RPM -- this is a vague term in my book
Threshold is the RPM at which you can make whatever you dial within a few hundred RPM. On the 6758, this was 3100 RPM. Going wot at that RPM or higher would result in massive amounts of tire rape, near instantly.

That's my take on it anyway.

 

http://blog.nulon.com.au/2014/05/turbochargers-turbo-lag-vs-boost-threshold/

This is a good article that kind of gives a bit of insight to that. Enki is pretty on track about it. If you're over the threshold, the time it takes to build targeted boost is lag.

 

Quick glance suggests that I was close, however I take issue with their definition; the EFR6758 produces positive manifold pressure below 2,000 RPM (it's only 1 psi but still).

I'm assuming this article is for the serious layman or casual reader with baseline knowledge...It could have used a bit more detail in parts.

 

It is basic but does help get the point across pretty good.

 

So according to this plot where does my car "spool" same map, same road, just started one at 2600 and one at 2800 (hit 20psi at 3200 and 3400 respectively)

 

Depends on when you WOT'd. I'll wager that your logs will show APP and Throttle Position are not the same at the same rpms between the two logs.

Also, spool rate is best indicated by the angle of the boost onset. Steeper angle = faster spool. Boost threshold, on the other hand, is best indicated by the rpm at which your car starts making "appreciable boost." I realize this is a subjective term, so the reasonable, arbitrary number I generally use to determine and compare this is 20psi.

 

Thats what Im saying. How can someone say their turbo spools at 3500 when you dont know the starting point?

In my logs APP is 99 at 2464 and 2791 for the 2 logs posted.

 

I've always based "spool" for the mazdaspeeds off when the car can achieve 20psi. I don't know why, but it probably has to do with the BT guys back in the day only running around 20psi and that being about where peak torque was. Probably a bad habit I should get out of, but it is a pretty good way to judge across the mazda platform since pretty much all of us run more than 20psi and it makes for a good standard pressure to judge by.

 

Yeah, a lot of people confute the terms "spool" and "boost threshold." As you've described it, I'd say you're actually talking more in keeping with boost threshold. This has a lot to do with the displacement of the engine and the volume of gasses that need to start flowing through the hotside before the turbo can really start making appreciable boost. Once the necessary gasses volume is reached, the speed with which the CHRA accelerates up to operating speed is about "spool." At least that's how I understand it. It's noteworthy that "spool" and "turbo lag" are often used synonymously. Here's a good article about it:
http://blog.nulon.com.au/2014/05/turbochargers-turbo-lag-vs-boost-threshold/
Then, as if this weren't enough, we can begin talking about transient response, and a whole new world of turbocharger performance opens up for consideration.

All three of these - boost threshold, spool, and transient response - are why the EFR7163 is my dream turbo. It's simply next-level and pretty much outclasses otherwise "very good" turbos in all of these areas.

 

IMO people usually say "it's spooled by X RPM" because that's the earliest RPM they see targeted boost. Sure you could start later and then yea it'll be spooled later but that's kind of common sense. As you get further and further from the threshold that spool time will drop.

Me saying my turbo spools by 3700 means that's the earliest it will be spooled. Not any earlier.

 

this is what has always confused me. I can probably hit 20psi below 3000 rpm if I want. I just have to floor it at 2000 and there it goes. I know there will be a lower threshold of where the exhaust gasses can move the turbine wheel, but going WOT at 2500 still gets me 20 psi by 3200. I feel like there needs to be a common starting point.
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I guess Ive never kept going down in RPM to see where it cant spool just as fast. Never wanted to floor it before 2500 rpm

 

Give it a shot. Tires might not be happy with you but low RPM WOT really determines how the turbo responds. IMO at least.

 

Might have to, just dont want to go too low and cause any damage. Still have that "dont WOT down low" mentality from 100k of a stock motor. 4th gear logs and RS3s on the hot days we have right now grip pretty well