A theoretical question for the turbo gurus

[Enigma_Man]

In reading and thinking about turbos, I had this idea:

Everybody talks about bigger turbos having more lag, and requiring more supporting mods, etc.

What about putting a big turbo on a basically stock car, but just keeping the boost down. I know that there would be more air going into the engine, due to cooler temperatures, due to slower spinning turbo. But wouldn't the lag time be not noticeably more, when running at approximately the same psi as on a smaller one?

Also, PSI is PSI, reguardless of turbo, the only thing that changes is intake temperature. I know that a larger turbo can flow more, but that only comes into play when the engine is sucking more air than the turbo can deliver, which would then make the PSI drop off because the turbo just can't supply enough air to maintain the pressure, which doesn't seem to happen on a good sized turbo.

I have a 16G on my car, and no fuel mods (I'm poor, I want them, I just can't afford the ones I want), and I just keep the pressure at 11 psi. I have no difference in lag (though my 14b was toasted, and the 16g isn't that much bigger really).

What about if I took something like the AGP L2R, and just ran that at 10 psi, assuming everything could keep up with the cooler air and whatnot. It would take very little time to build 10 psi on that turbo, I would think. This would help eliminate the buy-twice thing for some people. I dunno, I'm just curious about it, and super-bored at work.

-Jesse

 

[rdrkt]

You could buy a big turbo and run it at low boost but it would be laggier than your 16g and it wouldnt make great power at such a low boost level.

 

[crankbender]

I am not sure about your questions but i will answer what i can.

Turbos have efficiency curves. They are not linear, they are different from turbo to turbo, and they will basically define how the turbo will work at a given pressure. That means that your 16g may actually be more efficient at 10psi than a 20g. So the 16g will give you more power. This is because maybe the 20g requires higher exhaust pressures to make 10psi or anything. So basically no a bigger turbo will not always make more power at the same pressure.

As for lag here it is. A bigger turbo will always be laggier if everything else is kept the same. This is simply because the bigger turbo has alot more mass that it needs to get spinning. Pretty simple here (notice the everythign else being equal part don't come flaming me about going to a bb turbo and adding no2 or crap like that).

With your 16g, if it is a small 16g, you really didn't up the size of the compressor wheel much at all. This means there isn't much more mass to get moving so the lag isn't much worse.

 

[InferiorWang]

and you can run 15 or 16 psi on your car without fuel mods but not much more before a rewire/new pump

 

[EclipsingU]

Don't count out volume. A 20g at 5psi is going to "feel" stronger than a 16 at 10 because its pushing a larger volume of air. Large turbos aren't meant or designed for low boost settings. I would upgrade the rest of my car and build up to a turbo. That need for more hp can be very hard to refrain from sometimes.

 

[Enigma_Man]

Crankbender, thanks, the efficiency stuff is exactly the information I was looking for, in my long-winded approach.

And EclipsingU, airflow volume doesn't really matter in the way that you're talking about it. If the engine is only ingesting a small amount of air volume, than having a turbo that flows super volumes of air doesn't matter at that point. You can't shove more air into the engine than it's taking, by increasing the volume of flow, that's a pressure-based thing. The only point where turbo airflow volumes come into play is if the engine is eating more air than the turbo can supply, in which case the pressure will drop. The sole reason why a bigger turbo will feel stronger at the same psi as a smaller one is temperature. Otherwise, it's all just a matter of pressure (I'm pretty sure)

-Jesse