THURENfab.

So, here's my thinking...


Whats the big deal with a bigger better turbo? It seems to me if you are making boost, you are making boost right?

I know that adding a better turbo can get you more boost, but why is an aftermarket turbo putting out 40psi better than my stocker putting out 40psi?

Seems to me that the over-all torque curve of a stock turbo can cover a bigger power range being that it spools up NOW..

Comments?

morkable

Its not how much boost, but the quality of the boost... fellows like Nathan can explain it much better than I can. A stock turbo pushing 40 psi is well past its effiecent range,, whereas a bigger turbo can push this much out without much work at al

kevin

vzdude

I think there is a volume level too. Kind like the lift pump debates. Pressure is pressure, but at what volume?

maddog madden

And once your out of your effiecency range your stock turbo is gonna generate 40 psi at a higher temp which = lower volume. And with a bigger exhaust housing your gonna be able to get more air out of the motor droping your back pressure. But yeah let Nathan chime in here and he will make it make sense to ya.

cameroneod

Its also a question of what temperature a particular turbo is running at. Running that psi on a stocker will net you a whole lot more hot air than a bigger/better turbo would.

D.Wiggs

Don, I am no performance expert, but here is what I have learned (or at least think I have learned).

My current Twins setup will hit 75psi, but it is flowing like 1300CFM. My new Twins setup will hit higher than 75, but at 75psi, it will flow OVER 2200CFM. That's a LOT more air. It's like an air compressor. A small one will hit 90psi, but unless it is flowing over 7CFM (or whatever the measurement) you can't run an air cutting tool without it slowing down because of the volume. You want high psi and high volume!

matego

I think the answer you are looking for is the temperature of the air. The stock turbo will make 40 psi but since it is "overspooled" out of its efficiency range, the air is very hot and expanded. A higher flowing turbo that is designed for that pressure will be a lot cooler and denser air. Quality, not quantity makes a big difference.

GaveUpOnTV

I know a bigger turbo takes less boost to get the same speed cruising in miles per hour. I've heard people say that (I'm pulling these #'s out of thin air, just an example) at 70 mph, the stock turbo's boost will be say 9 psi, and their new 62-14 will be at 4-5 psi (and the EGT's lower too)
I thinks it's efficiency and volume.

OT-OF-Here

I've read recently that the more refined the flow, i.e., porting and polishing of the head, intake and exh manifold with exactly the same turbo setup and your boost will be significantly less as boost is resistance. So efficiency can be increased while boost is being decreased in the above example.

trik396

Excellent example. Boost pressure is really just a measure of RESTRICTION... Free up that flow and let the ponies roll...

soulezoo

And all this before you get into the question of TWINS! Yeah, let Nathan chime in. With twins though you get the best of both worlds. A smaller top turbo that spools fast and helps get the bigger bottom turbo going. Then the top turbo wastegates at a relatively lower psi (say 25-30 psi) and lets the bottom take over. With a good set of twins that transition is pretty seamless. But like everything else there are comprimises there too... The bigger the top turbo, the slower it will spool, but there is increased air volume.

Pitz

A bigger turbo is like having a bigger hose, more can get through at the same pressure. Also, most are designed to handle more PSI- so more air gets through because of the higher pressure and the "big hose" effect :-p

THURENfab.

Thanks so much guys!

I'm starting to understand some of this, but other parts still make no sense to me..

I did not think of the exhausts roll very much in my initial thinking, and that really does make sense that if the exhaust can spool the turbo up more freely, it's less backpressure to let more air in. So, if the exhaust side is more efficient, the intake side can work better too.. I'm I right on that?


What I don't get is the "higher flow deal" on the intake side. If you NEEDED a higher volume of air to charge the engine, wouldn't the boost gauge start to drop off? If the PSI is there under full throttle, that indicates to me that my engine doesn't want any more flow..

I guess if the heads were ported, and everything was opened up, I WOULD see the boost drop?

THURENfab.

I follow you here and fully agree with this statement. But it also kinda makes me think more about what I just posted...

It would seem to me, that without doing any modifications to the intake/exhaust path except for a turbo change, PSI is PSI. Surely making the exhaust path less restrictive with a better turbo will help the backpressure, but to me, it seems the only way to increase power is to get more PSI in the intake side..

VIN#Diesel

Yes... if everything else was a constant. It helps to remember that psi is pretty much just an arbitrary measure of the resistance stacking up in the intake tract. Not an absolute measure of the cubic feet of air actually getting pushing into the engine.

Think of it this way:
A sealed welding tank filled with gas held at 1500psi has a fixed amount of gas. Now take a torch and start heating up the tank. Pressure in the tank goes up to 2000psi. But there is the exact same amount of gas inside that tank.

A high boost level on a small turbo is like having that gauge on the welding tank read 2000psi because it is hot. You didn't create any more welding gas, you just added pressure from the heat.

What you really want is to force more cubic feet of air into your engine. Psi isn't really measuring that as an absolute.

Hope that helps. (oh and please don't actually take a torch to your welding tank. )