turbo charging

if i put two turbos together that put out 15 psi each, do i end up with 30 psi boost?

Almost 30 PSI but not exactly...You have to account for resistance when you combine the two. Besides, having two turbo chargers on your exhaust system, they probably won't reach 15 PSI boost each anyways. But if they do reach 15 PSI each, they would make ALMOST 30 PSI combined.

depends how the turbo's are routed. In parallel (most common config) it would be 15 psi. In series, it would atmospheric ratios mulitplied, IE, 15psi at sea level = 2.0. 2.0 * 2.0 = 4.0 * 14.7 = 58.8psi

there is no configuration that is straight addition. IE, 15psi + 15psi = 30psi

if you had 16 turbo's in parallel, and they were all set at 10psi. The total psi would be 10psi. Not 160psi

so what are the pros and cons of single turbos compared to twin, i would really like to in the future put twin turbos on a car and am trying to learn more about them

for gas engines, you're talking parallel. There is no performance advantage to 1, 2, 3, 4, 8 etc turbo's. Single turbos have a tiny advantage in efficiency. The only advantage to twin turbo's in this situation would be spacing issues such as tight engine compartments for a V-bank engine config

if you got the room, go with a single.

depends how the turbo's are routed. In parallel (most common config) it would be 15 psi. In series, it would atmospheric ratios mulitplied, IE, 15psi at sea level = 2.0. 2.0 * 2.0 = 4.0 * 14.7 = 58.8psi

there is no configuration that is straight addition. IE, 15psi + 15psi = 30psi

if you had 16 turbo's in parallel, and they were all set at 10psi. The total psi would be 10psi. Not 160psi

You forgot to convert absolute pressure back to gauge pressure.
Take 14.7psi off that 58.8, gives you about 35 psi boost.

Twin turbos (which is parallel routing) will provide you with additional flow volume but the same pressure. Let's say you need 400 cfms of flow in a V8 engine. You can get that with a single large 400 cfm turbo set to provide 10 psi. If you want, you could run two smaller 200 cfm turbos. That would retain the 10 psi, but the smaller turbos have the main benefit of a smaller mass to accelerate. Lag is decreased. You also can benefit with simpler plumbing in a V8 application not having to route exhaust gasses to one side.

Compound turbos (series routing) are kings in peak pressure and really shine with diesel applications where pressure is king. They take the air from the first turbo and pressurize it again. If you double the boost ratio in both turbos, you quadruple it in total. If you triple it, you multiply by 9 at the end. Some diesels with compounds are running nearly 150 psi intake pressure.

Going further - What if you have a twin Carb - The twin turbo can feed each carb - how would you calculate boost for that?

one of my turbo'd bikes has four seperate carbs. I figure I'm pushing at least 600 psi due to that alone! :D

You forgot to convert absolute pressure back to gauge pressure.
Take 14.7psi off that 58.8, gives you about 35 psi boost.the important point is, gas engines you never get over 40psi. Very very rarely anyway. Otherwise detonation becomes a very serious issue. That is why turbo's in series is nearly non-existant in gas engine applications

Turbo's in parallel are straight forward (regardless to the number of carbs or TB's) 10 psi = 10 psi regardless to the number of turbo's

you guys have been a big help, thanks a bunch for all the good info

Think about having a dual forced induction system. Super charger gives you boost at low RPM, turbo charger gives you much more boost at high RPM. Why spend money on two turbos if the people above me said they won't be very effective anyways.

there's also sequential turbo's, like the RX7's did for a little while, but that is a overly-complex way of solving the low RPM/high RPM issues.

Two turbo's, one is very small and boosts very early, the other is large and boosts late. Through multiple flapper valves in the exhaust and intake, it flows everything through the small turbo at low RPM's, then switches to the bigger turbo at higher RPM's.

VW has come out recently with a simular setup using a supercharger and a turbo.

I like to keep things simple. A variable vane turbo is a better answer to the issue IMO than sequential. Or just size a single turbo reasonably. You won't get the bragging-rights with huge HP numbers, but it'll be the funnest to drive

er, most fun that is.
jk

personally, i would prefer a twin turbo setup for the simple fact that you can use smaller turbos and get away with less room in the engine compartment.
although a single large turbo is probably more efficient in absolute terms.

the difference between single and twin parallel is so tiny its not even worth mentioning, as far as spool/efficiency.

The only puprose going to twin's, is space issues. (and the imaginary bragging rights, which is only good for ignorant people, of course)

Think about having a dual forced induction system. Super charger gives you boost at low RPM, turbo charger gives you much more boost at high RPM. Why spend money on two turbos if the people above me said they won't be very effective anyways.

That's called twin-charging. the Golf GT and VW Bluemotion (i think that's what it's called) both use it. there's also a car at my college being built by a teacher that uses a supercharger and a garrett variable-van turbo.

using the vacuum lines, when a certain pressure is reached, an actuator opens a valve and the supercharger is bypassed.

why would he twin charge a car with a variable vane turbo? wouldn't the extra weight negate any benefits from the reduced lag times because they'd be so small

there's also a car at my college being built by a teacher that uses a supercharger and a garrett variable-van turbo.
There's a guy on clubisuzu who did that to his Isuzu 4JB1T engine. That's a 2.8L 4cyl diesel.
Last I heard he was having engine troubles which were unrelated to his boosting (block was cracked prior).

On a petrol engine there're several big problems to work around. One of the main ones is what to do with that much boost?

I plan to fit staged turbos to my diesel truck, variable vane for the small one.
It's a work in progress.

this is on an 8-valve Golf MK II GTi. garrett varable-vane (looks like a T3) and an AMG supercharger. it sounds mental. serious machine, they're looking for 350bhp @ the fly. it's going to be used to hillclimbing. i'll try get some pics today.

this is on an 8-valve Golf MK II GTi. garrett varable-vane (looks like a T3) and an AMG supercharger. it sounds mental. serious machine, they're looking for 350bhp @ the fly. it's going to be used to hillclimbing. i'll try get some pics today.

You'll get more power on a fixed geometry turbo than you will on a variable vane. More efficient turbine so you get less backpressure.

Seems like a redundant experiment if going fast is the goal, but worthwhile if the goal is to build something interesting and different.

i dunno the goal, they told me they wanted the supercharger because there's no lag, then when the turbo's spooled a valve opens and bypasses the blower. but with a varable-vane that seems pointless, seeing as how the turbo pretty much has it covered.

either way, it's an awesome car. sounds like a beast when they give it some.