Single vs Twin Turbo Setups

[thehemi]

I can never seem to find a good physics-related
answer for this question. Is either one really
better than the other? Or are personal choices
and/or other factors best used to pick one?

My assumption is that single turbos are good
setups for inline engines, while twin turbos
are better for v engines. This being due to
the exhaust plumbing needs for a turbo.

In regards to general engine theory, is one of
the systems going to be more efficient than the
other? Does it depend on inline vs v config?

Anyone have links or articles with more info?

[TT440]

It really comes down to two things:
1) installation difficulties
2) cost

It can be a MAJOR PITA to cross the exhaust from one side to the other for a single turbo. On the other hand, it can be quite difficult to locate twins under the hood of some cars. Whatever fits is what ya run.

When you start pricing out turbos, a single large enough to do the trick can be VERY costly. Smaller engines aren't that bad, but a single large enough to feed my 440 was about $1800. I paid $572 each for my hybrids. Add in the $225 for the extra wastegate and I'm still bucks ahead.

For performance, it's pretty close. Twins can spool up faster, but assuming everythig is done properly, there will be no difference in power.

[dewme5]

you can't put a single on a hemi. it's sacralige.

[turbododge]

The physics related issues that are usually brought up have to rotational inertia, which if I remember correctly is a squared function of radius. Thus it takes a single turbo longer to spool (more resistance to rotational speed change) than two small turbos of the same capacity.

The rule that I have heard the most is that a single will make more horsepower (less parasitic losses), and twins will spool faster and give better throttle response.

I do think the differences are not very large, and packaging and cost are the major factors. Very few of us have the access and money to do an unltimate dyno tune, which is what would be needed to see the difference in power. You might be able to feel a bit of difference in lag, however.

[thehemi]

TT440,

Was your car at the Houston Mopar Show? If
so, I remember speaking with you briefly at
the show on Saturday. Really sweet setup.

Were you able to find a twin turbo 440 kit?
How much hand-fabricating did you have done?

[Duner]

My single turbo set-up that I did on my Dakota is the only turbo'd vehicle I have ever driven or worked on. One thing I do know is that there is no perceptible turbo lag. Once the engine has any load on it at all it's at full boost. This may become more of an issue farther down the road, since I generally tow a trailer with the truck during the winter months. I guess the only way there could actually be less lag would be if it were in boost at all times.

Packaging was the main thing driving the decision for a single. There is just no room for twins without changing way too much stuff. Crossing the exhaust was no issue at all. Probably because it's in a truck. The bottom side of the thing has tons of room.... it's the top side with all the clearance issues.

Anybody have any good links to building a cheap air/water intercooler system?

[dewme5]

as far as turbo lag goes.. if you have any, it's more or less the time it takes for more power. you go WOT, and then the boost kicks in. it's not like you are losing any power in that time. it's just a slight delay before you get the benefits of boost over your normal power. turbo lag has always sounded like a response time between hitting the gas pedal, and your car starting to accelerate. Not so.. it's just the time before you go from 300 hp and jump up to 450 hp.

[TT440]

thehemi... That be me! I must say taht you've got me at a disadvantage. I spoke with bunches of folks and dunno which one you are.
A kit? {chuckling} Is there such a thing? I've thought about producing one.
It was 100% hand made. I must confess that I hired out the welding since I'm missing a welder. The system was designed in my head. That explains why it appears a wee bit lop-sided.

Duner... if you've got no lag, your turbine may be a bit small. I had no lag on my first pair of turbine housings. I stepped up to a larger set and now make bunches more power at the same boost. The spool up is a tad slower but the engine can now breathe at higher RPM.
Sometimes "lag" can be good.

[thehemi]

TT440,

I was not expecting you to remember me.

The setup certainly had a more "utility" than
"fashion" appearance, and I prefer that look.
What good is a car that you cannot go drive?

Well, I guess there are -some- exceptions, one
being the guy that had the seriously clean '71
Hemi Cuda Convt 4-speed clone. Killer car!

Anyways, I think you guys have answered my
questions on the turbo issues. I am not in
the process of a turbo project, but just had
the ickling to find out the differences.