Can someone please explain this to a rookie?

[Anonymous]

I was reading through some old post and found one about putting three turbos on a three carb set up. They guys said it couldn't be done. But why? I obviously don't understand how a three carb set up works, but from what I read, it sounds like not all the carbs are open at the same time. Almost like they are staged. Is that right? I am just looking for a little more understanding. Got to learn somewhere I guess.

 

[Asa]

yup, that is why
the central carb produces the idle, and main A/F job, but at WOT the outer carbs crack open and it roars

and it would just be hell trying to get those three turbos and those three carbs tuned correctly

 

[CobraSix]

But, you don't have to have it set up for progressive, just have them 100% synced up, then you can run 3 turbos. you'll run crazy rich at idle and low speeds, so you'd probably have to re jet, but it isn't possible.

Slade

 

[Asa]

Slade - shouldn't it be "it isn't impossible" ?

 

[StrangeRanger]

Would you settle for it insn't practical?
More parts, more complexity, more tuning headaches and NOTHING gained over a properly sized single turbo

 

[Thad]

Cuss_'em_trkrs,
Beware some of the mods in car mags are for the Gee Whiz, Shazam, Golly Gee crowd, just to Wow them and sell mags to people who will never build.
Almost alway it is a picture stories w/ no tech right up. Some I've seen doubt seriously that the engine would even run more than a sloppy idle.

 

[CobraSix]

should have said "isn't impossible".

WOuldn't want to deal with that set up. a NA triple carb set up is finicky enough, imagine with turbos.

You'd have severe problems with pulsing.

I agree, most magazine articles at this point are all show and flash...no meat.

Slade

 

[Anonymous]

This may just be incredibly stupid and probably shows my lack of understanding on the issue, but what if you ran like two or three turbos through each other? Turbos have an exhaust side and an intake side right. The exhuast moves the turbine, which in turn moves the turbine on the intake side? Something like that anyway? What if you ran one turbo off the exhaust, and then where it would normally go into the intake manifold hooked up another turbo to it to get it to spin faster, and therefore make more power. Right? Theoretically? Then, I guess maybe you could do that with another turbo if you wanted to. Would that work? Or is it completely insane and I am just out of my mind? Which is probably the case.

 

[Anonymous]

no unfortunatley u are not isane,

its quite comon practice on tractor pulling rigs.

they use a smaller turbo to feed a larger one. the engine spools the smaller turbo which blows compressed air into the turbine of the MUCH MUCH larger turbine which then can supply boost pressures of 80+ psi some see 100psi

hmmm,,,,, may have to try this on my falcon...lmfao on 2nd thoughts i think not.

cheers.joe.

 

[StrangeRanger]

Multi stage turbos are actually fairly common. Third generation Mazda RX7s used a 2 stage and IIRC a lot of pulling tractors use multi stage setups. They're a way of making massive amounts of boost

 

[MustangSix]

Compound turbos are a common application. The thing to watch out for is heat. each successive squeeze creates more temperature and eventually could get to be too hot to use in a piston engine unless cooled significantly first. Ideally, you would intercool between the turbo stages to remove the heat.

The problem with that is obviously complexity, but also some loss of efficiency as the air is forced thru a heat exchanger of some kind. You very quickly reach an engineering point of diminishing returns.

That's largely why a single turbo with a good air to air intercooler offers such good value. You could compound the turbos and intercoolers, but the gain might not be proportionate to the effort.

 

[CobraSix]

The Volvo S80 T6 has a twin sequential turbo on a 2.8L I6. very smooth power delivery when compared to my S70 T5 (one larger turbo) on a 2.3L I5. I would think you definitely need an intercooler (at least one) for such an application or maybe an Air-Water intercooler.

 

[Anonymous]

Glad to know I am not entirely crazy. What if you have a split exhaust manifold on a 300 I6 and ran two turbos off the exhaust, then run a sequential turbo off of each one of those, giving you four turbos. Then , would it be possible to run both sets into a common airintake, some kind of pipe or something, then into a single carb or throttle body? Would that make any power gains over just having one or two turbos. Would the combined boost really be combined, or would they just sort of stay the same? If I am completely stupid, just tell me and I will stop asking these questions.

 

[CobraSix]

Don't know about how possible such a set up is, but I'm sure someone out there in the internet world has tried it.

But, twin sequential turbos generally aren't for more power, they are for quicker, smoother power delivery. The exhaust is only going to be able to turn so many turbos. being that you are making a set up and having only 3 cylinders worth of exhaust fire 2 turbos, I think you'd be pushing it and you wouldn't end up making much boost at all. have to remember that the turbos need heat and exhaust velocity.

One larger turbo making 16 psi of boost will have the same power increase at peak as 4 smaller ones working together to make 16 psi. Only difference is the smaller ones will build a more smooth boost curve, but would be terribly complicated. It may provide more power under the curve then 1 larger turbo.

Remember, the power is made by total system boost pressure, not how many turbos you have.


Slade

 

[StrangeRanger]

2 small low inertia turbos, 1 on each half of the manifold, would probably spool up faster than a single large turbo. When you add the multi stage pair on top of that, you've increased inertia and slowed the whole thing back down again but gained a lot of boost in the process. The plumbing involved would be a nightmare.

For the street, your best bet is a single turbo sized for the RPM range you're actually going to be using and a moderate amount of boost. It you're worried about response speed, an axially divided turbine housing and/or a slightly smaller turbine A/R will improve response.

If you're just trying to fit a junkyard/eBay turbo, start with one that gives the same number for (max RPM x displacement) as the engine you want to put the turbo onto and you'll be in the ballpark.

 

[Anonymous]

I am going to disagree with my friend, StrangeRanger, though purely on practical grounds. AFAIK, there are no inexpensive OEM-style turbos available in North America which are designed to produce less than about 175 hp. The practical implications of parallel mounting two of them on any of our I-6 engines is that there would be horrible turbo lag followed by lackluster performance. This might work if you could find a pair of turbos from a Mercedes "Smart Car". These cars come with a 60 hp turbocharged engine. I got to examine one of the turbos while visiting a frined in Germany last year, and it was a real work of art. Might be a bit difficult to get in NA, though.

 

[StrangeRanger]

I don't think the pair would be worth the effort, but there has to be something out there if you wanted to try. Didn't GM/Isuzu offer a sub 2 litre displacement turbo motor a few years back? That might get you close. If you're buying new, a pair of T025s would be an expensive but viable experiment.

All in all you'd still be better off with a large trimmed T03 or small trimmed T04 for most US Ford I6 applications.

 

[Lazy JW]

I saw the cutest little turbo on a Kubota industrial diesel engine that was powering a portable sawmill. The engine was about 45 hp so must have been in the 1.5-2.0 liter class. I have no idea what the rating of the turbo was, as I am pretty much turbo illiterate. I wonder what the availability of those would be?
Joe

 

[Anonymous]

So pretty much the advantages would be canceled out by the complexity? Right? Or, ou could get the same advantages another way? I am not asking because I am planning on trying this stuff, even though I would love to if I had a few thousands dollars I could waste on it, just because I am wondering what is available. What are the options and so forth. And to learn more about turbos. That is really why I am here, to learn. I don't have the money to even do some the most basic stuff. College is a very financially draining undertaking

 

[Anonymous]

...I would love to if I had a few thousands dollars I could waste on it...

A few thousand dollars? I have a grand total of $150 in my LP/Turbo project so far. $105 for the LPG setup, plus $45 for the turbo. I anticipate needed to spend about $25 for piping, $60 for a turbo rebuild kit, plus a vehicle propane tank (about $100 for a used one).