[Stian]

After strugling to register I'm here (kpa or bar did not get aproved for meshuring boost) and looking to broaden my knowledge a litle.
I have been playing with a turbo project for 10years with newer finish. 2L engine was replaced by a 2,2 then got a 2,4 crank for free, got a injection system so the carb was dropped, decided to go for a emerald EFI rather that the stock Bosh unit and so on.

I have been playing with a idea about compound turbos for just as long and now it look like I will get my hands on a 1978 jaguar xjs with a v12 and why not trow a few turbos on it.
Was thinking about a bi turbo setup where the exhaust from both turbos where collected in one pipe and blown trough the turbine of a second larger turbo.
I would save 1 turbo and have the advantage of quick spooling twin turbos so total 3 turbos.

The larger turbo could blow trough a custom intercooler with two outlets (one for each smaller turbo)
I would think that the best regarding spool time is turbos that deliver just the mass of air required by the engine to produce it's stock hp so they will get going as soon as posible and then pick the other to deliver the mass of air needed to produce target hp.

Would love to hear anyone having a good answer to how to pick just the right size.

Regards
Stian

[Robert]

Bone head me

[Stian]

Originally Posted by Robert

Typically compound turbos means you run one small unit off the motor with the compressor outlet (cold side) blowing into the compressor inlet of a larger unit also running of the motor.

??? All the units I have seen have the larger unit blowing into the smaler unit.
A picture say more than a 1000 word they say.

[Robert]

Originally Posted by Stian

??? All the units I have seen have the larger unit blowing into the smaler unit.
A picture say more than a 1000 word they say.

My bad you are correct. I was doing ten things at once when I replied and typo'd please disregard that post. My confusion was (again I wasn't concentrating as I should have been) related to the set up on the jag. Most compound units I've played with have one large blowing into one small or a turbo blowing into a roots blower. Back to what I should have been saying, my concern with the set up is the piping and turbine of the large unit. With the twins on either side it's going to be a little difficult to get the exhaust gas energy efficiently routed to the turbine on the large unit and of course would need a pair of wastegates to cut over to the large one when the boost hits the right pressure. It can be done but I think the piping will be a challenge. For compound units I would give the sales guys a call so they can work the numbers with the engineers and get the right wheel sizes for you. 805-581-0333

[Stian]

I was first thinking about 4 turbos, but was thinking about some cost saving.
If no one else have tryed it I think it would be worth the effort to just see if it can be done.
Also played with the idea to set up the two smal ones as a sequensial setup for even more low end power.

What I wanted to know is how smal turbos I could go for.
I would asume I would need to pick turbos where the larger one start to flow when the smaler one start reach the end of it's capasety.
I'm noot looking to make moster power, but just have a system with minimal lag.

[Stian]

Originally Posted by Robert

Most compound units I've played with have one large blowing into one small or a turbo blowing into a roots blower.

I once had some thougths about this and I reversed it in the end so that a roots blower would deliver the mass of air to the engine.
Roots blowers take power from the crank witch is not so good for mecanical efficensy so using a turbo as the second step would take the load off the roots as delta P would decrease and once the tubo working on full boost it would not be litle load and loss on the roots. Was a idea I newer had time to folow trough and I doubt it would be worth the effort.

For this Jag project I'm wondering how small the HP turbo can be. I want boost as quick as posible and would like to pick some turbos that flow just enough to supply the required air for the engine and thet the LP turbine deliver the performance increasement.
How would I pick matching turbos? Would be interested in some theory here.
I have the formulas to calculate the heat and boost in sutc a system, but not how to pick the turbos.
Would I use a HP turbo that is at the edge of it's flow capasety and a LP turbo that is delivering the same flow at this given situation or???