Let's Talk dual turbo

[moberle]

I jumped into a thread on the NG cars so I thought I'd dig up some bones over here to

I have been considering a dual turbo setup. I am thinking of a sequential configuration on the order of the Porsches of the past.

I am reasonably pleased with the basic behavior above 2500 RPM but the low end bores me to tears. So I want to fix that by using a second, smaller unit in parallel to the primary. Then reconfig the primary to produce more volume for higher RPM behavior.

I'd like to hear some opinions from you folks on the subject or if anyone has already done this.

[Eric van Spelde]

You sure you want to swap transmissions after every drive?

[Alex]

Adding another turbo is going to get very complicated in terms of exhaust manifolds, space for both turbos, intercooler piping etc.

You could probably get most of the gains you are looking for going for a fully mapped ignition timing system, and a single responsive turbo. Would almost certainly end up considerably cheaper and less complicated as well.

[NLspiked02]

i know the feeling of the low end sucks. but i swapped my T3 off for a TD-05 and wow is it better on low end. the car comes to life at about 1800-2000 rpms and then im gone. i think it would be a cool idea and different to run 2 tubos but i think it would be more of a head ach than it would be to get your 1 turbo set up to run correctly.

later
dave

[moberle]

I am not really looking for more overall HP, although a little more would be nice.

I expect that the plumbing would be the most difficult piece.

What part of the gearbox grenades under high hp/torque conditions ?

[Carl Hernandez]

sounds like a good idea but i agree, it would be really complex.
you might want to look into the 'disco potato' turbo made by garrett.
its used on project silvia in sport compact car but has good spool up and was used on a simmilar engine (DOCH,2.0l turbo).
said to produce 2psi boost at 1000 rpm and full boost by 2.5k-3k.
might be worth looking into for the boost crazy.

[MillerTime]

The amount of money, fabriction, and labor needed to do a twin turbo set up could be better spent elsewhere. You're going need a custom fab'd manifold, along with oil and water lines for both.

Then you're going to have to deal with getting both to run right. Making a squential set up isn't as simple as just bolting one turbo right after the other. Then there is what to do about the apc and keeping things stoic.

For less money you could buy a GT series ball bearing Garrett turbo and accomplish more or less what you want.

Ultimately you're going to have to accept the fact that you drive a low displacement turbo car. Lag is something you're going to have to live with if you want a high boost punch.

[saab90089]

Yes, i agree..........interesting as it would be, not worth the headache. You can get more then you need with a single TD-04 or TD-05 turbo correctly tuned.

I know even the TT supra's and Rx7's were neat, but if things ever got out of step, it got complex to figure out and fast.

Ian

[moberle]

Interesting being the operative word.

I admit that I have not studied Saabs in depth. I am familiar with supercharging. I am not particularly interested in a high end punch. I am more interested in low end response.

A smaller unit would spool quicker and alleviate that but flatten its delivery too soon.

A larger unit spools more slowly and delivers more on the top end.

I haven't seen a variable pitch unit small enough to be driven by a 2.0l motor. Maybe I'll dump the turbo and go to a blower.

[Alex]

Getting a good spread of power from the turbo requires careful matching of the unit to the car and choosing an efficient compressor wheel.

Brads 16G hybrid using a Mitsubishi TE-05 comes on boost around 2000rpm, with full boost at 2700, yet uses a compressor that can flow enough air to make 350bhp in the right application.

The Garrett T series turbos (T3,T4 etc) use compressor designs that originate from around 40years ago. Compressor design has come on along way since then.

[GearHead]

Originally Posted by moberle

Maybe I'll dump the turbo and go to a blower.

why not put a hugh turbo on then the supercharger...

[EastsideCustoms]

I think we could all argue one way or the other, although i have to say a turbo and super charged car would be amazing if its name was a saab.i honestly dont think the twin turbo issue would be that difficult if you keep a few things in mind: you would be in the dark most of the time and its all customized. This just means more satisfaction when you prove them all wrong. Throw the battery in the boot, or under a seat and move the airbox and intercooler and you will have room if you can fish the piping out. i say do it!

[moberle]

Thanks Eastside.

I am working on a turbo bike project now. When that is done I'll know a bit more about what I'll do with the 900.

[nickliv]

Change down?

[Marrk]

I haven't seen a variable pitch unit small enough to be driven by a 2.0l motor

I have a Hybrid T28 Garrett turbo with variable pitch vanes and asked the question on how it would perform....this is the response I got back from a well known tuner in the States....
Variable vane turbo a quite interesting to drive. They make so much boost early and do not suffer from high back pressure. Back in the early 80's we worked with Aerocharge for applications on SAAB's. The Aerocharge has the vanes on the exhaust side and the bearings are ball bearing mounted in the inlet side of the turbo. When we started we were using prototype units. While there were problem with them at the time most of the issues have been resolved. We had developed kits for the 8V and 16V turbos having patterns made for casting exhaust elbows to adapt the Aerocharge to the stock exhaust system. The first benifit was being able to make full boost before 1800rpm in an 8v automatic. We performed a lot of tests, the most interesting was comparing exhaust manifold back pressure to boost. On an 8V with stock exhaust back pressure would never exceed boost. On a stock car of the time a 5000rpm back pressure would be three times boost so at 7psi boost back pressure was 21psi, not good for power.
Most of the problems with the Aerocharge have now been solved the only current reason I do not have one on a car is they do not make the larger size at this time. The smaller unit will not flow enough air for my use.
A year or so ago we got one of the old ones out and put it on a 1986 900 16V NA automatic and made a 13.9sec run in the 1/4. This car would make all the boost we wanted at the line. We limited make boost to 8psi. At 8psi the torque converted that is a 1800rpm stall unit would stall at 3000rpm. A large increase in launch power.
As for the unit pictured further down the post the vane design is very simulair but not as many.
If the turbo you have is made to with stand 1900F and the compressor map is of the correct size you will be happy.

[Saab-Daniel]

Marrk, do tell more, are you planing such a turbo for your car?
Daniel.

[moberle]

Originally Posted by nickliv

Change down?

Nope. The 900 runs just fine and is reliable. The bike (Yamaha XJ650 turbo) is a new acquisition and is getting all the attention right now.

[Marrk]

Marrk, do tell more, are you planing such a turbo for your car?
Daniel.

I purchased a Hybrid T28 Garrett turbo with variable pitch vanes for my soon to be assembled modified 2.3+ motor (1991 Carlsson). I've had the crank knife edged, lightened and polished, block has been bored out to 90.8mm to fit machined Cosworth pistons, head rebuilt and ported for fast road/race. Inlet manifold ports matched to suit. Block mig wired, flywheel ultra lightened, rods dressed polished and stress relieved.
It doesn't require a wastegate as the boost is controlled by the pitch of the vanes. It keeps the rapid spool up of a smaller turbo with the ability to supply a adequate supply at top end, so in theory I get the best of both worlds, low down torque and top end power.

The motors built now just need to fit all the ancillaries back on and sort out the turbo, its only oil cooled thus some pipe mods and also exhaust mods need to be done also.
I have a goal of 350 hp, might even try at the wheels too....yes I know about the gearbox and the fwd, it'll be a nice to have....if I get it!

[Swedey]

half off topic...

About them BB turbos. To what extent do they improve spool up over an equally sized turbo? My T3 is on it's way out, i'm looking along the lines of a Garret GT25BB. Anyone know what kind of spool up you'd get on those compared to a T3?

[nefarious]

There was a Sierra Cossie in one of the last issues of CCC (penultimate I think) that ran a supercharger and turbo. I was only a short article and didn't go into much detail, but basically it used a magnetic clutch off a flymo to control the blower belt and a k-pipe with a butterfly on the intake side, both operated by the boost sensor.
The guy had geared the blower to be boosting the same as the trigger boost value, so the transition was nigh on seamless.
Looked like a pretty neat solution, as he was running 350+ brake, it would have been pretty laggy without.
I seem to remember him saying that the other upside is that the blower makes the turbo spool up faster (which I guess makes sense)