I am building a twin turbo setup for my 1991 z28. I was planning on using 2 T3 volvo turbo's since my buddy is big into the volvos and has extra ones. But I just found a t3/t4 for $300. Would there be any problems with running the two different sized turbos? I figure that the exhaust wouldn't care, but wasn't sure if there was anything that I am missing otherwise. Thanks, Jimmy

 

Don't do it as a parallel setup, everything needs to be matched properly that way. You'd have more backpressure on one bank, and turbos fighting each other to try to make the same flow at the same pressure, which won't happen.

You could run a sequential twin setup like that, but it isn't worth all the extra hassle and headaches. I'd say just find another identical turbo if you want to do twins.

 

would be VERY hard, if not impossible to tune. Bank for bank the motor would be running different due to the differently sized turbos. Exhaust temp/flow would be different on each bank. Could also cause premature wear on the motor. If someone has done it, please chime in and correct me if I'm wrong, but every one I know running TT"s says don't do it.

 

To answer the question, I would defenitely suggest using two turbos of the same size.

However, along these same lines, Saab has built a Turbo V6 that drives the turbo with only the front bank of cylinders (in other words the exhaust from only three cylinders drives the turbine, but all 6 get the boost). They called it assymetrical turbocharging and really bragged it up as being both powerful and very responsive. I don't agree with the idea, but it obviousely worked well for them to use it in a production vehicle.

 

Cool-- that is what I needed to know, so I will plan on running two of the same turbo's. Any thoughts as to if the Volvo T3's will be "good" enough? I have a fairly stock motor with a mild cam, so I only plan on running like 6 psi for now untill I can re-build the motor

 

What are the specs on the Volvo turbos? I ran the Volvo T3s with 50 trim compressors (.42 A/R) and a .48A/R turbine. These were small for my 350, but I got a few mid 12 second runs with them. 12.46 at 113 was my best ET (hot air on drag radilas), and 12.8 at 117 was my best trap speed (street tires and cold air).

If the turbos you are thinking of buying are the same as my original turbos, expect them to restrict your top end HP potential, but they will offer excellent response. My car put down 328RWHP and 467 RWTQ using the smallish Volvo T3s. IIRC, the peaks were at 4200 and 3400rpms, respectively. Bigger turbos would probably net you higher HP numbers and little or no loss of peak torque. Thats why my car now has T3/T4 hybrid turbos

Maybe your Volvo buddy can get you larger turbos than what I was running.

Also, the Volvo turbos I used had different turbine inlet flanges than a standard T3 (a regular T3 flange may not work).

EDIT- all the above #s were at 6psi on an otherwise stock L98.

 

I would use two of the Volvo turbos if you can get them at a fair price.

Are those Volvo turbos really 50 trim. All of the info I have found point to them saying that they are 40 or 45 trim. Is that 50 trim what you measured? Do you have a link to a site saying 50 trim?
I am curious because they look exactly like the SAAB turbos that I have. You wouldn't happen to remember what the compressor inducer size was? (34mm or 40mm)

The shape of the Volvo turbo inlet looks T3ish. Is it smaller or larger than a T3 flange. From your pics it looks like the turbo flange is drilled & tapped. Is that factory?

 

For the longest time I thought my original turbos on my TT IROC were 45 tirms. I ended up selling one of them on eBay. The other went on my, then I sold it to a local friend when I upgarded the Z24 to the T3/T4 hybrid turbo. My buddies engine was low on oil pressure, so we soon took the turbo to our local turbo shop. He pointed out to me right away that it was not a 45 trim like I had thought, but a 50 trim T3. He measured it right in front of me just to be sure, and showed me the specs. He was right, and I was wrong (no suprise there- he really knows his stuff).

SO I guess the 50 trim Volvo T3s are out there. I know for sure that my turbo was a Volvo unit because of the odd turbine inlet flange.

 

You can run them in series and get an excellent result. This has been done on turbo RX7's and Supra's. The smaller turbo spools up quickly and gets boost pressure and rpm's up quickly, which in turn then gets the larger turbo spooling faster and allows it to push more cfm's and higher boost levels if you want. It is actually a good setup. The only problem is find room to run both of them off the same line coming from both headers. You would have to run them around where the catalytic converter is right after the Y-pipe. I think you would have to make a custom shield to keep water from the road from splashing up and cracking the super hot turbine sections.

 

But doesn't the fact that they are inline engines make the idea of runnnig them in series a better one ? what may be good for an inline isn't for a V config ? Just wondering.

 

While the Supra and RX7 are "sequential" turbochargers they're not what you're thinking about. They use valves in the inlet/exhaust tract to cause one turbo to spool, then at a certain RPM they "pre spool" the second turbo by opening the valve partly, and after a certain time they open the valves fully. Really complex setup, why more then a few people switch em to singles, or re-work the system to make them true paralell turbochargers. If the sizes of both turbos are small, it's dubious that they'll work well in series.

 

It is two turbos in parallel with the ability to "turn one off". I had the same idea of running two Holset HX40's on a v8 that way. The only difference is that the V8 needs a crossover pipe to feed one of the turbos. It requires three valves: One vavle on the crossover, one valve on one of the turbo outlets, and one valve on one of the turbo compressor outlets.

I figured that this would allow a decent spool time and a very good amount of top end. I have up on the idea because of the ECM control to open and close the valves. I was worried about spinning the additional turbo backwards sometimes from the compressor end.

Anyway, that pic is a parallel setup. Do those imports mentioned use the setup from the diagram you posted? I don't understand what you mean by "pre spool". There is no such thing as pre spool unless you have an addition power source spinning the wheels.

EDIT - removed first line because it was incorrect

 

I was not reffering to stock setups. I have seen this done in person on more than on car. I've even seen it done on an Audi S4 with a traditional style turbo up front, and a squires setup out back. In series simply means that a single exhaust line runs both turbos. It cause a full equalization of back pressure just like a muffler or cat.

Yes it works just fine on a V style engine whether it be 6, 8, 10, or 12 cylinders. It's really a simple setup. A similar theory is applied if using a single turbo, by running a shot of nitrous at take off and then cutting it off with a pressure switch when the turbo reaches nominal boost levels. The only thing better about the nitrous setup is the fact it cools the intake air charge until the turbo is spooled and the fact there is absolutely no turbo lag whatsoever.

I'll see if I can find a photo somewhere or at least draw up something for you to look at.

 

to use one turbo to spool another is fine, but you would still need one turbo large enough to feed the motor on its own. - the best pic of this is in Summit/Jegs. Check out the TT kit for the Cummins(Dodge) diesel.

I would agree on simply finding two same sized turbos for the poster's (jimmysauter) intentions.

 

Again, it is not a series setup. It is a parallel setup. You just described a parallel setup and then called it series. Notice how the turbo sit next to each other (parellel) and not one turbo outlet feeding another turno inlet (series).

The only stock turbo engines I have looked at are diesel 6 to 18 wheelers. Are you saying that no factory cars did that setup you posted? Your post implied that the rx7 and supra had a twin parallel setup. Did they?

Yeah, in theory everything is simple. Run two parallel turbos or maybe a nitrous oxided booster shot. Spray it a little too long and boom. Not get the gate opening and closings right and after while a wheel flies off from a broken shaft. You need to be VERY careful about surging the "extra" turbo. It will take some time, but have it wrong and it will break. How many miles are on the setups that you saw? Not saying it can't be done reliable. For me, it required more effort than I thought it was worth. My clunky drivetrain can barely handle tiny turbos.

The only way I see it working is computer controlled via the stock ECM or a AVR-Risc or PIC with a simple solenoid driver PCB. Overall, I decided it was kind of a waste of time and resources for me because how much HP do I really need on the street.

It does bring up something I have been interested in. What are the exhaust & compressor valves made out of. I want to build my own wastegate for a Holset I have that needs an external wastegate. I need to look into expansion rates for materials & bushings (sintered). What do you think.....stainless & sintered bronze??

 

Yes, I would use two of the same size turbos.

True, you could use two different sizes and set them up like the pic posted above. You better know what you are doing going that route. The second turbo would have the effect as vaccuum secondaries have on a carb. I think there is maybe one or two people that I have come across that could make the that setup properly. I have come across hundreds that could make that setup half-*ss (although they would think it is right). The one thing that helps is the exhaust to intake pressure bias.
You could also use a huge turbo and mess with gating the turbo inlet (JY-homemade variable A/R) to get somewhat of the same effect as the pic that was posted

Point is this. If you are asking a question about using two different sizes then that means you don't know much about turbos. So keep it simple and use two of the same size.

 

I agree that for what he's doing two of the same sized turbos would be the best for his setup. However using 2 turbos in series is ideal when running very high horsepower and extreme boost levels. This comes into play in engines that are utilizing turbos producing 20lbs or more of boost with the main large turbo and the smaller turbo will typically produce about half that.

This is how a series turbo is to be setup

 

How do you keep the small turbo's small exhaust housing from restricting top end HP?

I'm not seeing an advantage to the above turbo system. The compressors aren't even staged to increase the PR. Or do you believe that because the small turbo is putting out 6psi and the big one is putting out 14psi that the intake manifold pressure will be 20psi?

I've seen many staged turbo systems, as many as four seperate stages producing intake manifold pressures over 200psi (not in automobiles though, tractor pulling), but still I'm not seeing the advantages of that system. I want to see pics of the real thing. And timeslips.

I have an open mind though- I drive a remote mount turboed Z24 to work everyday

Also keep in mind that we aren't dealing with import weeny motors here. We can make 1000hp with 20psi of boost with our small block V8s. Most turbos are happy producing 30psi or more within their airflow range in a single stage.

 

That documentation is from http://www.mkiv.com/, and is a factory manual. If you type 2JZ-GTE into a search engine you should probably get back some interesting results.

What is meant by "pre spooling is that the exhaust valve is opened on the second turbocharger so that it's not at a dead stop when the air outlet is opened, and potentially do a lot of damage to the second turbocharger due to surge. In a configuration like this, the second turbo usually is the one that pukes anyways, because it's still stressful to it.

Sequence means that one achieves an active state after the other does. Albeit this is not the conventional "series" turbocharger system people think of as sequential, it is indeed sequential. click here and read pages 85-89 or so, most notably page 88.

 

I grew up building small **** rockets. My last car was a 96 mazda mx-6 with a 2.5 v6 (a.k.a. ford probe gt) I will readily admit that I don't know everything about turbos and especially not on small blocks. The diagram was crude and thrown together in a few minutes. Yes the system would have to have a bypass system inline between the turbos and no I'm not saying 6psi from turbo a plus 14 from the next equals 20. I'm not a retard over here. The setup would still be considered seqential yes. But what makes it in series is the way the exhaust runs directly from one to another. It's similar to saying your running two batteries in series versus parrallel.

I was also told by a friend of mine tonight that it is only done in extremely high boost applications. Were talking 50psi or more. It's a situation where the first turbo is so big that it takes way to long to spool so a smaller turbo (not sure how much smaller) is almost required to get the engine up to use the huge turbo. I will try very hard this week to get some photos or get in touch with some one who has this setup. I would assume that since it's such a high boost level that it would only be used on smaller engines since if you could get your 350 tuned to handle that kind of pressure that your hp levels would be f***ing rediculous.


Another thing that has bothered me in this discussion is nowhere have I seen the mention of cfm flow. I would think anyone talking about performance would understand this. Just saying 20 psi doesn't mean jack. I could push 660cfm at 10psi out of a T22 or 1000cfm out of a T4 at the same pressure (not actual numbers obviously). A T4 takes much longer to spool than a T22 comparatively.

 

Okay got a couple things backwards.

1. The placement of either size turbo doesn't matter
2. Their is a bypass system so the drawing I made is sh*t
3. They both feed off the same line but have seperate oulets that usually meet after the second turbo and then into a muffler/cat
4. The way it was explained to me each turbo has it's own bov allowing a valve to close and hence seperating the air flow from each turbo. One is basically dumping until whatever system tells the valve to change positions and then starts dumping the other turbo. After hearing this I have no care to even talk about a system that is so wasting.

Yes it's true series and sequential. Yes it is stupid. I don't know who came up with this. I have seen it though, in person on an audi. I had no clue at the time what was going on though. Sounds crazy but whatever. A small block chevy doesn't need that kind stupidness. Might as well say "I need nos, 2 bottles, the big ones, and I need it by tonight!" Just get 2 small matching turbos, run around 10-15psi, run one off each manifold and be done with it.

 

I don't know where to begin. New ideas are always good. No one said you are retarded. No one really knows everything about turbo dynamics along with engine dynamics. The first non-colored drawing is not-series, but it is sequential. Series and sequential are not the same thing. Sequential is a followed order of doing things in a timely manner. Series is a matter on connection. The colored pic is like connecting two batteries in series. The non-colored drawing is like connecting them in parallel with a switch to disable one battery.

Yes, the sequential setup work work. That is what I wanted to do with the two Holsets. Designing the control mechanism for the actuator/valves takes a fair amount of work. Large engines can handle boost just as well as small engines. It is a matter of money.

The original thread said nothing about boost and CFM. Yes, boost is meaningless. CFM, efficieny, and wheel speed are what matters.

 

1) yes, the colored picture is not the same as the non-colored one. The colored one is not a good setup.
2) There isn't/shouldn't be a bypass system in the colored pic.
3) not sure what you are saying
4) yes, that is a sequential (not-series) system. It is not wasteful, it is usefull.

No, not both series and sequential. No, not stupid. Yes, a small block can use this. The first turbo is active and spools down low. When enough exhaust is flowing the second one is activated producing more HP. NOS??? that is why they have two stage (sequential) and progressive controllers. If you get two small matching turbos (HP limited) they will spool fast. Run two T70 sequential and it will spool fast and easily make over 1200+ HP along with being streetable.

Don't take all this as against what you are saying. You brought up a good topic. I was thinking about doing a sequential setup and didn't realize some factory cars already had it.

 

Yes, the sequential setup work work. That is what I wanted to do with the two Holsets. Designing the control mechanism for the actuator/valves takes a fair amount of work. Large engines can handle boost just as well as small engines. It is a matter of money.

Do you work well with computers and software? If so I can get you on the right track towards a microcontroller based solution. It's cheaper then ever to work with them, you can get started for under $50 learning how to work with them.

 

I mess with electronics stuff/software a little bit. I use Atmel AVR chips and GNU GCC for writing the code for the AVR. I use pcbexpress sometimes for the printed circuit boards. I like the AVR for the car stuff because of the temperature grades, cost, and free software (GCC & Emacs).
I am kind of stuck on the AVR chips. It would take a lot to get me to change, but I am open to it. What chip/manufacturer did you have in mind?

This looks to be a completely hi-jacked thread now.

 

Yes, we have officially hijacked. I usually work with PICs but have some work on "white bread" 8051s, I was just thinking that implementation with one would be pretty easy with the PICs, I think the Atmels have built in ADCs too though. I was thinking something along the lines of 2 MPX4250D MAPs, an LCD screen for the output and a few rotary encoders. A few of the problems IMO would be the variance in spooling rate from combo to combo. My thought for the bypass consists of using an exhaust brake from a big truck, I think they were OEM on some powerstrokes.

 

I plan on doing a standard parallel system for ease, and cost reasons, so I probably will just stick to twin turbo's of the same size (I think I will do Volvo T3's for now since I can get them cheap, then upgrade to the T3/T4's

 

Good choice with the same Volvo T3 units. It might be worth looking at the Master Power T3 ro T4/T3 hybrids. I think forcedinduction.com and B&G turbo sells them. They might be worth it if you have T3 that need to a rebuild and you can't do it yourself.

 

I like the AVR because of the one clock cycle per instruction. It gives know timing and runs at the full clock rate. The PIC (RISC) and 8051 (CISC) don't run at the full clock rate and end up being slower than the AVR.

GCC is a great universal compiler,linker, assembler and the AVR support is rather mature now. Plus I know how to code things to make the compiler/assembler create the assembly/bin that I want. It makes for easy to read code (C) and the assembly that I want in the end.
I was going to make a couple of steel boxes that had valves in them much like a stock internal wastegete setup. The actuators would be a couple of push/pull solenoids.

The valve leakage of the compressor valve seemed like a problem if it wasn't quite right. It would want to turn the turbo backwards.......but at the same time the exhaust valve and exhaust pressure would want to turn it slightly in the correct direction. The shaft would always be "loaded".
I wanted to toy around with the setup but put it to the side. I might mess with it this summer. I am too busy now learning how to make intercoolers & TIG welding.

 

Ahh, sounds to me like you're wanting to do more of a setup that the Supras/RX7s had, at least on the cold side. Looking into parts from someone that went to a single may be a good thing to do. I was thinking a series turbo system with a bypass for the small turbocharger's exhaust.

 

I wasn't trying to make you out as a retard. I didn't see how your diagram would work, and so I was starting to wonder What really cleared thing up was that you stated this system is used in extremely high boost situations (50+psi). This makes the whole idea take on a different meaning, and I can clearly see why you would need to do something like this. When you made mention of 20psi, I thought man you where crazy building a system like this for such a low pressure ratio (no matter what the airflow/cfm requirement, you don't need to stage the turbos for only 20psi of boost).

 

Both the non-colored and colored pics have the cold side setup in a parrallel fashion. This will make more volume for a fixed PSI. The cold side is the same as any generic twin setup........more volume, not more PSI. Both pics will give normal boost PSI.

The colored pic has the turbine connected in series and would look to the engine like a tiny turbine A/R. Very high back pressures and overall a bad connection.
The non-colored pic has the the turbine connected in parallel and would look to the engine like a huge turbine A/R. This setup has the ability to "turn off" one of the turbos to make the turbine A/R reasonable for spooling.

In general, the colored pic should not be done. The non-colored is a good setup if you know how to control it properly.

The only way I know of making very large PSI values is to "boost the boost" and that is done connecting the compressor (cold side) is series. Both of the pics do not do this.