So I had an interesting idea for a compound turbo and wanted to see what you thought about it. I have a 95gst completely stock, with a t25. And I was wondering what you thought about a3 turbo compound setup? Highly aggressive cams(280) stroked to 100 bored over.040 with single or double stacked metal head gaskets and highly aggressive auto trans setup, run the t25 to a 20g then to a hk40. Does this seem plausible or am I just thinking crazy?

Yeah your crazy. Compound turbo's are generally so that you run exteremely high boost pressure, or to mazimize powerband. I don't think you have a good selection of turbo's for that. Your going to want to double or more your cfm capability between stages I'd suggest like a T25, 50trim/HX35, then like an HX60. You'll have to run them all at a low pressure ratio.

You'd be better off with a 2 stage like a 16g, and a HX60

Well you see I came up with that idea after seeing that one of the moderators had run 47psi with a normal compound setup and I was trying to push it even further to as high as 60psi. I was thinking of changing the t25 to a t28 and waste gate the t25 and 16g to equal up to 35 then the hx40 at 25psi

Eventually you'll get to a point where you can't keep anything together from trying to run that much boost. There's guys that can't keep a 16g car at 20psi together....

While pauls compound setup was neat, it was a lot of pissing around for less performance than a decent modern turbo would do. Maybe it would be better if he didn't have an ancient 60-1 P trim in there. but it's a lot of pissing around for little gains.

Probably the best example of it was kevin jewer on his rwd 1g, but even he abaondoned it and went faster without.

edit, for 60psi, 2 stages is more than enough. I don't know what the compressor map for a T25 looks like, but I'd guess it has peak efficiency at around a 2:1 pressure ratio, and a HX52/60 anything big has peak efficiency in the 2.5-3:1 or even higher pressure ratio. That's a total of 5-6:1 pressure ratio. that's 60-75psi of boost and your still in the peak efficiency, if you pick the right compressors and get the mass flow right.

Just the logistics of running the exhaust to each turbo, oil lines, etc should be enough to make you not want to do it. Unless you were building a no NO2 car to compete in DSE, it's just not worth it. You better hardblock your bottom end if you want to run anything near 60psi...especially at .040 over. With that being said, if you still want to do it then go for it!

Well I don't want any no2 because I am planning on racing it and rather then changing the entire exhaust system I was going to pipe it like it was shown in a picture that I believed Paul posted of a Cummins diesel engine and it was piped like this on exhaust Exhaust from engine to small turbo. Outlet from small turbo to exhaust inlet on big turbo. Outlet from big turbo to muffler system. And like this on intake Exhaust from engine to small turbo. Outlet from small turbo to exhaust inlet on big turbo. Outlet from big turbo to muffler system. Just add in one more turbo to the equation

Alyster said:

So I had an interesting idea for a compound turbo and wanted to see what you thought about it. I have a 95gst completely stock, with a t25. And I was wondering what you thought about a3 turbo compound setup? Highly aggressive cams(280) stroked to 100 bored over.040 with single or double stacked metal head gaskets and highly aggressive auto trans setup, run the t25 to a 20g then to a hk40. Does this seem plausible or am I just thinking crazy?

Click to expand...

This has kinda been my plan all along for next year with my new built engine and transmission. With my mid mount FP Red HTA a BW SX475 right next to it there will be plenty of room.
My car as of now.
http://www.dsmtuners.com/threads/91-awd-black-cherry-talon-turbo-compound.490729/

Alyster said:

Exhaust from engine to small turbo. Outlet from small turbo to exhaust inlet on big turbo. Outlet from big turbo to muffler system.

Click to expand...

The biggest problem you have here is that you lack the understanding of how compounds work.

The whole idea is to put the largest turbo before the smaller one(s). This is the reason you read on diesel forums people describing their setups as say "S467 over HX35".

The larger turbo is physically over the smaller one. It's the amount of air that moves from the larger turbo that spools the smaller turbo so quickly. Since they are connected the entire system or setup works quickly. Spooling quick and making more boost.

Read the thread that has the picture you were speaking of.

You may just be misreading what he wrote unless he is writing something different than he is thinking he's right on. The exhaust goes to the minor turbo first then spins the turbine of the major. The intake comes through the major and its' compressor goes into the intake of the minor who's compressor then goes to the engine.

In essence, the minor turbo is "pulling" through the major and because the major is already compressing the air to a 2:1 or more pressure ratio, the minor's 1.5-2.5:1's ratio gets multiplied to around 4:1. It doesn't have to do with spooling up the larger quicker to rely on it's boost, thats a sequential system like on an RX7.

The goal of a compound setup is a wide powerband that can achieve a higher pressure ratio than the quick spooling small turbo could achieve on its own, it doesn't really rely on the large turbo to do a ton of work.

DSM in MN is right I looked wrong sorry I was on 40 hours of no sleep when I took my notes.. It goes exhaust to small turbo then big turbo then muffler and intake goes air filter to big turbo big turbo to small turbo then to intake

You're on step 20 when you should be on step 1. You have a completely stock car. What is your modding experience? What is the goal? What is the purpose of the car?

Agreed with Pauleyman

And, No need for 3 turbos.
I street drive a compound setup, 14b and hx35. The boost can get away on you fairly quickly if you are not attentive.

When side by side with another dsm similar framed turbo to my hx35, same boost. I will slowly pull about a car length while spooling, then hit full boost jetting forward about another length until he hits full boost.

It is hard enough controlling the boost on 2 turbo's, not to mention 3.
And I'm not even going to get into the space limitations in a 2g.

One of the biggest challenges is building the system to allow for maintenance.

Good luck, if you are actually capable.

The person that is helping me on the engine used to build and race with Keith black. And even though you say I'm on strip 20 and need to be on step one I am working on step one and up with all maintenance and ordering parts for the build. 100mm crank 156mm I been rods still haven't decided on pistons but chromemolley rings 280 cams 2mm oversized valves new springs seats arms pulleys everything but I have to know what I'm doing first before I just order.. And if I have to I'll cut a hole in the hood and put a breather slot to make them fit. And as far as accessibility I'm building this to race not as a DD so I'll just pull the damn engine if I need to maintenance it

Are we talking about building an engine now, or a compound setup?

Sounds like you want to build a monster race car, like every other boy racer with a dsm. You haven't said what kind of race you even want to do....

I assume drag?
In that case put on one single turbo for your goals.

Crazy talk, adding two more turbos that will not even have a chance to do their job as a compound setup(wide powerband).

bastarddsm said:

Probably the best example of it was kevin jewer on his rwd 1g, but even he abaondoned it and went faster without.

Click to expand...

This is generally true, but it wasn't compounds that was slowing me down, that's for sure. The car was just slow in general. The best pass on compounds was 8.80 at ~156, and to that point I had never been quicker on a single. Oddly, it was when I then went to a 16g that the car got fast. The changes I made on that turbo rippled down through the following turbos. During that time I made huge gains in chassis setup as well. That didn't happen until the car was already in the 7s. In hindsight, I would expect my initial compound turbo setup to run in the low 8s on my car right now. That's an old school T3 50 trim and off the shelf S475.

Additionally, the compound turbo 2g I worked on earlier this season went 5.99 at 117 at ~36 psi. The car made power with ease and made a shitload of passes. 60 foots in the mid 1.30s with no nitrous leaving at 37 psi and 3700 rpm. 36-37 psi down track as well, on a 60 psi capable setup. I really do not see any way the compound turbos were hurting performance here.

On top of all that, I'm back on compounds again this year on my car, which should say it all. I'm at a point where even with nitrous I can't leave hard enough with a 4 banger and 2 speed auto trans. And I have a lot of things I want to try. I've learned a lot since that first attempt at this in 2009. And there is still a lot to learn on SI compound turbo applications. I work with people all over the world building and racing compound setups, and more and more keep popping up. ~2500 hp V8 setups have been built as well. It's just a matter of time.

Alyster said:

DSM in MN is right I looked wrong sorry I was on 40 hours of no sleep when I took my notes.. It goes exhaust to small turbo then big turbo then muffler and intake goes air filter to big turbo big turbo to small turbo then to intake

Click to expand...

Engine, large turbo, small turbo, exits vehicle.

Small turbine is always first, but I believe it's possible to run it the other way around. On the compressor, there's no choice. Big one first, then small second.

Wow 2mm oversized valves and new springs seats arms pulleys? Should run good with nothing tuning it

Lol obviously it's getting tuned at a dyno shop with ecmlink