Compound turbo, thoughts?

[Billy1]

I think the only reason why you would want to go with a compound system is because the turbo is so big-it is becomes virtually un-driveable on the street i.e the turbo kicks in around 5k-like some big turbo Civics I see on the street. Street legal yes, but not daily driveable as any family sedan will walk them from a stoplight.

Compounds were tried in World Rally racing(WRC) years ago by Lancia. Now WRC uses a lot more modern turbo tech. along with anti-lag in all the cars, thus no need for a compound set up.

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[JerseyDevil]

ATM was talking about it, but nothing has come of it so far. Not sure if [MENTION=11871]JerseyDevil[/MENTION] has any new developments.

We have gotten done the tricky part of the development, i.e. Turbo placement and fabrication of the uppipe, converting the current battery box to be the air box etc. what we need more of is free time which appears to be in short order lately!

 

[Kjewer1]

I run a few compound turbo setups. I've run them into the low 8s in my Talon, low 9s in an AWD street talon, and I've helped design or tune at least 50 more around the world. There's a great thread on Yellowbullet in the turbo section that I started in 2010 on the subject, the best resource I know of on the entire internet, for anyone that would like to read about it in more detail.

In 2009 I ran a setup with a T3 50 trim and a BW S475 with the 96mm turbine and 1.32 T6 housing. Huge for a 2 liter, but it worked thanks to the 50 trim. I did this one cheap just to test the concept. It ran 8.80 at 156.

I went back to single turbo in 2012, but last year I took another shot at a compound setup, with better parts this time. Forced Performance T3 3582HTA as the small turbo (~700hp) and T4 4505HTA as the large turbo (~1200 hp). I had already run 7.90s on the 4505 as a single. I only made a handful of passes last year, but it easily went low 8s in testing. I've launched it as high as 55 psi, and it easily makes that on the brakes without nitrous, which is the whole point. There is also a lot of stuff going on with upstream injection, etc. Shaft speed sensors on both turbos, temp and pressure sensors everywhere, individual wideband sensors per cylinder, and so on. Compound turbo setups don't have to be this complicated, but they make good science projects.

Some pics of my new setup. I did all of the fab work myself.


















And a street class 2G auto AWD that runs low 9s at only 39 psi. It makes 40-42 psi at 3500 rpm, and is launched that way. Short times are limited in the tune to 1.35s to avoid breaking drivetrain parts. Turbos are a Forced Performance 71HTA (~500 hp) and a 4205HTA (~1150 hp). This car is set up to run ~55 psi, but it's not mine so I've kept it under 40.










At some point I'd like to build something for the Mustang too, but I'd like to enjoy it as it is for one more season I think.

 

[ypena02]

I was wondering what was taking you so long to chime in Kevin ;)

 

[Tune+]

I was wondering what was taking you so long to chime in Kevin ;)

Same - LOL

 

[perfweld]

Wow, That's some neat stuff Kevin !!!!

 

[mechanicboy]

Assuming you have all of the electronics to run the swap....

A compound build is more flair that functional IMO. The time spent getting it right and tuning it would be much greater than doing a proven build.

An EFR 7163 would be ideal. Quick spool, plenty of power up top to get you where you need to be. Other wise the PTE5558 is another smaller big turbo option to get you where you need to be.

But what about all that lag? Easy answer- Circle D torque converter. I added a 4K stall to my 5558 and the car went from sluggish pile of expensive parts to wicked beast. Off the line it would previously require a difficult to obtain foot brake stall or just patience as boost built. Now I can be sitting at a light and just mash the gas, the converter flashes, and the tire roast begins (at least on cold DR's on the street).

I really don't want a high stall converter. I want a be able to drive it anywhere, I don't like how high stall converters feel for DD.

ATM is doing a compound turbo setup that I will be tuning here shortly. I actually just tuned a supercharged and turbocharged Ecoboost the other day. Great results but a little too much boost down low for my taste but they understood the repercussions of such spool.

You can do it, but without a built motor you really aren't going to get the benefit that compound turbo setups generate.

That's thinking outside the box lol. I thought about adding a turbo to my truck to push it to 1k hp but the costs to get everything else up to snuff will far exceed what I will need to have this car done start to finish.

Building an engine in the future is not out of the question.

Maybe you just seen the wrong graphs? I make 30psi by 2900rpms and make 500whp, that is more than enough for a small displacement big turbo car.

Do you have that graph handy?

I think the only reason why you would want to go with a compound system is because the turbo is so big-it is becomes virtually un-driveable on the street i.e the turbo kicks in around 5k-like some big turbo Civics I see on the street. Street legal yes, but not daily driveable as any family sedan will walk them from a stoplight.

Compounds were tried in World Rally racing(WRC) years ago by Lancia. Now WRC uses a lot more modern turbo tech. along with anti-lag in all the cars, thus no need for a compound set up.

I'm not going to be using anti-lag or only using it for racing. As you said, it becomes less street drivable with a big turbo. By less drivable, I mean the rpms you'd normally turn for normal driving, under 2500, won't be in the engines power band.

I run a few compound turbo setups. I've run them into the low 8s in my Talon, low 9s in an AWD street talon, and I've helped design or tune at least 50 more around the world. There's a great thread on Yellowbullet in the turbo section that I started in 2010 on the subject, the best resource I know of on the entire internet, for anyone that would like to read about it in more detail.

At some point I'd like to build something for the Mustang too, but I'd like to enjoy it as it is for one more season I think.

That's some awesome! Any suggestions on turbo sizing for the second turbo if you did something like I'm looking into?

 

[Kjewer1]

I haven't really sat down and looked at LP turbo options for the stock turbo (since I still haven't decided what I even want to do with this car), but when I do I'll let you know what I come up with. I have an idea of what I think would work, but haven't done the math and don't want to steer you wrong. I've gotten pretty good at pairing turbos in the last few years. The YB thread has lots of good info that will get you started, but even that needs an update now. The compressor side is easy, size it for the power you want to make overall, at the low PR that it will inevitably run. The turbine is the tricky side, and where you have to really decide how you want the setup to behave.

I will throw the disclaimer out there that the vast majority of compound turbo setups people come up with don't work very well. You have to really want to mess around with this stuff if you're going to attempt it. If you just want to go fast, do it the easy way and have fun. If you're an engineering nerd, like spreadsheets, like staring at compressor and turbine maps until your eyes bleed, like math and thermodynamics, and like start trek, compound turbos might be for you.

 

[mechanicboy]

The turbine is the tricky side, and where you have to really decide how you want the setup to behave.

I will throw the disclaimer out there that the vast majority of compound turbo setups people come up with don't work very well. You have to really want to mess around with this stuff if you're going to attempt it. If you just want to go fast, do it the easy way and have fun. If you're an engineering nerd, like spreadsheets, like staring at compressor and turbine maps until your eyes bleed, like math and thermodynamics, and like start trek, compound turbos might be for you.

For daily driving the second turbo wouldn't really do much, if anything unless getting onto the highway quickly. For the 1/4, I was thinking that the stock turbo would be used to 60' and have the torque of the second turbo come on somewhere around 4500-5k rpm. I'm not expecting full spool out of the second turbo in 1st gear because I feel it would have to be sized too small and create even more heat.

As for your disclaimer, that's the hard part for me. I don't have any experience with compounding or twin charging so I don't fully understand how much the first will affect the other. However, I do like most of those and I've had to wrap my head around so much math in financial and economics classes it isn't funny.

So, how do you think Pine is doing as Kirk?

 

[Kjewer1]

For daily driving the second turbo wouldn't really do much, if anything unless getting onto the highway quickly. For the 1/4, I was thinking that the stock turbo would be used to 60' and have the torque of the second turbo come on somewhere around 4500-5k rpm. I'm not expecting full spool out of the second turbo in 1st gear because I feel it would have to be sized too small and create even more heat.

Those are all fair assumptions. Bringing the second turbo online at 5k just reminds how weak these motors are in the RPM department though. On a 4g63 I can make say 40 psi from 3500 to 10k rpm (the white 2g), which really gets it done. I'm sure the right size turbo could widen that power band some without adding too much back pressure. As I've consistently found with the race car, trading more back pressure for quicker spool almost always pays off, but you've got to try to keep it within reason of course.

So, how do you think Pine is doing as Kirk?

Don't even get me started, I already look like a big enough dork as it is.

 

[mechanicboy]

Those are all fair assumptions. Bringing the second turbo online at 5k just reminds how weak these motors are in the RPM department though. On a 4g63 I can make say 40 psi from 3500 to 10k rpm (the white 2g), which really gets it done. I'm sure the right size turbo could widen that power band some without adding too much back pressure. As I've consistently found with the race car, trading more back pressure for quicker spool almost always pays off, but you've got to try to keep it within reason of course.

Don't even get me started, I already look like a big enough dork as it is.

Yes, I wasn't planning on spinning the engine past 7k, maybe 7500. If I built it then maybe 8k but if I spinning that fast it starts to make the use of the small stock turbo a waste and might as well just throw a big stall in there and a large single. For now the plan is to stay with the stock turbo and add one on top.

If these change down the road that's fine, it Will keep me interested in the project all the more.

Don't worry, I used to nerd out too, now I don't have the time a a all the extra time I have goes to my projects or my kids.

 

[PewterCam]

... I added a 4K stall to my 5558 and the car went from sluggish pile of expensive parts to wicked beast. Off the line it would previously require a difficult to obtain foot brake stall or just patience as boost built. Now I can be sitting at a light and just mash the gas, the converter flashes, and the tire roast begins (at least on cold DR's on the street)....

Ohh hell yeah.. I Love the 4K stall in My Z28 and how it completely changes the way the car feels. Big turbo and stall is what I'd like to do.

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