i see some pullers and other company's either compounding the same two turbos rather than a small and a large like normal. just wondering if anybody has done this.

I was wondering if you could compound two stock turbos for more airflow.

 

That's a first for me? Who's doing that kind of set-up??? Doesnt' really make sense...

 

I dont want to start an arguement because Im not 100% sure, but I believe the 2 turbos on my cat in the peterbilt are the same size. they are dirty, and in a tough place to get a real good look, but they look the same. I was thinking about doing the same too. 2 stockers I mean.

 

It's possible I had never seen the question asked before....

 

a powerstroke puller overtime in diesel power has this set up running two Hx82 ( could be wrong size) compound the turbos are the same size. also seen this in a another magazine where they had two hx40 turbos compounded on a drag truck. I see banks uses two turbos of quite small size 38garret two make a 1000hp with a duramax.

might make sense two run two small turbos that make the same airflow a one large turbo.

 

When this is done the two turbos are in parallel. In the case of the Banks Duramax one side of the engines exhaust feeds one turbo and the other side of the engines exhaust feeds the other turbo. The output of each turbo then feeds directly into the engine. The exhausts from both turbos are then vented to atmosphere.

In a compound fashion, whats normally referred to as twins, the boost from a large turbo is fed into the compressor of a smaller turbo and the boost from the small turbo is fed into the engine.

The exhaust flow is similar. The exhaust first flows into the small turbos exhaust housing and then after spinning the small turbo the exhaust is fed to the large turbo to spin its turbine. After making it through the large turbine the exhaust is vented to atmosphere.

In this case the big turbo is called the primary and the small turbo the secondary. This is because the big turbo provides the first or primary stage of compression and the second smaller turbo provides the second or secondary compression stage.

 

So a person would split the exhaust and run the 2 turbos side by side then? Probly be a good idea to have a 6 into 1 into 2 set-up for the exhaust then right?

 

Right. Everybody throws around the term "twins" on here and nobody really has them. Twins are actually two identical turbos that are fed separately from half of the exhaust. I know of a truck that is currently having a custom exhaust manifold built to do just that to get around some pulling rules that restrict the turbo inlet that wouldn't allow a large enough turbo to run compounds. So in order to get adequate air to support a gob of power, he is going to run two 66s.

 

I thought somebody out there made a S300/S300 compound setup?

If you are talking compounds and they appear to be the same size, they could still have different size exhaust housings and different size compressor/turbine wheels.

 

Watching This Thread

 

Some of the pullers out their use dual compounds b/c the have enough fuel to spool that LAGGY hunky of weights. I saw them at houstoun and they are huge. The banks twin setups also use the same turbos in their setup, actual twin turbos. The most common setup is compounds using a small single to spool a large single. Other then that I havent really seen or read anything about this type of setup just doesnt make much sense for us dodge guys to use a setup like this, dmax and ford guys are a different story. Just my .02

 

This was discussed on TDR a while ago...

The consensus seemed to be that the stock turbo would be super-slow to spool with only 3 cylinders worth of exhaust, and is still boost-limited at 35-ish psi. An efficient big single or compounds are the way to go.

I still don't believe in compounds running the stock turbo as a secondary. The exhaust housing is just too small to push 600hp worth of exhaust through w/o extreme drive pressure. Now, if someone were to build that setup with an external wastegate I'd be all over it!

 

They do. Thats BD's setup. However if you look around you'll find there are TONS of S300 configurations.

The S300 that is the secondary has a 57mm compressor and a 14cm exhaust housing. BD calls this the Super B.

The S300 that is the primary has a 66mm compressor and a 26cm exhaust housing. BD calls this the Super B Special.

I may be a little off on these specs, I can't remember exactly what I've read on here, but you get the picture.

They are both S300's but they are different and are run in a compound configuration. BD has done a lot of work with them and for what they do, they do well.

Look up onetun's profile and find some posts where he switched to BD's R700 twins with a S400 primary. He has pictures of the two different S300's.



As to using a stock turbo in a compound configuration I spoke with Nathan Wright about using an external wastegate. He offers an external wastegate with his stock/S400 setup but recommends going to a larger secondary turbo instead of the wastegate. He did some testing and showed that there were some improvements but not enough to warrant the wastegate. His testing showed at WOT a boost of 67psi and 77psi drive pressure without the external wastegate. Using an external wastegate the boost remained at 67psi but drive pressure dropped to 73psi and egts only dropped 100 degrees. He said this was done with a Bullydog setting that dynoed 400 hp.

 

Do you have any data on drive pressures with and without an external gate, or is what you're saying based on opinion/speculation?

AFAIK Nathan has done DP tests with the stocker/S400 setup and it was very close to 1:1 all the way up to 70psi. I guess the later stock turbos have a decent sized internal WG and that helps to keep DP in check.

 

Well those are the specs that I have heard so I think you are right on.