As was alluded to before, spoolup of the big charger is partly a function of its own size, and partly a function of the smaller turbo on top.

IMO, the compressors should be sized so that the bottom turbo flows about twice of what the top does, comparing the centers of their maps. Then the bottom should operated at a pressure ratio of 3:1. This means about 28psi of boost in the "cold" pipe.

The temptation with twins is to run a bigger bottom turbo for more total airflow capability and to run a smaller top turbo for faster spool. This is a mistake, imo. If the turbos are too far apart in size, the small one can't get the bigger one lit very well. IMO, you should have no more than 20psi of boost before you see positive pressure in the in the cold pipe feeding the small turbo.

When selecting a top turbo, if the top turbo cannot flow at least HALF of the required airflow on its own map, then it's too small. For example, if you need a total airflow of about 100#/min (enough for over 600hp), then your top turbo should flow no less than 50# min on its map.

For ideal efficiency, you take the counterintuitive approach of running small, tighter housings on the big turbo and looser, larger housings on the top turbo.

The hotside of a set of compounds is where to majority of your effort should be focused. The cold side is easy: pick the big turbo based on how much air you've calculated you need, then pick a top charger that flows at least half that.

On the hotside, you are playing with the A/Rs and such that will have a huge effect on the efficiency of the set, and what hp range they are optimal for.

jmo

 

what is the contact information for rip...or did i miss it.

 

Turbo Resource and Piers Harry are working on a new set of twins. Both turbos are Garrett dual ball bearing turbos. Claim they are going to make 2 sets, 1 for towing and 1 for going.

 

Really?

Thats great to hear. Twins are in my future (>1yr) and I will probaly purchase a premanufactured set like Rips or BD since I work 80+hrs a week allowing no time to make my own. Heck, I'll have to take time off just to get them installed.

AND, if a set of BB turbos will be available, I'll just work some more OT to keep them in my price range!

Please tell me more.

 

Rip...

http://www.sourceautomotive.biz

 

Heck, I'll just wait for those, then. There's little sense in fabbing up my own set if someone's already working on what I wanted to do.

It's a little disappointing that these Garretts have been on the market over two years and we STILL don't have a marketed set of twins available that used them!

I distinctly remember posting a thread entitled "When did garrett start making a BB turbo for us?" or something to that effect, and it was a LONG time ago.

This has happened way too slowly.

jmo

 

Looks like I posted this in March of 06, and they had already been out awhile:

https://www.dieseltruckresource.com/...=Garrett+turbo

 

Wow, lots of great info and advice. Im gonna save up for the Garrett BB's, Thanks HOHN.

 

Piers put the twins on the back burner while putting together the 4bt for Southbend.

The towing twins he has in mind are a garrett BB on top (one of the water cooled ones) and a k31 on the bottom.

 

Dang, its been two years and your still researching these turbos! Even I would have bought something by now.

 

Hohn, have you thought about porting out the compressor housing? This would improve the choking effect that you get by running a large primary and smaller secondary. The project of putting a S400 or 3b with a garrett is pretty easy. Mine will be running mine shortly. I fab'd up the hot down pipe and I have a choice on either 3.5in air tubes or 4in air tubes. I still think that you have to massage the exhaust passageway some and open up the wastegate flapper size to get it work well as a secondary turbo. To me the garrett turbine housing seems too restrictive. I still like when the primary lights harder and pushes the secondary higher up its pressure curve. There is lots of things to consider as well. I want to use electronic wastegate controllers and put on an electronic controller on it. You do some funky tuning stuff then and make-up for issues caused by improper turbo sizing between both turbo's

 

if using a HX35/K31 what size piping is recomended for the hot and cold piping. some have told me 3'' some told me 3.5'' for the hot pipe. Not sure at all on the cold pipe. most likely 4'' unless it can be smaller.

 

3" would probably be the best size for th hot pipe. You don't want the gas to expand in the pipe, then have to compress again to get through the inlet flange, try and keep it all the same size if possible. Should be much easier with a T06 flange. Cold pipe, I will be going 3.5" out of the compressor and gradually expand it (if I can) to 4" to the inlet of the secondary.

 

OK, so I guess that makes me totally owned

 

Only in good fun sir. I didnt know you were getting ribbed in other threads as well or I would have never......

I enjoy reading your posts. Always informative and quality content. Dont let me get to you.