Need help with Sizing Secondary Turbo f/ 6.7 CR

[Mopar Muscle]

I have decided that I want a compound turbo setup on my truck. This is my daily driver that seems limited towing. I still want it to be able to do it all. My goal for daily driving use is around 500 whp. When turned up, I would like enough air for 650-700 whp.

I plan to use the stock HE351 VGT as the primary to maintain fast spool up and the factory exhaust brake. Long term, I will probably upgrade it to a GDP 62mm VGT when they get all the kinks worked out of it. The stock turbo with be wastegated with an external Tial MV-S 38mm wastegate. I plan to limit the boost from the VGT to 25-30 psi of compounded boost (as measured from intake of VGT to the outlet) to keep it in more efficient range so drive pressure are not excessive.

Right now I am looking at a Bullseye S476 turbo for the secondary. I think the 76mm will work well, especially when I get an upgraded 62mm primary.

My question is how to size the turbine side. It seems that the T6 housing in a 1.32 twin scroll combined with a 96mm inducer is the most common. Is there a better option? I want the secondary to provide about 1/2 of the total boost (approx. 50 psi total on the street, or about 60-65 for racing or pulling). For my application with the VGT and a street driven truck, would I be better stepping down to the 1.10 ratio housing or stepping down to a 87 or 83mm inducer? Is there a non-twin scroll housing? I have called some vendors, but so far none have given me solid advice. Let me know your thoughts on this.

[97Dodgeram]

i think you meen sizing for PRIMARY...but in any case that turbo should work well in a 6.7.......

i run a HE351/s475, and it does pretty much exactly what you want, i run 30psi on the secondary and 30psi on the primary. keep in mind the he351ve has a bit different exh. housing , so it may not be exactly the same, but i think your on the right track.

on another note, if you wont miss the exh. brake that much i know those 6.7's can spool a big single turbo with ease, maybe something to think about?

[Mopar Muscle]

Thanks. I have been calling it a primary for years ever since I found out about the compound setup, but recently I read something that called the low pressure turbo the secondary and I thought I had it wrong.

Anyways, I called Bullseye Turbos and they told me they don't make the 76mm anymore. He said it was all a marketing hype anyways. They only rework the 74.5mm units. The S474 and S475 are the same, but some refer to the wheel as a 74mm and others call it a 75mm. Bullseye adds are race cover and billet wheel upon request.

So now I'm torn since I can get the standard S475 for $600 or for an extra $300 I can get the unit with the race cover. It's hard to believe that the cover is worth 1/2 the price of the turbo. They said it should be good for an extra 50-100 hp with the cover, but I'm sure that's on a gasser with a single turbo.

[06 DIESEL]

I would just get the standard cover, the race cover is not worth the $300 IMHO. As for the exhaust side, I would look for a 1.1AR T6 instead of the 1.32AR. It will spool faster, better for towing and street fun IMHO. I am getting ready to do a set with a stocker over a S475 this winter and I will be doing the 1.1AR, although the 6.7 and 5.9 may be quite a bit different.