Amazing-- you actually have positive pressure in the cold pipe just cruising down the road at 4-10psi total boost? Then again, if you have a smallish housing it's not *as* amazing perhaps--but still very cool.

If the Primary and Secondary are showing you a 50/50 pressure split, then the Primary is doing most of the work-- amazing given the size of it.

If you could shift more of the PR workload to the secondary, you'd be able to maintain 1:1 at higher pressures-- probably over 80 even.

Your setup now has the Primary trying to streamroll over the secondary, and the secondary is hopelessly overwhelmed. This makes the secondary proportionally more restrictive and raises DP at higher boost pressures.

I'm impressed with your setup very much. Chris had it in my mind that the 4088 was a little laggy (his 12V setup had a 4088 on top). But apparently that's not the case for you. I'm guessing there's a lot to be said for the difference between the P7100 and HPCR in terms of spoolup.

Justin

 

The primary has a relatively "tight" 1.15 a/r EH. I have not been able, however, to exceed 1:1 PR in any circumstance on the primary.

 

I mean I could, I suppose, run a larger a/r, that would keep spool down a little more to keep it from catching the secondary... but why?

FWIW, the top turbo is not a off the shelf 4088 and that has a little to do with it. But laggy? Oh my no... not at all. The spool time reminds me of when I loaded smarty beta 4.4 sw7 the first time and I still had the stock HE341 on... and it starts at ridiculously low rpms like the stocker did too.

 

I think this is more of the norm, then amazing. I have 2 psi on the primary, with 6 total, during cruise. At 15psi total I am at 4psi on the primary. Remember these are third gens.


soulezoo - Very nice looking setup.

Paul

 

Drooling. Hopefully this'll take off and BB twins will start being mass produced so the price will drop a little.

 

The turbos themselves are the lions share of the price. So the turbo cost has to come down and the kit cost will follow. Some of the turbos have come down some already and as the regular turbos go up in price, the gap will narrow.

 

Terry, nice setup! I'd like to go for a ride in your truck sometime now that you have these turbos on to experience it.

Scott

 

We'll do it sometime soon...

 

So it could be assumed that a 3788 over a 4202 would spool nicely on a CR 5.9? I was thinking it would take a 3582 to get spool off idle. If I did run a 3788 would a Hamilton 178/208 SLA help with the real low bottom end spool? I had thought about using a 3782 over a 475 setup to help save some money (wanting that cam) but evidently the turbine side cannot be clocked properly to get correct orientation on oil drain. I like that turbine side for keeping DP in check but then again if there is a nicely sized external gate shouldn't be a real problem getting around the 3582? Balancing quick spool against drive pressure.

Thanx for any schooling provided... Sorry to bug you so much on this twin stuff but it looks like I will just have to pony up the cash for the BB twins as planned. That's OK will just take longer to get there.

 

I formally got my BB twins ordered and paid for today. I will re-use the 3782R (Pat is going to put a better EH on it though) over a GT4202R. Going to build a pedestal on the steed for a 44mm Tial external waste gate. Should be a very streetable and enjoyable twin set to drive and tow with. Drive pressure should be a non-issue with the 37 turbine wheel and new housing on the secondary. Spool should still be acceptable I think. Everything v-banded. And I really like the trademark sound that the Garretts make. I do need to get a drive pressure and interstage gauges. 60 psi for primary and 100 psi for total boost OK or are those too high?

Soulezoo thanks for the tutoring thru all this process. I think re-using my 3782 as secondary is a good call and helps with the cost. The new turbine housing will allow for clocking correctly to get the oil drain near vertical. Looking forward to getting them installed.

 

One other thing I am going to do is install studs in the block for hanging the manifold instead of struggling with it the way I did before. Trying to do it that way was a total pain.

 

Those gauges are too high.
Select gauges closer to where the turbos will run.

Use 60 for total boost, 35 for primary/interstage. If you end up with more than that, then you are pushing the set too hard anyway.

Having bigger gauges looks cool, but makes it harder to read at the low end of things where you do 95% of your driving.

 

^^OK I just was not sure exactly what kind of pressures to expect. The goal is to have the majority of the time the readings to be approximately in the middle third of the gauge range. That is pretty much instrumentation 101. Far as pushing the twins too hard I suspect that will hardly be an issue the way I drive. Wife says I drive like an old grandpa. :-\

 

For head studs what would be recommended if total boost not expected over 55 to 60 psi? Best to pay up and get 625s or 2000s (425?) ARPs?

 

Where do the coolant lines for the 2 turbos come from and return? Are there plugs in the head or block to feed and return the coolant lines.
I am starting to save for a BB twin setup. Like running my stocker over S478 but drive pressure is not my friend if I turn up the tune. I like the thought of having coolant on the center sections and from some reading on Garrets site they say to turn center section no more than 20 degrees as you want the inlet lower than the outlet in regard to coolant lines so coolant can flow after shutdown to keep pulling cooler fluid into turbo to assist in the cool down. Very nice..
I am thinking Steed with gate, then 2 Garret BB turbos. I think I will have plenty of time to decide on turbo sizes while saving some cash up.

If I get brave with my welding skills. Maybe I will find the Garrett BB secondary turbo and put it over my S478 and see if they frees up enough DP to get me by for awhile.