IKnowtheFuture

iTrader: (5)

I am planning out a series turbo setup since my 370 is 8.5:1 compression. I will probably run the HT60 I have as the larger turbo and I am still looking for a smaller turbo. I'll set the wastegates so the larger turbo wg bypasses around 20 psi and the smaller at around 10. the smaller wastegate will get the reading from the large compressor housing and the large WG from the smaller housing.

In case anyones wondering the cold side route is: filter on larger turbo, outlet pipes into small turbo inlet, outlets into IC then motor. Hotside is routed: Ex. manifold to small turbo, outlets to large inlet, then out to DP. It has a wastegate to route pressure past small turbo to before large turbo and a wastegate inbetween large turbo to the DP.

Its setup so the small turbo spools instantly and once the backpressure at the small turbo is alot the 1st wg opens and bypasses some of the exhaust gas and the 2nd wg opens to control overall pressure.

What small turbo option can I run that will get me to 10 psi at 2500 psi and have too much back pressure at around 14 psi?

anyone ever try to run a hx35 diesel turbo on an ls1 before?

bettonracing

iTrader: (3)

Look up KJewer1 on YB forums. While he's using a much smaller engine, he's the only one I've found publicly doing any predictive work on gas compounds - based on actual experience.

Based on what I've seen thus far I'd say size the small turbo for the low end curve u want, with the big turbo for the top end. There will be some efficiency losses but effectively the more exhaust u bypass around the small turbo on the top end, the more this kind of setup approaches a "sequential" arrangement of the two turbos.

Keep us posted on results.

Regards,

Kurt Betton

chuntington101

You will need ALOT of weastgate on the smaller turbo! There was a guy running compound boost on a 4G63T engine. He had a T6 trubo as his larger turbo! and aslo ran 2 x 44mm gates off the smaller turbo.

Def be intresting to see on a LS engine!

Chris.

bmech211

You should calculate your pressure ratios and plot them on various compressor maps to determine the best turbo(s) to use. Based on the numbers you've provided (10psi/small & 20psi/large turbo), at full boost you're smaller turbos PR will be around 1.28 which is well below even some T3/T4 turbos efficiency range (pretty much below the map).

I suggest running 15-20 psi through the small turbo and 10-15 psi through the large if your goal is 30psi. This will move the smaller turbos PR up a bit at full boost.

Why the need for compound turbo at only 30psi?

I can't stress enough that you should definitely be plotting out compressor maps, if for anything, for the sake of tuning at least.

One other question: how are you planning to hook up your boost/MAP reference lines to actuate the waste gates?

SATAN

iTrader: (2)

This is my buddy Marc talking about his compound setup he did on his 2jz. Maybe his build can offer some ideas. I don't know. Worth a look though. his car is pretty quick. Runs mid 10's but traps mid 140's. He's going for more though.

http://www.youtube.com/watch?v=y-Me6yWApzY&feature=fvsr

93formto98T/A

iTrader: (28)

You should prob look at the Precision Turbo 66mm WG or run dual WGs. I'd probably look at one of the mitsubushi 20g or big 20g turbos as the small turbo. Would be a sick setup if properly executed but again, much easier said than done right. That's why you don't see these setups done much. Arguably with a V8 you aren't exactly hurting for low end torque anyway.

IKnowtheFuture

iTrader: (5)

the whole point of compounding is the small turbo spools up instantly and by the increase in exhaust gases in a nut shell turning the motor into a larger C.I. motor which can spool the large turbo quickly. The way The larger turbo compresses the air so the small turbo sees more than ambient psi on the intake of the housing and then compresses it further is the math that everyone gets stumped on.

IKnowtheFuture

iTrader: (5)

I have seen the eclipse gst, the 300z, the supras and the sc300s, the 4 cyl ford ranger that already have the compound setup

bmech211

I ran some numbers and for your 6.0, looking for boost around 2500rpm, the Garrett GTX3582 (or similar) would be right up your alley for a high pressure (small) turbo. Again I suggest running 15-20psi, and that's what I used to calculate the numbers.

15 or 20psi @ 2800rpm will put you right at the compressors peak efficiency, 78%. I also calculated 10psi on the low pressure (large) turbo at 6800rpm, and factoring in those numbers to the equation, will push efficiency slightly to the right of the peak, around 74-75% on the high pressure (small) turbo.

Not too bad and the high pressure (small) turbo is barely breaking a sweat @ 6800rpm. Choose your turbine trim and housing accordingly to maintain as close to 1:1 as possible. You can go as big as you want on the low pressure (large) turbo, as compounding works not only on the compressor side of things but on the exhaust side as well.

Good Luck and hoped this helped a lil bit..

IKnowtheFuture

iTrader: (5)

I was talking about running 20 psi. Now that I reread my first post think i need to revise. I think I need to hook both wastegate vacuum lines to the outlet of the small compressor and set the first wastegate to bypass the small turbo at 10 psi and 20 psi on the second wg. therefore when the small turbo spools fast and hits 10 psi the 1st wastegate opens allowing some exhaust gas past the small turbine so the motor wont choke. soon after the big turbo will be boosting and once both turbos throwing boost at the motor reach 20 psi the second WG opens. controlling overall boost.

I'm just fuzzy on the math when the compressed air from large turbo(A) goes into the small comp. and gets compressed to 10 psi (B). is it A+B= total boost in manifold?, AxB?

LS1NOVA

iTrader: (12)

Props for trying this. If you can get the power to the ground, even better.

slow67

iTrader: (2)

Actually its PR * PR. So if both turbos are making a 2:1 pressure ratio, total boost = 4:1 PR, or a tick over 43 PSI (assuming sea level).

If you set your small turbo to 10 psi with the wastegate connected to your big turbo coldside, when it hits 20 psi, the small turbo will be trying to bypass ALL of its boost....I don't know if that's your goal or not, as that would be more of a sequential setup. If you truly want the small turbo to make 10 psi all the time, connect the bottom of the wastegate after the small turbo, and the top of the wastegate to between the turbos. Then it will try to maintain 10 PSI on top of what the big turbo is doing.

B18B1LS1

iTrader: (12)

20 psi total, driving the 1st stage at 10 psi, should put the 2nd stage a tad under 6 psi. A compound setup seems overcomplicated for only 20 psi. But it would be cool to have when you pop the hood! Do it and see how it goes.

IKnowtheFuture

iTrader: (5)

The main reason for doing this is because I can have a tiny turbo which spools instantly and then I get the large flow from the big turbo. the PR multiplication is the aspect that is screwing me over. you act like 20 psi isn't alot of power. I have 8.5:1 compression, which without a tiny turbo to spool up quick, will be a dog out of boost.

WheelsUp84z

iTrader: (14)

add more timing at low rpm's, or nitrous. Problem solved.

bmech211

Calculating PR using hypothetical numbers :: 15psi high pres. (small) turbo / 5psi low press (large) turbo. Plug whatever numbers you wish, as I'm only using this as an example.

--- Low Pressure (Large) Turbo @ 5psi ---
PR = BOOST + PSIA/PSIA

1.34 = 5 + 14.7/14.7


--- High Pressure (Small) Turbo @ 15psi ---
PR = BOOST + (LG. TURBO BOOST + PSIA)/(LG. TURBO BOOST + PSIA)

1.76 = 15 + 19.7/19.7

The determining factors used, as they relate to system set-up:

1. No boost bypass valve on the large turbo outlet (reroutes boost directly to the intercooler at "full-tilt").

2. Both wastegates boost reference ports (bottom ports) connected to manifold.

3. Large wastegate boost control port (top port) connected to large turbo pressure port.

4. Small wastegate boost control port connected to boost control solenoid (tee'd off of boost reference port).

BTW, pressure ratios are not multiplied in this type of set-up. They are, however, in a twin or sequential set-up.