The case for Asymetrical Turbocharging

[JBrady]

I have a 1999 LS400 with the 290hp/300tq VVTi 1UZ-FE engine and 5 speed automatic transmission.

The engine has 10.5 to 1 compression. The pistons and rods as well as transmission limit modification to maybe 400hp with any reliablility.

All things being equal it should take roughly 5psi of boost to reach 400 crankshaft horsepower (320-340rwhp).

From a weight, packaging and price standpoint a low mount single turbo seems to be the best option.

I can squeeze a T4/T3 sized turbo low into the passenger side engine compartment where the catalyst is currently located. Here is where things get DIFFERENT.

I am strongly leaning towards running ONLY the passenger side exhaust to the turbo. I will size the compressor for 2 liters and the compressor for 4 liters.

This will create a different exhaust flow/pressure dynamic for the passenger side vs. the drivers side. While this will bother many it should not be a problem especially since our engines have very minimal valve overlap. I can leave the drivers catalyst unchanged. Run a larger pipe from the turbo outlet to a catalyst.

This is the least complicated way to create a low boost turbosystem on a V engine. I may even retain the stock passenger exhaust manifold. For a maxium effort high boost design asymetrical design is not recommended but for this limited output design goal it may make the most sense of any boost option.

An additional benefit to this design is if a high boost upgrade becomes desireable by rebuilding the engine with stronger pistons and rods AND a stronger transmission is incorporated... the addition of another turbo of the same specification would then twin turbocharge the engine with power potential exceeding 800hp.

Saab built asymetrical turbocharged lpt V6 engines from 1999 thru 2003.
Here is the 1999-2003 Saab asymetrical V6 with only the front 3 exhaust ports powering the turbo to a max of 3.6 psi

 

[Thermactor]

Are you serious about boosting your LS?
I seem to recall some GM diesel from the 90s had a turbo running off of only one bank of cylinders.
I don't see it causing any failures in your setup. Do it

 

[cribbj]

Couldn't be much worse for the motor than a plugged cat on one side.....

Big turbine + small compressor = low boost with not much back pressure, hopefully.

Not my cup of tea, John, but it'll be an interesting project to follow!

 

[JBrady]

Are you serious about boosting your LS?
I seem to recall some GM diesel from the 90s had a turbo running off of only one bank of cylinders.
I don't see it causing any failures in your setup. Do it

I have been thinking boost since I first bought 1996 LS400

That did NOT change when I bought the 99

Seeing as your supercharged with the previous setup it encourages me that much more!

 

[JBrady]

Couldn't be much worse for the motor than a plugged cat on one side.....

Big turbine + small compressor = low boost with not much back pressure, hopefully.

Not my cup of tea, John, but it'll be an interesting project to follow!

Now now John... a turbine is nothing like a plugged catalyst. One is designed to flow and the other simply does NOT!

I understand the engineer in you WANTS symetry. That said think more about the design GOAL. Low boost, minimal weight, minimal complexity.

Divide the exhaust duty of 400hp and think what restriction that 200hp of flow is placing on the turbine capacity? Not much. Consider that on the stock engine some exhaust ports are unrestricted (3) while others are to varying degrees highly restricted (5). Furthermore 3 of the 5 are on the passenger side to start with

Show me a stock completey balanced exhaust pressure street engine? After blowdown it is the crankshaft power lost to return pumping. The beauty here is that this duty is shared with the rest of the power connected to the crankshaft (inertia and power stroke contribution of the other pistons). Isn't it nice how the connected forces balance?

 

[JustenGT8]

It's done here locally all the time on the equiv of your buick V6....not elegant by any means but works just fine for low boost

 

[JBrady]

It's done here locally all the time on the equiv of your buick V6....not elegant by any means but works just fine for low boost

With the stock pistons, rods and weak transmission low boost is going to be max boost! Thanks for the support. I think this may be a good choice for the GS400/430s looking for more power as well.

Intercooling may even be optional at low boost BUT would be a good idea as any heat load contributes to the total load even if detonation is not reached. Low boost is usually lower efficiency on most compressor maps but since the total added heat is low it is not the same concern as a high boost application.

Below is a 60-1 compressor map (I have this compressor). For those not familiar with compressor maps 10lbs of air per minute is roughly 100hp of air flow. Every 0.20 pressure ratio is roughly 3psi boost. 5psi (just over 1.30) is barely on the chart and looks terribly inefficient but at these levels the temperature difference between 55% efficiency and 70% efficiency is just not that much.

5psi @ 70% efficiency = +70 degrees F (adds 70 degrees over ambient temperature)
5psi @ 65% efficiency = +75 degrees F
5psi @ 60% efficiency = +82 degrees F
5psi @ 55% efficiency = +89 degrees F
5psi @ 50% efficiency = +98 degrees F

 

[XR8tt]

It's not hard to merge both banks of exhaust...
Especially on a low mount turbo...
One bank can have std headers...

 

[JBrady]

It's not hard to merge both banks of exhaust...
Especially on a low mount turbo...
One bank can have std headers...

True it is not hard but it is harder than one bank only so the question is what is the benefit of each option. For low boost the single bank design may have an advantage with less complexity, less weight, fewer hot tubes to deal with. The non-turbine side will have better exhaust flow and less back pressure on 4 cylinders on the exhaust return stroke. It will also have a smaller turbine section which will make packaging slightly easier. Less wastegate capacity is another benefit.

 

[XR8tt]

It's the engine tune where it could become critical...
With back pressure.. You can easy have 2 to 1 bp....
Detonation can be an issue?? I guess colder plugs on turbine side would help ???

Two WRX Subaru IHI VF23 turbo's are so small "internal gated"..
They flow 423 CFM each at 14Lb..
The wastegate is normally set at 8Lb...
Spool would be instant with compression your running...

 

[JBrady]

It's the engine tune where it could become critical...
With back pressure.. You can easy have 2 to 1 bp....
Detonation can be an issue?? I guess colder plugs on turbine side would help ???

Two WRX Subaru IHI VF23 turbo's are so small "internal gated"..
They flow 423 CFM each at 14Lb..
The wastegate is normally set at 8Lb...
Spool would be instant with compression your running...

I have been a fan of IHI turbos since I bought a new Thunderbird Turbocoupe in 1987. Ford went from the T3 Garrett to the IHI RHB5 and it was the largest of that series but VERY small externally. Lightweight and efficient it spooled nearly off idle. I ran it to 20psi and it lasted 200k miles. I would love a pair of the ball bearing IHI VF23s or Garrett GT28s but for this low boost goal that is a lot of money.

For ease, cost and options a T3/T4 with a .63 a/r turbine housing will work. As I said I already have a HI-FI 60-1 compressor wheel and housing. I can source a used T3 and build the hybrid for under $200.

Slightly off subject, I really like the Tial stainless V band turbine housings for the GT Garretts. Minimal weight and would look even better polished. Tial claims up to 33% turbo weight reduction. They look great.

 

[spf_lexus]

Are you planning on making your manifold and everything w/ the engine still under he hood? Yanking the motor takes maybe 2-4 hours but once out, fabbing a dual merge should be very easy. I would think a crossover pipe could fit snugly if routed in the high spot just past the bellhousing. Congrats on deciding to boost your LS, keep us posted!

 

[JBrady]

Are you planning on making your manifold and everything w/ the engine still under he hood? Yanking the motor takes maybe 2-4 hours but once out, fabbing a dual merge should be very easy. I would think a crossover pipe could fit snugly if routed in the high spot just past the bellhousing. Congrats on deciding to boost your LS, keep us posted!

Sean, no crossover. Turbine fed with ONLY the passenger 4 cylinders. I describe why this choice is reasonable starting at the first post.

Pulling the engine is an interesting option but part of the design goal is to make this as easy as possible. Stock exhaust manifold placement is part of the equation. Low mount single with minimal exhaust plumbing.

Internal or remote WG is undecided but leaning towards internal. The only real differnce is where and how the bypassed gas rejoins the rest of the exhaust. The goal is no added backpressure that will reduce the turbines efficiency.

 

[spf_lexus]

gotcha, im sure it will come out nicely. Very interested to see how your vvti responds to low boost.

 

[Avet4]

yea how do you tune it? I'm sorry, I'm awful at anything that's not pre-packaged and a reflash tune on stock ECU.

 

[JBrady]

yea how do you tune it? I'm sorry, I'm awful at anything that's not pre-packaged and a reflash tune on stock ECU.

No pre-packaged pre-flashed chips/tunes available for this car.

You will need to obtain some sort of interceptor device to allow tuning of the A/F ratios and someone that knows how to tune it.

ONE POSSIBILITY that exists will be the ability for the stock system to adapt to SOME boost. ScottURnot was able to do this on his 1997 SC400. Now that is a different engine and management system and I did not do it or see it myself just going on what a highly reliable extremely meticulous member here reported. I have to believe the possibility of running 1 psi is very high. How much can it/will it tolerate??? This will definitely be forging a new path. The meek should wait for the safe signal before proceeding.

 

[spdrcr771]

Im very interested in this, as well john. Ive been toying with the idea of a single turbo mounted @ the Y. But maiting a single on the passenger side of my S&S would be sweet too. Less piping.

 

[Avet4]

Has anyone considered a remote mount turbo such as the STS turbo systems?

This way you could do one low boost turbo, directly into the throttlebody.

A benefit of these systems is that the power doesn't "snap" into action, but rather has a more linear build up, therefore less chance of breaking parts, easier on the transmission.

 

[stevechumo]

This thread was started more than 1/2 year ago. I'm wondering how the project is coming along.

 

[JBrady]

Been busy with other things and no progress has been made.
Honestly with 183K miles I am wary of the engine and trans taking more abuse than stock. This means a bigger project than time permits for the short term.

If I had an early 1uz with the stronger internals and the 4 speed that would be different as a replacement engine there is only $500. VVti engines are much more and still weak internally.

I did consider a remote mount previously and it is possible but there is minimal clearance for a turbo(s) AND mufflers which means more noise.
Always concerned about air inlet to the turbos as well since ingesting water is a bad thing.