Push Rod

Hmmmm, I took another look and didn't see one from you, Mike. Can you resend that sucker for me?

Gypsyman

Rod,

What do you think of the Aurora 2000 and 3000? ATS claims a A/R of .85 for the 2000 and says it will handle up to 50 psi. Any thoughts or input?

HOHN

I'm curious how ATS rates the Aurora at 450hp but also 50psi...

Perhaps they mean it's efficient up to 450 hp, but will survive up to 50psi? If they're saying it takes 50 psi to make 450hp, then that's not very efficient at all!

Rod mentioned something worth paying attention to. Most of the turbos we have available were designed for larger airflow, but at lower pressures.

It's a TOTALLY different thing to provide 50psi to a 5 liter engine than 5 psi to a 50 liter engine!

Not only do we need a charger that can flow the air, we need one that can handle high pressure ratios: around 4:1 imho. That means the charger takes in 14.7psia and kicks out up to 58.8psia. IF this thing could do that and flow, say, 900cfm then we're getting somewhere. Oh, and I'd like it to spool yesterday too

That's the reason that twins are so successful. By keeping the pressure ratios lower (since total boost is divided between two compressors), the twins take the turbos back closer to what they were designed for. Now you don't need to have either turbo pushing more than 20psi of boost (equivalent).

Our stock charger are optimized for a PR of 2.4:1. Using them in twins with another charger optimized for 2.4:1 PR give us a total PR available of 5.76!

That means that twins can produce 80psi total from two chargers optimized for only 21psi. Theoretically, anyway. Heating and other effects will reduce what you see. But the point still stands.

It's time for a different compressor. Modified Holsets are a wrong step, imho, because we are getting away from what the compressors are designed for. That's why I favor the B1 and other turbos. They are NOT limited by Holset's original intentions. They can be optimized for what WE need them for-- higher boost on a smaller engine.

Justin

Push Rod

I honestly don't have a bunch of experience with either of the Aurora turbos. I've been trying to read what I can on them, but they haven't really caught on yet. Seems to me that someone on the DTR has a 2000 installed on a 400 HP truck, and EGTs were a little warm, but nothing too serious.

Rod

hoot

Couple of questions... BTW.. thanks for the indepth theory. You guys really seem yto know your stuff.

Whats the difference between exhaust scavanging diesel -vs- gas, standard overhead valve 4-stroke engines? I know gas engines are tuned to the exhaust or vise-versa and if you change the exhaust you mess with performance usually in a bad way. With diesels no one seems to worry about it and opens up the exhaust. Is it the fact that there is no intake restriction only?

That being asked, the effects of drive pressure on a gas 4-stroke are much more significant on performance than on a diesel 4-stroke. If what i have said so far is true than higher drive pressure (not drastically) isn't such a big deal on a 4-stroke diesel.

Isn't the answer here what GM and Ford have already both done?

Variable geometry?

Or is that more for emissions?

Battering Ram

Ah drivepressures, that little thing so many of us either forget about or don't even know exist but is one of the most important keys to making big horsepower in these trucks. I did a lot of testing with drivepressures with both sets of twins that I built. There is a difficult balance to keeping a turbo on its compressor map, keeping drive pressure less than boost pressure, and having a charger that will spool up fast enough to drive on the street. Its so difficult that there are very few chargers that we can buy for these trucks that can even acomplish this. In fact the only aftermarket charger that I know that falls into this category is an HX40 with an 18cm exhaust housing. I belive that at 40psi boost pressure is slightly greater than drivepressure with that HX40, but the spoolup is less than desirable and its only really good to 400hp or so. With my HX40/18 and HT4B twin setup I measured 47psi of backpressure at 60psi of boost. Twins work so well because of the boost numbers they can produce at low drive pressures, but even most HT3B setups are only 1 to1 up to 60 psi. What we really need to run a single charger on these trucks that would have good spoolup and low drive pressures is a VGT. I believe Weircummins and Banks are the only ones to do it.

Horace

CTDHokie

Out of curiousity how are you all measuring your drive pressures?

Push Rod

1) There are many more better qualified people on here to answer your question about the gas engines, so I won't even begin to try. On a turbo charged diesel, you want to eliminate as much exhaust as you can to make room for cooler, clean air and your new fuel. The less exhausted fuel left in the cylinder, the better off you are.

2) Again, I can't compare it back to a gas engine, but turbo backpressure can have a profound effect on a diesel engine. Simply opening up a turbine side of a charger can free up 20 or 30 HP with ease, depending on the circumstances of course. You can feel in the seat of your pants a diesel thats breathing freely.

3) I'm probably one of the few who isn't all that excited about VGT. Compressors on VGT turbos are still relatively small (about HX40 ish) as you need to ensure that you don't spool faster than the shaft and turbine assembly allows you to spool. So you mount an HX55 sized compressor on a VGT turbine side, you need to ensure that the shaft size and VGT assembly is strong enough to withstand the initial resistance to movement. Otherwise the first time you poke your foot into the fuel the shaft will break or the VGT assembly will come apart.

I'm not sure if VGT will ever take over from twins for the ultimate in drivability and peak horsepower. Where they will start to make a difference is in the under 450-ish market. Once they get a little bigger compressor, then you'll be able to have enough airflow for 450, enough exhaust evacuation to keep EGTs very safe, and still generate nice bottom side spoolup.

Rod