2 turbos, or 1

[Dakin Engineering]

I spent about 10 minutes on the phone with Kevin at Majestic today. Wow, is he good. Seems I have a T2 series. I'll post when the problem is resolved. Sam

[RatliffF]

Ryan - I've noticed now that Scott Guthrie is saying the same things I did about motorcycle tires (street tires safe, road racing slicks dangerous) YOU haven't said a freaking word on the subject.

[RatliffF]

Does anyone know the internal aerodynamics of a turbocharger, such as HOW it actually compresses air? At 60,000 to 100,000 rpm is a compressor wheel even subsonic? If a compressor wheel is going supersonic does the generation of shock waves play a role in compression?

[Ryan]

Air has an ever changing spacific gravity. Barometric pressure, humidity, temprature. All have an effect on the density of air. New-style compressor wheels have inducer blades to assist air into the more aggressive blades further in. The shorter blades are called "splitters". Oh, and were talking shaft speeds in excess of 240K here not 60K to 100K. Depending on blade-to-housing clearances, boost can vary. Supersonic? absalutely!!!! If throttle blade(s)close suddenly this can dead-head the turbo, leading to sheering, as the blades cannot continue to pack non-moving air. This is where a bypass valve comes in when designing a turbocharged system. They work by vacuum, ported so when the throttle blade is closed, vacuum is instantly present.
 
 What I beleive you are asking above, about the shock wave is; surge. At wot a too-small turbo compressor wheel will exceed it's abuility to grab air. Even a wheel with inducer blades has a "range" of operation to follow. We call this a "curve". Think this through at super-sonic speed. The first blade swipes air leaving nothing for the next blade to grab, nor the blade behind it. In an instant, the wheel is free without resistance from drawing air into itself. Shaft speed shoots up out-of-control. In time, boost drops off because exhaust pressure no longer has as much force driving the turbine. As shaft speed drops, the compressor blades grab air and control is regained. Boost shoots back up, the turbine speed increases and once again the compressor wheels blades loose traction on incoming air and shaft speed spikes back up. Over & over until either the shaft breaks or bearings weld themselves to the shaft, which also can break the shaft. If the shaft can withstand this sonic pounding, some do, the nut can work loose on the compressor wheel and fall off. Plumbing can shake loose on the system as well. This is called "surge". It can happen so fast all you hear & see is smoke and parts going every which way.
 
 Compressing air generates heat, it's a fact of life we must accept. Controlling this heat can be as simple as installing a heat exchanger or intercooler. How efficient the intercooler is depends on how well it drops tempratures with minimal air restriction. Which is never as good as no intercooler.
 
  <small>[ March 17, 2004, 10:50 PM: Message edited by: Ryan ]</small>

[Ryan]

Sam,
 Majestic is great for ordering parts and some info. Kevin is very knowledgable, he's been around a long time. When it comes to modifying, there are several shops that can do good work if you know what to ask for. Blaylock's, Turbonetics etc. are just two that have machine shops. Majestic sends out. Actually only three shops do machining that I know of. I'm at the point where I'd rather do my own machine work. T2's have a smaller diameter compressor wheel then a T3. Some people will argue the point that the T2's inlet size is the same as a T3's and will move the same amount of air. This is true. Moving air and compressing air are two different subjects. The larger an impeller, the higher pressure it will make. Then heat is brought up. Yes, compressing air generates heat. Water injection is an alternative. New systems use high pressure to atomize water now instead of like older systems just spraying big drops in there. New systems can actually allow water to vaporize and increase combustion to gain horsepower under boost. I'm always refering to 30psi of boost at wide-open-throttle so you'll have to bear with me. Most people cringe but, been running that kind of boost for a while now without any major trouble. A surge tank (intake manifold) exploded a few years ago, traced back to bad spark plugs and possibly a clogging fuel filter, maybe the combination of both caused it to sneeze back into the surge tank. Big percussion but still ran without boost for several miles. Repaired in a few hours, tuned & back at it the next day.

[John Burk]

Can somebody comment on how well water or water-alcohol injection works - The early 60's 215 CI turbo oldsmobiles used it to control detonation and I remember NHRA's tec director Ed Eaton telling Pete Robinson he couldn't use the water injection on his AA/GD at the 1961 US Nationals .

[smitty2]

Hi John,
  Back in the early 80's our H53 Sea Stallions were fitted with an alcohol injection system so we could operate in the Northern part of Iraq ( I mean Turkey ). The GE T64's normally put out about 4000 hp apiece, but with alky we could easily get around 4500 hp. Great for the mountanous region we were in. Helicopters are supposed to run out of air around 10,000 feet, but we could get "Advisors" into villages well above 12,000 foot altitudes. I really can't give you anymore info than that, because as a Navy mechanic we were more of an "R&R" person than an "R&D" person. I must add though that Ryan has given me great encentive to study the science (Art?) of turbocharging even to the point of my wife asking me if I'm okay;)
  Smitty

[Ryan]

Thank's smitty, were all hear to help one another. I have several links to informative sites on water injection, boost compression, intercoolers. 90% of what water injection is doing is cooling the heated air after it's been compressed by the turbo. Can't make the big numbers without some type of heat exchanger. There has been some writing that water contains oxygen, therefore just adding H2O will boost horsepower. I don't agree with part of that. Water does of course contain oxygen. Guys that have studied cumbustion agree that heat makes horsepower. A cool, dense intake charge will expand more then a hot intake charge, within reason... Tumble and swirl inside the intake runner and cumbustion chamber certainly make a big difference. Although boost doesn't care about tumble inside the intake system, swirl inside the cumbustion chamber makes a lot more horsepower then I can convey here. Big cumbustion chambers are bad, flame travel is relatively slow, detonation is the result. Notice how newer engines run 11:1 compression VS back in the mid eighty's 8.5-1 engines rattled terribly. Looking at two chevy heads one day, one was an old '57 power pack head & one was out of a '99 Mony Carlo SS. I couldn't see any differance between the two cumbustion chambers. The SS is a reverse flow engine, water goes through the heads from the water pump. Anyway, the reason why the new-style engine can run so much compression boils down to flame travel and the violant "spin" the incoming charge has. The more violant the explosian, the more power is available. Suzuki came out with the twin-swirl combustion chamber, which is a hemispherical cumbustion chamber with ears on opposite sides. Kawasaki used that chamber technology (along with other tricks) to compete against 4-valve engines for two years and actually do quite well against them.
 
 I've strayed from the main subject a bit... In light of having a good cumbustion chamber, compromise becomes less important. Injecting water reasonably close to the intake valve works the best. Thought being; humid air is heavy, moves slow. I'm not much into O2 sensors as most people seem to be now days. Exhaust gas temprature is much more usefull at tuning. When to start putting the water too it, to my thinking, would be relative to boost. A sensor in the surge tank or plenum area to trigger injection.
 
  <small>[ March 20, 2004, 01:59 PM: Message edited by: Ryan ]</small>