Landracing Forum
Bonneville Salt Flats Discussion => Bonneville General Chat => Topic started by: smitty2 on February 20, 2004, 05:19:00 PM
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I got a deal on a box of turbos.. I was wondering if it would be better to run 1 large turbo, or if 2 (1 for each bank of a v-8) smaller turbos would spool faster? As far as complexity of the setup.. either way is workable for me just don't know what would be best.
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Going with one may give you a bit more reliablity...just one less "set up" to go wrong. are you planning on running fuel injection with electronics or manual set ups....can get tricky with that much boost being slammed in the motor.
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Stick with a single turbo. What you mention about spooling up faster at bottom end, hurts top end and could sent the smaller turbo's into surge. Surge is where shaft speed is so high, the compressor inducers cannot "grip" the air. It's basically a run-away because exhaust continues to drive the turbine. The shaft will slow allowing the compressor fins (exducers) to grab air again. Now speed this event up to super-sonic speed and now you understand turbo surge. A large shaft turbo like a Garret T3 will take some surge, in fact I've seen a few where the compressor wheel nut had come off, it can't ingest the nut so it just wrecks the inducer fins. Completely rebuildable though.
Wouldn't have any Hitachi turbo's in that box would you???
Oh, you can "stage" turbo's. Staging turbo's is common in tractor pulling. Staging just two turbo's can build over 150psi. Crazy isn't it? Most pro-Mod drag bikes run 50Psi, that's enought to lift the cylinder block off the case. Even with APE's good studs & nuts. You'll see then run the oil externally to the head as the Kawasaki main oil passage to the head is one of the cylinder stud holes. Oil goes around the stud up to the head.
A critical area when installing a turbocharger is drainage. The turbo must drain properly or excess oil in the cavity will foam up causing pressure to build up, overheats the shaft bearings, bad.
A good turbo system to copy is the Porsche. They use a compressor bypass, when the throttle blades close, vacuum is instantly made on the engine side of the blade, boost will dead-head the compressor wheel. A compressor bypass is basically a diaphragm operated blowoff valve. Vacuum ported in front of the throttle blade opens the valve allowing boost to vent. Sounds like a whip cracking when shifting on my bike. I have an HKS valve with a 7/8ths hole. Fuel injection uses a rising rate adjustable fuel pressure regulator. When ignition is turned on, fuel pump starts, static fuel pressure is about 42psi. At 28psi of boost I see about 80psi of fuel pressure. This richens the injectors as boost rises and maintains a nice fuel curve. Lean-out will melt pistons very quickly. Older systems faught lean-out constantly. Carburetors can't richen at the rate nessassary, some did a great job at low boost pressures but for those modified turbo's making above 20psi, it's hard to put that much fuel through a carburetor. Consider this. I ran 5 gallons of race fuel through a 738cc engine in less then one hour.
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Wow! thanks for the info!
I don't have any Hitachies, but I did wind up with 3 Garret T3s. 2 of them have galled shafts..1 has broken compressor blades.. But I think I could get 1 good one out of the whole mess. I really wasn't thinking of going too high with the boost 10-12 pounds would be more than enough. This project is more of a "Proof of concept". (Read that as "Low Budget".)
Motor will have an EFI setup so I won't have to worry about presurizing a carb.
Thanks for the excellent information.. It will take me awhile to digest it all, but you have gotten me to thinking (Something I'm not well known for.LOL)
Smitty
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Something people do with those T3's is swap compressor wheels. All T3 wheels are the same overall diameter & shaft size. You can replace a 40 trim wheel with a super 60 trim wheel. Of cource the compressor housing would need machined to open up the inlet snout.
I'm not a turbo know-it-all but, I have talked with a lot of rebuilders, some even in person haha. You always hear "if the wheels have so much as tinged the housings, it's shot" Nothing could be as far from the truth!! While visiting a rebuilder shop, an employee walked up to a sandblast cabinet with a bucket full of turbine shafts/wheels and dumped them into the cabinet.
That makes you feel a little odd. At home your so carefull, even setting one down, you lay a cloth on the bench first...
The Hitachi turbo. What I did was nothing new, rebuilders had been mixing & matching parts in them for years. A T2 uses dynamic seals same as the Hitachi. It just so happends the T2's is a little bit thicker and has to be file fit about .004. Zero end gap on dynamic seals is desired. There are two styles of turbo seals. Dynamic, which look like piston rings. And mechanical seals, which look like water pump seals, having carbon/steel seal faces that rub. Sometimes there is no choice which seals to use. Say with a draw-through turbo setup. Once you see a good turbo system, draw-thoughs make you cringe. Never throttle a turbo from the inlet. This is what a draw-through does. Think of putting your hand over the inlet snout of the turbo right after a dyno pull. Get the picture? Sucking oil through the seals is never good.
A compressor bypass on a free blowing turbo really helps. Don't confuse a bypass with a blow-off. Blow-off's are set to release boost at a set pressure. Indy cars used them to regulate horsepower. Drivers said when they popped, it was like putting on the brakes.
Last year I built a big Hitachi for a friend. I used a T3/50 trim compressor wheel. A while back I had a machinist make several backing plates to make swapping wheels in the Hitachi possible. Otherwise installing a Garrett wheel requires reducing the boss on the back of the wheel. (I used an old valve grinder & did it myself) and grinding some of the boss on the front of the wheel so the nut will go on, I bullet shaped that boss while I was at it. A 50 trim wheel takes some horsepower to spin, so the turbine wheel needed some help. I looked around for a suitable turbine but ended up having a local welder, weld up the ends of the exducer fins. I ground the welds myself and made sure the blade thickness was consistant. This sounds easy and it might be but, it took me 16 hours to grind & shape the fins. I did my own clipping. Let me add in here that clipping the exducer fins lower back-pressure and has nothing to do with loosing drive power of the turbine. Anyway, I couldn't machine the radious on the fins myself, nor could I machine out the exhaust housing for this, now larger wheel. And of course balancing the whole assy. I drew up some prints, took pictures & made 8X10 glossy's with circles & arrows and writing on the back, then headed out to a rebuider.
This gets confusing I know. I've had compressor housings machined for larger compressor wheels. It's not that expensive and rebuilders don't seem to mind doing it. The only problem is, remember the remark I made about "even if the wheel slighly touched the housing, it was trash?" Well, after having your compressor machined, it will look like trash. They work, don't get me wrong but, the radious (if you can even call it that) doesn't come close to matching the wheels radious. I used clay to make an impression of a 40 trim wheel. Poured plaster into the clay etc. had a nice plug with the radious needed so the machinist could maybe use a tracer on his CNC lathe. What he did was, bored the inlet hole on the lathe, then sat down with a Dotco and sanded that radious by hand until the wheel stopped rubbing. Sound like precision to you? Like I mentioned prior, it works great, no trouble at all, makes enough boost to scare my friend so he's gone back to a smaller turbo until he's ready for that much power.
Right now I'm at the stage where I want to do my own "everything" Enco has a 12 X 36 lathe I need. Saving up $2100.00 is tough, plus lifting a 1000lb machine into the house.... Always something. I must add Saum Engineering made a wonderfull compressor housing for me. It took a few years off his life getting the .0010 tollerance and he never wants to see another one but, he shows that the radious can be made to match the compressor wheel, same a stock. I've had all kinds of ideas like, making a screw-in adjustable valute (inlet's radious area), adaptable screw in inserts for different inducer widths. Long list...
If anyone wants to talk turbo's probably be better to email me & we can swap phone numbers...
<small>[ February 21, 2004, 02:06 PM: Message edited by: Ryan ]</small>
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As for the 12x36 lathe, I got one very similar to the Enco at Harbor Frieght on sale for $1750. You can easily place it where you want with a engine hoist "cherrry picker."
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Thanks Ryan! Sorry to be so late getting back to you. I've decided to go with just the EFI for now. I sure do appreciate the Garret info, and will use it when I can come up with enough scratch to get one on the engine..( I shouldn't have let my wife look at the checkbook!)
Do you recomend any type of rebuild manual, or any books on these T3s that would be helpful?
One nice thing about being middle aged is that unlike a 20 year old.. We are not affraid to say we are ignorant about a subject :D
Thanks... Smitty
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Hello Smitty,
There are books that explain AR (on exhaust and compressor housings)sizing a turbo to an engine and mostly general information but, modifying a turbo? Mostly I've seen magazine articles where they show what wheel was used but no information about what wheel is shown beside the stock for compairison. Garrett T3's can swap compressor housings and exhaust housings to get different AR's
What I did was, stick a Garrett wheel in a Hitachi. Actually different wheels depending on what level of horsepower I wanted out of the engine. Same 750cc motorcycle engine at that. The hitachi has a very large turbine shaft, someone was playing around an noticed a Garrett T3 wheel fit the shaft. Not without some material off the bosses and making a new backing plate but rebuilders do sometimes fit different wheels in a turbo to "repair" it.
I've read arguments about "clipping" exhaust turbine fins. It's true that new design wheels are different and do not need this. If you look at the end of a turbine wheel straight in, as if looking through the shaft as if it was center bored. Called "exducers" these fins look bent over, just about 90 degrees. When you clip these fins, your not actually grinding flat across to remove some of the bent-over exducer. Strength would be lost where the fin joins the shaft. I use a 84 degree taper. What clipping does in the first place is reduce exhaust backpressure. It does not affect driving power of the turbine wheel. This where arguments start. Inside the scroll of the exhaust turbine. Exhaust is funneled down to the cut (cutwater) this is where the exducer tips are driven. Gasses are at maximum pressure at this point. As gas flows through the exducer, the longer the fin is, the more pushing force it can exert. This makes good sence however, the longer the exducer fins are, the less opening there is to allow gas to escape.
Finding the balance or how much to clip, takes a exhaust pressure guage. There is a formula to stay within between intake boost pressure and exhaust gas pressure. I can't get into cam timing or this post would never end. Lets take a factory turbo cam installed per the card specs for now. This will have a short overlap event.
For the hitachi I was working with, no larger AR housings were available, in fact it's a rare turbo to find. The T3 wheel was staggering larger then the stock hitachi's. Leaving the exhaust turbine exducers "unclipped" and fitting the turbo to the engine. Power came on softer and pulled great then nose-dived at about 7000 rpm. A quick point here; once a turbo engine has no resistance, like when it tops out, boost pressure drops and power does as well. Never gear a turbo engine lower, gear it to pull a load and it'll make more boost, therefore power. This is strange, while out cruising on the highway, the road curved into a headwind. My boost guage showed about 8psi more boost suddenly a the bike faught the headwind. To me I felt nothing and did not twist more throttle to it. Boost was taking care of how much horsepower was needed. This is the resistance I speak of. It's difficult to discuss these oddities with someone who's never felt a turbo at work. Anyway, since the bike nosed-over at 7000 I clipped .100 off the exducers, rebalanced the assy and this helped a ton. This engine has stock cams, no degreeing work, stock exhaust pipes into the turbo, some porting to remove bumps ect but nothing major.
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For the "collective",
I just installed a new Garrett on a project and oil is leaking past the seal on the exhuast side. Any help on where to send this for a new seal? Sam
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Have you run it under any real load yet? You may find that once the boost starts to build it will seal. If you have oil build up in there right now it may take a while to burn out.
It is a ball bearing turbo?
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Jorgen,
Yup, under load it gives a great crop duster effect. It was sold to me as new and appears to be. Ball bearing? I don't know as I can't get it apart. The S/N is C113460 XB383DEV with .40 A/R intake and .35 A/R exhaust. Any light you can shed on this is appreciated. Sam
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Sam, dbb turbos require mush less oil
to operate properly, you may have to
put a restrictor in the supply line, in
addition, your return line is immensely
important, does it gravity return, is there
ample drop from turbo to where you are dumping back into pan? is it dumping back into a low or non
windage area?
curious Joe :)
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Ryan... Yes I'm seeing the light on what you're telling me about load! Our turboshafts in the helicopters were always acting against a load even if the rotors were out of play, because they had the resistance of the gearbox to work against. I guess that would be considered a torque load. I hope I don't start sounding like FR, but I understand the SR71 had problems with "Runaway". Kind of sounds like what you are telling me about gearing.
thanks man.. You have gotten me to actually think about something other than overtime, and bills!
Smitty
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Naaa your nowhere close to FR. He was a pro, a real case of himself hehe.
I don't think restricting oil flow to the turbo is a good thing. The bearings need pressure then drain into teh cavity. The death of a turbo can be carbon buildup behind the turbine wheel. As carbon builds up it pulls the shaft & puts a load on the thrust bearing. This in turn wears on the seal. There are several reasons why a turbo blows oil. Depending on the type of seals, can have either or depending on what the guy ordered when bought new. Dynamic seals look like piston rings, excesive end gap will certainly blow oil out the exhaust. It has to come apart regardless. Just be sure to mark the wheels so they stay in balance. Rebuild kits are cheapest from Majestic in Texas.
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be advised its easy to "over oil"
a DBB cartridge, especially with the
oil pressure available from modern
bike engines, that is why oil restrictors
are needed in these cases
but dont listen to me, ask those who do this
for a living, ie innovative turbo, Mr. Turbo
etc, that is the advice I am passing on, your mileage
and smoke may vary :) :)
Joe :)
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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
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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.
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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?
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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>
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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.
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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 .
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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
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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>