Turbo Rant!!

[CF_KoiFry]

I just had to get this off my chest. Why? Cause it's the internet, and you don't have to hear me wanting to scream on the inside at the utter FAIL of the human race.

So, buddy of mine and I were talking. He is a builder of old V8's and my age. I'm 23, just to clear that up. OK! So we get to talking cause he's wanting to toy with the idea of turboing an older camaro he's got. I think it's a 91 with the the trottle body injection. So we're toying with exhaust manifold designs. He can't get past the N/A mindset that longer runners mean a more even pulse, thus better exhaust scavenging, and therefore better breathing engine. Now my own research has found that a turbo motor is DRASTICALLY different in exhaust design than a NA Exhaust. WHY!? Cause of BOOOOOOOOSSSSSSHHHHTTT!!! A turbo manifold should be set up with the shortest length runners possible. WHY? To spool the turbo of course! Funny thing about turbos...since you're forcing air through it, the nice long equal length runners will prove to be less than effective when compared to some nice equal length short runners. Do I preach equal length!? OH YES, pulse rate is still factor, but we're not scavenging exhaust gasses...cause there's gonna be back pressure before the turbo anyway...So where do we want the exhaust to breath? AFTER THE TURBO!! Why? Let's break it down.

1st action, push accelerator.
2nd action, motor begins to turn faster, thus creating positive pressure in the exhaust stream
3rd action, positive pressure moves from area of a high concentration to an area of lower concentration via this lovely little principle of air pressures derived by Sir Isaac Newton in the 1860's.
4th action, pressure differences in the exhaust causes the high pressure gasses inside the manifold, to move to a lower pressure described previously, across a turbine. Thus spinning said turbine.
5th action, Turbine acts as a wind break. It creates a barrier in which the motor must now overcome. Granted we have bearings and the sort to ease the work the motor must do to create enough positive pressure to turn said turbine, but none-the-less...there is air resistance there!!
6th action, after air moves across turbine, it is hot and STILL EXPANDING. So we open the exhaust as wide as possible AFTER the turbo.
7th action, due to the much higher exhaust flow AFTER the turbo, and a lower exhaust flow/higher pressure gradient BEFORE the turbo, we can kinda create a scavenging effect that would be LOST if there had been longer runners before the turbo.

SO, in short...

Short equal length runners before a turbo means a very quick buildup of hot exhaust gasses. This lends itself better to a faster spool. A wide pipe located AFTER the turbo give the turbine a nice place to DUMP these hot and STILL expanding exhaust gasses. So we need this wider pipe to reduce the backpressure AGAINST the spinning turbine on the EXHAUST side, not the manifold side. So this hot, lower pressure, and STILL expanding gas has somewhere to um...expand. So say...a 3" downpipe. Then a 2.5" exhaust piping afterwards. What this will do, is allow these hot exhaust gasses plenty of room to to continue out the back of the car. SO, as the hot gas leaves the manifold, it flows across a turbine, into a much wider area, and lower pressure gradient....it expands, and continues down the exhaust tube. This rapid expansion due to the sudden pressure drop will actually CREATE a scavenging effect, thus kinda PULLING hot gasses from the turbo, and the nice 2.5" exhaust pipe allows these hot gasses to flow freely without backpressure, once the gasses have expanded and cooled (albeit only slightly) in the downpipe.

This means that long runner before the turbo are not needed. All your doing is creating MORE pipe that the motor MUST FILL before the turbo can spool. Meaning that there will be MORE LAG. So...why not set up your exhaust accordingly so that when you stomp it, your turbo just spools right up, and the exhaust can breath, motor can breath (correctly), and power can be made....QUICKLY.

...end rant.

 

[JReichle1]

Very nice rant... I learned something, I think...

 

[Spiced MSP]

I think I learned a little something too..lol. Very nice and informative rant. Next time you decide to vent, please post so I can learn something else.

 

[CF_KoiFry]

And Further more!!

Why is ti that everybody always loves the tubular style manifolds!?
Let's take a look shall we?

Most log style manifolds, similar to the Calloway manifolds on the MSP, are actually REALLY efficient at spooling a turbo...not only that, but they hold heat pretty well too. I mean think, you've got steel tubing you've welded together that is probably HALF as thick as a cast manifold. Let's think of the bonuses of a tubular manifold.

Tube Manifold:
Bigger runners! We can make the runners leaving the exhaust ports larger, much easier than having to reconstruct a casting. But where does this have any REAL benefit? In motors that are pushing high horsepower numbers, or large displacement engines. With the previously described benefits of shorter runners before a turbo, one can surmise that even a tubular manifold benefits from short runners, so one must create a collector, and you end up with weird designs like this

Now don't get me wrong. That is a SICK SICK manifold. Very well designed, but let's take a look at the DRAWBACKS of a tubular manifold. First and foremost is the WELDS. A weld is the weakest point. It is where the manifold will fail MOST of the time. Also, When welding, one typically heats a small portion of metal via a gas or electricity or however you decide to do it, and blends two metal areas to create a fusion of molten awesomeness that is to cool into a nice seam...as seen above. Problem...since we're heating the metal in a small spot at any given time...it has a tendency to warp. Yes, one can control this tendency by using lower heat settings, different steel alloys, and thicker pieces of metal, but the fact of the matter is, a tubular manifold is much like a header design. The flange itself was machined BEFORE the runners were welded on, thus creating an environment that is prone to warp under heat stress...and in the header world, I've found even with a well known, good quality header, with good construction, and a good gasket, they'll still leak after they've been on the vehicle for a while. Thus another drawback to tubular designs, they are much like a header, and because they are thinner than cast manifolds...they tend to leak after a while.

So what are the positives to the big ass, heavy log style/cast manifold. First and foremost, you don't have to wrap it, or coat it, or whatever just to keep the heat INSIDE the exhaust. Cast manifolds respond very well to simple shielding techniques like...um...a flimsy heat shield, and do just fine at being long lasting, easy to repair, and keeping a good exhaust flow. In a N/A car, yes a cast manifold can rob horsepower, but in a turbo car, it's not so important. That manifold in a turbo environment will ALWAYS be under pressure. We aren't LOOKING to extend the runners to create an environment that will pull the exhaust gasses from the exhaust, cause we don't want it. We want the manifold to be able to breath properly, while lending itself to a rapid pressurization upon the event of the trottle opening and denser air/fuel mixtures are put through the engine. Cast manifolds usually spool very nicely, usually hold heat quite well, usually don't radiate heat as bad as a tubular manifold, and are actually less prone to failure through heat stress. How many times have you seen a tubular manifold get cherry red, and crack. I've seen it a bunch. Then how many cars have you heard of with a cast manifold (Just NA cars mind you) that wear out a catalytic converter, and end up heating a cast manifold hot enough you could cook meat on them, and dude still drives on it? Seen that happen quite a bit too. That and the cast manifold doesnt lend itself to warping as bad. The whole piece is cast as one item, and the flange is machined flat, flush, and true before the unit is installed. One piece design, fewer stress points (like a weld), fewer points of failure. The drawback to the cast manifold...weight. Darn things are heavy...really heavy...and they usually aren't cheap to produce/buy new.

But to be honest, manifold design and construction REALLY is all preference. If you're making ungodly power numbers and need your exhaust to be able to push more hot gas than a fire breathing dragon...oh yeah, tubular manifold all the way. It's cheaper to produce, and you're probably making more horsepower than one could consider "reliable". Why? Cause you can make your runners any diameter you want them...just realize that with a tubular manifold DESIGN, BUILD QUALITY, and MATERIAL QUALITY are the three MOST important factors...not how much heat is going through them, blah blah...design will allow for the gasses to pass quickly and efficiently. Hot gasses not being held up in the exhaust means it's not heating up like a space shuttle on re-entry. Build quality determines how well those welds are gonna stand up, how "perfect" is the flange, etc. And material quality...well, if the manifold manages to get hot enough that it's design and build quality are now moot points, you're relying on the comfortable notion that you've got top quality materials that are less prone to failure.
But if you're building a nice street queen, meant to be a reliable, turn key, go anywhere, fun little toy...than you shouldn't EVER NEED anything more than a log/cast manifold. Why? Cause of that really common word and a BIG BIG meaning. Realibility. Cast manifolds heat up...then they cool down. Will they rust? Yeah...but do I care? Nope, cause I know that cast manifold will outlast a tubular manifold usually by decades. Granted the cast/log style manifold must adhere to the same requirements of longevity a tubular manifold must, but design and build quality are less important, as it's a pretty simple design to begin with, and it's a one piece construction. Now you're relying on the fact that the quality of your materials will withstand the next...oh...life of the vehicle? And I know, I know, calloway kinda skimped out on the materials with the protege manifolds...but then again...i'd trust it to last better than many MANY tubular designs on the market.

like I said...preference of build.

 

[CF_KoiFry]

And another thing is the turbo itself!!!

I hear guys talk ALL THE TIME about the PSI a turbo or supercharge pushes. It's like currency to ricers...how much PSI you've got going to the engine, and I think to myself POPPYCOCK!!! Total Bologna!! The amount of horsepower your turbo can boost your engine to has ABSOLUTELY NO CORRELATION TO THE PRESSURE IT CAN MAKE.

BELIEVE IT!!

I work in the field of heating and air conditioning, and will tell you flat out, to your face, that you can TRY to push all the air you want through a pipe at ANY particular pressure gradient, and recieve less than predictable results....should you think on the mindset that PSI is what controls how much power your turbo can make. It's Luaghable actually!!

Your turbo can make 400 psi for all I care, but if you're not moving a QUANTITY of air...it's just a high pressure stream of little air. Like sucking or blowing air through a straw. Yeah, you can make a MUCH MUCH higher pressure inside the straw, but the fact of the matter is, you're only able to push so much air through that straw at a given pressure...so what's a better measurement of air you ask?

CFM!!!
That is Cubic Feet per Minute, not Pounds Per Square Inch.

Think about it. You've got two 4 inch wide pipe you're now going to positively pressurize with two turbos

Turbo one can push 780cfm at 4psi
Turbo two can push 540cfm at 12psi

...which turbo is doing more? Turbo one...with a third the pressure.

It doesn't matter how PRESSURIZED your intake is...it's all about how much AIR you're actually moving THROUGH it. Turbo one, at 4 psi is moving 780 cubic feet of air per minute!! Does it matter that it's at 4psi?

That's a resounding NO! NONONO NO NO NOO NOONOO NO. 780cubic feet per minute is a VOLUME of air moving at that given pressure of 4psi.
It doesn't matter whether or not you're pushing 780 CFM at 10psi or 100psi....you are still moving 780 cubic feet of air in that minute, as opposed to turbo two only being able to move 540 cfm. That's 240 cubic feet LESS in a given minute that Turbo One, AND said turbo is having to work harder.

...oh snap we just introduced another variable into the mix!! Work!

The amount of "work" your turbo has to do to create positive pressure thus negatively effects the temperature of your air stream. As the turbo spins, it creates friction. I don't care if you've got the best oil and bearings, and water jacket, and pumps and blah blah...you could have the best cooling system ON THE PLANET...the fact of the matter is, that turbo WILL CREATE HEAT. Why? FRICTION...it's everywhere. Literally everywhere. Even the air moving through that turbine is creating friction. Loootttsss of friction. So what happens as a turbo spools faster? It is exposed to an environment where MORE friction exists. Thus MORE HEAT. Yeah, you can push your turbo to spool to 30psi...but after what point are you just blowing hot air? Think about it like this.

And engine likes COLD, DENSE air, which the turbo is to provide. The Hotter the air, even at higher pressure levels, may not always mean MORE air. As air increases in temperature, the molecules spread out. As these molecules spread out, believe it or not, pressure drops. We see this in our weather patterns in cold and warm fronts. Warm air is "excited air". The molecules that make up that gradient are more energized, experienced via heat, and therefore can repel the magnetic forces that would otherwise cause the molecules and atoms to be more dense. As the air cools, it loses energy, and therefore becomes more dense, as the molecules and atoms move closer together. As we introduce this air into the turbo, we introduce it to this spinning compressor wheel capable of achieving speeds in excess of 75,000 revolutions per minute. That's fast, creates a lot of turbulence, which in turn creates friction. Friction is what? A transfer of energy. Remember, energy can't be lost or destroyed, only transferred, but that's a different rant. So as we are creating friction, we are thus introducing more energy into the evironment. This is experienced via HEAT. This heat is absorbed by the lower energy air stream, and thus the air molecules are excited, INSIDE THE INTAKE PATH...cool stuff huh. Then we put it through an intercooler, which then begins to rob our high temperature, high pressure stream of energy. Thus condensing said air stream BACK into a nice cold, dense air flow. But what happens when our turbo is spinning faster?

Your turbo does some weird things. Like say at 3600RPM engine speed, we are spooling that turbo to be able to make 250CFM at 18 psi.
That turbo is limited to 18 psi. Which is why we have boost controllers and wastegates and bypass/purge valves. All to make sure the turbo is ONLY pushing 18 psi maximum. Now SAME TURBO, at 7200RPM Engine Speed can push 508CFM 18psi.

wait...that statement RIGHT THERE just kinda summed up this whole rant. Even at 7200RPM i'm not pushing ANY MORE pressure through that intake path...only more air! So what happens to said air....it heats up. Notice...we're still ONLY pushing 18psi...but we've doubled our engine speed, and doubled our air flow...and probably more than doubled our friction and heat. THIS is where your intercooler plays its biggest role. As you increase the speed of the engine, we increase the speed of the compressor, thus introducing more power robbing HEAT. As we increase the amoung of heat, we expand the molecules of air inside the intake path. Thus, we lose efficiency. In theory that turbo at 7200 RPMs should have increased it's airflow at 18psi EXPONENTIALLY as it increased in speed. Instead...we only doubled said airflow....why? As the air heated up, it expanded, filled more area, and therefore allowed for LESS air to be present at 18psi. Granted we are in a pressurized evironment. That compressor IS SPINNING, and CHARGING air ALL THE TIME, but comparitively, at 3600 RPMS we were pushing MUCH COOLER AIR.

So how to we push lots of air with less heat? Increase the surface area!
What's that mean? Bigger turbo!! Larger turbos can provide larger amounts of air at lower pressure gradients, thus relating to the actual compressor wheel itself SPINNING SLOWER, Creating Less heat, Producing cooler air, blah blah blah. Now I'm not saying that a small turbo can't make 30psi...but how fast is it spinning compared to a larger turbo? That larger turbo may be spinning half as fast to produce the same pressures. One problem there....rotating mass.

Ever heard the old saying "It takes it to makes it"
This is a great analogy when referring to turbos. The engine must be able to create ENOUGH energy to propel the larger turbine. Thus we have this thing call Turbo Lag, Spool Lag, Boost Lag...whatever neck of the woods your from, it all means the same thing. Your big ass turbo is taking its sweet time to reach operating pressure because the motor must achieve a certain amount of energy, via hot expanding exhaust gasses, to spin the larger turbine. Which is why Bigger turbos are better for larger displacement engines....or why we spool big turbo with smaller turbo.

So in closing...it's not about how much pressure you can force through your intake...Yes can your gt25 make 25psi? Sure, but you were WAY Overspooling about 10psi prior to 25psi. How much air is that GT25 pushing at 25psi? That doesn't worry me...how much power robbing HEAT is being produced at those speeds? How much excessive wear are you submitting your turbo to?

Which is why we derive compressor maps. An engine in it's stock form can only produce so much exhaust. Said exhaust can spool a turbo. Turbo can provide more air. More air means more fuel. More burnable material means more burned material exiting, thus allowing for faster turbo speeds. The point of these compressor maps is to show us HOW MUCH AIR we can push at a given RPM at a given pressure ratio, not just to see how much pressure we can charge a pipe with.

 

[Preferio]

I really wish I could read that, but the random capitalization of words is distracting me too much.

 

[BRIAN_MP5T]

CFM!!!
That is Cubic Feet per Minute, not Pounds Per Square Inch.

Think about it. You've got two 4 inch wide pipe you're now going to positively pressurize with two turbos

Turbo one can push 780cfm at 4psi
Turbo two can push 540cfm at 12psi

...which turbo is doing more? Turbo one...with a third the pressure.

It doesn't matter how PRESSURIZED your intake is...it's all about how much AIR you're actually moving THROUGH it. Turbo one, at 4 psi is moving 780 cubic feet of air per minute!! Does it matter that it's at 4psi?

This part is false, or at least misleading and too generalized. You did not take into account that the engine limits how much CFM is used, rather than how much can be made.

 

[CX-SV]

So turbo experts, are turbos on latest cars (model years 2011/2012/2013) better and more reliable than turbochargers of the past?

We see Subie, Ford (Ecoboost), and GM using them extensively on relatively mundane vehichles and buyers are expecting longevity.

 

[BRIAN_MP5T]

My only issue with all of this is that a person who buys a $15,000 Econobox rather than something lets say like an EVOX is less likely to get service on a regular interval.

The turbo trashes oil and breaks it down. The longevity is only up to the owners desire to maintain a proper schedule.

 

[CX-SV]

I would hope most (key word is most) new car owners would follow oil change intervals in owners manual (not that they are always different today from NA engine.

Do modern turbos today still "trash oil" and have short lives?

 

[BRIAN_MP5T]

Anything spinning at over 100k RPM will create the sort of pressure and heat to put any oil through hell.

I have personally left the drain tube of the turbo, leak down into a glass jar just to see what it looks like.

It looked like SNOT, not oil and It was a real eye opener. The turbo in my car is a GT-30 and during the pleasant drive, I never broke over 6 Psi because I was worried that the capped return port would still leak.

Imagine what a little turbo would do to oil.

 

[CX-SV]

Wow, I hope the new designs are better than that, sounds brutal.

 

[CF_KoiFry]

Older turbos from days past typically were journal bearing, oil cooled turbos. One would hope that the availability of Water and Oil cooled Ball Bearing turbos would allow for better longevity, but then again...one has to take in the consumer aspect of it all. If the car companies are releasing just about every econobox these days with a turbo system, it could lead to problems. The average consumer has never owned a turbo car, and therefore is ignorant to the required maintenance of them. The old oil cooled journal bearing turbo systems, from what i've seen in my own experiences, don't last but say 30-50K miles before needing the turbo rebuilt. And I'm not talking about just the lubricated moving parts...the compressor and turbine itself will actually wear down and the blades become cracked, or chipped, or just dull...and the same is true for superchargers too. A good female friend of mine always complained her Buick Riviera Supercharged wasn't the car it was when she bought it...till her boyfriend decided to put another stock superchargerr on it, and the car was back to life.

Forced induction elements are mechanical devices and will wear. Highly worn devices are more prone to failure. Unfortunately, with all these N/A cars hitting the market for the last couple decades that have been capable of lasting 300K, the consumer has gotten a little spoiled. Oh, I can go buy a turbo car now, cause just about everybody has got one, but being the uneducated consumer I am, I will assume it's longevity will be comparable to that of a N/A car that'll run 300K. The point is...they just won't. Turbos just don't last that long before needing serious maintenance...IF you want to keep the same performance that the car had when purchased new. How many people have you all known with volvos that had 200k on them, with their original turbo...that would only keep the intake in a positive pressure of 2 or 3 psi due to a worn out turbo. I see the new car companies having some SERIOUS warranty issue on their hands really. People don't know how to take care of turbo cars, nor do many people know when to properly service them. Yes, keeping the oil changed regularly and on schedule is the single most important maintenance action you can take against your automobile's livelyhood, but turbo cars, compared to their N/A counterparts simply put more strain on all components.

Cars are faster, people like to feel that. So they stomp it a little more often. Well...there's wear involved there...every time you stomp it. Or even just start the engine. The idea of the turbo is obviously to provide positive pressure against an engine that want's to pull a vacuum. So the extra air means extra fuel, meaning a bigger explosion inside the combustion chamber. That puts strain on the pistons, rods, cylinder walls. what happens when a guy who has owned N/A cars all his life, goes out an buys a turbo car. Stomps it too many times, enjoying that nice turbo, only to have his timing system fail due to the constant extra stress he's putting it through, and ends up putting a valve through a piston. Or even better! Guy gets a turbo car, not knowing proper maintenance of the turbo components, and runs the car hard. Just dogs the piss out of it for a few hours, parks it and shuts the car off...no letting the turbo cool down...just shuts it off, and the heat surge cracks his turbine...is it the owners fault? Is such a tactic of, hey turbo timer or leave the engine running till the exhaust cools down in the owners manual? NO...and such a failure could lead to catastrophe. His compressor decides it's just gonna get a hairline crack cause of the heat stress of cooling too quickly so it just shatters into his intake, sending nice bits of metal through his valvetrain...awesome...and it's probably not in the owners manual.

Are turbos longer lasting these days? Yes
Are engines longer lasting these days? Yes
Does that mean the average consumer will properly care for a turbo car so as to avoid the catastrophes that are possibly associated with said turbo elements? Probably not...

In my opinion, even with newer turbos...rebuild them around 50k. I PERSONALLY like the idea of rebuilding the turbo's lubricated components, like bearing and seals, and shafts, and the sort every 30K. But after about 60k, most stock compressor wheels are simply so dulled out, the turbo is only performing at half efficiency anyway, so just replace or recondition the turbo at 50K to avoid that upset...then rebuild the motor the next time it needs a turbo...so around 100-110K. Granted somebody will chime in and say it's unnecessary to rebuild such a fresh motor, but I'm sorry, personal preference I guess. My mind says, I've been pounding on an aluminum block for over 100k, rebuilt the turbo twice, and replaced or reconditioned it once prior to said 100k, meaning I'm probably gonna need another turbo now anyway...pull the head and check the rings. Turbos burn big, turbos burn hot, turbos wearr out rings like a mofo. And rod bearings...
So if I'm replacing rod bearings and rings...just rebuild the block while I've got it apart...

So to answer the question...it's all up to the consumer. I mean just look at the new Ford Taurus SHO. Drivers are having to return them to the dealers around 30-40K for a full replacement of the factory transmissions. Why? That twin turbo v6 is putting out so much power, the drivetrain isn't even making it to its first fluid changes, but the NA taurus owners aren't having this problem...hrrmmmm, just goes to show you that you REALLY have to stay on top of the maintenance in a turbo car and the average consumer just...wont.

 

[CX-SV]

Wow, some good projections/guesses as any, thanks.

Too bad we have no visibility into the kind of durability testing done by the major automakers, while performing normal maintenance. Of course time will tell, certainly the number of these mainstream turbos being sold is significant.