Turbo Tech

[earlbrown]

The trick is to bag the girl while dressed like crap.


That means anal.   



Not sure how that compares to turbos though.    I'll have to dwell on it when I get done with the new blonde later.

[motorhead]

Building the best (most efficient) N/A engine you can and adding forced induction is usually the quickest way to the most useable power.  There are definitely nuances to this theory in a practical application like changing the valve events and dynamic compression to support positive manifold pressure.

So, when you are limited by your air pump of choice, like a stock LC2, you really have to rely on pressurized air past the valve to get the most out of it.  The trouble is between that "high boost" number and the bandaiding of an intercooler your back pressure sky rockets, and air pump starts working against itself... resulting in parasitic losses, heat, and a drop off in efficiency.

I believe it was mentioned earlier in this thread Duttweiller said not to waste time or money on the stock heads.  For the cost and potential to support a capable turbo - investing in really good heads will augment the air pump across the board.  Obviously, based upon the application putting too large of a head on a tiny 3.8L in a street car is going cause it to be very lazy off "boost" negating their overall advantage; and then you'll need a cam to round out the package as a whole.

Even the crappiest factory LSx head is capable of supporting ~1000hp -  talk about flow potential, right?   Having a calibrated MAF, a WBO2, a MAP or two, and an IAT is a great way gain an appreciation for how well a combination is working.

In HPTuners you can use the measured lb/hr from the MAF and a little mathematics to come up with calculated torque and horsepower, this can then be compared to accelleration rate to see if more "boost" really is better.

[BoostedRPS]

Could be, I am on the north end of lake Superior but no.


If you said a turbo at a certain rpm flowed, by itself, enough air to make 1000 hp I get that.




What started this is a guy locally wanted to put 2 stock gn turbos on a warmed over 400 sbc and I don't think that would work properly for a low 9 but I don't know how to explain why.Maybe  I'm wrong.


He ended up putting on 2 -70's.

If you are going to turbocharge an engine that had originally been designed to run NA, you have to make changes in the engine to reflect the increases in airflow the turbo will provide.


What I mean is that an NA engine will have a camshaft that will have the exhaust valve open later on the power stroke, compared to a turbo camshaft. This plays a role in the backpressure and amount of exhaust duration that is required from the camshaft. The more airflow entering your engine, the more time you need to remove that airflow. If you have an exhaust system that has backpressure in it (like a 3-bolt turbo Buick engine, for example) you need to make sure you allow ample time to remove the pressurized air from the cylinder, and minimize the amount of time of overlap in the valves. There is more, but you get the point that you need to change some things in a NA engine if you want to get the most out of a turbo setup.


A 400"ci SBC would probably make enough power on it's own, if it was a good build, to produce 450-550fwhp, which is what you would obtain from putting a stock GN turbo. The stock turbos don't flow more than probably 50-55lb/min, which translates to 500-550hp at the most.


If you put two of them on the car, you aren't going to have 500hp + 500hp. Rule of thumb with twin turbo setups is you only gain 80% of the second turbo's power potential. Not only that, but you need to make sure the cylinder heads can flow enough volume to support the airflow coming from these turbos, and your exhaust system needs to be free-flowing enough to minimize the backpressure.


With turbos like the stock GN turbo, which are quick spooling on an small engine like our 231ci, if you put them on a 400ci engine the amount of exhaust gas entering the turbine housing at even moderate rpm levels will be so high that it will quickly become a restriction, because the turbine housing will not be able to support the volume of exhaust gas flow coming from the engine. As the rpms climb, eventually the turbo will become incredibly inefficient because the wheels will be spinning so fast, due to all the exhaust gas entering the turbo. Yes, wastegates will help prevent this, but only to a point. The turbos are simply too small, and because of this they will be inefficient. If you were able to get 500hp from one of these turbos in an ideal engine setup, putting them on an engine where they are incredibly inefficient like that 400ci engine you would be lucky to get 350-400hp out of one of these. That is why even basic turbo LSx engines use single turbos with sizes no smaller than 67/70mm compressor wheels, because a turbo of that size will be able to support the amount of exhaust flow coming from the engine, while still being efficient. The cylinder heads on a LSx typically flow so well that they may only need to make 10-15psi to reach the max flow of a turbo of that size, because their cylinder heads have so little restriction in them. On crappy heads like ours, it may take 35+psi to reach the max flow levels of a 67 or 70mm turbo, for reference.

It just seems to me there is a basic ''premise'' missing.If I put said turbo on a 1 liter motor  it will make 1000 hp?If i put said turbo on a 16 liter motor  IT will make 1000 hp ?What does ''support'' mean in this context?

You need to change how you think if you intend on understanding this concept.


I am assuming your post is referencing a turbo rated to support 1,000hp?


If you have a 1L engine that had cylinder heads that were able to support the airflow required to make 1,000hp then putting that turbo on that engine would make 1,000hp. Think of the old Formula 1 turbocharged engines in the 80's. Small displacement, like 1.5-2L engines, that made over 1,000-1,500hp. The engines could support the airflow that the turbocharged produced, and therefore the engines were able to make that amount of power.

As for your comment about this turbo being put on a 16L engine and making 1,000hp..... The engine size does not matter. What matters is the engine's ability to support / allow for / provide the airflow through the cylinder heads that the turbocharger can produce, without causing any restrictions. If the cylinder heads can flow the amount of air, without issue or restriction, that the turbocharger can produce and flow, then the engine will be able to make up to 1,000hp. I say "up to 1,000hp" because things like combustion chamber design, fuel type used, camshaft design, compression ratio, pressure drop from turbo outlet to engine inlet, backpressure.. ...all of these things can influence how efficient an engine is. If you are familiar with the term Brake Specific Fuel Consumption, aka BSFC, this is a formula and number that tell you how efficient your engine is at burning all the air and fuel coming into the cylinder, and how much fuel is required to produce a certain amount of horsepower. The less fuel required to produce horsepower, the lower the BSFC, and technically the more "efficient" the engine is at burning all the fuel entering the cylinder. I am saying all this because engines have so many variables to them that can potentially cause drops in power output, that it is impossible to truthfully say that ANY part you put on your engine WILL produce X amount of power. This is why companies who are honest will rate a part's power potential by saying "it will support XYZ power" or "it can make up to XYZ power" because they understand there are so many things that can affect the power an engine can make.

We say "support" because every engine is different. I could word it by saying "This turbo has the potential to make 1,000hp" if that suits you.


What we are saying by using the word "support" is if your engine can supply all of the airflow through the cylinder heads that this turbo can produce and flow without any restriction or reduction in airflow volume, then your engine will be able to make up to 1,000hp. If your engine is built so that it can support all of the flow coming from the turbocharger without restricting it, then your engine will be able to utilize all of the flow that this turbo can produce, and will be able to make up to 1,000hp...assuming proper combustion / camshaft design for cylinder filling / etc.

It takes a given amount of air and a matching appropriate amount of fuel to create enuf heat to generate a theoretical hp.The turbo is an air pump and the amount of air it generates could be measured or calculated. When the turbo is employed, we must move away from cfm.One formula to compute a theoretical amount of hp is:       CFM x 0.069 x 10 = maximum horsepower that a turbo can theoretically support.We used to see turbos listed with a cfm number and max hp supported.  The above formula usually matched up between the two.  As turbos compress the air, we have to deal with lbs of air mass per minute instead of cfm to take into account the increased number of oxygen molecules per cfm.  I would guess the hp potential is based upon the compressor map at the peak of the efficiency zone.  I think one must have a good combination to get close to this numberTyler may have a more modern formula?

1 of the reasons is that the BSFC formula uses lb/min for the calculations of fuel and airflow requirements. Since the BSFC is used in calculating where a turbo for a certain engine may land on the compressor map, they use lb/min for airflow ratings. Also since the compressor maps use lb/min for the flow as well.

And since air has density to it, volume of airflow does not always translate to the actual amount of airflow entering the engine. Consider altitude changes in air density, for example. By using mass, which is the weight of the air, it is a little more precise in determining the actual amount of airflow. If we measured airflow that was at sea level, and the same volume of airflow but at 8,000ft elevation, the mass of the two groups of air would be different, since the density of the air changes with elevation. The sea level airflow would have more mass to it, compared to the 8k elevation airflow.

Does that make sense? I hope I explained it in an easy enough manner..

[Scoobum]

I'm likely oversimplifyin g this. A given engine can only swallow so much air? We've heard overturboing an engine. What dictates how many lbs per hour or CFM's a given engine can handle.

[Scoobum]

More testing for you. I bolted Norbs' 70 P trim with a .63 Garret exhaust housing on it. The car went 12.2 at 114 with the high/low gear 02's checking in just under 800 with alky on 23 PSI. I slapped the 6262 on it with the same tune and the car instantly went 11.5 at 121 on 20 PSI with the same tune and alky. C'mon turbo experts...tell me why.

[Steve Wood]

Tyler, if we use two stock GN turbos on a 400 inch v8, each turbo will see half the engine on a bank and bank mounting system.  Therefore, each turbo will be feeding 200 ci which is less than a single turbo on a 231 Buick.  Therefore, it will seem to be slightly larger as it is feeding a smaller system.

In this case, it will be able to produce a bit more usable air flow (more mass) than it would on a turbo buick and it will add quite a bit of power.

If you add some serious heads, and a big cam, then you have just changed the rules of the game.  In that case, you have limited the utility of the two turbos as the power band has been moved up and away from the capability of the two turbos to keep up.

It's the same with a 231 if you put higher flowing heads and a big cam in the engine...you just ran away from the turbo by pushing the power band to a higher rpm.

You have to keep a reasonable datum on the combination if you wish to demonstrate a point that is valid.  We are dealing with something that is fairly simple in concept but quite complex in application.

[Steve Wood]

Brad, you used too big a turbo for the combination and it did not have a chance to come into the zone where it was designed for.  It was lazy.

[earlbrown]

If you 'maximize' an engine for N/A and add a turbo, you're pretty much going to blow it up.   Or be happy at 2psi of boost.


an N/A engine with a turbo isn't right, and a turbo engine ran N/A won't be right.  Camshaft overlap alone knocks it out.

  An engine is a total system.  Not a standard that all applications start from.



Also: Everytime I hear or read the term ''back pressure'' I want to murder a baby bunny.

[BoostedRPS]

If you 'maximize' an engine for N/A and add a turbo, you're pretty much going to blow it up.   Or be happy at 2psi of boost.


an N/A engine with a turbo isn't right, and a turbo engine ran N/A won't be right.  Camshaft overlap alone knocks it out.

  An engine is a total system.  Not a standard that all applications start from.



Also: Everytime I hear or read the term ''back pressure'' I want to murder a baby bunny.

Exhaust restriction.


Blow me.


I dress like Shaft. I AM INTERVINCENTBL E!

[Steve Wood]

I have always been surprised by how well the stock camshaft worked under no boost conditions.  Engine is pretty peppy in NA form.  Be interesting to see the turbocam profile vs the na cam profile.

The engineers came up with a pretty good combo right out of the factory for 1986. 

[TexasT]

Well, those engineers had been working with the turbo v6 for a few yrs before 86. Just needed the port injection and computer to control it to get it Making decent power.

[BoostedRPS]

Brad, you used too big a turbo for the combination and it did not have a chance to come into the zone where it was designed for.  It was lazy.

Exactly!

The engine had more output because an old 70 p-trim is a dogshit turbo compared to a new Gen 2 CEA 6262 wheel.

For example, here are 3 Garrett turbos from 3 different lines they produce. All are within a few MM of each other for compressor wheel and turbine wheel size. In fact, the highest output wheel is actually 3mm smaller than the others...point here is that the old cast 61mm wheel flows a max of almost 70lb/min and it is rated to 675hp.. Why? Because for starters that last 5-8lb/min of airflow isn't putting the turbo in a very efficient range in terms of the compressor wheel's speed and the temp of airflow coming from the wheel. Second, the turbo needs to spin at almost 44psi in order to reach the max flow potential of that wheel. You could run the turbo at around 33psi and still get something like 65-66lbs/min airflow, but that is still a lot of boost.

Here is that turbo I am talking about, from the GT line. It is a cast wheel 61/62 :https://www.turbobygarrett.com/turbobygarrett/turbochargers/gt3582r

This next turbo is from the GTX line and is rated for 750hp, yet barely puts out 67lb/min of airflow. It is a 100% billet point-milled 58/62 sized turbo. From about 30-38psi you are still getting a lot of output from the wheel, with peak output being around 38psi. This turbo is a GTX Gen 2 turbo with a ball bearing center section. This line of turbos is the epitome of Garrett's tech achievements. Point here is that the newer tech wheels can support more power than what the compressor map would dictate, or have us believe. Considering the 62mm cast-wheel flowed 70lb/min and was only rated to 675hp, and this billet 58mm wheel flows only 67lb/min yet is rated for 750hp, that should be a pretty good indicator of just how much of a difference in output the newer vs. old tech wheels have. Link to turbo: https://www.turbobygarrett.com/turbobygarrett/turbochargers/gtx3576r-gen-ii

Last, a GTW turbo. It is a billet hybrid flank/point-milled 62/62 turbo putting out about 73lb/min, rated to 750hp. Link: https://www.turbobygarrett.com/turbobygarrett/turbochargers/gtw3684r

Tyler, if we use two stock GN turbos on a 400 inch v8, each turbo will see half the engine on a bank and bank mounting system.  Therefore, each turbo will be feeding 200 ci which is less than a single turbo on a 231 Buick.  Therefore, it will seem to be slightly larger as it is feeding a smaller system.In this case, it will be able to produce a bit more usable air flow (more mass) than it would on a turbo buick and it will add quite a bit of power.If you add some serious heads, and a big cam, then you have just changed the rules of the game.  In that case, you have limited the utility of the two turbos as the power band has been moved up and away from the capability of the two turbos to keep up.It's the same with a 231 if you put higher flowing heads and a big cam in the engine...you just ran away from the turbo by pushing the power band to a higher rpm. You have to keep a reasonable datum on the combination if you wish to demonstrate a point that is valid.  We are dealing with something that is fairly simple in concept but quite complex in application.

Crap. Yes you're right. Those turbos would be seeing roughly 200ci each. Where did my brain go when I missed that?!

More testing for you. I bolted Norbs' 70 P trim with a .63 Garret exhaust housing on it. The car went 12.2 at 114 with the high/low gear 02's checking in just under 800 with alky on 23 PSI. I slapped the 6262 on it with the same tune and the car instantly went 11.5 at 121 on 20 PSI with the same tune and alky. C'mon turbo experts...tell me why.

That P-trim wheel isn't going to flow worth a damn under 25-26psi with those stock heads of yours. Add to that the wheel wasn't in a very good efficiency range, therefore it was putting out less-than-optimal temps from the wheel.

The 6262 having a wider comp map, was probably right at the base of the more efficient parts of the comp map, so it was putting out colder air, for starters. Add to that the usable range in that turbo is much wider, so running it at 20psi you were still getting good airflow out of it. The design of the PTE Gen 2 CEA wheels allows for the turbos to help overcome a lot of the shortcomings most Buick engines have...like crappy camshaft selection/poor valve timing/exhaust flow restriction (for earl..)/etc ... Meaning that the turbo does not require everything to be perfect in your setup in order to provide great response and power output from it. Contrary to the 6262's design, the old 70mm turbo does not have those features, thus requiring you to either 1) run it in the pressure range of highest efficiency in order to obtain the best performance, 2) optimize your engine's setup for that specific turbo.

Remember my answer to the "what are the real benefits of billet wheels that you would see on the street?" question I received? That answer is the answer to this question of yours.

I'm likely oversimplifyin g this. A given engine can only swallow so much air? We've heard overturboing an engine. What dictates how many lbs per hour or CFM's a given engine can handle.

Exactly. Your cylinder heads dictate the volume of air that can enter the cylinder, to potentially create power. The compression ratio (dynamic/etc), combustion chamber design, fuel used, spark advance, valve timing, etc...all dictate how much airflow the engine will actually use and burn. Heads provide the potential for power, the rest of the engine determines if it can use that potential.

[Steve Wood]

Tyler said:   "Exactly. Your cylinder heads dictate the volume of air that can enter the cylinder, to potentially create power. The compression ratio (dynamic/etc), combustion chamber design, fuel used, spark advance, valve timing, etc...all dictate how much airflow the engine will actually use and burn. Heads provide the potential for power, the rest of the engine determines if it can use that potential."

And this is why we have seen a few cars with stock cams run mid tens.  Good heads with a good turbo to push the air in when the valves open in spite of a short duration, low lift opening.

Two things matter and I believe they have been covered already.  First you have to push all the air you can into the engine.  Second, you have to trap that air long enuf to burn it well before it goes to the turbo and out the tail pipe.

I disagree with Earl's comments about a turbo engine won't run well with a NA cam.  Many of the cams we have used to get better performance are NA profiles.  The Edelbrock 204/214 was very popular early on. Then we had/have the 206/206, 208/208, and the ever popular 212/212.  All of these are NA profiles but they work.  The really early cams like the 218/218 and such also made power but gave up the bottom end and have mostly gone away with the advent of better turbos.

And, yes, Mike/Earl, in theory, cams designed for turbos will be much better.  In theory, that is.  In practice, on street cars, no one has come up with the magic required to demonstrate theoretical superiority.  As most of us drive our cars on the street some portion of the time, performance walks, theory talks...   Maybe with dual overhead cams, or such, things will change.  Variable cam timing!  yeah, baby!

[BoostedRPS]

Tyler said:   "Exactly. Your cylinder heads dictate the volume of air that can enter the cylinder, to potentially create power. The compression ratio (dynamic/etc), combustion chamber design, fuel used, spark advance, valve timing, etc...all dictate how much airflow the engine will actually use and burn. Heads provide the potential for power, the rest of the engine determines if it can use that potential."

And this is why we have seen a few cars with stock cams run mid tens.  Good heads with a good turbo to push the air in when the valves open in spite of a short duration, low lift opening.

Two things matter and I believe they have been covered already.  First you have to push all the air you can into the engine.  Second, you have to trap that air long enuf to burn it well before it goes to the turbo and out the tail pipe.

I disagree with Earl's comments about a turbo engine won't run well with a NA cam.  Many of the cams we have used to get better performance are NA profiles.  The Edelbrock 204/214 was very popular early on. Then we had/have the 206/206, 208/208, and the ever popular 212/212.  All of these are NA profiles but they work.  The really early cams like the 218/218 and such also made power but gave up the bottom end and have mostly gone away with the advent of better turbos.

And, yes, Mike/Earl, in theory, cams designed for turbos will be much better.  In theory, that is.  In practice, on street cars, no one has come up with the magic required to demonstrate theoretical superiority.  As most of us drive our cars on the street some portion of the time, performance walks, theory talks...   Maybe with dual overhead cams, or such, things will change.  Variable cam timing!  yeah, baby!

Duttweiler said that it has been his experience with these new breed of efficient turbos with low backpressure ratios, that a cam grind similar to a NA engine works better than what we have typically thought a "turbo cam" should look like.


Granted, this is for 2,000+hp engines running turbos with crazy boost at high rpms with minimal exhaust restriction... but still..

[motorhead]

Don't get me wrong, Steve... a small amount of valve overlap 2-6* (typical in a mild NA performance cam) can work wonderfully in turbo engine, especially those 500-650hp range street combos.  High overlap is no bueno.  Yet, there is a point were we transition to race car mode and a spec cam is required.

I specifically chose the LS9 cam in our Procharged LS2 because its had more negative overlap than the stock cam, and caused an effective drop in dynamic compression. Handy when you are force feeding an 11:1 engine.  Conversely an 8:1 V6 needs more help off boost, so positive overlap is beneficial.

https://www.lingenfelter.com/PDFdownloads/12638427.pdf

Earl: Back pressure. Back pressure. Back pressure. :p