How is it that there are some companies out there that are making great products, but TOTALLY unaware of the progress that has been made in diesel performance? Ponder this:

A quote from TSTs web site:NOTHING? Shoot I guess all those guys with B1 chargers are melting engines all the time, right?

From the High Tech Turbo web site:It it true that you should never have more than 30psi of boost? REALLY?

The problem with this notion of performance is that it implies that you can flow all the air you will ever need at only 30psi... It would be WONDERFUL if you could. But the fact is, you have restrictions: intercooler restriction, cylinder head restriction, plumbing restriction.

Though higher boost becomes less and less efficient, there aren't many other feasible ways to get the airflow to the engine that you need.

Though I have heard good things about HT turbo, I am more than a little surprised that they see 430hp as the "upper limit" of hp for a CTD.

Also, I am shocked that TST sees no cure for high EGTs....

Anyone else have thoughts on this??

Justin

 

Those who say a thing cannot be done are usually interrupted by someone doing it.

 

Maybe it's a liability issue. In this day and age of litigation and nobody being responsible for their own actions, they probably just don't want to be sued.

 

I would like to discuss the 30psi of boost point. I think it is actually correct IN THEORY. But the fact is, you can't open up things enough (ported head, cam, etc) to get the airflow you need for lotsa fuel with only 30psi.

I would say that raising boost to really high levels is probably inefficient. But there's not a whole lot of other options.

HOHN

 

I'd be willing to bet that even with a B1 you won't be able to keep EGTs under 1300 degrees pre turbo when towing with the TST PMCR set to kill. Having the power and being able to use it safely all the time are two different things.

John

 

Agreed. But it seems logical enough that you CAN cool egts down if you can get enough air in. Especially in a twins setup, which tends to deliver much COOLER air for a given amount of boost.

It seems to me that if people like PIERS are marketing twins setups for high HP AND towing, then they have found a way to slay the EGT dragon.

I am not that familiar with the PMCR, but no doubt it will be THE CR box to have. TST is known for doing things right, even if it takes them a little longer.

Justin

 

I think that the majority of guys out there are missing the point of a turbocharger. Its not just airflow, the boost creates initial pressure in the cylinder prior to the compression stroke. Then the compression stroke takes the pressure the rest of the way up. Thus much higher pressures are reached at TDC than would otherwise be achievable with anything other than an unreasonably large stroke. This is somewhat similar to a two-stage air compressor many of us have in our shop. Compressing the air in a single cylinder to the required pressures is not as efficient as with one large cylinder to compress the initially large volume of air several times over, then a second smaller cylinder to compress the remaining volume, arriving at the final pressure. Turbochargers are like that first large cylinder in the air-compressor, a high-volume low-pressure compresor. A turbochargers' primary design purpose is not to increase the airflow of an engine, they are designed to recuperate energy in the exhaust and use that otherwise wasted energy to begin the compression cycle, allowing higher ultimate DYNAMIC compression ratios. Obviously you also achieve an increase in airflow for a given cross-section intake port and valve size, but the difference could be made up with large valves and intake runners. If you think its all about air-flow, think about this: say you have a 5.9L naturally aspirated diesel engine that has killer heads and intake an so it flows as much air as our turbo diesels do when ours are at say, 35 Psi of boost. Try, just try, to make as much power and torque as our turbo diesels do..... Not gonna happen, not even close. I have seen 55,000 HP marine diesels that are two stories high and 75 feet long, and only turn at 120 RPM, trust me they could make the intake passages and valves easily large enough to flow the designed airflow, but guess what...... Turbo charged, often twins at 60+ Psi of boost......

Sorry I know this is getting long but a quick example to complete the exercise::

Starting with atmospheric air and compressing it to 35 Psi. with the turbo, winding up with say, 15 Psi in the cylinder prior to the start of the compression stroke and completing the compression in a CTD (4.02" bore and 4.72" stroke), neglecting blowby, and assuming adiabatic compression and not beginning the burn, would put the pressure at TDC at about 600 Psi. To do that without the initial 35 Psi of boost from the turbo, would require a stroke of about 9.25" !!!!! Try reving that engine to 3,500 RPM!!! And you would have a static compression ratio of 39:1.. Don’t think the starter would like that either.

Zino

 

Amen!

 

Zino, we basically agree. Everything you said is true. When you say that the primary purpose of a turbo is not to increase airflow, it's to increase pressure.

Explain to me, please, how it is possible to increase airflow WITHOUT increasing pressure, given a certain rate of air consumption by the engine (constant rpm, port dimensions, etc.).

So, in a sense, it IS about the airflow. Normally aspirated engines can exceed 100% volumetric efficiency for only limited rpm ranges, and only with advanced tuning.

But with a boosted engine, you are doubling volumetric efficiency with each atmosphere of pressure. 14,7 psi of boost, you have roughly 200% VE. 29.4psi? 300% So on and so forth.

There are certain main qualities of any sample of gas- it's temperature, it's pressure, and the volume it is contained in. From these, you can figure out density, mass, etc. are ALL secondary things determined primarily by the three main one-- temp, pressure, volume.

Furthermore, temp, pressure and volume are all interrelated. You compress something, you get less volume, more pressure, and higher temp.

YOu are correct in your analogy of the single-stage to the two-stage air compressor.

But you can't discount the importance of airflow. Just like *I* can't discount the importance of pressure.

The bottom line is the it's all about increasing the mass flow into the engine... Whether it comes from pressure, air flow, etc... is all less important.

You make a VERY good point about how the pre-compression of the boosted charge makes possible certain engine designs that simply aren't feasible without it.

Justin

 

Justin, on the money no doubt. Remember, I never denied that there is also a desirable increase in airflow, I just was mentioning that it was a secondary bonus, if you will. You are correct, without increasing the dimensions of the intake valve, intake port and or/manifold you can't increase airflow without increasing the delta P across it. Such are the constraints we live with. However, modest porting of the intake runner and bowl area, and with proper valve size and quantity (lol) as well as a camshaft change can result in much larger effective airflows than a 10 Psi change in boost. Lets face it, ported head, custom manifold, big valves and 100 Psi of boost will make far more power than the crankshaft can handle anyway. So its all really about compromises, and I was just trying to point out the true importance of boost as a overall pressure ratio increaser, thus thermal efficiency improver.

Good post and great comments. Lets keep up the technical discussions on this matter.


Zino

 

This might be a dumb question but here goes...
Can an engine like ours benefit from more volume of air as opposed to more pressure?
I am kind of thinking outside the box on this one...why all the boost to give us the power if one can provide the volume required instead?

Follow my thinking?

 

As in ... porting? different cam? I only know what I've been told, but I HOPE this fine DD cam laying here beside me will help by "[improving] your spoolup, reduce smoke, improve mileage and help EGT about 300*F." (quoting an email from Keith at DD).

It would seem like both porting and cam accomplish the same thing... better/more air flow, same pressure. This results in the benefits that Keith listed. Would this be the more air that you're thinking of?

Just thinking out loud...
brandon.

 

No not really although that does work too.
I am thinking outside the box...as usual.
I am thinking about higher volumes of air and not necessarily higher pressure...and not by changing the cam or doing head work. I know a lot of folks are probably cratching their head about this as its not the 'way' its been approached. At least its not something I have read about or seen available. A cam sure would assist with this idea though.

A big turbo can move more air but most times it has some lag and needs to spool up to do its stuff...move more air then perhaps one stock turbo does.

So if you have a small factory turbo and your going to nearly double the power or more from stock, then why wouldn't two of those stock turbos do the job with fast spool up.

I can't get my head wrapped around the answers I have got so far from folks in the industry. They all say it will not work. Not enough cfm to spool them was one answer yet we put bigger turbos on in place of our stockers. The other answer was that it would not work because it would not be balanced. I already figured out and overcame that hurdle.

 

Scotty, perhaps you are referring to a parallel turbo setup instead of a series or compound setup. The reason people say that there is not enough exhaust flow to work, is that each of the twin HX 35's in a parallel setup would only be fed by three cylinders instead of six.
With regards volume vs. pressure, the main thing is that the primary restriction is the intake valve (valves for us enlightened ones, lol) and bowl area. As Justin mentioned early on, we simply cant get any additional volume past that restriction without increasing the delta P across it.
Also, you are neglecting the very subject of my reply a few posts up this thread. The pressure itself is a bigger factor than even the volume. As in other common thermodynamic cycles like the otto cycle( gas engine), brayton cycle (jet engine/gas turbine), rankine cycle (steam turbine), our beloved diesel cycle shows a enormous improvement in thermal efficiency with increased pressure ratios.


Zino

 

Now that makes more sense. Thanks

A hypothetical here...
What if a parallel system had assistance at the lower end rpm [off idle boost] and 'did' work well with the exhaust of three cylinders when the power of the engine is nearly double [or more] what the stock rating was? Wouldn't a turbo that is efficient with say 600 cfm work better if there was two in this configuration and the higher power?