Basic Question: What makes power?

[mickeyblueyes]

Ok I know that a engine is a giant air pump ,the more air in the more out. My question is this, I relize when you add a "programmer" like a Smarty it boosts the amount of fuel going in to the engine and adjusts the timing, ect... .



What does the amount of boost from the turbo do? If I have a relatively stock engine and and a 4 inch exhaust and a bigger intake, then put on a turbo that will produce more boost than the stock unit what could I expect.



Now lets be clear I am not talking about putting on a double or triple unit ,that would be used to pull sleds, I know that stronger head studs are needed for those applications. I don't know what a stock unit produces but what if I switched to a turbo that doubled it??? would I see a big increase in power?

 

[cerberusiam]

what if I switched to a turbo that doubled it??? would I see a big increase in power?

No, essentially you would see no increase in power if you did NOT increase fuel. In fact an increase air density, not neccessarily boost, could exhibit a net REDUCTION in power.





One of the first things I learned on the TDR is a simple formula:



More power = more air + more fuel



Simplified, to make more power you need more boost, to make more boost you need more fuel.

 

[Missouri Mule]

Definitely more fuel and with a turbo that equals more air advancing the timing doesn't hurt either.

 

[Adventure Bob]

Fuel has a very specific amount of energy in it per volume and it releases that energy when burned based on the stoichiometry of the reaction. Diesel burns best when there is 14. 6 parts air to 1 part of fuel. Changing that reaction stoichiometry changes the reaction to a point where you get less energy and more chemical by products out of it. Turbos and blowers copmpress the air going into the engine and therefore increase the 14. 6 side of the equation. To make use of it you have to squirt more fuel in. Engines are hugely dynamic so you also have to control when the fuel is squirted in and in modern diesels how many times to get the best reaction. Smoke out the tailpipe is products of a reaction that was unbalanced toward the fuel side. In big power motors this may be desirable, since the fuel is being used as a coolant in the cylinder. Gale banks would argue to the contrary in this situation, and would say that its just a waste and not very smart programing.

 

[CToney]

Fuel is power. If you have a nearly stock truck and don't tow or compete I would think adding an aftermarket turbo wouldn't do much for you. This is just my opinion. Fill out your signature so we know exactly what kind of truck you have. Guys will let you know what kind of boost you should see. But it is your time and $$ so spend as you see fit. If your truck is a bit of a hobby don't let much stop you.

 

[Wingate]

As others have stated... its slightly more complicated that just throwing a big turbo on. Remember, the turbocharger is actually driven by exhaust velocity/pressure. By adding a larger turbo that has a bigger exhaust housing and wheel combo, you need much more exhaust velocity to "light" the turbo(to get the turbo up to speed) Without the introduction of extra fuel to drive the turbo, you would get VERY sluggish response, lots of smoke, high EGT, and overall poor results.

It IS a balancing act, you have to get the programming for your intended results, the right injectors, the right intake and exhaust system, and the right compressor (turbo) to make it all work together without detrimental effects.

In my job, I commonly use a turbocharger shaft speed sensor to tune large natural gas engines..... It is an absolutely GREAT tuning tool. I don't think the Holset turbos have the provision for a shaft speed sensor. I think they use a photo-optic sensor.

 

[Joseph Donnelly]

The “air pump” story is popular with gas engines, where fuel is mixed with air outside the cylinders. Then, more air + fuel at the correct ratio will give more power. Diesels generally operate on an excess of air, and more fuel is the firsts thing to add for more power. Due to the nature of the turbocharger, it will give more boost as fuel (heat) is added, up to the limit of that particular turbo. Compound turbos increase efficiency and decrease the temperature of the compressed air. With moderation and proper turbo sizing, head studs etc. may not be needed. I am running the BD medium size set of compound (twin) turbochargers, the R700, with stock head bolts and not exceeding 55 psi boost.



After adding a certain amount of fuel, you will need a bigger turbocharger to continue increasing the air supply. Air + fuel = power, as I discussed in Issue 23, p. 38. Updates have been published periodically, with some recent examples being Issue 59, p. 94, Issue 60, p. 90, Issue 63, p. 78. There are many more articles on the topic in the TDR magazines.

 

[SRadke]

Don't get caught up in thinking more pressure, is more air, is better. A small stock turbo can be pushed over 40 psi but at that point you've pushed it so far beyond what is was designed to do you'd be better off with a more properly sized turbo at say 25-30 psi.