possibly retarded question

under pressure · Oct 4, 2012

all right, getting back in the diesel world,, soooo
I've been reading compressor maps, looking at boost numbers and maps for multiple turbos............. And my standing question is, if a turbo was set up at 30 psi and made X amount of clean hp........would swapping to a turbo that made 40\50 psi make more hp with the xtra combustion pressure....... All fuel parameters the same ?

TARM · Oct 5, 2012

The way you are looking at is not quite right but to answer the question I think you are trying to ask yes, it will.

You do understand that boost does not equate directly to HP. Point is it's not as basic as your question states it.

under pressure · Oct 5, 2012

Yes, thats understood, tried to simplify the question and that's what came out.
I thought it could... But I've seen same set ups make more power with lower boost numbers.

Basically, all things equal, if my set up makes 30 psi, and I switched to a turbo with a similar map that netted 50 psi that ran close to 1/1 with the same amount of fuel, there is a hp increase to be had.

Similar to moving from a 38 to 38R ( 20 peak psi difference)

Dieselboy. · Oct 5, 2012

I would think the CFM flowed at the same amount of boost would be the deciding factor ?

under pressure · Oct 5, 2012

maybe a simpler question......fueling stays the same...
Swapping a gt38 to a 38R = HP increase
Or, 38R to a S366 = HP increase

????

under pressure · Oct 5, 2012

Dieselboy. said:
I would think the CFM flowed at the same amount of boost would be the deciding factor ?[/QUOTE

precisely my point in question, with out adding fuel, does more cfm = gained hp
Then comes the questions...

Is X amount of air (cfm) too much for X amount of fuel.

Can you have too much turbo, as you can certainly have not enough.

Ad8 PRODIGY · Oct 5, 2012

I had the same question but thought it was stupid so I kept it to myself.

Your basically asking, if you force more air in with the same fuel, are looking to over-air it? The opposite of over fueling... and still make the same amount of HP?

I was told that's not how it works exactly but I'm in for answers.

under pressure · Oct 5, 2012

Or does more air equate to more HP. I've only read this scenario when more fuel is added to the equation, so what happends when the fuel stays the same and a turbo is able to provide X amount more air.

TARM · Oct 5, 2012

Of course it does; if it did not then NOS would not be nearly as effective. But there are always limits. Eventually you run out of fuel to burn with O2. SO it all depends how much fuel you had being injected with the original setup in ratio to how many CFM or lb/min of air that turbo was moving. Then you add more air as long as the original mix was not too lean you would get more complete burn so more power.

Gearhead · Oct 5, 2012

The boost wouldn't automatically make more power, but a turbo that makes 1:1 at 40 psi will make more power than one at 30 psi at 1:1 (with the same exact fueling) because it will be more efficient at making that airflow. When you start adding boost and playing with cam events, you can actually use boost to precharge the cylinder with compression and thus make more cylinder pressure with more boost, but where our intake valves close now doesn't do all that much.

97stoker350 · Oct 5, 2012

but going bigger on the turbo with the same amount of fuel affect the spool up? sorry if thats a derail

under pressure · Oct 5, 2012

Depends on turbo, and how it's set up,

Cota · Oct 5, 2012

2000 SD, switching from a stock turbo to a 38R, no other changes netted 30 HP on the dyno.
Going from a 38R to a 4294r netted 30 HP on the dyno no other changes.
Thats what I saw dynoed on my truck way back when.

under pressure · Oct 6, 2012

Interesting !

TARM · Oct 7, 2012

Cota said:
2000 SD, switching from a stock turbo to a 38R, no other changes netted 30 HP on the dyno.
Going from a 38R to a 4294r netted 30 HP on the dyno no other changes.
Thats what I saw dynoed on my truck way back when.

To help those and give it a more complete pictures maybe post the peak boost each turbo achieved with those power increases and no other changes. That IMO will help to show more of the picture.

littleredstroker · Oct 8, 2012

Ok so now I am more confused. What about just the stock 38, are you saying you will make more power at 20-24 psi than at 35 ? Because of efficiency ?

autocorrected by taptalk

TARM · Oct 8, 2012

Also do not forget about pumping losses from higher drive pressure. @ 25 drive pressure is taking a guess in the 45-50 range but @ 35 I would not be surprised if its in the 80-90psi range. Also look at the intake temp. 25 as it takes slower wheel speed may be 130F but what it 35 was 210 F? How much of a change in "air density" on the pressure side is there? You can get pressure from air compression but you can also get pressure from air expansion from heat. Less air molecules just expanded to produce pressure.

That is what I meant by it and that boost vs boost can be very different in terms of effect.

Gearhead · Oct 8, 2012

littleredstroker said:
Ok so now I am more confused. What about just the stock 38, are you saying you will make more power at 20-24 psi than at 35 ? Because of efficiency ?

autocorrected by taptalk

Stranger things have happened......

Every 2psi of drive pressure increase can be viewed as 1lb of boost loss in most cases not to mention possible egr effects from valve timing on some setups.

littleredstroker · Oct 8, 2012

So its better to have less cooler dense air, than more hot thin air? Is what you are saying. And forgive my own retardedness drive pressure is..?

autocorrected by taptalk

ken6881 · Oct 8, 2012

littleredstroker said:
So its better to have less cooler dense air, than more hot thin air? Is what you are saying. And forgive my own retardedness drive pressure is..?

autocorrected by taptalk

drive pressure is the pressure in the exhaust used to drive the turbo
2 to 1 drive pressure would be 2psi of drive pressure(manifold side) to 1 psi of boost (intake side)